Yeah, in an earlier post I proposed using a single DPDT to save on coil current, and someone, I forget who, didn't like the idea much - worried about isolation between the 2 sets of contacts since I'd have 12vdc on one set and 120vac on the other. I hadn't really thought that would be a problem - the contacts are supposed to be isolated!! But I started thinking about switching to 2 separate relays. Also, it might be handy to have the alternator relay up under the seat - there are all those unused extra positions for relays - I don't know yet what you need to order for relay bases in order to use those, but it would be a neat setup. It might make more sense to have a relay for the charger back near the charger. I have my BMV702 mounted near the side door where the light switch and step defeat switch are mounted (under the counter where the TV pops up), so it's about halfway from each.
The charger says input 1000w @ 120v. It's a 60 amp charger. So a 10A relay should cut it, though not with a lot of headroom...
BTW - I have a pretty good understanding of basic electric power generation and distribution, I understand simple logic circuitry - it's the practical details that slow me down - what relays, what bases, how to route the wiring when I don't know the RV very well, and making sure I understand the specifics of working with Lith batteries (if anybody actually does understand it well <g>...). I have some practical experience - built a 45KW hydro site and ran it for 15 years, was involved with installing and servicing data loggers for small independent power producers in VT who sold to the directly to VELCO, the VT power distribution entity. But I don't have any sort of EE training and I've never had a Sprinter before so everything in it is new to me. I also haven't done a lot of modern car work tho' I know something about vintage motorcycles and cars. So it's a bit of an adventure...
For the sake of getting the RV movable again, I lifted that D+ wire and extended it - also put a wire on the D+ terminal. So for the moment, both of them are reachable with the seat back in place, and I've got them tied together. As expected, the alternator charges the house batteries when I start the engine. I assume that if I untie them, the isolator will stay open and I won't charge the batteries, but I was waiting to hear from you - wanted to make sure I understood the M-B description correctly (beginning of post 8).
Thanks for the guidance - it's dark out now so maybe I'll look into the M-B upfitters site for a while.