diyBMS - Provisioning and Calibrating - 12v Solar Shed

With seven modules (almost) built it is time to provision them. I also look at the options for my bypass resistor and calibrate the voltage readings.
Items used in this video:
❗️These links are affiliated and I may earn a small commission if you purchase❗️
10W Ceramic Resistors: ebay.to/2lRl5xU
Crocodile Clips: ebay.to/2u2y2Zq
Wemos D1 Mini: ebay.to/2u12mUd
Vici VC99 Multimeter: ebay.to/2KEkY70
3d Printed diyBMS bracket: admw.uk/kq
diyBMS by Stuart Pittaway on Github: admw.uk/diyBMS

[@nomadic_rider42]

It's nice to see how you progress this project. Good luck with your projects.

[@MrKitesurfercharlie]

Thanks a lot for the update. I have been busy soldering my boards. Still waiting for some components to arrive though. I am looking forward to reaching the point that you are at.

[@AdamWelchUK]

Excellent to hear. I'm enjoying the journey

[@MikesDIYTeslaPowerwall]

Cant wait to see another update on this :)

[@Cavalier_Steve]

I really really like this!!! Now I want to build one.

[@AdamWelchUK]

It's been a fun project so far and has allowed me to do some surface mount stuff. Still lots of testing and playing (and possibly coding) to be done. It's a bit of a long project for me this one! Cheers Steven

[@Cavalier_Steve]

Adam Welch excellent I will be watching with great interest. Cheers Adam your videos are great!

[@xanataph]

Nothing wrong with croc clips...! Much of my system is held together by them...! Of course the *intention* is to replace them with more permanent wiring once the experimentation is done, but that can take longer than one expects..! lol We're now past the Winter Solstice here in NZ, so days are getting longer again. Yay. :)

[@AdamWelchUK]

Yes I think they may be a semi-permanent solution :-) The only better option in reality is to pop ring terminals on the end of the cables and sandwich them with the main block connectors. Another winter solstice on solar done - well done Xan!

[@MikesDIYTeslaPowerwall]

Are you going to be charging to 4.2v tho? Thought you would only be charging to 4v in which case i would do the math at 4v. Given the small pack size 200mA would be fine but you could do 500mA it really shouldnt make much difference. I would go 1amp. The benefit for the higher current would be if the charger is putting out 1amp it would mean the balancer would be able to keep up not letting the cell voltage rise. Looks great tho :) Nice work

[@AdamWelchUK]

No - I won't be charging to 4.2 volts in reality. My calculations were based on worst case I guess. I see the argument for a higher discharge resistor, and I may well be upgrading that further down the line. This is my third 7s pack I've built (7s4p, 7s8p and now 7s20p) and I've spent a lot of time testing the cells and building even packs. Balancing is wasteful, and I hope in reality there isn't going to be much balancing required due to the preparation work. In those previous packs I've used the capacity controller - and it discharges at about 25mA, but it kept those packs in balance really well. It's all experimentation and I'm enjoying the journey, it's great to get feedback and ideas and always good to hear people are enjoying the journey with me :-) Cheers

[@tengelgeer]

But it's not going to be more wast full with 4Ω than with 22Ω. Only with 4Ω you can keep up with a 1A charger as with 22Ω you can only keep up with an 200mA charger.

[@MikesDIYTeslaPowerwall]

Thats a good point too.

