Help & Advice with Batteries

[Suggs]

Hi everyone.
I'm completely new to E-biking and doing as much research as possible. I've purchased some second hand hub motors and parts. They also came with some Lithium batteries.

I tried charging the batteries today which seemed to go fine until I turned the charger off and unplugged the connectors. The batteries then started to get hotter & hotter which seemed very odd. My immediate thought was that they were shorting out but I couldn't see a sign of any problems. Does anyone have any advice?

Also, can anyone offer any details on what batteries I have based on the photos below?
Many thanks in advance.

 

[Suggs]

It's worth noting (only just thought of it) that I had the batteries on charge outside where it was quite cool late afternoon. Could this have been why the batteries didn't get too hot during charging and then when I disconnected them to take indoors, that's when they got really hot? I'm hoping I haven't fried them

 

[flangefrog]

Your batteries are most likely some type of lithium chemistry. Have you got a multimeter or other voltage meter? Check the voltage of each parallel string. Looks like your battery configuration is 7S3P (7 series groups of 3 in parallel) so measure with one probe on the top and bottom of each cell on one side. It certainly sounds like the cells went into thermal runaway, possibly from overcharging or a short. The cells shouldn't have gotten noticeably hotter when you took them inside. The batteries don't look to bad though so they can't have gotten too hot. So maybe someone else has an idea what could have happened.

Watch this for what thermal runaway can loook like:
[youtube]oBlac5gWLfI[/youtube]

 

[Suggs]

Thanks very much for the reply.
I do have a multimeter so I'll test them tomorrow. I didn't want to do anything whilst they were still hot.
How hot do the cells get under 'normal' charging? Should they be cold/warm/hot to touch?
It's strange that during charging the outer aluminium casing was only warm. Then, as soon as I turned off the charger the casing started to get hotter. Almost too hot to hold at its hottest point. There is no sign of burning etc so I'm hoping they are ok. Wouldn't be the best start to my E-biking experience if I fried the batteries first go!

 

[flangefrog]

The battery temperature while charging will depend on the charging current and the particular cell. They should only get warm while charging them at a high rate - I charge mine at .55C and they have maybe a 10 degrees celsius raise in temperature at most. You never want your batteries to get hot, especially while they are fully charged as that will reduce their lifespan. A low rate laptop cell will get a lot hotter than a high rate 25R or similar while charging or discharging at the same current.

 

[d8veh]

From the photos of the cells and BMS, you have a 48v battery of LiMnCo cells in a 13S3P configuration. The cells should be charged to 4.2v each. The charger and BMS should look after that.

If they didn't become hot when charging, but dd when you removed the charger, you myst have shorted something when you removed the charger. That power connector looks very suspicious with gaffa-tape insulation sticking out.

 

[Suggs]

Thanks again for the replies, all very useful.

A small update.... the overall voltage reading is currently 54.2V unloaded so it looks like they might be ok. Fingers crossed anyway.

The charger I was using is a Gaozhao.
Reading on the back of the charger:
PWY4805
AC 220V 50/60HZ
DC 60V-5A

The plug is something I added as a temporary measure to try and charge the batteries. The charger and batteries came with no plug (and the wires already had the gaffa tape on) so I cut up an old extension lead connector block hoping that it was capable of carrying the voltage/current.

 

[dilkes]

The charger I was using is a Gaozhao.
Reading on the back of the charger:
PWY4805
AC 220V 50/60HZ
DC 60V-5A

Not sure if this is the problem, but if that indeed is a 13S LiPo configuration, a charger that puts out 60V is too much. Should only be putting out around 54.6. You might check the charger output with your Multimeter to see what it is really doing (i.e. the label on the outside may be incorrect).

 

[Suggs]

Not sure if this is the problem, but if that indeed is a 13S LiPo configuration, a charger that puts out 60V is too much. Should only be putting out around 54.6. You might check the charger output with your Multimeter to see what it is really doing (i.e. the label on the outside may be incorrect).

I did check the charger output before using it and it did read 60V. I wonder if the charger isn't compatible then? If it isn't then I'm lucky I stopped it charging after about 1.5 hours. In that time the voltage increased from approximately just over 48V to about 56V (if my memory serves me right!). Its now reading the 54.2V I posted earlier.

