I would suggest a PWM (pulse width modulator) is what's needed. If your
electronic skills are reasonable, have a look through the Velleman Kits
(Maplin list them) as they do at least one. You will need to know what the
maximum current that the motor will draw and ensure the module can supply
this and, better still, has overload protection that can be set high enough
to get the required power from the motor.
On or around Thu, 30 Aug 2007 00:23:22 +0100, "Ben"
enlightened us thusly:
how much current, how much power supply?
sod-off variable resistor is the cheap-and-nasty method. But it's
inefficient, which is why the modern approach uses pulse-width modulation or
similar as suggested.
for similar reasons, light dimming is done by thyristors now, not resistors.
Then check the current rating of the wiper motor.... If its low enough,
model train controllers will do fine. But I suspect it might be too heavy
for many a train controller.
- Nigel (0.05A, Oooh a big model train !)
I've just done this exact thing.
If you have basic soldering skills get yourself over to
and order the Velleman K8004 DC to Pulse Width Modulator. =A37.95 each.
Basically you can assemble one in about 10/15 minutes, doesn't just to
allows you to adjust the frequency of the PWM oscillator and minimum
and maximum speeds, eg you can set minimum at 0 RPM or just moving,
instead of having a blank bit on the control put....
You'll also need a 4.7k ohm linear pot to control the speed, a box of
some sort to put it in, and a DC power supply for your motor, the kit
is not a PSU itself. *highly* recommended, used mine to control the x axis on my mill,
unspeakably vast improvement over the fitted current limiting speed
It sounds as though you are doing what I am doing, motorising a millin
table or similar. If so there is another source of 12 volt motors wit
lots of torque that you might not have looked at and they are 'sea
motors'. Modern high end cars have motors that adjust the sea
I've done some research on speed controllers, one I've found that look
useful is on e-bay
I've also found out that I will need a capacitor to smooth current an
some sort of overload protection.
Not being into electroncs I'm not sure of exactly what will be require
for those so I would be pleased to hear any ideas from the group.
There are a number of methods available, simplest is a straightforward linear
voltage regulator, using a LM3XX 3-terminal regulator. Dissipative regulation
wastes a fair bit of power in heat, but is is the simplest method apart from a
switched or variable resistor.
PWM controllers are the next step up, tend to be noisy as they chop the DC up in
a mark/space ratio control of the power.
Switch-Mode are similar, but higher frequency so usually inaudible.
Once you get past the basic linear regulator, there isn't a lot to choose in
terms of circuit complexity etc etc.
A lot depends on how much power you need to control.
If you need seriously high power and have 240V or 440V AC available, then a
controlled-thyristor power supply would be the thing to look at, but
Peter & Rita Forbes