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paralleling lipos

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Old 07-21-2010, 08:07 PM
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icarus46
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Default paralleling lipos

Does the C-rating double when you parallel lipos? I want to buy an eflite 60 but I want to paralell my batts to run it. How can I figure how many Mah will give me around 12min conservative flying time.
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Old 07-21-2010, 11:29 PM
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jdetray
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Default RE: paralleling lipos

When you parallel two identical battery packs, the "C" rating does not change, but the capacity in mAh doubles. The "C" rating and the capacity in mAh are two different things.

So If you parallel two identical 2200 mAh packs, the result is a 4400 mAh pack.

To determine flight time, you need to know the current that the power system will draw. That depends on the motor and on the prop you use and is best determined by direct measurement with a wattmeter.

Formula for Run Time

run time in minutes = (Battery Capacity in Ah/Motor Current in A) x 60

This is just a rough guide, and it requires that you know approximately how much current your power system draws. A wattmeter will tell you. The formula also needs your battery capacity in Amp Hours (Ah). Divide mAh by 1000 to get Ah.

The simplest method is to measure your current at full throttle and use that number in the formula. In reality, you probably won't fly at full throttle all the time, so your average current usage probably will be less than the full-throttle value. Also, a power system will often draw a bit less current in flight than it does during ground testing.

So if you use the full-throttle current in the formula, it will generally give you a worst case flight time. Actual flight time will usually be greater.

I've included some examples below.

- Jeff


Here are some examples.

Example 1
1500 mAh battery
power system draws 12A

1500 mAh = 1.5 Ah

1.5/12 x 60 = 7.5 minutes


Example 2
1500 mAh battery
power system draws 18A

1500 mAh = 1.5 Ah

1.5/18 x 60 = 5 minutes


Example 3
4000 mAh battery
power system draws 25A

4000 mAh = 4.0 Ah

4.0/25 x 60 = 9.6 minutes


Example 4
5000 mAh battery
power system draws 25A

5000 mAh = 5.0 Ah

5.0/25 x 60 = 12 minutes
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Old 08-04-2010, 01:49 PM
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aeajr
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Default RE: paralleling lipos

Jeff nailed it!
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