600w Inverter won't run 1.2a chest freeze?

Tobit · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

I have noticed that inrush current varies depending on how long the compressor has been off. I've unplugged it for the night and going to take a new reading in the morning. I've also borrowed my electrician friends Fluke 334 to compare it to my lower accuracy unit.

BB. · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

Yes, it can, for various reasons.

When the fridge sets for 10 minutes or so, the input and output pressure on the compressor are about "equal".

If you shut down the compressor and try to restart, there can be ~200 PSI on the output and ~10's of PSI on the inlet--The compressor will take much more current to start.

A second issue can be the way the compressor limits inrush surge. This can be done with a MOV (metal oxide varistor). When the MOV is cold, it has relatively high resistance to the AC current flow (soft start). If you start/stop/restart, the MOV will be hot and have a low resistance--Increasing surge current... I don't know if MOVs (or similar) in refrigerator start circuits, but it can be an issue (more common in some AC to DC computer type power supplies).

There is a third issue... The liquid refrigerant in the refrigerator sets in the bottom of the compressor in normal operation (or if unplugged). If the refrigerator is shipped on its side (or tipped when moving), the refrigerant can migrate in the compressor and create the equivalent of hydro-locking the compressor. You need to let the compressor sit for for a few hours for the liquid to migrate back to its correct location.

-Bill

john p · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

If its an older fridge they can be modified by any fridge mechanic to start and run of a 400w inverter.. I dont know if this is true or not but have been told the latest 2013 onwards fridges can be easily modified to do this..

It certainly does work as had a few modified for myself and friends and all worked fine.

jonr · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

If you replace MOV with NTC thermistor, I agree with BB.

Tobit · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

So, I left the freezer unplugged over night so I could compare a much more accurate Fluke meter to my cheaper meter. Connected the meters this morning, flipped back on the circuit breaker, and I am showing 12.7A inrush with the Fluke. jonr, there is a schematic on the side of the freezer, I will take a look at it later and see if I can find a part number on the compressor and look at what would be involved in trying to reduce inrush. However, I think the OutBack GFX1424, recommended earlier by someone else, would work well and I like how it has built in charging and generator support.

Attachment not found.

BB. · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

John P,

Are you installing an NTC (negative temperature coefficient) resistor in series with the starting capacitor?

-Bill

john p · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

No BB if it was that simple then would not need a fridge mechanic..
This is how its done.
The pipes in and out of the compressor are cut. Then an electric 2 way valve is inserted in each pipe.A piece of pipe is connected between the 2 valves other inlets/outlets. A timer set to 10 seconds is connected into the thermostat switch wire.
This is why you need a fridge mechanic to insert the 2way valves and regas the fridge.. Air conditioning parts suppliers sell the valves.
Thats it.
When the thermostat operates as usual it now turns the 2 x2way valves to the bypass position for 10 secs. When time up and the compressor motor is up to speed the timer switches switches off the valves go back to "normal" position and the compressor does its job.

This completely solves the starting under pressure. Even if you wait 1 hr the inlet and outlet are not equal and the motor still starts under pressure requiring a "big" inverter.And you cant predict how long it will be between start ups of the compressor.

I actually got a std sized fridge to start reliably on a 300w MSW inverter.

BB. · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

Cool John (pun intended).

Yep, an "unloader" valve. That is what most all shop sized (and larger) air compressors have a version of--Otherwise they would be just about impossible start even on utility power.

Roughly, how much to folks charge for that conversion? Up here, we have the whole freon recycling requirements (remember the Ozone Hole--which is still there and still seasonal/solar wind related--as I recall) that have made anything refrigerant related, even more, expensive.

I am waiting for propane/isobutane (or other hydrocarbon) to be used as a refrigerant again. I think this stuff is safer than the "new" "ozone friendly" refrigerants (and it is only ~1 lb or so of propane--So the fire hazard is relatively small).

-Bill

Tobit · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

Yeah John, that's pretty cool but not sure if I am that ambitious to go that route. I may still go with the GFX1424 and live with any inefficiencies caused by the low AC load. I'd consider a smaller Samlex or Exeltech unit and separate charger but the Exeltech 600W has a surge of only 1100W. The Exeltech 1100W has a surge of 2000W but has a very high no-load idle usage of 20W. The Samlex SA-1000W (2000W surge) could likely work and I like how it has a sleep mode dropping idle down to ~3.5W. I'm tempted to give it a try but only if the retailer has a decent return policy if it doesn't work. The Samlex unit is only $400.

