Re: [PSUBS-MAILIST] variable speed switch.

[Ian Roxborough <irox@ix.netcom.com>]

I was thinking something like this PWM:
  http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7588923867

The potentiometer is a far better idea than the DC->AC/dimmer/AC->DC,
although it would still be inefficient.  The potentiometer will
reduce the power getting to motor by disipating the difference
as heat, so at full thrust, the potentiometer doesn't do anything,
but at half thrust the potentiometer will disipate the other
half of the energy as heat.  This is still better than AC 
conversion, but the Pulse Width Modulation is far more efficent.

Ian.

On Wed, 8 Feb 2006 05:47:27 -0500
"Akins" <lakins1@tampabay.rr.com> wrote:

> A thought just occured to me. Wasn't it you Ian who told me this evening that dc voltage uses pulse wave modulation to enable a variance in the speed switch?
> If that is true then how does a 12 volt dc car radio's volume control potentiomenter work? Does it somehow convert the dc to ac for it's volume pot to work and then
> convert it back to dc again? From what you told me earlier about the pwm it is making me wonder now if my idea to find a 24 volt dc potentiometer would even work.
> Does a dc 24 volt potentiometer even exist or am I missing something? A little help?
> Bill Akins.



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