A2B Battery teardown and test

[pdarnett]

So rather than hijack http://www.pedelecs.co.uk/forum/threads/battery-care.19875/ I thought I'd start a new thread regarding the removal and test of the frame battery that lives in the downtube. It's very picture heavy so stick with me!


First job was to pull the "Switch Pack" i.e. the relay and fuse board, a job in itself.

 

[pdarnett]

Then the bike was turned over for the nail biting pack removal.

The pack is glued into the frame and has two straps on it for removal (yeah right). The glue is actually foam tape, i found out later.

 

[pdarnett]

Nearly there, lots of swearing and chipped paint.



You'll notice the straps are now broken.

 

[pdarnett]

So pack out and on the bench, its screwed and glued together. Great.



Heatgun and blades used to pry it apart.

 

[pdarnett]

All solder connections look good, nice neat BMS with a mystery button. Any ideas?

 

[pdarnett]

Results time, I measured each cell and then applied a 5 Amp load (bulbs) and measured during load.



Pack was 41.7v unloaded and 40.4 with a 5A load.
Not much difference in the cells apart from cell pack 10 being 0.03 less than the others. Ran this for an hour but no cell pack less than 0.05 than its neighbour. So no real culprit.

Any ideas anyone?

 

[Deleted member 4366]

Can you run some jump leads to your bike through your wattmeter, then run your bike with the wheel off the ground and the brake on? Maybe it's drawing huge current, which is making the battery sag.

 

[pdarnett]

I'll try that. I was also going to try charging the battery and connecting it to the B (external) connector to see if it's a wiring issue.

 

[pdarnett]

Some testing done with the back brake held on (burnt finger on brake disc) tested battery on both the A and B relays (internal & external). Still seems to hold its own with 20A.
On external relay (at rest and loaded)

On internal relay (at rest and loaded)


Tomorrows test is the frame pack on my pannier plugged into the B and do the same test ride as below.

If the whole pack is done, would one of the Woosh Square bottle packs be up to the task (the a2b has a 500W motor), would be a quick fix at £315 and could be taken off for winter.

 

[Deleted member 4366]

4v sag at 20A is not that bad. Your problem must be elsewhere.

 

[pdarnett]

Thats my thought. I may try a direct connection to the motor (controller is in the hub).

When riding my battery gauge is wired to the output of the switch pack (relay pack) and that shows the drop in voltage at the same time I lose power. This is a potted in box as well so nothing servicable there.

Unless one of the relays is failing under load, but the tests above should have ruled that out.

 

[pdarnett]

Also after trawling through ES I found a lot of people complaining of the battery connectors being poor. Maybe I can't replicate the fault because I've had everything unplugged an back in again. The connectors cause cutouts as they're so poor. Grr could have saved me some work. Will re crimp all the connectors or replace with andersons. Tomorrow that is...

 

[pdarnett]

Well some success today. Strapped the pack to the pannier rack and connected it to the external input. Rode round the block with no sag whatsoever, even up some hills. Pack dropped to 32v on the steepest hill but didn't cut out.

Wiring getting redone at the weekend, all the crappy bullets being replaced with 45A Andersons and replacing the brittle throttle and led connections while I'm on it.

 

[pdarnett]

Well the Andersons were a ballache so used high power bullets and wired everything back. It's not as bad as it was but I still believe the pack has degraded a bit over the winter as it struggles a bit on the hillier bits of my commute. So next project is to investigate building a rear pack and eventually retire (and remove for weight) the frame pack.