What is the acceptable line voltage from the power company? I am currently getting 244 and 122. Which would not be a problem but it is causing an over current draw on a motor I have that is running off a step down transformer.
-Dan
-Dan
Incoming Line voltage, how much is to much
- Thread starter engnerdan
- Start date
Stuart in MN
Well-known member
Nominal voltage from the utility is generally 120/240vac, so you're pretty close to right on. You're in Minnesota - is Xcel Energy your electric utility? I know 120/240 is what they provide.
What kind of motor is it, and what is the voltage rating of the transformer? If you're thinking the voltage is too high, if anything that would reduce the current draw.
What kind of motor is it, and what is the voltage rating of the transformer? If you're thinking the voltage is too high, if anything that would reduce the current draw.
PAToyota
Well-known member
I think that the last I checked, I was getting something like 255V.
Ryan87LX
Well-known member
Higher voltage will reduce the current draw of a motor, so if you have an overcurrent situation, you have another problem.
I agree with Stuart, what kind/type of motor is it?
I agree with Stuart, what kind/type of motor is it?
Its a 1/4 hp pump motor. It is rated for 115volts at 5.5 amps, when I plug it into the wall (122volts) it draws 6 amp (5.9..) when I run it off the transformer (~130 volts) it draws 6.8 amps.
I know what you mean that the higher the incoming voltage the lower the amps should be. But when you have a set resistance and you increase the voltage your amperage will go up.
I think I will just end up buying a motor capable of 230 volts then I can wire it into my welder directly and not have to deal with this step down transformer. This motor is for my circulation pump for my welder.
Can be seen here.
The motor looks new in that picture but really it is not, I just cleaned it and repainted it.
-Dan
I know what you mean that the higher the incoming voltage the lower the amps should be. But when you have a set resistance and you increase the voltage your amperage will go up.
I think I will just end up buying a motor capable of 230 volts then I can wire it into my welder directly and not have to deal with this step down transformer. This motor is for my circulation pump for my welder.
Can be seen here.
The motor looks new in that picture but really it is not, I just cleaned it and repainted it.
-Dan
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Tscott
Well-known member
This is wrong. As you stated above the formula for amp draw is
Amps=Volts/Ohms
This means that for a set resistance, i.e. the motor, That an increase in voltage will mean I higher amp draw.
As for your problem, I would say that any motor rated for 115 volts that can't handle 122 volts is faulty in some way. Is the motor tripping a breaker or something? The difference in amperage is not a significant amount and is to be expected. Motors can draw more than 5 times their amp rating on start up, and the 5.5 amps you specify is most likely a nominal running amperage. It sounds like everything is working just fine to me.
Tom
I can't contribute much on the tech. side. But when this house was built for about ten years we had problums with motors on dishwashers, dryers, frigg, and so on. they would burn out after two-three years I thought it was because I would buy the cheep stuff 
Things like light bulbs would burn out way to soon maybe twenty+ a year. I would blame the kids for leaving them on all the time (sorry kids) But I cheeked my voltage and it was 132v 247v 
I know it took ten years to cheek 
After a long talk with the power Co. they replaced the trans. Haven't replaced anything now for six years. And for light bulbs
maybe two a year. (The wife wants the old trans. put back in )
Things like light bulbs would burn out way to soon maybe twenty+ a year. I would blame the kids for leaving them on all the time (sorry kids) But I cheeked my voltage and it was 132v 247v I know it took ten years to cheek After a long talk with the power Co. they replaced the trans. Haven't replaced anything now for six years. And for light bulbs maybe two a year. (The wife wants the old trans. put back in )I don't have a problem plugging it into the wall and getting 122 (running at 5.8-6.0 amps). But I want to run the pump off the power coming into my welder (so when I flip it on it comes on, no forgetting). So I got a step down transformer to mount inside the welder and with the higher then normal line voltage coming into the transformer and the loss compensation in the transformer the output of the transformer is no longer 120 it is almost 130 which kicks the amp draw too high for the transformer (only rated to 6.25 amps) and the motor current is 23% higher then speced.