[@MikesDIYTeslaPowerwall]

7s20p. Is the next packs 40p? :) Its good your spending a lot of effort on even packs. It's much harder to do on very large packs given the time it would take. My other thought on this is how much is it really going to matter. At the start the packs will be in balance with even cells (great) and if the cells were band new and degraded at the same speed that would make sense. But they are not they are old cells pulled from different sources and put together (some might be a year old some might be 4ys old with the same capacity) and in which case each cell in the pack will degrade faster than others, so longterm after a year the cells in the pack have aged "differently" in which case the pack will no longer be as even as you first started. So my question is how important really is it to build the packs as even as possible given the changes of the cells longterm. The "longterm" could be just the first year and then the question is was it even worth it (timewise etc)to start with very even packs vs close enough. As long as the balancer can keep up with (close enough) then no problems right? :)

[@3dprint-tech787]

I don 't quite understand why a 1 amp discharge would be too high for a cell that size. Seems quite good to me. And the bms would stop the discharging anyway when the minimal treshold is reached. I'm not at all trying to say you're wrong, I'm just curious what the sience behind that is. Cheers, Bo

[@CrankyCoder]

awesome!! I have been working with Collin lately myself. I have my 4s80p now setup with the boards myself. very cool stuff :)

[@AdamWelchUK]

Super - Colin is a good guy. Are you working on the grafana code with him?

[@CrankyCoder]

That's the plan. Been going back and forth just trying to get some stuff stable and then the grafana piece and some other ideas like having auto balancing kick in only when it detects it's being charged up ect. very cool stuff :)

[@MaxintRD]

+1 - Interesting series! Looking forward to see how it al performs in the real world of solar charged energy...

[@spa3210]

Hi Adam, Thanks for the great videos and sharing with us your progress. I can't find your video on the WEMOS D1 ESP8266 Mini. Did you do one? How did you do the web server? Thanks and cheers.

[@AdamWelchUK]

The code I am using is all put together by Stuart Pittaway and is available in his Github - admw.uk/diyBMS He's created the web page which you see in this video. I mentioned in the programming video the little bit of extra hardware required for the wemos and showed how to upload the code on it too ( kzbin.info/www/bejne/kJLLc2Bua9-tnLM ).

[@DecDude84]

Adam I'm learning a lot from your diyBMS series, this is quite fun! One question, is there a maximum amp-hour that each module can handle?

[@AdamWelchUK]

Thanks very much Colin. The module is limited to about 2amps of discharge current, so that’s a lot for a 2Ah cell, but not a huge amount for a 200Ah group of cells. It’s as much to do with your charger - how much power might you need to dissipate if the cells go out of balance at the top of their charge? In my solar scenario the charge controller is limiting the current at the top end, so my few hundred milliamps of bypass current should be enough. Theory is you could add two modules to a bigger group if you needed it - the bms controller should cope with that.

[@DecDude84]

I was hoping to start by building a 7s24p system, and it everything goes well, expanding it to 7s48p, and seeing how I feel about it after that. It sounds like the diyBMS might be a good option

[@TheAnqueetas]

Another first. Your progress is pretty exciting. Well done. So what amps will your solar charger put into this pack? I'm thinking 8Amp'ish so each cell will receive approx. 1.2Amp during charge and will be fully charged in approx. 3hours.

[@AdamWelchUK]

Remember the current flows throughout the whole circuit, so each block will receive (in your example) 8 amps. The pack may be sat at 28 volts and being charged with 8 amps, but each block is sitting at 4 volts and being charged with 8 amps. Another way to look at that is power. 28v*8a is 224 watts. Each pack will be receiving a 7th of that overall power... 224w/7=32 watts. 32w/4v=8amps My blocks are about 50Ah is size, so its a 29.2v 50Ah battery effectively, however I don't intend to fully charge or discharge at any time so I've probably got 30Ah usable if I'm careful. So it's going to take me a fair few hours to charge if I've hammered the pack one night.

[@TheAnqueetas]

Thanks that's very precise. I do tend to over simplify things. So your 30Ah pack (7S20P) being charged at 8A will take 30/8 = 3.75 hrs.to charge from empty to full, yes. Also, each 18650 cell will receive approx. 0.4A during charge(8/20). So should not be stressed at that level of charge and all is good (average 18650 cell capacity to be 1.5 Ah)? I think that's right. Will your shed system migrate to your house and if so would you me looking at grid tie stuff and AC batteries. This seems far simpler, that's me looking for the simple way out. Micro grid tie inverters on solar panels, AC charger for the battery and some way to switch between solar and battery based on usage.

