Originally Posted by Smokymb
Setting up a 2008 Honda CRV with Blue Ox equipment as my first TOAD . Most everything is completed except the battery charging issue. I understand how to pick the 12V lead off the 7way from the RV and mate it to the 6way I'm using on the TOAD, but am still a bit hazy about what to do next.
Nothermark, can you be a little more specific about how you set up your "diode and fuse protected" line to the TOAD battery. Is it as simple as connecting the diode and fuse in series and attaching the line to the positive terminal on the TOAD's battery? Do diodes have "ratings"? Does it matter which comes first on the line - diode or fuse? What gauge line?
Sorry if my question is too basic; I've got a lot to learn.
If you are familiar with electronics or know somebody who is the easy answer is to put a high current diode and fuse in series with the power feed line back to the towed. High current shottky diodes are cheap and have a low forward drop. The diode is oriented to feed power to the towed but not let power get fed back to the tow vehicle so the tow vehicle does not accidentally suck down the towed battery. It will not maintain full charge but will maintain close enough too it to let you start the vehicle and not run the battery so far down you are damaging it. The idea is to trickle charge as needed and let the car battery pick up any short term high current loads like a braking system. I'd pick a diode in the range of 20-50 Amp depending on what I could get cheap and might toss in a fractional ohm resistor to limit current. The connecting wire will probably be sufficient for the last part. Disconnect it before you start the towed if you do not put in current limiting or the drop in battery voltage when the starter kicks in will take out the fuse.
FWIW a 20 A diode probably has a surge rating several times that so say 60 A. A 6 V drop during starting would need 6/60 = 0.1 ohm. At say 10 A charging that would drop 10 x 0,1 = 1 V. The closer the battery gets to full charge the lower the current thus the lower the charge. Fun playing with low voltage high current circuits. ;-)
I'd also carry a mid sized battery charger in the 20 amp range so I had a way to top off the towed battery. I am leery of the jump start boxes because if you read the manual most are only good for a couple of uses. OTOH with AC available from the coach a decent battery charger will top off the towed battery in a kinder fashion in an hour or so.