Stealth battery won't charge - suspect BMS

[PH001]

Hi Guys,

Not having much luck with my 1000W Stealth of late :-(

Had the original 48V battery replaced by Cyclotricity at 11 months from new due to going high impedance. New battery arrived and worked just fine for last 3 months (albeit very little usage, probably 5-10 charge cycles).

Went out for a ride, maybe used 50% battery, came back and plugged the charger in but didn't get the usual orange light showing on the charger (just stayed green)?? Left overnight and in the morning it was the same with only 2 bars showing on the LCD. Bike still worked OK, power going to motor etc.

Measured the voltage coming out of the charger and it was about 11v and unstable. Great, I thought...dead charger. Bought a new charger with a super spanking 54.5V on it's o/p and plugged it in. LED on charger still stayed green. WTF! Checked o/p voltage again and correct at 54.5V

Checked the voltage on the jack on the battery itself and was reading 50.2V, which sounds about right. It just won't take any current from the charger.

OK, must be a BMS problem I thought. Knowing Cyclotricity wouldn't extend the original warranty past 12 months I set about opening up the battery. This was a total bitch as they glue the plastic casings to the cells. Finally got it apart to expose the BMS module.

It looks like there are two FETS's control the charging (HY1807) and 4 to do the discharge (HY4008). The FETS all seem to measure fine and I can't see any bad solder joints / burned components etc.

It's defo not charging the battery though. With the charger plugged in, I can measure 54.5V on the C- terminal but only 50.2V on the B- terminal. The P- terminal has 50.2V on it with the battery enable switch on and nothing with the switch off, just as you would expect. Measuring down all the small signal wires they go up in voltage incrementally in 3.9V steps as you move along each pin. Again, sounds normal.

I'm not really sure where to go from here. Any ideas?

 

[Nealh]

Have you double checked all 13 strings to make sure one isn't higher then the rest if not do check them all again.
Some BMS don't have a balance feature and once a cell string reaches full charge first then all charging switches off.

 

[PH001]

Thanks for this. I'll post up all the midpoint voltages on Tues when I'm back at work. The thing is the pack voltage was 50.2V and I attempted to charge as soon as I came back from the ride. There was no charging at all. If one of the cells was high you would have expected it to charge (at least initially) and then stop.

 

[PH001]

OK guys, here are the string voltages:

1 - 3.91V
2 - 7.28V (3.91V)
3 - 11.73V (3.91V)
4 - 15.64V (3.91V)
5 - 19.55V (3.91V)
6 - 23.46V (3.91V)
7 - 27.37V (3.91V)
8 - 31.28V (3.91V)
9 - 35.19V (3.91V)
10 - 39.10V (3.91V)
11 - 43.00V (3.90V)
12 - 46.92V (3.92V)
13 - 50.82V (3.90V)

All look fine to me. I also disconnected the multi-way signal connector and plugged it back in the hope of some kind of 'reset' but alas still no charge voltage on the battery.

 

[PH001]

I guess I need to buy a new BMS. I was looking for one I could just retrofit but struggling to find one the same size (65mm x 35mm). I'm also not sure about the power on/off switch on the battery which connect to the red & blk wires on the bottom right. None of the aftermarket BMS's seem to have this?

I found this on Ebay which looks like it might do the job IF I can get it to fit physically, but it doesn't have the battery on/off facility??.... https://www.ebay.co.uk/itm/13S-48V-30A- ... 1438.l2649

Thoughts?

 

[soundwave]

https://www.bga-reworking.co.uk/

get them to sort it

 

[Nealh]

As you say they are fine.
If willing to use Ali express then switching BMS from Ann Battery is a reliable good seller I have used.
Three bms with switch.

https://www.aliexpress.com/item/3-7V-cell-13S-48V-40A-lithium-battery-BMS-With-ON-OFF-switch-and-balance-function/32847121949.html?spm=2114.search0204.3.9.538009c5zBSZgG&ws_ab_test=searchweb0_0,searchweb201602_5_5920015_10065_10344_10068_10130_10324_10342_10547_10325_10343_10340_10548_10341_10192_10190_10084_10617_10083_10616_10615_10307_10301_10303_10313_10059_10184_10534_100031_10604_10103_441_442_10142,searchweb201603_25,ppcSwitch_5_ppcChannel&algo_expid=66261682-49ad-45e2-958c-616e7fd1292d-1&algo_pvid=66261682-49ad-45e2-958c-616e7fd1292d&priceBeautifyAB=5

