ESC Overheating Issue

[Juanelm]

Hello all,

I have a quadcopter with four T-Motor MN3110-15 motors, four T-Motor s35a SimonK ESCs, four APC 10x5 thin electric props, and one 5s 5000mAh battery, and a MultiWii controller. After hovering for a few minutes, the ESCs get very hot, over 95 Celsius. I measured the hovering amperage and it's below 10A, which should be well below the ESC's limit. The ESC's are exposed to the air for cooling.

Could this be caused by the high refresh rate of the Multiwii PWM? Or maybe these SimonK ESC's aren't compatible with Multiwii in another way? They are T-Motor ESCs which are supposed to be high-quality, and I'm using them with T-Motor motors, so I don't see what else could cause the overheating.

I greatly appreciate the help.

[waltr]

Are you using the BECs in the ESCS?
Are all of the BECs connected together?

[Juanelm]

Thank you for asking that, I forgot to say that. The ESC's are OPTO ESCs and do not have BEC. I left all the red wires connected, and am powering the Multiwii using a BEC.

[brewski]

I think the 5 cell battery is the reason for the raised temps. With the size motors & props a 3 cell Lipo would be sufficient.
Current draw of 10 A @ 18.5V is 185W which is a lot to hover! What does your quad weigh with battery & whatever else you have attached.
With opto ESCs you should have all pins connected as they require +5V , GND & signal from from FC.

[Juanelm]

Thank you for your reply brewski. The quad weights 2.5 kg. The hover power is about 110 W per motor, so 5.95 amps at 18.5 volts. The ESC is rated for up to 6 cell batteries so I would expect it to work well at 5s, in hover.

[brewski]

5.95A @ 18.5V is pretty good for a quad weighing 2.5Kg. Are you using the ESC BECs? If so this will cause the ESCs to run hot.
You may need to position ESCs along booms if not already so that they get prop wash.

[Juanelm]

The ESC's are not in the propwash, but they are exposed. Also, the ESC's are OPTO so I'm using an external BEC.

After talking with T-Motor guys, I just concluded that the T-Motor s35A ESCs simply cannot be used with 5s or 6s (although they state they can be used with up to 6s) because they will overheat even at low amps. I guess I'll have to buy new ESC's. Thanks everybody for the help.