HF DC down, Cap or Centrifugal Switch?

[Turtlewood]

Hey All,

So my HF 2HP 120V dust collector is going through the often experienced "Turn it on, it hums for a few seconds, and then trips the breaker".

I always thought that this meant that the capacitor was gone, but searching the internet it appears that the "centrifugal switch" is often equally likely to have failed.

My question is, how do I best tell which it is that needs to be replaced?

To look at the centrifugal switch, I took the cover off of the shaft end of the motor not connected to the fan as recommended on a few sites. All I see is a small plastic fan and the whole assembly of, I'm guessing, the centrifugal switch. The small plastic fan moves freely, and the whole end is wasn't covered in saw dust. Tapped it lightly with a hammer and tried to turn it on, still no go.

As for the capacitor itself, I took off the over and it looks visibly ok. Though I've not disconnected it.

So my question is, how best to know which component is bad?

Also, where is the best place to buy a replacement capacitor and how much to they usually cost?

I don't know where-to/how-to replace a centrifugal switch.

Any pointers would be appreciated.

Thanks in advance,
-Turtlewood

Here are two pics I took of the centrifugal switch assembly on the backside of the motor:

View image in gallery​

View image in gallery​

 

[CrealBilly]

Hi Kevin I had the same problem with my gaspack this year the cap went out on fan. There is a test using a multimeter you check the cap - but due to system problems I lost the link... I did notice I could start the motor by hand if I caught it before it tripped the breaker.

A quick google search pulled up the cap test ---> http://www.ehow.com/how_4493634_test-electric-motor-capacitors.html

BTW mine looked fine too but tested bad. I replaced and no problems since.

Thanks

 

[jdulaney]

Mouser Electronics is a good place to look. You should be able to get it cheaper than if you went with the manufacturer of your dust collector.

 

[aplpickr]

Start caps are black plastic and round. They are filled with a salt solution. There is a brown wax plug between the terminals to keep the solution in. If it is cracked, puckered, or missing then the salt solution has boiled and the cap is bad. Are there visible salt crystals or solution? Run caps are usually grey metal ovals and full of oil. Bad ones are swollen and not oval anymore. Take the fan blade off the shaft. Scratch location marks across the seam of metal end-bell and body of motor, at both motor ends. Remove the end bell. The centrifugal switch is inside the end bell and has 2 or 3 wires attached. Take digital picture as you remove end-bell. Clean the area around the switch. Clean the switch contacts with a needle file. Wipe the closed contacts clean with a paper book of matches cover or similar stiff paper between the contacts. Be sure to remove ALL cleaning trash. RE-assemble and test. Bad contacts that are open prevent start winding from engaging. Welded or stuck closed contacts BOIL the solutions in the caps. Your picture of cent switch looks more like an overload reset. Sometimes the slider on the motor shaft gets stuck and will not slide. Cent force is what makes it slide. When motor starts, the switch should click and open the contacts at about 3/4 of full rpm. Start all four thru bolts, slowly tighten them in 3 or 4 steps, spin the motor by hand as you tighten the bolts. Contacts are closed (made) at start, they open during speed up and stay open as long as it runs, and close on stopping. Even if cap is bad: service the switch. Bad switches kill caps.

 

[Turtlewood]

Thanks for the pointers everyone.

Jeff, thanks for the link. Think I'll test the cap out first since digging down to the centrifugal switch sounds like a lot more tear-down and chance of mixing up reassembly.

-Turtlewood

 

[junquecol]

Carefully pry the fan off, using a couple of screwdrivers. Make sure there isn't a snap ring holding it. The centrifugal switch is located under the black cover. Most likely, you will find saw dust in there when you open the case. If so, take air hose and blow it out. Reassemble and try it.

 

[aplpickr]

A picture while tearing down should prevent mistakes. If your cap is bad, your switch caused it. The next cap will have a shorter life. Caps will live for 20+ years if not mis-treated.

 

[ehpoole]

With respect to capacitor testing:

If you have a digital multimeter with a capacitance function you may be able to accuretly verify the capacitor if the upper end of the meter's range can accomodate the capacitor's with over-ranging. If you have a dedicated capacitance meter, or an LC meter, then you can absolutely test the capacitor for actual capacitance. The measured capacitance should be within about +/- 25% of the capacitance rated on the capacitor (usually specified in uF or micro-Farads). Read below to DISCHARGE THE CAPACITOR BEFORE TESTING AND HANDLING! The capacitor can have in hundreds of volts DC potential between its two contacts or wired leads.

If you lack a capacitance meter (or meter with a suitable capacitance function) you can perform a rudimentary test that will verify whether the capacitor is atleast storing energy as it should.

