How much inverter power is needed to start a mini fridge?

[dustboy]

I have a 400w modified sine inverter, I was hoping it would run my 110V mini fridge. It blows its 30A fuse, and if I over-fuse it, it doesn't have enough giddyups to start the fridge, even though it claims a peak output of 1000w.

This is the inverter:
http://smile.amazon.com/gp/product/B00527Z664/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1#productDetails

The inverter is connected to the battery by about 2' of 10 AWG wire. 1000w/12V=83A...do I just need larger wires? If I upgrade the inverter, how much oomph do I need?

[MtnDon]

The missing data is the duration of that 1000 watt surge. Often with small cheap inverters like this the surge is limited to less than a second. A refrigerator is going to need 3 to 5 seconds of surge power. The surge current required may be as high as 5 to 7 times the fridges rated running power. The usual route is to use an inverter that is rated for maybe 5 times the normal running power. It is a guessing game; no hard rule that works for all fridges and all inverters.

The 10 gauge wires don't help. If you have some larger wires try it. Or try doubling or tripling up the 10 gauge if the terminals will accept larger or more wires. It might help but don't be surprised if the fridge still won't start because the inverter may be incapable of delivering the required surge current for a long enough time. When trying it out also be aware that the fridge has to be sitting with the compressor not having been run recently. The high pressure in the system has to bleed off before the compressor will more easily start. So if trying and retrying you may be in a "no-way" situation.


FWIW, the large surge will also cause the battery voltage to dip severely which compounds the problem of trying to supply a large amount of current to the inverter. As the volts drop the amps will go up to try and compensate. Volts X amps = watts, so when the volts drop the amps increase to keep the watts the same. Hard to win with a small inverter and a 12 volt battery.

[dustboy]

Thanks Don. Now the question is do I spend the bucks to upgrade my electrical (more PV's, bigger inverter) to the point where I can run the inefficient fridge I already use in my office, or spend the big bucks for an Engel 12V or 3-way fridge. Not crazy about top-opening fridges.

I think moar power is more useful in the long run, and probably still a couple hundred cheaper.

[lrrowe]

Try surfing through the many posts in the forum and there are many discussions on refrigerators which might help you.
Here is one.
viewtopic.php?f=42&t=61873&start=75

Bob

[daveesl77]

I did two, cheap Wally World dorm fridge conversions. On one, with 120v a running amperage of .7a, start of 5a. The other is .9a running and 4.5a start. Anyway, with the first, as long as I initially started it with either shore power or my little HF 800w generator the first time in a day, from that point forward it would run on my little 800 watt inverter. The second one would not start or run, so I upped the inverter to a 2000 watt. It does run, but once again, it needs an initial start for the day using shore power or my little 800 watt HF generator.

If the units have been in constant usage, then there is no need to do the initial start. I only have to do that if they have been sitting around for awhile. And they do cycle on and off. The first one I gutted and put the workings into a cooler, which then turned it into a freezer. Like 10 below 0 (F) freezer in 90 degree Florida weather. Second one I kind of kept normal, using it as a normal fridge. These are the small Haier fridges. One was like 2 ft3 and the other is maybe 3. The first is over 8 years old, as my daughter used it when she was an undergrad.

So yes, it does work and depending on the unit you can get away with a pretty small inverter. Trick is you need a hefty battery and good cables to run it. I figure with the 2nd one, it runs about 40% of the time, once it is cold, on hot days. So, doing fuzzy math, that requires about 5-6 ah average @ 12v. There is the loss on the inverter but the gain by it being less than 50%. On our trip to the Keys in December, my 50 watt solar panel and grp 27 battery kept it running for 3 full days without an external charge. I run 4 ga wire, about 18 inches from my battery to the inverter, all connections soldered.

dave

[MtnDon]

We have a Truckfridge 130. That is 4.something cu ft. Google. Runs on 12 or 24 vdc. I'd find the link but we're on a shaky connection in the mtns right now.

[AzAv8r]

http://truckfridge.com/models.html

Several front-opening 12V models.

[Gold5one]

If you are using an RV battery, it may be having trouble putting out enough amps- try it off the car battery with the engine running. Perhaps the inverter has an advertised rating that is a bit over rated.
My 2.7cuft refrigerator will operate from a Stanley 800 watt inverter (around $55) -- about 120 watts running current. The Stanley inverter has a LCD wattage readout, which is handy to have.

[Socal Tom]

Not crazy about top-opening fridges.

.

I understand what you are saying, but since the fridge is usually mounted low in the trailer, it's much easier to see into,the top opening fridge, than to have to crouch down to find the milk. Also, top opening is more efficient, since the ping pong balls can't get out.
Tom

[dustboy]

Thanks all, lots of options to think about there. I hadn't heard of the Truckfridge, that looks like the ticket if I'm going to drop the big bucks on a refer. Same price as a top-opening Edgestar.

Ultimately it comes down to what I can find for a couple hundred on craigslist. You would think there would be dozens of 3-ways salvaged from RV's but they still want top dollar even for the ratty ones.

I understand what you are saying, but since the fridge is usually mounted low in the trailer, it's much easier to see into the top opening fridge, than to have to crouch down to find the milk. Also, top opening is more efficient, since the ping pong balls can't get out.
Tom

Tom makes a good case for flush-mounting a top-opener in the countertop.

[wtcreaux]

Dustboy..... EXCELLENT idea......hadn't even thought of elevating my 12-v refrig....would certainly make it easier for my wife (and me).......and this is why I appreciate this forum........the ideas brought forth...

[Socal Tom]

I put mine on a slider under the counter. I pull out the slider when I need to get inside, and in a pinch it becomes extra counter space.

ImageUploadedByTapatalk1425834063.671278.jpg (100.47 KiB) Viewed 2656 times

this is a bad picture of the idea. I think there is a picture of it puller out in my gallery.
Tom

[wtcreaux]

Tom,

that's a good idea also......its nice having ALL of these options

[dustboy]

Picked up a 'furbie Xantrex 1000w inverter for $40 on fleabay, nice little inverter and it doesn't break a sweat starting the fridge. Also has a good low no-load draw, <0.3A. I've got it set up on a trial run to see how long it will run on the battery.



Had a pair of 2 gauge welding cables laying around, same as recommended by Xantrex. Seems a bit like a bomb without a fuse or breaker on the battery, anybody found an inline fuse that would connect to the battery terminal?

[MtnDon]

Therer is a link to one type in this thread....

viewtopic.php?f=30&t=62683