Community Forums

gary276 · 10-21-2014, 07:39 PM

Question:

I have a mini fridge that according to the literature that came with it has running amps of 1.0 to 1.4 and a base voltage of 115V(127V max). It also states that it uses 60-80 watts (last 1/3 of cycle), I assume this means last 1/3 of the compressor cycle.

I have 2 84 amp hour house batteries. Interstate SRM-24, not the best but that is what came with the MH.

I want to buy an inverter to run only the fridge off of the 2 batteries.

Doing the math of figuring wattage I get 115 (1.0 x 115) to 177.8 (1.4 x 127).

No info on start up amps/watts in the fridge literature. So guesswork of doubling or tripling the amps/watts for start up would suggest a 500 watt inverter would work.

Based on this the fridge would only run for maybe 5-6 hours, is this right?

And all of this does not take into account the lights (all LED) and fans also depleting the batteries.

I know bigger amp hour batteries would extend the time as would solar panels.

Trying my best to use the existing batteries.

mgscott4 · 10-21-2014, 08:27 PM

I would get a 300 watt inverter, don't pay more than $30 for one. Amazon has a good selection. Most can handle 600 watt surge for compressor start-up.

The important thing is mount the inverter as close to the batteries as possible but not in the same compartment. You can probably get away with 10 AWG wire but I would go bigger to ensure little to no voltage drop. Don't forget to fuse it, in case of a catastrophic failure.

Try your existing batteries first, I will bet they work fine, because the fridge will only run for a few minutes each hour, once at operating temperature.

If you find out you need more batteries, then upgrade with 2 (6volt) golf cart batteries. GC2 batteries are true deep cycle batteries that have approximately 220 amp hours.

mgscott4 · 10-21-2014, 08:30 PM

You can buy this to see exactly what the refrigerator power consumption is.

P3 P4400 Kill A Watt Electricity Usage Monitor - Low Temperature Alarms - Amazon.com

gary276 · 10-21-2014, 08:43 PM

Thank you for the reply, you can get a headache trying to figure this out.

KIX · 10-21-2014, 08:44 PM

I would suggest that you recharge your batteries when you have depleted the capacity by no more than 50%. Depleting them more can significantly shorten their usable life.

mgscott4 · 10-21-2014, 09:31 PM

Quote:

Originally Posted by KIX

I would suggest that you recharge your batteries when you have depleted the capacity by no more than 50%. Depleting them more can significantly shorten their usable life.

Yes, Kix is correct, but you need a good battery monitor to tell you where 50% is.

You can buy a hydrometer and measure specific gravity in each cell, the hydrometer will have a chart to reference specific gravity @ 50%.

Or use 12.0 volts as your low battery limit. This is close to 50%.

zman-az · 10-23-2014, 11:08 AM

You should get a pure sine wave inverter as a modified one "may" damage your fridge. I would think 300 watts would be fine but it all depends on the startup surge. When you fill the fridge make sure the items are already cold and keep the door shut as much as possible, this will reduce the fridge run time. Also a empty fridge runs more than a fully stocked fridge with cold items already in it. Consider getting a icepack and put in fridge (freezer section if possible) to help and if you drink a lot of tasty beverages you may want to keep them in a cooler as you will constantly be opening the door.

As far as run time there are to many variables. Most importantly is the outside temperature and humidity. The inverter will also use some power and then you have the lights and other things you mentioned. Do you have a generator, if so you will want to top the batteries off morning and night.

I think you need to just go for it and see how it works out and report back here of course.

vsheetz · 10-23-2014, 12:10 PM

If the manufacturer of the refrigerator states ok to use with a MSW inverter then good enough. If not specified I would go with a PSW inverter.

mgscott4 · 10-24-2014, 10:38 PM

The only problem I have had with my Freedom 458 MSW 2000 watt inverter is one of the 2 electric blankets I bought, would not run on the MSW. The other one works fine.

My 3 TV's, Sat receiver, microwave, 2 laptops, hair dryer, hair clippers, 2 phone chargers, fan, and ice machine all operate with no problems. (Not at the same time)

I do not operate my Refrigerator or electric hot water heater on the inverter, not because of the MSW, but because they draw too much power, and I can operate them both on propane.