Inverter 1000W on asynchronous motor of 800W?

[Christophe]

I would like to power an asynchronous 800W motor (pump) with a 1000W inverter (modified sine wave). The inverter allows a power peak at 2500W, so I thought that the "margin" was sufficient but it gets stuck at startup ...

After a few tries the engine started once but after 5-6 s of buzzing in the engine which frankly does not inspire me confidence ...

Do you think that by adding a "big" capacitor it can improve things in order to preserve the lifespan of both the inverter and the motor?

The inverter manual indicates that it does not like inductive loads BUT that motors can be connected to it without problem so ... I swim a little

I made a test with another motor of 500W and it works without problem: instantaneous starting and no noise with the operation which makes it possible to distinguish it from the 50hz pure sine of the network.

Is there any hope for a solution?

[edfed]

inductive loads (motors) have a rotten cos phi, it is necessary to correct with a capacitor, it is obligatory.

for the cos phi correction, there are a bunch of applets or ready-made formulas that will allow you to choose the right capacitor.

otherwise, you can also try with a very big condo of minimum 10µF 300V (those of the neons) to see if that improves something.
afterwards, you add as many as necessary to obtain a satisfactory starting noise.

otherwise, a gradual starting technique will have to be implemented and requires a very slow rise in voltage of the inverter. namely, is this possible on yours?

otherwise, switch to brushless, no need for an inverter, just a brushless driver and a battery.
the powers of these engines are modest, but the outputs and performance are impressive.

[Alain G]

Hi Christopher!

Do you have the model of the pump and the inverter to see what we are talking about?


For some motors with very high starting amps, the inverter must provide double the wattage! In your case it seems that your inverter is able to hold the load.
The use of a 5 uf capacitor (run capacitor) in parallel
to the motor can help it to start but be careful to leave a few seconds of delay between the starts so as not to induce an accumulated voltage in the capacitor and you place it on the side of the motor, therefore continuously connected to it!

[Forhorse]

I would simply say that the inverter is too tight since it works with a less powerful motor.

You should know that the power indicated on an engine corresponds to its useful power (at the end of the shaft) and not the power absorbed.
Look at the motor plate, the indicated current should not be far from what the inverter can deliver at the maximum.

[Alain G]

I would simply say that the inverter is too tight since it works with a less powerful motor.

You should know that the power indicated on an engine corresponds to its useful power (at the end of the shaft) and not the power absorbed.
Look at the motor plate, the indicated current should not be far from what the inverter can deliver at the maximum.

Hi Forhorse!

I thought the same thing as you for the capacity of the inverter but Christophe mentions this: "After a few tries, the motor started once but after 5-6 s of buzzing in the motor which frankly does not inspire me confidence ... ", so if" it can hold 5-6 seconds, it is because it is powerful enough and the problem lies with the waveform emitted by the inverter!

[dedeleco]

Asynchronous motors often have an internal capacitor to phase shift (case of my mower motor) and maybe, if the motor is old, the capacitor has aged and lost its capacity, in which case it might be useful to change it (old , the starting torque decreases).
The other possibility is (rather small motors) an inductive copper loop in the armature and the cos phi is bad and it must be corrected !!
The inverter has different means of achieving its undulations which do not give the same result on inductive load.
It is necessary to know whether it is the inverter which triggers its safety by cutting the current or the motor which does not start with an insufficient voltage and current supplied by the inverter, still functional (measurements with voltmeter ammeter).
A series resistor on start-up can limit the start-up current (torque, lower) with a capacitor (new in ten or so microfarads) and allow the inverter to continue operating.
Since it starts sometimes, the solution does not hold much.
The inverter is not too bad because it is not dead !!!

[Forhorse]

It is safe to correct the motor cos phi with a judiciously calculated parallel condo (there are plenty of sites on the net which explain the calculations in detail, and the motor cos phi should be normally written on the motor plate. ) could eventually allow the engine to run.
because bad cos phi = greater line intensity for the same useful power. If we improve the cos phi then the line intensity should decrease a little and it can pass.
Either way, the inverter will always be at the limit of its power.
And I guess the testing was done empty?
Not sure it will pass once the engine is loaded

[chatelot16]

first what type of inverter?

if it is a pseudo sinus it is the disaster: it is a rectangular signal vaguely calculated to be equivalent to a sine in the dreams of the manufacturer ...

in Chinese wrongly translated modified sinus is the same

no need to put a capacitor: the only effect will be to make the inverter suffer even more

this form of non-sinusoidal voltage heats up the motor more than it turns: if you put a pseudo-sine inverter big enough not to trip it will burn out the motor

with a truly sinusoidal inverter it works!

Single-phase permanent capacitor motors naturally have a good cos phi due to this capacitor: once started it works without the need for an oversized inverter

some good true sine inverter have large peak current capacity: look for a good inverter

a pump is an easy thing to start: a good inverter must be able to lower its voltage when it is asked too much power but still making a sinusoidal voltage: the motor will start slower but will start anyway and the voltage will return to normal

it's the same story for the generator: some group do anything in case of overload and start only small asynchronous motor: others have good regulator and manage to start engine almost at maximum power