# how do you rewire a 1952 Delta Unisaw Rockwell Milwaukee table saw from 230 (220) to 115 (110)?



## bbbben (Dec 26, 2014)

I would like to rewire the Delta table saw I just got from my grandfather from 220 to 110. I opened up the side of the motor and was surprised to find that the wires from the motor are numbered 1, 2, 3, and 4 … not colored (as the diagram on the motor indicates)!

*Does anyone know how I should rewire this motor for 110?*

Currently it is wired as follows (for 220):
1 to white
2 to 3
4 to black
green on screw to green on 220 plug

I bet it should be as follows for 110, but I want to make sure:
1 & 2 to white
3 & 4 to black
green on screw to green on 110 plug

Here is a photo of the diagram on the motor:









Here is a photo of the table saw:









Delta Rockwell Milwaukee table saw
CAT = MK-85B010
H.P. = 1
R.P.M. = 1725
Type = SR
Volts = 115/230
Amp. = 11.8/5.9
I based the year (1952) off the serial number

Thank you so much for any help you can provide!!!


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## Tennessee (Jul 8, 2011)

You are probably correct, but this is probably a motor with a start winding and a run winding and at 230 VAC they might have wired the start winding out of the picture. But I am guessing.

What I think did happen is the motor got rewound somewhere along the line, and the rewind shop put in the standard wire numbers and used all one color lead wire, which would be typical for a rewind shop.


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## bbbben (Dec 26, 2014)

Thank you for your input, Tennessee.


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## Dal300 (Aug 4, 2011)

Pull it out, take it down to your local electric motor shop and let them rewire it. 
I would spend the extra money and have them go through and replace everything that needed it and let you know what condition the motor is in.


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## dhazelton (Feb 11, 2012)

You'd actually be better off spending that same money to put in a 220 outlet. The saw will thank you.


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## bbbben (Dec 26, 2014)

More good input, thanks. I have decided not to put in a 220 plug because it would cost too much to run 220 to my detached car port… there's already 110 out there…and I'm not worried about the cost of drawing twice as many amps with it not being used daily.


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## johnstoneb (Jun 14, 2012)

220 and 110 draw the same amps. With 220 the load is split half the amps go down one leg and half down the other leg. You'll get more torque and a quicker startup with the 220. It may run cooler on 220 also. 
I would do as Dallas suggests. That is a 60year old motor probably still good but needing serviced. That would be a lot cheaper than replacing the motor because it needed a service and din't get it.


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## Dal300 (Aug 4, 2011)

*Bruce*, Not actually true.

120V draws twice as many amps as 240V because everything comes down to power consumed, This is expressed in watts. 
The formula for determining watts is V x A = P (P is expressed as watts).
In a perfect world without friction or other losses, 1 HP equal 746 watts. Real life makes it about 800 watts.

Therefore, using the 800 watt figure, 800w / 240v = 3.333a.
With 800w / 120v = 6.66a

HP, and watts always stay the same. Any change in voltage or current draw will effect the wattage number.


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## CypressAndPine (Jun 14, 2013)

Dallas is correct. 120V will draw twice the amps.

You are correct
1&2 to white 
3&4 to black. Run it like this without WITHOUT A BLADE and check that rotation is correct.

If the motor spins the wrong way wire it as follows:

1&3 to white
2&4 to black

Be sure your earth cable (green) is grounded properly to the motor frame or machine frame. Also remember to test it without the blade to be extra safe. Have plug in hand in case there is a short circuit so you can unplug it quickly. It should work, but be safe because it looks like an old motor.

I am an industrial electrician so I hope you can trust me.

Jacob


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## chrisstef (Mar 3, 2010)

Great score on a bullet motor uni. Shes a keepah!


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## TopamaxSurvivor (May 2, 2008)

I'm going to disagree. 1 & 2 are probably the ends of winding #1. 3 & 4 are probably the ends of winding #2.

1&3 to white and 2&4 to black should work for 120 volts. If it hums or blows your breaker, the winding are opposing one another. Reversing the wires will not reverse the rotation of this motor.


