Thread: DC motor behaviour

What DC and what motor?

Hi ncarcher ... It's a Hare and Forbes DC7

Does it still have the mesh in front of the impeller? Could still be the cap but check for obstructions first.

Yeah ... Had a look today ... Clean as a whistle. It's got the bullseye ... But its always had that. Even started it up without any ducting connected and she still struggled ... comparitively.

Oh ... Another whacky thing I noticed today. Through a 6" port .. or 2 .. or 3 .. it has never pulled anymore than about 4.8amps. Today I opened up a port and it pulled 4.6amps. Opened up 2nd and 3rd and she pulled up to about 5.1amps.

Unplug it and pop the cover off the capacitor/s. One or two? Touch a screwdriver shaft across the terminals of the capacitor before you touch them (to discharge the capacitor) and check that the connection isn't loose. If it looks good write down the details and pick up another. Shouldn't be expensive to swap it out and test it. Less than $20 on ebay. Your local motor repairer or electrical wholesaler may have one even cheaper. The scrap merchant could be a good option as well. They would scrap old motors for the iron and copper but keep the capacitor.

Thanks NCArcher ... Will have a look see ... Btw ... I think there are.two bulbous covers on the motor .. ..

I haven't done this yet ... But if there are 2 caps, how will I know which one is shot ?

Do they exhibit physical signs (scorch marks etc.) ?

Originally Posted by Glenn.Visca

I haven't done this yet ... But if there are 2 caps, how will I know which one is shot ?

Do they exhibit physical signs (scorch marks etc.) ?

One is a start capacitor and only engages while the motor is starting and is a non-polarised electrolytic. It uses a switch which clicks out once the motor is up to speed. You should hear a click when the motor slows.

The other is a polypropylene capacitor and is a run capacitor and is permanently in circuit.

Your issue is most likely the start capacitor. It *may* be the switch in which case you are in for a more interesting time.

If the capacitor has become leaky (electronically that is) then it may have signs of overheating or become bulgy. But if it is open circuit then it will not have any external indication.

I had an OC run cap and was directed to a local capacitor place. I tried Jaycar but they did not have the correct value. Mice cost $16.50 so was pretty cheap.

If you have or know someone with an ESR meter then you can check them out. Otherwise just take it in and get a replacement.

Originally Posted by Glenn.Visca

I haven't done this yet ... But if there are 2 caps, how will I know which one is shot ?

Do they exhibit physical signs (scorch marks etc.) ?

They usually swell up and eventually spill or pop their guts out.
If it has swollen or burst the motor would not even start.

The start cap usually has a higher capacitance (microfarad or MFD) rating than the run capacitor.

Thanks men !

I recently bought a start capacitor from machinery warehouse. Check their web site.

Peter


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Been trying to think where I bought mine. It was K. D. Fisher. The Adelaide store is not far from us but here is the Melbourne store.

http://www.kdfisher.com.au/contact_mel.php

Alternatively if you have a Jaycar store near you and your value matches... Mine was 16 uF so I had to send the little woman down to KDF.

http://www.jaycar.com.au/search?text...4-49e3c756a49d

Both jaycar and machinery warehouse close by. KD Fisher in Brooklyn on the other hand ... Cut lunch required.

Thanks for the pointers