110v vs 240 v

[reduni]

Hi
I have the rigid 3650 table saw and love it but I am going to be doing some rewiring of my garage and would like to know if there are any benefits to running my saw in 240v as opposed to the stock 110 it is now. Is it worth the effort to put a 240 outlet just for the saw? I know the outlet could then be used for a welder or DC but I currently dont have either and I dont believe my panel would be able to handle 2 240 outlets anyways without upgrading to a 150 or 200 amp service.

Thanks for any and all help and advice

[Mike in Orangeville]

What an electrical device needs to run is watts. Watts are volts multiplied by amps. If you double the voltage you halve the amperage to get the same amount of watts (same amount of power). This means less current has to flow, so the wiring can be skinnier and still do the job. If the saw is currently wired with a gage of wire sufficient for its needs, then there is no benefit to switching to 240V. If it was barely getting by with the wire it's currently using then it could be a minor benefit.

[Gene45]

Any large motor will benefit from a 240 connection, so I you can I suggest you add it. When I did my shop the only 240 volt thingy I had was a table saw. I put a plug in the ceiling in the centre of the garage with a 240 and two 120 plugs on the same two breakers. All the tools in the centre of the shop run on the same breaker, but I can't use (say) two table saws, band saw, planer and jointer all at the same time, so it is OK.

I have used the big saw on 120 and it works much better on 240.

I also put a total of six plugs around the walls about waist high for all the other stuff. Now I wish I had put one on the big door too.

[Peter in Maple Ridge]

I just converted my ridgid tablesaw to 240V. I can't say that I've noticed a difference yet but I have not used it much.

I've read on other forums people saying that the motor runs smoother and has more power but I can't say for sure if that's true.

[Lost in the Woods]

This question comes up every two to three months it seems. Doesn't anybody ever try using the search or tag feature?

Or how about looking in the sub-forum dedicated to electrical issues, where this thread probabbly belongs in itself.

[scott in rochester]

It's not worth putting a 240v line in unless your current 120v line is struggling....lights dimming, saw is slow to come up to speed. etc. If you've got 240v already available, then there's no harm, and might be some benefit....240v tends to have less voltage loss at peak current draw, like startups and recovering from heavy load.

[Mike in Orangeville]

It's not worth putting a 240v line in unless your current 120v line is struggling....lights dimming, saw is slow to come up to speed. etc. If you've got 240v already available, then there's no harm, and might be some benefit....240v tends to have less voltage loss at peak current draw, like startups and recovering from heavy load.

Right. At times of heaviest draw the increased resistance of a smaller wire causes a voltage drop. If the wire is heavy enough for 120V in the first place then this isn't an issue, but if the saw was improperly wired in the first place, or if it's a cheap Chinese motor with windings too thin to reasonably run on 120V, anyway, then you will see a difference. A decent quality dual-voltage motor, wired properly, will run the same on 120V or 240V.

[billh]

... or if it's a cheap Chinese motor with windings too thin to reasonably run on 120V, anyway, then you will see a difference ...

If "thin" refers to the gauge of the wire it makes no difference since the current in each winding is exactly the same whether it is running off 120 or 240V. In the 120V case the 2 windings are in parallel and in the 240V case the 2 windings are in series. Each of the 2 windings has 120V across it regardless of the configuration.

billh

[Gene45]

If "thin" refers to the gauge of the wire it makes no difference since the current in each winding is exactly the same whether it is running off 120 or 240V. In the 120V case the 2 windings are in parallel and in the 240V case the 2 windings are in series. Each of the 2 windings has 120V across it regardless of the configuration.

billh

So tell me, if the windings are in series at 240 volts, how come my motor is 12 amps at 120 volts and 6 amps at 240 volts? As somebody said earlier, you get the same watts.

In series the same current must flow through both does it not?

I don't know how the motor is wired inside, I only know how to switch it from 120 to 240, or I did when I switched it. The picture and instructions are inside.

[J.P. Rap]

So tell me, if the windings are in series at 240 volts, how come my motor is 12 amps at 120 volts and 6 amps at 240 volts? As somebody said earlier, you get the same watts.

In series the same current must flow through both does it not?

I don't know how the motor is wired inside, I only know how to switch it from 120 to 240, or I did when I switched it. The picture and instructions are inside.

Because it's alternating current. In 110 V the power line (L1) goes to one end of each winding, The neutral line (L2) goes to the other end of each winding. There is 110V at each winding and each draws 6 amps for a total of 12 amps at L1.
In 220 you have a line (L1) at one end of one winding and one line (L2) at one end of the other winding and the other two winding ends are joined together. The windings draw 6 amps each and you have 6 amps at L1 and 6 amps at L2. You are still drawing a total of 12 amps.
Because it's AC, the current alternates at L1 from power to neutral at 60 times per second. L2 is out of phase with L1 and alternates opposite. When L1 is power, L2 is neutral and vise versa.
HTH

[Mike in Orangeville]

If "thin" refers to the gauge of the wire it makes no difference since the current in each winding is exactly the same whether it is running off 120 or 240V.