If they are LiMnCo cells, is that a LiPo battery? I need to read up on the terminology.

 

[flangefrog]

Most BMSs cut out when a single cell's voltage is over 4.25V. For 13S this is 55.25V max before it cuts out. Due to inaccuracies it could have been about to cut out when you measured it at 56V. With a BMS that has a charger cut out function it should be possible to charge it with a higher voltage power supply than usual but it's much safer to limit it to 54.6V. Some BMSs have two ports, one for charging and one for discharging. If you charge it through the discharge port it won't cut out.

LiMnCo is Lithium Manganese Cobalt. I'm pretty sure d8veh is referring to LiNiMnCoO2 which the chemistry many newer high capacity and high discharge rate cells are based on. It's safer than LiCoO2 batteries often found in laptops and much safer than LiPo. You can read about some of the different lithium chemistries here: http://batteryuniversity.com/learn/article/types_of_lithium_ion

 

[d8veh]

60v is for a LiFePO4 battery, which would have 16 cells. Have look inside the charger if you can, and see if there's a block-type potentiometer in the corner that will let you turn down the voltage to 54.6v. Your BMS should still protect your cells from overcharging, even with the 60v charger, but it would be safer to turn it down if you can.

 

[Suggs]

From the photos of the cells and BMS, you have a 48v battery of LiMnCo cells in a 13S3P configuration. The cells should be charged to 4.2v each. The charger and BMS should look after that.

Could you explain how you can tell what they are? Is it just experience or is there something that gives it away? Until I'm confident what type of batteries they are I don't want to risk charging them again!

 

[Suggs]

60v is for a LiFePO4 battery, which would have 16 cells. Have look inside the charger if you can, and see if there's a block-type potentiometer in the corner that will let you turn down the voltage to 54.6v. Your BMS should still protect your cells from overcharging, even with the 60v charger, but it would be safer to turn it down if you can.

There is a good topic on the forum relating to my charger and that has a potentiometer. Mine however didn't seem to have one when I looked inside. Strange as its the same charger.

 

[flangefrog]

There is a good topic on the forum relating to my charger and that has a potentiometer. Mine however didn't seem to have one when I looked inside. Strange as its the same charger.

Post some photos of your charger's circuit board. Even if it doesn't have a potentiometer someone may be able to let you know which resistor to change or replace with a pot to adjust the voltage.

 

[Suggs]

I'll see if my Dad will as its at his house.

There is a photo in this link although mine doesn't have the potentiometer.

https://endless-sphere.com/forums/viewtopic.php?f=14&t=59549

The gentleman I bought everything off believes the batteries are from Golden Motor (the model before their current range which are LiFePo4) if that helps identify them any easier?!

 

[d8veh]

From the photos of the cells and BMS, you have a 48v battery of LiMnCo cells in a 13S3P configuration. The cells should be charged to 4.2v each. The charger and BMS should look after that.

Could you explain how you can tell what they are? Is it just experience or is there something that gives it away? Until I'm confident what type of batteries they are I don't want to risk charging them again!

I do a lot of battery repairs. The configuration of the cells tells us the type of cells. 10S is 36 VLi-ion 12S is 36v LiFePO4, 13S is 48v Li-ion and 16S is 48v LiFePO4. Li-ion are nominally 37v and charged to 4.2v. LiFePO4 are nominally 3.3v and charged to 3.65v. There's other types too, but pretty rare. Yours is a common or garden Li-ion battery. Technically, all Lithium batteries are Li-ion, but that's how most people differentiate them.

 

[dilkes]

Most BMSs cut out when a single cell's voltage is over 4.25V. For 13S this is 55.25V max before it cuts out. Due to inaccuracies it could have been about to cut out when you measured it at 56V. With a BMS that has a charger cut out function it should be possible to charge it with a higher voltage power supply than usual but it's much safer to limit it to 54.6V. Some BMSs have two ports, one for charging and one for discharging. If you charge it through the discharge port it won't cut out.

