Battery issues

Jekern,

Let me just say that you are not the first to do this and probably will not be the last. This is the sort of work I used to do on boats and may again if the market ever comes back.

The systems have to have some cross connection to charge the hotel bank from the main engine. More down the page.

When a battery gets installed backwards, there can be a lot of damage done as soon as the terminals are connected. Many things are protected from reverse polarity with sacrificial parts included. Unfortunately, often professional repair is still not economic. Before you started the main engine, you had already done damage to everything polarity sensitive.
Things to test right now:
-The converter/charger (most have fuses, but they may not be fast enough)
-The inverter (if you have) (also has fuses)
-The power supplies for entertainment systems even if "Off"
-Fluorescent lights
-Tank monitoring systems
-Energy control or monitioring systems
Things that will probably survive:
-Pumps and motors (if not on they were safe)
-Incandescent lights

Your Winnie uses a heavy contactor (looks like a Ford solenoid) to charge the house (hotel) bank from the main engine alternator. When you started the main engine, that contactor closed. As soon as that happened, lots of things in the main engine systems may have been damaged. First on my list is always the alternator diodes. I suggest that if you can't confirm that it is still completely operational, that you remove it and take it to someone that can test it. There is also a light gauge wire in the harness called a "fusible link". It is actually a multi-hundred amp fuse the protect the vehicle harness. It is in the main power harness either near the battery or the starter main terminal. If you can find that, and the insulation is saggy, you can get replacements at most auto parts stores. Most of these are lost to corrosion, but lots of them get burned up too.

I wish you luck.

Matt

Thanks for posting this, it may alert others to beware of polarity. Hopefully your engine's alternator and other 12vdc electrical devices were not harmed. If you are not savvy about electrics, have a mobile RV service or truck/auto electrical guy check it out.

Practically all Class Cs have some method of charging the coach battery when the engine is running. Mine has a solenoid that connects the coach battery to the chassis battery when the ignition is on.

Because the sparks did not fly until the engine was started, the RV may be utilizing a Bi-Directional Isolator Relay Delay. The BIRD would not connect the two batteries until it sensed a +13 Volts (appox) from one onf the connected batteries.....then poof, the smoke is out.

Sorry to hear of your problem, but you are not the first to do it. Many years ago I came home after a very long graveyard shift very tired and wanted to hook up the batteries in my boat. They hooked up OK and everything was fine until I put the battery selector switch to both and there was a loud pop. I blew the post off the battery and the 80 amp fuse at the alternator. After replacing the battery I did what I should of done to start with, I used some of my red electrical tape and color coded all of my positive wires. My MH is done the same way so there is no confusion on what cables go where. I have not had the problem since.

Are you saying you put the coach(house) batteries back in? Or the engine(chassis) battery?
Check converter/charger. Hopefully only the charge circuit fuses blew.