Substituting a digital pot for a mechanical pot in an AC voltagecontrol circuit

[eljainc]

Hello,

I have a question. I have been trying using a DS1867 digital
potentiometer in a circuit that will replace a mechanical
potentiometer of 250KOhm. The circuit/device that is uses the pot is
an AC voltage controller made by Radio Shack (cat 64-2054). When I
substitute the DS1867 digipot for the standard pot, the load is not
powered.

What might the problem be? I've now fried two of these Rad Shack
voltage controllers in attempt to test a digitally controlled pot. I
don't think the digipot was damaged. Is there another passive
component required in the circuit (cap or resistor) that needs to be
added?

Thanks
Mike

 

[Bob Monsen]

Hello,

I have a question. I have been trying using a DS1867 digital
potentiometer in a circuit that will replace a mechanical
potentiometer of 250KOhm. The circuit/device that is uses the pot is
an AC voltage controller made by Radio Shack (cat 64-2054). When I
substitute the DS1867 digipot for the standard pot, the load is not
powered.

What might the problem be? I've now fried two of these Rad Shack
voltage controllers in attempt to test a digitally controlled pot. I
don't think the digipot was damaged. Is there another passive
component required in the circuit (cap or resistor) that needs to be
added?

Thanks
Mike

Look at the datasheet, here:

http://datasheets.maxim-ic.com/en/ds/DS1867.pdf

The maximum input voltage is less than a volt above Vcc, which is also
limited to 5V. The pot, on the other hand, doesn't have the same
restriction.

I could not find the ac voltage controller you indicated on the radio shack
site, so I can't comment on whether this should work or not, but I'd keep
the 5V restriction in mind.

Regards,
Bob Monsen

 

[eljainc]

Is there any AC motor controller that is computer controlled? (RS-232/
USB or TTL)

I guess the Maxim/Dallas parts won't work.
I see that even AD digipots wont work (some will work with 10-15VAC,
but not higher)

 

[Bob Monsen]

Is there any AC motor controller that is computer controlled? (RS-232/
USB or TTL)

I guess the Maxim/Dallas parts won't work.
I see that even AD digipots wont work (some will work with 10-15VAC,
but not higher)

What kind of motor is it?

/bob

 

[eljainc]

The motor is an AC motor. I do not know the manufacturer of it.
However I have the following specs/attributes which may
help in choosing the controller for it.


single phase AC, 115VAC
1/7 HP at 4000 RPM
max current: 3.3A
150Watts
Permanent magnet motor
windings on the stator, but not rotor
two brushes, indicating that it is not an inductance motor

 

[Bob Monsen]

The motor is an AC motor. I do not know the manufacturer of it.
However I have the following specs/attributes which may
help in choosing the controller for it.


single phase AC, 115VAC
1/7 HP at 4000 RPM
max current: 3.3A
150Watts
Permanent magnet motor
windings on the stator, but not rotor
two brushes, indicating that it is not an inductance motor

The radio shack thingy controls the speed properly, right?

One possibility would be a motorized pot.

http://www.goldmine-elec-products.com/prodinfo.asp?number=G9962

This one probably won't work, but one of these might:

http://stores.ebay.com/familygate_ALPS-Motorpotis-motorized_W0QQfsubZ11

The other possibility is to measure the voltage that was across the pot
before you cut it out. If you post that information, it may well be that
someone can design a circuit that would let you control the control.

Regards,
Bob Monsen

 

[eljainc]

Bob,

Thanks for the idea of the motorized pot. I should have thought of
that one. I will look to see
if I can find a 250K Ohm motorized pot.

As far as the voltage across the pot, I would have to measure
it when in operation. I can imagine that it runs from 0 to about
100VAC.