BMS What would you use ?

[expresso]

Lets say - the PL8 is no longer being made - and we are all stuck with no charger to use as we did for years -

If we had to use a BMS today - because of no other way -

what would be the Best BMS today that would use ?

dosnt matter how bad they are - or how good they can be - if we had no choice and had to use a BMS from now on -

which would be the best of the bunch - with a dumb charger ?

[Burgerman]

They are all much the same. But it would need to be a very user adjustable programmable one. And it would need to be rated at at least 300A as they are very much chinese Amps... And it would need at LEAST 1A balance, or higher. And it must not begin balancing at less than 3.500V. Many do. Some do it all the time! You definitely dont want that.

As for fancy screens, BT, etc then if that is possible and you want it then it is useful because the ony important display thing is CELL VOLTS! If you have no PL8 you only have this to let you know what is happening. So that would be essential. Theres a milion cheap ways to do that though.

And that leaves the charger. A BMS doesent allow you to control the charge voltage other than by chopping on and off... So you want a charger that puts out more than 3.500V per cell. And less than 3.600V per cell to reduce the damage they do by bouncing the cells up and down. So 3.550V per cell. Or 28.40V exactly. Also you want one with a way to limit the time to what you tell it. Typically 4 hours CV should allow the thing to be safe and allow time to balance properly. 2 may be enough but with no cell log we cant know. And the charger must allow you to choose a termination current so that it will terminate at the right time as a BMS cant do that.

As for which charger or power supply, ANYTHING will work. Badly.
As for which BMS again ANYTHING will work badly. You need to find one that respects the above if you want reliability long term, or no problems.
I cant tell you whict BMS that is as every one I ever looked at was much the same with one or several problems or unknowns...

[expresso]

yes but the BMS we would need or use - we all want the same things you said -

If you had to get one now to use - do you know which models would be the best choice - on the top of your list ?

forget what it needs to do - what is for sale now - ? i never seen one that can handle 300A - i think my bounder handles 200A BMS in there -

that may be the best choice then ?

so based on what can be had right now - links etc.

[Burgerman]

200 is enough if it actually handles as much as it claims. I have a 30A one on my mower. It would fry at half that looking at it. I dont trust chinesium claims!

I have no idea of an actual model. Either charger or BMS. Because they dont interest me because even if they comply with the above its a very poor substitute to my hobby chargers at best. Will it work? Mostly. Like your bounder. Unless bad things happen that you cant see.

[expresso]

i am just saying IF we had no choice and had to pick one -

so if thats the case - you wont use lithium anymore then ? or just grab a BMS you feel is best and move on with it - i am just bored here haha - its a year now waiting on the PL8 - so what if it never shows up ever any more - and we all have to move to a BMS setup

thats what i mean -

[Burgerman]

I understand lithium. And electrics. I have many many ways to charge a pack! With or without a PL8. It just needs a little knowledge.

I could make a charger from 8 small floating isolated 3.600V power supplies and a timer. For E.G. All in one case. Theres many ways to skin a cat!

[expresso]

what about the rest of us

[Burgerman]

You would need to look at BMS and look at specs and see if they do as above.

Same with power supply. I would use my bench suppy and set correct voltage, and set to say 30A. and turn it off when it falls below say 0.5A.

[LROBBINS]

The ZDS supply could also be set to whatever charge voltage and current you want and to drop voltage (I think even all the way to 0) when current drops. The only thing it lacks (and so does John's bench supply) is a timer. Should be doable in its firmware, if we had access, but a simple readily available timer could be added on the mains side in any case. The BMS board problem then becomes one of finding one that: (1) only balances at/near end of charge, (2) has ample balancing current, preferably by transferring electrons from higher to lower cells rather than by dumping, thus lessening the problem of high cell continuing to go higher during balance, and (3) if possible, reduce power supply output rather than just cut it off if any cell goes high - perhaps less critical if (2) is met. Such a board might exist, but how in the world can we find out? Sellers usually just tell us "it's perfect" rather than telling us what it does.

[terry2]

"8s BMS 100a LifePo4 Battery Management System for 24v DIY Batteries, Programmable, Bluetooth Included."

https://overkillsolar.com/product/bms-100a-8s-lifepo4/

It's Open source https://overkillsolar.com/open-source-projects/

[LROBBINS]

I have now read through the Overkill manual twice. It answers some of my questions, but by no means all:

(1) It can be set to balance only during charge, indeed they recommend this.

(2) Balancing is passive - high cells have excess dumped through resistors rather than used to bring up low cells. Not the best solution, but can be OK. Compared with electricity use while driving, this "waste" probably doesn't amount to much. BUT (3) and (4) below raise a big IF about this.