https://www.aliexpress.com/item/48V-E-bike-lithium-battery-BMS-13S-48V-20A-BMS-Charging-Voltage-54-6V-With-balance/32809303903.html?spm=2114.search0204.3.2.538009c5zBSZgG&ws_ab_test=searchweb0_0,searchweb201602_5_5920015_10065_10344_10068_10130_10324_10342_10547_10325_10343_10340_10548_10341_10192_10190_10084_10617_10083_10616_10615_10307_10301_10303_10313_10059_10184_10534_100031_10604_10103_441_442_10142,searchweb201603_25,ppcSwitch_5_ppcChannel&algo_expid=66261682-49ad-45e2-958c-616e7fd1292d-0&algo_pvid=66261682-49ad-45e2-958c-616e7fd1292d&priceBeautifyAB=5

https://www.aliexpress.com/item/48V-13S-PCB-board-54-6V-with-40A-constant-discharge-current-and-bms-with-on-off/32838554666.html?spm=2114.search0204.3.16.580c8c77kAwpDy&ws_ab_test=searchweb0_0,searchweb201602_5_5920015_10065_10344_10068_10130_10324_10342_10547_10325_10343_10340_10548_10341_10192_10190_10084_10617_10083_10616_10615_10307_10301_10303_10313_10059_10184_10534_100031_10604_10103_441_442_10142,searchweb201603_25,ppcSwitch_5_ppcChannel&algo_expid=5c5da035-030e-4073-a7ff-140c097117d1-2&algo_pvid=5c5da035-030e-4073-a7ff-140c097117d1&priceBeautifyAB=5

 

[PH001]

Many thanks for the replies. Only downside with AliExpress is the 4-6 weeks shipping time. What are the ramifications of not having a battery on/off switch? Does the speed controller drain power even if the LCD is off?

 

[Nealh]

6 - 8 day is the max I have had to wait for any Item via Annpower.

 

[Nealh]

The switch is on the discharge side so no power when connecting battery to bike, means no spark crack to damage contacts.

 

[PH001]

The switch is on the discharge side so no power when connecting battery to bike, means no spark crack to damage contacts.

I never remove the battery anyway so it would only happen once! I'm just not sure how much power the other electronics draw with the LCD controller off. Not easy to measure.

Do many other bikes have an on/off switch on the battery?

 

[Deleted member 4366]

Test the charging by connecting the charger directly to C- on the BMS. Most likely, you have a connection problem between the jack and the BMS. This test will confirm that.

 

[PH001]

Thanks d8veh but as mentioned in original post, I can measure 54.5V on the C- pad with the charger plugged in, which rules out any connection issues unfortunately.

 

[PH001]

UPDATE - so it was definitely the BMS. Replaced with the one from Ebay on post #5 and all good! In fact, better than good - it seems the original BMS is a bit rubbish in terms of impedance, the new one seems to suffer from much less volt drop when really pushing the motor. This is probably not too surprising as the ANN one uses 6 FETS for the discharge and they have a much lower Rds On.

This wan't an easy mod though. For a start the ANN BMS is significantly larger than the original, so much so that you can't use the std heat spreader plate as it means the BMS won't physically fit. I removed the aluminium plate and replaced it with a 0.5mm thick copper foil, bonded to the FETS with thermal adhesive tape. Also the midpoint battery voltage string connector is a different pitch so you have to chop each individual wire, heatshrink and solder to the new connector. It's all very tight.

Finally - the ANN BMS doesn't have an on/off function so the switch on the side of the battery is now redundant. This also means I had to remove the 48 to 5V DC-DC converter that runs the USB port (otherwise the converter would be running all the time and discharge the battery).

Overall though, I'm sure it's a much higher quality BMS than the piece of junk Cyclotricity supply. I never used the USB anyway.

I did confirm the current draw from the battery into the rest of the system with the LCD controller off. It was under 0.1mA so no issues there. Good to be back on the Stealth again!

 

[Nealh]

A good result, satisfying when things turn out right.
The Ann BMS's seem to be very good and have used their products a few times now.

 

[PH001]

Yeh, got there in the end! Interesting to note that when I had my battery replaced by Cyclotricity the first time around at 11 months old, they said it was the BMS that was faulty but I suspect they don't class it as a serviceable item so ending binning £300 worth of cells for the sake of a £10 BMS.

 

[Nealh]

Possibly, possibly not.
Jimmy @ bga has many batteries from retailers that need looking at for simple repairs. When I was there last year there was a big box half full with batteries waiting for his attention form one retailer.

 

[PH001]

I only really say that as the battery casing is EXTREMELY difficult to open up. The battery is siliconed to the case on both sides (you can see it on the first pic in my first post). It is more likely to snap in half than come apart easily.