Electrical wiring help needed to isolate 2 batteries on singular lighting circuit

[Truefire]

I have a dual battery setup, both 12 volt batteries. One is the truck 'starter' battery and the other is an onboard deep cycle battery that is in the truck camper. I have a bright backup light installed on the rear of the camper that runs off of the truck battery with single pole switch installed in cab. This circuit is not wired into the truck's reverse lighting circuit but is altogether a manual switch.

I want to operate the same light off of a 3 way lighting circuit inside the camper. There will be two single pole, double throw switches being fed hot from the onboard deep cycle.

My issue is i cannot seem to figure out how I can wire the circuits and keep the batteries isolated. I have toyed with the idea of a SPDT relay install, but even that would not work for I would always have one hot leg due to the deep cycle.

Please do not talk too much trash about the schematic, the only program I had to utilize in order to draw same was MS paint.

If you have some ideas, please by all means...

Chris

 

[TFRI]

There are some great ideas here.
http://www.expeditionportal.com/forum/showthread.php?t=77503

 

[low277]

Is there a reason to use the truck battery at all?

 

[dwh]

I'll study it a bit.

First thing I can tell you though, is that 3-way (and 4-way) switches, as used in house wiring (with travelers) are internally different from normal switches. They do a "criss-cross" internally. The SPDTs won't do that.

Also, there is a variation called a "coast 3-way" which uses a single traveler - but it requires the internally criss-crossed 3-way switches to make it work:




EDIT: Okay, my bad. Spoke too soon. A standard 3-way switch in a house is a SPDT. Duh.

So yea, you can rig a 3-way with two SPDTs.

So back to the original problem - isolation...

 

[dwh]

Well...

It looks like you've achieved isolation anyway. At least...most of the time.

As long as the truck switch is off, then it doesn't matter what you do with the 3-way setup - the batteries will be isolated.
As long as the 3-way setup if off, then it doesn't matter what you do with the truck switch - the batteries will be isolated.

The only time the batteries would be tied, is when BOTH the truck switch AND the 3-way are turned on.

 

[Truefire]

Thanks guys. I am extremely busy right now, however I will get back with you regarding this in a couple of days. Once again, thanks for replies and for following thread.

Chris

 

[dwh]

Oh yea, that reminds me.

I thought of this the other day, and forgot to post it.

You could rig a Bosch type relay so that when no power is applied to the relay, there is power through it to feed say, the truck switch (though really, you could do it either way).

Feed power to that relay from the 3-way setup, and it will cut power to the truck switch when you turn the light on with the 3-way.

That way, it doesn't matter if both switches are on - the batteries stay isolated.

 

[Truefire]

As low brought to mind, do I need to even necessarily have the battery from the truck operating the backup light. It only makes sense to use the deep cycle for this for the backup light will only be available when and if the camper is in the truck bed. So now I just plan on using the onboard deep cycle to power all the switches, no need to worry about tying various batteries together accidentally.

Cannot tell you why i did not see this at first, i could not see the tree for the forest, I guess.

ANyway, i had thought of using a relay as you mentioned DWH, but the problem was I could not determine how I could use the single pole double throw relay and not have power on one contact of that relay at all times being fed from the deep cycle. Thus when the contact fell out, the switching would occur closing the normally open contact thereby tying those batteries together, I could not think of any other type relays to use.

Obviously, i am on a different wavelength than you are at this moment.

Enlighten me further.

Thanks, Chris

 

[dwh]

Um. What I had in mind was something like...




Uh crap...better if I make a cheezy paint drawing...BRB...




Which, in my head was working. After drawing it out though, I see what you are saying.

Yea, it wouldn't work without adding a diode (inside yellow circle) to prevent the dash switch from cutting its own power when you turned it on.



EDIT: Hummm. I guess it *might* work. Depends on how fast that coil returns to 87a when you hit the dash switch. Probably better not to chance it.

 

[Truefire]

Yeah i had originally thought, "just grab a relay"! But then I began to envision the circuitry in my mind and said, "Wait a minute!"....It would undoubtedly work if there was not multiple batteries in the scenario. The problem lies right there where the multiple connection is inside that wire nut at the light...I have never messed with any diodes so am not that familiar with types/makes/ and other intricate details involving them.

I really do not need it wired on both batteries anyway, really no real reason for the original plan. I already had a single pole switch in the cab served by truck power. I guess that was the reason for thinking along those lines. (just couldn't void that switch in my mind's eye if it were already there i suppose...:snorkel:

I essentially just need a four way switch installed between the travelers and then I would have three switching locations.

I really did not want to run more wire however, plus I have a 6 pin female, vehicle receptacle installed already inside the truck bed that will be the connection point from the pigtail protruding from camper. I robbed two pins inside this port to serve the switch inside the cab. If I were to install a 4 way, i would have to pull two more wires and upgrade the 6 pin to ??? something i believe they do not even make that is an 8 pin female port, to accommodate for the pair of travelers to and pair travelers returning....

I think i can do it like this instead, there will never be a time when power will be flowing through all contacts in switches in the schematic below, unless of course i leave a switch on...that should be a big no brainer there. but even if i do, there would be no problems.



chris

*EDIT* DWH, by the way what in the world are you using to draw such snazzy schematics man? I do not have any type software upon my computer...i'm almost jealous

 

[dwh]

Windows Paint.

I also sometimes use a freebie Photoshop clone called Paint.NET.

 

[dwh]

Oh, and I didn't do that first one with the 3-way, I just snagged that off the net.

 

[Truefire]

oh gotcha...you are still talented none-the-less to be able to make such clean looking 'paint' schematics...

on another note: Did you understand what i was sayin in the last posting? I was attempting to convey I would be using two three way switches and then a single pole, all upon the same circuit. They would all be fed from the same camper battery. There would never be a time when the three ways were both "closed", if i needed to engage single pole in cab. Should be no issue.

I know, its not the best method, but it will save me a lot work...well a lot of crawling around, underneath a truck on itchy grass attempting to run wiring (poor me = no shop). I have a wood shop just not large enough to accommodate the pickup truck. My next workshop is gonna be at least an acre in size, epoxied concrete floors, several large swamp cooler fans, and plenty of working room, tool chests, and a nice waist high work table....:wings:

You wonder where that came from????? its called working out in the North Carolina :sunny: just a tad too much...the dang humidity here...ugghhhh

thnks for all of your help, Chris