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## REO (Sep 20, 2012)

it is easy to check with an ohm meter to find which are opposing ends of the windings. For low voltage the windings are in paralell for high voltage the windings are in series. for those who say that there is a different draw current remains constant. Amps x volts = watts (power) therefore 110 volts 11.8 amps 1298 watts (low voltage). 220 volts 5.9 amps 1298 watts high voltage. The noticeable start up difference and a lower power on low voltage can usually be attributed to the connection wire size and voltage drop. if you want to run heavy gauge wire to the saw it will start just as fast and generate the same power. The power remains constant and heat generation is the same because the windings actually carry the same current in both configurations.
Just an experiment: plug a circular saw directly into an outlet and pull the trigger. The plug the saw into a 100 foot cord and the cord into the outlet and pull the trigger. There will be a noticeable difference even with a heavy gage cord.


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## bbbben (Dec 26, 2014)

Thanks again, everyone, for responding! Every bit of input is appreciated.

*Reo, do you mind going into more detail as to how I would use an ohm meter (voltage meter?) to make sure I wire it correctly for low voltage? (I am grateful for your patience explaining things that are most likely very elementary!)*


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## REO (Sep 20, 2012)

if you have a reading or continuity between two leads they have to be a continuous winding. if there is no reading then they are different windings.

Make sure all the leads are separate. put your meter or tester on 1 and 2. if they are both ends of the same winding then your meter will light beep or display a reading other than 0 or OL.
it could be 1-2 (A) 3-4 (B) or it could be 1-3 (A) 2-4 (B) you cant tell for sure without testing
if you GET a reading on 1-2
1-3-white 2-4-black
if you DONT GET a reading on 1-2
1-2-white 3-4-black
white and black from the cord can be switched around and make no difference.
switch off. plug in the saw without the blade and quickly switch the saw on and off again checking for movement and rotation. in a four wire dual voltage motor it is possible to reverse rotation by changing two leads.
check this far and get back if the direction is wrong or it just hums or buzzes.


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## Dal300 (Aug 4, 2011)

Reo, I disagree about your figure of 1298 watts per HP, except under certain unusual conditions. It's nearly as far off as my 746 watts. I have history and math on my side, along with the ratings on the motor pictured above.
Curiosity leads me to ask where the 1298 watt figure comes from. 
I'm seriously not trying to start an argument, but I have never heard that figure before. I would like to find out the reasoning behind it.

Most of the time, I figure 1Kw per HP, it makes life easier.

Horsepower and watts are both units of power, just from different systems of measurement. One horsepower (interestingly the horsepower was defined by James Watt) is 33000 lbf x ft/min (lbf = pound force). One watt (of course named after James Watt) is defined as 1 N x m/s (N=newton). To convert simply convert each underlying unit:

33000 lbf x ft/min x (1 min / 60 s) x (4.448 N / 1 lbf) x (1 m / 3.28 ft) = 745.85 N x m/s = 745.85 W

It doesn't matter what type of power we are talking about, the conversion between HP and W is fixed.

The difficulty when dealing with electric motors is (1) motors are rated by the number of HP they deliver (under very specific conditions) and (2) we are generally concerned with the current which they draw. The 745.85 W/HP conversion factor would only apply for a perfect (100% efficient) motor which presents a purely resistive load. A real motor will have less than 100% efficiency (consuming more power than is delivered to the load) and will present a reactive load (meaning that the current draw is higher than the number of watts consumed would indicate).


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## klassenl (Feb 13, 2011)

> Reo, I disagree about your figure of 1298 watts per HP, except under certain unusual conditions. It s nearly as far off as my 746 watts.
> - Dallas


All Reo did here was apply Ohm's law (in one of it's forms) Watts = Volts * Amps. There is where 1298 comes from.


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## REO (Sep 20, 2012)

Dallas I was using the same formula: Ohms law
your assumption is correct my product and your product would generate exactly the same inaccuracy. LOL I never said that anyone was wrong that said that it will draw twice the amps. My point was that both use the same amount of power. volts up amps down, volts down amps up, like a see saw, that maintains the constant of the equation being Watts.

This conversation takes place several times a year in forums all over the web. Without direct testing and monitoring exact losses and output cannot be determined for a motor. nameplate ratings are an average found over several test samples not just picked out of the air.

I have read examples where people claim that when wired for 110 the manufacturer has made special windings that de-rate the motor to use just under what a 110 breaker will take and that the only way to truly achieve the potential of the motor it must be wired for 220. since all the windings are used in both scenarios the "special winding" would have an effect at both voltages!

