Overvolting some servo motors, need advice.

[podbot]

I have a pair of Servo motors that I would like to overvolt from 20V to 36V. This is for use on a boat where they will have a constant load for hours, but I can keep the current to it's original 5.6 amp rating by sizing the propeller and monitoring the amperage. I'm thinking of dealing with the extra heat by milling holes in the ends and running forced air. I attached a photo of one of the disassembled motors, the wires are 21 awg.

Anyone think I can get away with this? Suggestions, comments based on experience?

 

[Kepler]

If its being used for a boat drive why not wrap a coil of small bore copper tube around the motor and water cool it.

 

[Solcar]

I have a little experience overvolting servo motors. The Pittman motor on my e-bike is rated at 12v, but I have taken it up over 30. It's power output can actually increase without getting any hotter.

I have always thought it best to tail off the current a little in proportion to the voltage for the sake of the brushes, if for no other reason.

I guess if the current is limited to something like 4 to 5 amps in your case, the motor won't get hotter than with 5.6 amps at 20v.

 

[piersdad]

i have used motors 36v 150 amps 1500 rpm at 144 volts and about 6000 rpm
very rough max voltage for any motor is 10 volts max for each commutator segment.
ie toy motor 3 segments 30 volts.
50 segments 500 volts ( but that might be a bit much.
but 10 segments will commutate 100 volts and as long as the prop is smaller so that the current is ok

 

[amberwolf]

I'm thinking of dealing with the extra heat by milling holes in the ends and running forced air.

Is this for a freshwater or saltwater application? If salt, you might consider that corrosion inside the motor is more likely with a forced-air setup, and using a liquid cooling loop, keeping the motor sealed, is a safer way of running them. Even in freshwater, there's enough salt or other contaminants possible, or even just humidity, that air cooling could be problematic over time.

 

[podbot]

Thanks for all of the responses. Especially interesting was the post about commutator segments and voltage. I have a pair of servos that are nearly identical except for voltage rating, and the high voltage one has more segments.

I read elsewhere that while the copper losses will be the same at higher voltage but the same amperage, core losses will increase and generate extra heat. Not sure how significant this is.

The boat is going to operate in salt water, but the motors will be in a large, well sealed compartment. I don't think humidity would be a problem since manufacturers usually derate motors in low humidity.

I'm guessing the coil would be very good for cooling the case of the motor, but not as good as air for cooling the rotor and commutator due to the insulating air gap. Sounds like the coil may be more than adequate and does have advantages.