Battery not charging BMS voltage lower than battery total

[pilotg2]

Hi guys

I'm in need of some help as I'm completely new to ebike batteries and troubleshooting them. I've learnt loads today and won't do anything I don't understand...

I have 3 48v 13ah batteries and 3 chargers. None were charging so I have opened 2 of them up.

From the BMS:
The battery voltage across the pack is 52.5 measuring B- and battery positive.
When I measure C- and the battery positive the voltage is 24.2
If I remove the balance plug with all the wires the voltage is 38.5
Currently the cell banks are around 4v each.

The charge port measures 24.2 so will not start charging.

Should the voltage after going through the BMS equal the total battery capacity? Are the above results normal?

The other battery I tore down has the same symptoms.

 

[flippy]

the bms is triggering on a fault. check your wiring and voltages of each group. measure where the plug goes into the bms to exclude a broken wire. careful you dont short the leads out. much smoke much fire much wow will result if you are not careful.

 

[fechter]

Your measurements indicate that the charge control circuit is tripped (or fried). It would trip if any cell group was above 4.3v or so.

Try measuring all the individual cell groups. If you can access the cells directly with the meter probes, that works. Otherwise, I like to measure at the BMS connector using a pair of solid strand wires. Something like this:



If you find a cell group that is over 4.2V, it needs to be drained down to the level of the other cells.

 

[pilotg2]

The results from measuring where the connector goes into the BMS are:
9 cell banks at 4.05v
3 cell banks at 3.925v
1 cell bank at 4.13v

So they are out of balance but would that cause the above symptoms? They are Samsung cells. I was under the impression these packs were not cared for and barely used over the last year and a half. So I'm not surprised they are not balanced.

In my case is the control circuit found in the BMS or charger?

 

[pilotg2]

I've just opened up the final 3rd battery pack and it's measuring 18.9v at the charge port and 42v across the batteries.

Another pattern I have noticed across all 3 batteries:
For the third pack I've just opened as an example, measuring the cell banks from the BMS port, the first 9 banks measure 3.4v and the last 4 measure 2.7v. Would one expect that?

How can all three have the same problem? Could it be the BMS has blown from faulty charges?

They came with 3 charges but only one appears to work.

 

[hemo]

Sounds like crappy bms's replace all three with bms with a switch so they can be turned off.
Ann/Ann battery on AliEx sell some good priced reliable bms, I've not had any issues with mine.

https://www.aliexpress.com/store/product/3-7V-cell-13S-48V-40A-lithium-battery-BMS-With-ON-OFF-switch-and-balance-function/623665_32847121949.html?spm=2114.12010612.8148356.22.1e347abe8xdL57


https://www.aliexpress.com/store/product/48V-E-bike-lithium-battery-BMS-13S-48V-20A-BMS-Charging-Voltage-54-6V-With-balance/623665_32809303903.html?spm=2114.12010612.8148356.12.1e347abe8xdL57


Your low cell group readings of 2.7v will prevent a bms from charging as is below lvc so you will need to manually charge them up to the voltage of other cell groups also the high cell group of 4.13v on another battery may be preventing charging.

 

[pilotg2]

Many thanks for the links. I've never bought a BMS before, is there anything I need to be aware of?

Would the above two works with my specs...

My specs are 48v 13Ah
Cells are Samsung ICR18650-26H M there are 65 cells

Be great if the BMS port that links to all the battery wires just plugs straight into a new BMS, is there a universal size?

 

[docw009]

Be great if the BMS port that links to all the battery wires just plugs straight into a new BMS, is there a universal size?

I just bought that Annpower BMS. Ordered it on 2/6. Shipped 2/16. Arrived yesterday 2/27. Not bad. I will install it this weekend.

Would be nice if they were all the same, but the connector size can differ and they can start right-to-left or vice versa. In my case, I knew they reversed the wire order, but was surprised to see a larger connector.

 

[pilotg2]

Thanks, that's not too long of a wait. I just counted and I have 16 balancing wires. B0 and the last 2 wires in a loop. Will try find one that matches up.

 

[pilotg2]

I'm now thinking i may buy a good battery charger that can balance the batteries, etc.

As I have to buy 3 BMS for the battery packs and as I don't know the history of these batteries would it make sense to rather buy a good charger so I can monitor the cells from the led?

I would feel more comfortable with that and I could use the charger for other projects.

So the batteries would have no BMS but would be balanced by the charger.

