Sundanzer DC vs. AC inverter fridge

dogdude

I see the happy users of new inverter refrigerators talking about the benefits due to lack of surge. I need help understanding the value of DC refrigeration as it relates to overnight battery/inverter “off-time”. 

I read that DC loads are good because they don’t need the inverter, which can then shut down when not in use overnight. I will be using a 2200w inverter, and was contemplating a Sundanzer fridge and freezer, but I guess I don’t yet understand why I wouldn’t just keep an efficient AC fridge plugged in all the time and let the inverter start it as needed. 

Sorry for not asking a direct question... I don’t know enough yet! Thanks.

mike95490

Most modern energy star fridges have a electronics package that manages the defrost cycle, and the electronics don't play well with sleep mode in the inverter,  when they wake up, many brands initiate a defrost cycle before running the chiller

dogdude

Thanks. Does it make sense to spend more up front for a DC fridge? And what about things like the clock on the microwave? Does that keep the inverter ‘awake’ at night?

BB.

A small solar system/small cabin... Running DC fridge/freezer can make sense. Assuming you are OK with manual defrosting.

As systems grow--Usually the inverters are on 100% of the time (enough loads, enough solar, enough battery) because the relatively small losses of 24x7 inverter losses are not that large of issue in big systems (just make solar+battery bank 1/0.85 or 1.18x larger to make up for losses).

The inverters in "search mode" typically (as far as I know) just output a few cycles of 120 VAC 60 Hz every couple of seconds looking for a >~8 Watt @ 120 VAC load... So, any AC timers are going to lose time during "search cycles".

One thing that would be interesting--I typically buy "cheap" fridge/freezers (frost free) from the big box stores. And the ones I have purchased used a mechanical timer for the defrost cycle....

One poster here said their fridge timer only "ran" when the compressor was operating (i.e., the longer the compressor ran, the "sooner" the defrost cycle would start)... I have never look at my "cheap" fridges/freezers wiring diagrams--But if that is true--Then, I believe, that they would be very happy running on an AC inverter [with search mode active--clarify. --BB] with an electro-mechanical defrost timer circuit.

But that is part of the issue of off grid homes--Finding appliances that will work with your power system/life style.

-Bill

dogdude

Thanks Bill. I am starting to think that my approach should be thoughtful use of efficient AC appliances, 120v LED lights, (no electric stove/heat etc..) and just build a robust system that can handle 100 percent inverter “on time”, as opposed to paying more up front in an effort to be super efficient. 

BB.

DD,

It would not hurt to do several paper designs and see what the cost/benefit issues are for you.

I am a big believer in conservation (saving energy) to keep the systems as small/efficient as possible.

120/240 VAC systems are pretty efficent these days--And make distributing power much easier (just standard AC Home main panel, and standard AC wiring). Low voltage DC can be done--But really on a smaller scale (lower power/current levels, shorter distances).

I also like having just one DC=>AC inverter vs a bunch of small DC appliances (and power bricks). The wide range of a solar power system (the full range can be from 10.5 to 16.0 volts for a 12 volt battery bank)... It is very unclear how many "12 VDC" (or 24/48 VDC) adapters really can run on that wide of voltage range... There have been 12 volt "car adapters" for good quality laptops that failed when operated on deep cycle / solar power systems.

And things like trying to get a non-standard DC refrigerators serviced can be difficult--As is losing the frost free option (at least for me as I am the person doing the dfrosting).

-Bill

dogdude

Thanks for the helpful reply!

Ralph Day

I found, years ago on my Xantrex 4048, that search mode really didn't save that much power (on the order of 100whrs/day).  And the elbow in the ribs from SWMBO when the central vac would do a zing up to power, just like when you first plug it in, at midnight or so, got old really quick!  The pulse was enough to just turn over the vac motor.

706jim

The inverter standby/search mode made sense when solar panels were expensive. As an example, my first two years were done with 170 watts of solar and having the inverter go into sleep mode probably saved enough power to be significant. But now with many posters have multi kilowatt solar arrays, I just think the standby mode has lost its need. And with that, the need for an expensive DC fridge sans defrost cycle.

mcgivor

706jim said:

The inverter standby/search mode made sense when solar panels were expensive. As an example, my first two years were done with 170 watts of solar and having the inverter go into sleep mode probably saved enough power to be significant. But now with many posters have multi kilowatt solar arrays, I just think the standby mode has lost its need. And with that, the need for an expensive DC fridge sans defrost cycle.

That largely depends on the inverter's self consumption, it's overnight that is of concern, my Schneider SW 2524 uses more  (38W) than the refrigerator uses overnight, my work around is to program the main Schneider inverter to block invert,  being taken over by a smaller inverter (12W self consumption) between certain hours via an auto transfer switch, two separate houses interconnected on the AC side, one built before the other.

Since no amount of PV works overnight it's the battery capacity that is of concern to most, actually I just do this because I can, but always thinking I had pondered the idea of using a timer to power a resistive load greater than the sleep mode, once every hour for a minute to draw the inverter out of sleep mode since my refrigerator failed to do so, thus allowing the refrigerator to work once awakened, it was just a theroy, but it would  probably work. Food for thought for those who don't have the luxury of abundant battery capacity.

dogdude

I’m picking up a lot just by watching your conversation. I’m such a novice that I can’t ask the right questions but you guys have been real helpful in telling me what I wanted to know. Thanks!