12V Switches When and Why

[Strop]

Ok, I am having a bit of confusion based on my limited understanding of electrical concepts and what I am see in some of the many photos I have looked at of these little creations we seem to have a fascination with.

I assume that all users of 12V systems should have a master switch that turns everything on/off. I am also assuming that for ease of installation it should be near the battery.

Next, as a result of discussion in another post, I think that charging stations using USB should be switched as they will still draw some current when not being used. It is in their design. The old traditional 12V cigarette lighter style charger only draws power when being used so it should not need to be switched.

Internal lights can be purchased with inbuilt switches - so you would think no need for any further switches.

So why when I look at photos do I see switched lights with what appear to be external switches. Charging stations (Non-USB) using switches. And why do I see fantastic fans with power switches next to them.

Am I missing something or are these people just being very careful in what they are doing or future proofing their builds in case they want to put unstitched alternatives in.

[tony.latham]

I'll answer two of your questions. Both are my opinion, as you'd expect.

-I think a camp trailer's 12V electrical system should have a master switch. Why? Same reason airplanes, boats, and autos have them. (I'll admit that's poor justification.)
-I don't think USB ports need a cutoff switch. Sure, they suck juice but it's an almost immeasurable amount. In fact I've tried to measure how much mine uses and have failed. (One of the photos you're looking at may be mine. Trust me, build #3 does not have a USB disconnect switch.)

Extra switch for a Fantastic Fan? Makes no sense to me.

Tony

[craigatx]

I think some fans have a switch which turns the fan on when you open the vent. A master switch would let you open the vent without the fan turning on. You'd have to look at the wiring closely to know, though.

[Strop]

Craigatx didn't think of that one. I have order my fantastic fan so will have to have a play and see if that is what happens. My fan won't be here for a couple if weeks though.

If that Is the case then a power switch does make sense..

Tony unless you are in the one place for an extended time I think I agree that there is no need to switch those little things. The car will be charging the battery on the way to where you are going and on the way back home. Master switch turns everything off stopping any drain apart from natural discharge when you store it.

Unless of course you hate those little LEDs glowing of a night.

[MtnDon]

Our Fantastic fans do have the 'safety' switch that prevents the fan from running if the lid is closed. However, you can open the lid and not have the fan run by simply leaving the factory fitted on-off switch in the off position. There is really no need for a second master switch.

IF someone has one of the entry level Fantastic fan that do not have a revering switch that could be a reason for an extra switch by the fan.
or possibly a speed controller switch to drop the speed even slower than the slowest factory equipped speed. ???

[tony.latham]

"Tony unless you are in the one place for an extended time I think I agree that there is no need to switch those little things."

In reality, those little lights draw such a tiny amount of electricity (about .02 amps) that it doesn't matter. If you put two brand-new marine batteries side by side and let one of them power one of those indicator lights, after two weeks, both batteries will be at the same relative state of charge since they are both going to self discharge. (You've sucked about seven amps out of the one battery over two weeks but both are going to be down to about 12.4 volts).

If the LED light bugs you at night put a drop of black paint on it**. If you still feel it's necessary, spend the time wiring a toggle switch into them to turn them off. The easiest way of dealing with this is to use a 12V cig plug with a USB adapter plugged into it when you want to charge your phone. Pull it out to save your .02 amp draw. (You're going to draw about 5 amp/hours while your phone is plugged in)

Not all 12V USB plugs have an LED light in them. Here's a combo USB and voltmeter that's going in my current build: http://www.amazon.com/Cigarette-Lighter ... +voltmeter

Sure, that LCD meter is going to pull another .02 amps or so. In a month, with or without that draw the battery should have some sort of maintainer on it (mine's hooked up to my solar panels as I write this) just to keep the battery healthy.

Tony

*If I let my phone charge all night, the USB outlet is behind my coat, so it can't be seen while I'm in dreamland.

[Kharn]

I put switches on everything in my camper except the galley light (I just couldn't find a good location to put one) and the roof vent (it has three different ways to turn it off, so I didn't think it was needed).

I chose to have the independent switches so that there would be a single location on each side of the camper to remember, plus it means the switches are accessible while laying in bed (no need to shine a flashlight out the window when we can just reach up and turn on the porch light from inside the cabin). Our general cabin lights are four lights controlled by 3-way switches (one on each side) and I wanted the dimmers for the reading lights to be down-stream from the switches to eliminate any power loss, neither of which could be done with switches on the fixtures. I switched the 12v outlets so that any transformers (and the ones for our CPAPs are pretty demanding) can be cut off without having to unplug all of our stuff every morning, and the external & galley ones could be cut off since they're out of our sight.

The master on/off switch is also the battery selector since I designed the trailer from the start to have two batteries, but even if I had not, I would have put a disconnect in the system.