alternator bad or isolator

Topic: alternator bad or isolator (Read 2006 times) previous topic - next topic

Re: alternator bad or isolator

Reply #25 – August 24, 2013, 03:30:53 pm

Quote from: wolfe10 – August 24, 2013, 01:38:59 pm

If turning on the lights drops voltage from 14 to 12, the alternator is the second suspect-- behind checking that connections between alternator and isolator are good, clean and tight.

Brett

Dave-- after John's further post, I agree that the alternator could be just fine-- makes a huge difference that the reading was on the dash gauge (I ASSUMED all the readings were at the isolator) when a small load (lights) dropped indicated voltage from 14 to 12. Had that been the reading at the alternator B+ or alternator (center) terminal of the isolator, the alternator would remain on the "short list" of suspects.

Right now, we really need to know what alternator he has and whether it has an internal regulator or an external one. And again, need to check electrical connections at batteries, alternator and isolator.

Re: alternator bad or isolator

Reply #26 – August 24, 2013, 03:57:56 pm

Hey Dave, is there a way to put the engine in fast idol or do I just do this with the foot pedal?

Re: alternator bad or isolator

Reply #27 – August 24, 2013, 05:12:57 pm

ok, pressed cruise on then resume and engine went to 9500 rpm and then turned on the lights.
I took this reading at the isolator with a digital meter.

9500 rpm with lights on
Chassis 13.7 alternator 14.8 House 13.9

9500 rpm with lights off
Chassis 13.3 alternator 15.8 House 14.7

Info from alternator
Transpo-CN
L79000LH-2921-12V

Thanks,
John

Re: alternator bad or isolator

Reply #28 – August 24, 2013, 10:16:19 pm

Quote from: John I. Smith – August 24, 2013, 02:55:31 pm

This morning before getting on the road we measured voltage at the isolator. Then once we got underway the voltage readings where coming from the meters inside. Now as we are traveling on the road the voltage is fluctuating from 13 to 14 volts......... We had the alternator off the day this started and they told me the brushes were changed and the alternator was new. They also said altrernator tested good on the bench........ so the connections on the alt. Should be good, I,ll need to check at the isolator. I have just had surgery so I am limited to what I can do right.

John

Had loose wires on the gauge back side

Re: alternator bad or isolator

Reply #29 – August 25, 2013, 02:16:06 am

John,

I think you mean "950 RPM", not 9500.

Re: alternator bad or isolator

Reply #30 – August 25, 2013, 05:12:34 am

Guess my trouble shooting did not work for John's problem.

Re: alternator bad or isolator

Reply #31 – August 25, 2013, 11:12:03 am

John ---- Hopefully you're home safely by now, and hope that your troubleshooting goes well. The more info you can gather the better diagnosis you can make. Electrical issues are certainly a large problem are are usually unique to that particular issue. Information that is accurate and complete is very important. An accurate schematic is also important and I had trouble in that area. The one I ended up with is mostly readable, but has some bad spots on it that are a little fuzzy and questionable to read. Your rig is alot newer and may not be a problem. Have a great day ---- Fritz

Re: alternator bad or isolator

Reply #32 – August 25, 2013, 01:27:53 pm

John,

Hope you are doing OK. We'd like to help, but need feedback.
I've been watching this thread, wondering if you are experiencing a problem that has affected many of us. There is a problem with the way that Foretravel terminated the Alternator Remote Sense Wire that affects some (not all) coaches all the way from model year 1993 to 2002.
The problem usually presents as a "fluctuating" or "spiking" battery voltage under different battery loading conditions (Lights on/off, AC clutch energized/deenergized). I had FT chase this problem on our coach, for years, and it cost us a lot of money in new batteries, new alternators, ruined isolators and fried lamping/DC switches.

A couple years after our 3 year/ 36,000 mi. warranty expired and in a frustrated defense of my pocketbook, I gave up on "experts" resolving my issues and went after it myself. I determined that the Alternator remote sense wire was landed on the output of the A/C clutch circuit 15Amp breaker (located on the the front bulkhead of the engine compartment). Each time large lighting loads changed or the A/C clutch energized, the damaged (oxidized and arced) contacts of the small 15 Amp circuit breaker would drop randomly varying amounts of voltage, the Alternator would "sense" the reduced voltage, would increase its output voltage (sometimes to maximum, 16 to 16.5 Vdc) and the damage to DC components would start all over again.

The problem verification is simple: Run a small gauge wire from the Alternator "remote sense" terminal to the engine battery bank (+) terminal. If the fluctuations and/or spiking cease, you have found it.

The permanent problem solution is shown on the following, marked-up, automotive wiring diagram for the '95 to '98 U270-295-320 coaches.

http://www.foreforums.com/index.php?action=media;sa=media;in=916;dl

Although submitted in the "old" Yahoo Group format, the narrative and the wiring diagram markup show up in current Foreforum searches. Many of the Foreforum members have found this narrative and markup to be useful. You might want to read them and/or make a copy if you will be having someone else do your troubleshooting.

