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?
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 ;)
The quick simple answer is that with 220 volt you can normally run a TRUE 3 hp motor. With 110 volt you are limited to motors with make believe hp ratings over 1.5 hp. If you think you will ever have a typical cabinet saw, you will need 220 volts.
Monty wrote in news:DhbUb.21490$2 snipped-for-privacy@newssvr25.news.prodigy.com:
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.
There isn't any decision to make if you have a 5HP motor. That probably draws something on the order of 18 amps on 220V. In order to run it on 110V (even if the motor is convertible) you will need to run it on a 40 amp circut breaker and #8 wire. Hardly a fun wiring job. On
220V, all you need is a 20 amp breaker and #12 wire.
By the way, it's neither efficiency or power as far as 110V vs 220V is concerned. The only difference to the motor is if the feed is a long distance. The voltage drop will be less at 220V by a factor of four. Otherwise, the watts is the same for either voltage.
The analogy about efficient breathing is really not valid for electric power usage. In fact trying to explain electric power in terms of any fluid is not really a valid analogy.
The two biggest practical advantages of 220v are:
you can run larger motors (already mentioned) over typical sized wiring.
You can carry more load for a given size wire. I had a 1.75 HP tablesaw on a #12 circuit. By converting to 220v, I could add a 2 HP dust collector on the same circuit.
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.
As an example, a 20 amp circuit at 220 will have twice as much power as a 20 amp circuit at 110. Power is current x voltage. For motors around 2 hp or larger, you most likely will not have a choice. You will have to run them at 220. If I were wiring from scratch, I would put everything at 220, but since you would have to rewire, probably just put the larger motors on 220. It's up to you
Sometimes, I think the efficiency issue is exaggerated.
240v is always preferred because you get one quarter the voltage drop for the same wire size. That only makes a difference when running if you have a very long cable, but is pretty dramatic when turning the machinery on. Also, you get twice the power capacity for an almost identical installation process. Supposedly motors last longer because they don't have to fight the voltage drop.
The only downside to 240v is having to change stuff over, and that outlets can cost a bit more.
That is where you are wrong. The current of 10A flows from one pole of the breaker, back to the other pole and vs versa. The total current in the conductor is 10A. The same motor on 110V would draw 20A from hot to neutral. Therefore, for the same conductor size the voltage drop is directly proportional to the current. Twice the current, twice the voltage drop.
Assume that the resistance of the wire is .1 ohms. The voltage drop for the
220 v motor is 10 * .1= 1 volt. For the 110 v motor it is 20 * .1 = 2 volts.
The power supplied is the same in both cases. P=V x I, 220 x 10 = 110 x 20
On the other hand, the power dissipated (P=I^2 x R) is higher by a factor of
I guess I should have said, "the % voltage drop is one quarter." The voltage drop is one half, but it is figured into twice the voltage; so the % drop is one quarter.
Since the actual voltage drop is irrelevant I was a tad sloppy; sorry.
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