Top Balancing a Lithium Battery Pack

[@somebody1869]

I prefer the 5A active balancers for top balancing new packs. The cells ship at roughly 50% SoC, and are not at all balanced, but also, they’re not wildly unbalanced (like 70% SoC and 30% SoC). Hooking them up in series, with their BMS, and charging at pack voltage allows more watts of charging faster at the bench supply max current. It also provides good per-cell voltage tracking. Once the cells start approaching knee of the curve (~3.40V/cell), you turn on the active balancer, and keep the bench supply charge voltage at 3.5v/cell. Once charge acceptance drops to about 1A, you creep the voltage up by 50mV/cell, and let the active balancer do its magic. Keep creeping charge voltage up until you get 3.65v/cell and less than 1A going in to batteries. I use a BMS that gives me some relays and event-logic I can use to control the active balancer circuit since leaving it on in the flat part of the curve is actually bad for long-term balance.

[@jasonmcintosh2632]

I really appreciate these videos and will be following them closely when I'm ready to put lithium in my boat. I hope everything's going well with you and your family!

[@RiggingDoctor]

Thank you very much!

[@ericblackburn9829]

Do yourself a favor and watch off grid garage. The information on batteries is much more thorough and correct. No offense @riggingdoctor.

[@jeffdege4786]

I can see this being important in a DIY battery, that you built out of cells yourself. But if you're working with a commercial battery, where the individual cells are sealed in the case, is there anything you should do other than hope that the manufacturer did this correctly?

[@RiggingDoctor]

This is why I insist on building your own battery. The cheap commercial ones are significantly cheaper than the cost of the parts which means they are made out of rubbish parts! The better batteries that you don’t need to worry about are so expensive. By building it yourself, you can use good parts and also do it properly.

[@uhjyuff2095]

Yes, I bought a prebuilt battery and if you follow a little procedure the internal bms can balance the cells. What I did was setup a charger connected with a smart outlet. I set my smart outlet so the battery would charge for 10 minutes (once fully charged) then turn off for 10 hours then on for 10 minutes and off for 10 hours for 3 days and then the battery slowly got more balanced. I just got the battery and I didn't know if it was perfectly balanced and now after reading the full charge voltage of the battery I can be assured its balanced.

[@melinda5777]

Loved it of course. DIY!❤❤

[@RiggingDoctor]

Yay! Thank you!

[@solosailingboatlife7203]

Why not just use a proper BMS with active top balancing capability ? Just adjust solar charge points every year to allow top balance to happen then put it back to the lower day to day charge cutoff point.

[@mikem720]

The context for this is if you are running component cells, presumably with a BMS, NOT one or more retail batteries of nominal voltage 12v, 24v etc

[@RiggingDoctor]

Yes, this is the third video in the series on making a lithium battery. This battery is a 12v battery but it could easily be reconfigured to make it a 24v battery (with a different BMS).

[@uhjyuff2095]

You could balance the battery very quickly with a RC style lithium battery charger because they have decent balancers for balancing multicell battery packs.

[@RiggingDoctor]

The issue with “quick” is the cell doesn’t accept the full charge quickly and it really does take a while. You will never charge the cells this full ever again, which is why the battery is said to charge very fast when in use. It takes a while but it’s worth it as it makes the whole battery work better.

[@uhjyuff2095]

@@RiggingDoctor When the battery cells are receiving less than one amp at full voltage the battery is very very close to 100 percent. Continuing to charge at less than one amp is not worth it because there is no more battery capacity to be stored in the battery. So the RC style charger will balance all the cells so they accept the same level of charge by using a resistor across each cell that is higher voltage than the others until every cell is perfectly even. The charger doesn't have to charge for hours and hours at a low rate it just needs to charge until it sees that all the cells are charging evenly when at 3.6-3.65 volts for perfect top balance.

[@RiggingDoctor]

Oh, you mean as a permanent part of the installation! That would be handy!! This slow process is to get them all balanced since we don’t have that and they are being charged by a 58v source.

[@03f150harley]

He talking about the Cellmeter 8 its 12.00 and i just ordered one. @@RiggingDoctor

[@mariam5964]

Hi there, long time watching....where is your painting at the marina in faial? On the ground or wall? Thanks..we are here in faial now 😊

[@RiggingDoctor]

So cool! It’s on the wall where the bench is instagram.com/p/Bm2eAoWDKE_/?igshid=MzRlODBiNWFlZA==

[@RiggingDoctor]

Could you send me a picture of it? My email is [e-mail]

[@RiggingDoctor]

It was on the way from the customs house to the bathroom/showers on the left side and I think about midway.

[@RiggingDoctor]

How was your crossing?

[@paulbiggs2276]

Your video is very interesting is it possible to repair Your bms when they go bad

[@RiggingDoctor]

If you know how to solder on a circuit board, then yes. For me, I just carry a spare. A few bolts and plugs and it’s back up and running.

[@mymobile5014]

The question is if you don't have access to each individual cell, as in an enclosed battery, how do you top balance then?

[@RiggingDoctor]

You top balance it before you put it in the case.

[@RiggingDoctor]

I couldn’t reach the cells in the case, so I top balanced the pack before I put them in the case.

[@mymobile5014]

Mine is a bought battery I didn't make it. I have no access to the cells inside.@@RiggingDoctor

[@ericblackburn9829]

@@mymobile5014 In that case, you don't need to top balance. The manufacturer should have done this.

[@uhjyuff2095]

@@mymobile5014 Yes, I bought a prebuilt battery and if you follow a little procedure the internal bms can balance the cells. What I did was setup a charger connected with a smart outlet. I set my smart outlet so the battery would charge for 10 minutes (once fully charged) then turn off for 10 hours then on for 10 minutes and off for 10 hours for 3 days and then the battery slowly got more balanced. I just got the battery and I didn't know if it was perfectly balanced and now after reading the full charge voltage of the battery I can be assured its balanced.

