Pushing an AC inverter over the edge...

[eccerr0r]

I got a dead 400W (800W surge) Pure Sine AC inverter running once more and was testing it against multiple loads. I've had a fair set of modified sine and even a squarewave, but this 400W(800W) surge sine wave inverter is the closest to be able to power my refrigerator from 12V DC.

It takes a few tries but it seems that I can get my refrigerator started with this inverter. My 300W triplite (MSW), 320W simha (MSW), and 275W Heathkit(square wave) don't even get close - they go to shutdown right away. Even my 800W generator will even stall.

(incidentally speaking, the "surge" rating for the MSW inverters exceed that of the fuse rating, so the surge rating was only for less than a second. The sinewave actually have fuses that cover the whole current during surge rating...that's power.)

I wonder if anyone had any general suggestions that could get this inverter to push it over the hump and more reliably start the refrigerator? (Or maybe it's just the refrigerator that needs to be hacked/replaced?) Or perhaps this is just what I should expect from a 400W(800Wsurge) inverter should be able to do?

[Th3_uN1Qu3]

Re: Pushing an AC inverter over the edge...

You could upgrade the switching transistors and increase the current limit in the protection circuit. Some pictures and part numbers will help.

[kc8adu]

Re: Pushing an AC inverter over the edge...

try a hard start cap on the fridge.
upgrading the switchers and lowering the current sense might work...
or may saturate the transformer and go BANG!
you need a big battery bank to get any meaningful runtime.
i ran a ge monitor top all weekend at a remote garage/party spot last month on a cobra 400w.
of course we have solar and a 1000+ ah battery bank.
i fully expected the inverter to fail and set it on a noncombustible surface.
but it barely got warm.and the burgers,beer,and mt dew stayed just above freezing.
i need to measure the start surge of the old fridge.
its from 1928.

[eccerr0r]

Re: Pushing an AC inverter over the edge...

I've wondered how to jury rig a hard start cap that work like the kits...

I wouldn't expect a refrigerator to overpower a 400W inverter, they should only take less than 200W -- except during startups. If you have it running 24/7 that startup probably totals less than a few minutes per day, and if you have good insulation, the whole refrigerator would be off most of the time anyway.

As far as I estimate, I think the start up power is probably at least 5x (some say 7x) or so its "on" power rating. I measured my 'on' power rating at 180W; 5X is 900W which is just about my generator (~900W surge; I think this was rated at sea level) and this inverter (800W surge). My generator will stall when the refrigerator tries to start up, and this inverter shuts down except for an occasional attempt that it would start up with some effort.

[kc8adu]

Re: Pushing an AC inverter over the edge...

did some research and the monitor top is from 1935.
a kill a watt showed around 75w running.
as for a modern fridge disable the door heaters and defrost if you can.
in an emergency you dont need either.
it will defrost itself during the off time.

[eccerr0r]

Re: Pushing an AC inverter over the edge...

What do you mean "monitor top"?

My kitchen refrigerator measured about 180W steady state and something ridiculous during startup. Yes, definitely should disable defrost and even the door light when using the inverter (in fact, maybe one should stick a LED in there instead of using that 40W light emitting heater...)

I wish the refrigerator designer was smart enough not to turn on the defrost heater and the compressor at the same time, though who knows...

[goontron]

Re: Pushing an AC inverter over the edge...

^ http://www.industrialdesignhistory.c...xport/html/148 ?

[eccerr0r]

Re: Pushing an AC inverter over the edge...

Ah. It would be best to properly capitalize proper names.

Some idiot wrote "of" as an abbreviation for Open Firmware which is completely ambiguous. At least write OF or O.F. to make it clear.

[goontron]

Re: Pushing an AC inverter over the edge...

Well, its just like CB, BF, OM, SPPF and the like.

[eccerr0r]

Re: Pushing an AC inverter over the edge...

But those are not generic words like "monitor" and "top" ... at first I was thinking a small refrigerator that's small enough sit on top of a (CRT) computer monitor... Yeah, makes no sense, but it's possible.

[goontron]

Re: Pushing an AC inverter over the edge...

CoreBoot, BaoFeng, Old Man, Single Phase Power Feed.

Not sure what you read.

[eccerr0r]

Re: Pushing an AC inverter over the edge...

I was thinking if you wrote a sentence:

"You CB BF OM SPPF."

That would clearly indicate these are abbreviations and not actual words. And I suppose this example really doesn't have meaning =D