MSW inverter and heating element

icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
Here is a kind of odd question for everyone.

I am entertaining rigging up a MSW inverter to run, when I have excess PV capacity, the 120vac heating element in my Dometic fridge. (I know it it a really inefficient way to run a fridge, but if I have the excess,,,

My question is, how do 120vac heating elements like running on MSW inverters?

I could run it off my sine wave inverter, but it would about max it out, AND, I want this to trigger ac when the controller has gone into absorb mode and there is excess capacity. I also don't think it is going to work very well (or much) so as an experiment I don't want to spend any real money. A cheap MSW is all I would need.

Thanks in advance for all your help,

Tony

Comments

  • BB.BB. Super Moderators Posts: 26,958 admin
    Re: MSW inverter and heating element

    Should be fine... 120 VAC, 120 VDC, it is all the same (assuming measured RMS). AC with switch contacts (mechanical controller) should be fine.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: MSW inverter and heating element

    Thanks Bill,

    I had that hunch,, but like to hear it confirmed by someone who really knows. Now if I can figure out how to get a few more ah out of my system...

    Tony
  • mike95490mike95490 Solar Expert Posts: 7,357 ✭✭✭✭
    Re: MSW inverter and heating element
    icarus wrote: »

    I am entertaining rigging up a MSW inverter to run, when I have excess PV capacity, the 120vac heating element in my Dometic fridge. (I know it it a really inefficient way to run a fridge, but if I have the excess,,,

    Is this to override the propane heater, or coil defroster ?

    Either way, a heating element "should" not be bothered with mod-sine. Should be just fine.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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  • BB.BB. Super Moderators Posts: 26,958 admin
    Re: MSW inverter and heating element

    Tony,

    For the amount of energy--what about trying the Chest Freezer Conversion (if you have room) at 1/4 or less of the energy usage (will probably cost more for the installation)?

    By the way--at least in winter, do you use some sort of outdoor cold box and/or root cellar for fridge/freezer/storage?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: MSW inverter and heating element

    Hey guys,

    No, this is really a solution in search of a problem. The Dometic works great, and we burn ~8-10 gallons of propane per month for all uses,, stove, fridge, hot water, so the expense is not that great. It is just that the fridge has an onboard 120vac heater and the capability to automatically detect when 120vac is available. My thought was to use the load controller from the charge controller such that when the panels had extra capacity, the controller could trigger a cheap msw on the fridge. I wouldn't expect to save very much propane but the idea of having PV go to waste irks me. ( and to tinker with the idea for future projects) The folks at RV mobile in Everett WA, who are, IMHO the best experts in gas fridges in N. America, suggest that the fridge came with a 325 watt 120vac element, and the 3 ways fridges had a 220 watt 12vdc element. I am going to change mine to a 220 watt 120vac, (Mine is a 2 way,, no 12 vdc system, and it is too expensive to change it or I would try to run it off 12vdc!) The idea is that the run time would be longer with the smaller element but it "might" work fine.

    As for different freezer/fridge combinations. The problem is outside only works as a freezer, not as a fridge. We could build a root cellar, and in fact had one years ago when we had an ice house, but then we would have to shovel it out all the time. (The ice house was great! We (not really we,, I was just a kid when we stopped cutting ice) would cut ice in March, after keeping the ice free of snow all winter so it would freeze well. Hauled the ice blocks out of the water, up the skid rail buy hand, stacked 10 deep, (2'x4'x~3' blocks depending on how deep the ice froze,, 24-36") all sitting on a layer of dry, fresh saw dust, then buried under a couple of feet of dry sawdust. The walls were 2' thick with sawdust lining. Every fall we would have to shovel out the ice house and dry the sawdust, as new sawdust was hard to get where we were. All summer long, shovel the sawdust off a block, grab it with the tongs, swing it out, hose it off, and then into the cold room. We would have fresh ice as late as the first of October. Few people cut ice these days. It was a great place for kids to play on a hot summer day,, hiding in the icehouse in the cool, damp sawdust! I did a bunch of work last winter, and I planed thousands of feet of boards, with the planer shavings piling up on the snow, several feet thick. On a whim in August, I dug into that shavings pile, and there, as fresh as it had fallen yesterday was the snow!). Sorry for the ramble!

    We are so well stocked with fridges that we certainly don't need to go getting any more. We used to have a outdoor winter freezer box, but the foxes liked it a bit too much. What we do during freeze up and breakup is fire up our smallest undercounter Dometic,,~4 cuft, turn it up full, and turn it into a deep freezer. It works well, keeping things ~0f, and once it is cold, and full, it burns about 2 gallons per month. We usually get to town every 2-3 weeks, so freezer space is only an issue during freeze up and break up, where we could be stranded for 4 weeks. Last spring it felt like months!

    As I said before, were to do it over again, I would buy a good compressor fridge, but since, as I said I am well stocked with Dometics I am going to stick with the program. I have found over the years that they are VERY RELIABLE. I have had one fuse failure in 12 years with one, and no trouble with other other in 6 years. I have a smaller 6cuft, no electronic standing flame that we seldom use, but it fires right up and gets perfectly cold. It must be 25 years old.

    Tony

    PS I do disable the auto defrost element on the Big ones. If memory serves it has a heating element that just heats the freezer door closing area. We don't suffer from high humidity very often, so defrosting is not a problem once or twice a year.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: MSW inverter and heating element

    Not that anyone cares what I say but ...
    Electric heating elements are just resisters - even calrods. You can feed them DC and they behave the same (the controls <I>don't</I> though).
    You may find, however, that the Inverter doesn't like it: sudden, heavy load that appears to be a dead short (resistance increases as the element warms up).
    Try it on a toaster first.
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: MSW inverter and heating element

    CC,

    Why doesn't everyone care what you think???

    T.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: MSW inverter and heating element

    Icarus;

    One of my 'standard caveats' I'm afraid. People rarely listen to what I say. If you have children, you know exactly what I mean. :)
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: MSW inverter and heating element

    I run my 1000W toaster oven off of the MSW inverter just fine.

    The problem I see , does the dump load turn on/off or is it variable on/off??
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