Thanks for that explanation of PWM controllers John. I had not understood the principle on how these worked, and your explanation was easily understood. The only question I have is this, is there any damage or undue stress caused to the electric motor to this constant on-off switching? I'm not a big fan of technology, so thank you John for your simple explanation.
Shin
The simplest things in life are beyond most people.
----Original Message Follows----
From: "John R. Farrington"
Reply-To: personal_submersibles@psubs.org
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Electric engine control
Date: Wed, 20 Mar 2002 16:58:23 -0600
I think that the preferred method may be to use a PWM motor
controller. (Pulse Width Modulation). You hook up your 36V
to the controller, and the controller then clicks the 36V on
and off very quickly, perhaps 20,000 times per second.
You get a verying amount of power going to the motor based on
the amount of time that the controller leaves the 36V on versus
off.
This would be controlled by a very simple rheostat. Based on the
setting of that rheostat, the controller may turn on the 36V for
say 25% of the time, then shut if off for 75% of the time.
(This on and off period is happening 20,000 times each second,
so you never notice it)
This would give you 25% power coming out of the motor.
Turn the rheostat up, and the controller may be putting out
80% on versus 20% off. All the way up, and you get 100% on
0% off. (36V continuous).
It works very well, is reasonably efficient, and uses the
energy from the batteries uniformly.
Hope that gives you a little background.
-John