Lithium Battery Monitor 48 cell

Threads relating to the BMS system begun by Peter Perkins

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dillond666
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Re: Lithium Battery Monitor 48 cell

Postby dillond666 » Sat Aug 11, 2012 5:37 pm

I got my first delivery of components from Farnell. The 0805 package looks miniscule when you see it!

I had a little trial run soldering 0805 resistors to a bit of stripboard, it's actually piss easy :D I gave the board "pads" a
little wipe from the flux pen first and then put a little spot of solder on one "pad" I offered the package up using
tweezers and applied a little heat from the iron to reflow the solder already on the pad. I then soldered the other side.
I used a small conical iron tip (I hate those!) and 0.7mm lead solder as it was the thinnest I could find. I consider
the flux pen to be essential to easy soldering.

There are no shortage of tutorials on YouTube, unfortunately many of them persist in discussing this weird stuff they
use in America called "sodder" :lol:

I am now happy to confirm I fear the surface mount soldering no more 8) The TSSOP-38 packages will be fun!

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dillond666
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Re: Lithium Battery Monitor 48 cell

Postby dillond666 » Fri Aug 24, 2012 7:26 pm

It was all going too smoothly. The TSSOP-38 package footprint is wrong :cry: I shortened a TSSOP-48 package included in KiCad but the original was the wrong width :evil:
This means that my chip sits about 0.1mm inside the footprint and makes it impossible to solder. To say I'm gutted would be an understatement as the wretched boards owe me about £100 (for 5!) no thanks to DHL and HMRC. I have ordered some adhesive pcb track to attempt a fix, but 0.5mm pin pitch will make the chances of success very slim. Probably beermats after all, boo hoo.

Re pcb expense, I think I'll be looking to get the equipment to do my own boards, as the cost for one off boards is just too much. I also note that it is possible to do the soldermask at home too.....dear santa......

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Re: Lithium Battery Monitor 48 cell

Postby GregsGarage » Fri Aug 24, 2012 10:27 pm

Maybe you could get some solder paste and try reflowing instead of using a iron. Check youtube for different methods of doing this and ebay for solder paste.
Greg Fordyce

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http://www.evalbum.com/4191

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dillond666
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Re: Lithium Battery Monitor 48 cell

Postby dillond666 » Thu Aug 30, 2012 4:56 pm

I've ordered a new board from Eurocircuits in Belgium. Cost will be less than having them done in China and they'll be ready in one week :)
I've only ordered one though and you need to order five from China, so like for like it would still be cheaper to use ITead in China.
I am happy that HMRC won't get to ream me this time though :D

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dillond666
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Re: Lithium Battery Monitor 48 cell

Postby dillond666 » Thu Sep 20, 2012 7:34 pm

Built up the board, no idea if it works yet :)

Obligatory picture!
http://dillond1.pwp.blueyonder.co.uk/incase.JPG

Should be getting cells early next week so better get cracking.
I've worked out the firmware in my head and will get it done asap, shouldn't
be too demanding.

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Re: Lithium Battery Monitor 48 cell

Postby GregsGarage » Fri Sep 21, 2012 8:13 am

Looks good, hope all goes well. :D
Greg Fordyce

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http://www.evalbum.com/4191

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retepsnikrep
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Re: Lithium Battery Monitor 48 cell

Postby retepsnikrep » Fri Sep 21, 2012 11:57 am

That does look nice.

Does it balance as well? I can't see any power resistors.
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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dillond666
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Re: Lithium Battery Monitor 48 cell

Postby dillond666 » Fri Sep 21, 2012 2:24 pm

It doesn't balance. The idea is a simple alarm on low cell voltage and stop charging on high cell voltage.

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dillond666
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Re: Lithium Battery Monitor 48 cell

Postby dillond666 » Wed Oct 10, 2012 9:26 pm

Yet again, I have snatched defeat from the jaws of victory :(
I got the picaxe master side of things running and working using a heartbeat generated by the signal generator, hunky dory!
The Maxim frontend however just kept alarming all the time (no heartbeat, bus held high). I couldn't really get to the bottom of things
but had a couple of ideas to try tonight. When I plugged the pack connectors in tonight I fried two of the Maxim chips, according to the
datasheet this should not have been possible. During the removal operation for the chips, I lifted a couple of those 0.5mm pitch tracks.....aaargh!
I can probably salvage the wreckage this time but I have no reason to presume it won't just go pop again. I hate being so out of my depth
but I suppose that's how you learn.....eventually :wink: Santa please give me a hot air rework station.

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dillond666
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Re: Lithium Battery Monitor 48 cell

Postby dillond666 » Thu Oct 11, 2012 8:37 pm

Got it all working tonight :D
I was extra careful soldering the two new chips on and I went round the pins of the existing two with some liquid flux and
reflowed them with a cleaned soldering iron. That must have been the fault all along! I have checked with the scope to
see the square wave heartbeat (4096hz)on the alarm bus and I have disconnected a cell wire to raise the alarm, all is good.

A little refining of the firmware and I can get the new pack into the car where it belongs 8)

I made a little error with some of the capacitor footprints and swapped a couple of picaxe pins round the wrong
way requiring a couple of bodge wires. I'll fix my schematic and layout and then I'll make all the information available on this thread.

D


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