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Old 07-13-2021, 11:49 AM   #21
Bus Nut
 
Join Date: Sep 2017
Location: Cerrillos, NM
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Year: 2002
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Quote:
Originally Posted by Booyah45828 View Post
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.

This is true. A really simple dpdt relay can be wired the same way as the switch I linked and the coil of the relay can be wired to ‘ignition on’ so the source is switched automatically… then if you want on off capability you can put a spst carling switch on the output to the cameras from the relay if you want to turn it off.

If you need or want help with this I can find the relay and draw a wiring diagram that you can follow.

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Old 07-13-2021, 11:50 AM   #22
Bus Nut
 
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Quote:
Originally Posted by Booyah45828 View Post
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.

This is almost perfect but would force him to join his negatives from house to bus batteries which he doesn’t want to do. A slightly fancier relay will keep them isolated.
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Old 07-13-2021, 12:25 PM   #23
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Quote:
Originally Posted by rffffffff View Post
This is almost perfect but would force him to join his negatives from house to bus batteries which he doesn’t want to do. A slightly fancier relay will keep them isolated.
Correct.

I guess I don't understand why someone would have a 12v house system, and not try to charge off the bus alternator while running.

And the whole thing can be wired right now, with parts from any auto parts store for less then 20 bucks. You can use a dpdt relay, and then have system isolation, but I'm not sure of their availability or cost. Truthfully, I think I'd run a pair of spdt relays if he needs isolation just to keep to using stuff that's commonly available.

I guess I also assumed the security system would be on all the time, just in a standby mode when not used. Having it on all the time allows you to record as well, which can be a nice feature for security purposes. You could always put a switch after the relays to turn it off if you desire.

But, I really didn't like the manual switching aspect of it, because I know I'd accidentally forget to flip it and likely drain the batteries. They're probably better at remembering things then me, though, so maybe a manual switch by the driver's seat would work good.
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Old 07-13-2021, 12:35 PM   #24
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Quote:
Originally Posted by Booyah45828 View Post
Correct.

I guess I don't understand why someone would have a 12v house system, and not try to charge off the bus alternator while running.

And the whole thing can be wired right now, with parts from any auto parts store for less then 20 bucks. You can use a dpdt relay, and then have system isolation, but I'm not sure of their availability or cost. Truthfully, I think I'd run a pair of spdt relays if he needs isolation just to keep to using stuff that's commonly available.

I guess I also assumed the security system would be on all the time, just in a standby mode when not used. Having it on all the time allows you to record as well, which can be a nice feature for security purposes. You could always put a switch after the relays to turn it off if you desire.

But, I really didn't like the manual switching aspect of it, because I know I'd accidentally forget to flip it and likely drain the batteries. They're probably better at remembering things then me, though, so maybe a manual switch by the driver's seat would work good.

You definitely make a lot of good points that should be considered. Dpdt relays are common and cheap too, maybe not at the auto parts store but they’re easily available so that part is simple, and the on/off switch is an easy add on, but wiring the alternator to the house batteries and leaving the cameras on the house batteries only seems like it could be a better plan overall when you step back.
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Old 07-13-2021, 06:44 PM   #25
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Quote:
Originally Posted by kazetsukai View Post
...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.
I'm missing something-what is meant by 'fully parallel'?
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Old 07-14-2021, 01:35 AM   #26
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with a 12V camera system, I personally would share a common ground, the bus body/chassis. With a high-wattage thing-a-ma-bob (like any of my inverters, even the small one) I would give it dedicated power and ground cables. But that's me.


Not sure what "fully parallel" means either.
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Old 07-14-2021, 07:23 AM   #27
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Quote:
Originally Posted by Rucker View Post
I'm missing something-what is meant by 'fully parallel'?
You wouldn't want to bind both banks negative to chassis and then somehow the positives on each bank together as well. Like a switch somewhere that unintentionally bound the two together.
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Old 07-17-2021, 04:22 PM   #28
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I’m not seeing the point. Why not just connect the cameras to a house battery and leave it connected if they don’t use much power?. It seems they wouldn’t drain the house battery much? Seems like a lot of fuss but maybe I’m missing something. Wouldn’t be the first time.
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Old 07-17-2021, 05:23 PM   #29
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Quote:
Originally Posted by Doktari View Post
I’m not seeing the point. Why not just connect the cameras to a house battery and leave it connected if they don’t use much power?. It seems they wouldn’t drain the house battery much? Seems like a lot of fuss but maybe I’m missing something. Wouldn’t be the first time.

thats how mine is.. and when the bus is driven or plugged into Shore power the house batteries get charged.. works great and is simple..



its just like many HIGH END UPS systems on critical components in buoldings are. phone systems, network gear etc.. run 100% of the time off of the battery and when the power is *ON* the charger charges then floats and maintains the voltage.. this acts as a buffer and filter against surges and spikes on the line power.. when the power goes OFF the equipment knows no different.. it continues to run off the batteries until they are dead (the BMS cuts them off)
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Old 07-18-2021, 11:09 AM   #30
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Quote:
Originally Posted by Turdle View Post
[edited for brevity]
...dedicated negatives back to the battery for each load...I'm sure it's ME that's missing something here...
.
We always run a negative line through a fuse near the battery.
We believe this forms a clean loop.
Why?
Well, that requires some LM history...
.
.
A ground-to-chassis story:
* 1990, I replaced the complicated V-12 in a 1987 Jaguar XJS.
The Chevrolet 350 weighed less with simpler parts.
.
For my conversion, I got ground-strap crazy:
* from each head to the firewall.
* tranny tailpiece to the cross-member.
* block to the cross-member
Probably around seven dedicated ground straps.
.
Each time I walked toward it, I thought "Now, this's a deeply grounded car!"
.
One day, I modified the replacement exhaust to eliminate a squeaky rub.
I loosened the header bolts so I could swing the exhaust-pipe slightly, then re-tighten it without the rub.
An additional donut support, and I was good to go.
.
Except I didn't.
No juice, dead starter.
Tracing my problem back to my recent changes (always a good idea), I realized the exhaust-pipe rubbing the frame was the sole functioning ground on the entire vehicle.
.
.
Turdle,
Your admission "...maybe I am missing something here..." generally applies to most aspects of my short sweet life.
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