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Old 12-23-10, 01:54 AM   #1
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Default DC electrical sub-system

Does anyone have a DC electrical sub-system in their house? If so, what is the voltage and what is it used for? I don't mean just a PV/wind-to-inverter setup, what I have in mind is a DC system that actually powers something directly, like electronic gadgets.

I've been thinking about setting up a DC system in the house, partially to directly power electronics (bypassing the transformer and its efficiency losses) and lights (I've heard that low voltage DC is more efficient for lighting), and partially as a backup for power outages.

What voltage would be best? Many electronics use 12V internally, but some use 5V, 8V, 16V, etc. Would a DC-to-DC converter be more efficient than the transformer+rectifier already installed? And if I want a battery bank with higher voltage (24V or 48V), then is a DC-to-DC converter the only way to get 12V out of it, or is it possible to wire the batteries in such a way (with diodes, maybe?) that taking 12V is possible?

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Old 12-23-10, 06:15 PM   #2
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I have a PV powered 12V system that lights my workbench using LEDs. I am experimenting with LEDs and am building a boat that will be lit by LEDs.

I have been using star 1W LEDs, and just ordered a bag of 5mm warm white LEDs to try out. The stars seem to get quite hot, and I am hoping the 5mm will stay cool and maybe be more efficient.
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Old 12-24-10, 02:00 PM   #3
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I wired up parts of my parents house so they could use their 12v sun frost fridge and LED lights if they wanted to, but they never finished connecting it up and chose to keep the Sun Frost in the garage closer to the batteries.
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Old 12-28-10, 10:49 AM   #4
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I'd imagine searching for 12v appliances used in RV's might help you a bit. Some RVs just use an inverter and run things at 120v but it seems that there is enough stuff out there to power most rudimentary things. ...then again I'm not sure what you have in mind. I don't think you'll save too much on lighting costs and for most things, pulling out transformers might be more work than it is worth and finding out of that 9v, 12v, or 15v appliance will work with a 12v battery that could be 11v discharged and over 14v charging could cost you while trying to set this stuff up.
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Old 12-28-10, 11:40 AM   #5
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this showed up on build it solar in the last few days
Solar PV System
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Old 12-29-10, 10:23 AM   #6
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I have run a 12V solar powered system in my boat since about 2004. My 28' sailboat is set up to be able to live at anchor with no power connection. There is a 30W solar panel, a charge controller and two deep discharge marine batteries, the type usually used for electric trolling motors.

With this small of a system, the key is efficiency, since it is usually cheaper to be efficient than to add battery and PV capacity. I have no fridge, no pressure water. I avoid using fans, but do have them on board. The most used lights such as anchor light and cabin reading light are LEDs.

The system powers cabin lights, navigation lights, navigation instruments (depth sounder and knot log), music, vhf communications, autopilot (a power hog), electric bilge pump (it never runs, replaced with a hand pump), charging of cell phones and portable radio, charging of a handheld vacuum cleaner, and a portable inverter used for hand power tools.

30W of solar panels is quite low, usually sailboats will have more like 200W of PV panels. By avoiding heavy loads such as refrigeration and anything that produces heat or has an electric motor, you can keep your power needs very low.

I have this controller, which would allow me to increase PV capacity if needed.

SunSaver 10 amp solar charge controller with LVD

This cheaper controller would work on anything less than a 80W panel:

SunGuard 4.5 amp solar charge controller
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Old 09-21-12, 08:35 AM   #7
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The closest thing I have to a DC subsystem is a few variable AC to DC transformers from Rat Shack. This is simply because any of my DC based electronics require an AC plug to charge them. If I'm working on an electronics project, I always use a battery so I don't fry what it is I'm working on.

I'm sure you know, the device will draw the amperage that it needs, but if you plug a 12V power source into a 6V device, you create a paper weight. I did that with an early (expensive) Olympus digital camera.

I have thought about adding wiring to my house to run off of non-grid connected green powered battery systems. I even thought about putting the outlets next to the grid ones and just painting them green. However, they would be fed from the batteries, through an inverter to produce AC simply because the majority of stuff marketed in this world is designed to plug into a 110V or 220V AC outlet.

To quote Scotty in one of the Star Trek movies, (get your Scottish accent in your head now) "Captain, the more you reroute the plumbing, the easier it is to stop it up".

I think that was the writers way of explaining the K.I.S.S. method. "Keep It Simple Stupid", no offence intended. I learned that one in the military.

I think we all need to take a hard look at what we are doing for effiency and sacraficing ease of use. There needs to be a happy medium.

Don't let that discourage experimentation, that's not what I'm saying at all! That's how new discoveries are made.

For a system in my house, that I live in, daily; I don't know if I have enough time to worry about what voltage my DC device needs, find the appropriate step-up/step-down transformer, and still make it to work on time. I don't know if I'll be alert enough at 0400 when I get up to be able to read what the voltage is. And lets not forget when friends come over (who have no idea about my DC subsystem). God forbid if they start drinking a bit and then get access to the DC subsystem. I see lots of paper weights in that scenario.

I don't have that kind of time to let those worries take free rent in my head.

Separate your experiments from your daily living. K.I.S.S. it, and don't re-route the plumbing.

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