Blackcherry04 · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

Tobit wrote: »

Yeah John, that's pretty cool but not sure if I am that ambitious to go that route. I may still go with the GFX1424 and live with any inefficiencies caused by the low AC load. I'd consider a smaller Samlex or Exeltech unit and separate charger but the Exeltech 600W has a surge of only 1100W. The Exeltech 1100W has a surge of 2000W but has a very high no-load idle usage of 20W. The Samlex SA-1000W (2000W surge) could likely work and I like how it has a sleep mode dropping idle down to ~3.5W. I'm tempted to give it a try but only if the retailer has a decent return policy if it doesn't work. The Samlex unit is only $400.

Here is the problem , any non analog modern Refrigerator has a circuit board that has to have constant power to run the controls. A Inverter that goes into standby will cause the Refrigerator to malfunction. It's easy for someone to make a post about Inverter efficiency, but you never see the numbers or data it's based on.

Tobit · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

Blackcherry04 wrote: »

Here is the problem , any non analog modern Refrigerator has a circuit board that has to have constant power to run the controls. A Inverter that goes into standby will cause the Refrigerator to malfunction.

That's true. In fact, I've been trying to determine idle current of my freezer but don't think any of my meters can read that low as they all show zero when the compressor cycle kicks off. The GFX1424, still at the top of my short list, has a full idle power draw of ~18W and search mode draw of ~6W but I haven't read the manual yet to see how "search" mode functions. I should do that now.

BB. · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

Can estimate the increase in size needed to run the inverter 24*7:

18 watts * 24 hours * 1/0.52 system efficiency * 1/4 hours sun = 208 Watt more panel
18 watts * 1/0.85 inverter eff * 1/24 volt battery bank * 2 days storage * 1/0.50 max discharge = +85 AH @ 24 volt larger battery bank

A typical refrigerator will run around 1/3 to 1/2 of the time (depending on temperature, loading, etc.).

You have to decide if running the inverter 24x7 is a make/break deal for you or not. It is certainly not an insignificant extra load.

Refrigerators/freezers with manual defrost typically can live just fine on "search mode".

Those with manual defrost (mine has a clock motor driving a 12 hour timer for a 1-2 hour defrost cycle)--May work on search mode (with less defrosting capabilities--Warm/humid environments may have evaporator icing issues). Many search mode inverters turn on/off based on a minimum of ~6 Watt AC load).

Those with electronic defrost timers--Many have been seen to reset to zero and start a defrost cycle whenever the AC power is interrupted.

-Bill

jonr · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

Blackcherry04 wrote: »

Here is the problem , any non analog modern Refrigerator has a circuit board that has to have constant power to run the controls. A Inverter that goes into standby will cause the Refrigerator to malfunction.

Other than the defrost issue, a smart inverter control circuit designed specifically for a refrigerator might watch current draw, and when it dropped (ie, compressor goes off), it might leave the inverter off for a full hour.

You can also put a timer on the refrigerator and set it to only run every other hour. That cuts idle losses in half and should be enough on time to stay cold.

Can the defrost cycle be disabled and the refrigerator converted to manually activated defrost? Or rigged to use a battery powered defrost timer?

Tobit · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

My freezers defrost mode is turn it off and open the drain plug.

Blackcherry04 · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

jonr wrote: »

Exactly what happens with these refrigerators when the inverter sees that the power draw is very low, shuts down and then restarts every few seconds? Edit: I see that BB says it will upset the defrost timer.

Other than the above issue, a smart inverter control circuit designed specifically for a refrigerator might watch current draw, and when it dropped (ie, compressor goes off), it might leave the inverter off for a full hour.

You can also put a timer on the refrigerator and set it to only run every other hour. That cuts idle losses in half and should be enough on time to stay cold.

I know mine has a fan that runs between the freezer section and refrigerator, is controlled by a thermostat somewhere. The Ice maker malfunctions and the fill valve, it will dump ( must trigger the inverter ) but not refill. The temperature controls on the door flash on and off as it samples the load. Bottom line, it's not worth effort for savings . If my satellite box, loses programming, thats a big pain.

