Bandsaw 120/240???

[Jason Solodow]

So, my bandsaw is a 3/4hp 120/240 motor. It is currently wired for 120, but I'm considering rewiring it for 240 volts. What do you guys think? Is it worth changing it to 240? Am I going to notice much of a difference?

[Tom Veatch]

Depending on the specific circumstances, primarily resistance/impedance in the lines between the supply transformer and the outlet, you might see an improvement going to 240volts. If I already had 240v available, I'd go ahead and make the change.

Otherwise, it's probably not worth running a new circuit. Any improvement would be due to lowered line losses due to the decreased amperage. Although there are a few with higher line losses that do see noticable benefit, most see no significant improvement. Because of the way the coils are wired (series for 240v, parallel for 120v), the motor coils see the same voltage either way. Therefore, any performace difference is due to voltage drop in the wiring.

[Jim O'Dell]

When I wired the shop, I wired a 220 for the spot the DP sits. I then decided that running 220 on a small motor just didn't make enough sense to buy the plug for the DP. So I didn't. I did wire my contractor saw for 220. I feel it comes up to speed faster, but that is all. I'd vote no. Jim.

[Jim Becker]

In most cases, there is no benefit whatsoever to rewiring a small motor like that for 240v outside of convenience to you if where you want to plug it in happens to be supplying 240v. Internally the windings are still the same and still getting the same supply.

[Chris Padilla]

Agree with everyone else, for the most part, it probably won't be worth it to change the motor voltage. I would change it for the following reasons:

(1a) You already have a 240 V/20 A (or 30 A) plug handy...they are $3-4...maybe more for the twist-lok version.

(1b) You already have a 240 V/20 A (or 30 A) receptacle handy.

(2) The 120 V circuit you have the DP on is overloaded because multiple things are run on it at the same time.

(3) You enjoy over-engineering your electricity. Technically, the change will lower the amount of current being drawn over the wiring in the wall by half. This means that the voltage developed across the resistance of the wiring in the wall will be smaller. This means less heating up of the wires in the wall and less wasted power. Is it a lot? No, not really...not a lot at all hence my somewhat eccentric reasons for making the change.

[Jason Solodow]

It's a new shop and I ran the wire for the bandsaw location with 12/3 so I don't have to rewire when I buy a new bandsaw in the next two years. I have not purchased an outlet, plug, or breaker for this run yet (it's a dedicated line either way). That's why I'm asking now if I would see any benefit to putting it on a 220 or should I just leave it as a 110.. I mainly use my bandsaw for cutting turning rounds up to 12" thick..

[Chris Padilla]

Jason,

I love over-engineering stuff so I would wire it up as a 240 V/ 20 A circuit. :) That way when you get your behemoth 3-5 HP monster 20-24" bandsaw, you will only need to pull the plug off the old BS and wire it up to the new behemoth. :D

[Ken Fitzgerald]

Jason,

Like Chris, I like to have the potential for bigger stuff in place in case I would ever need it. In my new shop I wired all of my 220/240 v circuits with 10 gauge just in case. Turned out to be wise because the first tool I bought was a MM-16 with a 4.8 hp motor. All I had to do was put on the appropriate outlet in the wall and plug on the cord.

In theory, running a b/s on 220 could allow it to spin up faster. Unless it has a different set of windings, it will not increase the hp....it will not run cooler. Because it spins up faster, it could recover from being bogged down faster. But it will not gain any horsepower.

[Jim Becker]

Jason, you only need 12/2 for a 240v only circuit. (Three conductors...white/black/bare) Four conductor wire, 12/3, is only needed for dual voltage circuits, such as some dryers and other appliances require.

That said, with 12 gage wire in the wall, you can easily install the circuit now as 120v and later on, change the breaker and receptacle for 240v operation if you upgrade to a bigger saw that doesn't draw more than 20 amps at its rated voltage.

