On Oct 13, 4:40 pm, Richard J Kinch wrote:

A variable autotransformer and bridge rectifier are suitable.

Electronic speed controllers are relatively cheap and standard, not worth
making unless you after a hobby.

Hi Richard,
here in OZ, such things are expensive - a really quick ring around ,
about the $400 mark for a controller. And we are not at your level of
affluence, where treadmills get junked and are virtually free for the
taking. (Violin music in background)

I don't want to manufacture the things, I just want to build one.
Sorta like cutting threads on a length of rod instead of going to the
store and buying a bolt - it interests me, stuff like this has all my
life - curious how things work, and like to try it myself. Will even
fix $10 toasters for the hell of it.

Yes, the variac and the bridge rectifier "would" work - but would
rather go the PWM route as I believe you can get better torque from
the motor at low speeds, and thats where I want to run it so I can do
thread cutting on my 9 by 20 lathe . Like I said, have the basic
theory (Google is your Friend) but theres a dearth of actual
schematics (and PCB layouts, but thats a luxury anyway) on the net.
And the ones I do find are for your mains of 120V. This one runs at
180V. from our 240V AC mains supply.

Correct me if I am wrong, but if used a PWM modulator (pair of 555's)
and made the mark-space ratio 1:1 would it effectively limit the
applied volts to half VCC? - or is it more complex than that? (almost
certainly)
The IR links from Jon and Winston were great, didn't even know such
specialized drivers existed - and probably not available here in OZ -
and they got lots of nice protection things in them as well - but
coupling to the single ended FET in the original board...might be a
bit spectacular if I get it wrong, as a tech. have a healthy wariness
of high voltage at high current...(add a motor to the mix, well, even
more interesting)

The mechanical conversion is going to stretch my neophyte knowledge to
the limit, so want it up and running on the bench before starting on
the lathe conversion...and its school tomorrow (Tuesday) so going to
learn how to do Morse Tapers..(rough it out on the lathe, then use the
cylindrical grinder to get to tolerance and finish)


Andrew VK3BFA.