Motor diagnostics..

[thelarkbox]

cheers @saneagle crossed posts.. residual charge in capacitors works for me

 

[saneagle]

ok correction time, in an attempt to document the 36v output with no +ve voltage suppled to the bms, i pulled the plug with the led meter attached and it died instantly??

I have no clue? I swear i measured 36-37v on the battery output without the bms multiwire plugged in MORE THAN ONCE as it was the 2nd or 3rd time the difference from the 'full' 39v registered??

OH well - still the sw pads are not functioning as I expected?

I edited the above post.

 

[thelarkbox]

I edited the above post.

Great.. that is easy to test, brb...

 

[thelarkbox]

still no joy ;( tried a couple of switches just in case the first was a dud..

the pcb is tiny and populated with micro components so unless i can break into a simple wire to fit a switch i may have dived a tad too deep here..

 

[saneagle]

still no joy ;( tried a couple of switches just in case the first was a dud..

the pcb is tiny and populated with micro components so unless i can break into a simple wire to fit a switch i may have dived a tad too deep here..

Cut any of the sense wires and join a switch to the two ends. If the BMS is working properly, it should give power when the switch is closed and cut it when open.

 

[thelarkbox]

Thanks for the patience Saneagle, so the 'multi wire plug has 11 wires feeding in , a black wire, 9 x yellow wires and 1 x red wire, I made a guess that the red wire indicates the group of cells the bms draws power from???? and that it and the 9x yellow wires are the 10x sense wires???

so i snipped the 2nd yellow wire as it appeared to be the easiest to connect to.. and.... Nothing..

Power is still pouring out according to the attached led volt meter, now perhaps it and the bms both have some caps to discharge so i shall revisit and check before posting this entry, but if not here is the picture proof..


yeah still 39.7v 1/4 of an hour later,, So perhaps thats not a sense wire after all??

What i take a sense wire to be is one of the wires connected directly to each group of parallel cells in series (10x) for voltage monitoring and balancing hence the assumption that the 9x same coloured wires would be sense wires??

almost 1/2 an hour on now and not a sign of any voltage drop..

The plot thickens, I have pulled the heatshrink aside enough to reveal the cell group the wire i snipped is attached to..

But i also pulled the whole plug and the output voltage died instantly, the volt meter is just on the bottom edge of the shot but dead - honest



any suggestions for which wire to test next after i repair the one i have cut??

according to the silkscreen on the pcb rear the black wire is B- and the populated pins from there on up are B1, B2, B3....B10(red wire). I snipped B2..

 

[saneagle]

Thanks for the patience Saneagle, so the 'multi wire plug has 11 wires feeding in , a black wire, 9 x yellow wires and 1 x red wire, I made a guess that the red wire indicates the group of cells the bms draws power from???? and that it and the 9x yellow wires are the 10x sense wires???

so i snipped the 2nd yellow wire as it appeared to be the easiest to connect to.. and.... Nothing..

Power is still pouring out according to the attached led volt meter, now perhaps it and the bms both have some caps to discharge so i shall revisit and check before posting this entry, but if not here is the picture proof..
View attachment 58564

yeah still 39.7v 1/4 of an hour later,, So perhaps thats not a sense wire after all??

What i take a sense wire to be is one of the wires connected directly to each group of parallel cells in series (10x) for voltage monitoring and balancing hence the assumption that the 9x same coloured wires would be sense wires??

almost 1/2 an hour on now and not a sign of any voltage drop..

The plot thickens, I have pulled the heatshrink aside enough to reveal the cell group the wire i snipped is attached to..

But i also pulled the whole plug and the output voltage died instantly, the volt meter is just on the bottom edge of the shot but dead - honest

View attachment 58565

any suggestions for which wire to test next after i repair the one i have cut??

according to the silkscreen on the pcb rear the black wire is B- and the populated pins from there on up are B1, B2, B3....B10(red wire). I snipped B2..

It should have worked. You snipped the correct wire. The idea is that if any of those wires go below 2.9v, the BMS should switch off. Maybe it's not smart enough for that.

I'd be interested to see what's on the other side of the pcb.

There are 4 MOSFETs. I'm assuming that they all switch together for charging and discharging, as you don't have separate charge and discharge wires. The pcb markings are anomalous because your main output is connected to C- (charge negative) rather than the normal P- (power negative) B- (battery negative) is the cell-pack negative that should be switched to P- and C-. It would be interesting to see if there's continuity between P- and C-, which would make sense of that arrangement. If they're separated, it might be worth checking whether P- is switched off when you cut that wire.

To help you understand how it works, when you look at the marked face of the MOSFET with the legs downwards, the right leg is the current going in, the middle leg is connected to the back-plane and is the switched current going out. The left leg is the trigger that switches on when it has around 12v - 14v. You can check that with your meter. All 4 left legs must therefore be connected to the same source that switches the trigger voltage on and off, which is a transistor somewhere. If you can find the common track, you can cut it and wire your switch to a convenient pad either side of the cut.

 

[saneagle]

Further study shows that the two pairs of MOSFETs are in series, which is unusual, but I have seen it before. I can't quite figure out the logic of why it should be like that. It doesn't make sense to me.

 

[thelarkbox]

I was out of my depth when i started on what i thought was a well laid out path.. Just understanding the steps to be taken

I can pull the positive power plug and test continuity and simple things without power running through the board, but am way too kak handed to fumble over a live board.. I will do this later..

I can throw cash at a replacement bms if a plug n play option exists adding a switch to a switch enabled bms isnt a problem but is at the limit of my current comfort zone

With the batteries all now using the same connectors the switchless battery can take the back seat in the rotation. I can still only ride one at a time..

i will report later with any meter readings im comfortable taking..

