Diode to Prevent Back Feeding from Trailer Battery to Running Lights

Updated 11/01/2016 | Published 10/31/2016

Products Featured in This Question

Hopkins Quick-Lock Diode for Towed Vehicles - Qty 1

(6)

$10.01

Redarc In-Vehicle BCDC Battery Charger - Dual Input - DC to DC - 12V/24V - 40 Amp

(87)

$620.00

Roadmaster Hy-Power Diode - (Qty 1)

(343)

$21.27

Question:

I have a small military type trailer that I built. I want to add a battery to it. I was hoping to run a charge wire off of the running lights. Which diode would be the best for something like this? I'm planning on running a couple of LED spot lights off of this battery and also have it as a backup jump start battery because I do overland exploring.

asked by: John K

Helpful Expert Reply:

For a diode I recommend # RM-790 which is rated for 85 amps. However, trailer wiring, both on the trailer and on the vehicle side, is too small to charge up a regular battery. And most vehicle alternators are unable to push back the amperage required to charge up a regular battery. At best it will provide a maintenance charge and keep the battery from depleting.

It can charge up a small breakaway batter such as # HM20008 though. But these batteries are rated much lower than a regular car battery, only 5 amp hours, and would be basically useless if you needed to jump start a vehicle.

In order to charge up a regular car battery you would need a DC to DC charger, # 331-BCDC1240D, but it is expensive...at the same time, it won't leave you stranded.

expert reply by: Michael H