Greetings Private, I think you have made a mistake in the above paragraph. When a motor is running it is also acting as a generator. This generator action is called "Back EMF". The Back EMF limits how much current the motor will draw. Different motor types act differently when the voltage is dropped. DC motors just slow down without drawing more current. However, when an induction motor recieves lower voltage it will start to slow down and draw more current. This is because the motor produces less Back EMF when running at reduced speed and voltage and so it will then draw more current. This higher current leads to more heat in the windings which can burn out the windings. The welder transformer doesn't work the same way as an induction motor and so it doesn't draw more current as the voltage drops. When a transformer type welder recieves less voltage it just uses fewer watts. At least, that's how I remember it. If I'm wrong someone will surely correct me. Cheers, Eric
I need to power my Lincoln SP 175+ in a remote location without bringing in a line off the pole. ($$$) It calls for 220v and 22 amp in. What would be a good size generator to look for that would run the unit, not get over heated, yet not be overkill? Some of the 220 plugs I've seen on generators look wimpy, too. I have a dryer plug on mine. Are the smaller plugs any the less capable?
240 volts at 22 amps is 5280 watts. For welders, that calc is not quite right since welders are notorious for having weird phase angles. That means that means you cannot be absolutely sure things will work correctly before you try it. A big question mark is if you need to run it at max amps or settle for something less. My 225 amp buzz box welder runs fine on a 4 kw gen set but not at full power.
There is a good chance you can run the unit with a standard 5kw el cheapo set from the big box stores. These run in the $500 range on sale, $700 or so full price, $300 to $400 is a fair price on a modestly used unit.
Going up to the 7200 watt base load size units would be a good bet but more money. This is the size I would think about for serious use. For the generator head alone see this:
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If you are going to do semi production welding for hours on end, the little one lunger powered units are just not going to hold up.
The recepticals on the generators are usually the minimum NEC rated size. Barely enough but good enough.
220volts x 22amps = 4840 watts = 4.84 kilowatts Add a little 'for mother' to account for losses in power cords and for the usually exagerated generator rating. Long power cords can cause voltage drop which results in increased amperage which could overload/overheat your welder.
If you are not using the highest power settings on your welder then you may not be pulling a full 22amps, a simple clamp type power meter can give you your true power draw when welding. I sugest you run a test in your shop using the heat and wire settings you will be using in the field.
An honest 5kw (theoretically) should do the job if you are not pulling max power, but as always YMMV and you can seldom have too much power. Too big will be better than too small.
I suspect that you will overheat before a 5kw generator.
Some of the 220 plugs I've seen on generators
Your dryer plug is rated for 30 amps, if the generator has a different size plug you may want to build an adapter, I doubt you will want to rewire the generator and it should have a plug capable of its rated output.
I am not an electrician or electrical engineer and defer to your obviously greater knowledge.
With respect, I had thought that all electrical loads would try to maintain output power by pulling more amps whenever voltage dropped. Will a DC motor not try to maintain output torque at the lower speed caused by reduced voltage? Does this not increase amperage draw? I am told that low voltage (resulting from continuing to drive with a failed alternator using rapidly discharging battery power as long as possible) can cause automotive fuel pumps to overheat and lead to failure. By your statement, if dropping input voltage does not increase amperage draw of a transformer welder then ISTM the output power must be reduced, this will likely cause the weldor to increase the controls to compensate and ISTM that this will result in the transformer drawing more amps.
I know just enough to keep my power cords as short as possible and as big as I can afford.
I dunno about the greater knowledge, but I do know that a DC motor will just slow down with lower voltage. So will a "universal motor". The universal motor is the type used in hand drills and the like. They have brushes and a commutator and will work on AC or DC. Variable speed drills may not work on DC. Now a welder operating at reduced voltage will indeed draw more amps if the operator increases the setting. However, I don't believe the welder can be adjusted to draw more amps than it can handle without some sort of safety device shutting down the machine. As happens when welding too long and exceeding the duty cycle of the machine. A good book on electric motors is "Electric Motors and Control Techniques" It is published by Tab Books. Cheers, Eric
Any type of static restive load will drop in current when voltage drops. This is standard ohm's law. P=I*E and I = E/R and P=E^2/R. When voltage drops, power drops by the square of the voltage. Cut the voltage in half and the power is reduced to a forth of what it was. This is true for lights, heaters, etc.