I've attached a copy of the original narrative, in order to help you find it. Feel free to PM me, or give me a call, if I can be of help six oh three, seven seven two, four one one four.

Best wishes,
Neal

Re: alternator bad or isolator

Reply #33 – August 25, 2013, 02:43:20 pm

Neal,

Yes, it is quite common to locate the external sense wire to the chassis battery terminal of the battery isolator. Very close (physically) to the OE location. This will give you 95% accuracy in terms of voltage to the chassis battery, as the majority of the voltage drop is across the diodes of the isolator, not in the large gauge wire from isolator to chassis battery.

I find either location an improvement. BTW, our sailboat has its alternator's smart 3 stage regulator sense wire direct to the battery, just as the instructions for the regulator suggest.

Brett

Re: alternator bad or isolator

Reply #34 – August 25, 2013, 06:16:33 pm

We did make it home late last night, sorry it has taken me so long to reply.
Sorry my bad on the rpm, yes it was 950. And I apologize for the lack of info that is needed for troubleshooting a problem. I am recovering from surgery and will dig further into the problem when I have fully recovered. I would like to try what Neal has suggested and see what happens with the fluctuation of the voltage. Thanks again for all the help.

John

Re: alternator bad or isolator

Reply #35 – August 25, 2013, 06:39:29 pm

Thanks Neal for the info you sent. I read over it and sounds very helpful. I just cannot do much right now but just walk around slowly. So when I am up to speed I will be able to go further into this problem.

John

Re: alternator bad or isolator

Reply #36 – August 25, 2013, 10:06:10 pm

Hi Brett,

In reply #6, you said "Go to your battery isolator (front edge of engine compartment-- under bed)."

and, in reply #34 you said:

Quote from: wolfe10 – August 25, 2013, 02:43:20 pm

.......................Yes, it is quite common to locate the external sense wire to the chassis battery terminal of the battery isolator. Very close (physically) to the OE location..........................

I'm not sure about the 1999's, but just for clarity's sake and to prevent confusing others, as you know, the battery isolator has had several different OE mounting locations over the years.

The 1998's mounting location for the Battery Isolator, for all three models (U270, 295 and 320), was curbside aft wheelwell, just inboard of the engine start batteries, just above the Allison Retarder accumulation cylinder. Thus, my large gauge cables from the engine starting battery (+) to the battery isolator terminal are less than (2) feet in total length and have just one interconnection joint. By the year 2000, FT had moved the Battery Isolator up onto the front bulkhead of the engine compartment. I'm not sure where the isolator was located in years other than 1998 and 2000 other than it moved from streetside aft wheelwell to curbside aft wheelwell to forward engine compartment bulkhead.
I had a nice call from John this evening and I forgot to ask him where it is in his 1999 U295.
John's a very nice individual and I think he will do fine, but needs rest and recuperation from his surgery before he can continue with his troubleshooting.
Neal

Re: alternator bad or isolator

Reply #37 – August 25, 2013, 10:53:29 pm

Neal,

Good point-- the battery isolator is not in the same location on all coaches.

So, let me rephrase-- the sense wire on the chassis battery positive terminal or on the chassis battery terminal of the battery isolator are virtually equal and the shortest/cleanest run is the one to use.

Re: alternator bad or isolator

Reply #38 – August 26, 2013, 10:16:36 am

I think that a previous post suggested attaching the sense wire to a source that became hot with the key on so it didn't draw power when shut down ?
Am I thinking of something else?

Re: alternator bad or isolator

Reply #39 – August 26, 2013, 11:25:16 am

John, Your are right. FOUR wires on our alternators, HOT, GROUND, 12V to isolator, and 12V IGNITION HOT that excites the alternator.
Gary B

Re: alternator bad or isolator

Reply #40 – August 26, 2013, 11:26:01 am

Quote from: John Duld – August 26, 2013, 10:16:36 am

I think that a previous post suggested attaching the sense wire to a source that became hot with the key on so it didn't draw power when shut down ?
Am I thinking of something else?

John,
It's easy to become confused.
Like most large engine vehicle manufacturers, over the years Foretravel has used alternators that have four connections (+, -, sense, excite), as well as alternators that have three connections (+, -, sense)...........these are called "self-excited" alternators.

The sense terminal/wire may always be at 12Vdc without causing any parasitic battery drain. That's the way my self excited, three-wire, alternator is.

Because the sense circuit should have an ABSOLUTE minimum chance of stray voltage drops, the fewer connections, junctions, components and other unnecessary (potential resistance) connections between the alternator sense terminal and the (+) battery terminal, the better. IDEALLY, the only component in the sense line is a fuse.....the rest is wire and soldered ring terminals at either end.

Four connection alternators have an external, ignition-actuated, 12Vdc source connected to the excite terminal. That's why they are termed "externally excited" alternators. Most externally excited alternators continue to draw a small current as long as the ignition key is on.

