How high load can an inverter manage?

[Arrandir]

I have two pure sine wave inverters 300 W which should manage peaks of double that. One is from EMC and one from MSW. The only use before have been for my computer and charge batteries.
Reasently I bought a multitool. I made sure to buy one which has lower power than the inverters, 260 W. Even though I should have 40 watt extra, I could only use it at 60 % power, which is enough. I worked with it on that power for over an hour. I often shut it off to do other things, I had it switched off maybe 1/3 of the time. The first inverter stopped working, except on very low load. I thought it was something wrong with that one and switched to the other one for the next time I used the powertool. Now that one has the same problem.
I can charge my computer, at least for a while, but only when it is switched off (use 4 amp). If I turn it on there is a warning peep from the inverter which could mean high voltage, low voltage, overheating or overloading.
Are inverters not supposed to be used close to their rating?

[GordMay]

Most inverters don't 'like' inductive loads, like motors.
Due to ‘Back EMF’, an inductive load, such as an AC motor, will use only about 70% of the electrical energy, to do actual work, requiring an inverter power supply rated at at least 142% of motor's rating [FLA].
This is in addition to the inverter’s “surge” rating, which allows for the motor’s starting inrush current [LRA].


The wattage ratings of resistive loads can be taken at face value, and are exactly as indicated on their labels.

[Arrandir]

Thanks for the reply.
Seems like if I need to buy a bigger inverter.

[HankOnthewater]

Another issue, advertised/marketing/brochure values are often just that, and actual/real values are often lower. It might well be that your 300 Watt is not continuous.
And as said before upthread, induction loads typically requires higher values of inverters, and some non-sine wave inverters dislike induction loads (ie motors).
So yes, a larger inverter may be called for. Hmmm, next issue you might encounter is that your battery (bank) may not be suitable for the larger loads. 500 watt draws at least 500/12=40 amp, plus 10-20% efficiency losses, makes it a draw of 44-48 amps.
Then the next issue how to replace those electrons, you need to charge the battery again.
Then..... you get the drift, each step is another assault on your wallet.
weapons of choice are: healthy credit card or boat simplicity.

[ttex]

What does your multimeter say you are drawing? Ratings don't tell you what is actually happening with your current.

Bad wiring is my guess. Corroded or loose connection.

[smac999]

You also need to make sure it’s dc feed is big enough to prevent voltage drop. Maybe it can produce 300w at 13v. But not at 10v.


You’re pulling 20A+ to that inverter. That certainly can’t be done though a cig plug without huge voltage drop. Which those 300w inverters normally plug into.

[Arrandir]

Originally Posted by smac999

You’re pulling 20A+ to that inverter. That certainly can’t be done though a cig plug without huge voltage drop. Which those 300w inverters normally plug into.

I think you figured it out for me. The first stoped working because of overheating, then some corrosion or something else made the connection bad so no one worked the next time I used them. They work again when I connect them in another way.
Thanks for all help.

[capt jgw]

Right. The cigarette plug kind aren't good for much more than charging your phone. If that's all you're doing it makes more sense to use a USB adapter and go from 12v DC direct to 5v DC instead of an inverter going 12v DC to 120v AC and then back to 5v DC. Uses probably half the power.