True. I didn't have my brain engaged when I typed that.

[billh]

So tell me, if the windings are in series at 240 volts, how come my motor is 12 amps at 120 volts and 6 amps at 240 volts? As somebody said earlier, you get the same watts.

In series the same current must flow through both does it not?

I don't know how the motor is wired inside,...

Dual-voltage motors typically have 2 coils plus the start winding coil which doesn't matter for this discussion. EDIT: This may not be totally true since in the 240V case the extra start winding current does flow through one of the run windings since the voltage has to be dropped to 120V (the start winding is always 120V so it can be used in the 120V connection as well. The start winding is a lower inductance, higher resistance coil so it does not provide the same magnetic field as a run winding.

For 120V operation the 2 coils are connected in parallel. The hot wire goes to one end of each winding and the neutral goes to the other end of each winding. Since each coil draws 6A there is a total current of 6A+6A=12A. The "power" is 12Ax120V=1440W. This is good enough for a simple discussion but being AC with a power factor it isn't quite correct.

For 240V operation the 2 coils are connected in series. There is twice the voltage but also, since they are in series, twice the impedance so the current remains the same at 6A. The coils have equal impedance so the voltage divides equally across each at 120V per coil (120V+120V=240V). A neutral is not required in this type of connection. The "power" as calculated above is 6Ax240V=1440W, exactly the same.

The heating losses in the motor from the resistance of the winding wire, the so-called "I-squaredR" losses are if we assume that each winding has a resistance of R ohms:
For 120V, 6Ax6AxR=36R watts. Since there are 2 coils in parallel the total loss is 2x36R=72R watts.

For 240V, the 2 coils in series make the total resistance inside the motor 2xR so the loss is: 6Ax6Ax2xR=72R watts, exactly the same.

This shows you do not decrease the resistive heating losses inside the motor by connecting it to 240V - which is often in the back of one's mind when first contemplating changing the voltage.

As pointed out the main benefit of using 240V is reducing the voltage drop on the supply wire from the panel by a factor of 2 and if the supply wire is sufficiently large/short then the voltage drop is too small to be a concern.

billh

[billh]

If you are interested in motor internal wiring and the colour codes used for the leads (be careful, your motor may or may not conform) here is a handy document with schematics of motor internal configurations.

Save the PDF document to your hard-drive since who knows how long the link will be available.

http://www.akmcables.com/MotorWiring.pdf

[Gene45]

Thanks billh, that makes sense. I guess I should have read yur first post more closely.

[fdaluet]

The other reason to go 220V is that for the same guage of wiring you can draw twice the number of watts.

I.E. Standard house wring is normally rated for 15A @ 110V. If you use the same wire in a 220V circuit you can still use 15A. 15A @ 110V ~ 1650W, 15A @220V ~ 3300W.

That means you can run a bigger motor without running special wiring.

As far as the same motor running at 110V or 220V I don't think there is much difference, the windings can only handle so many watts, whether they come in as 110V or 220V doesn't make much difference.

[John in Calgary]

The biggest reason you switch a motor over to 240 from 110 is for motor longevity, but this becomes less true if your wire is sized large enough for your 110 motor.

Ignoring the difference between how a 240 V motor is wired versus a 110 V motor (the end result is the same in terms of motor torque), the motor torque produced is related to the voltage at the windings (not supplied at the panel). For the same load, as the voltage at the windings goes down, the motor has to draw higher amps to make the same amount of torque. Higher amps mean a higher heat load on the motor, which means more degradation of the winding insulation, which means the motor will stop working sooner. Unfortunately, this effect is kind of like smoking - you won't be able to link the shortened life of the motor directly to using three skinny 16 gauge extension cords strung together to run your saw 10 years ago.

Now why is running the motor on 240 better than 110? Well, for a 240 motor, your amp draw is usually about half of 110 V motor on the wires between the panel (and, if the motor is big enough, even from the utility transformer) and the saw. So, for typical 110 wiring, there is a higher voltage drop to the motor windings than for typical 240 wiring. And, as I stated above, a lower voltage at the windings means more current required to drive your load, which means more heat load... This doesn't mean you can't have the same problem with 240 V wiring, its just less likely because its easier to install wiring that is big enough for the smaller amp draw.

John

P.S. I'm not an electrician, so I have no idea what would be the right size wiring for 240V vs 110V, but I have some pretty good knowledge of the torque characteristics of very large electric motors.

