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Motors cutting out at about 70% throttle

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Old 02-13-2019, 10:07 AM
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thome12371
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Default Motors cutting out at about 70% throttle

Specs:

Transmitter: FrSky Taranis QX7 2.4GHz
Receiver: FrSky X8R
Motors (2): Leopard LC3536-12T
ESCs (2): Turnigy Plush 60A w/BEC
Battery Packs: 9.6V 1600 mAh 10C max discharge, 2 series, 3 parallel
Propellor: 10x6

Have an extremely annoying problem with my dual-prop fixed-wing plane and I'm running out of ideas. The plane works fine until I get to about 70% throttle. Once I get any higher, the motors cut off until I go to a lower throttle. It seems to cut out at around 22 A total, or 11 A per motor. This is obviously way below what the motors and ESCs are rated for. I just bought these ESCs and reprogrammed them to the following settings using the Turnigy Programming card:

Brake: Off
Battery Type: NiMH
Cut Off Type: Soft-Cut
Cut Off Voltage: Low
Start Mode: Normal
Timing Mode: Low
Governor Mode: Off

I have been able to get the configuration to run at about 85% throttle for a few seconds before it cuts off. The motors aren't that warm, and the batteries are cool. I've tried a couple different settings on the ESCs and switching out some components (which is why I bought the new ESCs) to no avail. It just seems to cut out at the same current every time.

Any suggestions would be much appreciated, and I would be happy to answer any questions.
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Old 02-13-2019, 06:35 PM
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rcjetflyer0718-RCU
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Battery Packs: 9.6V 1600 mAh 10C max discharge, 2 series, 3 parallel

1600 X 10 =16000 mah = 16 amps

battery is too small
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Old 02-13-2019, 08:24 PM
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The batteries are three in parallel though, so isn't only 7.33 amps (22/3) being drawn from each individual cell?
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Old 02-15-2019, 04:20 AM
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You are right, but that may still be too much. Being 9.6v it sounds like you are using Nimh batteries? They can't give you the amps that a Lipo can. Your symptoms sound like you are hitting the low voltage cutoff.
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Old 02-15-2019, 06:57 AM
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Do you have a diagram of your set up? Your battery configuration really confuses me.
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Old 02-15-2019, 07:06 AM
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Originally Posted by thome12371 View Post
The batteries are three in parallel though, so isn't only 7.33 amps (22/3) being drawn from each individual cell?
But that's also assuming you're getting equal output from all three packs. Let's look at a few scenarios:
1) What if one pack is putting out less current than the others? Not so much of a problem.
2) What if one is putting out less voltage? That could be causing the very issue that Jester just mentioned.
3) What if the ESC didn't program properly and is at a higher than expected cut off level? That could be causing the very issue Jester just mentioned.
When you're dealing with electricity and electronics, never take it for granted that everything is working perfectly. It's possible that you are losing wattage across a connector. It's possible one pack has wires that have more resistance than one of the others. Even more likely is one pack's solder connections have higher resistance than the others. I've seen all three of these actually happen, both in R/C and full size aviation. In full size aviation, a slightly higher resistance across a connection will only result in a slightly elevated level of heat when you consider that most of the systems run on either 12 VDC or 110/220 VAC at 400 Hz. When you're running a nominal 9.6 VDC at fairly low amperage, even a few milliohms across a connector will affect the performance of the system as a whole.
BTW, is that 7.33 amps per cell or per pack? If you're drawing that much per cell, you've got a serious problem

Last edited by Hydro Junkie; 02-15-2019 at 07:11 AM.
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Old 02-15-2019, 10:03 AM
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This is a picture of my battery configuration, with a closeup of one series configuration in the top right

imgur.com/a/deLjGUa

Last edited by thome12371; 02-15-2019 at 10:06 AM.
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Old 02-15-2019, 10:10 AM
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It also may be helpful to know that I tested the configuration with a higher discharge, lower voltage LiPo and it worked perfectly with the exact same connections and ESC programming.
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Old 02-15-2019, 10:13 AM
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There you go. It's your batteries. They can't handle the amp draw of your system.
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Old 02-15-2019, 05:52 PM
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Motors cutting out at about 70% throttle
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Old 02-15-2019, 05:52 PM
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Thank you very much for your help everyone!
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