bluetooth BMS?

[Dui ni shuo de dui]

Just to put the question up front, does anyone know if any of these bluetooth BMS models can handle 72v at peaks of 450a and deliver the CAN signal to a TC Elcon 1.8kw 72v Lithium charger from AliExpress?

Yes, it can handle 450A peak, no problem. We tried pushing more than 600A through the ANT BMS 300A and it worked just fine, still works today.
It just doesn't like it when it lasts more than 10 seconds, at that point it will cut.

As for the CAN signal, I have no idea.

Just a remark: pushing 450A through a 40Ah battery pack made of old laptop cells doesn't sound like a good idea to me. Those cells are really not made to survive for that kind of power draw (that's more than 10C!). If you plan on needing that much power, I suggest you get some proper cells or you double the capacity, at the very least.

Just a little story about my own experience of reclaimed laptop cells:
I work in IT, so I have access to a lot of those. Once, I've bring home around 10 old laptop batteries, opened them and ended up with around 50-70 cells (all good brands, Sony, Panasonic, LG, you name it). Tested all of them, only 40 were still somewhat usable (just meaning they could take a charge, had a reasonable current leak and had a resonable capacity left).
Then I tried to use them on a small e-cig, at reasonable power (around 15 watts if I recall).
Only 3 of them were usable. All the other ones were trash, either they didn't have enough power to heat the resistor, or they would just last less than a few minutes.
My cell charger features a milli ohmeter. It is not super accurate, but it gives an idea. All the defective cells had very high internal resistances, if I believe the milli ohmeter they were all between 80-150mOhm.
The 3 cells that were ok had around 35-40mOhm. At the time, no knowing much, and since I only could compare with the other defective cells, I thought it was good. I could use the e-cig for around half a day before the battery needed to be charged again. The batteries were getting a bit hot during use.

Then, few months later, I purchased a couple Sony VT6.
Gigantic difference. First, the milliohmeter reads around 3-4mOhm. Then, the cells can last 2-3 days without charging, while delivering much more power. And they don't heat at all.
Basically that made me realize that all the cells I had in the first place were complete trash. Not a scientific test, of course, but that gives an idea.

Don't bother using these for a high power project, maybe just keep them for your 12V system or for some other, low power application.

 

[Belchinov]

After 15 charges, BMS displayed on the screen DISBROKEN and Android App show DISCARGE MOSFET ABNORMALITY.
Beep sound on 3 sec.

what can I do to work properly again?

So far, there have been no problems. But twice I happened to see a difference between 8 and 9 cells.
Cells are brand new Samsung 25R and have no difference between them.

 

[topcat36]

Does the BMS allow discharge in this state ? Disconnect the BMS and check with the multimeter if you have a short between B- and C-. Check both ways ( b->c and c->b). If any of them has, remove the power board (the one with the 2 rows of MOSFETs) and check which row has the short. Most probably, at least one had shorted. Check between Gate and Source/Drain if any shorts (they sometimes fail this way) and those are broken. If none, then is more complicated. You have to remove all row of MOSFETs to find the defective one.
With luck, the driver still works and once you remove the defective MOSFETs, the error will disappear.

 

[eikido]

Is there a smart bluetooth BMS where i can set a maximum charging limit? I don't want to charge my batteries more than let's say 80%.

 

[Taswegian]

That's really the job of the charger rather than the BMS. There are sophisticated programmable chargers like the Grin Cycle Satiator that allow you to configure difference charging regimes and switch between them easily. Cheaper option is chargers that have two target charge levels and a physical switch. Simplest is many regular chargers have pots that you can adjust the main parameter(s). (may have to open the case to access).

Then there is the matter of balancing. For many BMS balancing won't start until the cells are above 4.1 so to achieve balancing you can either occasionally give the pack a full charge, or use an adjustable BMS.

The varients of bluetooth BMS discussed in this thread typically allow you to set the balancing parameters such as what voltage to start at.

 

[eikido]

Great! Thanks for teaching me.
I will ask more about these chargers in another more appropriate forum section.

 

[john61ct]

Do any of these have higher balancing currents, say around or over 1500mA?

Ideally can set the start-balance V at as low as 3.3Vpc or so

 

[flippy]

why would you need such a idiotic balancing current?
if you need those currents your battery is shot and you need to replace it.

