RickyInman
Member
Someone near me has a used Kobalt 30 gallon air compressor for $150. It is 240v or 120v. I have a basic knowledge of electricity. What is the advantage of wiring the compressor 240v as opposed to 120v?
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Question about 240v/120v Compressors
- Thread starter RickyInman
- Start date
Mick56
Well-known member
I believe it will actually use less electricity, thus be cheaper to run on 240.
Lelandwelds
Well-known member
Same electricity used. Can use cheaper wire. Or run same wire further. Or, more toys on same circuit.
it is not cheaper to run on 220, but with 120 you are limited to primarily a 15 amp circuit.any 120v compressor that has any umff to it will be at the high end of amp draw on 120. even at that you will have limited air supply.
depends on what you're doing and how much air you need.
also do you need portability etc.
depends on what you're doing and how much air you need.
also do you need portability etc.
dtnel
Active member
Personally if you're doing work regularly a 60gal or larger belt driven compressor will help you long term vs getting something you'll struggle with which is my situation the last 16 yrs. I have a 60 gallon in the garage that I bought new that I need to wire up. It'll be 230 if I recollect properly and from when I checked the wiring I needed it was 2 12 gauge wires but I'll go larger since I have them ran and available as I'll be switching from a electric garage heater to a gas heater so I'll use the wiring from that to run the compressor.
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I believe it will actually use less electricity, thus be cheaper to run on 240.
Nope, the amperes are 1/2 of 120V but 120V X 2A, or 240V X 1A, equals the same, above 1 1/2 HP it becomes more common sense to use a 240V circuit because of the limits of a 20A 120 volt circuit, 1 1/2 HP is the iffy zone, where a 20A 120V circuit could be taxed enough to cause excessive breaker tripping, example was my Delta 10" contractors saw w/ a 1.5HP motor would trip the breaker it was on when doing a lot of ripping, solution was to move it to another circuit even though could have changed it to 240V with ease, saw was mothballed after getting a vintage Unisaw.
Not so. At the lower voltage it draws twice the current. The wattage is the same in either case. There is no free lunch.I believe it will actually use less electricity, thus be cheaper to run on 240.
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The advantage of 240 is that the wiring can be a lighter gauge. That is detirmined by the current. As pointed out, on 120 you are pushing the 20A limit of the circuit and may start tripping the breaker
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Stuart in MN
Well-known member
As mentioned, the power consumption in watts is the same, and you're paying for watts so the cost of operation is the same.
If a motor is small enough to run on a standard 120vac circuit there's no advantage to converting it to 240vac. You may as well leave it at 120vac, then you can plug it in anywhere.
If a motor is small enough to run on a standard 120vac circuit there's no advantage to converting it to 240vac. You may as well leave it at 120vac, then you can plug it in anywhere.
jsaw
Well-known member
one of My compressors can be wired to run with either 120 or 240. when run on 220, it started up a lot quicker, especially when cold.
the biggest disadvantage was that it was not as portable, because 240 outlets are not as common as 120 outlets
the biggest disadvantage was that it was not as portable, because 240 outlets are not as common as 120 outlets
dual voltage motors have two sets of windings - the windings are in parallel on 120V, and in series on 240V. either way, the windings only see 120V.
if you dual voltage motor works better on 240V than 120V, you're starving it for current, and that's why it doesn't work as well.
if you dual voltage motor works better on 240V than 120V, you're starving it for current, and that's why it doesn't work as well.
The wiring on the 120 circuit is probably not heavy enough to suppy twice the current with the same minimal drop he sees on 240.dual voltage motors have two sets of windings - the windings are in parallel on 120V, and in series on 240V. either way, the windings only see 120V.
if you dual voltage motor works better on 240V than 120V, you're starving it for current, and that's why it doesn't work as well.
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A friend of mine bought the same exact speedaire 30 gal compressor as me the same week. I wired mine for 240 and he wired his for 120. Not sure why, but his motor burned up after the first year. Mine is still original from 2003. Mine is also always on in an unconditioned garage.
nelstomlinson
Well-known member
The heat in your motor is proportional to I^2*R. If you double the current by going from 240V to 120V, you have four times the heat. Always run at the highest available voltage.
" If you double the current by going from 240V to 120V, you have four times the heat" -
NOT true - see post#11; the windings themselves will see the SAME current (AND voltage) in either configuration. The only place that would see twice the current on 120 volt is the wires TO the motor... Steve
NOT true - see post#11; the windings themselves will see the SAME current (AND voltage) in either configuration. The only place that would see twice the current on 120 volt is the wires TO the motor... Steve
bsaint
Well-known member
" If you double the current by going from 240V to 120V, you have four times the heat" -
NOT true - see post#11; the windings themselves will see the SAME current (AND voltage) in either configuration. The only place that would see twice the current on 120 volt is the wires TO the motor... Steve
No you spread the current out across more windings. You have less heat. If the current is half the heat is less also. Basic electricity.
Each half of the total windings would be designed to work on 120 volts, and wouldn't care which "hot" the non-neutral end sees - so each half of the winding would get the same WATTAGE either way. Same wattage, same heat. Again, the ONLY place that would change is in the SUPPLY wiring TO the motor, which would need to supply TWICE the current in order to feed BOTH windings (when wired for 120 volts)... Steve
bsaint
Well-known member
I dont know about that... Lemme use the thermocam and check
The heat in your motor is proportional to I^2*R. If you double the current by going from 240V to 120V, you have four times the heat. Always run at the highest available voltage.
Remember that when you change the motor over to 240V operation you double the resistance. Think of it as two resistors. In 120V mode the resistors are in parallel thus each sees 120V and half of the current (15A so 7.5 each). In 240 V mode you put the resistors in series. Now the current from one resistor flows into the other (7.5A). The 240V is spread over two resistors in series so each sees half the total or 120V. This each sees the same load.
Your thinking would be correct if the resistance was unchanged and the voltage was doubled.
To the OP's question, the advantage is less voltage sag under load or during start up. Generally 240V wiring is going to be the same gauge as 120V wiring but now the load is half. The voltage sag is lower which makes starting easier. It also might save some insignificant amount of electricity in terms of lower line loses.
Lelandwelds
Well-known member
It also might save some insignificant amount of electricity in terms of lower line loses.
Yes. And, if i visit the bathroom before running, I can run faster because i weigh less.
nelstomlinson
Well-known member
Oops, ya'll are right. We rewire the motor by putting the windings in parallel rather than series.