Inverter Output

[ronmc]

I am going to install an inverter. According to the Kill A Volt meter,the refrigerator draws 88 watts AC. How much would it draw at 12 volts?

[christopherglen]

If you haven't got the inverter yet, look at inverter/chargers. Once you have the inverter drawing down the batteries to run the fridge, you will need some way to put it back faster then the built in converter. I am hoping you have 250-300+ AH of batteries, or you could be seeing a fairly deep DOD overnight in hot weather (higher duty cycle of the fridge).

[MrWizard]

that 6.5a at 120v translates to almost 800w , thats going to be the compressor start up surge

our residential ridge runs 90~100 watts and we also have the Tripp-lite PV1250
inverter

it will power our 1100 cooking watts (1650watts consumed power) MW
but i prefer to use the generator when using the MW, unless its late at night no-genset hours

that is one very well built inverter

[Gdetrailer]

ronmc wrote:
Thanks,Gdetrailer, for a very clear answer.I should have posted that this was for a residential refrigerator only.It is rated at 6.5 Amps.max.It is a energy efficient unit,and 88 watts is the highest I'v seen on it.I am planning on using a modified sine inverter. Thoughts?

I would highly recommend a Tripplite PV1250 SEE HERE which is a heavy duty well built MSW inverter. It is the one I use and has no problem starting and running my home fridge.

The PV1250 also has a real nice additional feature, it has what they call a load sense. In a nut shell it is a power save feature which allows the inverter to power down into a sleep mode when there is no AC demand.

What this means for you is a savings of 10-20Ahrs PER DAY in battery capacity when the fridge thermostat is not calling for cooling. I have mine set to turn on the inverter with about a 9W load so when we open the fridge door the inverter turns on and the light lights up :B

The PV1250 IS designed from the ground up SPECIFICALLY for starting and running inductive motor loads. It uses and old school tried and true heavy duty 60hz transformer to "boost" the voltage from 12V to 120V.

The PV1250 is unique when it comes to surge ratings, it will sustain a surge of 2400W for 10 MINUTES 🙂 unlike most inverters (INCLUDING MOST IF NOT ALL PSW makes) which typically have surge ratings of SECONDS and MANY DO NOT GIVE A TIME RATING which makes those surge ratings totally useless and you should consider them as bogus info..

If you need auto transfer from shore to inverter Tripplite does make models based on the PV1250 with ATS (Auto Transfer Switch) but they do cost more.

Others will chime in for the need of PSW but that really is not needed if you buy a good name brand MSW like the Tripplites.

[time2roll]

I would go sine wave only. Make sure the surge rating covers max amps.

[pianotuna]

Hi,

For the extra cost I'd go with pure sine wave.

88 watts will "translate", after inverter losses, to about 8.8 amps @ 12 volts.

[2oldman]

household refer and inverter2009
Household refer Class A 2009
residential fridge- boondocking 09

[ronmc]

Thanks,Gdetrailer, for a very clear answer.I should have posted that this was for a residential refrigerator only.It is rated at 6.5 Amps.max.It is a energy efficient unit,and 88 watts is the highest I'v seen on it.I am planning on using a modified sine inverter. Thoughts?

[MrWizard]

either that is a residential fridge
OR
that the draw of the 'icemaker' in the RV LP fridge

[2oldman]

88 watts.

Most RV refers draw a lot more than 88w- somewhere around 350w. What kind of refer are we talking about?

[Gdetrailer]

88W at 120V is .73A

Typically converting from 12V to 120V is a factor of ten so that would be 7.3A at 12V BUT that does not include inverter LOSSES.

Typically inverters large enough to handle the inductive load surges a compressor style fridge will present you can easily add an extra 2A at 12V.

So your fridge will be drawing close to 9.3A at 12V so for simplicity round it to 10A at 12V.

Now hopefully you have not bought an inverter as of yet..

When attempting to run a home fridge from an inverter you NEED to account for the STARTUP SURGE. Inductive motor loads have a very large startup surge, this surge MUST be considered in order to successfully start the fridge.

Typically the startup surge is 9 - 10 times the run current.

So in your case .73A at 120V will see a surge of 7.3A at 120V

So your 88W run will be 876W, the typical urge is to use a 700W inverter with 1400W surge. RESIST this urge.

Instead consider at a minimum a 1000W inverter with 2000W surge. The reason for this is most elcheapo inverters have too little of surge time and typically result in unpredictable results.

By the way that startup surge will result in the inverter drawing at least 75A-90A at 12V so make sure your 12V wire to the inverter is heavy and as short as possible.

For my setup I used 1/0 and only 3ft each (pos and neg) long to the batteries.

Make sure you FUSE the 12V wire...

[westend]

It will draw 88 watts when running. Watts are a measure of power used.

What you need to know are: How many amps the refrigerator draws at startup (lock rotor draw), how many amps the inverter is capable of outputting at it's maximum, and if the maximum output has enough duration (time) to overcome the startup draw. You should also allow for some loss through the inverter (typically 10% in real world).
You can convert the above back to watts at 12v. Watts= volts X amps.

Reading between the lines here but you have almost identical the amount of watts that my Kill-A-Watt displayed when hooked to my dorm fridge at 120v. What happened when I tried to install an inverter was that my 600w inverter was unable to overcome the startup draw. Since the inverter's rating was 1200W, maximum, it should have been enough but the "duration" of the maximum was not enough, the inverter would go into protection.

Since I planned to use an inverter for some other low-watt 120v devices, I upgraded to a larger 1000w inverter. I may have been able to buy another 600w inverter that would have run the fridge but price is negligible in these classes of inverters. All is running well now.

The 600w inverter was a Samlex SW series, pure sine. The 1000w inverter is a Xantrex Prowatt pure sine. Good luck with the inverter installation!

[darsben]

88 watts.
Watts = voltage times the amperage

So you are using less than an amp at 110; you will use +-8 amps at 12 volts.
But is the 88 watts AC just for the controls while running on GAS or are you going to use a 12 volt heat element?
Seems to me a 12 volt heat element will draw more than 88 watts.

So more details would be helpful