Beginner Solar, questions about DC switches and Outlets

[Travis]

Hello all.

I recently completed a small power pack for my storage shed. The components are:

85 Watt Sun panel



The Quick Support Rods allow fast re-alignment, purchased from Northern Tool.

SunSaver 10A charge controller
Marine battery-select switch
Four 40AH deep cycle batteries, wired for two 80AH pairs.
4 Amp cheapo inverter.



I also purchased a couple of Solsum DC CFLs that use a standard screw-in socket.
These DC lights use just under 1 Amp per hour each, the brightness is a little lacking, If I put them in one of those over-sized 'trouble light' reflectors, then that puts a standard Edison plug at the business end.

My question is, can I use a standard outlet box from my hardware store (that would be rated for 110VAC) to plug in the cord? Further, could I control that with a standard light switch that would normally be meant for A/C? I hate using alligator clips every time I want to use the DC lights. Ideally, I'd like to be able to turn the lights on with a switch, just as if I were in my home.

I am guessing there are many ways to do this, but I'd like to be safe and convenient. My local hardware store doesn't carry DC switches or outlets. Thank you.

[Xringer]

I've used 120VAC hardware on DC sources before.
I believe the standard 120vac light switch is rated to 10 or 15A at 120vac.
It should be able to handle something like two little 1A low voltage DC lamps, without any problems.

What you will need to do for the DC (ex-AC) outlet, is to pick out it's polarity.
I would put (+) plus on the Hot/Load (small blade) side of the socket.
And make sure you follow convention with the Low voltage DC lamps you want to use.
Those lamp plugs MUST be polarized correctly.

Cover the DC socket with one of those outdoor water-resistant covers. Label the outside Danger DC voltage, DO NOT USE!
To keep someone from plugging in something nice that might get melted.

[Ryland]

Alot of people will either wire their 12v outlets up using an outlet designed for 220v (and label it of course) or wire up automotive style lighter plugs, but the most common thing to do if you use a 220v outlet or a 110v outlet is to not use the hot terminal in the outlet, only use the common and the ground, that way if you plug a standard device in it will blow a fuse instead of ruining your device.

[Travis]

One recommendation for the hot wire, and one warning not.

I tried it today, using the hot lead with a nonmetallic 1-gang box, and burned socket that was in it. I wasn't sure why, but I did learn that fiberglass insulation does not promote ignition. Luckily, only the outlet and box were lost, but I obviously did something wrong.

In wiring DC, I tried to think of a simple flashlight, with a single loop of wire connected in series from battery (Pos)->switch->socket->battery(Neg).
When I Ohm'd the socket and switch they were showing proper continuity. After energizing the circuit (no Edison cord connected) my solid core wiring melted right through at the socket. It must have been Aluminum since the Copper wiring held. It's hard to believe I shorted something with a nonmetallic box, so I am not understanding where I wired incorrectly. Can someone give me a clue?

Thank you.

[Travis]

OK, I figured it out. Even though my brain was thinking DC, my hands were wiring AC. As soon as the circuit was energized the socket was shorted (fused is more like it). The aluminum wiring melted through at the socket.

Re-wiring it the second time, I added a 3A fast blow fuse to the + side inbetween battery and outlet. Fortunately I got it right, and the fuse didn't blow. Now I have my two DC florescent CFLs illuminating the inside of my shop. Together they pull 1.7Amps, and are controlled by a standard light switch placed at the entry door.

This was the only time I haven't used fuses to protect my equipment. Everything else I've done up to that point, was deliberate, calculated, and cautiously executed with full protection. I don't know why I thought wiring in a light should be any less thorough. It's a lesson I am glad to re-learn.

I did remember to label the outlet for DC use only.

[Xringer]

Originally Posted by Ryland

Alot of people will either wire their 12v outlets up using an outlet designed for 220v (and label it of course) or wire up automotive style lighter plugs, but the most common thing to do if you use a 220v outlet or a 110v outlet is to not use the hot terminal in the outlet, only use the common and the ground, that way if you plug a standard device in it will blow a fuse instead of ruining your device.

I like the idea of using a 110v outlet's with the ground (-?) and N pin (+?),
and leaving the Hot line floating. That's going to make it pretty fool-proof.
And, I think it might be able to handle a bit more DC current,
since the ground pin has much more contact area than the Hot.

But, it also means you need to buy three pronged plugs, to hook up some DC..
An old 2-pronged lamp cord isn't going to work in a pinch.

[Xringer]

Originally Posted by Travis

One recommendation for the hot wire, and one warning not.

I tried it today, using the hot lead with a nonmetallic 1-gang box, and burned socket that was in it. I wasn't sure why, but I did learn that fiberglass insulation does not promote ignition. Luckily, only the outlet and box were lost, but I obviously did something wrong.

It sounds like you put the + & - DC on the same side of a socket,
instead of going across. If you put both + & - on the brass screws,
the socket could melt. (Same thing with the sliver screw connections).

[OffGridKindaGuy]

I use these everywhere. Very good quality and they have a built-in circuit breaker for protection.

As for plugs, I just find replacement ends or reuse old cords and make my own. Some have fuse holders built in and some don't. I just add fuse holders to the ones that don't and fuse accordingly.

I find that they will handle a 5 amp constant draw very well and just get a little warm. Any load heavier than that gets a direct connection. (hard wired and fused)

A little trick that I use to reduce line losses to light fixtures or for any load that requires a switched source with a lot of distance between the battery and the load and where you might want a switch.

I run the source directly to the load with the shortest distance possible. (fused accordingly) I install a relay that's heavy enough to handle the load. (light fixture, pump, whatever..) On the coil of the relay, I connect one side to the positive lead of the source. I then run standard El'cheepo telephone wire from the relay to where I want a switch. I connect one pair of the telephone wire (twisted together) to the ground from the source and the other pair to the other side of the coil. (Where it need ground to work) Now all you need to do is short the pairs together and the relay will close. (Giving the coil its ground through the phone wire) Connect to a standard wall switch and it will last for years! Only milliamps is going through the switch to activate the coil. The large load is being switched by the relay, not the switch. No line losses trying to loop the power to a switch and then to the load.

You can install a switch just about anywhere you want. I use this for my pump and the switch is at the opposite end of my house. (~50') Works every time! I even installed a 12 volt LED across the switch to let me know that the switch is off. The coil of the relay provides enough current to fire the LED. Close the switch and the LED goes out..

Just a little Hillbilly Technology..