Motor blowing cap

I stopped at a garage sale and found a 115v, 3/4hp Dayton long arm buffer for $15. We plugged it in and it ran a little rough, did not come up to speed (3450) and blew the cap in about 5 seconds. Big cloud of smoke and some oil in the bottom. The man said "take it", so I did.
I installed a new, same size, Dayton cap. It ran rough, didn't come up to speed, and within 5-6 seconds the smoke came out again. I pulled the end bells out somewhat and there is NO commutator or centrifugal cut out switch. I didn't fully remove the end bells yet since it requires a puller to get them all the way off.
The AC lead is only about 12" long with a nice 3 prong "aftermarket" plug. I don't know if it's factory or not.
What's the diagnosis?

Either the cap was bad or the motor is. Did you check the mf before installing the new one?

No. The original was a Mallory, replaced with a Chinese Dayton with the same specs.

What is the MFD? If the cap going up in smoke is a start cap, start caps must be removed from the start windings within a fraction of a second by a switch inside the motor or it will go up in smoke. If there is no end switch, then capacitor must be a run capacitor. Run capacitors ususally are in the 5-35 MFD range. If you replaced it with the right MFD and voltage, then either you got a bad capacitor or something is wrong with motor.

Without looking at motor, it's hard to say what you have. I would try removing cap manually after motor starts and see what happens. I would be leaning towards saying you have a start cap that isn't being removed from circuit. Is it possible you have an electronic switch inside the motor that has replaced the end switch and it's bad?

Usually if smoke leaves an electric device, it's time to get a new one.

George

The original was somewhere around 150mf, don't remember now, but it was replaced with 145-174mf.
Interesting about the electronic switches. I wasn't aware of them. I haven't got the armature out yet, so not sure what's in there with the end bells only about an inch out.

It's a start cap. Will go up in smoke if not removed. No end switch means you have an electronic device to remove it and it's not doint it's job. Guessing it's located the same place that the end switch would normally be.

I think you can buy replacement switches. If I couldn't fing a replacement switch, I would wire in a hard start capacitor used on an air conditioner compressor or refirgerator. It has a built in electronic device that removes the cap. Down side is you may have to wait a minute before you restart motor.

I wired a hard start cap on my 1/4 hp mixer motor.

If you can't find one locally, try ebay.

SPP5 Solid State Relay & Hard Start Capacitor for HS5 oem hard start kit
Seller : electron-parts ( 954)

$8.59 including shipping

George

check to see if that plug is wired up correctly.

One thing to note about Dayton electric motors,
from Grainger. You can get virtually any part
from Graingers parts service, and get parts
diagrams from them, as well.

They have no record of this motor (to old) and say to call for parts for the newest model. No wiring diagrams are published, and the store can't even order parts on the store computer.

I found this info:

3ARR18 Premium Duty
Current Type
Motor Starting Relay

The Basic 3ARR18 Relay is a Premium Duty, remote mounted, current type motor starting relay for Single-Phase AC motors used in the appliance industry. Generally the size of the motor is limited to 1/3 HP, 120 Volts AC and ¾ HP, 240 Volts AC. Motors may be resistance start-induction run, resistance start-capacitor run, or capacitor start-induction run.

It is a current-sensing relay, which utilizes the principal of a ferromagnetic plunger in a solenoid coil to be actuated by the motor main winding current through the coil, opening and closing the contacts of the relay.

The relay utilizes the correlation of the main-winding current and motor speed to actuate the contacts to energize and de-energize the start winding circuit.

As the motor accelerates and the main winding current increases, the relay solenoid picks up and closes the contacts to the start winding circuit. As the motor increases speed, the main winding current begins to decrease, and at the appropriate motor speed, the relay drops out, allowing the contacts to open and disconnect the start winding from the circuit. Gravity acting on the plunger opens the contacts.

What you found sounds like what has been used on refrigerators for years. Look it says up to 1/3 hp. Don't you have 3/4 hp? Don't think that's what came from the factory for your motor. Don't think that will work either.

I've come to the conclusion that 3 wires are required for the relay to work. It was only wired with 2: one from the motor and one from the cap with the coil in between. The cap has 3 leads, 2 to the motor from a double terminal and 1 to the coil from the other terminal. I can't find a diagram of the motor wiring so I don't know which leads go where. There is a winding of fine wire and a winding of heavier wire in the motor. Probably one is the start and one is run. A whle ago I remembered a fellow that owns a shop that rebuilds swimming pool and other motors, so he probably knows the answer.

Slowpoke,
Yes under normal conditions relays will need 3 wires. However the hard start kit I showed you from ebay for $8.49 (?) only requires 2 wires. You could just replace the cap that smokes with just using the two wires. This device claims to be a relay, it's actually an electronic device that conducts for a fraction of a second and then shuts off, removing the cap from circuit. It requires a minute of so to cool off and reset.

What do you have to loose, just try it. If you have a local HVAC friend, get one from him.

George