Should Alternator Charge House Batteries?

[RustyTools]

2006 HR Endeavor.

The other day I happened to notice that the house batteries were't charging while underway, altho the alternator was working. We live/travel in the deep south, so have always had the gen-set running for the house AC units, frig, etc, when moving and never paid attention. I do have a Xantrex Echo-Charge and it keeps everything topped-off (when camped or on gen-set).

When I fired everything up in the cool morning for a short run, I saw that the chassis batteries were getting their 14.2v charge, but the house batteries were slowing a slow discharge from frig.

Is this normal, or did I just find something else that I have to fix?

[Skip426]

Something's amiss, all the batteries ; coach and chassis: should charge from the alternator.
Probably a defective charge solenoid , that is powered up to connect the battery banks while driving , and your problem could be as simple as a blown fuse in the solenoid activation circuit from the coaches ignition switch.

[xydial]

The house batteries are charged from the alternator once the chassis batteries reach a full charge.

The probable problem is the Trombetta solenoid located in the battery bay, usually in the center on the back wall. This is also the "battery boost" solenoid. The contacts corrode over time. Mine failed two years ago.

You can verify the solenoid by pinning up the battery boost switch and measuring the voltage on both sides of the solenoid. If the voltages are different it is the Trombetta solenoid that has failed. You may want to try this several times since it can be intermittent.

Ordered a replacement for mine a couple of years ago from Amazon. If replacing try to get the solenoid with the silver contacts. Less chance of it failing again.

[MTK46]

I found this weekend that mine was doing the same thing. I figured it was a solenoid but wasn't sure where it was located at. I'll have to recheck the battery bay again when I get home from work. Thanks xydial

[Dupdyke]

Originally Posted by xydial

The house batteries are charged from the alternator once the chassis batteries reach a full charge.

The probable problem is the Trombetta solenoid located in the battery bay, usually in the center on the back wall. This is also the "battery boost" solenoid. The contacts corrode over time. Mine failed two years ago.

You can verify the solenoid by pinning up the battery boost switch and measuring the voltage on both sides of the solenoid. If the voltages are different it is the Trombetta solenoid that has failed. You may want to try this several times since it can be intermittent.

Ordered a replacement for mine a couple of years ago from Amazon. If replacing try to get the solenoid with the silver contacts. Less chance of it failing again.

Is it possible to post a picture I thought I had big boy in my 03 dynasty but that is not it.

[jacwjames]

Some models of Monaco come with a BIRD (Bidirectionsl Isolator Relay Delay) which will allow both the house and chassis batteries to charge from the alternator.

Here is some info on this

http://intellitec.com/assets/pdf/145...-00362-000.pdf

[distaff]

I'm seeing some info here that doesn't seem right. The Endeavor is not top of the line, but I expect it has similar systems for charging.

• Alternator charging the coach batteries is not dependent on the level of charge on the chassis batteries.
• The only way to tell if the coach batteries is being charged is if you can see the voltage on them - if you look at the inverter it won't show charging as it is not involved in charging from the alternator.
• There is generally a system that detects that a) there is a differential in voltages between the two 12V systems (meaning one of them is getting charged) and b) a way for that system to close a relay between the two systems so the charging voltage from one reaches the other.
• The system that detects charging will also usually have enough sophistication to stop charging if the engine is under heavy load, or during the first few minutes the engine is running.
• The system does this on many higher end Monaco coaches is the BIRD/BigBoy system by Intellitec.

There are many things that can go wrong with the BIRD/BigBoy system, but the main thing to look for is - when you stop are your coach batteries depleted or fairly well charged?

You can also test by starting the engine, waiting a couple of minutes and putting multimeter (DC voltage meter setting) on both sets of batteries. They should be at the same voltage, somewhere around 14 V.

There are other clues, if you have a BigBoy it makes a pretty loud "clunk", and then it has a high pitched whine.

[passerby]

My Monaco has a battery isolator that charges the house batteries. Did you check the house batteries with a voltmeter while the engine is running to see voltage?

[xydial]

Top of the line coaches (Dynasty, Execs, etc) seem to use a Big Boy/BIRD system. Mid range and lower (Diplomat/Knight/Cayman) use the Trombetta.

Just a matter of money!

