Re: (ET) volts

[Christopher Zach <czach computer org>]

> Um, applying a higher voltage to a PM motor doesn't weaken the field.  
> The motor speed will be approximately proportional to the applied 
> voltage.  No overspeed.  As you said the field strength does not change 
> (IE it's not weakened)

What I meant was that by increasing armature voltage you're changing the 
relationship of armature strength (now 125%) without changing field 
strength (because it's a magnet). Thus the motor will behave in the way 
that the shunt motors work when you reduce the field strength (ie: They 
spin faster, less torque, heat up more, and pull a lot more current 
under load). Not good things.

> Unless the motors are close to the edge I doubt increasing them to 48 V 
> will give enough current to demagnetize them but the extra 30% tip speed 
> might be dangerous.  Also the extra load from the higher speed may cause 
> the motors to warm up more quickly.

Both could be a problem; I would not like to see the blades rip apart. 
Worse yet when you hit a rock the blades would be spinning faster. Bad 
idea IMHO; get a 48 volt curtis motor controller and set the output for 
75% or so.

> I'de be a little worried about the field in a shunt wound motor.  You 
> are going to get a lot more heating there (close to double).

Interesting. I wasn't sure that would cause a problem. Since they are 
technically compound motors this would be offset by the increase in 
field strength in forward speed, but would do really weird stuff in reverse.

Hm. Eh, I'd just get a 48-36 volt motor controller and be done with it. 
Why go 48 volts anyway?

Chris