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Post by NorCalAirman on Apr 11, 2011 12:32:50 GMT 1
Okay, I have a motor that says it draws 20A (22A burst). So should I be shopping for a 25C LiPo minimum?
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Post by ginginho on Apr 11, 2011 12:46:18 GMT 1
Okay, I have a motor that says it draws 20A (22A burst). So should I be shopping for a 25C LiPo minimum? Nope. The Current rating of the motor has no relationship to the C discharge rate of the packs. Assuming you have a 1300mAh 20C pack, this (in theory) is capable of discharging at 26A (1.3(A) x 20(C)). I say in theory as the manufacturer's are known to exaggerate their products capabilities. If you have a larger pack, let's say a 1800 20C, then this theoretically can deliver 36 Amps (1.8 x 20), or a 2000 20C can deliver 40 amps. Hopefully you can see that this is a simple equation, and hence can budget your packs accordingly. Most want longer flight times and hence move to the (physically) largest pack that will fit the aircraft, roughly around a 2200mAh (44 A theoretical max output for a 20C or 33 A for a 15C), which is more than adequate for your motor. Remember as well, that 20A (22 burst) is at full tilt, propped correctly. How often you do this is down to your flying style. If an oversize prop is fitted it will pull more current, and possibly damage the motor. |
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Post by flydiver on Apr 11, 2011 16:15:28 GMT 1
Figure to whack about 20% of whatever the manufacturer claims for their C-rating. Treat the constant C-rating as the Burst and ignore the burst.
Either that or plan to buy a lot of lipos.
Read up on general lipo care:
-Do NOT over discharge.
-Do NOT fly to LVC (easy to over discharge)
-Do NOT store for an extended time at full voltage (for me this means anything greater than today)
-If they get hot in use you are discharging at an excessive rate and the lipo in not up to the task.
-Do NOT store in a hot environment, especially charged. You can wreck a lipo in a single afternoon storing it in a hot (trunk, dash, etc) on a summer day when it's fully charged.
These tips are in ADDITION to general lipo safety and care.
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Post by NorCalAirman on Apr 11, 2011 22:44:25 GMT 1
So the C rating on a LiPo is what it is theoretically capable of discharging, not what it is going to force into your ESC. That would be my voltage? So get a 3 cell (11.1V) pack with as many mAh and highest C rating my wallet can afford and that I can cram into the plane without weighing it down?
flydiver - I've read a LOT about proper care and I lean toward the paranoid side about electrical stuff blowing up. I will definitely be babying my LiPo's. Thanks for bringing it up though. On the topic of LVC though, my ESC has a programming card so I can give myself a LVC buffer (not that I'm going to fly until the cub falls out of the sky). As for getting hot in use, what is normal and what is hot? I know swollen is bad.
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