How Absorption, Tail current and a few clouds can trick you!

As per your recommendation, I have now set up a looooooong absorption time and also a tail current in the Victron solar charge controllers. We still have 3.4V/cell set as our absorption voltage.
And because this is such a low voltage, the absorption time and tail current can trick the chargers to prematurely go into float mode. This will then leave your batteries only partly charged. All thanks to some clouds...
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[@kcjones3368]

Andy, Thanks again for all your great videos.... sometimes we get a little worked up in the comments but that in no way minimizes the respect and gratitude I give you and your many contributions to the solar community and scientific inquiry 👍 Thnx -KC

[@OffGridGarageAustralia]

Thank you very much, that is greatly appreciated!

[@solarute5486]

In 2012, I installed 10 kW solar with 8kWH of winston LFP batteries on my offgrid property. I built all the electronics myself, and there was not quite the amount of information available on how to design for LFP as there is now. Fortunately, LFP is generally very simple to charge :-) I didn't use absorption time. I controlled max charge current at all stages. I used 2 setpoints and reduced the charge current on each. The last stage was only 5 amps until it kissed the final target. So I used 1/4 C for the bulk of Max Charge current, then 1/8 C Max charge current, then 5 amps. In the meantime the solar panels were heating the hotwater system and so on. This seemed to give a relatively consistent charge, irrespective of cloudy conditions.

[@OffGridGarageAustralia]

Very interesting, but you certainly have to set a voltage to change over from bulk to a lower amperage?

[@solarute5486]

@@OffGridGarageAustralia Yes, I did have voltage setpoints for each event.

[@wizzie2k]

🐸 Always watch to the end before commenting 🤣🤣🤣

[@OffGridGarageAustralia]

Hahaha, there is always more 🐸😁

[@mfgxl]

@@OffGridGarageAustralia I wish they would go on and on and on. I love learning about this stuff before I pull the trigger. Learn at other people's expense is lovely.

[@TheUndisputedGodFather]

I’m about to set up a Victron 24/3000 multiplus ll with 8 battery cells. This is to power a tiny off grid cabin in the Central Highlands Tasmania. Your vids have been so helpful.

[@williamjamesenkerwitz9495]

Oh my word so beautiful thanks for showing I still watch every episode you make regards to you from South Africa

[@Pim57]

Besides from a cloud moving over your panels, it can also be a (big) load switching on/off. Which then makes the voltage go all places! Or hit the tailcurrent accidentally.

[@OffGridGarageAustralia]

Yes, good point. I have seen this as well when charging the car and the charger stopped. If the solar charge controllers were on full blast charging the car and this load turned off, the SCC keep supplying energy for a few seconds and the battery voltage spiked.

[@egnegn123]

Andy, great new video! It shows clearly that the control of the charging by voltage/current is pretty much useless, because it is inconsistent. Absorption voltage, absorption time and tail current to charge to a specific SOC are parameters that work with a constant current charger on a unloaded battery, only. And even there they are only work when you are able to over-charge, like with a lead-acid battery. If charge current and load is changing all the time you cannot get a consistent result, especially if you want to stay below 100 %, but not to low. As mentioned below, a SOC controlled charging method has to be established for this. As the SOC is already available in the Smart Shunt, Victron should establish a control loop between Smart Shunt and and Charge Controller. Then it would be easy to establish charging to a specific SOC. Off course, there should then also be a calibration charge be done, like the equalization charge with lead-acid, to reset the SOC to 100 %. But this would be only be necessary ever few weeks. Actually the equalization mode within the charge controller could be used for that. Actually this can also be done with external gear. I have a battery computer from Mastervolt, which can switch the chargers off through as solid-state relay, when a specific SOC is reached, and turn on again when SOC has fallen to a lower limit. But from time to time the SOC meter has to be re-calibrated again, by a higher charge level.

[@AveRage_Joe]

Love all the information! Keep it up!!🐸

[@SVAdAstra]

Andy, switch to "Adaptive absorption." You have set "Fixed absorption" and with fixed absorption, Victron warns in the setup: "make sure to disable the tail current... tail current could end the absorption time sooner if the battery current is below the threshold." Which is exactly what you are seeing when clouds cause the PV output current to dip. Then test again using adaptive absorption and the tail current set. Hopefully, the clouds will cooperate to give you similar test conditions. Victron should explain the fixed versus adaptive absorption settings better.

[@kcjones3368]

Still using 3.55 Absorb / 3.5 Float... As soon as my SBMS120 hits 90% SOC the "dump loads" turn on: water pumping, electric heating / cooling of thermal masses / topping off air compressor....etc.... When I was using the lower voltages my outback charge controllers and SBMS would Pop in and out of float mode and I would lose a lot of charge for the day ..... by holding the batteries at 3.5 volts I'm somewhere over 90% when the sun goes down... When you're fully off-grid and living off your batteries you want that charge it's high as possible without damaging your batteries as soon as the sun sets. Something nobody ever talks about is load / size of bank... If your system is idle/ lightly loaded just being charged up as a backup your settings are going to be vastly different from a primary system that runs a whole house load (10-15KWhs/Day)... I have helped multiple friends set up off-grid circuits in their house and a large LiFePO4 bankand small solar array that basically act as a lightly loaded UPS for their setups I always go with a lower bulk/float voltage... I've said this before and I'll say it again ideal charge rate and voltage settings depend upon your end use, how big your bank / array is and the solar potential for your solar latitude!!! All of the variables have to be taken into account there is no one solution 😋

[@aureltanasan1413]

I couldn’t agree with you more, I have a oversized array to cover for the winter months. Fully off grid and sometime Genny deployed on long dull winter days. Those times I have bulk 3,55v and float set at 3,5v. In the summer, I get away with 3,45v float.

