115ltr Bar Fridge on inverter

Difference between MSW &PSW inverter is ?????

Google "pure sine wave vs modified sine wave".

Wave output & $$$ (-;

"Hidden 240v" obvious in a rescue situation...hmmm

My comment might have been misunderstood as I was just comparing an inverter which may be still connected and producing 240 volts to a generator that has stop working. The generator could easily be seen and easier to hear if running.

Honky

yes a generator running on a trailer wound be obvious.

cheers

Oops didnt think this posted so asked MSW / PSW question twice.......

Your 230V at home is basically a sine wave. In other words it is a single 50 Hertz frequency with no ( or little ) other frequencies called harmonics mixed in. All mains equipment is designed to work on this.

When they make 12v to 240v inverters, it is difficult and expensive to simulate the sine wave, so the cheap ones cheat by making a square wave and modifying it's shape and sometimes filtering it. The result is an approximation of a Sine Wave. This is *generally* called a Modified Sine Wave - MSW. ( see below) The advantages are that it is cheap, generates little power and fairly compact. The downside is that it is electrically noisy and a lot of equipment does not work or can fail when powered by it.

Pure Sine Wave inverters - PSW are more sophisticated and put out a signal that is very close to the mains in your home. Almost all equipment designed for 230V will work on these if you size it correctly for the power. The cost to do this is dollars, size, weight and heat.

Actually while most manufacturers call MSW a Modified Sine Wave, this is actually a recent marketing term. MSW actually means Modified Square Wave. This square wave roughly approximates a sine wive.

Modified Sine Wave sounds better in the ads though.

Have a look at this page - it takes more time to explain and shows some waveform diagrams for a better explanation.

Remember, that 808 watts will mostly be consumed by a motor driving a compressor.....the start up current may be as much as 4 times the runnig current AND you have to consider the power factor.

many inverters will supply short term peaks...but the correction for power factor will be continuous....that 800 watt motor may infact present a 1000w pluss continuous equavalent load power factor corrected.

An inverter deliveing 1000 wats on the 240v side will be drawing somewhere arround 40 amps from the battery.

typical portable fridges like engel and wacko will be drawing innthe 3.5 to 8 amp reigion.....from the battery.

The three way absorbtion fridges runnig on 12 volts will typically draw about 15 amps....and that is considered inefficient and engine running only operation.

its a no goer mate.

The only way that a 240V domestic fride is vialble is if you strap a generator to the drawbar and run it continously.

cheers

I notice further on that the figure is not 800 watts.

HI
OK, 240V x -.55A =132VA, indicates it has a PF of 0.606 which is around the figure for most frigs motors
The inverter will need to be capable of putting out THAT CURRENT continiously

That means min 150W pure sine wave inverter
But the starting current could well be6<8 times 0.5A. that for a short duration[A second or two]

So the surge or peak output required of the inverter would be near 1kVA
If you get an inverter with a 1Kw or 1kVA peak abilty you should be on the safe side.

PeterQ

Your help has been most appreciated Peter & cant thank you and the others enuf. At least now I have a better picture of where I stand.

Presumably any 12v DC cable supplied with most inverters would be considered more than adequate for basic use? Either way, what would you consider a maximum distance from battery to input, so as not to cause any problems? I have a place to put said inverter in dropdown cupboard under where fridge is located. I also have an existing 12v feed there, that used to supply the old 3 way fridge(wild guess is that is 20a capable wire).

For an old PMG/Telstra Technician I seem to have lost a lot of headspace on what I learnt over the years with them(left in 1998).

Hi Kev
A 1500W intverter will draw around 150A @12V at full load
The better ones will work down to around 11V input but will then draw even more amps
This is when voltage drop becomes a problem
If you can give the proposed length of cable run , from the battery to the inverter,we can workout some sizes for you BUT it will be much heavier than that old fridge feed .

PeterQ

distance would be around 3-3.5m all up. Reason I chose the spot I did, is that it becomes the easiest place to modify for air flow and available free space. Then if worse comes to worse could place in front cupboard and install vents and have slightly longer 240v cord or even install a specific 240v inverter outlet??

Hi Kev
In that case I would use at least AWG orB&S #1
[copper core dia of 7.35mmm]
At 150A will give around 0.75V drop


PeterQ

You have been more than helpful Peter, so will leave you in peace now, along with everyone else too!

Take care and happy travels