Re: [PSUBS-MAILIST] Interesting item on eBay websiteitem#275822570:X-9 "Y...

[Subscuba@aol.com]

Pat,

About your question about the stock controller. I think you might have a 
problem if the controller is not matched to your motor.

The parasitic I was referring to are due primarily to lead lengths which give 
rise to inductances. These inductances cause excessive voltage spikes across 
the power switches when they switch off. If not controlled they can destroy 
the power switches. 

If you are serious about doing your own you can send me the following data on 
your motor and what battery voltages you have or plan to use. Actually the 
higher the better. If the motor is 36 volts and you have only 36 volt 
batteries then you get no current reduction off the batteries but you still 
need a controller for the motor. I can come up with a preliminary design if 
you can supply the following:

1) Motor Voltage and current requirements.

2) Maximum current allowed through the motor armature before stator       
demagnetization occurs.

3) Motor armature inductance

You probably can't get the maximum current as in question 2) unless you talk 
to the vendor (Minn Kota). We could  assume some multiplier on the current 
requirements answered in question 1) and do without that data. I set my 
current at about 25% above the maximum run current. The times I gave in the 
previous messages were based on a switching frequency of 20 KHz.

I would need the armature inductance which is easiest if you can simply 
measure it. Measurement would be easy after you purchased the motor.

I can also supply you with my motor controller schematic if you want to get 
an idea of what's involved. Assuming you can read JPEG files. There is a 
chance you can use the same design with some modification.

For what its worth I have made a nice living designing power electronics. I'm 
not a welder though. 

Keep having fun,

Ken Martindale