Inverter refrigerators and their interactions with search mode energy conserving DC /AC inverters

mcgivor

A question was recently asked by@Graham Parkinson  about the search mode of inverters and their interactions with a LG inverter refrigerator, although mine is a Panasonic the tests I conducted may relate to some/all inverter appliances.

Including others, such as switching transformer led drivers.

The experiment proved, in my case, that the refrigerator would not wake up the inverter even if the wattage was set to its lowest setpoint of 5 watts and the widest pulse of 25 seconds, other settings were tried. At 10 second pulses the interior light remained on at all times, obviously powered by capacitors, at 25 sec. It would turn off momentarily.then the pulse would change the capacitor.

To increase the load I turned on one led light fixture, it just illuminated during the pulse, turning on 4 did nothing no illumination and the inverter remained asleep. Which is a bummer, all these wonderful energy saving devices and they don't work with an energy saving DC/AC inverter

The experiment was using a Schneider SW 2524, so the results may differ with other brands, so for now I'll just program a block invert time say around midnight to 5am, until a solution, which I will come up with, sooner or later, is found. 

mvas

Are you testing an SW 2524 230 ?
The SW 2524 230 online manual states, the minimum Search Load = 25 watts.
Maybe, this manual is not for your inverter or your have updated firmware?
Also, can you try a resistive 5 Watt Load, an old C7 Incandescent Christmas Bulb 5 Watt, to see if that works?
Maybe, your loads are only drawing current during a too narrow portion of the PEAK AC Voltage or
the pulse voltage is too low to even get enough current flowing through your non-resistive loads.
Schneider may need to look into their Search Algorithm, 'cause we don't have very many resistive type loads vs 1 decade ago.

Estragon

I had a similar problem with Rennai on demand water heater and Morningstar inverter. Turning on a light woke it up, but otherwise nada.

Solray

It sounds like you may have mis-read the minimum current required to activate it through the search. Might want to re-check that.

mcgivor

mvas said:

Are you testing an SW 2524 230 ?
The SW 2524 230 online manual states, the minimum Search Load = 25 watts.
Maybe, this manual is not for your inverter or your have updated firmware?
Also, can you try a resistive 5 Watt Load, an old C7 Incandescent Christmas Bulb 5 Watt, to see if that works?
Maybe, your loads are only drawing current during a too narrow portion of the PEAK AC Voltage or
the pulse voltage is too low to even get enough current flowing through your non-resistive loads.
Schneider may need to look into their Search Algorithm, 'cause we don't have very many resistive type loads vs 1 decade ago.

It is a SW 2524-230, the minimum search watts is 5W, it will wake up with a simple restive load, just not with the inverter refrigerator or led lights, could be as you say, just clipping the peak, if the pulse was longer in duration than the 0.25 second  (estimated) and more like 2 seconds ,it may be enough to get things started, but that is just speculation.at this point. Will experiment futher using a clamp on ammeter, to time how long it takes to actually draw current,  an adjustment to the algorithm may be all that is required , yes a decade has brought more challenges to the engineers who rely on feedback, which I certainly will provide, pending futher investigation.

Marc Kurth

Good information, I will be following this.

Marc

Dave Angelini

Back when solar was expensive and people were new at solar this was a valuable feature. Adding the incandescent or using an external thermostat was often done. I am sorry to not be of much help but there is little chance you will get a change to be made for this. It just is not used and on the Outback forum they basically said the same thing with slow start circuits. More solar is the fix along with a battery that can support it.

mcgivor

Thanks Dave, there are other ways around this dilemma that have been floating around my mind, all theoretical at this point, how about using a digital time clock to provide a resistive load for, let's say one minute every hour, which will wake up the inverter, thereby allowing any load which can't wake it up, to begin  operating, if required, otherwise it would return to sleep mode. Not perfect, but just ideas that may trigger the brains of others.  
 

Dave Angelini

I think if you wake up with spoiled food your wife will not smile!  That may trigger the brains of others also!

BB.

More or less, in my humble opinion, once you have chosen to run a refrigerator off of solar, you are in a whole 'nother ball game of higher loads, more variable loads, high starting surges, etc... A refrigerator can draw 100% more for a day than planned power just if you put a bunch of warm food or unfrozen stuff in the freezer, or even running the ice maker.

Many things can be rescheduled... Washing clothes, vacuuming, cooking with electricity (using wood/propane/etc.). Many of these loads are ones that you run when you are home/at the cabin. Refrigeration is a (relatively large) automated load, if you don't have enough power and your food warms, your freezer defrosts, etc.... That is it.

-Bill

mcgivor

Running a refrigerator off grid is the major consumer which is why planning is so important with regards to when items are put into the freezer, mornings only to opportunity load, along with the other loads mentioned, my wanting to use the search mode is more for night time when there is no opening of the doors. Setting the thermostat to minimum, brings the temperatures down to 1°C refrigerator and -20°C freezer, after an hour of no openings, the temperatures are 3° and -17 respectively,so still within the safe range , tested with a Fluke DMM with a thermistor inside, ambient, 25°C.

