amps draw on a motor

[zoaman]

sorry for the ignorance but my son has a micro gtb and we fitted a charisma 5700kv motor with a 25 amp esc.running gear is 16/68.then this week it has a lose of punch and top end speed.this happened in a instant.so is it the esc or the motor or ?.I have done a clamp test with multi meter between the esc and motor.1x wire is 8a 1x wire is 7.8a and the last wire is reading 4amp on start up of throttle then reduces to 2amp on full power.this is with drive train attached.
so I thought its the motor that was faulty due to a wire down on amps.so I fitted another to the same esc and get readings of 2a per wire,without drive train attached.
is this correct as not under load getting lower amp draw.??
or am I missing some thing.???:confused:

[SlowOne]

You are missing nothing! A DC electric motor will draw maximum amps at start up, and then reduce to very little when up to speed. It might be the case that even with the drive train attached the amp draw differs little from the free-running amp draw.

From your description I would be looking at the motor first. Check it looking for faulty bearings and burnt windings. If you can free the bearing up do so, but if the windings look burnt you're cooked. My other suggestions are that one of the rotor sensors may have gone down so it isn't seeing the rotor and the firing sequence for the coils has gone awry or that the sensor wire is faulty. Both of these assume it is a sensored motor!

Now you know you are not going mad, I hope you track the problem down. :)

[mattr]

7.8, 8 and 4A on start up looks like an esc problem to me, I think. Maybe one of the FETs is on the way out.

And 2A with no load is fine. But makes it difficult to see the difference between the phases of the motor. Might be with testing your other motor in the same way (with load)

[zoaman]

well I have not gone any further with the old motor and esc at the mo, but I bought a new motor same size ect and a 45a esc and noticed the amps per wire are 4a then drop to approx 2a under load.so now to look into the motor to see if I can find whats wrong.cheers for your replies

[ClydeBuilt]

That sounds like a dying battery.

[zoaman]

the batteries that have been used where swapped about to eliminate this without effect. but good to mention. thanx

[beale]

Does your multi meter measure ohms?
Test across red and yellow wires then yellow/blue then red/blue the resistance should be around the same if a winding is down you will see a big difference

I have had the capacitor on an ESC pop before and that affected the punch,

The move to the 45A ESC would of been my next suggestion