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Old Feb 09, 2015, 08:38 PM
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Help!
power up

I own a Thunder AC680 charger for my lipos and just bought a field box. My question is : can I purchase a 12v 7ah rechargeable battery and power up my Thunder charger to charge my lipos? I don't want to but a power panel when I have a charger. Any advice or recommendations is much appreciated.
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Old Feb 10, 2015, 02:57 AM
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Yes but....it depends what "my lipos" are. A 12V 7AH battery is only going to be able to charge one or two fairly small lipos before it runs out of power. You might just get something like a couple of 3S 2200mAh charges out of it.

There are good reasons why people lug 100AH charging batteries around with them.

Steve
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Old Feb 10, 2015, 05:57 AM
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You will also get a very short life time out of that 12v 7AH battery; just one or two deep discharges (below 11.9 volts at rest) will ruin it. A Pb battery takes a lot of care to keep any reasonable lifetime for it. Never fast charge, never deep discharge and never overcharge.
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Old Feb 10, 2015, 05:10 PM
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Quote:
Originally Posted by slipstick View Post
Yes but....it depends what "my lipos" are. A 12V 7AH battery is only going to be able to charge one or two fairly small lipos before it runs out of power. You might just get something like a couple of 3S 2200mAh charges out of it.

There are good reasons why people lug 100AH charging batteries around with them.

Steve
The largest battery I have is an 1800. Do you think a 20ah rechargeable would work?
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Old Feb 11, 2015, 02:38 AM
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It's the total energy that's important so just "1800" tells you nothing. If it's a 2S 1800mAh battery it only need half the energy of a 4S 1800mAh pack. One of them you could safely charge maybe 9-10 times from a 20Ah battery, the other only about 4-5 times.

If you do most of your charging at home and only the occasional charge at the field then you might be o.k. Only you know what batteries you have, how many of them and how many you want to charge in a day at the field.

I have used a 12V 17Ah battery to run a charger but mainly for indoor stuff (1S 150mAh batteries). Normally I do all my charging at home and only maybe 2 or 3 charges at the field. If I'm going to want more than that I run the charger from my (85Ah) car battery....with the car running to keep it topped up.

Steve
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Old Feb 11, 2015, 02:48 AM
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Quote:
Originally Posted by abecar9 View Post
The largest battery I have is an 1800. Do you think a 20ah rechargeable would work?
Take the supply battery's Ah, divide it by 2, then multiply it by the nominal voltage, and you'll get how much energy it can probably supply. So 12v x 20Ah x 1/2 = 120 watt-hours.

Then do the same with your LiPos, except don't divide by 2, and you'll get how much energy they need to fully charge. So a 3S (just guessing) 1800mAh LiPo will require 12.6v x 1.8Ah = 23 watt-hours.

That shows that, assuming your LiPos are not fully discharged, so don't need a full charge, you might get six charges out of your suggested battery provided it's fully charged and in good condition.
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