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Posted: 12/6/2018 12:10:13 AM EDT
ETA: Hopefully I can simply reverse the 3/4 horse motor I have, an induction motor the motor came off of a belt grinder and does not have indicate if it is, or is not, reversible on its name plate. Hopefully it is. i might eventually add a switch to make it run either direction, but in the mean time I am just trying to figure out how to make it run backwards w/o frying it.
I cannot get the housing apart, all I can see it winding through the holes in one end and the fan through the other end. Not sure if there is a second capacitor or centrifugal switch or anything in there as well. Here is the underside, can you say what these parts are? 
The black thing is just the backside of the power switch. On the right is a small coil w/ three wires terminated to three of four terminals. The black is the power coming in off the power switch. I am holding a round ac capacitor out of the way, has a brown going in and back out to one of the terminal of the thing w/ the coil you see. The capacitor says "Seka 125Vac Motor starting" Then a gray wire is on thing w/ the coil too and it goes into the motor. Here is from the other side. 
Any help on how to go about switching direction would be greatly appreciated!! |
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Posted: 12/6/2018 5:07:38 AM EDT
[#1]
Apprently reversing an induction motor can be done if you reverse the polarity of the secondary winding...
This guy explains it REALLY well https://youtu.be/__nS3OelY-s https://youtu.be/__nS3OelY-s |
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Posted: 12/6/2018 5:35:52 AM EDT
[#2]
Many furnace motors are reversible, you just change a couple wires around inside the housing, they are just spade connectors so it takes just a minute. Usually need needle nose pliers to do it.
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Posted: 12/6/2018 3:07:38 PM EDT
[#3]
I changed the OP, added pics etc.
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Posted: 12/6/2018 3:53:40 PM EDT
[#4]
Changing the correct winding leads should reverse the motor. The little black plastic bit with the copper coils is a starter relay. It kicks in when the motor is first switched on while the current is high, then drops out after the motor is up to speed and the current that the motor is drawing falls off. This takes the place of a centrifugal switch. The black thing on the left that you surmised was a relay is the on/off switch!
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Posted: 12/6/2018 3:58:51 PM EDT
[#5]
So I turned it on w/ it on its back and I notice that the AC capacitor ("Motor starting") was letting out a stream of magic smoke after it was running for about 10 seconds, and it was very hot to the touch. Hopefully it can hang on long enough for me to figure out how to reverse...
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Posted: 12/6/2018 4:02:37 PM EDT
[#6]
You have three wires going into the motor:: white, grey and brown.
Reverse the grey and brown wires. |
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Posted: 12/6/2018 4:14:47 PM EDT
[#7]
If you're getting the magic smoke you have a problem. Which wires did you switch? Sometimes this isn't as simple as reversing a couple motor leads, you actually have to take the motor apart and switch the actual winding leads around.
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Posted: 12/6/2018 4:16:54 PM EDT
[#8]
Read this for some insight:
https://woodgears.ca/motors/reversing.html |
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Posted: 12/6/2018 4:20:42 PM EDT
[#9]
Quote HistoryQuoted:
You have three wires going into the motor:: white, grey and brown. Reverse the grey and brown wires. |
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Posted: 12/6/2018 4:36:13 PM EDT
[#10]
@MitchAlsup
I swapped the brown and gray wires but it still runs normally. Swapping the terminals did not reverse the polarity of the starter winding, or maybe it is b/c the cap burned out? I need to read the terminals of the relay for continuity when the unit is off and on... ETA: to reverse polarity of one of the coils, and therefore reverse the phase shift between the starter & running coils you have to swap both wires of one or the other coil. I cannot as both coils are bonded together at one end w/ the neutral wire. This is one of those non-reversible bean counter specials. More detail at end of thread. |
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Posted: 12/6/2018 5:45:19 PM EDT
[#11]
Quote HistoryQuoted:
If you're getting the magic smoke you have a problem. Which wires did you switch? Sometimes this isn't as simple as reversing a couple motor leads, you actually have to take the motor apart and switch the actual winding leads around. ETA: for some reason the stater coil is apparently not shutting off after the motor gets up to speed, the cap is smoking b/c that relay is not working and the starter coil is never shutting off so that cap is getting constant current that it is not designed to have. |
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Posted: 12/6/2018 5:56:06 PM EDT
[#12]
Quote HistoryQuoted:
Read this for some insight: https://woodgears.ca/motors/reversing.html I'll read it over. My motor does have 3, not two wires going into it, one hot for each coil (presumably) and the neutral. But swapping the terminal off of the starter relay does not do the trick. |
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Posted: 12/6/2018 11:35:52 PM EDT
[#13]
ETA: from that guys blog:
The wires to reverse are always the wires that lead to the starter winding.
