Can I charge the house battery with the engine alternator?

The battery boost solenoid on your '88 serves double duty. It is triggered by a wire that is hot when the engine is running, which engages the solenoid to allow the alternator to charge both banks. The momentary pushbutton does the same thing (likely through the same trigger wire on the solenoid); connects the two battery banks to serve as an emergency start if the chassis battery is dead/low. As "enblethen" says above, it needs to be a continuous duty solenoid.

Adding a switch in the line WILL eventually lead to both battery banks being drained and you being stranded when (not if) you forget to turn it off once you get to your campsite. It's an extremely simple and foolproof setup. Don't try to reinvent the wheel.

heyobie wrote:
Which solenoid did you buy? I'd like to replace mine

Here's the Trombetta "Bear DC contactor" solenoid that I now use in our Class C that connects the coach batteries to the engine alternator system - note that the one I use is the 2nd one down in the chart, rated for 225 amps continuous duty, and is the version with silver contact material. It is not inexpensive, but IMHO on-the-road-reliability should be very high on one's list:

https://www.trombetta.com/wp-content/uploads/2019/07/bear-family.pdf

Tekonsha 7000 is agood quality battery disconnect relay. Comes as shown in link a three terminal and also comes with four pole. Tekonsha 7001
NAPA carries same type of relay. Relay must be continuous duty and not a starting relay.

heyobie wrote:
Which solenoid did you buy? I'd like to replace mine

I got 2 rated for 200 amps. I don't remember the brand name.

Which solenoid did you buy? I'd like to replace mine

theoldwizard1 wrote:

pnichols wrote:

The two voltmeters on the dash read just about the same whenever the engine is running (if the solenoid has been activated and if it's contacts aren't too corroded).

Curious. What kind of numbers do you see when driving ?

Both voltmeters read very close whenever the engine is running ... except for two times in the past of our 17 year old Class C when the two meters did not agree when the engine was running.

These were the two times when I had to replace the solenoid that connects the chassis battery system to the coach battery bank. Both times the solenoid had 12 volts on it whenever the engine was running and I had heard the "clunk" as the solenoid engaged as I started the engine.

I assume that the reason that the two voltmeters read differently in those instances was because the solenoid contacts had corroded/pitted surfaces badly enough such that there was resistance in the charging current path to the coach batteries.

This caused the reading of the dash voltmeter to be lower than that of the engine system's voltmeter. This meant that the coach batteries were not getting charged because they weren't seeing high enough voltage on their terminals from the coach's 12 volt system as we were traveling.

I replaced the solenoid those two times with much more rugged non-stock heavy duty 12V solenoids that had silver plated contacts - which were not carried in parts stores. I had to order them special.

So ... what these dash meters tell me as we go down the road is:

1) Is the coach refrigerator getting 12 volts as we travel so food doesn't spoil?
and
2) Are the coach batteries getting charged via enough voltage being applied to their terminals from the engine alternator?

Just compared my cheap digital gauges to my Klein multimeter. Identical.

Going down the road, the alternator reads 14.5 and the house reads 14.5 When I turn on the lights and the heat, both drop to 14.2

pnichols wrote:

The two voltmeters on the dash read just about the same whenever the engine is running (if the solenoid has been activated and if it's contacts aren't too corroded).

Curious. What kind of numbers do you see when driving ?

heyobie wrote:
Just added 2 digital volt meters to my dash. I can now see the house battery and car battery voltage levels with the engine off. When driving I can determine if I need to charge the house and monitor the alternator. Life is good

Some of those cheap volt meters are very poor quality. They can be off by a couple of tenths of a volt.

Love it