Need help converting bike from NiMH to lithium...

[dogman dan]

Makes sense, the temp probe wire was, in effect, the bms for the nimh battery. If it got too hot, the bike would know to shut off.

I was just thinking it sounded like a bms trip, since it would reset when you unplugged. I was going to advise trying to bypass the bms and see what happened. You could do that still, and if it still shuts off, that would leave a greater possibility that it is something on the bike.

 

[unclejemima]

Thanks guys. So I did not get a chance to test my temp probe setup yet...wife's birthday yesterday and I figured to avoid sleeping in the garage, I should probably not be tinkering on the e-bike.

So, just curious what the Li(NiCoMn)O2 pouch cells are? Are these ok technology compared to Lifepo4?

Thanks,

 

[arkmundi]

So, just curious what the Li(NiCoMn)O2 pouch cells are? Are these ok technology compared to Lifepo4? Thanks,

If you're not already committed, suggest LiFePO4 as the most safe & environmentally friendly chemistry, with plenty of C-rate and storage capacity to satisfy all but the most demanding application here at ES. All questions about batteries are answered at http://batteryuniversity.com/

 

[unclejemima]

Li(NiCoMn)O2 was the only choice I had to fit my application. The cell size fit exact like a glove and this was the only seller able to provide any other lithium battery that would fit in the case.

 

[unclejemima]

Did some MORE testing last night.

This time I hooked up a meter to the battery terminals and watched it while I drove.

It would show 29.2 to 29.3v when the battery was full. I confirmed the charger was also putting out 29.3v, so the battery would then be considered "fully charged" as that is the max the charger can give out.

Then I connected the battery to the bike and it still showed 29.2v. Took it for a rip. Depending on load it would drop to as low as 25.5v, but typically would show around 27.5-28.0v when using medium power.

Then it would just randomly cut out after using it for only about 20-30 seconds. The meter would display about 9.0v and then drop slow to 5.2v where it would sit. Turning the key on or off would not make a difference.

I removed the battery and it then showed 4.8v, inserted it again and it showed 5.2v. Weird. Anyway, removed it at 4.8v, then took it to the charger (all the while my meter is still hard wired) plugged it into the charger and INSTANTLY it jumped back up to 29.1V.

I could hook it back to the bike and then would be able to repeat the above steps.

One interesting thing to note, if the bike quit running and it showed the 5.2v/4.8V, if I removed the battery from the bike and then turned off my meter it would automatically reset to 29.1v. Only with meter on the whole time would it require the charger to reset it back to 29.2v

So guys, does this sound like a bad bms?

Is there anyway the electronics of the bike are able to shut off the battery?

Let me know,

 

[unclejemima]

Anyone?

I've contacted the seller as well and am waiting a reply.

FYI, i did try hooking up the temp probe and still no go.

 

[unclejemima]

Photos for those wanting them...

The original NiMH pack...

The lithium pack with LED meter, old charging port and temp probe...

drawing showing wiring of above setup...

The lithium pack without all junk. Just battery and BMS

drawing of simplified setup

Have at it guys Let me know whats going on here

 

[dnmun]

where are the sense wires? can you open the shrink wrap on the BMS so we can show you where to measure?

 

[unclejemima]

Ok guys. I took the bms cover off (but did not have my camera) and measured the voltage after the battery cut-out. It was 29.0v still before the BMS and 5.2v after the BMS

This means my BMS is bad?

 

[heathyoung]

Your BMS may be reacting to an actual fault - you need to measure the voltage of each cell, from the sense connector (many wires).

Measure this when the BMS has cut out. It doesn't sound like a current problem, but could be a weak cell, or an out of balance cell.

 

[unclejemima]

Thanks. I will tear the pack apart tonight and see if i can measure each cell. It does not appear very easy to get into with a protective skin...but we shall find out.

The vendor is sending me a new BMS as he figured the current is to high for the BMS.

Here is a photo of the BMS...

Front...

Back... (B- is the direct output from the battery.)

Could I try running the bike without the BMS, or would doing so IF there were any unbalanced cells cause a problem?

Thanks,

 

[dnmun]

7 channels, 29V is lipo or limn2o4 so you should put it on the charger and see if all of those leds turn on. if there is one led that does not turn on then that may be the low cell.

you measure the cell voltages where the sense wire plug is soldered to the BMS. if you put the probe tips of the voltmeter on adjacent pins you will see the full cell voltage for each cell.

for the first cell you measure between the shunt wires and the first pin of the sense wire plug, and each pair of pins up from there to #7.

knowing the cell voltages is important to understanding why it doesn't work. at full charge they should each be no more than 4.2V.

this one is almost if not identical to the ping v2.5 signalab BMS except it looks like they take the circuit current from the top of #5.

 

[unclejemima]

Thanks dnmun.

7 channels, 29V is lipo or limn2o4 so you should put it on the charger and see if all of those leds turn on. if there is one led that does not turn on then that may be the low cell.