 

[john61ct]

For very high capacity groups, maybe hundreds of amps, becomes a very tiny C-rate compared to half an amp for those tiny cylindrical cells.

6A is normal for dedicated balancers, which is another route.

And really, no need to use insults please. . .

 

[flippy]

battery capacity is not really an issue, even with the 250mA the BT BMS's discusses here cant keep a 100Ah battery equalized then the cells are simply unmatched or worn uneven and it needs to be looked at. just trowing more balancing amps against a defective or worn battery is a exercise in futillity.
if you got a yuge battery that has 200Ah or more then you should simply use active balancing and distribute the energy instead of cooking it off as heat.
managing big packs and balancing generates huge amounts of heat that needs to be removed, that means heatsinks, fans and other support compontens.
at such a point you should just use a higher tier BMS setup with active balancing, wich is still a small amount of the cost of the battery considering the price of such a big pack.

and it's not a personal insult, looking at high current balancing just means people are looking at their problem from the wrong angle. a balancing circuit is meant to keep the slight imbalance that happen naturally over time in check, not fix crappy batteries.

i have built plenty of 100+Ah batteries with even just 180mA balancing and they work just fine and have perfect balaning and the boards dont have any issue keeping up the natural imbalance that creeps in.

 

[john61ct]

I asked a simple question. If all these BT models offer is 250mA balancing, that doesn't mean I won't use them, just won't use them **for balancing**, haven't seen a BMS yet where I would, so NBD, just hoped I'd find an exception here.

No crappy batteries, some decades old zero capacity loss even with manual care, pack level protection only, so far I anticipate very rarely needing any rebalancing at all, if needed can do it with a charger, or manually, plenty of ways to skin that cat.

There are no heat issues at all in my use cases so far, never get more than a couple degrees above ambient.

 

[trazor]

Is there a smart bluetooth BMS where i can set a maximum charging limit? I don't want to charge my batteries more than let's say 80%.

JBD BMS can do what you want. You need to set a maximum voltage per pack, or per cell, and the charge mosfets will cut the charge at that voltage threshold. You need to set the balance voltage to a lower value too, if not you will never balance your cells.
If your bike uses regen, the previous setting can be a problem, your regen will raise the voltage of the pack and the BMS will cut the energy at this same moment and you will loose regen, braking, fry your controller, who knows.

I think that setting the upper voltage of the pack is a matter of the charger. You don't need to spend a lot, you can use one of these https://www.amazon.com/Voltage-Converter-DROK-Regulator-Transformer/dp/B076TTBKFG/ref=sr_1_3?keywords=boost+converter+1500w&qid=1557389498&s=gateway&sr=8-3 and 24v power supply, or something slightly lower than your pack minimum voltage.

 

[flippy]

No, a bms will not help. It will hiccup and continue to feed power into the battery.

Charge level us dicated by the charger, not the bms.

Using the bms for charge level control is like using airbags insted of using the pedal to slow down

 

[BotoXbz]

If his charger is shit and he doesn't want to get a new one then he can use a BMS to limit the max charge voltage of his cells.
A BMS is a safety device and should not be necessary to control his charge process, but it can certainly be used to do this.

Now first of all, if you are using regen you have to connect your controller to P- and not C- anyways, else you risk blowing up your controller if the BMS disconnects on a full battery + regen.

If you set the max cell voltage to 4.1 the BMS will turn C- off once a cell reaches this voltage and because of the higher charge current (due to CV voltage being higher than 4.1) means the cells voltage will drop again after a while.
You can set a release voltage where C- will be enable again if all cells are below this voltage.
So for 4.1V I'd probably try setting it up like this: cut off voltage 4.12V and release voltage 4.10V
But you'd have to monitor the charge process and maybe change this a little.
And balance min voltage 3.9V is fine too anyways.

The best is obviously getting a charger where you can set the CC and CV yourself, or modifying your current one.