[@jasondevine6014]

Thanks for your experiments. Great to see these different ideas tried out so I dont have to.

[@OffGridGarageAustralia]

Hahaha, Jason, you should do these tests too, just to confirm I'm right or wrong 😂

[@menimbamatahari170]

Yeah.. solar panel system is unique for each other.. soooo many variables can affect to the result. Keep enjoying try and error is the best way to learn..

[@benengelbrecht5637]

Even the Frogs in Aus is going "undercover". Clearly well trained in escape and evade... (naturally camouflaged for the terrain) Makes me wonder about those black spie birds, same colour as the panels. It is a very intriguing situation to take note of Andy. But after all the BS I just typed, back to reality. Thank you for the great videos and real testing the parameters, it is truly great stuff.

[@OffGridGarageAustralia]

Thanks a ton, Ben, great comment. Made me laugh 😁

[@LiudasJuodzbalys]

I use Winston/Thundersky lifeypo4 (yep the Y is Yitrium) cells in my off grid home, and interestingly enough, the manufacturer (for 24V set up) recommends 27.6v absorption voltage, which is in fact 3.45v. Also, we live in Ireland and the cloud/sun peekaboo situation is common, yet the batteries still charge (on a nice day) to a consistent 92-97% , also the slow charge helps the BMS balancing function , deviation is rarely more than 20mV and more typically 2-7mV, keeping in mind that the they are always under load. Lithium is amazing 🐸

[@OffGridGarageAustralia]

Great information here. Thanks for sharing. 3.45V is the better charging voltage, absolutely. I can now 100% confirm that with all the testing I did with single cells and CC and now also the big battery. I like the sun peekaboo term 🌤

[@aatdekwaast3968]

🐸 Andy you have made your point, 3,45V it is or 3,5V, or something in between. I live in a country with lower ambient temperatures so i go for 3,5V without absorption, that's good enough for me :)

[@OffGridGarageAustralia]

Absolutely, that sound a reasonable setting. It also gives you the opportunity to balance at these settings.

[@loganv0410]

At 16:55 you failed to mention frogs as a significant variable in charging. But seriously - please continue the great vids. I'm learning a lot from your efforts

[@ifyoucantjointhem]

🐸 Great videos, I thoroughly enjoy watching 🤙

[@graemezimmer604]

The reason that the State-of-Charge (SOC) value is not used to control charging, is that it's not an absolute value. It merely an estimate which is calculated for the convenience of the user. And by definition, it will constantly change. All the monitor can do is total the current in and the current out, estimate the full and empty points, and from that calculate the apparent capacity, and thus the SOC. In the days of Lead-Acid batteries a Hydrometer could be used to measure the true SOC. But a hydrometer is inconvenient, so the solar companies decided to calculate an "apparent" SOC by integrating the current in and the current out, and use the voltage trip points to calculate SOC. These modern controllers (for Lithium batteries) are no different. If you did try to use the SOC to terminate charging, you will end up destroying the batteries, as the system will no longer have any way to estimate capacity and SOC .

[@rickard1802]

Im using 3.525 bulk/absorb for 10 minutes then 3.4v float. 3.3v resumes bulk charging. Works great for me.

[@mw0lge]

🐸 very interesting. I am running a 150/35 solar charge controller in a 12v lifepo4 system on my van with 200w (due to increase to 400w). I am leaning towards setting the absorb and float both to 13.8v, and see how things go. Cheers.

[@jeffarpin1700]

Great info and the frog is cute 🐸🐸🐸

[@KevIsOffGrid]

At 15 mins - yeah, now your dialling in on it. I've said before i play with my settings - in summer where i cant use all the power - use this as a "feature" to stop overcharging, But in winter when i need max power for that 1 hour break in the clouds or that one sunny day a week to collect as many photons as possible and get my SOC up. Today was one of those sunny days after days of dullness and I needed it. You may just be going into summer but I'm at the time of year where weather matters a lot although only 8 weeks off where it wont matter how much sun it will be that low in the sky I'll get nothing.

[@KevIsOffGrid]

rather than change the Abs Voltage to check - note the voltage point the charger is collecting at. You'll know your MPP and if the charger tracks higher or lower then that how they limit the current for the abs, phase.

[@OffGridGarageAustralia]

Yeah, totally different situation if you have these rare moments of sunshine, you have to use them and harvest as much as possible.

[@john_in_phoenix]

Frog. I agree with all of your conclusions, but I live in the desert, and clouds are rarely a problem. Certainly you can push more amps with a higher voltage, and you should cease at 3.45v, since you are about 98 to 99% full then if you're top balanced. Good job illustrating and explaining it.

[@martinschoonover2812]

My testing has shown you need 3.45 volts per cell. I also set the float to the same 3.45 volts. Works great!

[@Banszi1]

Doesnt this create a risk of overcharging if the the battery is not used overnight and this continues for mutiple days?

[@martinschoonover2812]

@@Banszi1 3.45 volts per cell is not 100% charged.

[@aureltanasan1413]

@@Banszi1 you can not overcharge a charged battery, unless you raise the voltage. In this case it will just hold 3,45v at 0 amps if is full.

[@martinschoonover2812]

@@aureltanasan1413 This is exactly what happens, the current tapers to zero and no more charging takes place. I have tested removing all loads from the battery after charging and let it sit for days, it's still sitting very close to 3.45 volts.

[@joesrvhome]

Love your videos 🐸

[@petski999]

You need to account for the battery's internal resistance when programming the trip voltage to enter float mode. At 60A charging current you can easily see +100mV at the battery terminals due to IR drop. This IR drop gets worse at a lower state of charge which is why you see larger variations at lower trip levels.

