Need help converting bike from NiMH to lithium...

unclejemima said:
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
Click to expand...

I lied. Again, I'm new to this, so I tried measuring the voltage again tonight per cell, but this time used a different switch on my multimeter what gave a 2 decimal reading. For the initial test of the BMS output, 29.0V is what it showed. I could not use the 2 decimal setting for the output as it was to high...

As for the other cells, I finally found something different! Yes, we're getting somewhere...

Before charger plugged in. No LED's were blinking on the BMS board.
#1 4.13
#2 4.13
#3 4.13
#4 4.13
#5 4.12
#6 4.18
#7 4.19

Now when I plugged the charger in the last 2 led's would light up on and off. When the LED's were off, the charger showed it was charging. When the LED's were On, the charger showed green. The charger would keep blinking red in opposite of the LED's on the BMS. When the LED's on the BMS were off, the voltage per cell went up. When the LED on the BMS was on, the voltage per cell went down. These numbers are all with the charger plugged in. While the LED on the BMS was on, and when it was off.

volts LED ON / volts LED OFF on BMS
#1 4.14 / 4.17
#2 4.14 / 4.17
#3 4.13 / 4/16
#4 4.14 / 4.16
#5 4.13 / 4.16
#6 4.18 / 4.21
#7 4.19 / 4.22

So. Brings up a few questions.
A) why are only the #6+7 LED on the BMS blinking. (the blink slow while on the charger, and blink fast when I take the charger off)
B) why do cell #6+7 have different higher voltage than Cell 1 through 5

Hope this give more insight to those with technical knowledge.

Help me fix this!
 
unclejemima said:
.

volts LED ON / volts LED OFF on BMS
#1 4.14 / 4.17
#2 4.14 / 4.17
#3 4.13 / 4/16
#4 4.14 / 4.16
#5 4.13 / 4.16
#6 4.18 / 4.21
#7 4.19 / 4.22

So. Brings up a few questions.
A) why are only the #6+7 LED on the BMS blinking. (the blink slow while on the charger, and blink fast when I take the charger off)
B) why do cell #6+7 have different higher voltage than Cell 1 through 5
Click to expand...
The BMS works by bleeding down the high voltage cell (or banks).
#6+7 cells are higher voltage and are being bled down to "balance-equalize with the other cell.
Usually this takes 30min. +.
Leaving pack charging after light turns green is required to complete balance function.
 
you can also watch the gate voltage on the charging FET turn on and off as the high cells keep hanging on the HVC and then drain back down to the reset voltage. when the pack is outa balance like this it takes days and days of constant charging because the balancing current is so small. i use big cement power resistors on alligator clips to drain the high cells to force it to charge faster when i have to balance a pack manually.
 
using a resistor to discharge the high cells is not much risk and i can drain up to about 2A for short periods depending on how many cells i am discharging in series. this last pack i built from parts of different batteries which had totally different state of charge, the power resistor got so hot because i was draining about 7 cells total into about 15 ohms so the resistors got so hot i put them in a water bath to keep them from melting.

if you use a single cell charger it has to be set to the 4.2V for lipo. the 5V of a cellphone charger is too much.
 
Thanks guys. So the last 2 cells that are off, even by just a bit, is causing my BMS to shut off the power when I'm using the bike.

So remembering I'm a NOOB, where can I find a 4.2V charger? Radio Shack/circuit city type place?

Or should I discharge the 2 high cells down to same as the rest? I have a resistor that I was given by a friend. Its got 2 cables. I'd imagine I plug one into #7, and one into #6 plug (back from a few posts back) then I can charge the battery as normal and hope it all equalizes out?

FYI, I've left the charger on overnight before...still did not fix anything.

Let me know how I correct this the NOOB way :)

Will I then be good from there on out, or am I going to have to do this often?
 
Left the charger on all day, and to my surprise I had more LED's flashing on the BMS.

Now the 1, 2, 5, 6 & 7 were blinking...AND, all 7 were showing 4.19V. This was done with the charger on.

