48V batteries

[karen]

I have 3 48V batteries and one of them have a strange "behavior".... Under load it cuts out... I have to stop and turn off and on again... Is there anything I can do? I live in an area with a lot of hills and a few miles can therefore take many "unwanted" stops.... and I find it strange since its only one of the batteries having this behavior...

[Pwd]

My guess is that one of the cells is damaged. I have the same issue, I have dual pies and even with the settings cut back to half on each pie; it still cuts the battery out when doing a fast acceleration.

[e-lmer]

Karen:

Your battery is behaving normally.

Running 2 pies off one pack means you
 are pulling twice the current load from them.

When you draw current, the Voltage drops, more
Amps means more drop.

Two pies under full load draw 30 Amps or more.

That should make the Voltage drop enough to
reach the cut off Voltage.

[karen]

Probably one cell then.... I don't have a dual pie:) But I have more than one battery....

[Pwd]

Just on a side note, I received a new Pie and a new GM 48V LiP04 battery today for a friend. Out of curiosity, I charged this new battery and used it on my dual pie setup. All I can say is wow, my bike flys with that thing! On my battery when I press the throttle the battery LEDs go all the way down to red and sometimes cuts out. On the new battery I can mash the throttle and the green light doesn't even flicker. I think I can safely say in my case its definitely a battery issue. Now If I can somehow repair my battery to get the voltage back up...

[Cornelius]

The best (and only) way to find out for sure are to measure all the cell(group)s in the battery; they should not deviate more than 0.2V from each other.
It's best to measure a partly to fully depleted battery, because that's when the difference are most noticeable. (A cellgroup can be within the 0.2V limit when fully charged, but have almost no capacity left to offer, and thus dropping fast in voltage when discharged...)

[Pwd]

So last night I decided to dig into the battery pack to see what was going on. Here are some photos that definitely show a problem. The first thing I noticed before doing any voltage checks what-so-ever was that there is a piece on a smaller board on the outside of the battery that is damaged; that can't be good. I've attached the voltage tests and some pics to look at. Also note the piece of solder stuck to the cardboard...

Here were my test results:

The battery was partially discharged, not all the way but I would say about one third of what I've been getting out of it lately.

Actual voltages
4.04
8.09
12.15
16.20
20.25
24.31
28.37
32.38
36.5
40.6
44.6
48.7
52.7

Calculated voltages
4.04
4.05
4.06
4.05
4.05
4.06
4.06
4.01
4.12
4.1
4
4.1
4

Thanks in advance

[Pwd]

'Couple more

[Bikemad]

Your cell readings appear to be pretty similar under a no load condition, but the readings might be more varied if tested under load.

The component that is damaged appears to be a 100 ohm resistor, but I don't think you would be able to easily find an identical replacement, and most of these small surface mount resistors are only sold in large quantities rather than individually.

It might be worth contacting a local electronics specialist or TV repair shop to see if they can carry out an easy repair, and I strongly advise that it is completely disconnected from the battery before any attempt is made to repair it, to prevent further damage.

If it was mine, I would try and use a standard resistor and bend the leads and solder it to the contact area on the circuit board, while avoiding the adjacent resistor contacts as I've tried to show below, but I think it will be a very fiddly job to repair it.

Alan
 

[MonkeyMagic]

Hey I agree with Alan !!

You should first use a razor blade to gently put force the broken resistor upward, whilst applying your soldering iron so you can remove it with tweezers or something

Then cut a resistor to size, and put it in heatshrink - then tin the ends with small blobs of solder and carefully using pliers along with your soldering iron, place the resistor on one side first, then bend it across to the other

I'm not 100% sure, but those SMD resistors in there are 1/2W at least I reckon. So I would put a 1/2W or 1W resistor in there just to be safe.

How that damage occured in the GM case is seriously beyond me!

[GM Canada]

Ok My question is, what is easier or more reliable of a fix. Replace the resistor or replace the bms board?

Gary

[Bikemad]

A new BMS board would probably be best and might be easier to replace, but first you'd need to find the correct one, pay for it, and then wait for it to arrive.
 
Gary, assuming it's still within warranty, how long would it take for GM to send a replacement board?

Alan
 

[MonkeyMagic]

That resistor would be the best, first bet there

If the resistor does the job, then you won't need to remove the BMS

The BMS is a pain to remove !!!

Most people cut it out with a dremel, I spent a great deal de-soldering mine and would not like to do that again !

I'd try and replace the resistor and see how that goes.

[Pwd]

So if I were to replace the resistor, do you think that that would solve/help the problem of my battery cutting out so soon? I've tested my bike with two different batteries besides mine. One of the batteries was the exact same as mine (Lithium-Mag. 12ah 48V) and it was able to keep up almost as well as a brand new 48V LiFeP04. Thanks very much for the feedback,

 - Paul

[Bikemad]

Hi Paul,

The BMS monitors all the cells, and will automatically cut out if any of the cells exceeds a pre-set maximum voltage, or fall below the set minimum voltage.
I'm guessing that if the damaged resistor was not allowing 100% of the cell voltage to reach the BMS, it could cause the BMS to cut out under load, just because the actual voltage being measured by the BMS was too low due to the excessive voltage drop across the broken resistor, even though the true voltage of the group of cells being monitored is probably well within their acceptable operating range.

It's difficult to say for sure whether the failed resistor is causing your cutting out problem, but you should be able to tell by replacing the resistor and then testing the battery on the bike again.

Alan