Exploring A CHEAP 3-cell BMS Board!

[@SimpleElectronics]

Oh no - what was I thinking - "430" on a resistor is 43 and ZERO (no) Zeros, so 43 ohms - I'm going to let it ride. Thanks @Marsha Jackson !

[@MrJozza65]

Was just about to point that out 🙂

[@Sahel_prince]

Oooo ok

[@tanoryjakaperdana1419]

So whats wrong

[@ericklein5097]

Those 18650 holders have a ton of resistance. I did a little video on the difference in resistance between some of the cell holders I have and the Keystone SMD style cell holders have the lowest resistance of any cell holders out there. Not a big deal if you’re doing low current stuff but if you’re going over 5A (Like Jehu Garcia discovered) you’ll find out that the leaf springs on the cell holders become the hot point on the PCB.

[@frankowalker4662]

I bought a similar charging board to this last year, but for 2 18650's. I could'nt get it to work, there were no instructions in the ebay listing or for the board number when I googled it. The beginning of this video is priceless. It turns out I had wired it up wrong, so thank you for this information. It's working a treat now. :)

[@guymee]

Bro this is the testing I need to get my brain to learn I’ve been learning about BMS’ and balance charging and this right here gives me a lot of reference for why my cheap BMS heats up sometimes on discharge but not really, but generally on charge it warms a little, so that would explain why!

[@SimpleElectronics]

These little boards are a great starting point!

[@MrJozza65]

For using machine screws in 3D printed cases, I like to use those brass inserts that you can get, just make the hole a bit bigger and you melt the insert into the hole with a soldering iron, then you have a nice fitting and demountable fixing.

[@stinkycheese804]

Nice plan if you're opening it a lot, but if not, no need for them, just make the stud-portion a little thicker and use coarse threaded screws, even self-tapping if you don't anticipate opening it again until it needs repaired.

[@deankq4adj125]

Great job on the PCB's, loved the video. I'm such a LiPO battery nerd. Can't get enough of this content! Keep up the great work.

[@SimpleElectronics]

That's the kind of stuff I love to hear! Thanks!

[@EF-Electrics]

@SimpleElectronics the reasoninng is wrong as you're trying to play around with 18650 cells which max voltage shouldn't exceed the 4.2volts thus a pack voltage of 12.6 maximum (not setting up the charging to 13.6v @11:22 as that's wrong) you'll be doing nothing else but tripping the over voltage protection of that board. Also something else about this BMS board I noticed that those three 43ohm resistors do get quite hot while the battery is idling (even though no balancing is needed at all). I'm finding out that some KZbinrs have uploaded that swapping them out individually with a (1Watt - 2512) 100ohms SMD resistor solves the problem. Do you have the same encounter (SMD ‘bleeding / balancing’ resistors overheat)?

[@jec_ecart]

That's the problem with cheap passive balancing chargers. Their discharge on high cell is so slow that it never works. Then it cuts out charging. The balancing works only when charging, which means balancing never happens... Active balance is must if you want quality experience with your lithium.

[@michaelfischer6984]

The current rating on the BMS boards is usually peak current to allow motor starting. Also only salvages power tool batteries are good for over 3-5 amps max. Different construction/chemistry.

[@ericklein5097]

Scooter/e-bike packs sometime have MH1 or MJ1 LG cells that are 10A. Occasionally get Samsung 35E cells on high end packs too

[@stinkycheese804]

Your english is terrible. Did you mean to suggest that salvaged power tool batteries aren't good for more than 3-5 amps? If that is what you meant, it is clearly wrong. Power tool batteries in good condition (not worn out, or else what would be the point of using them in the first place?), are typically at least rated for 20A current on the major brand tools, and easily good for over 10A as proven when used in those tools. If you have some generic made out of string and glue, who knows what the cell really is.

[@stinkycheese804]

Meh, not necessarily. Peak current from that many fets is way more than that, properly heatsunk, would only take one or two fets for it, rather that rating is their rough estimation of both how much current it could handle before overheating in a steady state of discharge, AND in some cases a limit on how much current to draw because the design (powered load or wiring/fuse/etc, or cells themselves) shouldn't be subjected to higher than that.