I'm fairly certain only 1 of the led's turns on when its plugged in. If I recall, when its not plugged in but on full charge it will show only 1 led blinking. I'll check tonight. I would imagine all 7 LED's are supposed to blink if everything is working correctly?

you measure the cell voltages where the sense wire plug is soldered to the BMS

Sorry, I'm really not good with this electrical stuff. Can you draw on the photo where I should be measuring cell voltage?
'
Could you explain more what the shunt wire and the sense wire is? Perhaps draw it on the diagram. Please, please and thank you, thank you

knowing the cell voltages is important to understanding why it doesn't work.

I understand, and I'm excited to see if there is a more definite problem.

his one is almost if not identical to the ping v2.5 signalab BMS except it looks like they take the circuit current from the top of #5.

Is that a good thing, or a bad thing? Is the ping v2.5 signalab BMS any good?

Is there any merit in the vendor saying the current is to hight for the BMS?

 

[dnmun]

the current is not too high. those 4 silver wires that loop up out of the surface are where the current flows. as the current flows through them there is a voltage drop across the shunt from one end to the other. that voltage drop is what the BMS measures to determine how much current is flowing. it is called a shunt resistor or shunt for short.

it is connected to the B- terminal of the battery which is the bottom of the first cell.

that white plastic plug next to it is the sense wire plug. each of those wires runs to the top of each of the 7 battery cells. so the BMS can 'sense' the voltage on each cell through those wires.

the first pin next to the shunt is the top of #1. if you measure between the shunt and that pin you should measure about 4V. try it, then do each pair of the others. put the black probe on the lower pin and the red probe on the upper pin for adjacent pairs and record the voltages. WHILE CHARGING.

 

[unclejemima]

Thanks again dnmun.

I'm sorry. I ready your post about 10 times, but I'm still not 100% where to measure. I've got a better understanding of how it works though, thank you.

See my attached.

The blue arrow is the direction the power is traveling...or do I have it backwards?

those 4 silver wires that loop up out of the surface are where the current flows.

The area circled in red is the shunt then...? You mean 3 wires, not 4...or am I missing something?

The area circled in blue is where each cell connects to the BMS (each negative post of each cell?). 1pin for each cell, total of 7 cells. Got it.

The first pin is #1, through #7 (going right to left)

Do I measure on the pin #1 with black...but where does the red get measured from?

I'll buy you a beer if you can draw it for me in the photo :wink:

please and thank you again.

 

[dnmun]

you are measuring a voltage. red is positive probe and black is negative probe. the shunt is connected to B- so it is the bottom or negative of the first cell #1- and the first pin you have labeled #1 is the top of that #1+ and it is also connected to the #2- so to measure the second cell you put the black on the #1 and the red on the #2.

 

[unclejemima]

you are measuring a voltage. red is positive probe and black is negative probe. the shunt is connected to B- so it is the bottom or negative of the first cell #1- and the first pin you have labeled #1 is the top of that #1+ and it is also connected to the #2- so to measure the second cell you put the black on the #1 and the red on the #2.

Thank you dnmun...but I'm still confused. I'm sorry, I really have not done to much of this before. I just don't want to touch the wrong probe to the wrong spot and short something out.

I've re-uploaded the photos side by side.

I'm confused now. What side of the board am I measuring from. The front or back (i've labeled what I think is front and what is back. Correct me if I'm wrong)

So...then the pins i've labeled 1 thorough 7...are those the correct locations to measure from?

My probe has a black (negative) and red (positive). I touch the black to B-, and the red to #1...then black to B- and red to #2, and so on...? or is this wrong?

I'm assuming the black is common, meaning the same for all batteries, just the red or positive has its own pin on the board, no?

Let me know,

 

[dnmun]

yep, black probe on B-, red probe on #1 for voltage of cell #1.

then black probe on #1 pin and red probe on #2 pin for voltage on #2 cell, and so on.

once we know if the pack is balancing then we can guess what is wrong. then test for that.

 

[unclejemima]

I see. That makes sense. Thanks for clearing that up. I should check the voltage while charging, correct?

probe black on #2 red on #3, black on #3 red on 4, until I get to check cell 7 what will be black on #6 red on 7.

I just thought this would cause a short doing so I would never figured that out!

Talk to you soon with results

 

[dnmun]

if the probes touch while you are measuring the adjacent pins it will short the cell. it happens, so just be careful and if you stick the sharp tip of the probe into the solder at the base of the pin where it is soldered into the pcb then it has less chance to slip.

 

[999zip999]

Put tape or shrink tube on the probes so only the tip of the probe shows. This will help in not shorting out.

 

[unclejemima]

Thanks guys.

Got it done. Results are not what I was looking for. I was expecting to find one cell different...

Every cell on a a time (all 7 cells) registered 4.2V exactly. Not one a smidge different.

I did this with and without the charger. Results were identical.

So...what does this mean then? Does this mean there is something in the bike causing the problem?

Let me know,

 

[999zip999]

Then read them down
1. 3.9v
2. 4.1v
3.4.2v



7. ect.
This will help you and us. Just a small record.

 

[dnmun]

no, it is 7S lithium ion

can you measure the gate voltage on the mosfets?

 

[unclejemima]

Sure. stupid question again...where do I measure the gate voltage on the mosfets? Where and what are the mosfets

Each cell is exactly 4.2v. Not a smidge different.

#1 4.2
#2 4.2
#3 4.2
#4 4.2
#5 4.2
#6 4.2
#7 4.2