# 12 volt draw from 72 volt pack??



## Woodsmith (Jun 5, 2008)

Ever seen a lead acid battery explode? 

It won't work.
If you look at just one battery in your pack you will see a red wire going from the Pos terminal to the +12v terminal. You will also see a battery strap from that battery's Neg terminal being linked by a red wire from the adjacent battery also going to the +12v terminal.

That makes a dead short across that battery's Pos and Neg terminals.
Repeat for all your batteries in the pack and you will have a pile of melted 12v cabling or a large bang!


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## ishiwgao (May 5, 2011)

Trace the leftmost wire going into your 12v battery pack, and the rightmost wire coming out. Remove everything inbetween, and watch how it parallels.

Remember, electricity doesn't care how many wires. It just takes the shortest path.


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## mizlplix (May 1, 2011)

You can still use your DC/DC, just drop back a few batteries and hook up.

I know, you wanted to use the full pack...

Miz


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## Ziggythewiz (May 16, 2010)

Do what Miz says.

How much power does your AUX system use? In mine even with everything turned on it's under 10 amps. 

Whatever you're using, split over 6 batteries isn't enough to unbalance most lead batteries. The DC-DC's primary function then is isolation. What kind of lead are you using?

If you do decide to do a series parallel battery pack, please make the final connections using a mad scientist lever, aka knife switch, and film it for your posterity to put on youtube.


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## caffinefiend (Dec 14, 2009)

Okayyyy.... We DON'T do the dead short thing. Once you mention the short it all came clear. Thanks all for the heads up. It really is good to have wiser heads to bounce things off. Also, the Idea of using the same DC to DC converter just tapping off at the proper voltage is a good one.

I haven't put the battery pack together yet, and am planning on using US battery's 12V US185XC, 200 amp hr (20 hr rate), 106 min at 75 amps. I'm planning on using the EV as a commute vehicle, 10 mile round trip. The first leg with headlights on, which will be the major draw on the auxilary power supply. I might need to defrost the windshield a few times in the winter, it's pretty mild in my area though.


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