Batteries charging with motor running

[str8shooter_mn]

We have a 2015 Thor Tuscany. While running down the road with fridge on and inverter on, batteries do not charge. They charge just fine while on shore power or generator. Am I missing something? Help!

[dougrainer]

With Engine OFF, the Relay will have 12 volts on EACH large post. One side will have chassis battery voltage and the other will have Coach battery voltage. Since you have NO VOLTAGE on one side that means the cable that is dead is NOT connected to the coach battery system. The Relay system IS energized by the chassis battery and chassis battery Ignition side wiring. What you have done is just replaced a part and NOT checked out WHY. This can get expensive. Doug

[CA_Traveler]

The continuous duty SOLENOID has large wires to the positive post on both battery banks, hence each solenoid post will reflect the battery voltage w/o even starting the engine. Google ISO relay and you will see a small auto type that DOES NOT make a big clunk.

Post pictures to clarify what you are referring to.

[str8shooter_mn]

Have owners manual. Finally received new ISO relay. Replaced. Hear 'thunk' a few seconds after starting motor. One terminal reads 13.9 volts, other side zero volts to chassis ground. Voltage at batteries holding at 12.2 volts with inverter on and fridge on. I may be missing something here. Any help appreciated

[dougrainer]

Do you have the Owners manual? Page 100 if you do. Below from your owners manual.

https://www.rvroundtable.com/wp-content/uploads/Thor-Motor-Coach/Tuscany/2015.TuscanyOwnersManual(10...

The Battery Control Center (BCC) houses all the fuses for your auxiliary coach circuits.
The BCC is located in front of the drivers front tire inside the compartment of the
fenderskirt. To remove the BCC cover locate the tabs on each side of the box, pull
away slightly and remove. Inside you will find a series of fuses for the extra circuits not
available on the automotive or interior house 12 volt fuse boards. These style fuses are
available at any automotive or RV store. If it should become necessary to replace any
of these fuses, be sure to replace them with the same style and amperage rating. The
circuit wiring is sized for that particular amperage. The BCC will sense when to charge
either set of batteries. If the voltage falls below the minimum requirements, the BCC
will switch the charge to that set of batteries. Terminals inside the BCC are available for
testing its functionality.

[IAMICHABOD]

When I had this happen to me on my RV,the alternator was not charging the house batteries,I found that the CONTINUOUS DUTY SOLENOID had failed.

When you start your RV the voltage should go up to 14.4 or so then within a few seconds the solenoid will click and you will get power to the house batteries.If you can find it it is easy to check with a simple volt meter. The "battery isolator relay" (which is sometimes also used as an "emergency start relay) is a VERY common failure point.

Often, you don't even notice that it is no longer passing any charging current from your chassis battery to the house batteries while driving, because your house battery charger still recharges the house batteries after you arrive at your destination.

If it's still working properly, you will hear it "thunk" as it activates when the ignition switch is turned on, and you will measure almost exactly the same DC voltage on both of its large connection studs while the motorhome engine is running.

No "thunk" = relay coil is burned out, or isn't receiving any voltage

"Thunks", but big difference in voltages at its studs = Electrical contacts inside it are burned or corroded

[CA_Traveler]

It's a large solenoid with large cables from each battery bank. BIRD is one type of electronic controler for the solenoid.

[theoldwizard1]

Get a DC-DC charger.

[KD4UPL]

That sounds like the one. With the engine running you should have the same voltage to ground on each side. If it's different it's not connecting the batteries.

[str8shooter_mn]

Ok, only relay I can find is an iso relay according to the schematic both coach and chassis 12v goes to this relay. Is this what you call a charge relay?

[str8shooter_mn]

Is it the same as a (BIRD) bi-directional relay?

[str8shooter_mn]

Not sure what the relay looks like. Will look further when this storm passes.

[dougrainer]

Your Charge relay that combines the Coach and Chassis batteries is not working. Could be as simple as a blown fuse or a BAD relay. Doug