[@tim_bbq1008]

The battery charge controller doesn't manage this for you?

[@RiggingDoctor]

The expensive ones do, but not all chargers will, especially not a cheap solar controller. It is always best to have built in safety protocols integrated into the battery so that if you change chargers in the future and forget to set it up properly, it won’t kill your batteries. By installing the safety controls in the battery, you don’t need to worry about the amount of charging or quality of charger you use to power the batteries. They are merely receptacles for storing any power given to them.

[@ericblackburn9829]

@@RiggingDoctor You're killing me man! Don't depend on your bms for low voltage (or high voltage) cutoff. It should be a last resort! BMS's use mosfets to cutoff discharging and charging. Mosfets are susceptible to failure under "high" current (especially in the cheaper BMS's). FYI, your BMS will still work if one or a few mosfets fail, so you won't know you have a problem until you have a REAL problem. Always configure all other devices to cutoff at specific voltages and save your BMS safety for the time you really screw it up.

[@ericblackburn9829]

You're a little off on your "Don't charge to 100%" comment. Lifepo4 is not like other lithium chemistries. The rule with Lifepo4 is don't keep them at 3.65 volts for extended periods of time, but charging them to 100% then stop charging, use them and recharge to 100% every day is fine.

[@RiggingDoctor]

3.65v is 100% SOC I set the BMS to consider 3.50v to be 100% and to cutoff the charge at the high voltage mark. This keeps the battery almost fully charged on the high end and still with plenty of power to give on its way down to discharge. The bigger issue is a boat that sits all week charging from the solar panels and is full charge until the weekend, that would be an example of 3.65v for a long period of time most of its life.

[@ericblackburn9829]

@@RiggingDoctor agreed if the batteries sit at 3.65 volts for the entire week. I’ve had LifePo4 cells for four years now. Our boat stays at the dock during the week charges to 3.55 V every day and runs the refrigerator throughout the night actually 24 seven our solar panels bring the battery up to 3.55 almost every day.

[@uhjyuff2095]

@@RiggingDoctor I would hope the charge controller would have a float charge mode set at a lower voltage than the bulk/absorb voltage level.

[@ericblackburn9829]

Exactly @uhiyuff2095. The boat at the dock will have a float voltage. I set mine to 13.3 volts. That brings the battery down to about 97-98%. Not ideal but my manufacturer has confirmed this is ok for lifepo4.

[@ericblackburn9829]

Another thing I do is only use solar to charge my batteries. 3 -12v304ah batteries in parallel for a total of 12v912ah. They run the fridge and freezer every night to bring them down then charge back up the next day, stay at 14.1 volts for 15 minutes then float the rest of the day.

[@DowneastThunderCreations]

👍👍👍

[@mymobile5014]

So, you state that LFP's hate being charged to the max, yet later you say on a sailboat with solar panels they ARE going to be fully charged a lot of the time. So what's to do? Do we have to have a cut off on the solar controller and mains charger?

[@RiggingDoctor]

Just use your electronics a bit more liberally when you are at full charge to help bring them down. Running a high power appliance during the day would be great as it will bring the power down while the panels are cranking the power. Ideally, you want to keep the battery between 10-90% state of charge. Basically, if you are charged up, turn on the water heater and use up the power. If you have an electric dinghy, this would also be a great time to charge its battery as well. Basically, the panels will charge you all the way up but the batteries don’t like it but as you use stuff in the boat, especially that night, it will bring the batteries back down to a comfortable level.

[@ericblackburn9829]

@@RiggingDoctor You're confusing advice for other lithium chemistries with Lifepo4. Lifepo4 can handle being fully charged every day. The rule is, don't keep Lifepo4 at 3.65 volts for extended periods of time (like days to weeks at a time). This comes from my research and several manufactures advice.

[@RechargeableLithium]

@ericblackburn9829 You're correct, Eric. I've tried to help Herbie understand since his poor decision to spot weld (and later solder) small cylindrical cells. He appears to be immune from education, unfortunately, which I guess is the normal cycle of "content" creation on this platform. I've been working with LiFePO4 prismatic cells since about 2007, yet Herbie acts like they're some new invention. I've given up here, and continue to be concerned with his followers.

[@pelerocks]

Have you ever been on NCIS

[@RiggingDoctor]

I have not 🥸

[@offpro]

In my opinion, top balancing is not as relevant anymore as it used to be. A modern BMS will have active balancer that does the work for you.

[@RiggingDoctor]

This BMS that has very good safety features that actually work doesn’t do a good job at balancing.

[@offpro]

@@RiggingDoctor Cheaper to buy a new BMS then a PSU... 4 PSUs in your case... 🙃

[@mckenziekeith7434]

@@offpro you can also buy balancers that you can hook up until the cells are balanced. They are cheap. Way cheaper than 4 power supplies.

[@ericblackburn9829]

I know you mean well to help educate your followers but you are creating a large group of misinformed KZbin warriors. You might want to do a deep dive in to “off grid garage”. There are a ton experiments he has done to dispel many myths and misinformation out there about lifepo4. Some of which you are perpetuating in your videos. Just friendly advice, not trying to be unkind.

[@RiggingDoctor]

That is a good point, and while it is really hard to make a bad situation with LiFePO4 cells, fire or high heat on a boat is a very bad thing. My thoughts were two fold: 1. If I scare them, they will be careful and stay safe, 2. If they use Li-ion because they didn’t realize there was a difference, they will be ok (but the ion cells are the real danger cells on a boat. There are test videos where LiFePO4 cells catch fire, but the tester really “tried hard” to make them burn.

[@thomasthornton5737]

😀👍👍👍❤