Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 25, 2025 ...

Alternator and Isolator Replacement

August 31, 2020, 03:05:51 pm

I've researched the various posts here on this subject and haven't been able to determine a general consensus on the best battery combiner to use as a replacement for the original diode isolator on our 1995 U320 if I replace the original Leece-Neville alternator with a Delco Remy brushless alternator such as their 36si 8600126. Input is appreciated!

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Re: Alternator and Isolator Replacement

Reply #1 – August 31, 2020, 03:25:17 pm

David,

Not sure there is a single "here is the best/only way to go".

Are you interested in one that just replaces the diode-based isolator function, or one that is bi-directional?

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Re: Alternator and Isolator Replacement

Reply #2 – August 31, 2020, 03:34:24 pm

I don't anticipate the need for a bi-directional combiner or isolator system. I'm simply looking for a modern, direct replacement for the old diode isolator that with allow proper operation of the Delco Remy 36si alternator.

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Re: Alternator and Isolator Replacement

Reply #3 – August 31, 2020, 07:10:28 pm

David,
The Delco Remy 36si 8600126 is a brushless high efficiency alternator that will do well in your coach.  Use the battery sense wire connection to increase the maximum charge voltage to speed up recharge.  The smart voltage regulator in my 40si backs off voltage and current as the batteries are charged. Should be about the same in this one.

A simple zero voltage drop isolator could be a Victron ArgoFET isolator. It is about $140 at Bay Marine for a 200 amp version.

Victron Argofet Battery Isolator

There are other options as well, Justin at Bay Marine can help you through the variations.

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Re: Alternator and Isolator Replacement

Reply #4 – August 31, 2020, 07:58:18 pm

Yes, agree with Roger, the 36si is a great choice.

Note that Delco alternators need an isolator with an excite terminal to function properly. Here is my previous post with some isolator options. Also- the Delco "I" terminal is not for ignition excite, it is for an indicator lamp. Connecting ignition excite to the "I" terminal will permanently damage the alternator.

Delco isolator options
 

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Re: Alternator and Isolator Replacement

Reply #5 – August 31, 2020, 08:07:14 pm

The original alternator had adjustable voltage if I am not mistaken.  Why?  Because in warm/hot weather a std alternator puts out too high of a voltage and overcharges the batteries on long drives.

My magnum MS2812 temp corrects my charging voltages down into the low 13's in hot weather. 

If you hook up the sense wire that can be used with it you will be outputting 14.15 volts into the batteries regardless of temps.

Bmw's and such that are equipped with AGM batteries lower the voltage to not fry their batteries.

If you leave the sense wire disconnected you will overcharge the batteries less. 

I bought a new LN replacement alternator without the adjustable VR.

.1 to .2 volts higher than the previous adjustable LN's output.

May reinstall the rebuilt LN  to be able to have the batteries last longer.

The batteries will only accept so much charge rate. The alternators vr will turn it down after that.

The higher Amps might be helpful IF you are running a roof air off the motor while driving?

And have the complete system designed to pull that many amps.

A high output alternator with a complete system designed to use that many amps AND that has temp compensating voltage output like boats have and the user needing that many amps to run a/c down the road might be helpful.

All new coaches have combiners.  All.

The idea that something is less expensive(cheaper) normally gets me to look closer at what's going on.

SORRY.  Been 36 years in the rv biz.  Rv'ers are notoriously frugal. 

I would not hook up the sense wire unless it's cold out. 

See what your temp compensated inverter/charger out out voltage wise?  Anything more is burning up your batteries!

Look at your gauges from the engine versus the charger?  Boats offer temp controlled engine battery charging.

My 97's heart Freedom 25 had an optional link 2000R temp controlled alternator control 23 years ago.

Really?  14.15 volts regardless of temps is wrong.

Show me I am wrong. I will wait.

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Re: Alternator and Isolator Replacement

Reply #6 – August 31, 2020, 08:51:00 pm

Delco has sold millions of alternators used in over-the-road trucks that drive all day, every day, summer and winter - way more miles and harsher conditions than the typical RV.