 

[eee291]

So for 4.1V I'd probably try setting it up like this: cut off voltage 4.12V and release voltage 4.10V

These numbers a bit too close to each other. I tested this on a 36V15Ah Battery with a 43.7V2A charger.
I set it to cut-off at pretty much these values and once it reached the cut-off it immediately turned the C- on again because the voltage drop was something like 0.1V (not sure exactly), so it would turn off and on in rapid succession which could probably damage the Charger and/or BMS.
You def. want to set it to some thing like ~4.15V Cut-off and 4V (or lower) over-volt recovery. Because who charges their battery when it's almost full anyways?

And you can modify a lot of the Chinese chargers like this:https://electricbike.com/forum/forum/knowledge-base/chargers/38871-how-to-adjust-the-luna-charger-mini-and-advanced

 

[john61ct]

In fact keeping a bank sitting Full will shorten cycle lifetime.

Recovery / restart setting should IMO be well below resting voltage at 50% SoC, or whatever you want to routinely use as Storage voltage

 

[eikido]

If his charger is shit and he doesn't want to get a new one then he can use a BMS to limit the max charge voltage of his cells.
A BMS is a safety device and should not be necessary to control his charge process, but it can certainly be used to do this.

Now first of all, if you are using regen you have to connect your controller to P- and not C- anyways, else you risk blowing up your controller if the BMS disconnects on a full battery + regen.

If you set the max cell voltage to 4.1 the BMS will turn C- off once a cell reaches this voltage and because of the higher charge current (due to CV voltage being higher than 4.1) means the cells voltage will drop again after a while.
You can set a release voltage where C- will be enable again if all cells are below this voltage.
So for 4.1V I'd probably try setting it up like this: cut off voltage 4.12V and release voltage 4.10V
But you'd have to monitor the charge process and maybe change this a little.
And balance min voltage 3.9V is fine too anyways.

The best is obviously getting a charger where you can set the CC and CV yourself, or modifying your current one.

I'm definitely more up to getting a better charger.
Thanks.

 

[agniusm]

I have installed this BMS last year. Over the winter i left my battery unattended and this BMS drained it flat. Had brand new cells that went to the bin. Had no chance to go through all the posts but is this known issue? I have 2 of them, 15S and 20S.
Balancing and charging was ok but parasitic drain is WTF?

 

[eee291]

I'm sorry to hear that man, I had my pack drained to 10% over the Winter ( I knew about this issue but totally forgot about the Battery).
I guess if you leave it sitting for long periods you could unplug the BMS or get a low amp charger that will float your battery.

So for a 48V battery I would use a 36V charger to keep the cells above 3.0V: https://www.ebay.com/itm/12-24-25-2-29-4-42V-1-2-3-5-6A-Power-Supply-Charger-Converter-Adapter-Balance/113447888016?hash=item1a6a056490:m:mRCHyhoC0QEbwdJmhIx3VtQ&frcectupt=true&autorefresh=true

 

[agniusm]

If its an unfixable issue, they go to the bin or at least to last drawer for the time being. Its unacceptable.

 

[eee291]

If it makes you feel better the old models of Zero Motorcycles needed to have their batteries charged weekly or they would end up dead.
So this isn't exactly unheard of.

 

[larsb]

Did you switch the bms off? I thought this would stop any consumption. If you didn't then yes, it has some consumption, it's been discussed earlier in the thread.

How large was your battery and how long did it take? Ie what current did it actually pull?

 

[agniusm]

It was 20S6P battery. I assumed all was good and left it for 3 months. It should not be the practice for the hardware to malfunction or bad design. You should not seitch off bms, its added complexity. You will forget to do it eventually. Further more there should be notes on such conditions but what can you expect from chinese, thats why i swallowed bitter experience and moved on. Back to simple pcm.
Just wander what causes the drain? Blutooth module maybe?

 

[topcat36]

I have the AntBMS and if for a configured time of does not detect current flow, it shuts down completely.
The cheaper they are, the more likely they create problems.

Still I would investigate further. Maybe you left some load on the battery. I doubt the BMS could use so much power to empty that battery in 3 months. What is the Ah rating ?

Most of the time, the balancing fails, draining a cell but the entire battery ? Maybe the BMS protection kicked in and cut the power line. You checked each 6p group for voltage ? All 20 groups are flat ?

 

[agniusm]

I have contactor which cuts off the battery and only bms stayed connected. Cells were from nkon.
I have checked all my modules. All at 0.02V