Invertor size for a refrigerator

[ronmc]

I have a refrigerator rated at 6.5 amps max. Would a 1000 watt pure sine inverter be sufficient? Nothing else would be on the circuit.

[ronmc]

Thanks,Gdetrailer, A very clear answer to my posting.I am looking at a 1000W. PSW inverter on Amazon. I will check out the tag on the compressor.I will look at the Triplet site for MSW inverters.

[MEXICOWANDERER]

I like the idea of test-hopping a MSW by using a correctly sized one, and comparing the compressor motor temperature to that of household current power. If the motor runs much warmer, then the MSW is not used. There are NO standards and by the way many "pure" sine wave inverters revert to QUASI sine wave output after a certain power percentage is reached.

[Gdetrailer]

rkentzel wrote:

Perhaps you should post a few model numbers of those supposed "three phase" home fridges?

I would only expect that type of "technology" in an extreme "high end" close to commercial type fridge. Certainly not going to happen in ANY household fridge sold at most normal consumer outlets like Home Depot, Lowes and such.

Well your wrong GE Samsung, LG, Kitchen Aid, Whirlpol,Frigidaire. I am not going to post model numbers to many. One poster has shown he or she owns a GE momnogram with inverter 3 phase compressor. I have replaced several inverter boards on some Samsungs due to defective capacitors.

The power supplies like what would be used to drive a heavy duty three phase motor drive USE the exact same principles as any other switching power supply.

First, the 120V AC is rectified through a full wave bridge rectifier, that is brute force filtered with some healthy capacitors (470 mf at 400V DC) which produces 160-170V DC unfiltered and unregulated voltage (has some 120hz ripple).

Second, the DC voltage is then chopped at high frequency then run through a high frequency transformer, then rectified and final filtering.

Third, the now filtered voltage goes to the "three phase" motor drive outputs which often are nothing more than PWM SQUARE WAVES.

YOUR overall "feeling" that a three phase motor drive can not be run on a good quality MSW inverter is an OPINION not based on facts but because you "replaced" "bad caps" on some drive boards.

"Bad caps" happen in ANY electronic items and can not solely blamed by the use of a MSW inverter. In fact 100% of the UPS units on the market ARE MSW and have been since the 1990s.

Computer power supplies are switching power supplies and are not damaged by the use of MSW nor are they damaged by square wave inverters (yep, the early computer UPS units were in fact SQUARE WAVE output, I personally repaired the early UPS units back in the day).

Not to mention many people tend to gravitate to the CHEAPEST inverter which may not have enough surge capacity available to reliably start a motor under load.

I should also point out that MANY if not all RV manufacturers which offer 120V home fridges in fact USE MSW inverters to power those fridges. However they are not using $29 1000W MSW inverters...

[westend]

Gdetrailer wrote:

westend wrote:
Knowing what the locked rotor draw is where you should start. I made the mistake of matching an inverter to a fridge where the inverter should have handled the load but didn't. I replaced that inverter with a larger one and haven't had any issues since.
The Tripp Lite inverters that are built for motor startup have a good rep but prices are getting closer with the newer sine wave inverters. I am using a Xantrex Prowatt inverter and think it's a fairly well built device.

Many of the newer inverters use a high frequency chopper like a switching power supply. The chopper often is at frequencies above 20 khz which allows for the use of much smaller high frequency transformers or diode/capacitor voltage "doubler" technique in order to arrive at 160-170V DC. The high voltage DC is then run through basically the same setup as a audio amplifier. The AC load attaches directly to the output stage.

while it works one of the draw backs with this setup is the chopper circuit has very little surge capacity, in fact most inverters do not disclose the duration of the surge which the inverter can handle. This is extremely important when dealing with high startup surges of an inductive load.

The Tripplite PV1250 is expensive because instead of using a chopper circuit, they are actually using the old school tried and true method which employs and very large and heavy 60 hz transformer taking the 12V DC to 12V 60hz AC through the transformer and the transformer is multiplying to 120V. The PV1250 weighs in at 20 lbs compared to a chopper type at just one or two pounds.

This has several advantages over a high frequency chopper, one is much higher surge capacity, two is reduction of harmonics in the output (transformer actually filters out the high frequency harmonics which takes a lot of the edges off the wave form), three is the transformer absorbs the back EMF from the highly inductive load lick a motor (this is critical in preventing the output transistors from seeing these back EMF spikes).

Expensive, perhaps but not all that expensive if you think about how much larger of a PSW inverter you would have to buy to get the high surge capacity of the Tripplite. It is hard to beat at $280 and you get 1250W continuous, 2500W surge for TEN MINUTES additionally they give a 2400W surge rating for SIXTY MINUTES.