[Curt Harms]

as long as it's a dedicated circuit. I think where some get into trouble is they're running good sized loads i.e. 1.5 h.p. motors on 120 volt circuits that have other things on them. Having said that, I have a Rikon 10-325 band saw that would run on a dedicated 20 amp 120 volt circuit but took about 4-5 seconds to come up to speed. Hooked up to 240 volts it'd be up to speed within 1-2 seconds so in that case 240 volts does seem to help. YMMV I guess.

Curt

[Tom Veatch]

...run on a dedicated 20 amp 120 volt circuit but took about 4-5 seconds to come up to speed. Hooked up to 240 volts it'd be up to speed within 1-2 seconds...

You are seeing the effect of voltage drop in the supply wiring. During start up, the current surge can be several times the full load amperage for a short period. During that startup transient, the voltage drop is likewise several times what occurs during normal operation.

Doubling the voltage cuts the magnitude of the current surge in half which means a higher percentage of the available power is supplied to the motor during startup at 240v compared to 120v (percentage loss at 240 will be 1/4 the percentage loss at 120). If there is going to be a noticable effect, the motor start transient is where you'll see it first.

[Rick Christopherson]

A 3/4 hp motor only draws 7 amps when operating at full rated load from a 120 volt outlet. Your router probably draws twice this much. There is virtually no reason to ever rewire a 3/4 hp motor for 240 volts.

[Tim Byars]

Interesting thread...what do you guys think about the same question if it were a 1.5hp motor? That's my Steel City bandsaw, about which I've been wondering the same thing.

[Tom Veatch]

...what do you guys think about the same question if it were a 1.5hp motor?....

I wouldn't change anything I've said in this thread except to add that you'd be running about 14-15 FLA at 120V. But a 120V/20A circuit would handle that without problem as long as there was no other significant simultaneous use of the circuit. Also, the voltage drop should be acceptable as long as the wire runs were the appropriate gauge for the current and length. In which case, there's nothing really driving a change to 240V. But, as I said before, if it's available, I'd use it since there's no downside other than having to equip the tool with the proper voltage plug.

I will admit to being prejudiced toward the higher voltage and converting every dual voltage motor in my shop to 240. Reason being that, originally, the shop was at the end of about 150' one-way run from the shop subpanel to the main panel in the house which was itself about 200' feet from the transformer. I was looking for the minimum voltage drop I could manage in the service to the shop. So I wired the shop with several 120/240V 20A circuits (12/3 + ground) and dual voltage receptacles and used the higher voltage wherever possible.

[Rob Russell]

Interesting thread...what do you guys think about the same question if it were a 1.5hp motor?

If you're running that on a "good" circuit, preferably a 20-amp because that means it's wired with #12, I wouldn't rewire it for 240v. FYI, I overengineer everything I do.

If you're running the saw on a 15-amp circuit, wired with #14 and there's a pretty good run from your main panel to to your and then to the machine, it'd rewire it to 240v.

I guess the test I'd use is "How quickly does the motor spring to life when you turn on the saw?" If, when you turn the saw on, it comes up to speed rapidly (less than a second) - I wouldn't fuss with it. If, when you turn it on, it takes several seconds to come up to speed - I'd rewire it. Coming up to speed is when the motor is overcoming the inertia of the bandsaw wheels and will be drawing higher current.

On my circa-1957 Rockwell bandsaw (20", 1.5 HP) which is wired for 240v, when I turn it on - there's almost a bang as it comes to life. It does take a second or so for the blade to really get moving and a couple of seconds for it to really hit its final speed. I wouldn't want that saw wired on 120v, but 20" wheels provide a lot of inertia a long distance from the center of the wheel to get moving.

[Curt Harms]

You are seeing the effect of voltage drop in the supply wiring. During start up, the current surge can be several times the full load amperage for a short period. During that startup transient, the voltage drop is likewise several times what occurs during normal operation.

Doubling the voltage cuts the magnitude of the current surge in half which means a higher percentage of the available power is supplied to the motor during startup at 240v compared to 120v (percentage loss at 240 will be 1/4 the percentage loss at 120). If there is going to be a noticable effect, the motor start transient is where you'll see it first.

