Battery Isolator

Thanks for the instructions, enblethen. I have a Dodge with a 65 amp alternator and set the isolator as shown for group 1 alternators. So, no wiring mistakes.
dcg9381 - thanks for the input. I am measuring a no-load voltage from the isolator, not a charge controller. Therefore, the voltage to the battery would always be the same and never regulate down. That is of great concern to me since I have two new 6 volt AGM's and I don't want them to be on such a high voltage charge when ever the engine is running when the batteries started out at 100% SOC.
Should have said before I didn't have a house battery in place when I measured the voltage coming out of the isolator. Maybe I am just chasing shadows.
wolfe10 - Not sure if this is a DIODE-BASED or not. Do know there is no VOLTAGE SENSE WIRE. There are three terminals on the isolator, one connects to the alternator, one output to the chassis and the other to the house battery.
Soon as the rain stops this morning, I'll head back outside with the volt meter and do some more checking with with an old wet cell battery in place.

With a DIODE-BASED battery isolator, it is common to run the VOLTAGE SENSE WIRE to the chassis battery terminal of the isolator.

What is voltage at the chassis battery lug of the isolator with the engine running/shore power and generator OFF?

Makin' Do wrote:

I'm not so sure I like this solution. Is there a better way of getting the voltage down?

I'm an EE. If you're measuring the no-load voltage coming out of a charge controller when not hooked to a battery, I wouldn't be afraid of 15.5V. It simply doesn't mean much as no load.

What matters is how many amps are being pushed when it is connected and how high it'll allow the battery to charge.

Generally, connected, I wouldn't want to see a charge voltage much higher than 14.7v.

You may be chasing shadows here... It much more important for your charge source to be able to regulate-down when the battery gets full than it is to hit or miss any peak no-load voltage.

I would read through the instructions. I get to page three which shows a different isolator for Fords.
Instructions
I would also look at the polarity attachment to the coach battery.

No, not connected to shore power. I was thinking the issue was the battery isolator, that's why I replaced it with a new one I had on hand. The output from the isolator to the engine battery is 14.2 volts as read on the dash volt meter and 13.9 across the battery itself. Voltage output from the isolator is 15.3 - 15.5 to the house battery. Shouldn't the voltage out both sides of the isolator be the same? If so then I have two bad isolators. I don't understand why the alternator would be to blame.

I believe you were told before, to fix the problem, not mask it.
I ain't no expert on it, but I know if I had an alternator/regulator that was putting out 15+ volts, I'd deep six it.

I agree with Buds statement. I have a small DIGITAL DC VOLTMETER panel meter I installed on my truck dash coming from the truck start battery terminals taht always read my truck battery voltage. I have noticed it reads DC VOLTAGEs that coincides with the standard DC VOLTAGEs of the typical RV converter/charger units... I usually see 14.2-14.5 VDC when I first start the truck engine and then this drops back to around 13.4-6 VDC and eventually down to 13.2VDC... When the truck motor is running I always see a 13V range on the dash meter. I see the dash meter change from 13.2-13.5-6 as I am using things I suppose... I occasionally see it jump to 14.4-5 VDC while driving down the road but usually goes right back to the 13V level.

When I turn off the ignition key then the DC Voltage drops down to 12.6-7 VDC... If I turn on my truck lights with the motor not running I usually see a 12.3-4 VDC reading...

I have never seen real high DC voltages in the 15VDC range coming from my alternator on my 2010 Truck DC Meter setup... Perhaps I will look at it more closely now that the question has been brought up...

The main reason I installed my dash mounted DC VOLTMETER was to watch the truck start battery readings when I am using my Ham radio two way radios without the motor running. When it drops back to around 12.0VDC I will either run my truck motor or start up my 2KW generator with a battery charger plugged into it...

Maybe the different truck manufacturers do it differently...

Roy Ken

Just reviewed most of your original posting, whew.

Here is one question thar wasn't asked before, are you connected to "shore" 120v power?

If so your converter is the issue!

Try unpluging and recheck your voltages at the truck battery and at the house batteries.

Good luck
Bob

Isolator needs to be connected correctly. Post a pic.

The isolator will not increase the voltage.
Did you check the incoming voltage to the isolator from the alternator?