Inverter behaviour

CALLD

I've got a 2500watt inverter, 24V DC to 220V AC pure sine wave. It's a no-name Chinese make. Got it for the equivalent of $500 at current exchange rates. There were other inverters of the same wattage available for almost triple that price so it was a no-brainer for me. It works like a charm and is incredibly efficient. I tested the efficiency by running it through the load terminals on my charge controller which can only go up to 30A so that means the results could only speak for loads of under 720watts. The surprising thing was that it converted the power with nearly 100% efficiency when I crunched the numbers! Through every instance the DC input was between 5 to 10 watts higher than the AC output when measured by a Kill-a-watt meter. Thus I deduced that was more or less what the inverter needed to run itself and the rest it converted to AC without any significant losses. I can believe this because it runs very cool and the fans only kick-in when under loads of over 600watts or when the ambient temperature gets too high. That's the good part!

Now the annoying part: The sine wave is mostly very good and clean, however at specific loads (120 to 380watts) the voltage on the AC side seams to fluctuate rapidly between 200 to 220 volts. This is bad enough to cause CFL and LED lights to flicker very noticeably! The inverter also make a very rough sounding noise when this is happening. It's almost as if there is some voltage regulating system that doesn't work smoothly at these partial loads. Very annoying, but I suppose it is a trade-off for the low price and high efficiency.

jcheil

Re: Inverter behaviour

Unfortunately, you get what you pay for,. And you are seeing the result of that.
So many people here have learned the hard way about these off-brand inverters (myself included).
When it dies, you'll end up buying a real one and chalk it up as a learning experience -- and maybe even write a post just like this one

Cariboocoot

Re: Inverter behaviour

You should never connect an inverter to LOAD terminals of a charge controller. A 2500 Watt 24 Volt inverter would draw over 100 Amps at full power and no charge controller is capable of that. Testing it at lower outputs is meaningless because the efficiency rating is given for full power.

Your controller's metering is not accurate enough to give real results either. They don't need to be, as they are only giving relative performance indicators. Kill-A-Watt meters aren't highly accurate either.

I don't doubt you saw "near 100% efficiency" because almost all inverters run >90% these days. Factor in a +/- 10% range for the metering and you have anything from 80% to 100% (which is, of course, impossible). Not unusual at all.

BTW the Voltage sag you were wondering about in another thread is not out of line with expectations. (I've got something like 100 messages to deal with this morning so I'm going as fast as I can!)