Help Please, My Jet Mini needs a New cap!

Re: Help Please, My Jet Mini needs a New cap!

Dwight Rutherford

Have you called Jet?

Re: Help Please, My Jet Mini needs a New cap!

Dave Paine

Single phase motors need help to get the motor to rotate. The capacitor provides this by making a quasi second phase.

A motor with a single bump on the side of a motor has a start capacitor. This circuit is engaged on start up until the motor reaches a certain % of normal RPM. This is done via a centrifugal switch. If you have heard a click as the motor spins down when you turn it off, this is the centrifugal switch closing - ready for the next time you start the motor.

A motor with two bumps on the side has a start capacitor and a run capacitor. The run capacitor is to improve efficiency and is engaged when the motor is running.

Without a start capacitor a single phase motor will just hum and not rotate. If you are lucky you may be able to rotate the motor by hand and then turn on and it may continue to run.

Capacitors are rated by units called Farads, normally micro Farad since a 1 Farad capacitor would be very large.

The micro Farad rating is normally stamped on the side. If you are lucky the capacitor will have this still visible. The voltage rating is whatever voltage the motor is designed for. I expect 120V.

Remove the steel or plastic housing of the bump and then you should be able to inspect the capacitor to find any rating information.

You will be able to purchase a capacitor from a local motor place, electrical supply house or the likes of EBay. I would not waste time trying the big box stores.

Re: Help Please, My Jet Mini needs a New cap!

Brad Vietje

Excellent info that will benefit many here -- thanks!

Safe spinning,

Brad Vietje

Newbury, VT

Re: Help Please, My Jet Mini needs a New cap!

Chuck Engstrom

Hi Jim -- My Delta mini has a 30 microfarad 300 volt capacitor, a plain old-style five-speed mini, and I have another of the same rating in a drawer as spare for the Jet minis that belong to the club. You may be able to find the rating on yours by removing it from the protective cover.

Good luck with it -- Chuck

Re: Help Please, My Jet Mini needs a New cap!

Doc Green

Hey Jim,

On your old capacitor, the capacitance may be denoted as uF, mF, MF, MFD or etc. They all mean the same - microfarads.

For a replacement, be sure to get an AC (alternating current) capacitor with a voltage rating of 250 V or higher. A higher voltage does not matter. Electrical shops (motor and heating-air conditioning places) sell them as "motor-starting capacitors."

If you cannot read the size from the old unit, what I would do is get a replacement in the range of 8, 10, or 12 uF and try it out. If it works, Great! If the motor seems to lack starting torque, try a larger one. Polarity of the connections does not matter.

Electronic shops will have mostly DC capacitors, labeled something like 47 uF 200 VDC. Do not use one of these. The AC will blow them out in a matter of minutes.

Good Luck! ~Doc

Re: Help Please, My Jet Mini needs a New cap!

walta

It is possible the capacitor failed and that is why it went up in smoke.

It is also possible the centrifugal switch inside the motor is stuck and kept the capacitor energized to long destroying the capacitor.

It could not hurt to blow out the motor with compressed air.

Walta

A Little Caution

Bill Howatt

Jim mentioned that some searching revealed that the capacitor used on some Jets is a Start-Run capacitor and with a bit of Googling I saw the same.

It seems this capacitor is made to stay in the circuit after the startup to help with the torque so replacing it with a capacitor whose design is for brief startup operation may result in short life. There are some start-run capacitors that are really 2 capacitors in one package but this one does not seem to be one of those (?).

I'd call Jet because sometimes the physical size is a bigger PITA than the electrical size. There was also mention that phoning Jet results in lower shipping costs than doing an online order.

BIll

Re: Help Please, My Jet Mini needs a New cap!

Mike Brazeau

Jet will not ship parts into Canada. Active Tool Repair in Hamilton might have one on hand. Duke Electric in Hamilton also do motor repair.

Re: Help Please, My Jet Mini needs a New cap!

Bill Turpin in WNC mountains

Start caps are usually round black plastic filled with a salt solution. Run caps are usually an oval metal shell filled with oil. Years ago PCBs were used in this oil as a fire retardant. Unfortunately PCBs are carcinogens. The voltage rating of the cap is an insulation rating. Never reduce this rating, but you can go up. This will make it bigger and perhaps impossible to fit. Frequent starts or a defective start switch will boil the salt solution or oil causing pressure and rupture. If oval is swollen or salt leakage around contacts shows a defective cap. The voltage on caps is a factor of motor electricals, NOT the voltage supplied to the motor. Frequently 330volt cap on a 120v motor. The mfd rating can be increased by 10% if necessary because of availability. Never reduce the mfd rating. If new cap won't fit, extend the wires and mount remotely. Caps can hold charges and knock you on your can. If the cap holds a charge it is usually not defective. Discharging a cap by shorting across the contacts will ruin a good cap. A charged cap should be discharged with a 15K ohm bleed resistor. Be careful. A bite from a charged cap can cause you to pull your arm fast enough you will cut yourself! Good luck.

Thank You!

Jim in Milton, Ont

Hi All,

I really appreciate the great support given to me, Thank You for the great advice and detailed information!

Take care, Jim