I'm thinking if batteries are being destroyed by overcharging, wouldn't we have heard about it by now...Delco would have one big class-action law suit on their hands.
 

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Re: Alternator and Isolator Replacement

Reply #7 – August 31, 2020, 10:32:36 pm

Do you want 12 years life on your batteries?  Documented here many times.  Oem setup.  Why would Brett from the FMCA recommend 13.6 volts?  Why would Foretravel equip 1,000's of rv's setup with adjustable voltage alternators set purposely at lower voltage?

No temp compensation.

Every battery maker requires temp compensated charging.  Every inverter made since my 97's heart has the ability to add temp compensated charging.  23 years.

It's nice that delco has sold millions set at 14.15 volts.  At zero degree battery temp that's about correct for flooded cell or sealed VRLA batteries.  Oh AGM or gels require less.

I bought AGM batteries for our old Lexus cars and the Lexus gurus mentioned that the alternators output was NOT set for agm's. BMW abd mercedes have lower output alternators MADE for their std AGM batteries. 

Like I said repeatedly what voltage does your temp compensated charger input into your batteries?

Start your motor.  What does your alternator put out?

Or are you telling me the temp compensated charger is a bad thing?

Judging by the extremely long battery lives reported here many times the lower voltage output seems to be correct?

If I had the time I might install a switch to disconnect the alternator If I were driving with the gen on and charger on to avoid overcharging the engine batteries.

Since the uni coaches were made the batteries are in the engine compartment.  Physically hot.  Needs closer to 13 volts. Not 14,15.

Trucks might have their batteries in cooler locations and/or not mind a 3 year life?  They might think it's normal?

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Re: Alternator and Isolator Replacement

Reply #8 – August 31, 2020, 10:36:34 pm

Sorry for the distraction.  Here is a link ML-ACR Automatic Charging Relay with Manual Control - 12V DC 500A - Blue Sea...

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Re: Alternator and Isolator Replacement

Reply #9 – August 31, 2020, 10:42:54 pm

[I bought AGM batteries for our old Lexus cars and the Lexus gurus mentioned that the alternators output was NOT set for agm's. BMW and mercedes have lower output alternators MADE for their std AGM batteries.}
BMW and MB both have regenerative braking. Therefore they do not charge batteries up to normal voltage and leave capacity for this system.

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Re: Alternator and Isolator Replacement

Reply #10 – August 31, 2020, 11:39:50 pm

am I incorrect that regardless of bmw or Mercedes final voltage setups in their regenerative  models that a AGM requires a lower voltage alternator setting than a sealed lead acid flooded cell battery?

So at winter low temp an a alternator set for 14.15 volts at the battery might be ok for a sealed lead acid battery.

Warm?  No.  Agm? No. 

Larry when you find your coach or if you have a current  coach with a temp compensated charger compare the chargers voltage to the battery banks versus you start and run the engine for a bit. 

Why is the alternator higher?  No temp compensation. 

Hard to imagine a coach in operation that has a battery bank and temp that a 14.15 at the battery is correct?

Why did Foretravel set all their alternators at 13.6?  Of course every uni had optima's and gels std. they are made to handle temps better especially the Optima spiral wound engine batteries

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Re: Alternator and Isolator Replacement

Reply #11 – August 31, 2020, 11:54:23 pm

The link 2000r has a multi step charging profile applied to the alternator  like my original Heart freedom 25.  Neither one had temp compensation.  1996 production. 

I think the sterling boat system has the same profiles but adds temp compensation.

All I am saying is that Foretravel used high quality batteries and turned down the voltage versus temp compensation as the hot compartment for the engine batteries make that very difficult to do. 


What are Remote Sense Alternators | Delco Remy

Says made for different use than a rv. 