Nope. It's not a constant torque device. The torque is a direct function of voltage. The higher the voltage, the greater the current, and the stronger the magnetic field, and the higher the torque. Drop the voltage, and the torque drops.
I don't know anything about fuel pumps so I can't comment on what might be happening there. But I can guess. If the fuel pump has some sort of feed back control of the pump that regulates fuel pressure, then a drop in voltage would require an increase in current to get the fuel to the correct pressure.
Or, thinking about this from a different direction. If the fuel flow rate is regulated by other systems (like a carburetor), then the pump will be forced to move the correct amount of fuel no matter what the voltage is and probably require a fairly constant amount of energy to move the fuel at that rate. As such, if the voltage drops, the current will end up rising to move the required amount of fuel.
But if this happens, it's not because the motor itself will naturally act as a constant torque device - it's because there are other external feedback systems forcing it to be used that way.
And likewise, with your example of the welder turning up the current when the voltage drops, you have added another example of an external feedback system regulating the system to make it act like a constant power device.
Simple welders just control the current by selecting a different tap on the transformer. If the taps are A to D, the welder is welding at C, he can turn it up to D if the voltage drops. But if he is already at D, and the voltage drops, he can't turn it up. The net result is that the system will always be putting out less voltage and less current than it was designed to put out for a given tap setting and no damage will be done. So a drop in voltage will have no effect for one of these simple welders than making it put out lower voltage and current than it normally does.
However, most welders have other electronics in them (a fan if nothing else), that could malfunction if the voltage drops too much so there's a limit to how much it can drop and still be useful.
Inverter based welders however might be a very different story. They might do just what you suggest because they have internal feedback systems in them. If they are set to output 100 amps, and the input voltage drops, they will draw more current so they can keep delivering that 100 amps.
Most power supplies used in modern electronics also work as you suggest. Because they are regulated power supplies which attempt to keep their output constant, they will often draw more current when the power drops. But it depends on the design of the power supply. This is true for newer switching type supplies (which are like welding inverters in design), but not true of older types which regulate by throwing extra power away as heat. The old type will use a transform to drop the voltage to say 12 volts, and then use transistor based regulator to drop than down to 5V. But the power loss in the drop from 12 to 5 is just converted to heat. If the input voltage drops, the transform output could drop to 8 volts, which means there is less energy to burn up as heat to get the 8 volts down to 5. Small current power supplies all work that way (such as your typical wall-warts). High current supplies like for PCs (and invert based welders) are the switching power supply design which doesn't waste the energy as heat but will increase current draw when voltage drops.
I wonder what the typical inverter welder design does when the voltage gets too low? Does it sense the issue and limit the output current to limit the current draw from the input? Or what? Or does it has a temp sensor on the transformer and cut off because the transformer is getting too hot?
My inverter welder (only a Chinese cheapie) has an input voltage sensor so it will shut down if the supply (actually it monitors the input capacitors after the rectifier) drops too far. This is for self-protection because if the IGBTs saturate and get much voltage across them when conducting they get very hot very quickly. There is also a temperature sensor but this is mounted on the output heatsink so it monitors heat from the output diodes rather than the IGBTs.
What, you want to see while you weld? I like to just poke around making sparks until I find the right place to weld. :)
If you work by yourself, you won't be welding and grinding at the same time, so you don't need any extra power for the grinder since it shouldn't need more power than the welder. So you would just need the extra power for the lights. So how much light do you need? If it takes 5 kw for the the welder, a 7kw generator should give enough extra power for 2 kw of lights - that's four 500 watt halogen work lights. (or a lot more light if you use LED or CF lights). That's a lot of light, but it's just a function of how big an area you want to light up so that you don't have to keep moving the lights as you work (and how blind you are - I need a lot of light these days to see what I'm doing).
Be aware that cheap generators will only run for approximately 200 hours until they die. So if you are planning something other than occasional use, you will need to spend more money to buy something more seriously made.
I bought a 40' container. Instead of having the power company come in and run a new line to it, put in a panel, get a permit, etc, etc, etc, I figured that it might be easiest to just get a generator. Yes, lights, and a drill or grinder would be all I'd be using at one time. But, I'd have on some lighting rather then dragging around a light on a stand.
Why don't they put that SEND button in a safer place?
What I MEANT to say was that I anticipate paying a good bit for a generator in the 7kw range. I'm familiar with cheapos, but not from owning myself. I've seen a lot of them die after their owners touted how good they were, and how cheap they were. So, I'll look around, and probably do what's common to me. Buy used.
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