I was thinking how strange it was to be hooking up a battery maintainer to the engine battery of the small class C parked in the driveway when I have a surplus of power from a solar panel on the roof. Too much work to run a new wire - yes. But there is already a wire from the engine battery to the house battery through the Ford auxiliary battery relay in the engine fuse box. I took the relay out and replaced it with a wire:
Presto, the voltage on the battery jumped from 12.5 to 13.6.
Other small MH's might be using the Ford auxiliary battery charging system, which is just another relay in the fuse box like the ones below and to the right of the yellow circle around the missing one. It connects the engine charging system to the wire heading back to a trailer electrical connector and, in my case, to the house batteries. There are four connections on the relay and a nice little schematic with labeled connectors. To be sure, I checked the voltages on the two connectors marked as points switched by the relay. One had the voltage of the house with its solar panel working (13.6) and the other the voltage of the engine battery (12.5). I removed the relay, put spade connectors on each end of a short #12 wire and (after filing the spades narrower and tapered) connected those two points with the wire.
I intend to replace the relay when traveling and camping to avoid unnecessary discharge and the dreaded dead engine battery on a rainy weekend. In winter, I will still disconnect both engine and house batteries.
Presto, the voltage on the battery jumped from 12.5 to 13.6.
Other small MH's might be using the Ford auxiliary battery charging system, which is just another relay in the fuse box like the ones below and to the right of the yellow circle around the missing one. It connects the engine charging system to the wire heading back to a trailer electrical connector and, in my case, to the house batteries. There are four connections on the relay and a nice little schematic with labeled connectors. To be sure, I checked the voltages on the two connectors marked as points switched by the relay. One had the voltage of the house with its solar panel working (13.6) and the other the voltage of the engine battery (12.5). I removed the relay, put spade connectors on each end of a short #12 wire and (after filing the spades narrower and tapered) connected those two points with the wire.
I intend to replace the relay when traveling and camping to avoid unnecessary discharge and the dreaded dead engine battery on a rainy weekend. In winter, I will still disconnect both engine and house batteries.
Interesting, as are all your posts! Your system is a full order of magnitude bigger than mine, which has a 100 watt solar panel and the greatest engine charging of my 2 house batteries I have observed is 6 amps.
I don't think there is a larger relay. I spent a fair bit of time looking for the kind of selenoid or solid state disconnect that people with larger motorhomes have posted pictures of. Just now, I went looking for the .88 amps you mentioned. I connected the engine battery through a multimeter set on its 10A range and put another multimeter on 10A in place of the jumper wire. I observed about 0.4 A coming in from the house on the jumper meter and 0.35 charging the battery. With no current coming from the house, about 0.05 A flows out of the battery, which must be the parasitic current of the vehicle. With a door open and courtesy light on, an extra amp came in from the house solar system and didn't go into the battery.
The relay I replaced with a jumper is called the "Trailer battery charge relay" (E). There is a 40 A fuse also named "trailer battery charge relay" (8).
No current rating is given for the relay in the book or on the relay itself, otherwise so well self-documented. However, I happen to have a spare one still in its package that is rated at 40 Amps.
I find it interesting that the system is set up for 40 Amps but only achieves 6 A of battery charging. Maybe I could benefit greatly from one of those DC to DC voltage changers.
I like my little jumper better than a trickle charger. Such an efficient simple solution. No converting DC to AC and back again; only 4 inches of wire! I accidently made it just long enough to work with my clampmeter.
What the heck is the "auxiliary battery relay" (fuse 20 in the photo) for?
I don't think there is a larger relay. I spent a fair bit of time looking for the kind of selenoid or solid state disconnect that people with larger motorhomes have posted pictures of. Just now, I went looking for the .88 amps you mentioned. I connected the engine battery through a multimeter set on its 10A range and put another multimeter on 10A in place of the jumper wire. I observed about 0.4 A coming in from the house on the jumper meter and 0.35 charging the battery. With no current coming from the house, about 0.05 A flows out of the battery, which must be the parasitic current of the vehicle. With a door open and courtesy light on, an extra amp came in from the house solar system and didn't go into the battery.
The relay I replaced with a jumper is called the "Trailer battery charge relay" (E). There is a 40 A fuse also named "trailer battery charge relay" (8).
No current rating is given for the relay in the book or on the relay itself, otherwise so well self-documented. However, I happen to have a spare one still in its package that is rated at 40 Amps.
I find it interesting that the system is set up for 40 Amps but only achieves 6 A of battery charging. Maybe I could benefit greatly from one of those DC to DC voltage changers.
I like my little jumper better than a trickle charger. Such an efficient simple solution. No converting DC to AC and back again; only 4 inches of wire! I accidently made it just long enough to work with my clampmeter.
What the heck is the "auxiliary battery relay" (fuse 20 in the photo) for?