As for me having an odd bms thats kinda par for my particular course. so c'est la vie..

 

[thelarkbox]

hope the 2 pics attached show the pcb front and back ok..

I have tested for continuity between C-, P- , and B- there is none all 3 are isolated from each other.

the wire attached to C- is attached to the charge socket via the output terminal,
B- is attached to the last cell group. as is the black B- wire feeding the 11pin plug pin 1

Now i read this properly..

. it might be worth checking whether P- is switched off when you cut that wire.

hmm after i fix the cut wire, cut another (red B10, Its RED!) and fix that too.. HA!


Gollox IM torn.. I should just backtrack rewrap and close up the battery and accept the loss I did the main thing change the connection terminals to match all other bikes/batteries..

But since i now have 2 batteries to select with switches fitted before this one it can sit on the bench a lil longer perhaps.. In for a penny etc..

decluttering the output terminals and wiring the bms up as expected is not a biggy (well shouldnt be) and is easily back-trackable(should be)

i will sleep on it or get stuck in at 3 am.. ..

 

[saneagle]

hope the 2 pics attached show the pcb front and back ok..

I have tested for continuity between C-, P- , and B- there is none all 3 are isolated from each other.

the wire attached to C- is attached to the charge socket via the output terminal,
B- is attached to the last cell group. as is the black B- wire feeding the 11pin plug pin 1

Now i read this properly..

hmm after i fix the cut wire, cut another (red B10, Its RED!) and fix that too.. HA!


Gollox IM torn.. I should just backtrack rewrap and close up the battery and accept the loss I did the main thing change the connection terminals to match all other bikes/batteries..

But since i now have 2 batteries to select with switches fitted before this one it can sit on the bench a lil longer perhaps.. In for a penny etc..

decluttering the output terminals and wiring the bms up as expected is not a biggy (well shouldnt be) and is easily back-trackable(should be)

i will sleep on it or get stuck in at 3 am.. ..

If c- is connected to the charge connector, where does the power come from that's connected to the negative output terminal? Normally, it comes from p-, which is empty on yours!

 

[thelarkbox]

What can i say the battery was working fine, until i plugged the repaired wire fed plug in, AND?? -No output voltage!!, attempts to test continuity between B- and P- with a meter resulted in the volt meter attached to the output register circa 18v until i broke the connection.

all the +ve in wires are fine, i managed to test the voltage at each nicely stepping up in 3.9v increments (suspiciously conforming to expectations, no 3.7 groups????)

Anyway we may never know on attempting to test B10 against P- for voltage i slipped up and shorted a few things releasing a hint of magic smoke? perhaps residual flux??

still no output voltage..

Pictures attached showing
1) low 2.8v between B10 and P- (expected 39v)
2) taking that measurement
3) taking the next reading B- and B10
4) 39v
5) the output terminal connections
+ve 3x Battery power charge port and voltage indicator.
-ve bms C- charge port and voltage indicator..

ps shorting out the sw solderpads had no impact on P-

still no output voltage? both cut wires are repaired and are reading the correct 39v and 7.8v as expected?? But the voltage present on the output when both were cut is now effin absent!!

I think the magic smoke was just heat from the rapid discharge when i shorted 2 cell group sense connections for a split second, my arm lift away reaction was pretty quick.. ??

 

[thelarkbox]

Think i need a new bms..

 

[thelarkbox]

oh and output voltage is back??? wtf? I was just about to pick up mu mug and empty pop tins.. and the led meter flashed on..?? 39.5v now, result of my lil short??

And 39.4v between B10 and P- !!

and shorting the sw solderpads has no impact on P-

 

[saneagle]

oh and output voltage is back??? wtf? I was just about to pick up mu mug and empty pop tins.. and the led meter flashed on..?? 39.5v now, result of my lil short??

And 39.4v between B10 and P- !!

and shorting the sw solderpads has no impact on P-

If you can figure out why, that's where you need your switch!

 

[thelarkbox]

If you can figure out why, that's where you need your switch!

Yeah if i can deal with the 1/2 hour or longer delay in restarting I was not a fast typist or photographer when prepping my first message of failure this evening..

Its sure not behaving according to my 'Janet and John' level of comprehension of what should be going on..

Any links to sellers of good bms boards known to work as required?

 

[saneagle]

Yeah if i can deal with the 1/2 hour or longer delay in restarting I was not a fast typist or photographer when prepping my first message of failure this evening..

Its sure not behaving according to my 'Janet and John' level of comprehension of what should be going on..

Any links to sellers of good bms boards known to work as required?

When you fit a new BMS, you can be lucky to find one with the same wiring arrangement on the multi-pin connector, but most will be different, so you have to cut all the wires and join them to the new connector.

In that respect, the pins can be reversed from one end to the other. Yours has 11 pins, but you can get 9 pins and 10 pins as well.

 

[thelarkbox]

When you fit a new BMS, you can be lucky to find one with the same wiring arrangement on the multi-pin connector, but most will be different, so you have to cut all the wires and join them to the new connector.

In that respect, the pins can be reversed from one end to the other. Yours has 11 pins, but you can get 9 pins and 10 pins as well.

Cheers, yes im aware, ive already blown up a few adds to triple check and count connecting interface pins a few times, and squint at the silkscreen print looking for a label match ha ..

Im in more of 'if it aint broke .. ' frame of mind today and am leaving the battery on the bench over the w/end for now,, life etc.. and make any decisions when not so bogged down in the mess of it all next week