The bottom line is that the same windings are used. In the case of 110 v power is split into two windings in a parallel arrangement. in the case of 220 v the windings are in series. 110 is one phase of power to neutral having an amplitude of 110. This alternates from positive to negative 60 times a second here in the US. 220 is also 110 volts to neutral which is why you can "split" 220v into two 110v circuits BUT the phases are 180 degrees apart so when the phases are at their peak (one at 100+ and the other at 110-) you get a reading of 220.

So lets apply Ohms law. Just for example and to make it easy to follow we will use voltages of 100, 200 and windings with a rating of 10 Ohms.
to calculate ohms in a series pair we add the resistance value, so 10 +10=20
for parallel the equation is one devided by the added reciprocals or 1/10+1/10=1/20 or .2. 1/.2=5

One of the Ohms law derivatives states: E squared divided by R= P.

100vx100v=10000 10000/5=2000
200vx200v=40000 40000/20=2000
Power IS the same whether you use 100 or 200 volts. inefficiency will be the same because the same windings are used!

it is the added inefficiency through added resistance of the power cord that lend to slower starts and decreased power at the saw. Start ups take MUCH more than the nameplate rating for a moment but not long enough to take out the breaker. like sucking a shake through a small diameter straw or a large diameter straw. small diameter=restricted delivery large diameter=faster delivery. this does not equate to higher voltage. In this scenario higher voltage would be higher atmospheric pressure lol. increase the diameter of the wires to reduce resistance.


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## Dal300 (Aug 4, 2011)

Thanks for clearing that up, sometimes my drugs mess up thought processes.

When I multiply 115v x 11.8a I get 1357w. The same answer with 230v x 5.9a.

Since I haven't had my days ration of drugs yet today I can see you used 110v and 220v.

I apologize for any mix up.

I spent half my time a few years ago explaining these same things to RV owners and explaining why they had 11,000 watts available with a 220v line but only 3300 watts with a 110v line.


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## bbbben (Dec 26, 2014)

*My saw is up and running!*

*Thank you all for your help! Thank you Reo for the very detailed, helpful instructions!*

For the sake of archiving an answer = 1&3 had continuity (beeped with an ohm meter) and so did 2&4. So I connected 1&2 to white and 3&4 to black and my 1952 Delta Rockwell table saw works perfectly at 110volts.


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## Bluepine38 (Dec 14, 2009)

That is what was called a bullet motor as well as induction repulsion motor. If you ever take it apart, be aware
that the motor has to be timed properly after it is put back together for it to work properly.


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## REO (Sep 20, 2012)

Great Job Ben!!
Dallas, No sweat! it made me do some digging for the right information.


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## pjones46 (Mar 1, 2011)

From the motor plate shown it indicates Green & Red to one side of incoming power and black & Yellow to the other side of incoming power as Jacob said 1&2 to White and 3&4 to black.


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## andrew14 (Jan 9, 2016)

Hi I am rewiring my 1952 bullet delta Unisaw from 120 to 220 and have colour code wires. However when I follow the instructions on the plate (join the red and yellow and then connect the black to the black and the geen to the whitefrom the power supply) it runs but doesn't get to full speed and makes a strange noise. Has anyone had this problem or know the answer?


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## MrUnix (May 18, 2012)

> it runs but doesn't get to full speed and makes a strange noise. Has anyone had this problem or know the answer?


Did it run at full speed on 120v?

Cheers,
Brad

(Initial suspicion is a faulty shorting necklace)


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## Bluepine38 (Dec 14, 2009)

As I stated above these bullet type repulsion induction motors have to be timed, there is a plate on the 
inside that has to be rotated, it is marked F and R for forward and reverse if I remember correctly, if the 
plate is not in the right position-the motor is not timed- and it will not start, or if it starts it will not rotate
right. That noise you hear might be the brushes arcing on the armature, which could ruin the armature.
This is just a possibility since I can not hear the motor or check it out. When changing voltage, I am 
sure that the motor has to be retimed for the new voltage. If the brushes were arcing, the armature
will have to be turned and the ends of the brushes smoothed.


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## andrew14 (Jan 9, 2016)

The motor worked perfectly at 120, it tries to turn in the right direction now but won't quite get going. So I will be checking the timing tomorrow.