If you have a motor where the label is missing, the starter winding typically has about three times the electrical resistance of the main winding and is always in series with the starter switch and capacitor (if there is one). If you can isolate both ends of this winding and swap them, you can reverse the motor. If however there are only three wires coming out of the windings, then the main and starter windings have one end tied together and the motor is not reversible. 
So, yes, I will have to swap the thing around mechanically in its housing, or just disable the starter winding and push start the motor before flipping the switch, if I do that I'll probably tie a wood starter stick to the work station so I don't run chance of my hand getting stuck between the belt and rest lol. |
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Posted: 12/6/2018 11:56:36 PM EDT
[#14]
Quote HistoryQuoted:
Changing the correct winding leads should reverse the motor. The little black plastic bit with the copper coils is a starter relay. It kicks in when the motor is first switched on while the current is high, then drops out after the motor is up to speed and the current that the motor is drawing falls off. This takes the place of a centrifugal switch. ... But, this starter relay, is it like a mechanical or solid state relay that opens/closes? How does it know when to open to turn off the stater coil? There is the power going into it from the power switch, coming out there is the wire that goes through the capacitor to the starter coil (brown) and the other wire that goes out tot he main/running coil (grey). But where is the circuit or linkage to tell it to open the stater coil circuit after it gets up to speed? How does it work? Just wondering generally. If I google this I mostly get results about car starters and solenoids. Thanks everyone! I leased a lot anyway and I can afford the new grinder assembly if I can use this motor, for a while, anyway. |
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Posted: 12/7/2018 12:44:54 AM EDT
[#15]
How about if you knock the end covers off and swap them left to right. That'll put your shaft on the opposite side, then turn the motor around so the shaft is back on the right side, you should end up with it turning reversed then.
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Posted: 12/7/2018 12:33:32 PM EDT
[#16]
The relay works because of the increased current drawn as the motor starts up. As the motor comes up to speed, the current drawn drops off drastically. So when the current is high, the coil on the relay generates a strong magnetic field, drawing the solenoid toward the coil and closing a contact that puts the capacitor in series with the start winding. As the current drops the magnetic field weakens, allowing the solenoid to be pulled back open by a spring (or sometimes even gravity) and removing the capacitor (and start winding) from the circuit. Turning your motor upside down may be causing the magic smoke problem - especially if your start relay is the gravity version.
You CAN still reverse your motor, you just need to cut the bonded windings apart and reconnect them in the manner that reverses your motor. That's what I meant when I mentioned earlier taking the motor apart - you need to get to the windings. Some motors this is pretty easy, some not so much. The higher end motors will have this connection external to the can in a junction box so it can be easily switched. The start winding basically just "kicks" the motor in whichever direction you want it to start with a good boost of current to get it moving quick. This is why the start winding is easy to identify - they are always the one that consists of the larger diameter wire. |
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Posted: 12/7/2018 1:00:37 PM EDT
[#17]
@sneaker
Thank you SO Much. That makes great sense how the starting coil pulls lots of current through that relay coil opens or closes a contact until the motor comes up to speed and the current drops. That switch is definitely not working, hence the cap cooking. But maybe that is just b/c of its orientation. I found some new caps that will fit right in there. as for making it switch, maybe when I beat the housing apart I will be able to get at where the starter and running coils are bonded together and make separate leads coming out. |
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Posted: 12/7/2018 1:03:54 PM EDT
[#18]
Quote HistoryQuoted:
How about if you knock the end covers off and swap them left to right. That'll put your shaft on the opposite side, then turn the motor around so the shaft is back on the right side, you should end up with it turning reversed then. |
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Posted: 12/7/2018 1:52:03 PM EDT
[#19]
You're welcome, glad it was helpful. Regarding the push start - if you want to disable the start winding you'll be just fine. I have a beater bench grinder that has a failed centrifugal switch. I hand start it all the time. It's been years, just haven't been motivated to fix it. It still works just fine after a push start. Be very careful with the magic smoke situation if you want to actually reverse the motor with the windings though - if it's overheating that much you can easily cook the insulation right off of the start winding, which will make it unusable. In that case, you'd need to rewind the motor to use the starting function - not an easy task for the novice.
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Posted: 12/7/2018 2:05:53 PM EDT
[#20]
I did pull that relay out of the thing so that I could shake it back-and-forth and the solenoid rattles around in there free, it is NOT spring loaded.