(3) It does not have a mechanism for throttling charge if a cell goes high, but disconnects it. However, the high trigger point can be set to a safe value, such as 3.65 or even 3.6 V, rather than the cell-killing examples, such as 3.8 V, that John described. ('Twould be nice if its software could output a signal when cell voltage gets near trigger, and if the ZDS could be programmed to reduce output based on that signal, but that would require some collaboration from both Overkill and the ZDS modifiers. Alternatively, with some more information it might be possible to come up with an external kludge for this. Use an MCU to monitor cell voltages - they already have Arduino software for this - and when cell voltage goes high switch a series resistor into the ZDS output so current drops enough to trigger the ZDS two-stage charger software to lower the output voltage a bit. Just a top-of-the-head idea though and not really thought through.)

(4) THERE IS NO MENTION THAT I COULD FIND OF WHAT THE BALANCE CURRENT IS. Given (3) this is pretty critical. If too low, the BMS will repeatedly go into high-cell voltage cutoff, cells will be bouncing up and down - which does them no good, and balance time will be excessive. This is not of much concern in something like a solar power bank, but could be a major, major problem in dealing with imbalance that happens with the very variable, and sometimes quite high, drains in a wheelchair.

(5) There are also no numbers given about heat-dissipation during balancing to allow rational design of heat sinking or ventilation, so the first users are on their own to carefully experiment.

(6) PC-based (or even microcomputer-based) monitoring seems quite adequate.

So better than the usual battery-killer BMS, but still missing essential information for deciding whether it's a decent option.

[Burgerman]

Its ony 100A though. On say a r-net or dx2 the max each motor can pull is 120A each. And while at stall battery current is less than motor current, thats not true as you accelerate or on a ramp as you drive up. So it must do 200A or will go pop... Or just remove all power at 100A sfter a second.

That could be used only to charge if the motor controller was directly conected to the battery rather than the BMS. So then all its safety nazi stuff we dont need or want are avoided. So it only affects charging. And the charge connection only was connected to the BMS. With suitable settings. Remember that the correct charger and the DETAILS of the settings on both charger and BMS are essential.

[LROBBINS]

That could be used only to charge if the motor controller was directly connected to the battery rather than the BMS.

That's certainly what I'd do, and it's also what you do with the PL8. Given that it also has a remote on/off connector to which the charger could be connected, it can be completely inactive except when the charger is live.

[expresso]

this may sounds crazy - i dont know - But - What if we can just use a BMS modular - not connected to the battery at all during use

and just plug it in when charging ? we make all the connections we need and mount them to the chair - do the same on the BMS side

like we do our own charge cables etc, - dosnt solve what the BMS does - but at least during riding - no BMS and no worries of cutting off or how many amps it does etc,

it will only be connected when charging to balance - 100A would be enough for that -

doesn't any one - China - make custom made BMS ? cant we write up what kind of BMS we need and have them make one that way ?

[Burgerman]

Thats what ShIrley does, and what I do on my mower, and exactly what I described above. All you need do for that to be the case is to run the chair directly off the battery and not through the BMS. In which case all its safety nazi stuff, and mosfets etc are unused during use. No need to disconnect.

[greybeard]

this may sounds crazy - i dont know - But - What if we can just use a BMS modular - not connected to the battery at all during use

and just plug it in when charging ? we make all the connections we need and mount them to the chair - do the same on the BMS side

like we do our own charge cables etc, - dosnt solve what the BMS does - but at least during riding - no BMS and no worries of cutting off or how many amps it does etc,

it will only be connected when charging to balance - 100A would be enough for that -

doesn't any one - China - make custom made BMS ? cant we write up what kind of BMS we need and have them make one that way ?

Excellent idea. Just reflect on how far your knowledge of electronics has come in a few years. Many smiled at the number of questions you asked, but time has proved you were right to do so. Congratulations are in order, Expresso.

[expresso]

thanks - Grey - BM - thats my last resort situation - i cant vision exactly how it would have to be connected etc, but with a few pictures posted here - i love pictures - i can follow

[Burgerman]

You connect the wheelchair directly to the battery and dont charge via the XLR.

You connect the BMS to the battery cell wires, and the battery main wires, and charge via the BMS charge wires. Needs a seperate charge connector connected to the BMS.

Thats all.

[LROBBINS]

So, we're really just using it as a balancing board with cell over-voltage protection. However, looking at the picture of the balance dump resistors in the manual, they seem to be 150 ohm, so the balance current is only about 24 mA (at 3.65V). That fits with their small physical size consistent with a 1/10th to 1/4 watt rating (24mA at 3.65V is just under 1/10W). An expensive way of getting a not-very-satisfactory result.

What we really need is a balance board adequate balance current and over-voltage protection with settable trigger point, without other BMS functions, that is just active when the charger is connected.

[Burgerman]

So if just 1Ah out of balance pack, that would be 24mA max, meaning a 41 hours till balance... Marvelous! Many so called lithium chargers cut off as soon as they rech their usually too high voltge. Or when it sees 1A or something. So the pack would never be balanced. There are BMS that can do 1A balance around.

[expresso]

You connect the wheelchair directly to the battery and dont charge via the XLR.

You connect the BMS to the battery cell wires, and the battery main wires, and charge via the BMS charge wires. Needs a seperate charge connector connected to the BMS.

Thats all.

