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help with variable speed motor

leeknivek

Jul 18, 2019
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Jul 18, 2019
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Hello -

i have a few motors that i got from a job, trying to figure out how they go. they are 1/2hp 120vac single phase, and controlled with 24vdc, i think. i was unable to find a manufacturer or schematic or anything. these came out of some blower fans built into ceiling grills. i do hvac for a living, so bear with me please :)

there are three 14 gauge wires (black, white, green) & four 22 gauge wires (red, black, white, green).

the motor works, however i can't figure out how to control it. with everything connected, the motor revs up to 200 rpm for a few seconds, then 1200rpm for a few seconds, brakes, then repeats. putting a heavier load on the motor causes it to stay at 1200rpm.

there is one potentiometer, on the board says "rpm control", doesn't seem to change anything much - at one point it changed the delay on it's 200-1200-brake cycle.

there are two banks of DIP switches, one with two switches, one with eight switches. #1 on the 8-switch DIP says "on", 1 & 2 on 8-switch DIP turns everything off. the rest don't seem to do anything.

there are test leads built into the board, as well as two phone jacks. haven't played with those yet.

there are two more 2-pin connectors on the board, one goes to two 24g wires, red and black, perhaps a thermostat or some other external control. tried shorting them, connecting to a pot, no change. maybe needs a hot signal. the second two-pin connector says "ext rpm control", i think that calls for 10vdc, don't have a supply for that handy.

they are essentially set up as i took them apart. i don't know how much of that^ is relevant but thought i'd tell all i know about them.

i can solder ok and would like to just bypass this whole board, not sure where to start. i don't have them in front of me but i can take some photos tomorrow.
 

Bluejets

Oct 5, 2014
6,901
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Oct 5, 2014
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Without knowing brand, style, specs of the unit, your guess is as good as anyone elses. Contary to popular belief, McGyver's colour codes and which wire to cut are all simply fantacy.
If you can show some detail, nameplate or whatever it may help. Usually make and model required though.
 

leeknivek

Jul 18, 2019
4
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Jul 18, 2019
Messages
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1124ztz.jpg

having a hard time uploading photos from my phone -

that nameplate is on the motor, there is a second nameplate on the bottom part of the motor where the control wires go.

US MOTORS PerfectSpeed

EEPROM DATA E077906820000
PART NUMBER X177906810001

IN 120/208-240 VAC 1 PH 6.6/4.0-4.8 & 6.2/4.2-3.8 AMPS

US PATS xxx xxx xxx FOR USE WITH AA251702
xxx xxx xxx xxx xxx FOR USE WITH 1/2HP MOTOR
xxx xxx xxx xxx xxx MO55PWCVU-0345

NIDEC MOTOR CORPORATION www.usmotors.com
 
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leeknivek

Jul 18, 2019
4
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Jul 18, 2019
Messages
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click the spoiler to reveal the photo. helps to not clog up the thread - sorry

i zoomed in on a photo of the pcb and found that the four control wires are labeled,

PWM - red
COM - green
TACH - black
ENBL - white

spoiler]
 
Last edited:

Braeden Hamson

Feb 18, 2016
240
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Feb 18, 2016
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240
Not sure if you're still around, but it looks like you can adjust the speed be feeding 0-10v into those screw terminals. Apparently it can also take serial communications and PWM.
 

leeknivek

Jul 18, 2019
4
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Jul 18, 2019
Messages
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thanks, i was curious of that. i did find that it has three "modes" - constant rpm, constant torque, and constant cfm (being a blower fan, fed from a probe). i am not sure what mode it is in or how to change it.
 
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