Upright and off the switch is open to the starting coil. Starting the motor induces the field and lifts the solenoid closing the power to the AC cap and the starting winding, then when current falls gravity would make the solenoid fall and the starting coil circuit, and cap would shut off. I got another cap of amazon for $5, so no biggie. Looks like i might be able to beat the ends of the housing off w a hammer screw driver to either flip the whole thing around or get at the ends of the windings. I should be able to tell them based on what wires are terminated to them. Thanks so much! |
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Posted: 12/9/2018 6:38:18 PM EDT
[#21]
I recently reversed a non reversible induction motor (a 2hp air compressor motor) to run my 2x48 grinder.
The start and run windings were terminated together in mine as well. I ended up carefully untying and getting the ends of the windings out so I could work with them. They we're just crimped together with what basically ammounted to butt connectors. I then cut both ends of the start windings and switched them, then connected everything back up with insulated butt connectors. Make sure that you get everything tucked back out of the way, other the shaft will grab your handiwork and rip a bunch of stuff up, resulting in emergency exploratory surgery in the motor to get it working again. My next project is to figure out how to wire a switch in (it's 240v), because as it sits now, I "turn it on and off" by unplugging or plugging it in. |
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Posted: 12/10/2018 3:09:15 PM EDT
[#22]
I believe tou just hace to put an I/0 on one leg only as each leg goes through eachother after the load...
Only diff is that in a single pole switch tou will still have 1 pole of power present inside the housing w switch open and the unit plugged in. A light switch should work even, if it is rated for the amperage. |
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Posted: 12/10/2018 11:28:43 PM EDT
[#23]
Quote HistoryQuoted:
I believe tou just hace to put an I/0 on one leg only as each leg goes through eachother after the load... Only diff is that in a single pole switch tou will still have 1 pole of power present inside the housing w switch open and the unit plugged in. A light switch should work even, if it is rated for the amperage. I'll give it a try when I get time to go shopping |
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Posted: 12/11/2018 5:33:17 AM EDT
[#24]
That's a very iffy way of doing it. I wouldn't do that. I'd advise getting a DPST (double pole single throw) switch and doing it right. Both hot legs should be switched, don't leave one hot all the time.
Edit: you can get one at a home store that will handle most motors for not much more than doing it the wrong way: https://www.homedepot.com/p/Leviton-30-Amp-Industrial-Double-Pole-Switch-White-R62-03032-2WS/100356941 |
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Posted: 12/11/2018 9:49:36 PM EDT
[#25]
Quote HistoryQuoted:
That's a very iffy way of doing it. I wouldn't do that. I'd advise getting a DPST (double pole single throw) switch and doing it right. Both hot legs should be switched, don't leave one hot all the time. Edit: you can get one at a home store that will handle most motors for not much more than doing it the wrong way: https://www.homedepot.com/p/Leviton-30-Amp-Industrial-Double-Pole-Switch-White-R62-03032-2WS/100356941 Awesome, Thank you. I definitely want to do it right. Especially since I don't know as much as I probably should to be messing around too much with AC electricity. |
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Posted: 12/12/2018 2:30:21 PM EDT
[#26]
Yeah, like I said, if tou only switch one pole it will turn off but you will always have one pole still hot in the init even if the switch is off. A double pole seitch is definitely safer.
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Posted: 12/14/2018 11:18:39 PM EDT
[#27]
Yep. And I understand that - including how to work safely around it by cutting the power at the breaker first. But always remember, giving advice on the internet, anyone could be reading. Including folks who think that if the switch is "off" then so is all the electricity. In this particular case, flipping the switch and then touching wires could get someone killed.
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Posted: 12/15/2018 12:40:25 PM EDT
[#28]
I picked up a 30amp double pole switch, box and cover this week. I'm going to try to get it installed this morning. Thanks for the help.
Did the OP have any luck getting his motor reversed? |
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Posted: 12/15/2018 5:29:58 PM EDT
[#29]
Yeah, if i disable starting windong i can push start it in either direction
To do it proper id have to flip motor in housing or seperate the windongs and invert terminations. |
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Posted: 12/15/2018 7:53:35 PM EDT
[#30]
I pulled mine apart and reversed the connections for the start windings. It really wasn't hard. It took about 30 minutes, start to finish, with a catastrophic mistake made in the middle.
If the housing is symmetrical, swapping ends would be really fast. |
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Posted: 12/15/2018 11:30:26 PM EDT
[#31]
Quote HistoryQuoted:
Apprently reversing an induction motor can be done if you reverse the polarity of the secondary winding... This guy explains it REALLY well https://youtu.be/__nS3OelY-s https://youtu.be/__nS3OelY-s 
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