Another "almost circuit" breaker question

[Bruce Cohen]

Finally, after about three years of drooling at pictures, I finally got a Rikon Deluxe 14" Band Saw.

Haven't even started to assemble it yet, the motor comes wired for 110 V, but can be easily rewired for 230 V.

My shop (read that as the wife's ex-garage) has two seperate 20 A dedicated lines run into it. As the breaker panel is just on the other side of the wall, another line (230 V )will be easy.

Now to the question. Is there any significant difference (other than the lower electric use) between these two voltages. I mean will the motor run better at the higher voltage, or any other reliviant factors.

Once I get this puppy assembled, I'll let you guys know how it performs.

BTW, it has two speeds, when do I change from 1145ft/min to 2950ft/min.

Thanks,

Bruce

[LCHIEN]

Originally Posted by Bruce Cohen

Finally, after about three years of drooling at pictures, I finally got a Rikon Deluxe 14" Band Saw.

Haven't even started to assemble it yet, the motor comes wired for 110 V, but can be easily rewired for 230 V.

My shop (read that as the wife's ex-garage) has two seperate 20 A dedicated lines run into it. As the breaker panel is just on the other side of the wall, another line (230 V )will be easy.

Now to the question. Is there any significant difference (other than the lower electric use) between these two voltages. I mean will the motor run better at the higher voltage, or any other reliviant factors.

Once I get this puppy assembled, I'll let you guys know how it performs.

BTW, it has two speeds, when do I change from 1145ft/min to 2950ft/min.

Thanks,

Bruce

You don't say what the current requirement is. But I'll assume it can run on less than 20A at 120V.

1) There is NO DIFFERENCE IN ELECTRIC USAGE, the number of watts will be the same either way and watts and time is what you pay by. Altho the current is halved at 230V the total power is the same.

2) There will be a itty-bitty teeny-tiny performance advantage in the 230V setup because the wiring voltage losses will be less. But in reality we are talking probably less than 1% and you'll never notice the difference.

It really comes down to whats more convenient for you. With a 20A 230V circuit, you could run two high amperage pieces of gear simultaneously on the one circuit (and two outlets) - another possible advantage (e.g. saving one set of wiring). Like a DC and a saw.

[Bruce Cohen]

Loring,

Thanks for the quick reply, I knew I could count on you. The amperage draw is 14A @115v, 7A @ 230V.

I assume this shouldn't change any of your answer.

As I mentioned, there already exists 2 seperate 20A dedicated lines and although its not a big choir, I'd rather not spend the time running another line using up time I could be playing with the BS.

Many thanks,

Bruce

[Slik Geek]

Originally Posted by LCHIEN

1) There is NO DIFFERENCE IN ELECTRIC USAGE, the number of watts will be the same either way and watts and time is what you pay by. Altho the current is halved at 230V the total power is the same.

2) There will be a itty-bitty teeny-tiny performance advantage in the 230V setup because the wiring voltage losses will be less. But in reality we are talking probably less than 1% and you'll never notice the difference.

Perhaps it would be more accurate to say that there is not a significant difference in power consumption between the 115V/230V configurations. In the higher voltage configuration, the current is halved. Because resistive power loss is proportional to the square of the current, the 230V configuration has 1/4 the power loss due to resistance. With a properly designed motor, and electrical wiring per code, that power difference is probably not terribly significant. (Which is Loring's point).

[lrr]

I've got an old Craftsman RAS that is 110V/220V capable. I switched it to 220V many years ago, mainly after a simple experiment. Running at 110V, there was always a slight lag at motor startup. On 220V, no lag.

I had extremely short runs of Romex (garage shop with outlet near the breaker box), so IR loss would have been minimal. But, it may have been the primary factor.

Given a choice on a dual voltage tool, I'd always pick 220V over 110V. But, it's an easier decision for me now, since my shop has a 60A subpanel. I've got plenty of 110V, as well as a few 220V circuits, and room for growth.

[Slik Geek]

Originally Posted by lrr

I've got an old Craftsman RAS that is 110V/220V capable. I switched it to 220V many years ago, mainly after a simple experiment. Running at 110V, there was always a slight lag at motor startup. On 220V, no lag.

I had extremely short runs of Romex (garage shop with outlet near the breaker box), so IR loss would have been minimal. But, it may have been the primary factor.

During startup is where the difference is most significant, because the startup current is generally several times the motor's rated current. (That's why you sometimes notice lights dimming momentarily when you start a motor).

In my shop, I have about a 50 foot wire run (each conductor, so 100 ft total) from the breaker to the shop outlets. Suppose I run 20A, 115V 12AWG service and 15A, 230V 14 AWG service to compare setups. Ignoring resistances in the service to my breaker box, the interconnects, and the main and branch circuit breakers, and using the 14A / 7A currents earlier in this post...

The 115V line has a resistance of about 0.19 ohms, the 230V has a resistance of about 0.30 ohms. (Because I ran larger wire for 115V).

At the motor's rated current (not a usually operating mode, probably), the voltage drop in the conductors is about 2.6V for the 115V line (2.3% droop), and about 2.1V for the 230V line (0.9% droop). The power dissipated in the wiring is about 37W in the 115V line, and 15W in the 230V line.

Let's assume the startup current is 3X the motor rating. (It could be higher). The peak voltage droop is roughly 8V (~7%) in the 115V line, and roughly 6V (~3%) in the 230V line. The peak power loss at startup is about 330W in the 115V line, and about 130W in the 230V line.

Given the theoretical maximum power delivery during startup of 4,830W, the 115V line is delivering about 93% of the theoretical power at startup, while the 230V line is delivering about 97% of the theoretical power.

That extra power makes a difference in the available motor starting torque. Hence, the difference you noticed in startup lag. (Your results were probably less dramatic, given your shorter cable run).

BTW, for those who are wondering, if you ran 20AWG for the 230V service, you would deliver nearly 98% of the theoretical power in our startup example.

[LCHIEN]

Originally Posted by Slik Geek

...That extra power makes a difference in the available motor starting torque. Hence, the difference you noticed in startup lag. (Your results were probably less dramatic, given your shorter cable run).
....

gee, you remind me of me. (P.S. No wonder, you're a middle-aged EE like me).

The point being anyway that 230V differs in that it can deliver somewhat more at startup but very little extra during normal use. So its of no real benefit other than this transient thing.

I'll repeat, all things being equal, I'd wire for 230 but if it were to really cost anything in convenience or money, there's no real advantage worth spending much for.