Capacitor suspect

[Speedy Builder5Participant @speedybuilder5]

I have a Warco Economy mill. Motor 240 a/c 50hz 1/2 Hp 3.9 amp rated, capacitor start, reversing . I have owned and used it for nearly 30 years with no problems.

Today, cold workshop 6deg C, it tripped the house RCD.  Basically, the motor started to run but never got up to the 1440rpm. I  slackened off the drive belt, reset the RCD and had another go – same result.

It’s a bit of an effort (heavy) to get the motor onto the bench, so after checking the starter switches, cables etc, took a look at the start capacitor housed in a tin box on the motor, it has a rating of 110volt 200 MFD. Strange voltage I thought, so for the cost of a new 240volt 200MFD cap, I have decided to replace it before being forced to remove the motor for further inspection.

Why would there be a 110 volt and not a 240 volt cap being used ?

Bob

[Andrew TinsleyParticipant @andrewtinsley63637]

Very weird! Start capacitors have always been 240 Volt AC (or higher) in a standard common or garden single phase motors, in my experience, Not too sure about things like capacitor start capacitor run motors as I have never had one of the less usual configurations for starting single phase motors.

Andrew.

[MacolmParticipant @macolm]

Unfortunately for positive diagnosis, these days RCDs can respond to both earth leakage and to over current. The dangerous way to investigate would be to remove all earth connection and insulate the complete thing. Then with sensible precautions, see if it trips or not. If it still trips, overload, if not earth leakage.

Regarding the capacitor voltage, it is bad practice to use less than supply rating. If all is working properly, the voltage across the capacitor may well never exceed 110V. However, any fault condition, even a jammed motor, will upset things. So assuming the capacitor needs replaced, 240V or higher would be my suggestion, though it could be quite a bit bigger.

[MacolmParticipant @macolm]

For clarification, “bigger ” in dimensions. Best stick to the capacitance value that previously worked.

[john fletcher 1Participant @johnfletcher1]

Well, I think you have a swing connection motor (cheap & cheerful and I could be wrong ), a 110 volt capacitor might be a bit cheaper than a 240 one ? I’ve seen the same motors on cheap drilling machines. These motors have three windings, two are connected in series and the third is centre tapped to the middle of the pair, together with the capacitor. So both start winding and the capacitor are both are continuously rated for 110 volts , no centrifugal switch either, so a bit more saving . The two, together form an AC series circuit R L C, so thought went into it at the design stage, not quite simple as it first looks. Anyway depending which way you push the switch you get for  off  Rev. You haven’t done any harm by buying a new cap, keep us posted.   John

[MacolmParticipant @macolm]

I had forgotten that configuration (or botch!), which is intended for lowest cost. It seems to be reliable, but presumably has little margin for starting and overload abuse.

[Speedy Builder5Participant @speedybuilder5]

Just a bit more info – Motor of Chinese origin 30+ years ago. 1/2 Hp 4phase ?

[larry phelan 1Participant @larryphelan1]

4 Phase ??????

[bernard towersParticipant @bernardtowers37738]

I think thats 4 pole

[SillyOldDufferModerator @sillyoldduffer]

Here’s the plate, showing 1/2 HP 4P

I think that’s P for poles not P for phase.   4 poles at 50Hz is 1500rpm, consistent with the 1440rpm on the plate.  (1440 due to slip)

Popping an RCD implies an earth leak, and a faulty capacitor could well cause that.  Fingers crossed, because that’s not hard to fix.  Might be damaged insulation in the motor, due to overheating, damp or vibration.  Have a look at the centrifugal switch if there is one – dirt, chafed wires etc.

Dave

[Speedy Builder5Participant @speedybuilder5]

New 240 volt 200MFD cap arrived today, 20€ , fitted and it seems like the problem is resolved. Motor runs forward and in reverse without tripping the RCD.

Thanks for your interest and replies.

Bob

[Speedy Builder5]

On Speedy Builder5 Said:

New 240 volt 200MFD cap arrived today, 20€ , fitted and it seems like the problem is resolved. Motor runs forward and in reverse without tripping the RCD.

Thanks for your interest and replies.

Bob

I think that should be2 μF not 200 MegaFarad  🙂

Russell

[Speedy Builder5Participant @speedybuilder5]

Seller’s description:-

Condensateur, 200Uf/Mfd 250VAC 15% Tolérance 50/60Hz Moteur Démarrage.

Is that the difference between MFD and Mfd ?

Bob

[Charles LamontParticipant @charleslamont71117]

No: using SI: mF – millifarad, µF or uF microfarad, MF megafarad (a 1 MF capacitor would be the size of a house, or, for QI watchers at least a blue whale).

[Author]

Posts