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Battery Isolator

Hello everyone I have been having dialogue with chuck on my charging issue.  I just had my alternator rebuilt and installed it and still have a problem.  Chuck suggested I post to you all the results of my Battery, Alternator and Isolator test for your thoughts:

Here are the results:

Engine Battery voltage 12.47 not running at the battery

Alternator voltage at + on the back of the Alt 8.8 volts
Not running
Sense wire at Alt 12.48 volts
Not running

Isolator test not running (4 post)
Aux 12.83 Alt 10.07 Aux 12.8 Main 12.49

Running
Aux 16.43 Alt 17.28 Aux 16.4 Main 12.15

** Also the alternator shop said my alternator was burned up **

What do you all see here?

Thanks,
Woodie
Woodie Lee Jr
93 U300. 40'
6V92ta

Re: Battery Isolator

Reply #1 –
Running: Aux 16.43 Alt 17.28 Aux 16.4 Main 12.15

Assuming 12.15/main is the chassis battery.  First "guess" is that the isolator is bad (not passing current to that lug of the isolator/that battery.  And, since the sense wire comes off the "chassis battery side of the isolator" (doesn't matter whether at the chassis battery lug of the isolator, at the chassis battery, or other location between) it is giving false low readings to the alternator causing it to produce excessive voltage. 

You could rule out the alternator as the source of the high voltage very easily. With engine off so you can work back there, disconnect the sense wire from the alternator and isolate it so it does not contact ground.  Run a temporary wire from the Aux post (that was receiving charge from the alternator) to the sense terminal of the alternator.  If voltage drops to "reasonable" range (14.0- 14.2 at Aux and .7 higher than that at the B+, the alternator is OK and just being fed inaccurate information causing the high volt reading.

Next step is to verify that the isolator is bad/not passing current to the "main" battery. But, if readings at B+ terminal of isolator and one "output" lug (aux) are charging, but the other is not, you have your answer. Temporary work around would be to take the wire off the main lug and ADD IT to the Aux lug.  Both banks will be charged but they would also discharge together if dry camping.

Replace with proper amp rating diode-based isolator, battery switch or relay-based isolator.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Battery Isolator

Reply #2 –
Thanks Brett On my way back out to do more diagnostics.

Woodie
Woodie Lee Jr
93 U300. 40'
6V92ta

Re: Battery Isolator

Reply #3 –
So I ran a sense test wire from the back of the alternator to the Aux post on Isolator.  The voltage reading on the Aux post running  was 12.96 volts down from 16.4 volts prior.  I also tested the voltage directly from the + on the back of the alternator reading was 12.04 that seems weird but I don't know much about this.  Seems the Isolator is bad????

Thanks,
Woodie
Woodie Lee Jr
93 U300. 40'
6V92ta

Re: Battery Isolator

Reply #4 –
Also, the Isolator is original Powerline 4 post PLI -190-3 22-33 so 190 AMP I think.  Do I have to replace it with a 4 post since with this application the have a jumper wire connecting the two Aux posts.  Suggestion on a replacement?  The replacement Powerline 4 post is $298.00

Woodie
Woodie Lee Jr
93 U300. 40'
6V92ta

Re: Battery Isolator

Reply #5 –
Quote from: leejrfla –
Also, the Isolator is original Powerline 4 post PLI -190-3 22-33 so 190 AMP I think.  Do I have to replace it with a 4 post since with this application the have a jumper wire connecting the two Aux posts.  Suggestion on a replacement?
Some members have the opinion that the four post isolator was fitted by Foretravel for a reason, and so any replacement should also have four posts.  Other members believe it is not necessary to have four posts, and that a three post isolator (of suitable capacity) will work fine.

Opinions - everybody has one.

Read the following thread for a in-depth discussion of this subject, and a couple recommendations for a possible replacement isolator.

Bad Isolator?

If you don't wish to slog through all the rhetoric, here are the units (3-post and 4-post) recommended by upstanding Forum member prfleming:

Sure Power 24023aIB Battery Isolator

Sure Power 2403 Battery Isolator
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Battery Isolator

Reply #6 –
OK, please describe the FOUR different "functions" of a battery isolator. Three are easy to identify. If the fourth is ignition hot, there are a number of alternative sources right there in the engine room.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Battery Isolator

Reply #7 –
Quote from: wolfe10 –
OK, please describe the FOUR different "functions" of a battery isolator. Three are easy to identify. If the fourth is ignition hot, there are a number of alternative sources right there in the engine room.
Brett,

I've tried to explain this a couple of times before:

Bad Isolator?