I challenge anyone who can find a 1200W PSW inverter which makes a 2500W TEN MINUTE SURGE capacity inverter for a mere $280 (most if not all that do give a time rating will be seconds or even microseconds).

Thanks for taking the time to explain the electronic differences between the two inverters. My issues with the smaller Samlex pure sine inverter and the fridge probably existed from just what you explained, a chopper that doesn't have enough duration at higher surge.
Sometimes, there just isn't a good substitute for a large chunk of copper. :B

[vermilye]

Just to be clear - the 3 phase refrigerators "make" 3 phase to run the compressor, but they are designed to run on standard single phase 120/240 AC. There are commercial 3 phase refrigerators, but they can' t be used in the home since most homes don't have 3 phase electricity available.

[rkentzel]

Perhaps you should post a few model numbers of those supposed "three phase" home fridges?

I would only expect that type of "technology" in an extreme "high end" close to commercial type fridge. Certainly not going to happen in ANY household fridge sold at most normal consumer outlets like Home Depot, Lowes and such.

Well your wrong GE Samsung, LG, Kitchen Aid, Whirlpol,Frigidaire. I am not going to post model numbers to many. One poster has shown he or she owns a GE momnogram with inverter 3 phase compressor. I have replaced several inverter boards on some Samsungs due to defective capacitors.

[RVs-R-Fun]

Short Simple Answer: A 1,000W Pure Sinewave Inverter should certainly be able to run a 6.5A Max. rated refrigerator... if, indeed, that is the maximum amperage it will ever pull.


I hope that helps.


- RVs-R-Fun! 🙂

[Gdetrailer]

westend wrote:
Knowing what the locked rotor draw is where you should start. I made the mistake of matching an inverter to a fridge where the inverter should have handled the load but didn't. I replaced that inverter with a larger one and haven't had any issues since.
The Tripp Lite inverters that are built for motor startup have a good rep but prices are getting closer with the newer sine wave inverters. I am using a Xantrex Prowatt inverter and think it's a fairly well built device.

Many of the newer inverters use a high frequency chopper like a switching power supply. The chopper often is at frequencies above 20 khz which allows for the use of much smaller high frequency transformers or diode/capacitor voltage "doubler" technique in order to arrive at 160-170V DC. The high voltage DC is then run through basically the same setup as a audio amplifier. The AC load attaches directly to the output stage.

while it works one of the draw backs with this setup is the chopper circuit has very little surge capacity, in fact most inverters do not disclose the duration of the surge which the inverter can handle. This is extremely important when dealing with high startup surges of an inductive load.

The Tripplite PV1250 is expensive because instead of using a chopper circuit, they are actually using the old school tried and true method which employs and very large and heavy 60 hz transformer taking the 12V DC to 12V 60hz AC through the transformer and the transformer is multiplying to 120V. The PV1250 weighs in at 20 lbs compared to a chopper type at just one or two pounds.

This has several advantages over a high frequency chopper, one is much higher surge capacity, two is reduction of harmonics in the output (transformer actually filters out the high frequency harmonics which takes a lot of the edges off the wave form), three is the transformer absorbs the back EMF from the highly inductive load lick a motor (this is critical in preventing the output transistors from seeing these back EMF spikes).

Expensive, perhaps but not all that expensive if you think about how much larger of a PSW inverter you would have to buy to get the high surge capacity of the Tripplite. It is hard to beat at $280 and you get 1250W continuous, 2500W surge for TEN MINUTES additionally they give a 2400W surge rating for SIXTY MINUTES.

I challenge anyone who can find a 1200W PSW inverter which makes a 2500W TEN MINUTE SURGE capacity inverter for a mere $280 (most if not all that do give a time rating will be seconds or even microseconds).

[BFL13]

Reading the manual for my MSW 2000w Vector inverter, it says it is "ideal for powering ...refrigerators/freezers...."

It says though, to check the label on the device (fridge eg) so it does not overload the inverter's rating (such as the surge on starting be within the inverter's surge rating)

Then it makes an important point. If the voltage drops below 11v on start-up so the inverter alarms, this is not the inverter's fault, but the problem is you don't have enough battery to keep the voltage above 11v.

None of which addresses PSW vs MSW, but that too should be (but is it?) specified for the fridge as in mena's post above.

