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Old 07-13-2021, 08:38 AM   #1
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One device powered by selectable power system

I've been scouring the forums trying to find similar questions and either my google-fu is weak or maybe I'm using wrong terms and missing the relevant information... My apologies if this has been asked and answered.

Basically, what I want to be able to do is power a single device, in this case my external camera system, to be able to run from either the Bus electrical system or my PV/Battery system. If at 2am we hear something funky going on outside, we can turn on the camera system to see what's going on without having to drain the bus battery, and if we're driving, we don't have to drain the house battery.

I found DPDT on-off-on switches which seem to be an answer, but after noodling on it a bit, I realized those switches don't handle the negative leads. This would mean I would have to have two negative leads coming from my load going to both system's negatives. This sounds bad since it would effectively link the negatives/grounds of which I was trying to NOT do.

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Old 07-13-2021, 09:01 AM   #2
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You could use one single pole on/off switch combined with two relays to get the effect you are going for. The relays would be powered by the NO (Normally open- alternative) power source.
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Old 07-13-2021, 09:06 AM   #3
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Odd. Seems you could use something like this:
https://www.amazon.com/TWTADE-Univer.../dp/B07R9V39Q8


Load positive/negative goes to the center two conductors, then each end goes to one of the power sources (positive and negative)? I don't see how you'd need to combine negative that way.
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Old 07-13-2021, 09:52 AM   #4
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Quote:
Originally Posted by kazetsukai View Post
Odd. Seems you could use something like this:
https://www.amazon.com/TWTADE-Univer.../dp/B07R9V39Q8


Load positive/negative goes to the center two conductors, then each end goes to one of the power sources (positive and negative)? I don't see how you'd need to combine negative that way.
Nifty, those look like they could work. I was looking at the Carling rockers. They don't even have negative leads as far as I can tell.
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Old 07-13-2021, 09:55 AM   #5
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Are you running an isolated negative on your low voltage system? Typically the frame is the common ground for batteries and their respective loads. You would just need to switch between positives. Maybe I'm missing something here...
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Old 07-13-2021, 10:00 AM   #6
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Are you running an isolated negative on your low voltage system? Typically the frame is the common ground for batteries and their respective loads. You would just need to switch between positives. Maybe I'm missing something here...
Everything I've been reading says I don't want to use the chassis as negative for my "house" power and I should be running dedicated negatives back to the battery for each load. Maybe I'm reading between lines that don't exist? Should I be "grounding" my negative bus bar to chassis for the "house" battery system? Will that cause any issues with the fact that the manufacturer grounded negative for the bus systems to chassis as well?

I can appreciate the difference between grounding/bonding the negative for the "house" side to chassis while ALSO running dedicated negative leads all the way back.

This is all so very confusing and I'm sure it's ME that's missing something here...
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Old 07-13-2021, 10:00 AM   #7
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Quote:
Originally Posted by Rwnielsen View Post
Are you running an isolated negative on your low voltage system? Typically the frame is the common ground for batteries and their respective loads. You would just need to switch between positives. Maybe I'm missing something here...
Its optional to have a negative/chassis bond for solar/DC non-starter side... I used to but with the recent battery upgrade I removed it. Its entirely reasonable to have a floating DC house system.


Whether you combine negative for house/chassis systems or not, what you really don't want to do is fully parallel them in any way.
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Old 07-13-2021, 10:04 AM   #8
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A DPDT switch will handle positive and negative and would work fine. Itíll have six terminals, two for bus power, the middle for the load and two for house power. Unless Iím
missing something thatís really what theyíre designed for, and wonít connect anything that you donít want connected.

A SPDT switch only has three terminals and would force combining of the negative wires.

Iím tired and may have misread but look into that again because Iím pretty sure itís that simple:
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Old 07-13-2021, 10:11 AM   #9
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A DPDT switch will handle positive and negative and would work fine. Itíll have six terminals, two for bus power, the middle for the load and two for house power. Unless Iím
missing something thatís really what theyíre designed for, and wonít connect anything that you donít want connected.

A SPDT switch only has three terminals and would force combining of the negative wires.

Iím tired and may have misread but look into that again because Iím pretty sure itís that simple:
https://newwiremarine.com/product/on...ependent-lamp/

Maybe I'm ignorant (hint, I'm probably ignorant) but it looks like the Carling rockers don't handle negative back from the load.
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Old 07-13-2021, 10:15 AM   #10
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Quote:
Originally Posted by Turdle View Post
https://newwiremarine.com/product/on...ependent-lamp/

Maybe I'm ignorant (hint, I'm probably ignorant) but it looks like the Carling rockers don't handle negative back from the load.
The wiring diagram shows the use of two positives rather than a positive + negative, and the negative on that switch I believe is to power the light in the switch itself, which wont work without combining negatives.
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Old 07-13-2021, 10:18 AM   #11
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Originally Posted by kazetsukai View Post
The wiring diagram shows the use of two positives rather than a positive + negative, and the negative on that switch I believe is to power the light in the switch itself, which wont work without combining negatives.
Ok, perfect, that's what I thought it was doing which is why I created this thread. Now it sounds like there are rather large differences between DPDT switches. In this case, doing what I want, the Carling rockers (which would match the other switches on my panel) may not do what I need and connecting loads to other DPDT switches may be required.

