What's this?

[RF Lighting]

I've got a customer with a planer thicknesser. It currently will not run.

It is a single phase machine with a 4hp motor and a DOL start stop with overload.

There is also another thing in with the contactor, which I don't know what it is.

At the moment when you try and start the machine, it'll run for about 5 seconds before the overload trips.

Measured with my clamp meter, it's drawing about 80A, so clearly something is not right.

The motor bearings seem fine and really free, and the windings test out ok.

There are two 100μF capacitors in parallell connected to the bottom left terminal of the contactor overload, and to the top left connection of the unknown thing.

The capacitors both test out as being dud, but I don't know if this is a symptom or the cause of the problem.

Here's the overall starter:

Here's the device I don't know what it is. It sits to the right of the contactor as seen above:

 

[Nozzle]

Is it one of those gadgets that "converts" single phase into three phase by way of a capacitor and inductor tuned to give 120 degree phase lead n lag for the specified load?

4hp for a single phase seems quite a lot, does it plug in via a normal 13amp plug?

Nozzle

 

[RF Lighting]

Not sure! I know there's some clever motor chaps on here who I'm sure will know the answer.

No there's a hard wired supply for it. The motor plate states FLC of 20A

 

[Nozzle]

The thing on the bottom left looks like it has a scale on it, graduated perhaps in AMPS? This could be a thermal overload device. A large current for a small time causes it to trip, but so will a small overload for a larger period.. and this is perhaps the adjustable element.

Nozzle

 

[RF Lighting]

Yeah that's just an overload. A variable circuit breaker if you will. All motors over 0.37kW have to have one.

That is working fine, and is only tripping as the motor is pulling four times the rating of the overload.

 

[333rocky333]

a bit of a quess but i recall something similar years ago, from what you say i cant make out if yours is wired with the load or wired in the control circuit.
The thing i recall somehow reduced that humming that you sometimes get from the coil,

 

[securespark]

Not a soft-start device?

 

[ericmark]

Think it is part of the starting system only ever seen them before on Flyght water pumps and I am going back 35 years so sorry can't remember exactly how they worked. Pump had multi windings as 110 or 240 volt and it was removed for maintenance and the electrician had not noted the connections he some how thought same as three phase swap any two wires if goes wrong way and I remember it took us ages to work out how to wire it.

 

[mfarrow]

Can't you just shine your camera on it?

 

[sparkyy]

Could it be a rectifier? Does the machine have a brake? It could be to release a brake. No brake release, high motor current.

 

[RF Lighting]

There is no brake on the machine. The motor continues to run really freely for a minute or so after trying to power it up.

There are four terminal posts in the motor, which are each wired back to the contactor box.

One is connected to live, one to neutral and the other two to the mystery box.

 

[AdrianUK]

I reckon its a type of timer to drop out the start winding after a few seconds & by the sound of it that isnt happening.

Or maybe a thermal start relay similar to what used to be fitted to 'fridge compressors ..... the start current causes the element within the relay to heat up which then trips the relay disconnecting the start winding.

Adrian

 

[ericmark]

This link see bottom of page there is also a diagram of how wired but for Flyght pumps so likely wrong terminal names but top right

does seem to be same device. Think it's a thermal start relay which connects capacitors to start.