The tradeoff between 110 vs 220 - please explain

Page 1 of 3  
I'm about to start building my shop in the garage. I currently have an old small subpanel in there with a bunch of 110 outlets scattered around that the last owner installed. It's all pretty old stuff but still in working order.
Many of the new machines I'm going to purchase can handle 110 or 220. My question is should I rewire the garage with a new subpanel and make all those machines 220 and scatter some new 110 outlets around as well or just make everything 110? What's the benefit of running a machine like a saw or shaper at 220 vs 110? Does it have more power? Can someone explain the tradeoff?
Monty
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Consider the current being draw through the wires as the air you breathe. When you're working hard (running uphill or whatever) you need more air and the faster the better, right? The same is pretty much true for your equipment. Let's take your table saw. When it starts up it pulls a lot of current (I think it's like 40-80amps) right off the bat to get the motor spinning at full speed. That's one instance when a lot of current is needed right away, another is if you're putting some wood through the blade and it pinches a bit (hopefully you have a splitter -- but that's a whole 'nother discussion), anyway the motor is now suddenly under load and needs more juice to keep the blade spinning.
Ok, now to understand how 220 vs 110 helps with this -- imagine you're breathing through a straw, a small one :) Now run up the stairs but only breathe through the straw. Don't try this by the way -- you'd probably pass out from a lack of oxygen, but that's the key -- you can't pull the air in fast enough for your heart/lungs/brain to handle the quick load. On the other hand if you were breathing through a large tube it would be pretty easy right, might not even notice a difference.
Now the question is why this is a good/bad thing for the equipment. Here's where it becomes a bit fuzzy for me. I believe you get a benefit from spreading the voltage drop across 2 poles in your house (where most things are 1 pole or 110) so you don't have a large drop on a single pole you have 1/2 the drop on both poles, kind of evens out the load on your house. That has various benefits for delicate equipment like stereos, tvs, computers etc. Also, I thought I read somewhere that it's better on your motor itself and thus it should last longer (don't know if it was heat related or what).
Now, the real question is, is this fact or did I just pass along bad information I've gathered over the years? For that you'd probably need to ask an EE or electrician. If someone is one of those and has better info I'd be happy to have it :) (or even happier to know I've more or less got it right ;)
Thanks, Mike

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Man, thanks for taking all the time to answer my question. That all makes sense. It seems to be more of an efficiency issue as opposed to power. The motor for a saw is say 5HP and it'll always be 5HP if it's running at 110 or 220. No more "power" with one or the other. It's just more efficient to get the current to the motor via two poles (220) instead of 1 (110). Maybe it'll be harder to bog down at 220 and maybe the lights in the house won't dim as much if I'm running 220. I think my question about rewiring the garage to 220 has been answered. It's better to run them at 220. Thanks.
Mike in Idaho wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yes, but not quite in the sense you're thinking, I beleive. When you run 110 you draw more current for a given amount of output power, which causes "resistive" losses in the wires, etc (so you have to draw even more current to make up for that). The problem is in where those resistive losses go - which is into heating up the wires, motors, and everything else in the circuit. Heat is not a good thing; at best it shortens the life of the motor, and at worst it sets the wiring on fire.
John
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks John,
I think this is what I had read about heat and motor wear. That makes sense.
Thanks, Mike

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I think you are over rating the heat effect. If wiring overheats, the breaker was oversized. That is why we have breakers. Properly sized wire should have negligible resistive heating. Some people say a dual voltage motor will last longer when run at 220v. I think the biggest motor longevity factor is the quality of the motor itself.
Bob

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I always enjoy the creativity and imagination that these 110/220 threads produce.
--

Larry Wasserman Baltimore, Maryland
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Lawrence Wasserman wrote:

That may be, but everything that's been said echoes what a recent WW magazine said about the issue. I don't remember which magazine it was, though.
--
gabriel

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

If only you knew what you were talking about.

Depends on what you mean by 'negligible'. To coin a "Clinton". :)
To deliver the same amount of power to the load requires *twice* as much current at 120V as is needed at 240V. Losses in the wiring, etc. are proportional to the _square_ of the current. Thus the losses in the wiring are *four*times* greater at 120V vs 240v, for the same power at the load.
In a properly designed system, these losses are "relatively small" at either voltage. But, regardless, the losses are only 1/4 as large when you run things at 240V.
EVEN WITH 'properly sized' wiring, the allowable voltage drop _in_the_wiring_ between the panel and the device can be several volts. A 5V drop in the wiring, with a 15A load, and the _wiring_ is giving off as much heat as a 75 watt light bulb. And that's "within specifications" for a properly constructed circuit.

You're free to think whatever you like. :)
Needless to say, the 'quality' of any given motor is *unchanged* by being run at 240V instead of 120V. Regardless of whether it's a 'cheapie', or a 'top of the line' unit.
Motors are, in general, more efficient when operated at higher voltages. This means the internal "losses" are lower at higher voltages. This means that there is, all else being equal, _less_ heat build-up in the motor, when run at higher voltages.
Excess heat _is_ one of the biggest enemies of longevity.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

on myself consider the following:

they are wired in series.

winding and that the heating is a result of I^2 * R.