Is this a sensible (reasonably), possible approach?

 

[docw009]

I've just opened up the final 3rd battery pack and it's measuring 18.9v at the charge port and 42v across the batteries.

Another pattern I have noticed across all 3 batteries:
For the third pack I've just opened as an example, measuring the cell banks from the BMS port, the first 9 banks measure 3.4v and the last 4 measure 2.7v. Would one expect that?

How can all three have the same problem? Could it be the BMS has blown from faulty charges?

This last post is at odds with your earlier post, where you reported 9 cell banks at 4.05 and 4 others slightly different. I'll assume you meant just one battery. The above results suggest to me that those 4 groups at 2.7V are disabling the charge function. If true, not a BMS problem. The cells that power the BMS got run down. I guess it happens. Was there an ON/OFF switch on this battery?

If this was the case, bringing them up to 3 volts each should get it working again. If it will charge thru the discharge port, you can briefly charge it under observation til those 4 groups get up to 3 V. Then switch it to the charge port. Since you are bypassing the charger safety circuits, you have to watch it to make sure those cells come up, while the others do not goo over 4,1 volt. If the battery now charges, let it rebalance.

With your first battery where you have 52V across the cells, something else is happening.

One more thought. What's the voltage measured on your good charger with nothing attached? What if you had a 36V charger when you thought it was 48?

 

[pilotg2]

Yeah my first post was in reference to the first battery at 52.5v. The second battery has two 0.6v banks which I won't use so that one I'll be tearing apart for another project. Another reason I'm keen on an adjustable balancing charger. The third battery was at 42v.

I'll try what you mentioned but I tend to agree that all the BMS are shot. I read that B- and C- and P- on the BMS should be equal or its failed. Is that correct?

Yes it had a key on battery and then on/off on handle bar.

The voltage on the charger is 54.5, so it does seem OK.

 

[amberwolf]

I read that B- and C- and P- on the BMS should be equal or its failed. Is that correct?

Not necessarily: That can just mean that it's switched FETs off for either charge or discharge.

That's not (by itself) a failure--it's the way it's supposed to operate. If it did not do this, it could never protect the cells from overcharge or overdischarge, by disconnecting the charger or controller.

To know if it is a failure you have to test the cells and the sense wire connections from them to the BMS for conditions that would cause the BMS to do it's job. If no conditions exist to cause it to do so, yet it has, *then* there's a problem with the BMS.

 

[pilotg2]

Thanks I thought it was weird all would be the same, but it does show how little I know hahaha.

This is where I read it https://www.elecycles.com/blog/post/how-to-diagnose-the-lithium-battery-bms-damaged-or-the-battery-cells-damaged/

I see they do say within range not the same. Is that correct?

 

[amberwolf]

Hard to tell exactly what they're trying to say; it's not a very good English translation from whatever the source language was (guessing Chinese?).

The articles there could be just clickbait to get you to their site so you buy things from them, for all I know.

 

[hemo]

For BMS get one rated a bit more then your controller rating, if controller is rated less then 20a max then use a 20a discharge BMS.
Most BMS have an over discharge feature so can deal with higher spikes for 5 -30 secs depending on the specs which you should check out to confirm.

The fact/coincidence that 3 batteries are all unbalanced suggests cheap BMS not doing their job properly, most likely bleed resistors may not be closing and are stuck open so when battery is not in use the cell voltage bleed back.

As an aside what do the voltage output of the chargers all read, if they are wrong then depending on the charger they should have a trim port for adjusting. The cheap basic plastic Sans/generic type black chargers all have a trim port inside which can be adjusted.

 

[pilotg2]

Thanks for the tips on the BMS. My controller is rated at 18amp and my motor is only rated at 250w.

I may build another ebike with a mid motor so may get one with higher than 18amp, maybe around 25 to 30 amp. Is that OK?

I'll get one BMS as my balancing charger idea doesn't sound that easy with 13S.

Yes there are two adjustment screws for the voltage though one doesn't seem to do anything. It can go from 53.5 to 60v. I've set it to the lowest setting.

What is the easiest way to drain a bank of cells? Hook a light bulb up to them?

 

[TommyCat]

As far as the charger trim pots. That's not something that you just get into and start twisting adjustment screws. Usually there are three adjustments. One for output voltage, one for charging current, and one for desired current shut-off point. Read this good thread here before you do any thing else with the chargers.

https://electricbike.com/forum/foru...-to-adjust-the-luna-charger-mini-and-advanced

Some batteries need to be turned on to charge...
Some chargers need to be plugged into the battery before the wall to charge...