[@ZeroDot42]

🐸🐸🐸🐸🐸🐸 another awesome vid and info and research ,Thanks Andy

[@JeremyAkersInAustin]

Here's my frog: 🐸 This looks like a defect in the way Victron is handling absorption time. If the voltage drops below the absorb voltage, it should drop back to bulk. It's not "absorbing" if the voltage is lower than the absorb voltage. I haven't used the Victron settings for bulk/absorb/float in a few years. I currently just have loads that trigger at 3.4v to keep my battery from getting to 100%. I swear I remember Victron not behaving like this when I was using their bulk/absorb/float settings many years ago. I would report this to Victron. This seems like a defect in the way they are handling those trigger points. If the voltage drops below the absorb voltage during the absorb time (Either defined by time or tail current) then it should switch back to bulk. It shouldn't switch to float unless it maintains that absorb voltage for the entire duration of the absorb time or tail current. Your discovery at the end of your video regarding the higher voltage = higher solar yield is exactly why I stopped using bulk/absorb/float altogether. I have my BMS set to charge at a flat constant voltage of 56v and I simply have diversion loads that turn on to divert that extra power to water heaters, air conditioning, etc when the battery reaches 98% SoC which is around 3.4v/cell. By keeping the MPPT voltage high and by diverting that excess power to useful loads you can really maximize your total solar yield while still keeping your battery at a lower voltage to maximize battery longevity.

[@wayne8113]

Thanks Andy

[@SpeakerKevin]

The Victron Smartshunt is very accurate, so it would be nice if there was a setting to stop charging at any user selectable state of charge.

[@OffGridGarageAustralia]

This will come soon. @Brad Cagle is working on it...

[@SiriusSolar]

@@OffGridGarageAustralia is Brad with victron? So is this coming to everyone's units in a software update or new hardware? Or is this something Brad is developing that we'll have to apply ourselves aftermarket?

[@OffGridGarageAustralia]

@@SiriusSolar Brad is a software engineer and a viewer here in the channel. He offered help to get the BMS connected to the Pi but also wanted to provide broader more general support for all of us to read information from our BMSs to control charging. Most devices have the RS485 port for that already build in.

[@kcjones3368]

Look into the Electrodacus charge controller / BMS combo setup... Pretty cool tech SBMS0, SBMS120!!!

[@USA-GreedyMenOfNoIntegrity]

Percent is the way to go, along with accurate measurements and calibrated sensors. 3.5!

[@akimi0222]

🐸🐸🐸 comprehensive video as always

[@551moley]

I can't say I ever really taken much notice of the Sun in the first 50 years of my life and here in the UK it doesn't seem to show up most of the time anyway, then nearly 3 years ago we ended up off grid and suddenly your whole life revolves around it! We have a problem with Frogs 🐸 here aswell 🇫🇷

[@GBCobber]

It seems that ideally you'd want both conditions to be met before switching to float, rather than one or the other. That would make the solar charger much more compatible with Life cells, and should only require a simple firmware update. Perhaps the manufacturer could be persuaded?

[@Y2KSailing]

Another possibility is to talk with the uart port on the bms and use those information with a raspberry to pilot everything

[@2flight]

I'm glad you're doing all the experiments so I don't have to. The one conclusion that is without question is: you have to water the frog!!

[@rcinfla9017]

Also need to consider balancing maintainance when BMS does balance dump a cell until it gets above 3.4v and has small amount of balancing bleed current.

[@heinvandenbroeck3184]

To charge my battery to 90% I connect my Victron Multiplus via modbus to a 'Home Assistant' server. If 'Home assistant' reads out a battery SOC of 90% it wil send a modbus command to the Victron multiplus to stop charging. Once every week I fully charge my battery. I set my absorb voltage to 3.47V/cell for 20 minutes.

[@OffGridGarageAustralia]

Great solution! Is this with LiFePO4 batteries or regular Li-ion?

[@john_in_phoenix]

I agree, the only real way to hit 90% state of charge is by tracking amp hours in vs amp hours out. The voltage measurement will really only let you get to 98 or 99% accurately. Below that, "it depends" is the best you can get.

[@heinvandenbroeck3184]

@@OffGridGarageAustralia Yes, LiFePo4 cells. I have 18 Lishen 272ah cells in series. So I have a higher voltage (around 60V), Less current for the same power and a JK BMS with active ballancing. I only use the active balancing from a voltage above 3,44V/ cell.

[@justdoityourself7134]

My finding are exactly the same. Charging to 3.4 leave a lot of solar power inaccessible.

[@OffGridGarageAustralia]

Great, thanks for confirming that. It is just a tiny bit too low. 3.45V is far more consistent.

[@mitchrothermel8157]

Why not just charge to 3.5 volts high cell?? A 100ma balancing on the bms is easy to achieve. My BMS automatically reduces current as battery becomes full. You keep saying it’s ok to charge up to %90+. Mosfets are awesome!! Mitchell

[@IkkjeDus]

Green energy. Diego 🐸

[@OffGridGarageAustralia]

🐸

[@henvern]

🐸 If you had 2 batteries and software control over the charging current and discharging contactor of each then it would be possible to smoothly fully charge/balance/calibrate one battery while the other takes any remaining charging capacity and supplies loads.

[@mitchrothermel8157]

This creates unnecessary energy flow one battery to the other as he already stated in a previous video. Besides I tried to tell him before to use another battery that uses 3.7 nominal @ 14 cells that pack will have a higher charge voltage which will allow balancing to to optimal conditions. But he wants nothing to do with that.

[@aprilsteel9466]

Yes 3.45 volts would be better. However the problem then becomes having one of the cells topping over 3.65 while the others are lower , This happens a lot if you try to get too high.As you know the balancing in the passive BMS is only probably 30 mA so that won't help. It will get better when Victron finally converts their chargers to LFP only. But they are trying to cover both markets with the one product at this time.

