compact fridge

pianotuna wrote:
A 300 watt pure sine wave unit may work well.

No, 300W inverter even a PSW inverter simply will not have enough surge capacity to reliably start a fridge compressor..

Startup surge on the compressor will be about 9A-10A at 120V.. That would translate to 1080W-1200W of surge current.

Typically most inverters will have a surge rating of double the continuous output..

Which would put you about a 600W inverter as an absolute MINIMUM and that would be really pushing it since most inverters do not give any real surge info as far as the duration of the surge they measured. Most cheap inverters (including PSW) will never give the surge duration so it really is sketchy at best..

To be on the safe side it is better to error on the LARGER capacity inverter..

I would recommend at a min of 1000W CONTINUOUS which will give lots of headroom for the startup surge.

Inverter needs to be as close to the batteries as possible and use HEAVY gauge wire to the inverter from the batteries.. I used 6Ft (3ft for pos and 3ft for neg) of 1/0 to ensure minimal voltage drop under startup surge.

I would highly recommend a Tripplite PV1250, yes, it is a MSW inverter but it is designed and built to handle inductive loads like a fridge compressor. It also has a power save feature which allows the inverter to turn on/off with the AC load demand. This important feature will save a lot of battery capacity..

As far as a fridge recommendation, your going to have to go out to the stores and kick some tires.. There are a lot of small fridges and your going to have to look at them to determine if they will work for you..

Thanks folks for lots of valuable info. I now have a feel for what I'm up against. As a ballpark figure any thoughts as to how 2 group 31 batteries and 170 watts of solar would play with a compact fridge. I know lots of questions but I also know lots of fab work and $$$ just to find out that the set up is not a viable one.

is this for a weekend, a week, or full time ?

that 3 ampHrs be hour, will be 72ampHrs per 24hours

170w flat on the roof, might avg 8~10 amps in good sun

it just might be a break even situation, on good sunny days
and a loss on cloudy weather bad days
necessitating the use of a generator for catch up
and this does not include other power uses
it really depends on the cycle time of the fridge and how much power is actually used everyday

255w of solar just keeps up with our 3.2 cu ft fridge with about the same power requirements as the proposed 4.5 cu ft fridge, during a string of mostly sunny days. That is with a four battery bank.

If the fridge is cycling on half the time and it is half cloudy during the day, and it is half day and half night, then you have the solar needing to do twice what the fridge uses at night to stay even in a 24hr period. One overcast day and you are behind and might never catch up till you get shore power or have a generator and charger as well as solar.

If you have a generator and charger and lots of time allowed to run the gen if solar conditions are not so good, you can get by longer. Even if you had twice the solar it would not help if it is overcast.

Having a 120v fridge is very challenging for off-grid! Your rig has to be able to carry that generator and charger along, and IMO more than two batts so there is some reserve for when the sun is not shining. How much solar is needed is too scenario-dependant to be exact about. IMO 170w is not going to keep up, but then it depends on how long you will be camping before the batts get down to 50%. You lose some every day, so how many days "depends"

The 120v fridge requirements dominate everything, and makes camping off grid too much of a nail-biter IMO. If at all possible, have a propane fridge!!!!

I tried a similar fridge with a Samlex 600W inverter. It couldn't handle the LRD of the compressor. I now use a 1000W Xantrex and it doesn't flinch. Cloudy days mean I am looking for backup power. I have 235 W of solar and 300AH of battery capacity.

If the budget allows and you don't already have the residential fridge, you might want to consider one that uses a 12 volt Danfoss compressor. Both Dometic and Norcold make such units. Typical running current at 12 volts is about 3 amps.

If you're looking at a small fridge to save energy, be aware that many times a compact fridge will use as much, or more, power than an efficient full-sized fridge. In other words, you could have a lot more fridge space for hardly if any more power budget.

(On the other hand, if you're looking at a small fridge to fit into a small space, a small fridge does indeed invariably take up less room than an efficient full-sized fridge.)

Actually the smallest refrigerators use as much power as one 10x it's size.

I have seen where people use a capacitor on a 5000 BTU A/C to get it to start on a 1000w generator, why not do the same to a mini fridge to get it to start on a smaller inverter.

Listen to Wizard and GD.

This is what we have been doing since the DC Norcold died. It is the starting load that is the killer. You do not need PSW, the motor will just run a little hotter with a modified square wave inverter. I ended up with a 750/1500 Cheap Chinese unit and got one replaced in short order under warranty, but they are so cheap that I actually carry a spare NIB.

Put the inverter near the house bank. Run Gonzo heavy cable to the house bank. (The starting surge may be near 100 amps.) Place the inverter where it can get cooling air and not get wet. You can also use it for lots of other AC things while it is taking care of the reefer.

Matt

JiminDenver wrote:
Actually the smallest refrigerators use as much power as one 10x it's size.

I have seen where people use a capacitor on a 5000 BTU A/C to get it to start on a 1000w generator, why not do the same to a mini fridge to get it to start on a smaller inverter.

might be possible
IF you have the skill to open up the compressor and get at the wiring

in a fridge the start relay etc.. is inside the compressor cover
NOT external to the compressor, like the wiring in A/C units