[@jettcam5784]

I must now saw this video. Not sure if you’re monitoring comments from so long ago, but I’m completely confused. How are each of the PCB boards connected to the actual batteries? How are the batteries from each module being controlled?

[@tiborkiss9186]

Hello Adam, I watched your vdoes the BMS ideo and went to Stuart`s Github - still have a few questions: i understand that this BMS is doing cell balancing, monitors under/overvoltage and over temperature. What i am missing is the over current limitation - Is the BMS able to limit a preset overcurrent - charging or discharging - by driving a relay? Best regards!

[@republicofvegans712]

Does the whole setup need a precharge circuit? Bc im using this for an ebike

[@aaronkashmer5882]

The open or lack of covering on the ends of the cells makes my OCD itch. other wise inspirational.

[@shtl0rd364]

Dude, this is awesome. Is that app available in the App Store or is it custom? I’d love to even purchase it if I decide to do something similar.

[@MrKitesurfercharlie]

Roonie Edward Mitchell IsUnamused it's open source. Look up Stuart pittaway DIY BMS.

[@shtl0rd364]

MrKitesurfercharlie Thank you kindly, boss.

[@drwhowhogrub3908]

Nice video thanks, do you step down the voltage to 12v? If so what are you using or have you said that in another video?

[@AdamWelchUK]

I'm intending that I'll probably drop the voltage down and use it at 12 volts for a number of things. I did a video a little while ago about dc2dc converter efficiency and found the one that worked best for me (ie. going from ~29v to ~12v). There are a couple of things in the shed though that may work more efficiently at a higher voltage, so perhaps theres another video in that! Cheers

[@battery_solar_ev]

Im intrested to see what you have in mind on the charging like CC constant current (the proper way) or CV constant voltage (the wrong way) many charge controler will say they are "lithium compatible" but ask them if it charges under "constant current" most likely the answer is going to be no. Thats the problem im having with my LiPo4 cant find a charge controler that charges with CC although i know others are using the CV method Im not willing to trust that method. Are you going to use buck or boost personally ive done both but primary is buck CC. LiPo4 4S 12P is what im using with a combination of 4S 20P 18650's just to add the extra capacity and already had the batteries so might as well give them a home. Neat Set up i will say puts me in mind of the way over priced Batrium stuff

[@AdamWelchUK]

Hi Steven and thanks for the comment. I haven't found a solar charge controller which does constant current charging, and there is a very good reason why. Solar is unpredictable. An array can produce 10 amps one moment, and barely 1 amp the next. Unless you have a buffer (another battery bank) then it's only ever going to be able to achieve an attempt at CV charging - even then, an array might struggle to produce enough power to maintain a voltage for any length of time. To do a proper off grid CC/CV charge you need a lead acid bank charged by solar, and a lithium charger powered from that. I'm going to be using a buck solar charge controller for this setup, at least for now. Batrium is a great system by the looks of it, and the software is quite powerful if you buy all the bits. As well as maintenance it's an insurance product in a way, so I guess it depends how much you spent on your pack (for me, not a lot in terms of money) and how much you rely on it (again I have alternatives if required). Cheers

[@cirelefebure5485]

Great video/project sir, thank you.