[@OffGridGarageAustralia]

If you did an initial top balancing at close to 3.65V, none of your cells should peak at 3.65V when you only charge to 3.45V. That would indicate there is something wrong with the cell or the connection to it.

[@aprilsteel9466]

@@OffGridGarageAustralia With 8 years up the sleeve I can but tell you.

[@OffGridGarageAustralia]

@@aprilsteel9466 oh, 8 years. Yeah that's a long time. Well, I'll keep this in mind. Thanks for sharing.

[@JeremyAkersInAustin]

@@OffGridGarageAustralia ​ @April Steel I've got 4 years on my large 48v pack and have seen similar issues. As the cells age the imbalance gets worse which is why I had to add active balancers to my pack. My pack also has an issue with temperature imbalance because one side of the pack is near the inverters and the other side is far away from the inverters. So the cells near the inverters always have a different internal resistance due to the temperature variations. I also had some cells fail due to a BMS problem and having some new cells in the same pack with older cells causes even worse imbalance issues. Life is always easier with brand new well matches cells. :D

[@MotorhomeDIY]

Hi buddy I went to your website thanks also did some tests of my own and I agree Victron settings need fine tuning I’m scratching my head here lol After the bulk phase with 10% current there is a SOC of 80/85%. But At the end of the absorption phase there is a SOC of 99% if the absorbed current is less than 2%. In fact, the battery chargers or solar controllers (also victronenergy) that terminate the absorption With the tail current, they do so below 2% or less. A current of 4% on the other hand does not indicate 100% SOC, rather than 95%. I did some tests, 115ah battery is not at 100% when it draws 4.4 Amps in the absorption phase. It is at 99, ×% when it absorbs about 1.7Amp in the absorption phase. Otherwise why do Smartsolars terminate absorption with a tail current of 2%? And not 4%? lots of settings need fine tuning

[@Aconda]

🐸 I also think that 3.45 volt is the way to go. Or to start with when trying to find the most suitable settings for tail current and absorption time. Thank you for this video. I really liked the ending.

[@OffGridGarageAustralia]

Thank you 🐸 I'll do one more test today with 6h absorption time and 5A tail current. Battery is at 60% SOC atm, so it should fully charge. I also want to see how much the shunt has drifted since the last reset 2 weeks ago.

[@johnc5937]

Andy, I was thinking that if you could access a clock you could make decisions based on time of day as well as SOC… but you have a form of clock, you have a roof, and it’s solar panels, that get more power in the morning than in the afternoon. In the AM your most likely to have a lower SOC and therefore set your battery options to be more aggressive in the AM… while the west roof can be assumed to be more for the end of day functions and therefore less aggressive. As long as the two charge controllers don’t “Fight” I don’t see why they need to have the same settings. Frog 🐸

[@janosvarga962]

Beautiful frog.

[@andrewradford3953]

That 32° day brought out the first green tree frog here too.

[@firpofutbol]

Frog was probably scared out of it's mind. 😂😂

[@PrincessLiFePo]

Hello Andy! Deeply grateful for all your tests and videos. Extremely helpful! Question: Have you ever tested/made a video of the "adaptive absorbtion time"-function in Victron Smartsolar chargers? I have heard it works great also for LiFePO4 but I have no idea HOW it works.

[@kevinmills5293]

I only use the tail current to determine when the batteries are charged and I have a long absorb time to ensure there is sufficient time to reach the target tail current (1% of the Ah capacity @ absorb voltage). When the tail current is less than the target current for 30mins, the charge controller goes to float. If the battery voltage drops below absorb voltage or the tail current goes over 1%, the 30min timer resets. BTW, I hope Diego could get out of the watering can!

[@OffGridGarageAustralia]

Thanks, Kevin. What voltage do you charge to? I guess, the problem I showed does not occur when charging to a slightly higher voltage.

[@davidchristensen1219]

"Hangin' with Diego" should be the title of this video!

[@mflo1970]

Claro que si una curva de carga está pensado y desarrollado para un cargador fijo donde el voltaje es constante y la tensión es decreciente hasta alcanzar un estado de carga predeterminado, entonces en un sistema solar es complicado obtener los resultados previstos por múltiples factores y es ahí donde debemos adaptar nuestra carga según esos factores

[@USA-GreedyMenOfNoIntegrity]

You see the same results while playing with voltage adjustment knobs on our EBC-A40L. 3.5 V is my minimum.

[@mfgxl]

Frog: After reading everyone's comments, you some it up best with this reply - "3.4V is a bit high for floating. It is over the tipping point and can overcharge you battery if it sits on this voltage for a long time. I would go lower to 3.35V or 3.375V. That is close to the natural resting point of the cells." And I repeat - That is close to the natural resting point of the cells

[@aureltanasan1413]

Not necessarily on a off grid working system with loads. Float at 3,4v, and a sun set you go into the night with discharged battery. I don’t believe one voltage fits all, its a matter of finding a balanced setting for a given usage. If the system is idle, yes I agree, float at 3,35v.

[@camielkotte]

@@aureltanasan1413 i think you are making a good point here. Every setup may need different fine-tuning based on load, geo location, cloudiness and shade. Humanity still has some work to do to make it plug and only play. This is a great corner of the web for that. Cheers you all. Thx Andy

[@nzubeotor9073]

Hello Andy, Great Videos as usual. You have really given practical proof why 3.45v is great voltage for charging. I have a question, is 3.4v (54.4v) too high a voltage for float?

