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Field box battery charging

Old 04-09-2009, 12:56 PM
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BEAR-AvHistory
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Default Field box battery charging

I have a field box with two Hanger 9 - 12V 7Ah gel batteries wired in parallel . How can I calculate how many charges I can get with my various flight batteries? My current flight batteries are 3S1800, 3S2200, 3S3200 & 3S3300.
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Old 04-09-2009, 03:08 PM
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slipstick
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Rough calculation:

Energy available in two 12V batteries = 2 x 12(V) x 7(Ah) = 168 Watt hours

The lipos are all 3S and a 3S battery charges to 12.6V and you need to make an allowance of about 20% because charging isn't 100% efficient, so energy required to charge each battery is

12.6(V) x 1.2 (efficiency allowance) x (battery capacity / 1000) Watt hours

E.g. 3200mAh battery needs 12.6 x 1.2 x (3200/1000) = 48 Watt hours approx

168 / 48 = 3.5 so you could probably charge that battery 3 times.

I'll let you do the calculations for the other batteries. But 14Ah total is not much of a charging battery. I use 17 Ah for indoor flying (biggest lipo 200mAh ) and an 85Ah battery at the field and I've often run that almost flat if I have a good day out (and I spend a lot of my time at the field chatting to people ).

Steve
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Old 04-09-2009, 06:19 PM
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kyleservicetech
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Agree with Slipstick, I've got two 6S2P and one 5S2P A123 packs in three different airplanes. They are good for a day of flying with my 120 AmpHour Deep Cycle battery. But, the drawback is you need a lift truck to move that battery.:o

If you run the numbers that 120 AmpHour battery is good for about one horsepower hour between charges, allowing for efficiency in recharging, and so on.

Take a look at chapter II of the following Wattflyer posting.
http://www.wattflyer.com/forums/showthread.php?t=45222
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Old 04-09-2009, 09:47 PM
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BEAR-AvHistory
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To All,

Thanks for the math & the link.

I have a few of each type battery except for a single 3S3200 that came with an E-flight T-34 so I should be OK with the gel batteries. If I get hung up I have one of those chargers that comes with some RTF planes that you can clip onto a truck battery . I back my pick-up in at our clubs flight line so it would be easy to hook up.

Quick question on a standalone battery; I have a spare 17lb Die Hard 12V 230cca garden tractor battery in the garage which seems to be good when I put a tester on it. Can this also be used since its not a heavy to lug around as a normal deep cycle battery?
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Old 04-10-2009, 02:43 AM
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Quick question on a standalone battery; I have a spare 17lb Die Hard 12V 230cca garden tractor battery in the garage which seems to be good when I put a tester on it. Can this also be used since its not a heavy to lug around as a normal deep cycle battery?

You can use it, but the problem is its rated for 230 Cold Cranking Amperes, which has no relation as to how many ampere HOURS it has.

230 CCA represents how many "horsepower" it can put out for a few seconds during cranking the engine. Ampere Hours represents how long it can put out a given amount of horsepower.

If the battery is a spare, it won't hurt to use it, but it physically won't last as long as a marine or deep cycle battery. It also will not give you as many flights as a marine or deep cycle battery. But, these marine batteries are heavy! As in boat anchor!

Last edited by kyleservicetech; 04-10-2009 at 04:06 AM.
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Old 04-10-2009, 02:54 AM
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Bub Steve
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Originally Posted by BEAR-AvHistory View Post
To All,

Thanks for the math & the link.

I have a few of each type battery except for a single 3S3200 that came with an E-flight T-34 so I should be OK with the gel batteries. If I get hung up I have one of those chargers that comes with some RTF planes that you can clip onto a truck battery . I back my pick-up in at our clubs flight line so it would be easy to hook up.

Quick question on a standalone battery; I have a spare 17lb Die Hard 12V 230cca garden tractor battery in the garage which seems to be good when I put a tester on it. Can this also be used since its not a heavy to lug around as a normal deep cycle battery?
I've been useing them for years, I use a 1.5amp charger While chargeing at home,
they do just fine at the field as wellbub, steve
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