[Santos]

pure sinewave 300w mark
needs to be able to handle a 600-700w surge

my current 800w modied will not handle fridge

[Bugsta]

A discussion for another board really, but does your fridge not have a 12v input?

800W is HUGE for a car battery. That's 66Amps at 12v. Even 300W is 25 Amps. Something is wrong there. Plus extra for loss and cobversion of course.

[Santos]

Bugsta wrote:

A discussion for another board really, but does your fridge not have a 12v input?

800W is HUGE for a car battery. That's 66Amps at 12v. Even 300W is 25 Amps. Something is wrong there. Plus extra for loss and conversion of course.

Nothing is wrong with the 115l industrial chest 'fridge' (was freezer, now with digital thermal controller) . It just needs a pure sinewave to drive the compressor motor. Proof is in the fact it runs flawlessly when connected to the mains. The sticker says i runs at 247w draw however i have meassured it and it has a 640w to 'kick start' the compressor often refered to as 'surge'


Once running the compressor only needs to go for about 3-5 mins every hour. So 20.5A for 5 minutes every hour for 20hours shuld be ok for a 100Ah deep cycle Battery between recharges on a 2T generator. In fact it wil probbly run less than this since the cold air stays in the tub and when full it will retain its thermal mass better than empty, last christmas it worked really well by just doing it manually, since i have wired up the controller i have only tested it empty.

[Bugsta]

I wasn't necessarily referring that the 'someting wrong' was with the fridge. Just that an 800W, even non pure-sine wave should be ample.

Such a difference in the way fridges work. My 40L draws only 2.5 Amps, for a longer period of course.

[Santos]

Windings, compressor size etc.

Bit like gearing, small engine needs lots of turns to do the same work as what large engine could do in less turns.

Modified sinewave is usually just a 'pulsed DC' and' isn't really a wave pattern but a constant 0v 240v 0v 240v etc AC motors struggle to spin on this.

[Santos]

ooh and most caming fridges are absorbtion fridges with no compressor so a little different to what i'm doing.

I suspect dedicated camping compressor fridges have a 12v DC compressor rather than an AC 240v so they would run on modified sinewaves without issue as the 240v would be stepdowned back to 12v (in any event yu probably just plug it directly in to 12v anyway)