Powacycle Milan 2 battery issue

[Cobblers66]

Hello I found your forum after googling about battery issues on my mrs ebike.

We bought it used last year very cheap, it was sold because it cuts out occasionally on hills. My Mrs used it a few times but it only cut out once or twice as she is a bit lighter than the bloke we bought it off. It didn't really get used after October and I charged it a couple of times in between as the manual recommends that it be charged at least every 3 months.

After trying to use it the other day the red lights on top of the battery pack cut off pretty much after the first acceleration and you have to turn the key on and off to make it go again.

I charged the battery back up this morning and measured the voltage at the terminals at the bottom of the pack at 41.8v.

I stripped the pack down at it consists of 30 22650 cells 2500mah hour. I tested individual groups and found most were sitting at 4.19v except the top row of 3 closest to the bms which was 4.14v and the next row of 3 which were at 4.06v. Is it OK to manually charge them rows like this with my multi charger?

Would the pack being out of balance like this potentially cause this issue?

 

[wheeliepete]

Is it OK to manually charge them rows like this with my multi charger?

It won't do any harm to manually re-balance the cells so they are all the same voltage, but the inbalance is not necessarily the problem. Packs can show good voltage and then sag really badly under load, esp. when using the throttle. Try this and then leave it for a few days and you will see if any cells are self dicharging. There's a good chance your battery is approaching the end of it's useful life.

 

[Cobblers66]

It won't do any harm to manually re-balance the cells so they are all the same voltage, but the inbalance is not necessarily the problem. Packs can show good voltage and then sag really badly under load, esp. when using the throttle. Try this and then leave it for a few days and you will see if any cells are self dicharging. There's a good chance your battery is approaching the end of it's useful life.

 

[Nealh]

You can try charging the two low groups manually at very low current < 500ma & voltage less then 5v, the most common way is to use an old phone charger by cutting off the charge jack and soldering a pcb strip pin to each wire end then heat shrinking each end leaving 5mm of pin showing. Charging is then done via the BMS sense wires keeping a careful eye on the voltage.
Since the battery is naked with no covering you can apply current direct to the two cell groups separately again take care not to allow current to go over 4.2v and low ma charge value.

As Pete has mentioned a failing cell pack will still show good voltage but if the cells are knackered the voltage will collapse under load before rebounding, inclines are a good way of putting a battery under load and your issue is indicative of this.
The low group is suspect and may be the cause of your problem but that is not say the others are much healthier, it isn't worth repairing some cells in a failing pack as all the new cells do is take more of the load to counter act older cells and eventually they will also suffer.

If you balance the pack up, temporary or permanently wire up a voltage gauge or meter to the pack or between the pack and the controller to see what happens to the voltage on a ride out. This will give an idea if the cells are at fault.

 

[Cobblers66]

Yeah I know its probably had it now due to age I just wanted to know if a. 14v difference in voltage was a significant imbalance. I just made a 36v lead acid battery to test the bike with some np17s I had lying about and the bike seems to operate fine with that.

I might solder on a couple of test points so I can easily test the battery voltage from outside of the battery box while its fitted and then put it under load to see the voltage drop.

 

[Cobblers66]

You can try charging the two low groups manually at very low current < 500ma & voltage less then 5v, the most common way is to use an old phone charger by cutting off the charge jack and soldering a pcb strip pin to each wire end then heat shrinking each end leaving 5mm of pin showing. Charging is then done via the BMS sense wires keeping a careful eye on the voltage.

I've set my charger to 3.7v lipo pack and amps to. 2a it will auto cut off at 4.2v would you still recommend using a old phone charger instead of a dedicated charger like I'm using?

 

[wheeliepete]

Safer to use your charger as you can set voltage/charge rate.

 

[Nealh]

I've set my charger to 3.7v lipo pack and amps to. 2a it will auto cut off at 4.2v would you still recommend using a old phone charger instead of a dedicated charger like I'm using?

If you can set the lipo charger to 1s then no issue and safer, not many would have a lipo charger to hand.

 

[Nealh]

22650 is not a popular ebike cell in use, 18650 has always been king until now.
21700 now appearing. Finding the specs for the cell might shed some light on them but don't expect them to be a great cell.
The battery is only 3P and low mah at 7500, the cell current will likely be quite low and guess 1.5C which is a standard nominal C rating is 3.75a discharge so 11.25a.
Max discharge rating is likely 3C for occasional burst of less then 20/30secs.

The last cell group at 4.06v is bad and a long way out of balance for cells, typically for cylindrical cell balance 0.02v is usually the max imbalance limit.

 

[Cobblers66]

If you can set the lipo charger to 1s then no issue and safer, not many would have a lipo charger to hand.

Used to race model cars so still have my old multi charger so it comes in handy

 

[Cobblers66]

Used to race model cars so still have my old multi charger so it comes in handy

I couldn't find the exact cells online. I took a photo of them in my first post. The 4.06v group are now fully charged but while it's apart I think I will charge each row individually to give its the best chance of working. I will also make a external test point so I can watch the voltage while it's under load, I might as well cause as things stand it's junk. I will probably have a go at building a new pack for it as you couldn't justify the cost for what the bike is worth. I know I will need a welder but I plan to build myself a ebike in the future so it would be a good thing to have.

 

[Nealh]

18650 are the ones of choice, 21700 is a bit too new and not much real world info on how they perform, except possibly the new Sam 50E looks very promising if not flogged to death.
Some are better then other but it all depends on the current required and capacity.

 

[Nealh]

Your 22650's look like an unbranded China cell, I don't think any of the big six bother making them for ev use.