Cheap BMS?

fishguts · Sep 24, 2009

I confess I know almost nothing about electronics. I can fabricate almost anything, but this stuff is a mystery to me.

I'm planning on 23 LifePo 3.2 v 60ah cells, which I think will work pretty well on my fairly light (under 1500 lbs.) reverse trike. I don't need to travel over 50mph and no more than 25 miles, usually much less than this.

23 60ah cells I can just afford (about $1,600 from evcomponents), but BMS can cost as much as the cells. DIY versions run around $350. But on Ebay I found this:

http://cgi.ebay.com/ebaymotors/Lith...QcmdZViewItemQQptZOther_Vehicle_Parts?hash=item1c0c7f67bd&_trksid=p4506.c0.m245

It's $25 (plus $20 shipping) and handles up to 12 cells at 20A continuous, 40A peak.

Just wondering if there was a way to gang a couple of these things together to provide BMS for the pack. My Curtis controller is 72v, 400A.

Please forgive my ignorance, but trying to figure this out gives me a headache! Any help for an electronics virgin appreciated.

Sutitan · Sep 24, 2009

Never seen that before around here, so i dont know what to tell you.

The most common cheap solutions are the voltblocher
http://www.voltblocher.com/
there is also the TPPacks BMS
http://www.tppacks.com/products.asp?cat=26

They both balance the cells. the voltblochers can include high/low voltage protection. TPPacks only has low voltage.

Sure someone here can offer you more info. just gotta wait for there replys. hope i helped

brainzel · Sep 25, 2009

Sutitan said:
The most common cheap solutions are the voltblocher
http://www.voltblocher.com/
there is also the TPPacks BMS
http://www.tppacks.com/products.asp?cat=26

They both balance the cells. the voltblochers can include high/low voltage protection. TPPacks only has low voltage.

I think thats not correct. I decided to take the Goodrum/Fechter (TTPacks) for my 38 cells and it will also have an upper limit and shunting (high voltage protection).
There is a problem in the actually version 2.6 but they will fix it soon (I hope so).
Look at that forum to read more about it too:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=5416

jorhyne · Sep 25, 2009

fishguts said:
Cheap BMS?

That's an oxymoron my friend. Cheapest full featured BMS I know of is http://www.convertthefuture.com/index.php

Since your conversion will have less than 25 batteries he can make you a custom version for around $700.

AmpEater · Sep 25, 2009

The voltblocher LiFePO4 DIY kits w/ HV and LV will cost you $276 for 23 if you can solder (its not that hard). As long as you can throttle your charger back when one hits HV then you're golden.

23 cells at 60 ah is about 4.4kwh. You'd need to use less than 175 wh/mi to hit your 25 mile range target. Certainly possible, but hopefully your design is pretty aerodynamic. Its best to not completely drain the cells for long life.

Cheap BMS?

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