I am investigating a no go and have opened a 36v battery pack from a Pendleton ebike and discovered that there is a healthy 41v at the board but only 4v at the output pins. There are4 bars illuminated and after a few seconds drops down to a single bar 20 percent. Can anyone advise?.
BMS issue possibly
- Thread starter Hedgesteeper
- Start date
If not a fuse then the BMS is faulty and a component is at fault .
One could try and repair the component part if it can be found with some micro solder surgery , otherwise it is likely best and simplest just to desolder the BMS and fit another one.
The fault may be a discharge mosfet or a diode .
Personally I don't bothe repairing and simply replace , cost is about 12 - 20 quid for a BMS.
One could try and repair the component part if it can be found with some micro solder surgery , otherwise it is likely best and simplest just to desolder the BMS and fit another one.
The fault may be a discharge mosfet or a diode .
Personally I don't bothe repairing and simply replace , cost is about 12 - 20 quid for a BMS.
It very much depends on the year of manufacture. Early ones were made in China, later ones in different countries and were equipped with different batteries from different manufacturers.
As Neal mentions, there's a sleep mode to save depletion when not being used. How you wake up the battery varies from maker to maker. Early ones, you hold down the button for 20-odd seconds, later ones need the charger plugged back in, even if it appears full.
The 4 LED's back to one suggests a later model... four LED's showing state of charge, the one LED after a few seconds indicating it's working.
You need to refer to the manual that came with your bike... many many prior posts have the exact same query, and most threads include links to the manual relevant to your particular year of make.
41v isn't great BTW... there's a world of difference to a battery hot off the charger being 41v (being suspect) and 41.7 (being about right).
The voltage is good and the Sam 29e is a great low /mid power cell, for £ per mah it rates as a best buy.
Before thinking about swapping out the BMS try to see if the BMS will wake up.
As mentioned by CB a long press up to 30 secs of the on/off may do the trick , if not try placing said battery on bike switch it on and then plug in the charger (make sure the charger is live first).
Not recommended but some have reversed charged via the discharge for 10 secs to wake up the BMS if the other two options fail.
Before thinking about swapping out the BMS try to see if the BMS will wake up.
As mentioned by CB a long press up to 30 secs of the on/off may do the trick , if not try placing said battery on bike switch it on and then plug in the charger (make sure the charger is live first).
Not recommended but some have reversed charged via the discharge for 10 secs to wake up the BMS if the other two options fail.
This worked for my partner's bike that we bought with a supposedly 'dead' battery after it had been left untouched for many months and would not charge up or produce any output.
I saw the method on youtube.
Having tried to charge it normally without success, I rigged up charging wires to the output pins taking care about the correct polarity and the BMS woke up in a few minutes. It might have woken up more quickly than that, but I was waiting to see a sensible looking voltage on the output pins. That took about ten minutes in this case.
Like you imply - this is not regarded as good practise. It did work for me and my partner has found the bike great ever since. It isn't ridden that much but it has a good range when we go out together.
Just to emphasise in case anyone with no experience finds this post. The Not Recommended point is there because connecting a charging voltage like that means there is no protection against over charging and consequent risk if it was left to charge up for anything more than a VERY short time. Leave well alone if in doubt.
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I tried the back charging exercise but without any success; once the charger is withdrawn the voltage drops from 41.5 back down to 0.9v within 20 seconds. Here's a pic of the serial number. 
If you can't wake it, I doubt it's worth bothering wasting too much time on it when you can buy a brand new replacement with perky cells for about £150 from Yose (it's this one I think). It's higher capacity at 10.4Ah against your worn 8.6Ah too. It depends how you value/measure the worth of your time.
Your call.
That said, I'd be inclined to fix multimeter probes to the output pins and give it a charge, carefully monitoring the voltage to see if it comes up. Could be your battery has gone rather low while being neglected, before you got it. If you are watching over it, what is to lose?
That said, I'd be inclined to fix multimeter probes to the output pins and give it a charge, carefully monitoring the voltage to see if it comes up. Could be your battery has gone rather low while being neglected, before you got it. If you are watching over it, what is to lose?
I reverse charged and connected a borrowed battery in parallel but it still drops down to 0.9v once the charger leads are removed. Where could I source a BMS from ?.