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| 02 May 2008 07:26:44 |
| eljainc |
| Substituting a digital pot for a mechanical pot in an AC voltage |
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 |
| 02 May 2008 08:48:43 |
| Bob Monsen |
| Re: Substituting a digital pot for a mechanical pot in an AC voltage control circuit |
"eljainc" <eljainc@sbcglobal.net > wrote in message news:c9aaf12b-d266-4a8a-9481-94c6294d7b70@y38g2000hsy.googlegroups.com... > 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 |
| 02 May 2008 10:08:26 |
| Peter Bennett |
| Re: Substituting a digital pot for a mechanical pot in an AC voltage control circuit |
On Fri, 2 May 2008 07:26:44 -0700 (PDT), eljainc <eljainc@sbcglobal.net > wrote: >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 The datasheet states that the voltages on the resistor terminals must be between -5V and +5V - if any voltages are outside that range, you will probably destroy the part. You can get the full datasheet from http://www.maxim-ic.com -- Peter Bennett, VE7CEI peterbb4 (at) interchange.ubc.ca GPS and NMEA info: http://vancouver-webpages.com/peter Vancouver Power Squadron: http://vancouver.powersquadron.ca |
| 02 May 2008 11:23:59 |
| eljainc |
| Re: Substituting a digital pot for a mechanical pot in an AC voltage |
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) |
| 02 May 2008 15:14:21 |
| John Fields |
| Re: Substituting a digital pot for a mechanical pot in an AC voltage control circuit |
On Fri, 2 May 2008 11:23:59 -0700 (PDT), eljainc <eljainc@sbcglobal.net > wrote: >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) --- Did you post a schematic of the radio shack circuitry? No. Is it available on their web site? No. Are we mind readers? No. So how on earth do you expect anyone to give you any sort of meaningful help if you don't even know how to ask a proper question and tell us what it is you're up to? Hmmm... I see you're posting form Google Groups, so never mind... that explains it. JF |
| 02 May 2008 13:20:10 |
| Bob Monsen |
| Re: Substituting a digital pot for a mechanical pot in an AC voltage control circuit |
"eljainc" <eljainc@sbcglobal.net > wrote in message news:7fd7254e-74b2-4489-adaa-b31e42f6611c@l64g2000hse.googlegroups.com... > 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 |
| 02 May 2008 14:04:11 |
| eljainc |
| Re: Substituting a digital pot for a mechanical pot in an AC voltage |
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 |
| 02 May 2008 16:08:36 |
| Bob Monsen |
| Re: Substituting a digital pot for a mechanical pot in an AC voltage control circuit |
"eljainc" <eljainc@sbcglobal.net > wrote in message news:41dbac1f-6dc3-4493-bf69-c4dfc980cb46@26g2000hsk.googlegroups.com... > 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 |
| 03 May 2008 13:50:32 |
| eljainc |
| Re: Substituting a digital pot for a mechanical pot in an AC voltage |
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. > 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 |