Old BMS General Thread

Threads relating to the BMS system begun by Peter Perkins

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Re: BMS General

Postby retepsnikrep » Thu Mar 11, 2010 11:44 am

Gents if you post your parts list for the 16 cells slave and the Master V2 i'll check it with my schematics and the various tweaks/errata etc and add some comments. Peter
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

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Re: BMS General

Postby GregsGarage » Thu Mar 11, 2010 7:52 pm

The 16 cell slave parts list can be found here;

http://www.go-ev.co.uk/projects/bms/partlist311009.txt

Peter, your schematic program should be able to output some sort of parts list in text or .csv format that you can then edit with part numbers, comments etc.
Greg Fordyce

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Re: BMS General

Postby retepsnikrep » Tue Apr 06, 2010 8:09 am

Any updates please from those using the system or building one based on the principles. I'm especially keen to hear from those who are using alternative displays and how they have interfaced with laptops/netbooks etc. Please post the details. Thanks.

FYI I am now tinkering again with the various software packages and will hopefully be able to convert the Watchdog and Remote Display Picaxe 08M software into native Pic 12F683 versions over the next few weeks. I'll also look again at the I2C eeprom data logging problem I had with master V2. I've been on a bit of a winter wind down to be honest. No excuses now though. 8)
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

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Re: BMS General

Postby steiner » Wed Apr 07, 2010 3:40 am

Peter,

I have a small situation that I wanted to ask you about. It is occurring on my multi-slave boards which are based on your design but contain 12 channels vs the 16 channel boards that Greg has.

This situation is this. If I put a power supply across any one cell it will charge up to 3.65 volts and turn on the bypass resistor which is where it should. I have check each cell individually and they all operate this way. When I am charging the entire string of cells (24), one cell will reach the 3.65 volt threshold first which is what you would expect. However, the adjacent cells will usually turn on their bypass resistor within a few seconds. I have measured the adjacent cells and their voltage is usually about 3.6 to 3.62 volts. This isn't a major problem but I was wondering if you have seen this issue before.

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Re: BMS General

Postby retepsnikrep » Wed Apr 07, 2010 4:46 am

Yes we have seen this problem cause by the voltage drop in the wires leading to the cells. You need to use as thick a wire as possible for the bms to cell leads within reason. The slaves share a lead so when one turns on it changes (increases) the voltage the other next to it sees! That's why we see a cascade effect of slaves turning on the loads. It's a bit of a pain and could be reduced by.

1) Making cell leads as thick and short as possible/reasonable reducing voltage drop

2) Reducing load resistor current thereby reducing associated voltage drop. i use a 50ma load on my boards (This is a bit low and i should have gone for 100ma) The standard is 350ma.

3) Change the slave software to compensate. I did offer a version of the slave software with a voltage compensation routine you could try this. It is still a work in progress. It's on the software thread. you can send commands to the slaves to use voltage compensation.

4) Using seperate leads for each slave cell + & - but this requires some track cutting on the slave boards and twice as much wire. This solves the problem at a stroke.


I'm still looking at the slave software stuff and may well send a command to turn off all the loads and only measure cell voltages when loads are off for the entire pack.
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

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Re: BMS General

Postby steiner » Wed Apr 07, 2010 1:01 pm

Peter,

Thanks...I knew about the issue with the voltage drop when a by-pass turned on but I didn't know what the affect was (cascading of adjacent cells). I was thinking about simply adding a line of code in the slave that turned the by-pass off just before a cell reading was taken. I see you are addressing this in your latest code. I will give that a try and see what the outcome is.

Rick

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Re: BMS General

Postby retepsnikrep » Wed Apr 07, 2010 2:31 pm

steiner wrote:Peter,

Thanks...I knew about the issue with the voltage drop when a by-pass turned on but I didn't know what the affect was (cascading of adjacent cells). I was thinking about simply adding a line of code in the slave that turned the by-pass off just before a cell reading was taken. I see you are addressing this in your latest code. I will give that a try and see what the outcome is.

Rick


All the cell loads have to be off as adjacent ones cause errors reading high or lower if the one above and or below is on or off. It's a pain. You can't just turn the load off on the cell you are reading, the ones above and below also have to be off. The new code turns all the slaves off before carrying out the voltage readings then turns back on only those that are required as per Cell max V etc. It does remove a bit of independence from the slaves but I think we have to sacrifice that to get the accurate error free readings.
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

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Fritzing

Postby GregsGarage » Sun Jun 20, 2010 8:58 am

Just ran across this today, could be a useful tool. http://fritzing.org/
Greg Fordyce

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Latest files on Launchpad.net

Postby GregsGarage » Wed Jul 28, 2010 12:55 pm

I have thought it would be good to have all the latest files available in one place to make it easier to find them. Originally I was going to start a separate thread for this but have decided on a different approach. I have registered the bms project on Launchpad.net. It can be found here. https://launchpad.net/evbms

I have uploaded a few files relating to the Master. More to follow. The advantage of this is it has tools to track differences between files, ie what changes have been made, bug reporting, feature requests, etc. We don't have to use all of this, just keep it simple at the moment. You don't need to sign p to launchpad to view or download files, so anyone can use it, however if you do become a registered user you can submit code into a seperate branch of the project and request it to be merged with the main branch (usually called trunk) if you wish. So Peters code can be the main "trunk" branch. I can submit my own branch for my specific changes for my vehicle and so can anyone else. I am not suggesting moving the project to launchpad, rather having it as a complement to the forums, an easy place to find the latest software, schematics, etc. Have a look and tell me what you think.
Greg Fordyce

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http://www.evalbum.com/4191

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Re: Old BMS General Thread

Postby retepsnikrep » Wed Jul 28, 2010 1:58 pm

Looks interesting Greg. I am a bit confused about how it all works though. I'll let you tinker a bit more with it.
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.


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