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Compatability of motor amperage & LiPo battery amperage

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Compatability of motor amperage & LiPo battery amperage

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Old 06-18-2006, 12:30 PM
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Default Compatability of motor amperage & LiPo battery amperage

Hi to all,

Two Questions:
(1) Can a 48A rated LiPo battery be used on an inrunner motor that has a maximum current rating current rating of 35A?

(2) Many battery vendors do not have the battery amps listed in their specs. How can I determine the battery amperage if I am only given the folloewng info: "3Cell, 11.1V, 3200 mAh battery that can be discharged at up to 66 amps"

Thanks,
Ernie
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Old 06-18-2006, 02:13 PM
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Default RE: Compatability of motor amperage & LiPo battery amperage

Hi,

1) Yes, you need to have a battery capable of being able to deliver more amps than can be taken from it anyway, so that it doesn't make it work too hard and damage it.

2) To determine the amperage that a battery can supply, you need to know the 'C' rating.
Modern lipos now have around 10C 12C or 20C

This means that for a 10C battery, it can handle upto 10 times it's capacity, so for a 3200 mah battery in your case, it would be able to handle 32 amps
If it was 12C it would handle 38.4 amps,
If it was 20C it would handle 64 amps.
Easy when you know how.

But if there is no 'C' rating on the battery, then you won't know what it can safely take.
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Old 06-18-2006, 03:07 PM
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Default RE: Compatability of motor amperage & LiPo battery amperage

Chocks Away
Many thanks,
Ernie
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Old 06-18-2006, 03:46 PM
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Default RE: Compatability of motor amperage & LiPo battery amperage

Your Welcome Ernie,
Craig
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Old 06-18-2006, 07:19 PM
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Default RE: Compatability of motor amperage & LiPo battery amperage

ORIGINAL: Sailplane
(1) Can a 48A rated LiPo battery be used on an inrunner motor that has a maximum current rating current rating of 35A?
The amount of current used by a motor is determined by the power system (including the motor, prop, and even the drag of the airplane), NOT by the battery. What's important is that the battery be capable of providing at least the amount of current that the power system requires. If the battery can provide even more than the required current, so much the better.

ORIGINAL: Sailplane
(2) Many battery vendors do not have the battery amps listed in their specs. How can I determine the battery amperage if I am only given the folloewng info: "3Cell, 11.1V, 3200 mAh battery that can be discharged at up to 66 amps"
If the battery can be discharged at up to 66A, that's the maximum current the battery can provide. If you use this battery with a small motor and prop that need only 5A, then 5A is all that the battery will be asked to provide. If you use the battery with a power system that needs 25A, the battery will provide 25A. If, however, you try to use the battery with a power system that requires 75A, problems may occur. The battery might overheat and be damaged. The battery voltage will drop.

In summary, the battery provides whatever amount of current the power system needs, until you exceed the capability of the battery.

Another point to consider is that the current capability is often overstated by battery makers. Many people routinely discount these claims to 70% of the stated specs.

- Jeff
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Old 06-18-2006, 10:41 PM
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Default RE: Compatability of motor amperage & LiPo battery amperage

Jeff,

As usual, your writing is great...you explain your topics extremely well. You must be a teacher or professor with a lot of knowledge about what you write.

Once again, I thank you for taking your time to help someone else. I placed a second posting on this general subject, but with more specific questions; however, with your answers to this post, there really isn't any need for anyone to reply to it. I placed it before I knew that you had replied to this one.

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Ernie
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Old 06-18-2006, 11:23 PM
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Default RE: Compatability of motor amperage & LiPo battery amperage

Hi Ernie-

I'm not a teacher, and a lot of people know more than me, but I'm glad to help when I can.

- Jeff
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