latching swicth to avoid invertor standby losses?

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nyarelathodep
nyarelathodep Solar Expert Posts: 99 ✭✭
in Solar Beginners Corner #1
ok, so a rather non-technical guy with a question here. basicaly, im looking to build a smallish off grid set up that only has two higher draw items, a shallow well pump and a chest freezer compressor. Everything else will be electronics which I wish to run off a ts-300 inverter. Having read Wayne's write up on his chest freezer conversions set to operate off of said inverter and thinking its much too technical for me, Im wondering if another route (suggested by a friend with an electrical background) would be to set up asub panel with a cheaper, appropriatly rated inverter wired with a latching switch which only powers the invertor when the compressor or water pump calls for power, in order to avoid the standby losses since the inverter would be idle for most of the day. The bank will be relatively small (maybe 400ah/24v). Having found little information on this across various forums, I am wonderingif this is viable? Is there a reason this would be ill advised, and if so, is there another way of setting up automated process to accomplish the same thing? Any and all info from the solar sages is greatly appreciated.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: latching swicth to avoid invertor standby losses?

    It's possible but ...

    A cheap, large inverter is going to be MSW type which your motors 'will not like'. If you go to a better-grade PSW type you can get one with 'standby' mode which will reduce its consumption until the load is detected.

    Otherwise you are faced with the problem of telling the inverter when power is needed by the load and switching it on. This would mean re-wiring the pump & freezer to activate the inverter on demand.

    For the water pump that's fairly simple: change the pressure switch wiring to activate a low Voltage relay that has two poles (or activates two separate relays if need be) one which turns the inverter on and one which turns the pump on. The tricky part here is that ideally you want the inverter to come on first so that the power to the pump is stable to begin with. Starting an inverter under load is not a good idea.

    With the freezer it's a bit more complicated because the thermostat has to be used to trigger the inverter & then freezer. The wiring is perhaps not as easily accessible. Plus some refrigeration units have electronics in them that require constant power.

    Here is an example of an inverter that might do the job for you without any modifications: http://www.solar-electric.com/sa2wa12vosiw.html
    It has a standby draw of 0.6 Amps or about 7.2 Watts.

    Another concern here is that starting the freezer or the water pump from a 12 Volt system will take a lot of current, requiring a good size battery bank, large and short wires, and good connections. On the whole you'd be better off going up to 24 Volts and using just one inverter such as the 24 Volt version of that Samlex.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #3
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    Re: latching swicth to avoid invertor standby losses?

    Most quality Inverters already have this feature, it's called " Standby " . It uses 6-8 watts to power the electronic circuitry. One issue using it is most modern Refrigerators for example require power to their control circuits 24/7 and will not function with demand power. Any item that uses a remote requires power 24/7. Could someone design a demand switch, yes they have been around for 50 years on generators. Heat cycling is a issue with any modern circuity it's best left with the power on.
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  • nyarelathodep
    nyarelathodep Solar Expert Posts: 99 ✭✭
    #4
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    Re: latching swicth to avoid invertor standby losses?

    Wow, you guys are quick. Thanks, I think I misread the idle consumption on some of the inverters I was looking at (unless the cheapo 1k units really do drain ~70w). 8ish watts wouldnt be a problem, and it looks like the ts-300s standby load is virtualy non existant. The bank will defintly be 24v at any rate. Considering that the pump and compressor (converted chest fridge thing), and a couple led lights, a small led tv, external solid state hard drive/roku 3 setup will be the sum total of my normal electric use...as I have a yamaha ef2000is for anything else including backup battery charge...and 5 gifted sharp 135 watt panels at my disposal, does a 400ah 24v bank sound feasible with attentive power usage? Or is that just setting myself up for additional expense?
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  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    #5
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    Re: latching swicth to avoid invertor standby losses?

    The TS-300 is a 12V inverter. What are your plans to run it off of the 24V bank?
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  • nyarelathodep
    nyarelathodep Solar Expert Posts: 99 ✭✭
    #6
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    Re: latching swicth to avoid invertor standby losses?

    yup, your right. I must have looked at that inverter a thousand times and kept thinking it was offered in a 24v version. In that case, I would think everything listed could operate off the samlex 2k. Question, if the 12v version consumes Xwatts, does this mean the 24v version consumes X2 watts?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
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    Re: latching swicth to avoid invertor standby losses?
    nyarelathodep wrote: »
    yup, your right. I must have looked at that inverter a thousand times and kept thinking it was offered in a 24v version. In that case, I would think everything listed could operate off the samlex 2k. Question, if the 12v version consumes Xwatts, does this mean the 24v version consumes X2 watts?

    No, the Watts are the same; the Voltage doubles, the current halves. The 24 Volt version of that inverter draws 0.3 Amps in standby. http://www.solar-electric.com/lib/wind-sun/SA-2000K-specs.pdf
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