[mena661]

BFL13 wrote:

No need to be so sub-tile. That 1250 seems alright. I like my MSW Vector 2000w, but they don't make them anymore. It runs the MW ok. It runs any kind of motor ok. Lawn trimmer, air compressor, drill. Can't see why it would not run a fridge.

There is the usual list of things that don't run on MSW, but these are fussy things that have SCRs or whatever. Laser printers, etc. I never saw a fridge on any such list.
.

Some recently have said that the Fisher & Paykel fridges (seem to be gaining some popularity here) require PSW (according the manufacturer) or the warranty is void but the Samsung RF193 (??) does not.

[westend]

Knowing what the locked rotor draw is where you should start. I made the mistake of matching an inverter to a fridge where the inverter should have handled the load but didn't. I replaced that inverter with a larger one and haven't had any issues since.
The Tripp Lite inverters that are built for motor startup have a good rep but prices are getting closer with the newer sine wave inverters. I am using a Xantrex Prowatt inverter and think it's a fairly well built device.

[BFL13]

Gdetrailer wrote:


What a bunch of bovine droppings.....

.

No need to be so sub-tile. That 1250 seems alright. I like my MSW Vector 2000w, but they don't make them anymore. It runs the MW ok. It runs any kind of motor ok. Lawn trimmer, air compressor, drill. Can't see why it would not run a fridge.

There is the usual list of things that don't run on MSW, but these are fussy things that have SCRs or whatever. Laser printers, etc. I never saw a fridge on any such list.
.

[time2roll]

My home fridge has a compressor driven by three phase electric. GE Profile(or is it Monogram?), cabinet depth, built in. I believe the three phase is created electronically by an inverter of sort. I wanted to add a timer to stop the compressor during peak TOU electric rates. After reviewing the set up I let it alone. I would not trust it to MSW but then it would be rare in an RV.

[Gdetrailer]

rkentzel wrote:
There a few refer out there now that are three phase run from inverter boards for it. Plus it may have two to three boards running different functions. I would only want a psw inverter for mine. I speak from being authorized service for the majors now retired. I have seen people who go out and spend all kinds of money tearing out there rv frig and replacing it with 2500-3000 dolar refer and cheap out and put some cheap junk modified sine wave inverter in makes me cringe.

Most all the boards are under in the back or on the back panel not a normal installation so you would have to unistall it for a tech to repair it. If its just static coil design just stick it in leave so room for air circulation and put in which one you want. Ya and I know some of you say you run MSW on you big dollar fridge but you pay for that at some point.

:R

What a bunch of bovine droppings.

Perhaps you should post a few model numbers of those supposed "three phase" home fridges?

I would only expect that type of "technology" in an extreme "high end" close to commercial type fridge. Certainly not going to happen in ANY household fridge sold at most normal consumer outlets like Home Depot, Lowes and such.

Please don't get me started on the MSW/PSW thing, I have as of yet had very few things not work well with MSW. But keep in mind I DON'T mess around with those $29 2000W junkers. No instead I stay with a GOOD brand name like Tripplite which makes one whopper of a heavy duty MSW inverter.

The one I use for my home fridge conversion is the PV1250, starts and runs the fridge without any additional noise from the compressor. I listened to the sound when running from shore power and from the MSW inverter, NO discernible difference in sound nor sound level of the compressor.

I also checked to see if the compressor ran hotter on MSW, the result was only a couple of degrees and that could have been attributed to the difference in the ambient air temps when I checked it.

For the OP,

While your fridge is RATED at 6.5A, most likely that is including any and all FANS PLUS door heaters and or the DEFROST HEATERS. Basically the name plate rating INCLUDES any and all devices current draw contained within the fridge which may or may not be running at the same time.

I have found in most cases the actual compressor will be about 1-1.2A run draw which translates to about 10A startup surge of the compressor.

If you get the chance, you can remove the back or get to the compressor and read the data plate on the compressor to confirm the draw, this is where the majority of the startup surge happens.

If you don't have the inverter yet I would highly recommend the PV1250, it IS designed to handle heavy inductive motor loads plus it has a neat power save feature called "load sense". It detects if there is a AC load demand and turns the inverter output on. When no AC load is detected it turns the inverter output off. This saves you a massive amount of Ahrs in battery capacity.

Additionally don't skimp on the 12V wiring, that startup surge requires you to ensure the voltage drop from the batteries is very small. 10 ga wires will not cut it, you will need to consider 1/0 and keep it short. I have 6ft of 1/0 (3ft for negative and 3ft for positive) on my inverter, so far have never had any shutdowns or alarms.

So far, my 10 cu ft home fridge is on its 6th camping season and only cost $300 so it is well paid for in my book.