FT design has used a four post isolator to provide:
    • a one diode protected (check valve analogy) current flow to the engine start battery bank
    • a two parallel diode protected (check valve analogy) current flow to the house battery bank
    [/list]

    A four post isolator, with the second and third battery bank diodes (Aux 1 and 2) wired in parallel (as in the FT design), gives a higher current capacity to both battery banks at an insignificant cost differential and a higher reliability factor than a three post isolator, with the same diodes and frame rating could provide, better matching the routine expected uses of the coach, the expected extremes being:
     
      • Deeply discharged engine start batteries: "Power post to power post" use of the coach, where the main (engine start battery) battery bank may require a heavy charge to replenish an engine cold start evolution (and perhaps extended power post time with no engine start battery charging current having been supplied).
      • Deeply discharged house battery bank: Dry camping use of the coach, where the house batteries may have been deeply discharged and then no makeup charge was given to the house battery bank (from the Generator) before driving the coach down the road, leaving the heavy house battery bank recharging duties to the alternator.
      [/list]

      A three post, two diode isolator rated at 190 amps will simultaneously pass 1/2 of the alternator output current through each diode and not exceed the current rating of the diodes and the heat dissipation capability of the frame (cooling fins).

      A four post, three diode isolator rated at 190 amps will pass MORE than half of the rated current through either the main diode OR through the two parallel paths of the TWO AUX diodes without exceeding diode and frame (heat dissipation) ratings.  That is why a 4 post isolator is physically larger in size (because the heat dissipation fin area needs to be larger -- not because the diode size(s) require more room).

      For those contemplating changing from a four post (1 alternator, three battery/three diode) isolator to a three post (1 alternator, two battery/two diode) isolator, you are potentially making a significant degradation in design, without any significant (just a few $'s) cost savings.

      HTH,
      Neal
      The selected media item is not currently available.
      Neal (& Brenda) Pillsbury
      '02 U320 SPEC, 4200, DGFE, Build #5984
      '04 Gold Wing
      '07 Featherlite 24'
      '14 Jeep Grand Cherokee Summit
      MC #14494
      Exeter, NH & LaBelle FL
      Quality makes the Heart Soar long after Price is Forgotten

      Re: Battery Isolator

      Reply #8 –
      Neal, is there a year Foretravel changed to a three post diode? My '99 looks original and has only three posts.
      1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
      prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
      2014 Grand Cherokee Overland
      Dream as if you will live forever. Live as if you will die today.  James Dean

      Re: Battery Isolator

      Reply #9 –
      Same as mine

      So a four post isolator would allow faster house battery charging than 1/2 of my 160 alternator?
      "Riding and rejoicing"
      Bob
      1997 U320 40' Mid entry, build 5132,  wtbi ce27, 4th owner
      2007 Solara convertible
      2 prodeco tech outlaw ss electric bikes

      1095 watts solar
      08 Ls 460 and a sc430
      2000 Ford F-250 superduty 4x4

      Re: Battery Isolator

      Reply #10 –
      My 2000 has a three post PowerLine isolator.
       
      Trent
      Trent and Jean Eyler
      2000  U295  4003  WTFE  ISC  350
      Build#5603 MC#17385

      Re: Battery Isolator

      Reply #11 –
      Quote from: craneman –
      Neal, is there a year Foretravel changed to a three post diode? My '99 looks original and has only three posts.
      I've never tried to decipher why some FT's have three vs. others that have four post isolators.  I don't know if it was deliberate or just what was available at the time any given coach went down the production line or through service.  Our 1998 U270 started out with a 3 post and when we had a warranty replacement, within the first year, they replaced it with a 4 post.  It also failed and I went back to a 3 post isolator.  We had numerous charging system problems in the first few years, until I found and resolved our alternator remote sensing line design problems (well documented in FoFums History).
      Quote from: Caflashbob –
      So a four post isolator would allow faster house battery charging than 1/2 of my 160 alternator?
      First, your isolator must be rated at or higher than the rating of your alternator, to reduce the potential for shortening the life of your isolator. Then, a four post isolator will allow more charging current to either one of your deeply discharged battery sets than an equally rated three post isolator, without damaging the isolator or shortening it's lifespan.
      Quote from: TulsaTrent –
      My 2000 has a three post PowerLine isolator.
      Our 1998 U270 and our 2002 U320 both came with 3 post PowerLine Isolators.
      HTH,
      Neal
      The selected media item is not currently available.
      Neal (& Brenda) Pillsbury
      '02 U320 SPEC, 4200, DGFE, Build #5984
      '04 Gold Wing
      '07 Featherlite 24'
      '14 Jeep Grand Cherokee Summit
      MC #14494
      Exeter, NH & LaBelle FL
      Quality makes the Heart Soar long after Price is Forgotten

      Re: Battery Isolator

      Reply #12 –
      Neal, if my isolator fails and I go to a four post, do I just jump the two posts to the house batteries or do I have to run another wire?
      1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
      prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
      2014 Grand Cherokee Overland
      Dream as if you will live forever. Live as if you will die today.  James Dean

      Re: Battery Isolator

      Reply #13 –
      As a sort of prepper and a dry camper a lot having the max charging ability if needed could be another backup/alternative .