[stevem]

ive used my 3650 at 120 for 3 years and never had a problem, i did consider running a 240 circuit and converting the saw, but i never did
i have plenty of 120 receptacles all over my shop so i never never need an extension cord for the saw
ive resawn white oak up to 2 1/4 thick with no problems, like the saw never even slowed down that i could tell and has never over heated
i guess if i had to run it off an extension cord, it would be a different matter, but i dont
its on a regular 15 amp outlet with 14-3 wiring(all my outlets are splits) and even major resawing doesnt affect the lighting or the dust collector
i have never tripped the overload or the breaker

[fdaluet]

A single 110V @ 15A circuit normally uses 14-2, 14 guage with 2 conductors plus a bare ground wire. You have a hot, a neutral and a ground.

220V @ 15A circuits normally use a 14-3, 3 conductor plus a bare ground wire. You have two hot wires that are 180 degrees out of phase ( a.k.a. both sides af the mains), a neutral and a ground. Some circuits are 14-2, two hots and a ground with no neutral. In either case the fuses/breakers back at the panel must be tied together to ensure both hots are turned off. It is possible, but unusual, to have more than one hot going into a receptacle box that are not tied together so always check for live wires before fiddling around in a box.

[John in Calgary]

ive used my 3650 at 120 for 3 years and never had a problem, i did consider running a 240 circuit and converting the saw, but i never did
i have plenty of 120 receptacles all over my shop so i never never need an extension cord for the saw
ive resawn white oak up to 2 1/4 thick with no problems, like the saw never even slowed down that i could tell and has never over heated
i guess if i had to run it off an extension cord, it would be a different matter, but i dont
its on a regular 15 amp outlet with 14-3 wiring(all my outlets are splits) and even major resawing doesnt affect the lighting or the dust collector
i have never tripped the overload or the breaker

A motor's life is based on how long the insulation on the windings lasts. Insulation breaks down with heat load and is cumulative over the life of the motor. So, if you run a motor on 110V, but your panel is at the far end of your house instead of right next to your shop, you will have a greater voltage drop to the motor and a shorter motor life. If you run a motor on a 110V circuit with 14 gauge wires, you will have a shorter motor life than if you run it on a 220V circuit with 14 gauge wires. Similarly, if you run the motor on the same circuit as all your lights, or maybe the same circuit as the dust collector (and it doesn't trip the breaker), that will be worse than just running it on 110V on a circuit by itself.

Will you be able to tell how much shorter? Unfortunately no, that is why I likened it to smoking. It will have an effect, but you won't be able to tell in 10 years time whether it was running at 110V, or if it was because you overloaded and stalled the motor a bunch of times (which causes a higher heat load, which has a greater cumulative effect) or if it was because you got the cheaper emerging country motor instead of the good (insert country here) motor and it had more issues or cheaper winding insulation.

Unfortunately, you can't tell with only 3 years of experience, because the typical life of an industrial motor is 20-25 years under continuous use, and a consumer model 15-20 years (depending on how you use it). Do I think you are doing anything wrong with how you have run it, nah, we'll never be able to tell unless you use it daily and it dies in 5 years instead of 15.

For the record, my cheap craftsman contractors saw runs on the same 110V circuit as the garage lights, I sometimes run it to stall (lots of wet cedar definitely causes me grief!), but I'm not too worried about letting the smoke out because one day I will likely upgrade. In the mean time, I will someday run 110V circuits on 12-3 wiring (so I can split plugs too) when I get around to it and will also have a couple of 240V circuits run at the same time.

John

[stevem]

yes i hear your point, my 3650 runs sometimes for hours on end, like 10 hours or more, mostly with no load, just iddling, i rarely shut if off during a days work
my electrical setup is simple, my panel is in the garage, saw is 20 feet away, all receptacles are splits like your kitchen countertop receptacles
so my saw gets 120 regardless of load minus line losses
my dust collector is on the same circuit but on the opposites phase, ie on the "other side" of the neutral
so they cancel on the neutral leg just like split kitchen outlets
a good friend of mine is an electrical inspector and he described the situation to me and why its safe
split circuits are designed so that 120 volt is available on both sides of a kitchen receptacle, ie for a toasteroven and say a kettle usually way over the 15 amp breaker
but each side of those plugs are fed from a differnet breaker on ooposite sides of the neutral so one is 120 positive the other 120 negative and the neu
tral current is far reduced
ok this is a simplification, but two 15 amp appliances in a kitchen plugged into a "split" receptacle will give a zero current on the neutral leg
and thats the way i wired my shop, with the full agreement with the ESA
i can startup my tablesaw, jointer, planer and dust collector and run them all day and have many times with no problems
every tool runs on 120 v no prob
ok so maybe the'd run better on 240, i know half the current but lets be practical here
slo newbies/beginers, dont be scared off here, chances are pretty damn good that the single outlet in your garage will do you just fine for quite a while, mine did me for a long time
later you'll want extra outlets, lights, etc etc and heat, you'll get there
but a separate 100 amp box, or12 circuits in a garage?
never need it!!