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Re: Alternator and Isolator Replacement

Reply #12 – September 01, 2020, 12:19:50 am

My Delco Remy 40si 240 amp alternator with a voltage sense wire will put out up to 14.5 volts into your start batteries when you start, if you hurry with your volt meter and check the voltage at the battery by the time you get there the voltage regulator has already trimmed that to 13.8 or less.  A little while later maybe 13.4v.

My old LN alt was cranked up to push 14.5 - 14.8 volts through the old diode based isolator in hopes of seeing 13.8 at the start batteries. It may have been OK 20-30 years ago. Times change, there are better, smarter solutions out there now.

I have both in the barn if anyone wants them. Soon to the scrap yard.

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Re: Alternator and Isolator Replacement

Reply #13 – September 01, 2020, 01:12:25 pm

I would like the ability to run my front AC off the alternator/inverter. It currently can off the lithium batteries and inverter with solar charging, but my alternator doesn't charge my house batteries. I would like to change that.
I would like to take a more marine way to do this. Since I have oddessy agm start batteries and lithium house the voltages are not the same so therefore boost is not connected in my coach. Nor do I want it at this time. But want a good way to temp compensate charging of both the start bank and the house bank when driving.
I was thinking of going with external alternator 300 amp rating or more, and something like a Balmar MC614 controller which can charge both agm and lithium batteries. Not sure if I would need 2 though, one for each bank. I have used it before in my sailboats but both boats and banks had agm battery systems. Having 2 different systems makes for a more complicated setup.
Any thoughts ?

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Re: Alternator and Isolator Replacement

Reply #14 – September 01, 2020, 01:29:37 pm

Smarter people can explain better than  I can, but there is a battery to battery charger. Have the alternator feed one bank and the charger feed the other.

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Reply #15 – September 01, 2020, 01:47:02 pm

Yes, my recommendation as well. Beef up the alternator and 12 volt AGM chassis side to handle 350-400 amps. Then parallel a couple of battery to battery chargers with a lithium profile to supply the lithium house side. Sterling makes a 120 amp model, 2 would give you 240 amps to work with. No isolator needed with this setup. Bay Marine can help.

In addition to the Delco 40SI and 55SI series, Delstar has some excellent 300+ amp brushless alternators with a J180 mount and remote sense capability.

DELSTAR - Heavy Duty Brushless Alternators
 

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Re: Alternator and Isolator Replacement

Reply #16 – September 01, 2020, 05:06:59 pm

I have a Sterling Battery to Battery charger.  Started with a 120 amp version but there was something wrong in the core software that as far as I know has not been fixed yet so I went with a 60 amp model. I could do two in parallel but so far 60 amps is plenty especially when you add in solar.  Battle Born estimates lifetime cycles (one cycle = 100% to 0% to 100% SOC) will go from 3500 to as many as 5,000 if you keep max charge rates no more thn 20% of the total capacity of your bank.  I have 600 amp hrs so 60 amp charge is only 10%.  It is a good choice if you have 400 amp hr capacity.

The Sterling B2B charger is a smart multi-step battery friendly charger.  You can set if for any of 9 different battery types/profiles.

With a B2B charger there is no need for an isolator. When it is off the battery sets are not connected.

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Re: Alternator and Isolator Replacement

Reply #17 – September 01, 2020, 07:15:04 pm

A rough amperage budget (based on measurements when I did my alternator upgrade a few years ago to run 1 AC on inverter) and 2 brushless alternator recommendations that should fit your existing mounts.

Chassis load (engine/dash overhead, headlights on, heater fan on)
80 amps + 30 amps charge reserve
110 amps

House load (A/C on, accounting for 85% inverter efficiency)
170 amps + 60 amps charge reserve
230 amps

Total
340 amps + 20% margin

Recommend 400 amp alternator

Delco 55SI 61003345 430 amp

http://www.delcoremy.com/getmedia/91a69d28-4bda-4669-a55f-569fdee22c72/Delco-55SI-Sheet-5-18.pdf

Delstar 100-18101 435 amp

https://delstar-hd.com/pdf/180/D100-18101.pdf
 

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