Old BMS General Thread

Threads relating to the BMS system begun by Peter Perkins

Moderators: GregsGarage, retepsnikrep

isaac_alaska1
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Joined: Sun Apr 03, 2011 7:41 pm

Re: Old BMS General Thread

Postby isaac_alaska1 » Tue May 22, 2012 4:22 pm

thanks,

i told him how to check the cell voltages with a meter to see what the cells are actually at.

i think next time i will add a breakout board somewhere that i can keep covered, but then just remove one cover and have access to somewhere that i can measure all the cells. right now it is kind of a pain to get into the box to access the cell terminals.

i guess that's why it's called trial and error ;)

isaac_alaska1
Posts: 100
Joined: Sun Apr 03, 2011 7:41 pm

Re: Old BMS General Thread

Postby isaac_alaska1 » Sun May 27, 2012 2:34 pm

i'm up in your guy's neck of the woods for the next couple weeks, i'm in cornwall right now. not sure where you guys are all located but if you're nearby it would be fun to check out your projects and see how it's all been implemented :)

GregsGarage
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Re: Old BMS General Thread

Postby GregsGarage » Sun May 27, 2012 3:34 pm

I'm in Scotland about 30 miles south of Edinburgh and Peter's in Yorkshire. Bit of a trek from Cornwall :shock: , but you are welcome to stop by, just pm me.

Any news on your pack, have you found the problem?
Greg Fordyce

Daewoo Matiz
http://www.evalbum.com/4191

isaac_alaska1
Posts: 100
Joined: Sun Apr 03, 2011 7:41 pm

Re: Old BMS General Thread

Postby isaac_alaska1 » Sun May 27, 2012 3:40 pm

no, mechanic hasn't gotten back to me. seems the least he could do is reply to his email and tell me if it's done anything new or not....but i guess he's pretty busy up there. seems like a decent job....work in pretty much full isolation for six months or so and then they buy you a ticket anywhere in the world and give you six months off and it pays enough to still make good money (:

should convince them they need another tech up there to keep the machine going...i could send one of my guys up.

GregsGarage
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Re: Old BMS General Thread

Postby GregsGarage » Sun May 27, 2012 4:18 pm

The biggest worry would be if the problem is due to some cells being low, then something is draining them. The longer it is left, the more likely it is that you will permanently ruin the pack. :(
Greg Fordyce

Daewoo Matiz
http://www.evalbum.com/4191

isaac_alaska1
Posts: 100
Joined: Sun Apr 03, 2011 7:41 pm

Re: Old BMS General Thread

Postby isaac_alaska1 » Sun May 27, 2012 5:06 pm

if the problem is caused by low cells it's because they over used it without charging it. there isn't a fail-safe cut off on it at low voltage, all it does is flash the fault screen and sound the alarm when it gets to the low voltage cut off. next version i'm adding a hard cut off across the throttle so it can't be driven once the cells reach a certain point. i shipped it over and over the course of 3 weeks the cells barely fell at all, so i'm not horribly worried about the pack. of course if he's leaving it outside without charging it the cold is probably going to hurt them and the very slight normal draw from the bms and the self discharge isn't going to help matters.

live and learn i guess. i keep hoping for an even better battery but so far nothing looks like it's going to be released in the next few months, which is when i would need it by for next year.

isaac_alaska1
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Joined: Sun Apr 03, 2011 7:41 pm

Re: Old BMS General Thread

Postby isaac_alaska1 » Tue Sep 18, 2012 5:35 am

Finally got to tear into the machine today. it's been...almost 4 months. the cells are all pretty dead, gonna try to revive as many as possible. found out the problem was somehow caused by the BMS. it might have been the cold, but somehow the bms was reset to 0 cells. i tried to set it to 0 cells through the menu and the menu doesn't allow it, so it must have been an onboard problem instead of them pushing buttons. all part of the learning experience. just something to keep in mind if any of you are going to be using your system at -40* ;)

GregsGarage
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Re: Old BMS General Thread

Postby GregsGarage » Tue Sep 18, 2012 12:29 pm

Hi Isaac, sorry to hear about the pack, I know how it feels. :cry:

I've had my master reset to 0 cells once when I was having a problem with slave 25. The slave was behaving erratically and I finally tracked it down to a poor connection between the 12F683 and it's socket, reinserted it and its been fine since. But when it was playing up I did have to drive 10 miles with the alarm going and it did cause the cells to reset to 0 in the master. I reset the cells to 48 in the menu and its been fine since. I suspect that the misbehaving cell sending garbage data somehow reset the master, you might have had the same thing, low cells causing garbage to be sent back to the master, causing it to reset. So I think the cells being reset to 0 was probably a result of the pack being over discharged and not very likely that it was the cause.

The real question is what caused the pack to get discharged. Since it's all the cells, it has to be something that affected the whole pack. A fault in a single slave can cause it to turn on a load resistor and start discharging a cell, but that would only affect that 1 cell, not the pack. Could the cold have affected the slaves (and the cells themselves)? Electronic components are sold in different grades, each with different operating temperature ranges. Components used outside their rated range might not behave as expected. Testing would be required. A resistor ladder could be used to simulate a pack and test the slave operation in cold temperatures.

Or something else drained the pack, Peter has killed a couple of packs this way. :shock: It's important to make sure everything gets disconnected like dc-dc converters when storing an ev for extended periods. In my Matiz I have a contactor in the middle of the pack that opens whenever I switch off the ignition. Hope you get to the bottom of what went wrong.
Greg Fordyce

Daewoo Matiz
http://www.evalbum.com/4191

isaac_alaska1
Posts: 100
Joined: Sun Apr 03, 2011 7:41 pm

Re: Old BMS General Thread

Postby isaac_alaska1 » Tue Sep 18, 2012 3:11 pm

Thanks Greg, that makes it all a bit more clear. I think they discharged too far because the people using it kept driving it after the alarm went off. And then kept driving it... The next one is gonna have a hard disconnect that will open both contactors when the cells are discharged.


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