Running electric pumps with an inverter

You might TRY putting a/some motor RUN capacitors across the line when you try to start the motor. You might find that you need more capacitor when starting than when running.

IF the caps work you can get a potential type starting relay to switch out the start capacitor.

Starting current for a motor can be up to 6 times run current. Is your inverter that big?

This sounds like a job for a 12vDC pump. Look in a boat or RV store.

I think you need a sinewave inverter with plenty of momentary (5 second type start-up surge current at maybe about 15 amps). You need to talk to the maker & ensure that their inverter will be able to produce such large currents for several seconds to get it started. Once it is moving at full speed (after a few seconds), steady state current might indeed be only 0.5 amps, but the startup current for electric motors (blower motors & refrigerator compressor motors, too) have caused many inverters to fail (you are lucky the inverter did not smoke !!!) prematurely. Be prepared to pay a lot more money for these sinewave, motor-start capable inverters than the cheap squarewave versions for a few hundred bucks (which are good mostly for lighting applications, but not for anything else, really).

The cap in the motor is a 5 uF. Should I just add more capacitance by sticking another 5 uF in parallel with the one already in the motor? I'd probably put a series switch in to take the added caps off-line.

Why do you think I'd need a sinewave inverter? I was thinking it was a start-up current problem.

Both are issues. The start up is going to be simple math, but even when you overcome that (maybe) with a high rates square or quasi sine unit, watch out for heating in the motor. All those harmonics in those waveforms will play merry hell with the flux in the motor. The inverter is more likely to burn out than the motor tho. A square wave gives the same RMS over the cycle, but just picture what that must mean. Draw a sine wave, calculate the area under it. Now superimpose a square wave with the same area under it. Now try and tell and ac motor to behave properly with that sort of crap going on. It just doesn't happen.

Have you tried e-mailing a manufacturer. (both motor and inverter) The former will tell you the limitations on the motor, and best values for capacitor to reduce start current. The latter will be able to offer guidance on application of their devices.

Sine wave is at least fivefold the cost. Maybe a DC motor conversion would be, as the earlier post said, the best and cost effective solution.

Neil

No expert but happy to share an opinion. (No guarantees!)

I think too, that's a job for a DC motor.Besides incadescent lights, everything else operating on AC needs a sinusoidal wave to operate properly.

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The cap you have now (I suspect) is wired in series with a extra winding in the motor). Leave that cap alone and in place.

When I am talking about is a cap to "fool" the inverter so that its load doesn't look like a big inductor. The cap would be across the power leads from the invertor.

Hi there,

wow I didn't know there were such thing as sine wave AC inverters. Ok It's my fault because the place where I live in, inverters are rare here.

How do sine wave inverters work? I know square wave ones just use a switching transformer to switch 50hz and pass that 12v through a transformer.

So if we were to use a capacitor to overcome the inductive load issue, I believe what happens is that the motor will take ages to get up to speed as compared to the motor in our home AC circuit? Would that be a risk of spoiling the motors?

So can square wave inverters be used to power PC, power adapters, audio systems, etc.etc?

Thanks.

Do ALL sine wave inverters have the function to start up high inductive loads like motors? If they do, how do they work? charge up a large capacitor to handle the inductive load?

Thanks.

No, not all sinewave inverters can handle motor starting current (which can be 5 to 6 times the steady-state or rated current) which last several seconds. Most inverters in fact will either go into a current limiting mode (voltage will sag and current will be limited to

125% or so of max. rated inverter current with the result that motor will not run). Some cheaper inverters might trip its circuit breakers, blow fuses or even could smoke & fail permanently.

You have to ask the maker of inverter if the particular inverter is capable of starting a motor (worst one is the air moving blower motor found in your furnace - it takes very high startup current for several seconds). The ones that can maintain the voltage & provide 5 to 10 times start-up current for a few seconds are rare - and they are not cheap, either. If it is not written on their spec's as "motor-start capable inverter", it most likely will not be able to start a motor.

Thank you !

I'll give it a try.

I'm using a 700 watt modified sine-wave inverter.

It actually does start the motor, but the motor hums or buzzes as it's running.

If the 700 watt modified sinewave (or more accurately, a modified squarewave) inverter) starts the motor & runs it, then great. But the motor hum & buzz means motor is being stressed (like if your car engine produces strange hum & buzz, you know that something is wrong). So limit use of the motor to a few minutes (only under emergency cases where you HAVE TO operate the motor). Continued hum/buzz might mean that motor will start overheating after a few minutes/hours (how knows when?) burned winding wires might be the end result.