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I have a motorhome and tow my car behind. Since I have to leave the car in accessory mode so the steering wheel is unlocked, the battery doesn't last a long time.

I want to run a DS line from the motorhome hookup (fused at motorhome) to the battery in a car to utilize the motorhomes charging. I plan to fuse at the car battery. Really would like to add a diode to prevent the car battery from backfeeding into the motorhome.

All batteries are flooded lead acid, 12V. Since there is a good possibility of backfeed when starting (diesel draws a lot of power to start), I'm not sure what size of a diode I should use or even where I could purchase one.

I live about 40 miles North of Toronto Canada.

Any suggestions on where to get or improve the circuit would be greatly appreciated.

Thank you

DucatiKiller
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Bob
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5 Answers5

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The fastest, cheapest and easiest solution is to add a battery disconnect switch to the car. After placing the ignition switch into acc mode the open the hood and disconnect the switch. When you arrive at your destination, open the hood and reconnect the switch. This costs under $20. It also eliminates the need to run anything or calculate anything. Many auto parts stores carry this in stock.

PS put this on the negative battery cable not the positive.

enter image description here

vini_i
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adding a diode would probably be counterproductive as it will cause an extra voltage drop, I'd look into fitting a relay such that the socket was not connected during engine start.

Jasen
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Disconnecting the battery messes up your radio, etc. Instead of a diode which causes a voltage drop you could put a 55 W lamp in series. It will limit the current to the battery but as the battery charges up the voltage drop across the bulb will reduce and the battery gets full alternator voltage.

When cranking the motor home its battery voltage may drop to 6 V or so. The charging lamp will glow at half-voltage (about 1/4 power) and won't load the car battery.

enter image description here

Transistor
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I found this online.... Should solve your issue:

enter image description here

Dee
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maybe you can fit a a battery with more reserve power

Jasen
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