Antique motor wiring

[-NikD-]

Hey all

I have an old motor that I would like to repurpose. Its an old Lister/Hoover

I have searched the net but cannot find any specifics on its wiring. It says 200/220V but I am not sure which terminals to connect to and if I need to check anything else

There are 4 terminals at the rear and what appears to be an oil port for the bearing

the resistance readings across the terminals is as follows

The capacitor has been laid against some cardboard inside the casing for quite some time and some of the markings are illegible

Any help you could give would be great

TIA

 

[timhoward]

if I need to check anything else

It needs testing with an insulation resistance tester (not just a multimeter). This is a must.
You need to check the level of insulation between the windings and the case. (From what you have done already, I might be missing something but I can't instantly understand the 6 ohms between terminals 4 and 6)

In terms of the wiring, I wouldn't want to tell you what to connect where without having it in front of me, but in terms of first principles of a single phase motor with permanent capacitor:
There are two sets of windings, main, and starter.
The capacitor would normally be connected to one end of the main windings, and one end of starter windings.
The other end of both windings are joined together and that is the Neutral connection point.
(Your diagram matches this and the numbers appear to add up)

The casing should be earthed. I suspect you will find terminal 6 has negligible resistance to the metal casing of the motor, and is the earth terminal.

But again, it needs IR testing before anything else happens.

 

[Marvo]

Lol, you gotta love those old motors. It's 1/4HP which is about 186 watts shaft power and it's rated at 3 Amps FLA which is about 690 Watts of electrical power meaning its efficiency is around 0.27.

The resistance readings are a bit confusing. Do you know if it has an internal centrifugal switch that disconnects the start cap when it's running?

As well as testing the insulation at 250v as Mr Howard recommended I'd also suggest you don't connect that old capacitor anywhere near a supply voltage. Those old capacitors didn't age well so just replace it now as a matter of course.

 

[Simon47]

Well the label says CAP ST which I assume means its capacitor start so should have a centrifugal switch.
What is probably worth doing is to carefully disconnect all ends from the terminals so you can identify each winding separately - measuring with everything connected up gives false readings. But be really careful to note what goes where before you start.
If you are able to spin it up, perhaps with a drill, you might find two terminals go open circuit at soeed.

 

[-NikD-]

Sorry for not getting back sooner.

See attached image of the inside of the motor

I managed to get a lend of an insulation tester so I will post results once I have them

Any idea what rating the replacement capacitor should be?

 

[timhoward]

Right, so centrifugal switch, two coils, and a start capacitor (google 80 micro farad start capacitor)
There are lots of diagrams online showing you how a single phase motor with start cap and centrifugal switch is wired up.

 

[-NikD-]

Right, so centrifugal switch, two coils, and a start capacitor (google 80 micro farad start capacitor)
There are lots of diagrams online showing you how a single phase motor with start cap and centrifugal switch is wired up.

See wiring diagram I think is correct with insulation test results and better resistance readings

When I tested the Green to Black connections I made sure they were not wired together at the back of the motor.

There is a push reset button on the back of the motor that is a normally open switch which closes temporarily when pushed and opens on release. Where does this fit in to the wiring above?

Also on checking various websites I get a range of differing capacitor values to use ranging from 2mF to 40mF. I have no idea which to use.

I am assuming that something rated above 350V is okay to use

 

[-NikD-]

See wiring diagram I think is correct with insulation test results and better resistance readings

View attachment 117335

When I tested the Green to Black connections I made sure they were not wired together at the back of the motor.

There is a push reset button on the back of the motor that is a normally open switch which closes temporarily when pushed and opens on release. Where does this fit in to the wiring above?

Also on checking various websites I get a range of differing capacitor values to use ranging from 2mF to 40mF. I have no idea which to use.

I am assuming that something rated above 350V is okay to use

Just thinking about this last night my diagram was slightly wrong, the green comes from the winding and not the capacitor.

Would the reset button be wired in parallel to the capacitor as in the following diagram?

 

[Simon47]

In no particular order ...
I'm no expert, so can't comment on whether you have the run and start windings correct. My gut feeling is that the start winding would have the lower resistance so as to pull more current and give a better starting torque, but I could be completely wrong there.
Otherwise looks OK (your first diagram).
No, the reset button wouldn't be wired there - no idea what it would do if it is indeed a N/O switch.
You set the direction of rotation by swapping ends on either winding. I.e. swap red & green OR swap black & white.

Are you sure the reset button isn't an overload device that's gone faulty ? I'm thinking that if it's an overload device, but the latch has failed, then it might look like a N/O switch. Perhaps that's why the motor was ditched ? If my guess is correct, it would be wired between the supply live and the motor internals.

 

[-NikD-]

In no particular order ...
I'm no expert, so can't comment on whether you have the run and start windings correct. My gut feeling is that the start winding would have the lower resistance so as to pull more current and give a better starting torque, but I could be completely wrong there.
Otherwise looks OK (your first diagram).
No, the reset button wouldn't be wired there - no idea what it would do if it is indeed a N/O switch.
You set the direction of rotation by swapping ends on either winding. I.e. swap red & green OR swap black & white.

Are you sure the reset button isn't an overload device that's gone faulty ? I'm thinking that if it's an overload device, but the latch has failed, then it might look like a N/O switch. Perhaps that's why the motor was ditched ? If my guess is correct, it would be wired between the supply live and the motor internals.

I'll take the reset switch off this evening and post photos of it.

For the windings I read somewhere that the main winding was the thickest wire and the auxiliary was the thinner. But I could be very wrong.

 

[-NikD-]

I'll take the reset switch off this evening and post photos of it.

For the windings I read somewhere that the main winding was the thickest wire and the auxiliary was the thinner. But I could be very wrong.

Here are some images of the switch

External view

Internal View with adjustable screw to adjust the distance of the connecting metal parts

Removed switch

 

[Moley]

That looks like a bi-metal thermal cutout to me. I could be wrong though, it has been known on rare occasions

 

[-NikD-]

That looks like a bi-metal thermal cutout to me. I could be wrong though, it has been known on rare occasions

so should that be adjusted so its normally closed? and how does it fit into the wiring diagram? or do i leave it out?

 

[Simon47]

It should be adjusted such that it "snaps" open at a certain temperature. When cooled down, pressing the button should then make it snap back again.
It needs to be wired in series with the supply so it cuts off the power if tripped.

The manual "Press to reset" function is essential to avoid it starting up again when the motor cools down. Depending on what it's driving, automatic restart could be very dangerous.

 

[freddo]

I would expect there to be pressure applied to some part of that cutout for it to snap open and closed correctly. It looks to me like it is already in the 'on' position but the contact is open due to something not pushing on a certain part of it from the other side. Is it pushed in by something in the plastic housing? I've attached a photo of a thermostat that shows pressure being applied to 2 points in the mechanism (the 2 purple insulating pieces). The bi-metallic strip is the bar of metal at the top of this photo. as it gets hot it bends down pushing the copper contact piece in the middle down past the centre point and the lower contact on the left suddenly moves down away from the fixed silver upper contact. The lower pushing piece is adjustable up and down to set the switching temperature. The further down it is the more the bi-metallic strip will have to bend to push the copper strip past the centre point to switch it off.

Without the second pressure point the switch will just slowly move causing severe arcing. I wouldn't adjust anything to make the contacts close at this stage.