[@ericklein5097]

Sorry to keep comment spamming but they are old cells. 4.13 is its resting voltage. It triggered over voltage protection at 4.25V and the cell rested at 4.13 because it’s an old cell. It didn’t Balance all the way because the balance current is so low and you were charging at 5A so cell 3 was only balancing from 4.10’ish until it hit 4.20-4.25 which didn’t take long. If you charge at a lower current it gives more time for the other cells to catch up

[@ericklein5097]

Ahhh you figured it out! Good job! Be careful if those are Sanyo cells they are known as heaters. For some reason old Sanyos like to heat up when being charged. To see a cell test at 4.13 means it is quite degraded

[@ericklein5097]

The flying capacitor boards are AMAZING. they work based off the voltage difference between cells so to see the full 5A balancing current you gotta have a cell at 3.00 and another at 4.00. Also keep in mind that the max charge current for 18650’s is 1C in most cases. So charging a cell at 5A is likely double its max charging rate and I HIGHLY recommend avoiding that with used cells especially with Sanyos. Those cell holders are not going to tolerate 20A and the added resistance of the holders plus the traces and every other aspect of the PCB means you’re going to get a huge voltage drop even if the cells are rated at 20A. When your voltage on the discharge is different than the pack voltage your BMS is tripped and you have to apply a charge current or wait X amount of time for it to reset

[@ericklein5097]

Charging the cells at 5A was very dangerous

[@borayurt66]

I may be wrong here but as far as I knowi SMD resistor coding works like this: first 2 digits are the value and the last digit shows how many zeroes will be added to it. So, 430 means 43 + "zero" zeroes = 43 ohms, 431 means 43 + one zero = 430 ohms and so on... Later edit: Yeah, the #1 rule of commenting is; read previous comments first. :-)

[@ptsoris]

@SimpleElectronics nice video! What's the use of the two Bms contacts FD CD (Full Discovered / Charging Discovered)? LEDs can be used there to indicate the operation status of the board?

[@hishamfarid9206]

Thank you, amazing video! do you think it is safe to charge and discharge with this module at the same time?

[@SimpleElectronics]

Should be!

[@kyleallred984]

Awesome video, loved the level of detailed explanation of the design. Have you heard of "Battery hook up", it looks like a seller of used battery packs for us tinker's to salvage. Is a revision 2.0 possible for this board with, indicator LEDs , easy connector to add parallel batteries, potentiometer to adjust charging current... I figure I should stop before I feature creep too much. Will definitely be using the provided info in the building of my 3s7p pack for a mobile pi station. Would love to see a clip of you Shorting the pack or at least a cell, maybe demonstrate high current/ voltage on old/dead components you have laying around. I say a suggestion on another channels video of have the multimeters screen record on a separate camera then placed in a small overlay in the video that way we can easily read the display with out you struggling to fit everything in one frame, although e would up the editing time.

[@mikejones-vd3fg]

I had the same experience with the red rounded one, same thing, once a battery got to 4.2 it stopped and the rest were at 3.7. To be fair mine wasnt advertised as a balancer, so i manually balanced it, took a 2.8ohm 20w reistors and put it across the 4.2v cell. It took 5-10 minutes and it got smelly hot to get it back down to 3.7-8. This was with the rest not being charged. It would take way longer and youd need to dissipate more heat if you were trying to balance this cell while everthing else was charging id imagine, so no wonder these dont do any balancing. They'd need some heavy duty resistors to keep a discharge while everything else is charging. 20w worked fine in my case but only when everything was off and it took awhile. Anyhow this doesnt seem like a good way to balance, youre basically draining the life cycles of all your best cells to wait for the weakest one. You should just stop charging the 4.2, and charge the rest, but it seems a series connection doesnt allow this to happen, easily. Maybe you could just disconnect everyhting charge them individually and connect them again, that seems to me it would be the best way to balance without wasting lifecycles to do it, but i wonder why no balancer does it like this.

[@ManojBam-b9p]

Hi @SimpleElectronics, Could you please help me with the charge and discharge terminals? Can I connect them to a common terminal? I am planning to use this in a UPS that has the same load and power on a single terminal. I have the same BMS.

[@joaoncr]

You shouldnt go all the way up to 13.6. The first cell is Getting all the charge before the others get any juice. Not to mention the resistance on those slots, which impedes the energy flow from the first cell to the others.

[@onecircuit-as]

Lovely work. Board ordered! 👍😀

[@SimpleElectronics]

Nice! I didn't think anyone would, I am thrilled!