Andrew 60 year apprentice carpenter


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## MrUnix (May 18, 2012)

> The motor worked perfectly at 120, it tries to turn in the right direction now but won t quite get going. So I will be checking the timing tomorrow.
> - andrew14


Is there any particular reason for switching it to 240v? If it ran fine on 120v, I'd be inclined to leave it alone. I've also never heard of the need to adjust the brush holder when switching voltages, but it might still be a good idea to adjust it for maximum startup torque anyway. There are several good threads describing similar problems (slow startup, sometimes up to 45 seconds or more until the shorting necklace functions, etc..) over at OWWM in the 'everything electrical' section that you may want to review. There is also some good info on the VintageMachinery Wiki regarding troubleshooting and repairing the bullet motors.

Cheers,
Brad


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## TopamaxSurvivor (May 2, 2008)

> The motor worked perfectly at 120, it tries to turn in the right direction now but won t quite get going. So I will be checking the timing tomorrow.
> 
> Andrew 60 year apprentice carpenter
> 
> - andrew14


You don't have it wired correctly for 220. You will just cause yourself more grief if you take it apart.


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## MrUnix (May 18, 2012)

Might be obvious, but have you also made sure you are supplying 240v to the motor?

Cheers,
Brad


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## TopamaxSurvivor (May 2, 2008)

That is a good point. The last 220 problem I remember on here only had 120 ;-)


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## andrew14 (Jan 9, 2016)

Thanks Guys, but yes the supply is 220, checked with my meter. It is snowing here today, too cold to sped time on the floor in the shop.


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## MrUnix (May 18, 2012)

> Thanks Guys, but yes the supply is 220, checked with my meter. It is snowing here today, too cold to sped time on the floor in the shop.
> - andrew14


Just switch it back to 120v and start making stuff 

Cheers,
Brad


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## stopecat23 (Jun 24, 2016)

I suspect that what we have here is a repulsion start - induction run motor. Notice where the label says REP. IND. 
MOTOR. These motors have a wound rotor with a commutator and a set of brushes. There is NO starting winding.
The rotation of this type of motor is reversed by shifting the position of the brush holder. As with all dual voltage single phase motors, the windings are in two parts. For low voltage they are connected in parallel - for high voltage they are connected in series. As one other post pointed out, the two parts of the windings must not be connected opposing each other. 
Repulsion start motors are fairly common on old air compressors. They have very high starting torque. However, they are much more complicated and expensive to manufacture than a capacitor start single phase motor.
Also you might have a repulsion motor. The difference is that the repulsion start/ induction run motor has a centrifugal device that shorts the rotor windings at running speed so that it runs as an ordinary induction motor. So if you find a set of brushes inside the motor, you have one of these two types of motors.


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## Notbrick (Feb 6, 2018)

> *My saw is up and running!*
> 
> *Thank you all for your help! Thank you Reo for the very detailed, helpful instructions!*
> 
> ...


To not start another thread, Ill bring this back up. I too am taking this same motor and switching from 220 to 110.

Two questions:
1) I will need to remove this motor from the cabinet, yes?
2) Is all the work required of connecting the correct wires in the motor junction box? , or do I need to do any disassembly of the motor and mess with timing?

From my 1945 Delta Unsiaw. 1 HP, 1 Phase, 110/220


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## MrUnix (May 18, 2012)

> Two questions:
> 1) I will need to remove this motor from the cabinet, yes?
> 2) Is all the work required of connecting the correct wires in the motor junction box? , or do I need to do any disassembly of the motor and mess with timing?
> - Notbrick


1 - no, you should be able to get to the wiring box on the motor without removing it. Might be a bit tight though.
2 - yes, just move some wires and you are done, provided that yours is one of the older machines that just has a on/off flip switch. If you have a starter, then there is more work to be done.

Cheers,
Brad


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## Notbrick (Feb 6, 2018)

Thank you Brad,

I appreciate you helping me with my original post about identifying my saw. I still have yet to post more detailed photos of that. I may start a blog for the site. It has the original switch, but was essentially bypassed to the newer safety-switch.

The saw will be on a 120 volt, 20 amp circuit. No other loads will be on the circuit at the time. With 1hp, 1Phase, I don't see it being a problem. Now to open the box, see what is currently wired, and go from there with the motor still in place.


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## runswithscissors (Nov 8, 2012)

1725 rpm with a 1 hp motor seems like it will not be a high performance saw. Doubling blade speed with different pulley diameters will result in less power at the blade.


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