I have a remote controlled battery disconnect on the positive post of the battery, but have add-on accessories which are still fed from the battery. The accessories are the hood lock remote control system, battery disconnect remote control system, radio memory, and dash camera / security camera.

I currently have the add-on accessories fed via separate fused circuits (wires) from the battery positive post, but grounded thru the normal system grounds. The starter cable, #10 red wire to the charging circuit/horn relay, and # 20 black wire to the battery gauge are thus not powered when the disconnect is open.
I also have separate switches to isolate power to these add-on accessories when the car is in storage as they will discharge the battery if left connected for a week or more.

An 'expert' stated I should be concerned that there may be a backfeed thru the add-on radio and/or dash cam to the original circuits of the car as they share the same ground.
The add-on radio is still connected thru the ignition switch to the fuse box for the tuner / amplifier circuits. I am assuming there is no cross tie between the memory circuit and the tuner/amplifier circuit as they require separate feeds.

If I put the remote battery disconnect on the negative side of the battery I would need a secondary 12vdc battery to power the accessories when the car battery is disconnected. A secondary battery would also require a separate charging system. Not my desired option.

As a test, I isolated the battery via the remote disconnect with the radio memory and dash cam remaining powered. I turned the ignition switch on did not get any indication of the original circuits (lights, radio, etc.) being powered.

Am I missing something which leaves the possibility of a backfed to the ignition switch and / or fuse box?
Should I add a separate fuse box to totally isolate the add-on accessories from the original fuse block?

Thanks,
Ron

 

Diagram?

 

How would adding another fuse box for the add on accessories isolate them? Do you mean add another cutoff switch?
Do you have a digital DVM with an AMP circuit that you could use to check the amperage draw from the battery?

 

You're doing some bizarre stuff there, but it's your car. I don't ascribe to the "backfeed" theory, but again, it's not me doing this.
Move the cutoff to your negative battery post so NOTHING is grounded when the switch is open. Then disconnect and run your desired excluded options (left on with disconnect open) negative wires to the negative battery post side of the cutoff so that when you disconnect they will be the only things with a circuit to the negative battery posts. Make sure NONE of those any longer have a connection to the car ground, but ONLY to the negative battery post. Then when you activate the disconnect all your normal car grounds will make no connection (starter, headlights, etc), but your added connections will still work. This will work ONLY if you do not have ANY of those options connected to the car chassis ground, but have wires run from their negative (usually connected to ground on the car) straight to the battery post side of the disconnect.

 

Your battery will gradually lose voltage regardless of whether you have a parasitic current draw or not. Battery disconnection will only slow down the process. The easier way to avoid this, and the way that best preserves the health and longevity of your battery is to use a trickle charger whenever the car is not in use. No need to open any circuits, original or add-on.

 

Dave,
Here is a rough schematic of what I have now. It allows the remotes, which draw upon the battery all of the time, to be shut off which of course also shuts down the device it feeds.
cbernhardt, The additional fuse box was to isolate the aftermarket radio which has two power leads, one keyed from the original fuse box and one from the battery for memory. The thought was feedback thru the radio switched power which should not occur with the ignition switch off - right? I checked for draw from the battery with all switches and remotes off and get no reading, but my VOM is not the best.
65GGvert, I understand the circuitry of moving the disconnect to the negative post, thus running separate grounds to each device and thus isolating the ground side of the original circuitry. The only problem is the memory power to the aftermarket radio is grounded thru the radio and thus is not separate from body ground unless I isolate the radio and thus remove the switched connection at the fuse box. That is an option as the radio has an on/off switch.
Little Cat, yes, the battery maintainer will keep up with the draw of the remote units, radio, and dash cam, but I chose to put a switch in each circuit for maintenance and long term storage.
I had a manual disconnect on the battery, but changed to the remote controlled disconnect as it is easier (I am lazy), and I don't have to open the hood. The remote battery disconnect is for use going to car shows, stops at the watering hole, etc.
Thanks for the input Gentlemen.
Ron

 

Ron-
I agree with 65GGvert. And I'm no fan of unnecessary complication in wiring or plumbing. If you must have all that, I advise wiring it as he suggested.

Dan

 

I could see a potential for back feed, especially if the radio is left on. I guess you would have to try it to find out for sure.

I'm thinking it could be solved with a diode placed in series with the radio's main power wire. This would keep any current from back feeding through the wire.

 

Thanks for the reply. I did try turning the ignition ON with the disconnect on and the radio did not energize, however I didn't try starting the engine, nor turning on any original accessories or lights. I also thought of a diode in the power wire of each accessory, which would be much easier than separating the grounds from the vehicle ground.
I asked as my electrical knowledge is limited to a B&H television repair course back in 1972 and OJT in the power industry. A lot of things have changed in the last 50 years with the domination of the IC chips in lieu of transistors and resistors. Even though I am rather ignorant of the new technology, I still love to tinker.
Ron

 

Maybe a good thing. You don't want to start the car or turn on the lights and try to pull all that current though the radio wire if there is a back feed. You would want to try something that draws little current.

 

I think I will add a diode to all of the devices as the largest load is 5 amps and one can buy 25 of them for less than $10. Cheap insurance and little labor to solder them in.
Thanks again for the help.
Ron