0.25 ohms ( [R1 * R2] / [R1 + R2].

ohm ( R1 + R2 )

than 240v?

There isn't any difference noticed in the motor itself. As you note, the motor itself sees the same voltage and current on it's windings. The losses are generated from the wiring which supplies the motor. All the way from the main electrical panel, through any sub panels, to the outlet and though any extension cords.
Frank
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Good, we agree on that. So the 20A 120v motor will need to be fed from a 30 A breaker using #10 wire while the 10A, 240V motor will need to be fed from a 15A breaker using #14 wire. Givint this installation, there will be negligable difference in the performance of the motor when the system is examined in total.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

30 A breaker using #10 wire while the 10A, 240V motor will

installation, there will be negligable difference in the performance

I agree. I'm not one that thinks the losses from wiring is a big deal, I was just sumarizing the other side of the argument. Truth be told, I like 240volt runs mainly because I can run smaller wire which is cheaper and easier to use.
Frank
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 5 Feb 2004 13:45:27 -0500, "Al Reid"

Nobody who cares about I^2 * R losses and voltage drop is going to take the trouble to run a motor on 240V and then turn around and cheap out by using #14 wire just because it's legal to do so. Most people would use #12 wire or better (I personally would never use #14 for anything, given a choice; the stuff is a gift to the power companies. Feel a piece of #14 romex when it's carrying 10A or so sometime - it is noticeably warm).
And if you really want to go overboard, you could even use #10 for your 10A, 240V motor, in which case your I^2R losses would be one fourth of what they would be in your example for the same #10 wire at 120V, 20A. Bottom line is, if you've got room for the double pole breaker, there is no good reason not to use 240V for your motors, it can't hurt and will always same some amount of energy over time, even if it isn't huge.

Tim Carver snipped-for-privacy@twocarvers.com
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Two things - one is that these are AC motors, and so there's inductive effects (so I^2 * R isn't accurate, you need to consider the impedance and the phase angle); and secondly because you're drawing more current at 110, the drop in the circuit to the motor is greater, in order to produce the same output power you need more than twice the current than the 220 motor draws.
John
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
and 2.0HP @ 240V. with a similar 'mis-match' in current draw at the two voltages.)
With the same power in, and lower _mechanical_ power out, it should be obvious that some power is going 'somewhere else'. Which it is. into heat.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 06 Feb 2004 09:48:13 +0000, snipped-for-privacy@host122.r-bonomi.com (Robert Bonomi) wrote:

Which rule is that?

If the windings in a dual voltage motor are split and are wired in series at 240V and parallel at 120V, how is the motor to know to produce less shaft horsepower when the voltage (and current) in the individual winding is the same for either source?

There shouldn't be a difference.
LRod
Master Woodbutcher and seasoned termite
Shamelessly whoring my website since 1999
http://www.woodbutcher.net
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

     The 'one with the typo', isn't it obvious? <grin> E=I*R I=E/R R=I/E
I was doing the math right, just got the wrong symbol in the formula. thanks for the catch.

I don't know all the theoretical underpinnings, I can state it is "observed fact" from having motors on a test stand.
The electrical characteristics _are_ different, depending on whether the windings are in series or parallel. If the windings are not _exactly_ identical, you get different voltage/current relationships depending on the type of inter-connect. In series, the current through both windings is identical, but the higher resistance winding will have a larger voltage drop across it. OTOH, in parallel, the voltage across both windings is identical, but the lower resistance winding has more current flowing through it.

"In theory, there is no difference between theory and practice. In practice, on the other hand ....."
If you want a _real_ mind-bender, try and figure out why motors run at 1725 RPM or 3450 RPM.    The 'obvious' speeds are 3600 RPM, and even sub-multiples thereof (1800, 1200, 900, 720, 600, etc.), depending on The number of 'poles' in the motor design. Yet, 4+ percent 'slow' is nearly universal -- pretty much independent of any combination of manufacturer, HP, or operating voltage.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

In the real world, there are inefficiencies which contribute to actual performances being different than calculated performances.
Frank
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@host122.r-bonomi.com (Robert Bonomi) wrote:

It's only a mind-bender if you've never studied how an induction motor works. There are many different ways to build a motor. The most common design that you find in shop machinery is what's called an induction motor.
The electric field created by the stator windings rotates at 3600 RPM (for a 2-pole motor). The rotor rotates a little slower than that (say, 3450 RPM). The difference, 150 RPM or 2.5 Hz, is what induces current to flow in the rotor windings (hence the name). There are no brushes. As the load increases, the rotor slows down and the slip frequency increases, causing the rotor current to increase. It's a very clever design.
One of the drawbacks of induction motors is that the rotational speed is not constant. As load increases, the rotor speed drops. For many applications, this is not a problem.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Site Timeline

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.