[@zarbonida]

Floating to 3.35V or 3.4V gives you the same energy storage, so why do you stay high up to 3.4V? Stay at 3,35V

[@dredre9484]

Something cool I learnt from a E bike builder he recommends that every 10th cycle charge your battery fully 100 this helps with balancing the pack (frog)

[@zarbonida]

Ebikes use an other kind of chemistry: NMC (Nickel, Manganese, Cobalt) Andy uses LFP batteries

[@dredre9484]

@@zarbonida Your absolutely right but this guy was using like Andys battery put cylinder cells story short he was not looking for instant power he needed longitivity when I find the vid I put up the link

[@scooter6334]

Australia has such awesome creatures :-)

[@haraldhannelius]

So I figure that tail current is quite OK to use in a AC-DC charger, but not in a solar charger. Thanks edit: Apparently my JK BMS connected to a raspberry running Venus OS isn't able to communicate voltage limits to the Victron Smart charger, which only has bluetooth.

[@peterwareing3045]

Higher voltage 55.5 to 56 achieves the Float mode quicker (less asorb) which then reduces input / output battery losses with the power going straight from panels to load - got to be a win / win situation especially if your a frog

[@electrojessy4270]

Nice video as alway’s 🐸

[@ltcmdrdata4611]

Andy, as accurate you are, try 3.47V and you should be fine. Regards to Diego.

[@OffGridGarageAustralia]

Everything over 3.45V will just work. I was just curious to see what I can find about the absorption time and tail current.

[@stephsoltesz6731]

Tail Current - EndAmps is calculated as 0.05C of the Highest Battery Pack within the battery Bank. For a 280AH Pack that is 14A. General convention by Known Manufacturers (Like Battleborn and others) ss well generally recommend 15 Minutes Absorb per 100AH Storage Capacity. These settings work, are observable & reproducible. Try to ABSORB @ 56.4V FLOAT @ 55.8V Rebulk @ 55.2V PAY ATTENTION to the BMS when running Absorb and monitor it from 15 Minutes and you will see the deviation kick off and run a bit. REAL TIE observed, Absorb on my systems are set for 1 Hour but within about 25 Minutes Absorb Stops as EndAmps is reached and Float starts. IF Power is drawn which the Float cannot service & battery power is withdrawn, then the system will kick back into Absorb & Float once Tail Current is reached again. I watch this EVERY DAY and being 100% offgrid solar, it is LIFE @ WORK.

[@jmaus2k]

Victron needs to have a trigger with Amps and Volts. Something like 2A at 54.2V, 5A at 54.4V, 10A at 54.6V.

[@1981dasimpson]

i was going to say something like this but when i think about it i would just set a max voltage they be no need for current shut off as the loads will always draw power keeping this load setting on as long as the solar is powering the loads and no current is flowing into the battery due to full charge voltage reached i feel this would be fine and alot less settings to worry about

[@jmaus2k]

@@1981dasimpson The theory is that you want to charge to a higher voltage than if you float. So full charge would happen with 54.6V @ 10A or 54.2V @ 2A. Then float at 54.0V so you never overcharge. Setting at 54.2V would overcharge and wouldn't charge as fast as if you let voltage to increase with more current.

[@1981dasimpson]

@@jmaus2k my idea is the top end tapers off due to the voltage been more equal at this point your loads are drawing power none stop so the battery is fine to slowly charge if loads are not drawing the solar plus some

[@upnorthandpersonal]

Victron should just communicate the actual state of charge from the shunt to the charge controller. Then there would be no mucking about with tail currents and voltages...

[@1981dasimpson]

@@upnorthandpersonal yes they is that

[@Refael302]

Why not 3.65v?

[@oogie-boogie]

1 of the prob's im having,, is my charge controller in float but its still charging the batts, its still pushing 1000 to 500 watts , with nothing connected to it,, sooo why is it float if you still have volts and amps coming in?

[@jackoneil3933]

Andy, I was just thinking about how large a supercapacitor bank would be required to even out the transient solar peaks and lows, but if at 8:06 the time slider on your phone is showing from 0 to 2.49 hours rather than mins, you would need a pretty large supercapacitor would you not?

[@OffGridGarageAustralia]

Yeah, that would make no sense. The MPPT are highly capable of adapting to the peaks. The 'problem' here was the voltage was too low to allow the MPPTs to go full speed. At 3.45V, these problems don't exist and we don't hit that ceiling any more and cap out charging. It was just another test to show how absorption and tail current can fool the system (an you).

[@jackoneil3933]

@@OffGridGarageAustralia Yup. However, If the Smart Shunt is accurately gauging charge level, then it seems simple enough to add a BT channel to the MPPT controllers and a software feature where Float only happens at a set percentage. Perhaps you should send Victron the video and see if they can implement that or have other suggestions.

[@photocromax]

🐸 can't believe Victron hasn't a better charge logic/trigger. Does the charge controller accept external commands? I mean can you tell it "charge!" Or "float!" ? Or is just a consequence of the triggers parameters? Could be nice, if possible, to implement an external supervisor for the controllers.

[@رسمينوفل]

Required Information For me And nice

[@jackoneil3933]

Excellent useful information Andy. I'll be building some LifePo4 packs using cylindrical 32650 cells to confirm your result. Also, do you see a charge controller feature that measured internal resistance to detect when to float, or possibly an external trigger circuit that sensed charging current and disabled float whenever charging current was at or below float current as being worthwhile features?

[@OffGridGarageAustralia]

Thanks Jack, interesting project you're working on. Measuring the internal resistance (Ri) to determine SOC or control charging speed is highly unlikely. The accuracy will be very low. There are lot of other factors influencing Ri. But @Brad Cagle is working on some other cool stuff ata them moment to read out parameters from the BMSs and feed this into the charge controllers. That would be a precise way to stop charge at any given SOC.

[@kcjones3368]

I'm building a 60280 bank.. 11.7KWhr I'll let u know how it goes... I can fortunately bolt everything together because these cells have studs on either end of the cylindrical cell... Are you going to have to spot weld yours???

