No output from battery pack

[Peter Brigg]

You will recall that I mentioned earlier that I have two 36v elec bikes. I bought one BMS recently and installed it-now the second bike appears to need a new BMS also. They are getting a bit old now(like me!) so it is not unexpected.

On the first occasion a stray piece of wire entered the charging port and melted the port and ruined the BMS.

On this occasion there was no dramatic end to the BMs-it just doesn't work.

Here are the tests I have done.

On the battery outlet I placed a 240v light bulb (approx 100w) on the + and - terminals-the bulb didn't light even tho with a multimeter you get a reading of approx 38v.
I then put the light bulb over the + and - terminals of the battery pack before they entered the BMS and the bulb glowed a dull red for some time-about 3 minutes-I could have gone longer however this test indicates to me that the battery pack had power and the BMS is not passing it on. The voltage over the terminals before they enter the BMS is approx 41v

So the BMS is faulty?

Is may reasoning correct here?

Thanks
Peter

 

[amberwolf]

Most BMS's only lock off the output when something is wrong with the pack it's connected to, to protect the pack itself from overdischarge (and to prevent fires, etc).

If you read around the various battery pack troubleshooting threads, you'll see a lot of advice on various steps you can perform to check different parts of the pack to isolate it to the BMS or the cells.

First thing I would do is check the individual cell (group) voltages.

 

[d8veh]

If you have access to the BMS, charge up the battery to maximum, then remove the charger and measure the voltage on each cell at the multipin connector to the BMS. That will tell you whether it's a faulty cell-group that's switching off the BMS.

When your charge socket shorted out, it could have been from connecting the charger without it being switched on, which causes an inrush current that welds the earth contact to the outside of the jack. When you remove the jack, the earth strip gets pulled back until it shorts out on the positive.

 

[Peter Brigg]

I had checked the voltages of individual cells but forgot to mention that in the introduction.
Fully charged the voltage of each cell measured either 3.4v or 3.3v-which probably indicates all is well with each individual cell.

I had been apprehensive about how the system works however becoming a bit more familiar now-no electronics background however when you get the basic theory into your head the road becomes a little easier.

I am surprised by the amount of power in these packs-at 36v I didn't expect welding type power -to mistake where you put multimeter probes can cause a lot of damage. (to the multimeter as well!)

Thanks again
Peter

 

[d8veh]

Is it a LiFePO4 battery?

 

[d8veh]

Is it a LiFePO4 battery?

How many readings did you get? You might have missed one.

 

[Peter Brigg]

Yes-it is a LiFeP04 36v system and I got 12 readings-all either 3.3v or 3.4v.

With this being the case perhaps the BMS is faulty?

Peter

 

[d8veh]

Yes-it is a LiFeP04 36v system and I got 12 readings-all either 3.3v or 3.4v.

With this being the case perhaps the BMS is faulty?

Peter

Some BMSs rest when you unplug the multi-pin connector, others require that you remove any positive wire. It could also be a faulty switch if it has one, or even a faulty temperature sensor.

 

[Peter Brigg]

I am looking for the temperature sensor in the battery pack shown.

Is it built into the BMS?
I have had a look elsewhere however can't find anything.

Regards

Peter

 

[redilast]

It might not have a temperature sensor. It would be a 2 wire sensor usually that its taped or glued onto one of the cells going from the PCB board. The ones I've seen are around 10K ohms @ 25C.

 

[Peter Brigg]

A follow up to my earlier posts on this topic-I bought a new BMS and before I fitted it I checked the voltage of each cell in the battery(the battery had been sitting unused for a month)

To my surprise one cell was down to 1.8v so I charged it (just that cell only) and bought it up to over 3v

When I installed the BMS all worked perfectly however the battery now has limited life-the elec bike will now only travel for 1 or 2 KM whereas previously it had a range over 10 or 15 km

I think that faulty cell probably drops below the required voltage and the BMS shuts the battery down.

Are Headway cells a replacement for the faulty cell? The interior of the battery is shown on a photo in this post.

Regards

Peter

 

[Peter.bp]

If you brought that cell to only 3.0V before putting the battery on the charger, it is highly probable that that cell is still flat. It is important to check the voltage on that cell when your charger stops charging the battery.

Before you replace faulty cell, try to charge it to 3.7-3.8V after you got all other cells over 3.65V on charger...

You'll have to do this couple discharge/charge cycles before the battery becomes back in good condition...

 

[Peter Brigg]

Thanks for that -I will give it a go.
If I replaced the cell there would be issues about getting an identical cell-I see there are cells of a similar dimension however with greater capacity.

Here in Australia the freight is almost the same cost as buying the single cell-not good.


What you propose is somewhat similar to what I have heard about other types of cells ie cycle them a number of times and they may rejuvenate.

I bought the battery pack from BMS battery some years ago and so far it has given good service.

Regards

Peter