Forced cooling of permanent magnet DC motors

[idiota2000]

I have some sealed servo motors that I would like to operate above their rated amperage. I wish to accomplish this by drilling holes in the endcaps and mounting a fan on the end of the motor.

I have a spare motor that I can destroy testing, so I can determine the amperage limits empirically if necessary (although I'd like to keep it as a spare).

Here are the motor specs:

Electrocraft E722
Max voltage 100v
Max continuous current 5.6 A
Peak current unknown
Kv 26 rpm/V
Kt 0.36 Nm/A
Winding Diameter 0.5mm

I'd like to operate these motors at 36V, 10A if possible. I attached a photo of the stator/commutator/windings of the motor, and another motor to compare. The motor with the green stator is the one I wish to use, the motor with the blue stator is as follows:

Electrocraft E712
Max voltage 60v
Continous current 8.9A
Peak current 44A
Kv 34rpm/V
Kt 0.28Nm/A
Winding diameter 0.43

Since the E712 operates at lower voltage and higher amperage with smaller windings, Intuitively it seems like I would get away with lower voltage and Higher amperage with the E722. The brushes on both motors are the same size and are interchageable, but the material looks different. The E722 brushes have a more matte/charcoal appearance, while the E712's brushes appear more like pencil lead (anyone know if they are interchangeable?)

Anyway, suggestions and comments would be greatly appreciated. I'm interested in feasibility/ effects on efficiency, etc.

Thank you.

 

[itsmoked]

I would get some tubing an inch bigger than the motors and then use a serious blower and hoses to force high velocity air past the motor cases. Perhaps a hole or three in the end plates. You want the carbon from the brushes to blow out the end with the brushes and not pass thru the motor.

Of course a much better solution is to pick up the correct motors on ebay then sell yours there.

What is the application and the duty cycle?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[idiota2000]

The application is a small boat with two of these motors, so the motors could be on for hours. In most situations the motors might only see 200W, but in some situations, such as a headwind, the motors could see 350W for an extended period of time.

I've been told since I posted this that not only will I have thermal problems, but I will also have efficiency problems because of the high resistance windings. So, like you said, it would be best to sell the motors and buy new ones.

 

[itsmoked]

Interesting.

You should look at trolling motors. A whole lotta bang for the buck generally. They also are water cooled!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

You may consider using a higher voltage and optimize your propellors for the higher speed that will result from the higher applied voltage.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[idiota2000]

"You may consider using a higher voltage and optimize your propellors for the higher speed that will result from the higher applied voltage."

Several reasons why I don't want to do that, mostly because of time and cost:

1. Unfortunately in this application propellers get the best efficiencies at lower rpms, so if I were to use high voltage it would be wise to build a belt reduction. I believe with high rpm the propeller losses would become even greater when I operate the boat below the designed speed.

2. 3 large 12v batteries will cost much less per watt hour than 6-8 smaller 12v batteries, and will be less time consuming to install at launch. The boat is intended to be transported on my car, and carried to the launch site separately from the batteries.

3. I already have some 36v controllers laying around and I'm on a tight budget.