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anyone here know what the resistance of a TS motor field coil should be?

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Forum topic by captainmorgan posted 02-10-2019 09:49 PM 587 views 0 times favorited 12 replies Add to Favorites Watch
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captainmorgan

16 posts in 16 days


02-10-2019 09:49 PM

I’m trying to troubleshoot a unisaw single phase motor i just rebuilt (new bearings and cleanout) and am measuring a resistance of 0.5 ohms across the field coil – well across the red and white wires to the switch – (should be the same resistance though Im guessing) – at first I was thinking I had a dead short but in all the articles i’ve been poring over it seems (?) that the field coil resistance may actually be QUITE low … i just wanted to verify with someone with some hands on experience here …

http://lumberjocks.com/topics/303029


12 replies so far

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ibewjon

161 posts in 3064 days


#1 posted 02-10-2019 10:04 PM

I just put my Fluke meter across the plug of my TS motor. The leads dead shorted are .2 ohms. Add in the motor, cord and switch and it goes to .9 ohms. This is a 2 HP motor wired for 120 volts. Hope this helps.

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captainmorgan

16 posts in 16 days


#2 posted 02-10-2019 10:15 PM

ok thanks – that’s encouraging – plugged the motor in and just got a BUZZ – i checked the capacitor start switch inside the cover plate and it was distorted and not making contact so i figured that was it – then put it back together and tested again – STILL doing it … HMMMMM (scratching head)

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captainmorgan

16 posts in 16 days


#3 posted 02-11-2019 12:01 AM

OH – just had a realization … do you think that if the copper plate (centrifugal switch plate) is in contact with the shaft that it’s shorting out the start capacitor?? kind of a ‘duh’ moment but i’m amazed i’ve seen nothing on this …

the problem is it’s impossible to know if it’s coming into contact with the shaft once the motor end caps are on …

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ibewjon

161 posts in 3064 days


#4 posted 02-11-2019 01:19 AM

If it is a short it should trip the breaker, depending on breaker brand. Some breakers were designed to trip on overload only, not short circuit. If motor hums but won’t start, I would replace the capacitor. Not a high dollar item.

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captainmorgan

16 posts in 16 days


#5 posted 02-11-2019 02:54 AM

thanks – no breakers being tripped – but i don’t have the guts to leave power connected for more than is long enough to hear it’s humming and not starting up – yes already checked the cap – seems just fine mostly – but the weird thing is – the contact terminal on the centrifugal switch does not seem to make connection with the contact itself – so in all orientations i do not see HOW it’s possible that the capacitor charge can actually get to the starting coil … hmmmm … curiouser and curiouser …maybe there’s a part that came out i didnt’ notice at some point bridging the two?? no idea … going to google images of the centrifulgal switch – there dont’ seem to be many (or any in fact) diagrams of a centrifugal switch assembly for a rockwell 83-621 motor online – would sure be nice to see one.

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captainmorgan

16 posts in 16 days


#6 posted 02-11-2019 03:08 AM

OK – just as i suspected… I’M AN IDIOT – seems to be the reason for most of the problems i have with electrical and mechanical equipment! but at least thinking about the above issue seems to have gotten me going in the right direction! I was looking at this video for clues (even though my motor and switch are nothing iike it) – https://www.youtube.com/watch?v=M-j6PhthXJY at 4.05 they show the contact of the switch – and i realized (NO WONDER THEY WEREN’t CONNECTED) – THE CONTACT iS SUPPOSED TO BE BETWEEN THE TWO SIDES – if you look at that moment in the video you will see what i mean – the clue was right there in the pic in my original post too! gosh … well anwyay – i haven’t hooked up yet but this changes everything electrically speaking – makes WAY more sense thanks

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ibewjon

161 posts in 3064 days


#7 posted 02-11-2019 03:17 AM

How did you test the capacitor and decide it is good? A meter or eyes? Just fine mostly? Not laughing at you, just wondering what that means. You are not an idiot, you just have different experiences and knowledge. These forums are here to trade knowledge and experience.

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captainmorgan

16 posts in 16 days


#8 posted 02-11-2019 03:22 AM

yes ibewjon – not to worry – when i say ‘idiot’ it’s just meant to be self effacing – not a final judgement! :)

i tested the cap with a DVM and ESR tester … not to mention the fact that the motor was starting just FINE before I started the motor teardown – i see no reason why it would suddenly stop working … the only weird thing about the cap is that it was a very tight fit under it’s housing and I can’t see how it wasn’t shorting under there – there was absolutely no insulation between terminals and the cover – except for all the sawdust in there … god only knows how it got in .. unless that was someone’s idea of ‘shadetree’ insulation

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captainmorgan

16 posts in 16 days


#9 posted 02-11-2019 03:24 AM

can’t really blame myself THAT much though – considering by the time i got the motor cover off the switch had already come out from between the contact terminals … anyway- hopefully one day someone else will see this post and it will help (?)

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captainmorgan

16 posts in 16 days


#10 posted 02-11-2019 03:54 AM

SPINS!! crossing fingers for everything else to go okay now :) thanks all

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captainmorgan

16 posts in 16 days


#11 posted 02-11-2019 04:48 AM

now to mount the damned thing in the TS … :P

so far no fun had

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MrUnix

7186 posts in 2469 days


#12 posted 02-11-2019 06:12 PM

now to mount the damned thing in the TS … :P
- captainmorgan

Don’t make it harder than it needs to be:

Chair with some 2×4’s and your body weight makes it easy :)

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

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