[@oldtimeengineer26]

If I did that for my rack I would need 49 modules. Have you done the cost per balance board yet? Thanks for showing

[@AdamWelchUK]

Not yet - I have a spreadsheet which needs updating. I'll try to add this to a video soon :-)

[@christopherschrachta2870]

I wish I had more intellect and knowledge to offer to this, but I am trying to learn as much as I can, what do you feel the maximum current that the DiyBMS can support? It seems to me that is the real limitation to the size of the pack you are designing for the system. The total current load determines rate at which power from an outside source can be pushed back into the pack of cells. With parallel cells we know the maximum voltage should be 4.2Volts but the Amperage makes up the test of that current calculation and of course how long it takes to charge that block of cells being charged. I am truly sorry for being such in idiot about this and I know I have a long way to go and sooooo much to learn, but your videos have sold me on the concept. I just want to understand how large and how many blocks of battery cells I need to target to make this a usable and safe way to use and store energy. Forget the specific cell if you will and think about it as Ah of storage, that way the particular battery involved is irrelevant and really this comes down to how much charge energy this BMS module can support??? It also intrigues me that you chose your pack to all be parallel and not series. There are quite a few other sites out there that choose to make the cells series and stack these into parallel to achieve the desired result. I think I like the parallel and then build the series after method, but as I have said I am sort of an idiot in this space and really just looking for some awesome advice of anyone is willing to offer. The BMS module seems to care more about current than voltage as part of its operation, just hoping someone of your knowledge can shed a bit of light on the difference. Thank you so much for doing what you do, its absolutely awesome that you explain each step and thought you take through the process.

[@santosvella]

Awesome. Good work Adam.

[@jamest.5001]

Could the thermistor go on the back. Contacting the cell or in-between cells. In contact with both? I really need to start looking into battery management and monitoring. Along with balancing. All I have is the cell meter with manual balancer. I haven't put them in service for this reason. I'm at over 150ah 7s bank. And about to nearly double that! I hope to have them connected by the time I have 4-500 ah. I also have lead acid golf cart batts. And a set of HUGE L16 batts 450ah. I'm going to use these for back up until I get enough lithium battery to not need them under normal use. Maybe emergency power. And in my garage. Using a ups for lighting and small loads. And mostly DC lighting. Ac lights for when really bright light is needed. I'm looking in to a 12/24v inverter that works good with starting motors and dependable. Maybe 2000-3000watts. And have clean enough power to run my home if needed. I prefer a pure sine wave. A good modified would work I guess. I need it to run saws and charge batteries for cordless tools. Which I'm transitioning to. Since I'm off grid. But still need good tools for work! . nice work. I need to get something like this ...

[@jamest.5001]

Is this available in a kit. Or more of a diy pick your own parts. I am not really able to do any programming and stuff on a pc rt now. I can solder and build. I am needing a way to manage my bank and balance. I will be able to do more pc related projects later. After I am moved and un packed. That may be a few months. I really like this design. Would you be interested in doing another for me? I can asemple it . I was considering a E bike bms and a extra balance only board. If I don't figure something soon . I guess I will go that route! Great video again!

[@AdamWelchUK]

Unfortunately building this has taken me, well a few months due to my lack of free time. I can't be building them for others I'm afraid. From a programming point of view the code is available and programming isn't very hard. You either need an ISP programmer for the modules or an arduino - both pretty cheap and readily available on eBay. Hopefully you can get something organised. Cheers

[@dejayrezme8617]

So how does the balancing work? Does it balance while charging by bypassing and burning off some charge when charging? Or does it discharge the pack? I figure that balancing through discharging will reduce the lifetime of the battery pack. Or is this irrelevant for battery life? Or could you reprogram the BMS to do this? Would this work for 48V too? EDIT: It appears it's balancing by discharging. I'd still be curious if this is a relevant downside to this.

[@Chickey]

I'm curious did you have to reset your wemos inbetween provisioning each pack? My setup has been rather finicky of late and will run a while then the modules go into panic mode so some digging is needed i think.

[@AdamWelchUK]

Nope. I had one issue but I think that was a loose cable. Otherwise it was smooth sailing. Your cables are a fair bit longer than mine, someone suggested twisting the cables (or at least the two data wires) to help reduce interference. Is yours worse since you put your inverter in?

[@nigeldolman954]

Good work Adam!