BEFORE PERFORMING ANY TEST, DISCONNECT POWER, then either use a meter set to DC Volts to test for residual voltage on the capacitor. If you measure anything greater than a few volts, use an OLD screwdriver and use it to bridge the two sets of contacts to discharge. If there are no contacts, but rather leads, then carefully disconnect the leads (taking care not to touch the exposed ends) then carefully touch the two lead ends together to discharge. EXPECT A BRIGHT ARC IF THEY HAVE A HIGH CHARGE REMAINING. I suggest closing your eyes or wearing UV-blocking sunglasses as it can be quite intense (though extremely brief) with large capacitors. If you get a visible arc then you have already verified the capacitor is in reasonable working order since it had a stored charge.

A BETTER WAY of peforming the above DISCHARGE PROCEDURE, if you have the necessary components, is to take a 100K 1/2-Watt (or greater) Resistor and clipping two sets of alligator clip leads, one to each end of the resistor. Then use the alligator clips (and resistor) to clip to each wire or contact of the capacitor and give it a minute to fully discharge the capacitor.

If you did not get a visible arc -- or had your eyes closed (or used a resistor) during the discharge process, you will need to perform a rudimentary test with your digital meter. First inspect the capactitor to verify that it does not have an OEM resistor intalled across the terminals -- if it does then this will greatly reduce the period you have to observe the desired effect to determine if the capacitor is working -- in some cases you may need to temporarily disconnect the resistor (but reattach when done). Set your meter to the RESISTANCE (Ohms) mode -- if not auto-ranged the set the range to the highest (Meg-Ohm) range for this test, some auto-ranged models will require setting to manual ranging for this test -- and connect the red and black leads from your meter to the two terminals of the capacitor. You should measure a slowly ascending resistance as the capacitor is slowly charged by your meter's Ohms/Resistance test mode. If you don't get a good reading on the Meg-Ohm range then try backing off to the 100+K (or thereabouts) range and try again. You can doubly verify the test by quickly switching your meter to the DC Volts range -- you should be able to measure a small residual voltage now, a side effect of the resistance check.

If you had a problem with the resistance check method -- or if your capacitor has a bleeder resistor across its terminals -- then there is another way to peform a function check on the capacitor. Find a GOOD 9V battery, you will need it for this test. Set your meter to DC Volts range (if manual ranging, setup for a maximum range of 10VDC). Now use alligator clips to your meters test probes and connect each probe's alligator clip to each side of the capacitor so that your meter is continuously reading the DC Volts on the capacitor. With the meter continously displaying the DC Volts charge on the capacitor, use a test lead or alligator clip (or screwdriver, improvise) to discharge any remaining residual charge from the Ohms test performed earlier -- your meter should now read less than 1VDC. Now touch the 9V battery to each terminal of the capacitor (use an alligator clip or piece of wire if needed) -- this will place a roughly 9VDC charge across the capacitor's plates. Your meter should now show either a nearly steady 9V DC reading OR a slowly descending reading if there is a bleeder resistor installed across the capacitor contacts (or if using an old meter with a low impedence value).

Either way, afterwards, double-check that the capacitor has been discharged with your meter (again, it should measure no more than a few volts on the DC Volts range). If not sufficiently discharged, then repeat either of the above discharge procedures, otherwise you can progress to either reinstalling or removing and replacing the capacitor.

If replacement is warranted, replace the capacitor with the same type (running or starting), rating (both uF and either equal, or greater, volts) and size (length and width/diameter). I would suggest a novice purchase these from a motor shop or the original manufacturer -- DigiKey and Mouser offer far too vast an array of varying capacitors -- most (as in 99.99%) of which are not suitable for the job at hand -- for the novice to discern a suitable replacement.

HTH

 

[dvo]

Cap on ebay. Cheaper and free shipping for most of them. Just search for starter capacitor or running capacitor and get the one that matches your cap value. Just did a HF 2hp motor last week. Cap came in a couple of days.

 

[ehpoole]

Cap on ebay. Cheaper and free shipping for most of them. Just search for starter capacitor or running capacitor and get the one that matches your cap value. Just did a HF 2hp motor last week. Cap came in a couple of days.

Don't just match the capacitance value, the replacement must also equal or exceed the rated voltage of the original. It is also a good idea to ensure the dimenisions of the replacement cap are not greater than the original capacitor or you may encounter mounting issues. Things are a bit more standardized these days, but this is not always the case. These are not issues if you purchase an OEM replacement, but are aspects to be aware of when substituting a non-OEM replacement capacitor.