Using the load circuit for opportunistic refrigerator power

[Timmy]

Hi,
I have a houseboat I'm refurbishing on the water and have built an off-grid setup for power. I have a 24v battery bank and am using a Samlex 24v inverter for various 120v needs. I have begun with the 120v wiring and got to wiring up the Dometic RV style refrigerator which came with the boat. To my surprise (and disappointment), this type of fridge doesn't use a compressor but instead a boiler which can easily take 8+ hours to produce a usable chill inside the fridge. Since this boat is for sunny weekend daytime use only this basically renders the fridge useless as by the time it cools off we would be heading home for the evening. The question -

Is it possible to use the load circuit to power my refrigerator only once my batteries are fully charged? This would let the fridge stay cool during the week and greatly reduce cool down times (fridge continues cooling long after 120vac is removed) when we arrive for the weekend. The settings for the load circuit seem in place for this, but it specifically says no inverter should be connected to this circuit. If that's true, what else would I possibly do with 24VDC? The fridge only accepts 120v or LP. The boat is generally unused during the week and so lots of potential power is wasted...at the same time I don't want to needlessly cycle my batteries running this fridge which will only be used to cool beverages.

I was thinking of using the load circuit to engage a relay, but that's super not cool. Are there any other options or ideas? Why exactly can't I use a small inverter here?

Thanks

[tecnodave]

Timmy,

I gave up on Dometic refrigerator a while ago.....they are real energy pigs! They use 300 watts on 120 volts AC and have a real long run time!  I was using them in my mountain cabin/RV. Mine had 12 volt and 120 volt elements and ran almost 100% on time running on 12 volts DC.

I have found a solution however.......There are DC compressor fridges around and I have found a good one.  The Grape Solar GS-5.  These are the same physical size and will slip in place of the Dometic. They have a converter board built in that converts 120 volts AC to DC to run the frig but also have a DC cord as well........they will work on 12 volt or 24 volt systems......(10-15volts or 20-30 volts)....at very good efficiency. Power use is 46 watts!.....1.7 amps on my 24 volt system!

BUT BEWARE!   Do not try to run this unit from the load output of the KID!......Run it straight from the battery......WHY?......The compressor has its own inverter built in which converts the 12 of 24 volts to high frequency 3 phase AC !   The inverters switching spikes will knock out the MOSFET's in the load circuit of the KID!

There units are rated to run with only a 100 watt panel and 100 amp hour battery.....I ran one of mine (I have two of these) on a 35 year old Seimens SM-55 solar panel ,cheep Chinese PWM controller and a 43 amp hour used Mazda battery for a month in California.....100 degree days! No problem....temperature always in normal range......

I have been using these for two years now and am super impressed! The first one suffered a broken freezer door on its last month of warranty.......but one call to Grape Solar I got a real person who shipped me a new unit right away.......No hassle support!

These units are a bit light.....not at all like your '60's refrigerators , they do dent easily....they are light weight!.

Search online ....Google DC refrigerator...other players are EcoSolarCool (1300$USD) Sundanzer (1400$USD). ( rare upright  Sundanzer)

Home  Depot ONLINE has the GS-5 for $600 or so.....delivered to your local Home Depot at no (shipping) cost to you!     ...I paid $670 for the first and $585 for the second.....warranty replacement was shipped free to local Home Depot.

Bottom line.....quit banging your head on the wall....these new inverter compressor fridges are great!
(The SunDanzer and the EcoSolarCool also have the three phase inverter compressor system as well)

Calculeted energy use.   Dometic on 12 volts DC.          7.2 kWh/ day
                                   Grape Solar on 12 volts DC        .25 kWh/day

EDIT...added info.......do not use any switch mode device on the load output of the KID!  Absolutely do not use an inverter , Buck converter , boost converter or any other fast switching device on the load output of the KID!  It will cause the output MOSFETS to short!
David

[ClassicCrazy]

As Dave said - the absorption type refrigerator you have operate more efficiently on propane because they use heat to make the magic happen with the ammonia in them  that is the refrigerant . Trying to use electricity instead they just don't work well and are huge power hogs.  If yours is taking that long to cool down I wonder if there isn't some other issue with it . I have seen some old ones get the vent tube plugged up by soot or bugs. Or it could have a refrigerant leak too.

I don't know about the Grape units Dave is talking about - but there were some 12v fridges at the energy  fair made by an Amish company out of Indiana - they may have had the same type compressors Dave is talking about . I believe most of their models could be used as fridge or freezer and the top loading unit had two compressors - so you could have it be fridge , freezer , all fridge, or all freezer. I can dig up the info on those if needed .

Larry

[Resthome]

As Larry said why not run it on LP. Much more efficient.  Have to assume you have LP on board for things like stove and oven, but maybe not.

[mike90045]

Put the drinks on ice in a cooler in the car on the way to the boat, and use a small block of dry ice in the freezer compartment (keep it wrapped up)

[Timmy]

Thanks for the responses.

The fridge came in the boat and while I had considered replacing it I'm really reluctant to do so. The reason (besides trying to save a little $$$) is the back of the fridge has it's own little area at the back to keep the heat separate from the interior. The little area has a lower intake grate and upper exhaust vent. The fridge and this compartment are framed into the boat so it'll be tedious to remove all the framing and seal up intake/exhaust  The interior is almost completely gutted and so no LP is in place, but I may end up going that route.

Good to know about the load circuit, glad I read the manual 

[Resthome]

Timmy, where is the HB located?

[Timmy]

Lake Norman. I looked up Lake Don Pedro on Google maps and wow does it look cool. I see lots of solar houseboats!

Most of Lake Norman is day boaters or wealthy residents playing with mini-yachts. We have a very small piece of vacant land with a private pier which we live about 20 minutes away from. There are plenty of houseboats on our lake, but most (basically all) are docked at marinas which provide shore utilities.

[Resthome]

Timmy,

I'm a little familiar with Lake Norman. My sister and niece live in North Carolina.

Don Pedro has a marina for houseboats with shore power but there is a waiting list that will never be used. Only way to get on it is to buy a boat already on it.  The rest of us are on a buoy. You are correct a lot of solar being used. They need it for all the toys they installed.