You can also put a timer on the refrigerator and set it to only run every other hour

If you have something to power it.

BB. · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

jonr wrote: »

Can the defrost cycle be disabled and the refrigerator converted to manually activated defrost? Or rigged to use a battery powered defrost timer?

It depends, but for the ones I have seen--No (I am not an appliance repair person).

The evaporator has a fan that circulates fridge/freezer air through it. As it cools the air, it condenses water/ice on the coils.

The defrost cycle turns on a heater (below the evaporator array in my freezer) for ~2 hours to melt the ice.

If you disable the heating cycle, some folks have reported in as little as 24 hours, their fridge/freezer starts using more power because of restricted air flow. I would worry that if I left the ice to build up over several days, the defrost heater would not be able to clear all of the ice.

-Bill

Blackcherry04 · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

I'v played around with the defrost timers a few times, ( by stopping them or advancing them ) Another problem is if you leave them off to long the Ice build up will break the glass tubes that the defrost heaters are inside of and you'll end up with buying one and they are not cheap.

Back in the day some were like a heat pump ( reverse cycle defrost or off cycle defrost ) We'v came forward and backwards at the same time. Some defrost timers are 12 hr and some 8 hr. I would think once every 24 hrs would be ok if you could find one or rig something up. My Ice maker heater uses more power than the defrost heater does.

jonr · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

I see that some of the better defrost designs only run the mechanical defrost timer when the compressor runs. So they would work fine with intermittent power.

I also see that the defrost process is thermostatically controlled. A thermostat senses when the ice is done melting. So there should be some flexibility in timing.

Would be interesting to know if refrigerators with microprocessors use non-volatile storage or a battery backed up timer to keep track of defrost timing.

john p · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

cost was about $35 au the valves ea and $18 the timer. made from kit. and $160 for mechanic to remove the gas .and reuse it with some new added.
Best bet for valves is eith a Samsung or Panasonic service place . Air conditioning section ..
Dont go to Carrier they overcharge big time.

Its hard to know if its economical or not.. If its the only big power user then you only need buy mabe a 600w inverter ..
My first one was 10 yrs old when modified and was ok after for 4 yrs.. It hard to know if it died because the MSW inverter or not. it did "buzz" a bit.
The idea was in first place mine. As Itook a compressor apart and say theproblem. but then saw how easy it could run if connected to no pipes and gas.. An engineer at work told me about two way electric valves.. so then it was just a matter of buying them. and findinf a fridge mechanic to do it..

jonr · May 2014

Re: 600w Inverter won't run 1.2a chest freeze?

I suppose that anyone buying a new refrigerator or freezer could bring an amp meter to the store and check both start-up load and that the unit doesn't suffer from the "do a defrost every time the power comes back on" problem.

It would be ideal if the refrigerator only defrosted during the afternoon when there is likely to be excess power available.

Refrigerators with inverter driven compressors are (supposedly) good for startup load. Has anyone tried one with intermittent power?

jonr · December 2014

Re: 600w Inverter won't run 1.2a chest freeze?

I finally got around to trying NTC thermistors as a way of reducing motor peak start-up current. I got a 16% reduction and more is probably possible. A good place to start would be some NTC-1.3D20's and then use one alone, or two in series or parallel to tune to the situation.

This isn't as good as what Wayne has done, but it's a simple and low cost add-on to many devices (just put it in series with the power input). They run very hot, so be careful where it sits.

jonr · December 2014

Re: 600w Inverter won't run 1.2a chest freeze?

I had everything set up, so I tried using a variac (variable auto transformer). I adjusted the voltage down from ~117V to 108V (105V when running) with the assumption that a refrigerator could safely start and run at this voltage (but your equipment may not!).

Startup current dropped 26%. So this is a more effective but more expensive "simple" solution.

jonr · December 2014

Re: 600w Inverter won't run 1.2a chest freeze?

I checked a microwave and the current flow has a big inrush spike on startup and then some nasty harmonics. The NTC thermistor was very effective on the former. Not even a line reactor had much effect on the latter.

600w Inverter won't run 1.2a chest freeze?

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