12 volt transformer?

Out ThereOut There Solar Expert Posts: 96 ✭✭✭✭
This has probably been brought up many times, so I apologize (as a newbie) for starting a whole new thread.
I'm seriously considering installing a DC load center and running appropriate wiring for 12 (24?) volt "things" in the house. I expect some 12V lighting, but it's time for a new refrigerator and I'm considering that as well. My wife would probably love to have a 12 volt hair dryer (I know.... I know....) and there are other items from the RV world which might be better powered by DC voltage than running them through the inverter. My system is 24 volt, so I know I need a DC-DC converter... any recommendations on such a beast? Any recommendations in general? Thoughts?

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 12 volt transformer?

    I have a recommendation: don't do it.

    Higher Voltage has less power loss over any given distance/wire size.

    If you have 120 VAC to begin with dropping it to a lower Voltage and rectifying to DC costs power.

    Off-the-shelf 120 VAC wiring and appliances are easy to find and cheaper than their low Voltage DC counterparts.

    The only time to go wit 12 VDC is when you have no choice, such as in an RV/camper where the vehicle power is also 12 VDC and therefor a convenient charge source.
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: 12 volt transformer?

    I have another recomendation: go for it.

    It does depend on the scale or your operation though. See a couple of recent threads for extensive discussion, one called "advice on mountain cabin" or similar.

    We run most of our house on DC satifactoriy but its only 60m2. We run the inverter during the day or part of the day as tasks require, but lighting, water pumps, fridge, computers, cell phones, wifi etc all dc.

    For the fridge you are limited to marine stuff and it is pricy, but go 24v. I wouldnt worry about a single 24-12 converter. Reticulate 24 and then down convert for each group of items, using products like these:

    http://dx.com/p/mini-dc-dc-voltage-stabilizer-regulator-module-red-126106

    But again, if you use more than a few kWh per day, forget it, do as Coot says. If you use more than 3kW/d you need 48v anyway.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • Out ThereOut There Solar Expert Posts: 96 ✭✭✭✭
    Re: 12 volt transformer?

    Okay. Based upon yours and Coot's recommendations (despite them being somewhat different), I'm guessing the 12 volt idea is out. I still like the idea of some DC lighting, though.
    Brian
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: 12 volt transformer?

    go 24v and get some 24vdc lights and other accessories is a possibility. or go with the 120vac and have a 24v to 12v converter for some 12v stuff. won't do a hair dryer though.
  • Out ThereOut There Solar Expert Posts: 96 ✭✭✭✭
    Re: 12 volt transformer?

    Thanks for the feedback, everyone. I think she'll just have to use a towel.:D
    ... now does anyone have any recommendations for a refrigerator?

    Brian
  • TecnodaveTecnodave Registered Users Posts: 418 ✭✭✭✭
    Re: 12 volt transformer?

    SAMLEX America makes some decent DC to DC converters that are reasonable for a small system. I am using a SAMLEX SDC-15 converter to run 12 volt electronics. It is 20 to 32 volts in and 13.8 volts out regulated. +/- .1 volt
    It's rated efficiency is 92%. 15 amps max 12 amps continuous , I run a auto stereo /CD player and R.V. 24" LCD/LED T.V. /DVD Player and charge iPhone & iPad With this from 24 volt batteries it was about $75.00 on Amazon. My L-16 batteries charge at too high a voltage to consider a tap on the batteries. I am using LED Strip lights rated at 12 volts with a LED Wholesalers PWM dimmer which is rated 12-24 d.c. volts in 8 amps. $4.00. Amazon. Strip lights are DELE Technology 300 ea. Type SMD5050 LED's. 75 watts per strip. $12.00 Amazon. Real cheap and real efficient. All my lights are low voltage LED's. Only run the XANTREX Pro Sine Inverter for appliances all else is 12/24 volt

    Small off grid. 28 Siemens 55 watt mono plus 2 280 watt Suntech Wuxi poly. 4 Interstate L-16
    Going to upgrade controller to MidNite Classic 150

    Hope you can use this info

    Tecno
    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Exeltech XP-1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or LiFePO4,
  • DavidOHDavidOH Solar Expert Posts: 109 ✭✭✭
    Re: 12 volt transformer?

    Excellent TecnoDave. I am considering that Samlex unit myself. For now just a more simple device, in my thread "Regulated DC".

    I agree if you are running 24v system, keep as much as possible to run straight off of 24v or the AC inverter. KISS. :D

    A Refrigerator? Consider this one: http://www.compactappliance.com/CRF320SS-EdgeStar-Midsize-Compact-Refrigerator-Freezer-Stainless-Steel/CRF320SS.html
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: 12 volt transformer?