I see - BMS is left connected but with a connector for charging only - which you use the charger on - sort of an ADD ON pack - need more room for wiring and BMS now - if ever need to add one - i dont plan on using one unless theres no other way

[expresso]

worse case - would be curious if there other charges - the bump one - what if you test one now BM ?

use it as it is - and see what it does - connect both chargers - use the PL 8 to monitor what the other charger is doing

maybe it may be just fine - even if you cant see the graphs

[Burgerman]

With no PC software I am not interested. And I think theres a few more dumbed down problems. I cant modify presets in the way we need for e.g.

[expresso]

it may be a better choice than a BMS maybe - can use the PL 8 to monitor and see how good or bad it is - what if its OK and work fine ?

[Burgerman]

I know what options are on the modified presets. I know it isnt.

I will give you a single example from many. On the PL8 I can change the point where it monitors the charge where it allows a max cell gap of 250mV to 350. Because otherwise when we have an unbalanced pack that exceeds 250mV the charger goes into a thing called safety charge and starts charging at a very low current... 0.5A. Indefinitely. On a LiFe pack that happens all the time if its a bit out of balance. On a small hobby pack thats not an issue. But you cant charge a 200Ah pack at .5A as it will take 400 hours! And its limited to 16 max. It isnt needed on LiFePO4 anyway and is a left over from the lipo algo they use for "safety"... I can also move te trigger point above the charge voltage we use, so that it never kicks in to stop us charging even highly unbalanced packs. Which I also do.

Theres many more small changes that I make. No PC software means I cannot do this... Or any other behind the scenes stuff. It affect lead and lifepo4. And more. So its a definite no here! Not interested.

Other chargers have similar hidden things that screw us up. Or may do. Extensive testing finds these. But then starts the arguments with the manufacturers like I did with hyperion and revolectrics in the end to fix things. So nope! No use to me. If you dont mind struggles with problems where it wort charge because of all the safety nazi stuff then go ahead! Its also why you must use my presets even if you change everything. Theres hidden stuff!

[expresso]

So i guess a BMS is starting to look like the much better choice and option down the line - i dont see why they cant make the changes to any new chargers they make - the same way they did to the PL 8 - since they already know it now - and with your help your input

we shall see the say

[Burgerman]

The reason the PL8 works so well is that I got them over 2 years and a lot if effort and argument to make some firmware changes. For e.g. it used to only allow specific voltages when hooked up.
Balance had to start at 3.3V.
It wouldnt allow a 12V lead battery to charge if it was below 10V. It gave incorrect cell count errors. It also wouldnt allow anything above 15V and it did that itself and overshot on start up... And many other stupid things. They changed maybe 5 things in firmware. And they allowed wider settings that helped us set things correctly in the presets. And then we also found a way to modify the presets, in a bunch of non visible ways, to fix the remaining issues. So its a long time and a combination of fixes. They started again with the new chargers with 101 extra safety nazi additions. Those will be a nightmare!

[expresso]

Since they did it already - worked with you - made all the changes that were needed on the PL8 - then it should be easy to make those same changes on the new charger ?

they already know or should know since they already did it - its not new from scratch - may take them a day or two at most -

still dosnt make sense anyway - having two chargers doing the same things - no reason to have two then - well lets see if they keep the PL8 as it is and cater to a few of us - how much longer you think they will keep both - i bet they already decided and may not even offer the pl8 any longer - or for not much longer -

if you were the company - just more work to get the parts for two different chargers - or maybe they feel its better in case they cant get parts for one - they may have options for the other and still get parts - keeps them alive -

they offered my money back a few times when i called to check on it - i didnt want it back - i just said i will wait - now its end of Feb -

i bet in Feb - it will be end April - and so on -

[Burgerman]

And around and around we go.

I know what options are on the modified presets. I know it isnt.

I will give you a single example from many. On the PL8 I can change the point where it monitors the charge where it allows a max cell gap of 250mV to 350. Because otherwise when we have an unbalanced pack that exceeds 250mV the charger goes into a thing called safety charge and starts charging at a very low current... 0.5A. Indefinitely. On a LiFe pack that happens all the time if its a bit out of balance. On a small hobby pack thats not an issue. But you cant charge a 200Ah pack at .5A as it will take 400 hours! And its limited to 16 max. It isnt needed on LiFePO4 anyway and is a left over from the lipo algo they use for "safety"... I can also move te trigger point above the charge voltage we use, so that it never kicks in to stop us charging even highly unbalanced packs. Which I also do.

Theres many more small changes that I make. No PC software means I cannot do this... Or any other behind the scenes stuff. It affect lead and lifepo4. And more. So its a definite no here! Not interested.

Other chargers have similar hidden things that screw us up. Or may do. Extensive testing finds these. But then starts the arguments with the manufacturers like I did with hyperion and revolectrics in the end to fix things. So nope! No use to me. If you dont mind struggles with problems where it wort charge because of all the safety nazi stuff then go ahead! Its also why you must use my presets even if you change everything. Theres hidden stuff!

[expresso]

you enjoy it also - going round and round with me -