LiMnCo is Lithium Manganese Cobalt. I'm pretty sure d8veh is referring to LiNiMnCoO2 which the chemistry many newer high capacity and high discharge rate cells are based on. It's safer than LiCoO2 batteries often found in laptops and much safer than LiPo. You can read about some of the different lithium chemistries here: http://batteryuniversity.com/learn/article/types_of_lithium_ion

Yes..I forgot about the charge/discharge ports. If that alloy case is the same as one I have (and it looks like it may be), it will have a charge port under the handle on the black plastic end of the case...opposite end to the discharge side. On mine it is a round oversize RCA looking plug. Attaching a picture of the charger side connector on mine. At least if you charge thru that port, the BMS will have a chance to limit the voltage to the cells.

 

[Suggs]

Unfortunately the battery case is missing it's ends and didn't have connectors on. There were 4 bare wires effectively. I added a connector to the red & black wires but the green & yellow have been left bare for now as I'm not sure what they are for? Maybe as you described above? You can see where they attach on the BMS circuit board photo.

 

[d8veh]

The BMS should be marked. B- for the negative from the pack to the BMS, B+ for the positive if it has it, otherwise the positive from the pack goes straight to the output positive and charger positive. P- for the output negative, and C- for the charger negative. Here's a schematic that might help. It's for a 10 cell pack, but the connections are the same:

 

[Suggs]

Ah....that's making more sense to me now! I wondered what the green and yellow wires must be for. They must be the charging wires which means the red & black I was using to connect to the charger is wrong. Doh!
You can see from the photo below that the red & yellow wire is attached to 'P+/B+' on the BMS, the black wire is connected to 'D-', and the green wire connected to 'C-'. There is nothing connected to 'B-'.

 

[flangefrog]

I think that P+/P- connection must be the battery positive connection. From the pictures it looks like the small red wire from this terminal goes to the battery positive terminal. I don't understand where the large red wire comes from though. [Edit: top down picture shows that the large red wire is connected at the cell rather than the BMS] Green will be charger negative and yellow charger positive. Are you sure B- isn't connected to the nickel cell tab?

These should be the correct connections to use with d8veh's wiring diagram:
P+/P- Cells positive
B- Cells negative
C- Charger negative
D- Battery output negative
P+/P- Battery output positive

It seems pretty likely that the cells got hot from overcharging. Lucky for you the BMS should have still bled the cells down to the right voltage after disconnecting the battery from the charger even though it was not charged through the correct port.

You should be safe charging the battery again (after testing individual cell voltages) with your current charger once you connect it to the right port, but monitor the voltage and temperature the first time. It would be better to get a lower voltage charger for the long term.

 

[Suggs]

You guys are great

So.... rang my Dad and asked him to confirm a couple of things.

- There is no wire coming out of the B- on the BMS but at the rear of the circuit board its clear that B- is connected to the negative cells.
- I did a typo before.... the red and yellow wire coming out of the circuit board is P+/B+

Now that I'm fairly sure about the batteries I think it might be worth buying a different charger. Any recommendations? I'm in the UK which might make my options limited unless I go for international shipping.

 

[Suggs]

Quick question....how do I test the voltage of each individual cell? Will I have to disconnect them from the series?

 

[flangefrog]

No need to test each individual cell. When they are in a parallel string they just act as one big cell. Easiest way to test is probably by unplugging the balance connector from the BMS and with both multimeter probes on adjacent pins, move along the connector to the end. If you do find one parallel string is different from the rest it could be a faulty cell or cells, but I would probably see how it works after charging/balancing (you need to leave it on the charger for quite a while to balance the cells). You should monitor the temp of any faulty cell strings because it is possible that a single cell could have an internal short, dragging down the voltage of the other cells and continuously drawing current from the charger. When the current isn't transformed into potential energy, it's instead transformed into heat.

 

[Suggs]

From what you've just described it sounds like that might have been happening when they became really hot. I'm concerned that my 60V charger is too powerful to use if I can't reduce the charging voltage. Monitoring them during charging is sensible but I did that and they didn't get hot. It was only after unplugging them which is what really confused me. I'm going to strip the pack as safely as possible to check for shorts.