Electical back feed from 12V stereo battery connection

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OOCustoms
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Electical back feed from 12V stereo battery connection

Post by OOCustoms »

Hi, I have a Pinzgauer that has a 12v stereo head unit. When I connect the battery lead (for clock and all the presets) to the 12V hot lead on the middle connection on the battery, I get back feeding voltage that energizes the led indicators on a custom switch panel, and several other circuits. I think I need to add a blocking diode somewhere in the wiring, but exactly where and how big a diode do I need? Any advice is greatly appreciated.
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Andre
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Re: Electical back feed from 12V stereo battery connection

Post by Andre »

the ghost is because you should have used a 24-12v converter. The system is making a ground through your stereo because you pulled from the middle battery.
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rmel
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Re: Electical back feed from 12V stereo battery connection

Post by rmel »

As Andre pointed out, better off with a 24-12V converter.

Unless your load is infinitesimal you run the risk of unbalanced discharge on
your batteries with a corresponding aging effect. You do need a blocking diode,
as there is a reverse bias possible when you open the battery cutoff switch.
Equalizers should use a blocking diode as well -- and one designed for that
purpose e.g. Battery isolater diode. 24/12 converter is just cleaner and is
compatible with the cut-off switch.
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Jimm391730
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Re: Electical back feed from 12V stereo battery connection

Post by Jimm391730 »

The answer depends on how you have wired the stereo - obviously the +12V is coming from the tap between the batteries (I'll assume both the clock/presets memory "keep alive" power and normal 12V power), but does the stereo ground connect to the battery directly, or to the chassis through the battery disconnect switch? It is possible to have bad things happen if ground goes to the chassis: with the disconnect switch open, there is a possibility that the stereo can get REVERSE 12V power applied if lights or similar 24V devices are switched on; as Ron said, a blocking diode can help to prevent damage to the stereo.

I've resigned myself to expect that I can't easily use devices that require "keep alive" power. I have heard of people using a 9V battery for just that reason, but I suspect the life of the battery depends on the specific piece of equipment - some might last for years, others might drain a 9V battery in days. YMMV.
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OOCustoms
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Re: Electical back feed from 12V stereo battery connection

Post by OOCustoms »

Thanks for the replies. I have a 24v-12v converter installed-I know enough to not tap directly off the battery for anything that pulls any kind of significant load. The stereo, cb, and back up camera all run through a fuse panel thats connected to the converter- however as soon as the battery cutoff switch is thrown, no more juice. The stereo's battery cable needs to have constant 12v, just for the clock and display presets, and to stop it from switching into demo mode everytime it loses power. I have an auxillary golf cart 12V battery that I believe will solve my problem- If I wire it into the system downstream from the converter (which puts out 13.6V) I think I can keep 12V going to the stereo that way, and the converter should keep the battery topped off. Thoughts?
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Re: Electical back feed from 12V stereo battery connection

Post by Jimm391730 »

DC to DC voltage converters are not intended to be a battery charger; it may or may not charge the battery and/or be damaged from too much charging current. You'd be better off wiring the aux battery between chassis and the 12V preset power, ONLY, and just charge that battery every 3 months or so (mostly from its own self discharge more than any drain from it).
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Re: Electical back feed from 12V stereo battery connection

Post by OOCustoms »

Yeah, after I posted I thought about it and realized that I'd probably just cook the converter. 12V battery to chassis ground and stereo battery connection will be the short term solution (hopefully) for now.
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