[@jackoneil3933]

@@kcjones3368 Yes I am going to spot weld some 6000mah Fbtech cells to keep the size to a minimum. Are you using the 5000mah cells with the screw terminals? I'm also going to do some experiments with paralleling electrically isolated small, 120amp, 6ah 72V Li-on cell pack with solid state relay for interment high amp loads and a 48V, 50amp, 20ah LifePo4 packs for lower amp cruising in for an EV test application.

[@kcjones3368]

@@jackoneil3933 Nope...I've gotten ahold of 64 monster (55Ah 60mmx280mm) cylindrical cells with 12mm studs...pack will bolted together with copper plates...4p x 16s...51.5vdc nominal 11.7 KWh pack... I've Got all the batteries (checking for capacity now), 4.8KW solar array and the overkill solar 100A BMS... I need to save up some more cash for The all-in-one growatt 6KW 230VAC inverter... But in the meantime I've got plenty to do building the pack and ground mounting the panels... This will be an auxiliary system that will run a secondary water heater, well pump, and 2 mini splits separate from the 22KWh off-grid system that already runs my house 👍 Those multiple packs will be interesting.... I've played around without a little but it can be pretty complicated to get everything working right ... Good luck Hope you do a video on it 😎

[@jackoneil3933]

@@kcjones3368 Sorry I missed "60280". That's a pretty robust storage. Are you planning on running your water heater off the battery pack and/or inverter? If so, it might be worth looking into feeding DC direct into heating elements an taking the load off your inverter. Years ago I did a 30kw 480VAC 3-phase hydro electric system where we used a surplus industrial AC to DC SCR drive to to feed a variable load to heating elements in hot water storage tanks to load the AC generator and control the speed of the water turbine to keep a constant frequency.

[@grahamwinn979]

There is life out there but not as you know it. Will the next video start from the watering hole and Diago. Thank you.

[@dig1035]

Thumbs up and subscribed!

[@OffGridGarageAustralia]

Are you not writing this under every video? Or is there more than one Dig, like 26 or so?

[@wenhaowong5549]

oh, finally the frog is back

[@TheMickSyd]

Andy, great video! 🐸 I have experienced the same frustration with lack of coordination between Victron smart shunt and charge controllers. In my case the shunt occasionally resets the SOC to 100% much to soon based on tail current falling away. This is not due to the pack being full it's due to the power from the panels dropping off at the end of the day. The charge controller knows what is happening because the panel voltage also drops off so why can't it tell the shunt this is what is happening and improver the SOC reporting! Perhaps there will be some firmware updates from Victron some day to properly take advantage of the shunt and charge controller pairing?

[@aureltanasan1413]

For the shunt to work with the charger on network, I believe those functions needs to be enabled on a GX hub under dvcc. You enable voltage temp amps, limit amps etc.

[@camielkotte]

Andy, my victron charger goes into bulk e every day again despite the fact the battery is full? Or is the history diagram wrong?

[@dennisdevreede2113]

does the tail current setting not also allow you to set the period the tail needs to stay below set value?? sometimg like below 4A for a period of 5 minutes?? that would help with these pesky Queensland clouds...

[@sjdtmv]

I use 3.55V and regularly get 100% SOC

[@matthewbryce8694]

G'day. Can you translate theses settings to the parameter settings of an Epever?

[@graemebushell7531]

My case is a little different, I'm setting up a LFP system in a motorhome that spends significant periods not used. I want to keep the cells away from 100%, but also keep them balanced (I realise these goals conflict somewhat). I'd prefer to keep the system connected to the solar, because there is a small constant load of about 15W for ventilation. I'd also like to not have to actively intervene too often. The balancing for my (DALY) BMS kicks in when it sees cell voltages of 3.35V. I'm thinking that an absorption voltage like this (3.4V) and a long absorption time might do the trick, or slightly higher at 3.45. What do you think?

[@Raphael_Hofmann]

I thought that the tail current only triggers the Absorption, if the end of charge voltage treshold is reached. Temperature also has a major impact on the voltage...especially in colder climate. 🐸

[@OffGridGarageAustralia]

So the tail current tells the charge controller, that the battery is full and does not take any current any more. That is true for systems where you have either a constant current from a grid charger of heaps of solar and a smaller battery. But with clouds you could have a small current too and if absorption time has triggered, it tells the charger to go into float because the current is low so the battery must be full. It's not a good indicator for that in my experience. 🐸

[@benengelbrecht5637]

Andy. Hallo from South Africa. Does your Victron Charge controllerd (larger models) have "adaptive absorbsion" ? I am working with 12volt and set my 75/15 victrons all to that setting. Seeing I just changed to Lithium batteries i have no idea if that is a good idea

[@OffGridGarageAustralia]

Hi Ben, no, they don't have adaptive absorption either. Never heard of this before. I'm getting 150/70 soon, so maybe these have such settings...

[@benengelbrecht5637]

I am using 75/15 models, much smaller than yours, and then also "12volt" systems. I still have to test what the adaptive does and how it infleunce the final result. Thank you for all your testing! You should call it "DC SOLAR TECNOLOGY RESEARCE" 👍👍

[@benengelbrecht5637]

I tapped on "fixed time" in the app above the 2 hours and it opened the option

[@OffGridGarageAustralia]

@@benengelbrecht5637 Ah, I see what you mean, yeah, nah, you leave this on 'Fixed' as we have Lithium batteries here. The Adaptive Absorption is for lead acid batteries. Once they have been deep discharged they need a longer absorption time to recover. That's what the setting is for.

[@benengelbrecht5637]

@@OffGridGarageAustralia Thank you for that answer. I will then rather play with fixed absorb time.👍

[@SiriusSolar]

Can you override the system and force it into a certain charge state? If yes then you could hook up a raspberry microcomputer to monitor the state of charge and force the charge controllers to go to float when you hit the percentage you're looking for. And then you could program it to at least every so often allow it to go up to a higher voltage for a time in order to achieve a top balance and recalibrate the state of charge meter.

