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Home Forums General Discussion DC powered lights and fans

Viewing 6 posts - 16 through 21 (of 21 total)
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  • #64886
    rustyfingers
    Participant

    I’ve only ever used the 12v d.c. for any of my previous adventures off-grid, so it does make sense to stick with what you know. Future plans of mine are calling for the use of an inverter & genset, but again, I’m well familiar with 120v a.c. too, through decades of home construction & renovating.

    If you’re somewhat familiar with 12 v already, it would make more sense to stay with it at first & then progress into using a higher voltage afterwards. Your shack is only to be around 240 sq. ft. so you won’t require a great deal more than what most RV’s have already. By reverse engineering one of these units, it would be a simple task of setting up your own place to re-use most all of the equipment & fixtures from one f these RV’s. If for some reason, you want to convert to 120 volts or more & have your home opened to the scrutiny of an inspector later, you’ll of had lots of time to study more about it.

    #65172
    frankT
    Participant

    Hello

    I just read through this discussion because I’m interesetd in this AC vs DC argument. I’m new to solar – and here so it might seem an offkey first posting! – but it strikes me as a key issue if you are going to set up an installation. I’m thinking of minimum gear, a few lights, fans, some electrical appliances, battery chargers. It appears that there are favourable and valid arguments for either an AC or DC system, almost 50/50 by the way I read this. Leaving aircaft circuit breakers and other finer points aside for now, and assuming I don’t already live in a standard wired up AC circuit, is there are a bottom line here? Is it a good and efficient idea to go DC and get the matching DC appliances if I am running a smallish solar set up? Or is it best to ‘stick’ with AC and an inverter?

    I hope I haven’t missed something in the thread that gave an obvious answer.

    Thanks for reading.

    #65173
    elnav
    Member

    FrankT

    You have a valid question. This forum attracts a wide range of people with greatly varying expectations. If you are going to live in a space equivalent to a small trailer with a floor space no greater than 200 square feet then it is possible to keep the wire run lenghts short enough so the line losses are not too great. As Reboot mentioned long wire runs will produce high losses which in turn requires bigger batteries and or solar panels to compensate with. I have been designing systems both low voltage DC and regular higher voltage AC for several decades. I routinely use a program to calculate how big a wire has to be for a given load current. The other side of the issue has to do with appliances. Doesn’t matter if its a water pump, fan or light. To do work requires power. 65 watts at 12V = 5.4 Amps and the same power at 120V is only 0.54 amps.

    Current not voltage creates heat. I’m a Fix-it kind of guy. I have found that DC appliances fail more often than equivalent AC devices, other things being equal. Due to volume of devices being sold you are more likely to find a quality product using 120V AC than a similar product using 12v DC. My observation is that RV type devices typically fail sooner and are generally cheaply made because they are intended for occasional intermittent use.

    Most of us drink coffee. Check out how many 12V coffee makers there are; then compare for 120V AC coffee makers. How many 12V coffee makers do you see that last 10 years?

    I lived in an RV for five years. When the heater quit I replaced it at a cost close to what a house furnace cost. It failed in 13 months. That is when I was informed I should have bought a ‘parkside’ version with 120V AC fans instead of the 12v DC model. That version had better bearings and last a lot longer.

    A lot of people approach OFF-GRID from the pespective of moving from a conventional house. The transition is less stressful if they have familiar things just needing to remember energy conservation.

    Almost any home Depot, Hardware store and such have great books for DIY on how to wire houses the safe way. That takes the guesswork out of it.

    Finding a GOOD 12V DC book is much more difficult. Some of them are useeless and do not provide data on calculating safe wire sizes. My know it all neighbor burned up his car when his 12V dash wiring modifications caught fire two weeks ago. He figured he knew how to wire.

    If you contemplate living in a space bigger than 8′ X 16′ the lenght of wire runs as measured along the wire could be a problem in terms of losses. Overload a wire and you have the potential for overheating and starting a fire. If you do not have the background and knowledge to judge then following a code book is a better guideline.

    Cost of copper has recently skyrocketed. Buying larger size wire is being safe but can become very expensive real quick.

    #65175
    frankT
    Participant

    DC or AC?

    Elnav

    Thanks for coming back with this really thorough outline, highlighting some of the potential problems and dangers of going DC too, especially for an amateur. It makes sense, for me you’ve solved the dilemma. I will stick to the wiring I know a little bit about…just a little that is!

    Your time is much appreciated.

    #65177
    elnav
    Member

    FrankT

    You never mentioned how big your living space is nor what loads you expect to drive. I advised one person who wanted to outfit a small trailer for off grid. Only a few AC devices and one LED light would be used so the system ended up with no wiring. The existing cords on the few AC appliances were long enough to reach the centrally located battery pack plus 400 watt inverter. As a result no wiring was required.

    I suspect this is a special case and most people would want a bit extra like maybe two LED light locations and maybe a conveniently placed outlet for plugging in the charger for a laptop.

    Speaking of which laptops are often 15 – 18V these days and are not happy wired directly to a 12V battery. Cell phones, PDA etc typically use 4.5V and also are not happy wired directly to 12V. Last time I checked the AC charger for a cell phone or lap top was cheaper by far than a cigarette plug in for use on my car 12V system. something else to consider when deciding on system voltage for of grid.

    #65212
    elnav
    Member

    Generally speaking long runs of DC wiring tends to be very lossy compared to delivering the same watage at a higher voltage. HOWEVER there is one technique which will reduce wire losses to about half for the same size wiring. UK residents may recognize the term ring main. Using this approach you can run DC wiring in a limited size small house or RV traailer and minimize losses. If your principal use is LED lights this will work. I have used the approach for larger installations but it can get complicated. In one such install I was building bus bars for 600 amp service using solid copper bars. However this is not suitable for the average amateur DIY electrician.

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