We need to be careful here. It is true you can use a higher voltage on a motor as discussed below, but the original poster was asking about a trolling motor. A trolling motor is a motor plus a controller built in. I would never recommend running a 12V trolling motor at 24V unless the manufacturer specifically said it was OK. It might only last a few milliseconds before the electronics fried. The motor itself would still be OK, but the "trolling motor" purchased product would be dead.
Pat
--- In electricboats@yahoogroups.com, Ben Okopnik <ben@...> wrote:
>
> On Thu, Oct 06, 2011 at 08:17:11PM -0700, Femm wrote:
> >
> >
> > Ahhh Gerald I hate to tell you this but you are still feeding 24 volts to that
> > motor...
>
> True enough... but it doesn't actually matter, since motors don't really
> care about voltage. What matters is the total power dissipated across it
> - which is what PWM is intended to control. In a DC application, the
> voltage would determine that P(d) by working across the resistance
> presented by the motor, which would result in a given current - but PWM
> is not DC. You could, theoretically, apply 100kV across a motor; as long
> as you pulsed it at a low enough duty cycle, that motor would work
> perfectly, last just as long, etc. (Granted, 100kV would have its own
> problems - spark gaps, for one - but the overall point remains valid.)
>
> I used to design pulsed power systems for Hughes Aircraft way back when.
> If we had tried driving those Gunn and IMPATT diodes that we were using
> with DC to the output levels that we needed, we would have sent them up
> in a cloud of smoke in literally fractions of a second. With PWM, we got
> incredible power densities, and enough signal strength that we routinely
> bounced our millimeter-wave signals off the Moon as a test. Great heat
> transfer characteristics, too (although I don't recall the physical
> basis for why that was the case.)
>
> Voltage/resistance ratios - i.e., Ohm's Law - aren't all that applicable
> once you start chopping the drive power. Especially around inductors,
> which motors are.
>
>
> --
> Ben Okopnik
> -=-=-=-=-=-
>
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