When I unplugged the charger and let it sit for a minute, the same result except cell #5 was 4.18V

This is much better I assume...perhaps the cells are almost equalized fully now. I hope this solves my problem.

I'll leave it on the charger again for a few hours tomorrow and see if I can get 4.19 across the board with the charger unplugged.

So, ideally, should all 7 LED's be blinking?
 
unclejemima said:
So, ideally, should all 7 LED's be blinking?
Click to expand...
Apparently so.

Although it uses a different balancing methodology than I've seen before ...
Method seems valid, and effective.

Still no explanation for the output failure ... sorry.

An unbalanced pack shouldn't have that effect.
 
So an unbalanced pack would not cause the BMS to shut down the power then?

What could be the issue then?

Is there any way the bike is causing the BMS to shut down, or is it all happening in the battery.

Keeping in mind this bike had a NiMH before, could that somehow be causing the problem? I just don't think so as the battery is its own device, and don't see how the bike could shut it down.

And if the BMS shuts down, do they typically shut down to zero or is it normal for them to go to 9.8v and then slowly down to 4.8V? And would removing it from the bike somehow reset the BMS?

Looking for any advice I can. Perhaps the voltage is just to much for the BMS?
 
999zip999 said:
I just unhook the bms and just give the battery a test. If all cells are full. It's just a short test.
Click to expand...

I see. Only, I kind did that already...that is, I hooked leads to my tester direct to the battery (while the BMS was still hooked up...I hooked up the tester before the BMS) and when the BMS cut, the battery still showed full juice.

So...this would pretty much be the same thing...unless of course there is actually something in the bike causing the short...then it would perhaps really wreck the battery?

Is there some other way to test how much juice it takes to trip the BMS? How can I draw power from the battery without actually having it hooked up. Is there some sort of device I can use to test this?
 
dnmun said:
are you able to measure the current that is triggering the BMS to trip? is it in the 15A range? 30A?
Click to expand...

I'm not sure how to test this. Can you suggest a method or a tool that I could do to test this?

Thanks,
 
i was just rereading and you mentioned the vendor is sending a new BMS?

to test this one for where the over current shut down cuts in you would need a dummy load and some way to measure the current into the load. for a low voltage battery using a resistance heater is harder because it takes so many, but if you have a cycle analyst or watt meter with a shunt we could try to get the shunt into the B- lead where it comes from the battery to the BMS. that way we would be able to save the current measurement when the BMS cuts off. so very difficult considering the practical problems and skills involved here.

so maybe it would help to wait and see if the same problem recurs with the new BMS. the pack is charged so it should be working. new cells so don't expect sag to eat it into the LVC but if he though the current was too high for that BMS then he may send one that doesn't cut out for the over current. that could help solve your problem.
 
I would install the new bms.
I was saying you can just hook the battery to the bike. Now this is just for a short test up and down the driveway. No bms just a short test with the cells being full. 4.18 or higher voltage. You are now the bms so be careful, this is not a test for range.This will tell you if your amp draw from the controller is shuting down the bms or the bms is broken or too low a amp output.
It's just a way of finding if it's the bms cutting off the pack.
 
I measured the space I have, and the BMS I included inthe link above will be to big...

Does anyone know where I can find a BMS that will plug and play? I'm still waiting for my battery guy to send mine out...and summer is soon over :)

Thanks
 
If you don't want to just hook up the battery for a short test with out bms. You can wrap the shunt on the bms with some small copper wire for 4mm then solder. This will raise the amp draw of your bms. This will show that your bms is to small for the controller if this fixes the problem. I would do this if a new bms is in the mail. This might over tax the cells. But you will know it's in the battery and bms and not the bike. You never answered the question on the amp draw of your controller ? We need this answer. No cell should go below 3.7v in this test. As this is a short as most people will get on the bike and ride till it's dead. We are not testing for range just to see if we can get it up and running.
 
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