[@SiriusSolar]

A frog...

[@harrycrawford8517]

The frog must be monitoring your amps, they only come around when there are lots.

[@OffGridGarageAustralia]

Hahaha, you would think so. I never thought about that! 😂

[@martinmalm7254]

🐸 Andy, What’s your smart shunt setting for “Charged Voltage”?

[@OffGridGarageAustralia]

At the moment, I have turned it off because I want to test how accurate it still is over time with no calibration at all. Usually I set it to 3.44V/1% tail current and 2min if the absorption voltage and time is 3.45V/15min for example. That gives the shunt time to re-set back to 100%. That's the reason I have set a 15min time on the absorption to let the current come down enough to trigger the smart shunt reset. Victron recommends far lower reset numbers which I don't agree with at all.

[@michaelbouckley4455]

🐸

[@OffGridGarageAustralia]

@@michaelbouckley4455 🐸

[@martinmalm7254]

@@OffGridGarageAustralia when you say turned it off, is that 0,0V?

[@OffGridGarageAustralia]

@@martinmalm7254 I have set the re-calibration to 3.65V/cell (58.4) so it never triggers the shunt to reset to 100%. I'll watch the drift over time at defined voltages then to understand why it is drifting.

[@tcloud24]

what SOC do you start the day at?

[@OffGridGarageAustralia]

can be anything from 20%-70%. You can see it here in the live view: vrm.victronenergy.com/installation/100328/share/2e028071

[@tcloud24]

@@OffGridGarageAustralia COOL!!!!! looking at yesterday's graph shows max soc about 13:00. after that it falls off never to see that soc again that day. feels to me like you need to go back and watch your "float" video. i can only guess at when sunset is, but it appears you are leaving at least 3 hours of energy on the table. causing a lower soc to start the next day, etc., etc, etc.

[@OffGridGarageAustralia]

@@tcloud24 yes, that was with 3.4V settings. You can see the battery voltage being constant at 54.4V during midday. Yesterday, the battery was at around 85% when I plugged in the vehicle to charge. That's the step drop in SOC afterwards.

[@tcloud24]

@@OffGridGarageAustralia how much energy does it take to drop to float voltage?

[@MotorhomeDIY]

Hi I’m very new to this so looking for some advice if this is ok to ask . I have 12v battery 200ah with Victron mppt I have found the absorption and float of my battery which is 14.6v and 13.3v but I’m unsure on the tail current which at the moment says 1amp I also have the Victron bmv-712 which I’m told the charge voltage needs to be 0.2v below my absorption which will be 14.4v but again I’m struggling with tail current in the bmv I’m wanting everything to work correct with mppt and cerbo and bmv I also have multiplus I’m so confused on the tail current and detection time I’m finding even tho I have 480w of solar it’s in bulk mode all day long I wake up the bmv says 96% so mppt in bulk all day and by sun down it’s still in bulk at 99% I’m not getting the float the only power getting taken from the van is wi fi router not even 0.70amps

[@OffGridGarageAustralia]

I have made a lot of videos about this and you also can have a look here on my website for more information: off-grid-garage.com/my-settings/

[@MotorhomeDIY]

@@OffGridGarageAustralia thank you

[@DaddyResonance]

Dude please help me.. My 100/20 is going into float mode stating on the app it's 13.8volts but when I test with multiple multimeters it's only 11.4volts and my inverter is giving me a low voltage alarm when adding a load?!?!? Please could you help I'm going to loose my mind ?!?!

[@dig1035]

Absorption to float, sorry newbie question, is this a change in charging rate?

[@OffGridGarageAustralia]

Absorption means, that the charger keeps the voltage constant and the battery takes less and less current over time. It absorbs until the current hits 0A. The it is fully absorbed for that voltage. You usually drop the voltage then to a lower value to keep the battery there and float (this is at around 99% state of charge). In this phase, the charger supplies power to the load and nothing goes to the battery any more. If the load takes more power than the charge can supply, the battery will add this extra power and feed it to the load. After the load has been disconnected, the charger will recharge the battery then again but keeps it on float voltage.

[@john_in_phoenix]

Float is what the charge controller drops to when you are full, and the real purpose is to have the charge controller supply as much of your load as possible without micro cycling the cells. When a cell is full, even if you use the max voltage of 3.65v, the first amp you draw will drop the cell voltage to 3.35v (or very close). This is easy to see on the discharge curve the EBC-A40L records.

[@leandrosphotostudio]

I need your help . What tail current in the charge controller? Batteries eg4ll lifepo4 600 AH, victron 250/85, 24v system.

[@OffGridGarageAustralia]

I have my tail current turned off. I absorb for 1h and then go back to Float voltage. Have a look at my settings here: off-grid-garage.com/my-settings/

[@leandrosphotostudio]

@@OffGridGarageAustralia see!! I copy ypur settings. My rhing is that ibsee a consistency in absorption time, ive been getting 20 miniutes only, time to check the victron smart shunt, undecided aboit having 2% of tail current ladt week its been on .5%.

[@RustyRoseAdventures]

Frog 🐸Once again great video andy. I'm with you on the 3.45 it seems a good voltage👍

[@Y2KSailing]

Super nice Diego! I have bmv-712, not the SmartShunt. On the back of the instrument it is available a small relay with dry contact that you can manage with the SOC parameter. Do you think using that relay to pilot a big and huge industrial relay to stop solar to enter in the solar controller can be an idea? So for example if you reach 95% SOC, no matter of the setup of your solar controller, you can stop the charger. When SOC will go under 92% (example) you close again the relay and charge again. What do you think?

[@aureltanasan1413]

Yes you can do that, or trigger a diversion load and make use of extra solar going into a hot water or air con, heat pump etc.

