I built half of a controller already with an ISOTOP MOSFET and
schottky. It's rated for a maximum of around 200 amps so I think I'll
keep it around 100A peak. I built a PWM circuit from a 555 to try it
out, but I think I had some spikes kill the 555 already.. I haven't
gotten to my AVR circuit yet ;-)
The starting resistor is a good idea. I am planning on hooking it up
with a contactor controller before getting the semiconductor
controller hooked up.
--
Martin K

On 4/23/07, James Newtons Massmind <jamesnewton@massmind.org> wrote:
>
> > Very nice work!. Imho look into a starting resistor before
> > you build a controller. You could ruin the motor without it.
> > A starting resistor will limit the torque at start. Take the
> > wire element from a 500W space heater and fold it in half 5
> > times. Twist the resulting bundle and put it in series with
> > your existing cabling, with a second switch to short it. This
> > will limit start current to about 30 Amps (about 1Hp). If the
> > start is still to brutal cut wires from the strand and keep
> > trying. Eventually the wires will glow (ignore that but mind
> > anything that may catch fire from it). Normally the throttle
> > is arranged to make the main switch and as you push it
> > further make the start resistor shorting switch. I am sure
> > that you can make such a thing by bending the contacts on a
> > contactor a little and then using it manually (footably? <g>)
> > as a foot switch.
> >
> > Peter P.
>
> I remember seeing a very nice power control that rewired a set of small
> batteries (I think they were 6 volt Motor Cycle types) in different series
> and parallel combinations to provide from 6 to 48 volts over a series of
> steps. E.g. the first one was all the batteries in parallel so the result
> was 6volts at high amperage for starting out, then in parallel sets of 2 in
> series for 12 volts, and so on until all the batteries were in series for
> the maximum voltage. The advantage, so I remember reading, was that startup
> was smoother and a smaller starting resistor could be used.
>
> The mechanical design looked like a ships engine speed indicator system but
> with a set of knife switches built into it instead of the dial. It was break
> before make and there were detents so that it jerked from one position to
> the next in discrete steps.
>
> Building that might be an interesting project on its own, although you have
> to wonder if an electronic controller might actually be simpler...
>
> ---
> James.
>
>
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-- 
Martin Klingensmith
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