600w dc to ac invertor

[marsh]

Hi there,

Hope someone can help me please.
I've recently brought a 12v DC to 240v ac 600w invertor in the hope it will cut down on my electricity bills.
For those of you who do not live in the UK, electricity customers in the UK have been advised of very high price increases in excess of 35-60%.

I've wired my invertor to a 110 ampere deep cycle leisure battery which i bought last week. The voltage measured 12.73. I've also bought a 60w solar panel to keep the battery charged up. The voltage on the battery now is around 13.1-13.4.

The problem ive encountered is that the ac voltage from the invertor is around 190-199 volts according to my voltage meter. Have measured the 'normal' mains voltage and it is around 230-234volts.

I've checked all the connections to make sure they are all tight etc.

Has anyone have any ideas as to why the output voltage is so low? Is the invertor faulty or is there something im missing here? The only thing i can seem to run off this so far is a light bulb. I thought that with the voltage being much lower than the normal 230v the invertor may damage my tv and fridge freezer etc.

Any help or advice would be most appreciative.

Many thanks

Paul

[skimask]

Could be that your meter is messed up. Cheap meters don't really measure AC very well.
Easiest thing I can think of is to plug something in that NEEDs 230-240 volts and see what happens.

[keithdoxey]

Could also be the waveform from the inverter.

I have a 150W one and it will happily drive a tungsten light bulb but just screams when connected to a fluorescent light fitting. It als does strange things with the power supply for my new Dell Laptop. It runs for a short while before shutting off whereas my previous laptops have been fine with it.

[mackrackit]

And if the inverter is a modified sine wave the meter will have a harder time getting a correct reading.

[Melanie]

Also, a 600W Inverter is very lightweight. It is unlikely it will handle the starting current requirements of a standard domestic Fridge/Freezer.

I actually calculated the peak power requirements of a farmhouse I bought last year (just to see how self-sufficient I can make it)... including the swimming pool that I've had put in... 15kW - and that's even after considering it has about 60% LED lighting throughout the building!

[Archangel]

My Dad bought an older motor coach which has a generator. The A/C unit would nearly stall that generator, it pulled over 30 amps when starting. I bought him a new A/C unit and the generator handled it easily, < 15 amps to start. Reefer units are power hogs, the newer they are the more efficient they are, but 600 watts is not going to cut it. I would (in fact I did) enquire about a TOU (time of use) power meter and offset all of the big power uses to off peak price hours. It saves me a bunch of money every month.

[skimask]

I missed the fact the he's trying to drive a fridge/freezer.
600W? Ya, not so much. And besides, a 600W inverter, most likely one of those cheap ones, probably not even a modified sine-wave type. Try to drive an induction motor with one of those. You'd be lucky to get the thing to even turn much less drive a load.
Light bulbs? Sure... TV...maybe, but probably have a load of 60hz noise (amongst other harmonics) in the audio and maybe even in the video.
Laptop (and other) power adapters? Other than wattage, I don't really see any issues with driving those with a goofy square wave inverter...unless the peaks are too high or something.
I've got a Dell laptop also, 90W adapter/charger for the batt's. My small 200W inverter won't run the laptop AND charge the battery (laptop kicks into low power mode), but it'll either run the laptop OR charge the battery just fine. My 750W will run AND charge just fine.

[Archangel]

One other issue not addressed, is power in vs power out. The inverter likely has rather poor economy, as 600W out likely takes 1000W in, a better use of battery power can be had by using 12v RV light bulbs or even LED lights and keep the fridge hooked to the mains, the inverter could be used in the car, for 240V to go.

[keithdoxey]

I've got a Dell laptop also, 90W adapter/charger for the batt's. My small 200W inverter won't run the laptop AND charge the battery (laptop kicks into low power mode), but it'll either run the laptop OR charge the battery just fine. My 750W will run AND charge just fine.

Interesting !!!!!

My Dell PSU is a 90W one and when I first connect it the laptop is running from the power supply and it is charging but after a while the inverter shuts down. Flicking the power off and on again to the inverter restores power for a while. The inverter doesnt seem excessively hot when it shuts down so not sure what is happening.

[sougata]

Hi,

Different overload protection scheme results in different behaviour of an inverter. In case of square wave PWM inverters based on general purpose chips like the SG3525 relies on the principal of pulse by pulse current limitation.

SMPS (notebook adapters mainly without an input PFC stage) converts the incoming AC to DC and there is almost always a NTC in the input side to limit the inrush current while charging the bulk reservoir capacitor.
In case of square wave inverters the current demands while charging the capacitor may be quite steep causing a pulse-by-pulse shutdown of the output stages of the inverter. This results in a lower average output voltage which in turn causes even more currents due to a higher duty cycle of the SMPS operating to keep its output stable. Thus this may drive the inverter protection mechanism nuts.


In case of sinewave the capacitor draws a fairly non-linear current with the input wave-form when no PFC is used. Thus again misleading the overload protection mechanism which almost always relies on a complete cycles current demand to startup heavy loads.

Modern Sinewave inverter firmwares takes care of this by running a separate tight loop on every waveform lookup point to correct distortion and differentiating between steep sustainded overloads and peak current demands. In case of a properly desinged system the system would definately have a softstart and at least 300% overload capability for a period of 15 to 30 seconds. So an AC/Fridge/Compressor connected to such inverters may have starters arranged in a fashion that can be engaged without power and let the inverter startup alongwith the load to take advantage of the soft-start function.

So I think it all depends upon the nature of load and inverter types which should be considered. Only having an equal voltage may not be sufficient for a grid-tied inverter if it is not synchronized with mains. You would not gain energy points rather loose and possibily destroy the inverter if it is not synchronized with the mains and also dynamically adjust the base frequency when the mains frequency varies.