[@1981dasimpson]

damn thats green for a frog i still wounder if you set the float voltage so the batterys are 3.45 each no bulk or absorption i feel they is no need for a current shut off as dc loads will draw that off the solar bank and not the battery and nothing will flow into the battery as they have reached the set voltage this way the cells should stay fully charged untill they is no sun to keep them there and you wont have them dropping into the low voltage set for float they are now and have the banks discharging putting small discharge cycles on the cells

[@OffGridGarageAustralia]

That's correct. but 3.45V is too high for float. It may overcharge your battery. There is a tipping point in voltage. Below that point, the battery charges inconsistent, above it can overcharge as the voltage is too high and current can constantly flow into it. If you charge to 3.45V and stop charging altogether, you're already at 99%SOC. If voltage then drops to say 3.35V you will loose 0.5% of capacity but keep the batteries below that point. That point it directly when the charge curve leaves the flat area and voltage starts rising. It's somewhere between 3.4V and 3.45V and depends on other factors as well (absorption, temperature,...) So staying below that point for floating is recommended, 3.35V or 3.375V is great.

[@1981dasimpson]

@@OffGridGarageAustralia if max voltage of fully spec charged battery is 3.55 or 3.65 i dont really know on lifepo4 i play with 18650's how would charging to 3.45v each cell overcharge or do you mean if one cell is lower then the others due to a balancer not able to keep up

[@tg_privat]

Buck DC-DC converter before solar charge controller may solve such problems. Maybe.

[@SiriusSolar]

QUESTION or video idea. With all of your Hands-On knowledge regarding what voltage it takes to fully charge and balance cells what is your opinion in relation to off-grid use on bottom balancing versus top balancing?

[@OffGridGarageAustralia]

Thanks Travis. I would always recommend top balancing. In solar storage installations, you will use your battery rather in the medium to higher SOC area than completely depleting it on a regular base. So it should be optimised for that. All gear you buy does top balancing. I never heard about a bottom balancer or a BMS which does bottom balancing. At the end, it does not really matter in terms of capacity. The cell with the lowest capacity will determine when your pack turns off either way. I think bottom balancing is a bit outdated these days.

[@TheComputerGuyDR]

FROGS!!! Now was that Diego? Next one should be Rango :P

[@Martkl]

Question. Can you use a pwm controller to charge a lithium battery who has its own bms? With solar

[@s.mendez7160]

Using PWM is not recommended with Lithium due to inherent voltage spikes seen during the rise time of the Pulse Width.

[@danielardelian2]

(frog) Just set both Absorption and Float at 3.40 V per cell. You are not gaining anything by dropping the charge controller voltage to a lower level. The loads will discharge the battery (micro-cycling) during that time and you will lose solar energy. Eventually, it might go into re-Bulk / Absorption again and do another micro-cycle. If you don't want to charge to 100%, then just set a lower voltage. It makes no sense for LiFePo4 to charge to 100% just to quickly go into discharging afterwards. Absorption and Float at different voltages are remains of the Lead-Acid technology. For lead-acid, it does make perfect sense to charge to an Absorption voltage, stay there for a while and drop to a float voltage. But that is a requirement of the chemistry. It does not apply to LiFePo4.

[@magicmanspaz]

I don't care about the weather temp Andy "How many amps" is it outside :-) hahahaha

[@gregb1714]

Why not just set the float voltage at 3.4V per cell?

[@ssyoumans]

That’s what I do as well. Charge to 3.45, float at 3.4. May even charge to 3.5v, float 3.4.

[@OffGridGarageAustralia]

3.4V is a bit high for floating. It is over the tipping point and can overcharge you battery if it sits on this voltage for a long time. I would go lower to 3.35V or 3.375V. That is close to the natural resting point of the cells. From a capacity perspective there is only 0.4Ah difference between 3.45V and 3.35V.

[@gregb1714]

@@OffGridGarageAustralia OK. But if you start charging when when the sun is out, it will take some time to charge up the batteries. It doesn't seem like the battery cells will be at a 3.4V float too long because when the sun goes down, you will start using battery power (maybe sooner if you have high power usage). Seems like another test is needed lol.

[@Mr.X3D]

@@OffGridGarageAustralia Please give a reference to that statement. I’ve found no evidence whatsoever that any voltage below 3.65 would bring any damage to a lifepo4 cell. To me it’s just an urban legend. How can you ever overcharge at 3.4v?

[@OffGridGarageAustralia]

@@Mr.X3D There is a tipping point somewhere between 3.375V and 3.5V If you keep the voltage constant below that point, the battery will not charge consistently (see my previous tests when charging to lower voltages). If you keep the CV at say 3.5V there is a risk, that the current neve goes to 0A and it keeps charging the battery forever. You could end up adding far more energy as the cells can take. It depends how long you keep it there for. Some users have grid chargers, they just keep the battery there forever. It is known that the higher the voltage will damage the cells over time too. 3.25V is considered a neutral voltage and there is no stress or damage as such. Going below or above that, the degradation starts to increase. The higher/lower you go the more stress you put on the cell. 3.65V is just the maximum voltage you can charge the cell too. That does not mean it's good doing so.

[@timos144]

Mess mal direkt an der Batterie die Spannung, wenn du solche schwankenden Spannungen vom Solarregler bekommst bei wechselnden Strömen. Wenn die Spannung direkt an der Batterie auch so schwankt, ok. Wenn nicht, mal den Kabelquerschnitt prüfen bzw Spannungsabfall an verschiedenen punkten messen. Bei 50-60A bleibt schon mal was auf der Strecke...

[@magnuspernemark2339]

How big is you r battery? I have a 28kWh LiFePO4 battery that I charge with 95A. I have seen voltage variations when amps change, but nevery to the extent you experiance.