Wiring up backup camera, asking for advice for my beginner electronics question.

[Vision.Urban.Reed]

I have a major blockage in my solution finding here. I am 95% sure that everything else checks out here in my circuit, but I have reached todays limit on thinking through the circuit for a solution to my primary problem, as I am a major electrics beginner. My primary problem is as follows: I need to figure out a way to power the back up camera screen/receiver when the transmitter is being powered by the house battery, and the ignition is fully off. This question is asked in the attached photo below, in the notes section underneath the diagram. If you have an idea to help kickstart my next step, I would love to hear it and be grateful for it. I am always open to critique and suggestions etc. I will keep a few updates going below, in the hopes that maybe it helps some other beginner think through these things as I am. Thanks amigos.


UPDATE 1:
I went on a walk with my dog and thought about it some more.
I think I could wire the positive lead of the 12v cigarette barrel jack (that powers the screen/receiver) to the same point on the DPST switch (center terminal) as the transmitter. Then, both devices (transmitter and receiver) would be powered by whichever power source is selected by the switch.
Both devices require only a couple hundred mA each. All of this would be properly fused near the batteries, of course.
Photo of alteration:

 

[SeaGal]

wouldn't it be simpler to keep the reversing camera for use in the van and have a completely separate webcam/light on your house pointing to the drive and van?

 

[Vision.Urban.Reed]

wouldn't it be simpler to keep the reversing camera for use in the van and have a completely separate webcam/light on your house pointing to the drive and van?

Hey SeaGal!
It is my fault for not clarifying that:
This van IS (will be) my house, so any lighting-for-security set up is being planned here for use while I am sleeping inside the van.
My thoughts about adding more lights to the already included backup camera led lights, are only there to take advantage of the fact that there is already light-on-demand on the rear of the van, so adding more to the two sides and front might be a two birds with ...3 more smaller stones .... solution of sorts.
I hope that helps.

 

[SeaGal]

Ja.. sehr gut... regarding your update...

a) You will need a SPDT switch to do what your circuit is showing, not DPST. A DPST is just on off for 2 (separate) circuits. ?‍?

b) The design will also need to incorporate a relay (to isolate one supply) at a suitable point. As you have it drawn, if you turn the ignition on, without changing the position of the SPDT switch you will connect your LiFePO4's directly to your van's battery and, being at different voltages, will blow a fuse or worse ?.

 

[Vision.Urban.Reed]

Ja.. sehr gut... regarding your update...

a) You will need a SPDT switch to do what your circuit is showing, not DPST. A DPST is just on off for 2 (separate) circuits. ?‍?

b) The design will also need to incorporate a relay (to isolate one supply) at a suitable point. As you have it drawn, if you turn the ignition on, without changing the position of the SPDT switch you will connect your LiFePO4's directly to your van's battery and, being at different voltages, will blow a fuse or worse ?.

OK that sounds terrible. I will put on my thinking cap and go back to the drawing board, and ponder a long while on your points there. I had the lingo backwards on the switch, good that you caught that. Thanks SeaGal

 

[SeaGal]

my bad.. maybe it looks like you removed the connection to the 12v socket from the van's supply in your update. Anyway, just make sure you don't parallel connect the two

 

[SeaGal]

I had a further thought for you...

Rather than have a regular "on-on" SPDT switch - as your diagram suggests, you could get an "on-off-on" SPDT switch. Exactly the same function apart from having a central "off" position. Then you can power the camera from LiFePO or Van batter or switch it off completely.

Like this one..

https://uk.farnell.com/te-connectivity/a103syzq04/switch-spdt-5a-120vac/dp/1197668

 

[12VoltInstalls]

had a further thought for you...

Rather than have a regular "on-on" SPDT switch - as your diagram suggests, you could get an "on-off-on" SPDT switch. Exactly the same function apart from having a central "off" position. Then you can power the camera from LiFePO or Van batter or switch it off completely.

I think one also could configure a Bosch-type relay for this as there is a contact that goes to closed when signal power is opened on the signal of the switched circuit…

 

[Vision.Urban.Reed]

I think one also could configure a Bosch-type relay for this as there is a contact that goes to closed when signal power is opened on the signal of the switched circuit…

ah nice, like a 5 terminal relay instead of 4? I am only just getting familiar with that recently, good idea.

 

[12VoltInstalls]

like a 5 terminal relay instead of 4

Yes. They are available in 20,30,40A. I buy them by the dozen in a Chinese sortofa-brand for <15A use (20A or 30A labeled) because they get used up quick for various things. I try to buy a long-standing cheapo brand like nilight or whatever.
If I’m using one to a) actually do something (like 40A) or b) anything over 10A in a house/residence I buy a real German, Japanese, or Israeli brand but prefer Bosch.
Having said that, in actual use in road vehicles and boats the nilights have not had a high failure rate* for me, so… I just have fire aversion and Bosch is made well. Although I guess they could be China, as well.
*actually no failures I’m aware of other than an automotive air horn that welded the contacts closed on a very wet, road-salt slushy day in my jeep.