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9th May 2013, 02:11 AM #1SENIOR MEMBER
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How to reverse a Cap start motor with only 3 wires a terminal box?
Guys,
I have a Cap start lathe motor wired as below:
IMG_0002 (Small).JPG
Normally a cap start motor and reverse it direction by reversing ONE of the windings ( 4 wires in terminal box ) This motor only has 3 and has me stumped.......
Also, cap is rated at 125V. I thought it should be at least 250v?!
I need to find a new rotary switch as well. Needs to be 3 pole with FOR, OFF and REV.
IMG_0005 (Small).JPG
Steve
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9th May 2013, 07:18 AM #2Golden Member
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You definitely need to get at the junction of the two windings to include the ability to reverse the motor. I would look on the back of the terminal board to see if there are two wires connected to the common terminal. I would use a two pole change over switch with a centre off and add a no volts relay
for safety in case of a power outage and you forget to turn the motor off.
HTH.
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9th May 2013, 08:40 AM #3Senior Member
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Not all capacitors are disengaged once the motor is up to speed. Ive got a motor pretty similar to yours, and I had to remove one end of the motor housing to find where the wires were distributed to the two coils and my junction box looked just like yours. I went to the non-pulley end (with the cooling fan) and pulled it apart from there and thats where the wiring was done, but there is nothing to say it couldnt be done at the other end.
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9th May 2013, 09:59 AM #4GOLD MEMBER
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How to reverse a Cap start motor with only 3 wires a terminal box?
I guess the voltage drop across the cap is less than 125V. The difference would be dropped across the start winding. Might be worth confirming that with a motor rewinder though.
The terminal box on your motor is identical to the one on my pedestal drill motor. Assuming it's the same type of motor, it does have a centrifugal start switch.
Chris
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9th May 2013, 11:29 AM #5GOLD MEMBER
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For a bonus point. If it is wired as per Steve diagram and there is in fact a switch on the starting(?) winding. Why would they bother to bring three wires out?
Stuart
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9th May 2013, 12:21 PM #6
Hi Steve,
As a general principle you only need to reverse the polarity of the start winding to reverse the motor,
In this case you might be struggling, it looks like a non-reversible high voltage motor with low voltage start winding, they do this to reduce the voltage rating on the start cap. Basically the start winding is tapped off the center of the run winding and therefore is half voltage.
If you can find the other end, and bring out the extra wires, it might work.
Not sure why there is an extra terminal, as Stuart said why is it there? It might be just a connection point for the start cap.... it's not multipole ( 2 speed? ) is it?... over to you Stuart
Regards
Ray
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9th May 2013, 12:50 PM #7SENIOR MEMBER
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Yes, maybe there is no switch. I speculated there. I'm starting to think this motor was not mean't to have reverse on it at all. I think the owners may be mis-informing me.
Its a fairly simple chinese lathe ( 12 x 24 )
IMG_0004 (Small).JPG
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9th May 2013, 12:53 PM #8SENIOR MEMBER
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I don't want to modify it if its wasn't meant to be reversible. I just wanted to get revers working if it was meant to do that.
No, its a single speed 4 pole motor, 1 hp.
edit: Just had a thought...If the wiring WAS modified for the Australian market, The 4th wire may have been tucked back inside the motor. ( for what ever reason....)?
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9th May 2013, 01:18 PM #9
Hi Steve,
You should be able to get a wiring diagram for that, is there a model number or something that you can see.
Regards
Ray
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9th May 2013, 01:35 PM #10GOLD MEMBER
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Hi Steve,
If you do much thread cutting you'll want reverse sooner or later.
Hi Ray,
Assuming Steve's diagram is correct except M6 is indeed a center tap of the run winding.
Lets say
V=active
U=neutral
M6=neutral
What if we swap to V=neutral and U=active, leaving M6=neutral.
Havent we reversed things?
I really have no idea and am just having a stab. Dont try this at home
Stuart
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9th May 2013, 01:52 PM #11
Hi, Where do the mains connect to, and is there a diagram inside the terminal cover.
RegardsHugh
Enough is enough, more than enough is too much.
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9th May 2013, 01:57 PM #12DISCLAIMER
No liability is accepted by UBeaut or the Wood Working Forum's administrators
or moderators for advice offered by members posting replies
or asking questions regarding electrical work.
We strongly advise contacting a Licensed Tradeperson for all electrical work.WARNING
Information supplied within posts is not to be considered as detailed formal instructions to complete a task.
Members following such information do so at their own risk
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9th May 2013, 02:09 PM #13
Hi Stuart,
Short answer, there are so many ways it could be done, it's hard to tell....
Long Answer, ( after digging out Rosenberg..)
The most common type of capacitor start motor has the run windings at the bottom of the slots and start windings over the top, but displaced 90 electrical degrees, so the start poles are midway between the run poles.
The run windings will happily work either way, forward or reverse, the only thing is which way you kick it... The start winding polarity I think determines the direction that you kick it... so reversing the run winding polarity might not reverse the direction.
I'm going to guess that the extra terminal is for the external start button.
Regards
Ray
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9th May 2013, 02:14 PM #14SENIOR MEMBER
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Hi Ray,
Yes, I've got a wiring diagram in the manual but it appears to be in-correct.
It shows a 4 wire motor. It also has control wiring which the lathe does not have. It only has a rotary 3 pole switch. It appears to have 3 positions but I can't be sure as most of it is missing....
I'm guessing the the wiring was changed for the Australian market?
IMG_0004 (Medium).JPG
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9th May 2013, 02:25 PM #15SENIOR MEMBER
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I have no idea if they have ever cut any threads on this Lathe. If I had to guess, I'd say no, as they are Farm Boys, with no formal training. ( I've known them a long time. )
The 'centre tapped winding' theory is interesting. I've never heard of that in single phase motors before. ( had not much exposure to them. )
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