Where do the 3 wires on the charger connect to?

The two wires looped from the BMS connector, is this a single non-spliced wire?

 

[docw009]

Yeah my first post was in reference to the first battery at 52.5v. The second battery has two 0.6v banks which I won't use so that one I'll be tearing apart for another project. Another reason I'm keen on an adjustable balancing charger. The third battery was at 42v.

To summarize.
-FIrst battery almost has a full charge, but won't take a charge. You don't know why yet.
-Second battery has two dead groups at .6 volts. That battery is toast. Do not try to recharge it or it will make toast of everything around it when those groups burn up.
-Third battery might have disabled the BMS with low cells.

Is it too much to hope they are all the same make? Move the BMS from battery #2 to battery #1?

 

[fechter]

The results from measuring where the connector goes into the BMS are:
9 cell banks at 4.05v
3 cell banks at 3.925v
1 cell bank at 4.13v

Those voltages are all within the "healthy" range. Nothing that should have caused a trip. It's also strange the the voltage reading is low on the charge port. Even if the BMS is tripped and the charge control transistor is turned off, you should read nearly full pack voltage there due to the internal diode in the FET (your meter is really trying to discharge through the charge port).

Sounds like a bad BMS.

 

[amberwolf]

The BMS on an old "mini" Luna pack I've got here does that sort of thing sometimes. When it does, I actually have to drain the pack some (hook it to a bike, ride or run the motor, or hook it to a heater or other load for a bit, etc), and *then* I can charge it. I think but can't remember for sure that unplugging the balance connector and then replugging it in also fixes it....

The fact/coincidence that 3 batteries are all unbalanced suggests cheap BMS not doing their job properly, most likely bleed resistors may not be closing and are stuck open so when battery is not in use the cell voltage bleed back.

Might sound pedantic, but for functional clarity, that would actually be " resistors may not be *opening* and are stuck *closed* (on)", for that particular fault. (and it's really that the transistors that operate the resistors are stuck closed (on), but that's irrelevant since the point is that the channel will always continuously drain any cell(s) attached to it).

FWIW, a simple test for this is to measure voltage across the bleed resistors, and unless the pack is on a charger or recently has been, none of them should have *any* voltage across the resistors themselves. Any that do are stuck on, and will always drain that channel's cell(s).

 

[pilotg2]

The two wires looped from the BMS connector, is this a single non-spliced wire? Yes it's a single looped wire from Port 15 go 16.

With some manual balancing on one battery I got all cells within 3.98 and 4.04v. I then connected each BMS to this pack. Each read out roughly half the voltage of the pack across the BMS but all were slightly different voltages.

I'm going to order a new BMS tomorrow and will report back when it's in.

I am happy to test anything but I'd need exact instructions as I don't know where the resistors are located on the BMS I'm afraid.

 

[docw009]

I installed that Annpower BMS yesterday. It works.

What I liked about it. The C-, B-, and P- terminals had 4" lengths of silicone wire already attached. That kind of wire is hard to solder onto a circuit board pad, so that was nice. The other end I soldered. The silicone wires were easy to squiggle into the cramped spaces you often see inside a battery. Moreover it worked. The prior BMS for Aliexpress from a different vendor worked on a hairdryer, blew up on my ebike first time it was used. Both were under $20. I'm not going to worry if the other vendor stiffs me.

 

[docw009]

The BMS on an old "mini" Luna pack I've got here does that sort of thing sometimes. When it does, I actually have to drain the pack some (hook it to a bike, ride or run the motor, or hook it to a heater or other load for a bit, etc), and *then* I can charge it. .

I have a 52V Luna Mini and their fancier 52V 80/90/100% charger. It never starts charging on the Luna charger when taken under 48V. I have to start it off on a generic cheap 48V charger, and then switch over. Crappy Luna charger, I guess. The original 52V unit blew up, and I also had one of their 48V units die.

 

[amberwolf]

Never had one of their chargers. I get that problem with the pack whether it's charged with a generic 2A charger, or one of my Sorenson lab PSUs at any current level, or Meanwell LED PSUs, or the Cycle Satiator (with any appropriate profile).

Additionally with the Satiator it sometimes even causes a Power Fault error for reasons I dont think I ever figured out (with any firmware).