My only question now is how do I mount "other" style switches to a panel meant to house carlings...
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Old 07-13-2021, 10:36 AM   #12
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Quote:
Originally Posted by Turdle View Post
Ok, perfect, that's what I thought it was doing which is why I created this thread. Now it sounds like there are rather large differences between DPDT switches. In this case, doing what I want, the Carling rockers (which would match the other switches on my panel) may not do what I need and connecting loads to other DPDT switches may be required.

My only question now is how do I mount "other" style switches to a panel meant to house carlings...
Wait a second... you might be able to wire that switch after all.
switch.png


Lead wiring:
#1 to Positive on power source A
#3 to Positive on power source B
#2 to Positive on device
#4 to Negative on power source A
#6 to Negative on power source B
#5 to BOTH Negative on device and #7
#7 to #5


Thoughts?
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Old 07-13-2021, 10:40 AM   #13
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Originally Posted by kazetsukai View Post
Wait a second... you might be able to wire that switch after all.
Attachment 59408


Lead wiring:
#1 to Positive on power source A
#3 to Positive on power source B
#2 to Positive on device
#4 to Negative on power source A
#6 to Negative on power source B
#5 to BOTH Negative on device and #7
#7 to #5


Thoughts?
If that would work it would be awesome!
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Old 07-13-2021, 10:41 AM   #14
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Quote:
Originally Posted by Turdle View Post
If that would work it would be awesome!
I think so, since negative will come from the power source currently active.
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Old 07-13-2021, 10:49 AM   #15
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Using a DPDT switch (basically 2 switches controlled by 1 action) should be possible. Just make the grounds one of the "loads" the switch controls. Both the power and ground will be switched at the same time.
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Old 07-13-2021, 10:59 AM   #16
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Quote:
Originally Posted by Mr4btTahoe View Post
Using a DPDT switch (basically 2 switches controlled by 1 action) should be possible. Just make the grounds one of the "loads" the switch controls. Both the power and ground will be switched at the same time.
That sounds right to me. This entire thread has gotten way too complex. Its a bus with two separate power sources, switching between the two is not difficult.
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Old 07-13-2021, 11:23 AM   #17
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Ditch the lamp and itís fine. I canít copy the link but if you search that same site for VJD1-S00B itís the switch you need. Only six terminals, cameras in the middle and one power source on top and one on bottom.
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Old 07-13-2021, 11:25 AM   #18
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https://newwiremarine.com/product/vj...rocker-switch/

That one.
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Old 07-13-2021, 12:20 PM   #19
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my 24/7 bus network server / router / etc is powered by the same base power-source all the time.. my House batteries.. when im docked up I plug the victron charger in which keeps the house batteries charged and topped off. when im driving the alternator keeps the house batteries charged..



my network doesnt worry about its power source.. its always the same..
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Old 07-13-2021, 12:29 PM   #20
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Quote:
Originally Posted by Turdle View Post
I've been scouring the forums trying to find similar questions and either my google-fu is weak or maybe I'm using wrong terms and missing the relevant information... My apologies if this has been asked and answered.

Basically, what I want to be able to do is power a single device, in this case my external camera system, to be able to run from either the Bus electrical system or my PV/Battery system. If at 2am we hear something funky going on outside, we can turn on the camera system to see what's going on without having to drain the bus battery, and if we're driving, we don't have to drain the house battery.

I found DPDT on-off-on switches which seem to be an answer, but after noodling on it a bit, I realized those switches don't handle the negative leads. This would mean I would have to have two negative leads coming from my load going to both system's negatives. This sounds bad since it would effectively link the negatives/grounds of which I was trying to NOT do.
I'm going to presume this camera system is powered by 12v?

If that's the case, your house bank will also have to be 12v in order for the system to function correctly, and if that's the case, I see no reason to not have a common chassis ground between the 2 systems.

The only reason I'd not want a chassis/negative bond for a house bank would be if the voltage of the bank is high enough to create a shock hazard. You'd then want it to be isolated, to try and prevent electrocution.

So, if the house bank is 12v, and the bus is 12v, I'd use your standard 5 pin automotive relay to do the switching. Connect pin 30 to your camera system, 87a to your house bank, 87 to the vehicle bank, and your coil (85/86) to ground and ignition switch power.

That way the camera system is fed from the house bank when the ignition is off, and from the vehicle batteries with the switch on. I doubt your camera system would be pulling so many amps to exceed the rating of a relay.

With a carling switch, or any other switch for that matter, it leaves the possibility of you forgetting to make the switch. With a relay, the switch over is automatic whenever the key is on.
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