Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 11, 2025 ...

The 3 post isolator will work fine.  The original 4 post isolator had a jumper between two of the battery posts.  The theory around here is that this increased the capacity by using 2 diodes to control voltage going to the house battery bank.

Many members have replaced the 4 post isolator with a 3 post and it works fine.  200 amp capacity is more than enough.

Search "isolator" with the forum search tool for many posts on this subject.

Just to be sure I understand, since I have the 3-post isolator, the diode drops the voltage 0.7v and the sense wire from the alternator ups the input voltage to the isolator to make everything fine on the other side?

If you change to a combiner from an isolator, be sure to check voltages as it may be a little high. Our alternator on our 1993 U300 has an easy to adjust voltage screw on top of the alternator.

Pierce

Foretravel I think uses a combiner with optima red tops and gels on their new coaches as far as I know.

My guru buddy when asked the same exact question said he had no issues with using combiners with the two battery types.

His answer covers a lot of non optima batteries.

All the manufacturers use a combiner. 

 Almost no one here has a battery temp controlled alternator that I am aware of. 

As hot batteries can be overcharged by as low as 13 volts and in winter weather they need as much as 14 volts or over the voltage mismatch can obviously happen but the incorrect alternator charging voltage would seem to be more of a problem.

Maybe that's why every Unicoach ever made had optima spiral wound engine batteries and mk gels and either an isolator or now a combiner.

My understanding is the both battery brands can take low or high charging volts and non corrected by temp charging voltages or non 1/5th or 1/20 C charging rates .

My buddy has replaced every problem isolator with a non manual combiner for 10 years.  Regardless of battery types with no issues.

Like I said I asked the same question.

AGM engine and AGM house would lessen anyone's concern. 

Damaged  agm's from mischarging is normally not fixable. 

All inverters for the last twenty years have had a battery temp control available. 

Unfortunately the engine batteries temp is way different. 

Everything is a compromise.  I would rather eliminate the run the batteries flat and kill them versus a voltage mismatch which is already present from the locations of the battery banks.

I killed two sets or red tops from failed small chargers.

Versus the combiner and using a small solar panel set to make sure when I open the coach up that both batteries are at 100%

We a sort of preppers in shaky town.

Dead batteries is not an option.  If they last 10 years versus 12 or more so be it.

Bought a new geared Delco starter just to be sure I can start the engine even with low volts in the start battery bank.

The isolator consumes power.  The combiner has 100k cycle magnetic latching.  Versus 3 amps and getting hot.

I have both dash plugs filled with second digit digital meters and monitor the dash gauge and the digital ones and the audit one.

Plus the VPMS shows the engines ECU voltage.

As Wolfe mentioned I turned down the alternators nominal voltage as well as the solar output to be 13.6 at the batteries.

In that same vein I added a magnum Battery Monitoring System. 

It's connections to its control box  are directly at the battery terminals themselves..

At the same area I already had a Xantrex power pro gauge. 

Both the inverter and the Xantrex gauge and the audit have voltage drops because of the longer wire runs.

The Magnums short 5' leads should be more accurate.

My guru said I would be able to compare the magnum and the Xantrex units for accuracy.

The magnum auto resets at 100% versus manual matching on the Xantrex.

Plus integrates better with the inverter with the me-arc new panel. 

Working up the the ME-AGS-N and the power trace 100 amp  solar controller and the integrated heat and air auto gen start.

The link 2000R control panel that was available for the heart freedom 25's did adjust the alternators voltage depending on battery temps as far a I have seen





Bob, you and your guru need to research lithium ion batteries, it's a new world, nothing like agm or gel cell.
Welcome to the 21st. Pretty sure agm and gel cell will be like 8 tracks in 10 years.
Just bought a new battery for my old Zuma 125 scooter, not cheap, but is a 3 lb lithium.

Agree, ALWAYS a good idea to keep an eye on charging voltage-- from alternator, solar, converter or inverter/charger.
And, there is always the KISS way to combine-- a marine simple ON-OFF switch. Alternator B+ and chassis to one lug, house to the other.  OFF, chassis battery is charged.  ON, both banks are charged and a heck of a battery combiner. If going from CG with power to CG with power, I always left the switch OFF.  No point in burning diesel to over work the alternator to over charge the house bank.
Several very good ways to do it! IMO, the diode-based isolator is at the bottom of the list.

Yes, the marine A, B, both and off is the perfect solution.