[@RS-dj4pp]

You should top balance the batteries first, it's the Bms job to cut off the current if any cell is fully charged

[@stinkycheese804]

Yes and no. Better BMS do not cut off the current to the entire pack if one cell /parallel-group reaches full charge, just that cell/group and the rest continue to charge. Even that one, looks like it is supposed to drain the charged cell and allow charging the rest, if only you keep the charge current low enough.

[@AnotherMaker]

You should definitely short one. You could probably make a short of shorting one.

[@akki_dalvi23]

Can I charge & descharge from descharge point? Or not?

[@jimmyross1672]

not sure but i got like 4 of them and so far they have been working ok but not sure if its even doing anything or not but im using them lol

[@belenhedderich3330]

Does it charges back balanced after the discharge? Your board?

[@SimpleElectronics]

It does! As long as the cells are well matched and/or your charging current is reasonable

[@stevenbliss989]

60A * 60A * 0.006 Ohm / 10 mosfets = 2.16W ....you would not want too much more than about 4W continuous for that board, BUT, I assume the mosfets are "chinese" rated, (usually nominally about 2x Rds i.e. 10-12 mOhm - test one and you will get a surprise :) ) making the power loss likely to be around that 4W mark. It may look over kill, but it's likely not. BTW I always design for "chinese" mosfets operation, because they are SO MUCH CHEAPER (even in spite of the higher no. of devices) so if you design for it, it works better than using full spec mosfets.

[@stevenbliss989]

You mention the gate voltage, I have no idea how this is set up, so if the mosfets are not getting 8-10V, they may be roughly 9mOhm (full spec) or 15-20mOhm (fakes). Let me know what voltage you measure on the gate, and if you bothered, were they fakes?

[@stevenbliss989]

I just noticed that there is NO current sense shunt on the BMS, so is the 60A an operation limit before melting and only voltage controls it, or am I missing something?

[@xXKisskerXx]

"this cell is charging too fast" - common problems when your cranking 4A into the circuit - the proper solution, and longer lifetime of cells, is to charge with lower amps. Takes longer, but works better all around. 250mA is what most work the best with. In a pinch hit them with 500mA or even 1A until 80% full, then trickle down to 250mA. I forget the math and all but it has to do with the "C" rating of the cell, and like dividing it by a number. A commercial charger for 18650 cells has 300mA, 500mA, 700mA and 1A settings. You literally cranked 4x what most chargers would slam into them, by setting your desktop power to 4A. The faster you charge a battery- the more likely you are to drain it's total capacity. a 2000mAh cell will deplete down to even 1500 - if you keep 'quick charging' it with 1A+ power. I typically don't push used cells past 500mA, because of this.

[@krzyzakpolska]

How did you figure out the max charge voltage?

[@electroniquepassion]

Merci 👍👍👋

[@larrypridgen4785]

How can I use this type of BMS to charge battery pack with solar panel and charge controller?

[@stevenbliss989]

What are the mosfets switching in the 43 Ohm Rs? If they can handle higher current, maybe replace the 43's with 22s or lower (higher wattage of course) and see if that works ? :) maybe even replace the mosfets with something like AO3400 or AO3401 or better? :)

[@killabee623]

43 ohms is correct the 3rd number is the multiplier example, a 430 ohms would have a marking of 431.

[@stevenbliss989]

Interesting! ...thank you for doing all that testing, I was wondering if those boards actually work :) The 43 Ohm resistors are 1/2 watt? I guess so but surprised, ...did it get hot?

[@SwisssblisS]

Why do you charge them @ 13.6v and not 12.6v ? I dont get it 😅

[@SimpleElectronics]

That's what the details for the BMS board says is the max charging voltage

[@ericklein5097]

@@SimpleElectronicsit’s a typo

[@TheDefpom]

430 resistors, is 43 with 0 multiplier, so 43 is correct

[@SimpleElectronics]

I had a moment :) Addressed it in the pinned comment!

[@jimmyross1672]

lol tell me about it ive been trying to figure this dam BMS out and i dont understand how it works but im using them still so who knows but i hope you tell me something i need to know lol you allready showed me a couple things i needed to know about this product so thanks but i need to know more about this item

[@DimaProk]

20:00 mark, the middle battery is off by 1/100 of a volt only and you talk about the cell "not well matched". That's very small and acceptable.

