Running deep cycle batteries in parallel?

[hoggs222]

I know this has been covered, but there's no search function at the current time.

I have 2 Interstate group 27's that are the same age. I am looking to run them in parallel.

I believe that I need to run + to + and - to -? Am I missing anything?

The TV that I am running draws 42 watts. How much more will I get out of the battery life? The interstate group 27s say 20.4 hrs at 5 amp load and 5.7 hrs at 15 amp load. I will also be running a few lights off of it that are 12 volt lights.

Also, what guage wire should I use? What works better to run in parallel, the screw down posts or the aligator clips on the wider posts to make a better connection, or doesn't it matter?

Thanks,

Hoggs

[federline]

Those group 27's are 100 amp-hour units if I remember right. Yes, you would hook them + to + and - to -. So you'd get 200 amp-hours under optimal conditions, but in the real world, you can only count on what the manufacturer rates a battery at for DOD, Depth of Discharge. Most recommend not discharging more than 50% of capacity. Regularly discharging to 80% of capacity will shorten battery life. 100% discharges wreck deep cycles, they're never the same. 60% to 70% is a good rule of thumb.

Lets take 60% DOD. That means that if you like to keep your your batteries healthy, you can eek out 120 amp hours (60% of 100 amp hours, times two).

Now we need to calculate amperage draw to find out how much runtime you will get.

You have a TV and 2 12v lights. We can get the TV amps draw since watts = amps x volts, or 42w divided by 12v = 3.5 amps.

But your lights, you don't give watts or amps - a single incandescent lightbulb can draw 1 or 2 amps, while an LED might only be 0.2 amps. We'll guess you are drawing 2 amps with a couple small incandescent bulbs.

So total amp draw is 5.5amps. With two group 27s at 60% DOD and the lights above and the TV on together non-stop, you would get 120 amp-hours divided by 5.5 amps, or about 22 hours. I've be frugal with the TV if I were you.

If your batts are cold you will get less. If the draw is higher, you may get less, deep cycles have less DOD capacity under higher amperage loads, but you're probably not what most would call "high load".

For the wire for just running your house, you don't need anything fat to parallel them, your amperages are not outlandish. But, don't try to charge both batteries in place with thin parallel wires in place, charge them using their posts. I would also use the screw down terminals and not alligators - alligators sometimes get positioned so they spark a bit, and connections aren't that good sometimes.

[hoggs222]

Sweet! Sorry, I forgot to add that the lights are NOT LED. Screw down it is and the Wild game will be on tomorrow night!

We usually only use the batteries for a night or so, so the battery life won't be as big of a deal. Plus, that's what cribbage is for!

Federline, I see you're from Buffalo. I'll be out on Beebe tomorrow night in a green with a tan stripe wheelhouse. If you're in the neighborhood, stop on in for a cold one.

Thanks,

Hoggs

[federline]

Quote:

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Federline, I see you're from Buffalo. I'll be out on Beebe tomorrow night in a green with a tan stripe wheelhouse. If you're in the neighborhood, stop on in for a cold one.

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I may take you up on that, keep one on ice.

[hoggs222]

Jim,

I saw a few days ago, you posted your email. With the last few days posts missing....what is it again?

Anyway, it was great to meet you. There's more hospitality where that came from!

My email is [email protected]

Later,

Hoggs aka Jon