      I see the new small rv's in a no generator camp ground running their engines for the 300 amp output at sequoia last year.

      Ah ha moment.  Fast idling their Mercedes diesels was audible a fair distance.  Mine would be way more noticeable and not something I would do or need to do but you never know in a emergency

      Not against the rules to run the motor.  Noisy but ok. 

      "Riding and rejoicing"
      Bob
      1997 U320 40' Mid entry, build 5132,  wtbi ce27, 4th owner
      2007 Solara convertible
      2 prodeco tech outlaw ss electric bikes

      1095 watts solar
      08 Ls 460 and a sc430
      2000 Ford F-250 superduty 4x4

      Re: Battery Isolator

      Reply #14 –
      A 3 diode isolator will divide the rated current between the 3 diodes, 1/3 to the chassis battery, 2/3 to the house batteries.

      In our ex-U300 I ran 2 wires, one from each isolator diode to the house bank to double the charge current capacity.

      I run the underhood generator (300 amp house alternator) in our Roadtrek anytime day or night when camping. The 6 L gas engine is very quiet at idle.
      Peter and Tammy Fleming
      1991 U300 GV 40 - Sold, owned for 4 years
      Downsized to Roadtrek Popular 210 class B

      Re: Battery Isolator

      Reply #15 –
      I used a Sterling ProSplit R Zero Voltage Drop Battery Isolator.  This has no diodes and virtually no voltage drop between the input post and the two or three output posts.  It has a built in microprocessor that determines which batteries need charging. Microprocessor control means the ProSplit R can monitor the charging needs of the house batteries separately from the engine battery. Doing so allows the ProSplit R to permit charging of the auxiliary (house) bank at a higher rate without affecting the other batteries in the same system.  This splitter determines charging need and distributes power accordingly.  If you only have a start battery bank and one house battery bank then you only need the two output model.  As the start battery gets closer to fully charged (which happens fairly soon) much more than 1/2 of the available charging capacity is sent to the house batteries.  It is an alternative to diode based isolarors that made sense to me and it works very well.  I am on my third year now.

      Sterling ProSplit-R – Zero Voltage Drop Battery Isolator
      Roger Engdahl and Susan Green
      2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
      Hastings, MN

      Re: Battery Isolator

      Reply #16 –
      crazy thought - but instead of a $4-10K solar setup - how about a Honda 2000i invertor/generator and a 2 gallon can of gasoline? almost can't hear the thing, and put a lot of amps to your charger to recharge the battery bank.

      Maybe carrying a gas can not the most comfortable idea, but probably in my case I could add a rack to the tow hitch on the aft of the coach pretty simply and keep the gas out of the coach

      Crazy idea?  now if you boondocks a LOT and never plug in, solar is a very nice deal, but people saying  !KW and up needed seems like you would never get back your $$$ even with a 30% tax credit
      Tim Fiedler    2025 LTV Unity MBL on Order
      2000 Chevy Tracker 2 Door Convertible 4WD Now lifted 4.5"
      1985 Citroen 2CV6 Charleston
      Murphy Rebel on wheels with 175HP Titan
      Cessna P337
      1980 48' Westport MY (!/4 Share)

      Re: Battery Isolator

      Reply #17 –
      OOOPS!
      Sorry to hijack the isolator thread.... will post elsewhere...
      Tim Fiedler    2025 LTV Unity MBL on Order
      2000 Chevy Tracker 2 Door Convertible 4WD Now lifted 4.5"
      1985 Citroen 2CV6 Charleston
      Murphy Rebel on wheels with 175HP Titan
      Cessna P337
      1980 48' Westport MY (!/4 Share)

      Re: Battery Isolator

      Reply #18 –
      Finally installed the new battery isolator.  I purchased the replacement model from Powerline which was a 4 post.  Not cheap $298.00.  Anyway things seem normal again the volt gauge on the dash reads 12v when you start then if you increase the rpm to 1k it jumps up to about 13v.  Here is something interesting though I had a new front AC installed several months ago Dometic 15k brisk air with a LCD thermostat.  About one week after it was installed an error code E4 was flashing on the screen (in the manual that indicated low voltage) had the RV tech out again and called dometic they sent out a new thermostat and electrical box.  Same thing on the screen it was not affecting the AC function so I decided to live with it.  Now that the isolator has been replaced the error code is gone. 

      Thanks for all your advice!
      Woodie
      Woodie Lee Jr
      93 U300. 40'
      6V92ta