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How many batteries?

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Posted by Michael Shaffer on January 2, 2005, 4:18 pm
I want to power a 1650 watt Metal Halide bulb off of an inverter,
approximately how many deep cycle "car batteries" would I need to power
it for 30 minutes?


Posted by William P.N. Smith on January 2, 2005, 4:43 pm

You really don't want to use car batteries in this application, that's
on the order of 150 amps.  I'd use a couple of golf cart batteries in
series, that'll last more than a couple of cycles, which is about all
you'd get out of car batteries.

Posted by Steve Spence on January 2, 2005, 9:26 pm
 The answer, regardless of battery type is 14 amps at 120 vac, or 140
amps at 12 vdc, so 30 minutes would effectively need 2 70ah batteries
for 50% DOD.

Reality suggests Two 27dc-6 deep cycle 115ah batteries from walmart at
$3 each, and a 2500 watt inverter from BJ's at $69.

How are you going to recharge the batteries?

Steve Spence
Dir., Green Trust

William P.N. Smith wrote:

Posted by Bill Darden on January 4, 2005, 8:25 am
 Hi Michael,

You have asked a simple question that requires a complex answer.  The
simple answer is a lot.

Please see Section 7.9 in the Car and Deep Cycle Battery FAQ on
www.batteryfaq.org on how to size the batteries, inverter and charger
for your application.  By "car batteries", I assume you are talking
about the physical size and weight, e.g., Group 24 or 27 because you
should use deep cycle batteries for much longer battery service life.
The most important conversion is the 1650 watts (12.1 amps) at 120 VAC
to 145 to 169 amps at 12 VDC, depending on the efficiency of the
inverter and loss.  You might need to increase the battery capacity
due to a lower temperatures, higher current rate due the Peukert
Effect, and Depth-of-Discharge based on battery type.

Kindest regards,


On Sun, 02 Jan 2005 11:18:00 -0500, Michael Shaffer

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