How to reverse a Cap start motor with only 3 wires a terminal box?

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Originally Posted by Sterob

I received the new Caps today and wired it up as my diagram modified by Stu in post #10.
I'm happy to say that that diagram is correct. There IS a centrifugal switch on the start winding circuit.
Swapping the U and V connections does give opposite rotation.

The only thing of concern is the current draw is little high at 9.2A with no load.
The name plate says its a 240V ,1 HP motor and FLC is 7 amps.

The 400uF Cap would not fit under the housing, so I used a 240V , 200uF Cap. There was no difference to the way the motor started and the NLC was still 9.2A.

The motor is either REALLY a 220V motor ( the incorrect 1 phase wiring diagram mentions 220v ), there is an error on the name plate, or the motor is beginning to fail. I don't have a Megga the winding resistance to earth although my RCD's in the shed have not tripped.

I don't have a reason to suspect its failing ( besides the higher than expected current draw) as the original fault was the control switch 'fell apart'.

This journey is almost over.....

Steve

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Hi Steve,

Sounds like things are moving in the right direction..

I guess you are using a clamp meter, if so, can you see the drop in current when the start winding cuts out?

The reason I ask, is that maybe the centrifugal switch isn't working, and it's staying on the start winding.

Regards
Ray

something seems strange there to me ?

7amps x 240 V = 1680 watts / 746 watts = 2.25 HP

but then again I am mathematically challenged :wink:

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Originally Posted by RayG

Hi Steve,

Sounds like things are moving in the right direction..

I guess you are using a clamp meter, if so, can you see the drop in current when the start winding cuts out?

The reason I ask, is that maybe the centrifugal switch isn't working, and it's staying on the start winding.

Regards
Ray

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Hi Ray,
Good point.
I have a clamp meter but it decided not to work. :((
I used a Fluke DVM.

You can hear the switch close as the motor stops. It spins up too quick to hear it open.

I've been doing some Googling.... 7A at 220V is about right for a 1 HP motor, so it looks like 9A at 240~ 250V is about right.

Steve

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Originally Posted by shedhappens

something seems strange there to me ?

7amps x 240 V = 1680 watts / 746 watts = 2.25 HP

but then again I am mathematically challenged :wink:

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Yeah, I think there are other forces at work here....lol ( eg losses and efficiency, lower voltage.... )

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Originally Posted by shedhappens

7amps x 240 V = 1680 watts / 746 watts = 2.25 HP

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Only if voltage and current are in phase. It's gets more complicated if they are out of phase.

Quote:

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Originally Posted by Sterob

Hi Ray,
Good point.
I have a clamp meter but it decided not to work. :((
I used a Fluke DVM.

You can hear the switch close as the motor stops. It spins up too quick to hear it open.

I've been doing some Googling.... 7A at 220V is about right for a 1 HP motor, so it looks like 9A at 240~ 250V is about right.

Steve

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If its any help I've just amp clamped my 1hp lathe motor. At switch on the current jumps to around 12/13 amps and drops back to just a little under 9
amps no load. Using a killowatt meter it shows 780 watts and 244 volts. It didn't change much when I ran the spindle, but I wasn't cutting metal.

Regards:
BaronJ.

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Originally Posted by BaronJ

If its any help I've just amp clamped my 1hp lathe motor. At switch on the current jumps to around 12/13 amps and drops back to just a little under 9
amps no load. Using a killowatt meter it shows 780 watts and 244 volts. It didn't change much when I ran the spindle, but I wasn't cutting metal.

Regards:
BaronJ.

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Thanks Baron, very helpful.
It all seems to fit then.

Steve

Quote:

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Originally Posted by shedhappens

something seems strange there to me ?

7amps x 240 V = 1680 watts / 746 watts = 2.25 HP

but then again I am mathematically challenged :wink:

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7a x 240 does not give Motor output capacity..that is consumption watts (input)

there is 746 watts (or .746kW output) to one (1) horsepower (output)
dont confuse output watts with input watts

Thanks Jack and Eskimo, I have just had a bit of a read about phase shift, resistance, capacitance, back emf, impedance ect........ and now that I have warped back from the matrix I think that I'll just stick to turning switches on and off :oo:

I've just had another attempt at finding a reference to such a motor and have found this:Electrical Diagram for a CSIR Motor

This is VERY similar to the motor I am playing with.
Don't know why I couldn't find it before.............Must have used different wording in Google.

Steve