[@AdamWelchUK]

Thanks

[@bub1683]

love your videos. No one to ask about solar where i live, may i ask you a question, or where i can find answer on my question? Got a panel 100w. i daont need all power to my litle battery, can i use extra power im not needing to just feed my little refridgerator? it runs on 12v 100w. no compressor. any suggestions? it wont be powerful enough but will it work? Risks? just to take 12v from the battery cabel betwen solar charge controller and battery? is it ok to take the direct frome panel? it is to strong some days, i think. to many volts maybe /please respond Thomas in Sweden

[@AdamWelchUK]

Thanks for the kind comments. I wouldn’t connect the panel straight to the fridge - but is there a reason you can’t run it from you battery? In the day the panel will charge the battery and power the fridge, at night the battery will have to take over. Otherwise you’ll need some way to switch over the panels from one setup to the other, and a buck converter to convert the panel voltage down to a more suitable level - you’ll need one that can auto adjust to the situation though - which is basically a solar charge controller! Perhaps the best investment is a larger battery or additional batteries so you can store and use more of the power?

[@bub1683]

Thank you Adam

[@MrBrymstond]

Pretty interesting Adam.

[@tomgeorge3726]

Is the thermistor to measure the heat in the battery module? Where it is, it will be more likely measuring the heat generated when you equalize with the load resistor. Wouldn't it be better to fit the thermistor on the other side of the board closer to the batteries?

[@AdamWelchUK]

No the thermistor is there to monitor the module - and presumably the discharge resistor. Thing is I know the discharge resister is going to get hot when it's in bypass mode - that's what you expect. I was interested to know if any cells were getting warm in other conditions. So yes - I had intended to solder the thermistor in the 'wrong side' of the PCB and poke it in-between some cells, but the bead was too big using the thermistor Stuart suggested.

[@MauroSedrani]

Great job!

[@energiavadasz3328]

Not bad, but to complex, check out 1S Balancer on aliexpres. The are aktiv balancers, symple and works fast.

[@8001010]

They are all 4,2V fixed , bad for long cycles count.

[@electronic7979]

Excellent

Wish i could buy some of these...

[@timrauscher3965]

Would it make any difference if you used a smaller resistor. I'm figuring that it is trying to draw the pack down so fast that it is only drawing power down from the closest cells.

[@AdamWelchUK]

The module is connected at opposite ends of the pack so this should help even the draw across it. A lower value resistor would increase the current, a small resistor in size would be rated for less power typically, but multiple smaller resistors in parrallel is a good way of doing it - but the pcb isn't set up for that.

[@GeertDroid]

What software did you use to design the diyBMS brackets ?

[@AdamWelchUK]

I just used tinkercad online.

[@tharunkumar6955]

Hi, this is 7s20p right? In that 20p cells are u measuring random cell voltage? I need to measure all the cells, what can i do ?

[@AdamWelchUK]

When you place cells in parallel they will basically all have the same voltage. Any cells that are weaker will be charged by the stronger cells. So ensure they all have a very similar voltage when you connect them in parallel to reduce any high currents.

[@tharunkumar6955]

@@AdamWelchUK thanks for the reply. I am thinking of doing this as my engineering project. I am Electrical background so the program is little bit difficult to understand. Anything to understand better?

[@fourzerofour7860]

So... this is now the 25.9 volt solar shed? :P

[@bengrobben2582]

can you buy the diy bms? or do you have to solder it all yourself?

[@AdamWelchUK]

It’s self build. If you want a commercial product then many have found the batrium system works well - although I haven’t tried it myself.

[@bentelefoon5769]

Adam Welch would you Build Some For me? That i can buy from you?

[@bengrobben2582]

I really like the design, will you sell me some that you build for me? the big white resistors i can do myself.

[@AdamWelchUK]

Ben Telefoon I’m sorry I haven’t enough time to do my own projects and video KZbin content as it is. I’m afraid I can’t help you.

[@AdamWelchUK]

ben grobben Sorry. I’m too busy as it is - I can’t dedicate any time to building these for others.

