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Old Dec 30, 2005, 01:13 PM
my passengers on landing
Cactus1552's Avatar
Rhode Island
Joined Sep 2003
197 Posts
Discussion
Amps vs volts vs performance

I've been doing some testing with an Esskay 400xt with an APC 9x4.7 prop and 3 cell lipo packs.
1st pack is 900 ma 3 cell rated 15c. Starting and running for aprox. 20 seconds the voltage drops off to around 9 volts.
2nd pack is 800 ma 3 cell rated 20c. Same as above but voltage stays over 10 for quite a while.
Motor is warm-hot after these tests. Amp draw is between 9 and 10 amps. 900ma pack is warmer than 800 pack after this test.
I don't fly full throttle, don't need to. I am wondering from the above results, it seems that the smaller ma pack is better able to handle the amp draw from the motor.
Am I assuming correctly? If so would a pack that can sustain a higher amp draw be a better choice (disregarding weight)?

Jack
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Old Dec 30, 2005, 02:39 PM
Master of 1 point landing
Naperville, IL
Joined Jul 2005
2,841 Posts
Quote:
Originally Posted by Cactus1552
I've been doing some testing with an Esskay 400xt with an APC 9x4.7 prop and 3 cell lipo packs.
1st pack is 900 ma 3 cell rated 15c. Starting and running for aprox. 20 seconds the voltage drops off to around 9 volts.
2nd pack is 800 ma 3 cell rated 20c. Same as above but voltage stays over 10 for quite a while.
Motor is warm-hot after these tests. Amp draw is between 9 and 10 amps. 900ma pack is warmer than 800 pack after this test.
I don't fly full throttle, don't need to. I am wondering from the above results, it seems that the smaller ma pack is better able to handle the amp draw from the motor.
Am I assuming correctly? If so would a pack that can sustain a higher amp draw be a better choice (disregarding weight)?

Jack
Your battery is not up to the task and if the voltage is sagging that quickly in seconds, not minutes - you are overdrawing the packs and can damage them. Your better option is to prop down to drop amp draw, or get true 15C packs at that size.
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Old Dec 30, 2005, 07:37 PM
Oldie but goodie
Popsflyer's Avatar
United States, CA, Orange
Joined Jun 2003
3,890 Posts
Same here.

Your pack is rated @15C continuous or burst? If not stated, you would normally assume it was cont, then the pack should be able to sustain a 13.5A discharge rate. Either the pack is over rated, or you are actually pulling more amps than you think.
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Old Dec 31, 2005, 07:01 AM
my passengers on landing
Cactus1552's Avatar
Rhode Island
Joined Sep 2003
197 Posts
I've run the test several times with the same results. Used a scale for thrust, a Medusa watt meter and a tachometer for rpm. I agree that the 900 pack must be overrated. I ran the test again and only used half throttle. Held about 5 amps. Both battery packs were warm but the 900 pack was a bit warmer than the 800. Wish I had a thermometer to measure temp but how many tools is one supposed to own?
I thought it was the one with the most toys... not the most tools.
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Last edited by Cactus1552; Dec 31, 2005 at 04:40 PM.
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