My battery is large enough to support the refrigerator, no problem there, the purpose of the post is mainly to share results of experiments, so others might not make the assumption that an inverter type refrigerator will work with search mode, by thinking  it dose, only to discover later, with spoiled food perhaps, that their wonderful energy saving purchase could  actually cost more to run, energy wise , due to the DC /AC  inverters self consumption needed to support it at all times, is higher than that of a regular refrigerator used in conjunction search mode. 

The question was asked in this thread, didn't want to derail 
 http://forum.solar-electric.com/discussion/351398/lg-inverter-refrigerators#latest

Estragon

Pity they can't be made to run on DC and bypass the external inverter entirely.

Dave Angelini

DC wiring in living space would never pass a code inspection for a new home. Thinking more on this,  it might

mcgivor

They probably could run on DC because the AC is rectified anyway, catch is the polarity would have to be correct and the battery voltage would have to meet the input parameters, so a 120VAC unit would need a 120VDC battery, which  is not that common. 

Estragon

Could use a dc/dc converter, but hacking their shiny new fridge probably isn't on for most folks, and would no doubt void warranty.

mcgivor

The one I have allows 110-270VAC, 50 or 60 Hz,, no mention of DC, probably for polarity reasons??

Dave Angelini

In the US/Canada, and in all the new homes I have installed a power system in (over 100 including some old ones) if there is an inspection, the home must be wired for normal AC wiring. Absolutely no DC except at the battery to inverter and solar connections.

I know you do not care so much for warranty in Thailand so go ahead. It would be nice to know. A friend did this with a mini-split heat pump and saved about 3% of the energy so do not expect much other than fixing the search. If all of this has value to you, go for it!

jonr

A "one minute per hour resistive load" sounds like a great idea to get a refrigerator to start.   Perhaps inverters should include this feature (ie, normally scans for loads, but occasionally fires up to see if loads are waiting).

Almost every AC->DC circuit uses a bridge rectifier.  So when applying DC, the polarity doesn't matter.  But the peak voltage does - so for a 120VAC device, apply ~170VDC.    But only after checking the circuit to verify that the 120VAC is only fed to a rectifier.

Hill_Country

I faced a similar situation with my Magnum MS4448PAE inverter and the search mode requiring a minimum of 5 watts to "wake-up".  I would try to turn on a 9.5 watt LED light and it would just flicker according to the search pulses put out by the inverter.  The key here is that it takes a 5 watt resistive load, like others in this thread have alluded to.  I'm guessing you're facing much the same thing with your inverter refrigerator...an LED with a power supply acts as an inductive load, not a resistive load.   The search mode on the inverter can much more accurately sense a resistive load than it can an inductive load.  I ended up having to turn on multiple LEDs to get the inverter out of the search mode...in the end I just turned the search mode off and dealt with the tare loses.  Hope this helps!

westbranch

This discussion makes me wonder if there is a similar reason that GE put a filament bulb in our 3 yr old fridge, instead of LED, for an interior light?  My Cotek inverter is in 'search ' mode... and no problems starting, but I can not find any info on the compressor, it's not soft start at 30A 24V is it? at least not to me. I would expect ~ 5A  to be called soft start...

mcgivor

westbranch said:

This discussion makes me wonder if there is a similar reason that GE put a filament bulb in our 3 yr old fridge, instead of LED, for an interior light?  My Cotek inverter is in 'search ' mode... and no problems starting, but I can not find any info on the compressor, it's not soft start at 30A 24V is it? at least not to me. I would expect ~ 5A  to be called soft start..
.

With a clamp on ammeter on the DC input to the DC /AC inverter, the inverter refrigerator will climb slowly to about 5.4 amps above the tare load on start up, this takes about 5 seconds, the duration of the pulse is too short to recognize the load. Unfortunately only the frequency and watt recognition can be programmed, not the duration of the pulse, which is less than a second.

petertearai

Turning off search mode..... in  the end isn't a big deal . Most inverters need to run for lights at night  tv . washing machine  etc.
so in effect  your not running the inverter unnecessarily for 24 hours a day but maybe only 12 hours a day . An extra pv panel will easily sort that .

Graham Parkinson

Great responses to the original question re LG Inverter Fridges.  Good behavior on search mode is really useful for weekend cabins that keep the fridge/freezer going full time but no one is home opening doors, adding food etc.   There was a post on the other thread that the LG fridges woke up successfully but I didn't catch much in the way of details - i.e. search mode settings that made the fridge work.

We are looking forward to getting our main solar system up and running soon and getting off of noisy construction gensets. 

Just wired a separate (alternate) fridge power outlet to the utility room so I can run an LG Inverter Fridge off of small always on low tare sine wave invertor if search mode operation doesn't work out well.

Thanks!  Yrs,  Graham and Laurie