Charging Starter/Chassis Battery

I was told, today, by Thor tech support that my 2010 Four Winds Sprinter electrical system is set up so that both shore power and generator will first charge the coach/house battery and then, after 90 seconds, switch to charging the starter/chassis battery. As this is a new vehicle for me, and Thor has discontinued the Four Winds model, I thought that I should check to confirm with another owner of this, or similar, model. Can anyone confirm from their experience?

Buy (or get free from Harbor Freight) two voltmeters.
Put one on each battery.
Watch for two minutes after connection shore power.

If it's true, you should see one battery voltage go up (as the charger connects) a volt or so, and 90 seconds later the starter battery's voltage should rise, too. Repeat test with generator.

Ground truth overrides theory any day...

--dick

I bought a new Thor 2013 Four Winds Sprinter Siesta 24R. It has never charged the coach batteries while running the engine. I was told that Mercedes did not allow them to connect to the charging system. Now after warranty I decided to install my own solenoid. I also installed an auxiliary battery tray under the hood (factory part). The ignition wire I needed to find was under the drivers seat. In searching for the ignition wire to connect to the solenoid, I found a solenoid under the seat which connected the coach batteries to the chassis battery and charging system. I tested it and found it to be faulty. I replaced it with a good quality Stinger solenoid, and I now have my coach batteries charging while driving. The old solenoid appeared to be cheap in quality.

KW-- Right On!
While on a trip last spring, my first with this rig, my chassis batteries went flat and I stopped at a favorably-reviewed RV shop in GA for diagnostics. They went through the rig with a voltmeter and told me, "Yep-- your coach batteries are not connected to your chassis charging system."
When I got home, I pulled the driver's seat and pedestal, saw the isolator solenoid and saw it wasn't switching anything and replaced it... no big deal since there are lots of isolators used in lots of apps.
Bingo-- coach batteries charge and chassis battery is happy.
Its tough sometimes to cut through folklore, supposed expert advice and other bull****-- but when we do, VICTORY!
Cheers, Peter

Ok guys, Please enlighten me on the type of solenoid you're talking about. I lost all electrical charging capabilities to the coach batteries on my last outing even when plugged into A/C power. Photos or Part #s would be outstanding!
Thanks, Mark
2008 Siesta FourWinds (Thor)

If they're using the MB-supplied isolation relay, it would be item (1) in this photo.



... If they're not using MB's, it would still look kind'a like that (two honking BIG WIRES) and a 3rd little one.

--dick

Dick, Thank you! Great photo! Also found a similar post with almost identical problem:
https://sprinter-source.com/forum/showthread.php?t=50577

So glad my rig appears to be functioning properly. The Sprinter charges the houses batteries just fine. However, I am thinking of adding a roof solar system that will charge the house batteries while boondocking. I dont see an issue with that in itself but if I upgraded to lithium house batteries in the future is that an issue for the chassis? I'm checking with Thor to ensure the RV components are compatible since someone mentioned that could be an issue with the converter etc. Should I be concerned with the Chassis?

thanks in advance.

I would recommend a new thread with a title along the lines of "changing a Thor's Aux battery to lithium??" to attract the knowledgeable people
(and the rest of us gadflies)

--dick

autostaretx said:

I would recommend a new thread with a title along the lines of "changing a Thor's Aux battery to lithium??" to attract the knowledgeable people
(and the rest of us gadflies)

--dick

Click to expand...

agreed. Thanks.