HELP, NEED MFD for start capacitor FOR DOERR MC154 3600 RPM 220 VOLTS
- Thread starter 264killer
- Start Date
I'll take "what is a crawdad" for $600, Alex.
Find the 'unloading' valve on the air side of the system and make sure keeping the pump unloaded during start up.
Most air compressors have a system to allow the pump to come up to at least partial speed before they pump into the tank, That may be why your starting of the capacitor without a load on the motor, but not with a load.
Most air conditioner parts suppliers carry a large variety of capacitors.
So do places that that sell parts for water wells.
You will probably get a better price than Grainger at one of them.
Most air compressors have a system to allow the pump to come up to at least partial speed before they pump into the tank, That may be why your starting of the capacitor without a load on the motor, but not with a load.
Most air conditioner parts suppliers carry a large variety of capacitors.
So do places that that sell parts for water wells.
You will probably get a better price than Grainger at one of them.
I know about the unloader ,
GREEK TO ME.
I assume you don't have the original capacitor and can't simply read the label to get the size worked out.
At 10 to 20 bucks a pop you don't want to just buy capacitors hoping they will work.
Also, many air compressors use a capacitor start, capacitor run configuration. Its not electrically efficient, but it allows them to pack a lot of power in a smaller package. Air compressors are typically intermittent duty, so the lack of efficiency is not noticed by most. You will need to understand the motors internal circuits to know if that's the case. If its a capacitor run system, you may be way way too high on your capacitance guess.
A typical capacitor start motor will have a centrifugal switch that disengages when the motor comes up to speed. If you hear a click as the motor comes up to speed, that the switch.
If there is no switch gear to disengage the start windings, it's probably capacitor start, capacitor run.
There are a few motors that are both, and switch between a start and run capacitor.
All bets are off if its a water well motor or air conditioner. Those use a different switching system that's not on the motor.
Quick way to find out if its capacitor run, is to put on a black plastic cased capacitor that starts the motor. If it runs for a minute or so and the capacitor does not get hot, start belching smoke, or burst into flames, it's probably a start circuit only. I am not saying I recommend the test, but I think you already did it. With that in mind be sure anything you bench test you can shut off remotely after a second or two if the motor does not spring to life.
Options
Practice your google fu and attempt to locate information on your motor that gives the answer.
There are "universal Capacitors" used in the air conditioning world that have 6 taps allowing you to play around until you find something that works. You can find them on-line for about 60 bucks, and it will be too big around to fit on your motor. If you know an air conditioning repair tech, they might let you borrow one for diagnostics.
You can "borrow" capacitors from other capacitor start motors and try to find something that works. Once you figure out the capacitance, buy one the correct size and diameter.
Short them with a road-kill screwdriver before pulling them loose.
A charged cap will notch the blade.
.
Wiring a few in parallel and/or series will give you more values to bench test.
If you have a multi meter that measures capacitance, measure the capacitance, so you know what it really is, otherwise look up the math and work out your test values.
Taking notes as you go is a good idea. size, rotation direction, and how fast it came up to speed.
You should see a range of sizes that work without a load.
Then try something mid range with the compressor hooked up.
At 10 to 20 bucks a pop you don't want to just buy capacitors hoping they will work.
Also, many air compressors use a capacitor start, capacitor run configuration. Its not electrically efficient, but it allows them to pack a lot of power in a smaller package. Air compressors are typically intermittent duty, so the lack of efficiency is not noticed by most. You will need to understand the motors internal circuits to know if that's the case. If its a capacitor run system, you may be way way too high on your capacitance guess.
A typical capacitor start motor will have a centrifugal switch that disengages when the motor comes up to speed. If you hear a click as the motor comes up to speed, that the switch.
If there is no switch gear to disengage the start windings, it's probably capacitor start, capacitor run.
There are a few motors that are both, and switch between a start and run capacitor.
All bets are off if its a water well motor or air conditioner. Those use a different switching system that's not on the motor.
Quick way to find out if its capacitor run, is to put on a black plastic cased capacitor that starts the motor. If it runs for a minute or so and the capacitor does not get hot, start belching smoke, or burst into flames, it's probably a start circuit only. I am not saying I recommend the test, but I think you already did it. With that in mind be sure anything you bench test you can shut off remotely after a second or two if the motor does not spring to life.
Options
Practice your google fu and attempt to locate information on your motor that gives the answer.
There are "universal Capacitors" used in the air conditioning world that have 6 taps allowing you to play around until you find something that works. You can find them on-line for about 60 bucks, and it will be too big around to fit on your motor. If you know an air conditioning repair tech, they might let you borrow one for diagnostics.
You can "borrow" capacitors from other capacitor start motors and try to find something that works. Once you figure out the capacitance, buy one the correct size and diameter.
Short them with a road-kill screwdriver before pulling them loose.
A charged cap will notch the blade.
.
Wiring a few in parallel and/or series will give you more values to bench test.
If you have a multi meter that measures capacitance, measure the capacitance, so you know what it really is, otherwise look up the math and work out your test values.
Taking notes as you go is a good idea. size, rotation direction, and how fast it came up to speed.
You should see a range of sizes that work without a load.
Then try something mid range with the compressor hooked up.
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