That's a fact. Startup amperage on 120 volts ran around 50 amps for a 2-3 seconds. 240 volts startup amperage was around 26 as expected but the peak was shorter, 1second or less. This was on a 120 volts 20 amp dedicated circuit. I have an early serial #.saw. The motor that came on the saw would trip the 20 amp CB on startup. It would start fine if I "hand propped" it, i.e. get it spinning then hit the start switch. I called Rikon and said it acted like a bad start cap but they sent me a whole new motor. I tried it again on 120 volts with the new motor and it would start without tripping the CB but I had 240 volts available so I left it on 240 volts. Interesting to me is that resawing a 10" board only raised amp draw 3-4 over idle amperage.

HTH

Curt

[Rick Christopherson]

Even though it is not a big deal, there are some significant flaws in your logic that will cause confusion for other people that read this posting, so I would like to clarify them.
That's a fact. Startup amperage on 120 volts ran around 50 amps for a 2-3 seconds. 240 volts startup amperage was around 26 as expected but the peak was shorter, 1second or less. This was on a 120 volts 20 amp dedicated circuit. I have an early serial #.saw. The motor that came on the saw would trip the 20 amp CB on startup. It would start fine if I "hand propped" it, i.e. get it spinning then hit the start switch. I called Rikon and said it acted like a bad start cap but they sent me a whole new motor. I tried it again on 120 volts with the new motor and it would start without tripping the CB but I had 240 volts available so I left it on 240 volts. You had a motor with a bad start capacitor, which is affirmed by the performance of the replacement motor at 120 volts, yet you make it seem as though the difference was with the change in voltage. With a bad start capacitor, your motor would have started slowly at either voltage.
Interesting to me is that resawing a 10" board only raised amp draw 3-4 over idle amperage.This is typical with any motor at any voltage. An idling induction motor will draw approximately 50% of its full load amps, but the powerfactor is extremely low, and therefore, the motor is doing very little "real work". As the motor load increases, the change in current does not increase proportionally, but instead, the powerfactor increases, as the current and voltage become closer to being in-phase with each other. So even though the magnitude of the current is not increasing very much, the amount of work that it performs is increasing because of the reduction in the phase shift.

[Curt Harms]

Even though it is not a big deal, there are some significant flaws in your logic that will cause confusion for other people that read this posting, so I would like to clarify them.You had a motor with a bad start capacitor, which is affirmed by the performance of the replacement motor at 120 volts, yet you make it seem as though the difference was with the change in voltage. With a bad start capacitor, your motor would have started slowly at either voltage.
Sorry, I wasn't clear on that. The new motor starts slower on 120 volts than on 240 volts as well. I'm sure this isn't typical and it may be something with the design of this motor, but in this case, both motors (bad start cap & replacement motor) were/are slower to come up to speed on 120 volts even though it was on a dedicated 120 volt 20 amp. circuit about 50' from the service. The difference was that the new motor didn't trip the 20 amp CB while starting. Others that have the Rikon 10-325 say their saw works just fine on 120 volts so I don't really know. I was using a short extension cord but it was heavy enough, 12 ga. High resistance connector or something like that? Possible I suppose but the same cord works fine with other 120 volt devices albeit universal motors.


This is typical with any motor at any voltage. An idling induction motor will draw approximately 50% of its full load amps, but the powerfactor is extremely low, and therefore, the motor is doing very little "real work". As the motor load increases, the change in current does not increase proportionally, but instead, the powerfactor increases, as the current and voltage become closer to being in-phase with each other. So even though the magnitude of the current is not increasing very much, the amount of work that it performs is increasing because of the reduction in the phase shift.

[Jay Yoder]

I have a bunch of machines that have the 120/240 motors. I also have a 100a breaker panel...Is it generally a better idea to convert the larger ones (1.5 hp and greater) to 240? I have noticed the RAS (supposedly a 3 hp c'man) tends to dim the lites at startup but is fine once i get up to speed. I am thinking of converting it to 240v for this reason and it also seems to take awhile to come up to speed. I can only use one at a time...well actually i could use DC with the jointer, ts (which is on a dedicated circuit), and Delta Bandsaw, which i have not converted to 240v...