[@jarnoorasmae]

Great work :)

[@milvolts1]

Why not a high amp BMS? Why individuals. Doesn't a single BMS balance charge and balance discharge?

[@HC4L666]

Adam, Would you sell the compleet bms system ?

[@AdamWelchUK]

Sorry no. I haven’t enough time to do my own projects, let alone make things for other people.

[@mous24000]

alls ok bis auf die holz wand warum kanne satl platte oder kasten aus stall

[@miguelacorrea1]

where can I buy the yellow bases

[@AdamWelchUK]

They are 3D printed and the stl file is in the description. If you need to buy them, you’ll have to use one of the 3D printer production houses.

[@trickyriky1]

Dude i think you should have started from the most negative point, look at your balance leads on batteries 0 4.2 8.4 12.6 16.8..... And 0.2 amps discharge on a 40Ah pack? Depending how much solar your putting on it i'm expecting those loads to change lol

[@AdamWelchUK]

I think you’re right that module one should be the most negative. I’ve already reconsidered this today (video was uploaded yesterday). I’ll re-do that. As for the discharge current - I’d be inclined to agree with you on that too - except for the fact I’ve been fairly careful with testing and building the packs, so they are already well balanced. Hopefully the that will have ensured these won’t get far out of balance in the first place. My 7s8p (about 22Ah) pack was being balanced on the capacity controller and that was only balancing at about 25mA!

[@ahaveland]

My thoughts too - convention says Cell 1 starts from the most negative, so best to follow at all times because simple human mistakes can be expensive. Yes, 0.2A balancing is tiny but time will tell if it's enough. It only needs to bypass at ToC if charging doesn't shut off before pack voltage it reached. If any cell goes too high, then the charging should also shut off while still allowing the high cell to discharge.

[@trickyriky1]

Haha i am thinking in terms of my own system, i dont want to be dumping 32amps into fully charged packs, i really should do a vid on my setup sometime. :D

[@trickyriky1]

Dont cut the charging, divert it ;) ohh i know about mistakes, building my solar monitor has cost me an adc and both laptop usb ports :(

[@ahaveland]

TW, no charge controller should ever try to dump 32A into a fully charged pack, with or without a BMS! As you say, diversion to a dump load such as a water heater or the grid is a way to go. As a pack reaches the end of its CV phase and current falls, the bypass current becomes a more significant fraction, so 0.2A might be enough to thumb the scales to keep them in check.

[@RWBHere]

Nice progress Adam. Thanks. Maybe this is just my OCD, but 'to beg the question', or 'to beggar the question' is one of the most misused phrases in the English language. It means 'to make the question worthless, irrelevant, or pointless'. In other words, your phrase had the opposite meaning to what you wanted to convey. Better phrases could be 'this raises the question', 'this promotes the question, 'the question needs to be asked', or 'the question is', followed by your question. Better still, you can simply ask the question, with no preamble. O.K., I'll close the door behind me...

[@michaelbreslin9116]

Would it be worthwhile using a fan, like this one, www.ebay.co.uk/itm/Small-PC-Fan-Cooling-Heat-Sink-Computer-Case-40mm-5V-2-Pin/173166885826?hash=item28518cfbc2:g:vlQAAOSwhwBaigbN. ?? Instead of a resisitor, assuming it will work down to your lowest expected voltage, 3.3V?? I haven't tried this, just wondering, then the cooling action could also be used to keep the batteries cool.

[@buttondeity3933]

would be nice if you could just buy the modules completed.

[@AdamWelchUK]

Less fun though! I do wonder if a through hole version would be better received by some.

[@buttondeity3933]

for sure it would. those small compenents scare people off. I would spend money on complete modules.

[@chadhouser1]

@@buttondeity3933 I would spend money on completed modules as well. Ever find anyone willing to assemble?

[@johndii2194]

7S5P