I think I am going to just **** it up and buy a new 230 volt motor so I don't have to use this step down transformer, and can just tap into the 240 in the welder.
-Dan
I think I am going to just **** it up and buy a new 230 volt motor so I don't have to use this step down transformer, and can just tap into the 240 in the welder.
-Dan
Actually, at startup, the reason an electric motor draws significantly higher current is because the motor is not turning at that point, so it looks similar to a dead short. When energy flows into the motor, the electricity produces a magnetic field that generally opposes the magnets around the motor, causing it to spin.
The hard part with all of this is that an electrical motor is not a constant resistance device. Too low or even too high of a voltage can cause the device to operate at higher currents.
Back to the OP question. 122VAC is not considered over voltage for a 120V system. Its been too long to remember the exact limits, but 5% rings a bell...
Tscott
Well-known member
No, when a motor is at rest, the current required to start the motor spinning is higher than that which it needs as it runs. The windings in a standard induction motor are switched on in off in succession to allow the next winding in series to attract the shafts magnets. Otherwise the stator would be pulled to the first set of winds and stop. When the shaft first begins to spin, this switching is delayed (i.e. each winding is on for longer) allowing current to flow unchecked through the windings. The windings are typically very low resistance and are nothing but very thin long wires. The magnetic fields in motors actually help to limit the amount of amperage that a winding sees, but when a motor is switched on those fields take time to establish and in that short period amperage can be 5-8 times running amperage. It is known as Lock Rotor Amps, and is just what it sounds like, the amperage through the motor windings when the rotor is locked in position and cannot spin.
This applies to running motors as well. The harder you load a motor the higher the amps will be.
Hope this helps
Tom
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Tscott
Well-known member
This is correct. Here we will only correct voltage issues greater than 5% over or under the base.
Tom
Charles (in GA)
Well-known member
Why are you using a step down transformer? Put a four wire cord on the welder, and drive the motor off one side of the incoming 220v and the neutral.
Charles
Charles
My point was that you said
"This means that for a set resistance, i.e. the motor That an increase in voltage will mean I higher amp draw"
I took that to mean that you thought the resistance was fixed on the motor. That's why I asked you if you thought it was 1/5 the voltage due to the amps=volts/r relation.
As for the above description, of the operation of an induction motor, it's quite unique..... You do know that the rotor has no magnets in it, but rather it's an induced current that creates a magnetic field??
William...
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VDubJoe
Well-known member
Where i work our range is 114 to 126 on a res service.
Joe
Joe
Tscott
Well-known member
Well, what can I say, It is tough to get my thoughts into words. I did not know what kind of experience you had with such things and tried to dumb it down as much as I could. I guess there was something lost in the translation.
As for the whole magnet thing, I guess it depends on how you look at it. I guess I should have typed electromagnet to be more proper.
Tom
Ryan87LX
Well-known member
A motor is not a set load, the harder you work it, the more current it will draw.
My above phrase is correct, the higher voltage you are working with, the lower the current the motor will draw. What is probably happening in the described scenario is that the transformer is taking power to run. Transformers get hot, heat is wasted energy.
I work on pumps for a living, including pumps that can run on 120 and/or 240. At 120v they will draw 20 amps, and 240v they draw about 11 amps, all with the simple relocation of a couple jumper wires.
*Edit, I beleive the reason this works is because most motors are rated at a certain power output. Therefore, the variation of ohms law I=V/R is incorrect. The proper variation should be I=P/V, where P is the power rating of the motor, and V is the incoming voltage.
My bet is still on the transformer.
My above phrase is correct, the higher voltage you are working with, the lower the current the motor will draw. What is probably happening in the described scenario is that the transformer is taking power to run. Transformers get hot, heat is wasted energy.
I work on pumps for a living, including pumps that can run on 120 and/or 240. At 120v they will draw 20 amps, and 240v they draw about 11 amps, all with the simple relocation of a couple jumper wires.
*Edit, I beleive the reason this works is because most motors are rated at a certain power output. Therefore, the variation of ohms law I=V/R is incorrect. The proper variation should be I=P/V, where P is the power rating of the motor, and V is the incoming voltage.
My bet is still on the transformer.
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