Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 06, 2025 ...

Not sure but I think something is wrong.

1.  Remove your isolator.  Connect the 24Si alternator you have directly to the chassis (start) battery bank, and remove the two small wires.  With this "One Wire" hookup it should work properly.  You would then need a way to direct charging current from the chassis batteries to the coach batteries.  This could be accomplished with either a manual combiner switch (or the BOOST switch), or with an automatic combiner relay (VSR).

If you try Brett's test (above) I would advise also removing the small wires from the "I" and "R" terminals.  No matter where those wires terminate, they shouldn't be connected to those terminals on the alternator.

...wire from B+ of alternator connected to chassis battery lug of isolator
13.6 volts at idle
13.5 volts at 1100 rpm with lights and dash fan on high

One of those terminals should be for remote sense.

13.6 is somewhat low, but not conclusive, so don't condemn the alternator yet.

Where are you taking the voltage reading?  Ideally you should check the reading at the alternator B+ post, then at the isolator chassis battery lug, and finally at the chassis battery itself.  This is to eliminate any chance of a bad cable or connections.

Try leaving everything connected as you have it.  Turn the engine off.  Turn ON headlights and switch to high beams.  You could also turn on fog lights and docking lights for more load.  Wait 5-10 minutes, then turn all the lights OFF.  Check (record) the voltage at the three points listed above.

ONext (with all the lights still OFF), start the engine, and set to about 1100 rpm.  Check (record) the voltage at the three points.

Finally, with the engine still running at 1100 rpm, turn all the lights (including high beams) back on.  Check (record) voltage at the three points.

Let us know the results.

What are you using as a volt meter?

 I was given a Milwaukee volt, continuity,  and ohm meter that was totally automatic. It would automatically change to whatever I was looking for. I then learned it was about  1/2  or more volts off when checking DC and way more on AC. When I learned i couldn't trust it, ithrew it in the trash.

Dennis,

We have already determined that the OP's alternator does not have a sense terminal.  See earlier posts in this thread.

Ok, here it is...
I also disconnected my amp-l-start just in case it was messing with my readings...

Lights off after draw down, Engine off
Alt  12.5
Isolator chassis lug  12.5
Batteries  12.5

Engine on 1100 rpm, lights off
Alt 13.8
Iso chas lug13.8
Batt 13.7

Engine on 1100 rpm lights on

Alt 13.5
Iso 13.4
Batt 13.4

If the rig has a diode block for house battery isolation it needs an alternator with remote sense. Sorry for being late to the thread. Just trying to help. Is this a new alternator install with the plan of eliminating the diode block?

13.8 volts is a common set point for trucks running long hours using standard lead acid batteries. 13.8, 2.3 volts per cell is just below the Gassing voltage for a standard battery and is also desirable for the low maintenance versions. AGM and Lithium need higher. This indicates alternator is functioning. The voltage drop is due to the alternator getting loaded down. Does it increase if you increase engine RPM further? Often takes 1,200 rpm or more to reach full output. Pulley can be changed to increase low speed RPM of alternator. Would be good to know actual current draw on alternator. Regulator can be changed to increase voltage.

The thing is, I often get voltage in the low 12's intermittently when I'm driving at highway speed so not sure that's it...

Ok, here it is...

Lights off after draw down, Engine off
Alt  12.5
Isolator chassis lug  12.5
Batteries  12.5

Engine on 1100 rpm, lights off
Alt 13.8
Iso chas lug13.8
Batt 13.7

Does this only happen when the headlights are on?  If so, do you also show lower oil pressure?  Do you also show higher coolant temperatures?  Do you have the electroluminescent dash?

There are a couple of issues.  First, especially with coaches with an EL dash that have a headlight conversion, is high coolant/low oil readings when the headlights are on.  It's been mentioned sporadically over the last 12-15 years.  James Stallings at Xtreme is working on a fix (wiring harness.)

Second is what Foretravel sometimes used for connections on the chassis battery wiring (low voltage readings).  See this post

Chassis Battery Compartment Refresh

Either issue could cause intermittent voltage fluctuations.

We have not ascertained what type chassis battery you have.  I am going to assume that it is AGM.

So, looking at your test results, first thing we can say is you don't seem to have any cable or connection problems, because volt readings at all three points remain consistent in all 3 tests.

Next, with your chassis battery bank pulled down to 12.5 volts, you started your engine.  With engine running at 1100 rpm, and no big loads on the battery, you read 13.8 at the alternator and 13.7 at the battery.

In my opinion, your alternator is not producing sufficient voltage.  Yes, it does seem to be "functioning", but it is NOT acting in the manner required to fully charge AGM batteries.  The internal voltage regulator may have been damaged by running the alternator for several years with those two small mystery wires improperly connected to the "I" and "R" terminals.  You can search online for "AGM Battery Charging Voltage Chart" and find this info for yourself.  The excerpt below is from Google AI search:

Charging Stages:
AGM batteries go through three charging stages: bulk, absorption, and float.
Bulk Stage: The charger provides maximum current to bring the battery to about 80% capacity, with the voltage rising to around 14.7V.
Absorption Stage: The charger maintains a constant voltage (around 14.4V to 14.7V) to reach full charge, reducing the current.
Float Stage: Once fully charged, the charger drops the voltage to a lower level (13.6-13.8V) to prevent overcharging and maintain the battery's charge.

I went back and found the Forum thread where you first had this alternator installed.  That is when your battery charging troubles started:

Alternator output

8600310 24SI New Alternator | Product Details | Delco Remy

You received the information at that time suggesting that you had a problem.  But, as you say, because you also have solar panels and a generator to help keep your chassis batteries charged, it never became a BIG problem.

Again, IN MY OPINION, your best move would be to replace your 24Si with a proper DUVAC alternator.  This will allow you to retain your battery isolator (which appears fairly new) and it should solve your charging problems.  You can search online for J180 Hinge mount DUVAC alternators.  Try searching for genuine Leece Neville 2824LC (beware of cheap clones).  If you go this route, there is plenty of installation info available on this Forum.

If you want to stick with a Delco alternator, i would recommend your upgrade to a 200A 28Si (with "S" terminal).  This will also require replacing your battery isolator.  See the isolator links in my Reply #1 in this thread.