    If you look at the Energy Star rating on that it is estimated at 337kwh per year. (basically 1kwh per day)
    You can get a full sized 18cf fridge/freezer that uses that same amount (or less).

    Those little units have poor insulation and will usually use a lot more power than the larger "real" fridges that have the right amount of insulation. Especially if it is in a room that is over 78 degrees. My neighbor had a small one like that and it was using closer to 2kwh per day in the summer. Not worth it.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 12 volt transformer?

    Basic rule-of-thumb on refrigerator sizing is that the larger the cubic capacity the smaller the surface area (through which heat is gained) per cubic foot. As such a bigger refrigerator can be more efficient than a smaller one for that reason alone.

    Having tested a number of refrigerators myself I agree with jcheil that smaller is not necessarily going to equal less power use.
  • jcheiljcheil Solar Expert Posts: 722 ✭✭✭
    Re: 12 volt transformer?
    Having tested a number of refrigerators myself...

    I am wondering, has anyone ever considered attaching some of that foil backed 2" foam insulation all around a fridge? Do you think it would help in any way? Sure it may not look too pretty, but then again it might give it that "stainless" look :)

    And I also wonder about some better way of getting rid of the heat it generates. Not sure how. And I don't care about reclaiming it, I would just be interested in a way to get it "out of the house".
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 12 volt transformer?
    jcheil wrote: »
    I am wondering, has anyone ever considered attaching some of that foil backed 2" foam insulation all around a fridge? Do you think it would help in any way? Sure it may not look too pretty, but then again it might give it that "stainless" look :)

    And I also wonder about some better way of getting rid of the heat it generates. Not sure how. And I don't care about reclaiming it, I would just be interested in a way to get it "out of the house".

    Tony/icarus has done this with propane 'frige and got positive results.

    One of the problems with 'modern' refrigerators are the hidden coils (gives it that smooth look), usually at the back, which you not only do not want to cover but also are difficult to increase the airflow over.

    You could experiment easily with a refrigerator, some rigid insulation, and one of those infrared thermometers. Check the surface temperature and see if it goes higher with the insulation in place.

    Redirecting air flow to improve the efficiency of the cooling coils is another matter and would be model-specific. One thing you do not want to do is duct in cold air for this; it may be great in Summer but this morning I got up to 10F temps and that's too cold for anything - even a refrigerator! (It's peculiar to look out the window and see the penguins bundled up in fur coats.)
  • BB.BB. Super Moderators, Administrators Posts: 30,485 admin
    Re: 12 volt transformer?

    An issue to watch... When you insulate the outside of a refrigerator (and especially a freezer), you can collect water (and ice) between the cabinet and the extra insulation (especially in humid regions). Not always a workable solution.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SCharlesSCharles Solar Expert Posts: 123 ✭✭
    Re: 12 volt transformer?
    Out There wrote: »
    This has probably been brought up many times, so I apologize (as a newbie) for starting a whole new thread.
    I'm seriously considering installing a DC load center and running appropriate wiring for 12 (24?) volt "things" in the house. I expect some 12V lighting, but it's time for a new refrigerator and I'm considering that as well. My wife would probably love to have a 12 volt hair dryer (I know.... I know....) and there are other items from the RV world which might be better powered by DC voltage than running them through the inverter. My system is 24 volt, so I know I need a DC-DC converter... any recommendations on such a beast? Any recommendations in general? Thoughts?

    You can easily run DC appliances, etc., off your battery bank. I agree with others that a higher-voltage system for the house is beneficial, I won't repeat why. However, our house system is only 12 volts. That's because I set it up that way in the mid-80s and 12 v. was not unusual back then. Meanwhile, our fridge and freezer [Sunfrost], our SolarChill swamp cooler in the greenhouse, our Dankoff water pump, lights, and so on, are all 12 volt. So for me to "upgrade" to a higher voltage system would entail either replacing all those pricey items or coming up with a 24- or 36- or 48-volt conversion to drop the voltage down to 12 and have a separate circuit or circuits to facilitate that.

    We have many 120-volt things, too, such as several computers and etc., TV, kitchen appliances, tools, the usual. I do have two house circuits, one DC and one AC. It is quite simple.

    However, I built the house myself and ran the two circuits as I did so. If I were starting over, with today's better options and more efficient inverters and PV panels and controllers [my first controller was a home-made job], I would probably opt for no DC circuits or appliances. Back then there were much greater inversion losses to consider, less efficient controllers and the like, and less efficient AC appliances and computers and TVs and so on.
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