[@MaxintRD]

I think he said not well matched in terms of capacity and one cell going lower faster than the others.

[@MarshaJ8800TU]

430 is 43 and zero zeros 431 is 430 ohms... A minute later you even referred to a 101 resistor as 100 ohm

[@AnotherMaker]

Yep.

[@SimpleElectronics]

Oh no, I pulled a stupid haha thanks for mentioning that!

[@stevenbliss989]

Is it the board not working, or are the cell voltages going down below 2.8V at higher current, which would be correct of course?

[@stevenbliss989]

Oh, ok, the last part of your video suggests it's the batteries.

[@electrotsmishar]

I have been planning on buying one of these. Thanks for the video. I have a question though. Can I activate cell balancing if I charge at very low current? Or would that be too low PSU voltage to do anything?

[@stinkycheese804]

Yes cell balancing works at very low current. It is not too low a PSU voltage because in order to be putting charge into the pack, you will have to have a voltage above the series sum voltage of the cells. Keep in mind that you should not just use some *dumb* charging circuit for Li-Ion cells, even if your current isn't quite constant, it still needs an upper threshold voltage regulation equal to the fully charged cells' series voltage. Normally this means the PSU has a voltage setpoint and is current limited below that.

[@electrotsmishar]

@@stinkycheese804 thank you. I've actually put some LEDs across the board to figure out the behavior. Thinking of making a video about it

[@RubberDuckTime]

Is it not just a protection board !?

[@sashascarface]

I have the same problem with this bms I try 3 psc all do the same thing voltage drop . This olso happens wen you charge the pack . Not a good bms

[@jimmyross1672]

i bet i will learn a thing or two in this video lol

[@lucienlescanne]

Charging voltage for this BMS: 16.8V - 18.1V so 13.6V is far too low

[@stinkycheese804]

This is not correct. You must be thinking of a 4S BMS instead of 3S, and float voltage, not loaded.

[@TBL_stevennelson]

I like the whole project board. I would buy one as a kit if you had it available.

[@SimpleElectronics]

I have extras - hit me up if you want to talk about buying one - but be warned, shipping from Canada is very expensive

[@ericklein5097]

I’m very surprised the BMS activated the balancing circuit so early. Usually they don’t turn on until 4.18V

[@singlesteve2011]

Can you send me Gerber files but with a 4 in series for a 16.8 BMS?

[@jimmyross1672]

so yeah the whole things shuts off instead of charging other batteries first lol

[@WA_IP]

You got me at 430 ohm 😅

[@ardufreak6973]

Are you serious? 60A from a single used 2Ah cell without protection??? These cells can draw up to 6A when they are new and valid for 3C, but used cells have an higher inner resistor, so they getting warmer up to thermal run through because of the inner(!) temperature. For this BMS you need much more parallel cells.

[@SimpleElectronics]

Relax, everything is going to be fine - just a bit of experimentation.

[@GlishaSo]

i think you pushing too much amps to that 5A is a lot!

[@Ove_Bjerknes]

430 = 43 ohm. 431 = 430 ohm.

[@SimpleElectronics]

I had a moment :) Addressed it in the pinned comment!

[@pavelrafique108]

oh no! 13.6V! 4.5V per cell. man oh man. that’s not good

[@SimpleElectronics]

I mean I did explain that it cuts off the voltage at a per-cell level so, I'm not sure what to tell you

[@CollinBaillie]

​@@SimpleElectronicsAt 4.2v maximum voltage, 3 in series, that's 12.6v. Obviously 13.6v is too high. If you charge to 13.6v, and the cells were perfectly balanced, that would be over 4.5v per cell. Don't be afraid to ignore the manufacturers info if you know better! 😊

[@QoharElektrik]

Oke

[@arebear4797]

it seem like you dont know what your doing bro... please dont play with 18650 like that.

[@jimmyross1672]

thats cheating you cant use another charger to charge another charger lol thats doesnt work you mise as well be only using the one of them to charge the dam batteires not 2 chargers how does that make any since lol it doesnt i wouldnt use to charger to charge one battery so why are you doing it here just to see if it will work no it wont lol there is something wrong with these BMS thats why there so cheap

[@jj74qformerlyjailbreak3]

Yes. Very dodgy. Plus those old Sanyo cells are garbage after 2 years of laying around.