[twinboat]

Originally Posted by distaff

[*]Alternator charging the coach batteries is not dependent on the level of charge on the chassis batteries.
.

That's not correct, because the BIRD is voltage controlled.

When you start your engine, your batteries may be run down a bit, intake heaters running and alternator turning slow, creating low output.

Since the BIRD won't close the isolation solenoid until it sees 13.4 volts from the chassis battery, there will be a time that the alternator will only be charging it.

Once the chassis battery reachs 13.4 volts, which is about 80% charged, it will tie the house batteries into the system.

If the house batteries are low, or handling a heavy load, and drag the chassis batteries down below 13.4 volts ( volts go from hi to low ), the BIRD will open the isolation relay to protect the chassis system from low voltage.

At that point the BIRDs delay funtion will hold it open for a set time, to allow the chassis battery to recover and charge further.

This cycle will repete until the charging system can maintain 13.4 volts on both battery banks.

[RustyTools]

Well, I guess this gives me plenty to get started with. Thanks all!

[distaff]

Originally Posted by twinboat

That's not correct, because the BIRD is voltage controlled.

When you start your engine, your batteries may be run down a bit, intake heaters running and alternator turning slow, creating low output.

Since the BIRD won't close the isolation solenoid until it sees 13.4 volts from the chassis battery, there will be a time that the alternator will only be charging it.

Once the chassis battery reachs 13.4 volts, which is about 80% charged, it will tie the house batteries into the system.

If the house batteries are low, or handling a heavy load, and drag the chassis batteries down below 13.4 volts ( volts go from hi to low ), the BIRD will open the isolation relay to protect the chassis system from low voltage.

At that point the BIRDs delay funtion will hold it open for a set time, to allow the chassis battery to recover and charge further.

This cycle will repete until the charging system can maintain 13.4 volts on both battery banks.

Lots of almost true info out there about these systems. Attached is the Service Manual. Not to belabour a point not related to the OP's problem, but it is the CHARGING voltage the system detects, not the battery voltage. If the alternator or the inverter is putting out 13.3 volts or more, the BIRD unit detects the CHARGING voltage. If you put a multimeter on the battery at this point it will show the voltage being put out by the source (inverter or alternator), if you remove the charging source it will then show the voltage on the battery.

It is NOT related to the amount of charge on the battery. It monitors the OUTPUT voltage from the charging source to make sure it is not sending charging voltage to the other set of batteries when the charging source is under load.

[RobRoy]

Originally Posted by twinboat

That's not correct, because the BIRD is voltage controlled.

When you start your engine, your batteries may be run down a bit, intake heaters running and alternator turning slow, creating low output.

Since the BIRD won't close the isolation solenoid until it sees 13.4 volts from the chassis battery, there will be a time that the alternator will only be charging it.

Once the chassis battery reachs 13.4 volts, which is about 80% charged, it will tie the house batteries into the system.

If the house batteries are low, or handling a heavy load, and drag the chassis batteries down below 13.4 volts ( volts go from hi to low ), the BIRD will open the isolation relay to protect the chassis system from low voltage.

At that point the BIRDs delay funtion will hold it open for a set time, to allow the chassis battery to recover and charge further.

This cycle will repete until the charging system can maintain 13.4 volts on both battery banks.

Correct and that is the way my coach's charging system works also. It takes the continuous extreme loads off the alternator in the event of all the batteries have been run down which doing so makes for longer service life of an expensive alternator.

ps When starting diesel pickup truck the PCM does not command the alternator to start to charge until the glow plugs have shut down ( sometimes a min or more ) for the very same reason.

I have not checked my coach's alternator function on startup to know for sure but wouldn't be surprised that it did and that many coaches do the same, cutting out alternator output at initial start up until everything settles down.

[Jeff753]

As some have mentioned you may have two items. One is a battery isolator that hooks to the alternator (middle post) and feeds the two battery banks independent of each banks voltage. This is just a diode block that keeps one bank from depleting the other (one way current flow). If you have one of these there are easy test methods
Here's mine
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
This is likely your problem.
The other system you may or may not have is a battery maintainer. This system senses a charge voltage from one bank and if it sees charge voltage it opens the other bank and allows it to charge. Again to keep one bank from depleting the other. Do you have a rear run bay you could post a picture of.