The sense and excite wires always need to be circuit breaker (or fuse) protected, as near as possible to the 12Vdc source, to prevent any over-current and fire potential. We have close friends that had a Bluebird LXI consumed in flames by a simple modification to their sense circuit. The new, unfused, sense wire, connected to battery (+), chafed and shorted to ground. When it overheated due to the high current, it damaged the insulation on a house battery (+) cable (six, 8D house batteries) which also shorted to the coach frame. Fire extinguishers wouldn't put out the fire and by the time firemen arrived, the only option was to use fire axes to chop off battery cables (no battery disconnects). The $1.2M coach was totalled.

Hope this clears things up for you.
Neal

Re: alternator bad or isolator

Reply #41 – August 26, 2013, 12:01:27 pm

Got it!
Thanks!

Re: alternator bad or isolator

Reply #42 – August 30, 2014, 06:17:01 am

Hello to all that commented on this and tried to help. Sorry it has been so long sense the post and just now letting everyone know how it came out. Thank God I did recover from my surgery nicely and life has happen sense then and just kind a been wide open.

Any way thanks again for everyones help. Donald hit the problem just after this post started. Then Mr Neal Pillsbury hit it with the fix. It was the Alternator Remote Sense. The problem verification is simple: Run a small gauge wire from the Alternator "remote sense" terminal to the engine battery bank (+) terminal. If the fluctuations and/or spiking cease, you have found it. I did this myself just before a long trip down south and have had no issues. We were at Foretravel having some other work done, and I ask the mechanic about this and he would not acknowledge this problem and said he could check some out things. I told him no it would be ok. Anyway the problem is solved. Thanks again.

John I. Smith

Re: alternator bad or isolator

Reply #43 – September 11, 2014, 04:45:45 pm

I did the sense wire mod last weekend to rule out this potential issue for my new alternator. It was a very easy install and a cheap insurance policy, although I'm not sure I actually had voltage fluctuation problems. During the install, I had a general question about the voltage sense wire. Since the alternator is charging 2 banks of batteries and the voltage sense is only seeing the chassis batteries, how is the charging voltage to the house batteries regulated? Does the isolator provide any voltage management through the diodes to prevent damage to the house batteries when the chassis batteries demand higher voltage or does it only balance the current (amps)? It seems to me that charging the house batteries with the alternator is either done with some inefficiency (slow charging at low voltage) or some risk (overcharging at high voltage), depending on the condition of the chassis batteries. Yes, no?

Re: alternator bad or isolator

Reply #44 – September 11, 2014, 05:14:59 pm

Quote from: bdale – September 11, 2014, 04:45:45 pm

I did the sense wire mod last weekend to rule out this potential issue for my new alternator. It was a very easy install and a cheap insurance policy, although I'm not sure I actually had voltage fluctuation problems. During the install, I had a general question about the voltage sense wire. Since the alternator is charging 2 banks of batteries and the voltage sense is only seeing the chassis batteries, how is the charging voltage to the house batteries regulated? Does the isolator provide any voltage management through the diodes to prevent damage to the house batteries when the chassis batteries demand higher voltage or does it only balance the current (amps)? It seems to me that charging the house batteries with the alternator is either done with some inefficiency (slow charging at low voltage) or some risk (overcharging at high voltage), depending on the condition of the chassis batteries. Yes, no?

Until Wyatt gets here with the complete answer, no, there isn't any "regulation" in the isolator. If your alternator is sending out 15.0 volts, as some of the regulators are set to do, then (minus the voltage drop on the lines) any Gel batteries will receive a too-high charge. Been there, done that, not pretty. Having Gels in my system, my alternator's regulator is set at 14.0.

Re: alternator bad or isolator

Reply #45 – September 11, 2014, 05:30:50 pm

I switched my house batteries to AGM a couple of years ago so it's not as big of a concern for me now. But, it seems like a weakness in the design with no voltage regulation to the house bank. And really no way to prevent high voltage from going to the house if the chassis batteries get low without adding relays or switches. Maybe the boost switch should be left on for while to equalize the banks before starting the engine? Interesting. Good to know.

Re: alternator bad or isolator

Reply #46 – September 11, 2014, 06:46:28 pm

At 15 volts, you are cooking an AGM battery. If my memory hasn't been fried by all the drugs lately, absorption charge for an AGM battery is 14.1-14.7 volts. Gels are 14.1-14.4 volts. I know on sailboats, most people with large battery banks have switched to a smart charge regulator that can be programmed for Absorption and Float charging. If you set your alternator regulator to 14.7 volts, the house batteries will likely see no more than 14.4 volts due to the much longer wire runs. If the gels are seeing a little too much you could adjust the regulator accordingly.

Re: alternator bad or isolator

Reply #47 – September 11, 2014, 08:13:54 pm

Quote from: sedelange – September 11, 2014, 06:46:28 pm

At 15 volts, you are cooking an AGM battery. If my memory hasn't been fried by all the drugs lately, absorption charge for an AGM battery is 14.1-14.7 volts. Gels are 14.1-14.4 volts. I know on sailboats, most people with large battery banks have switched to a smart charge regulator that can be programmed for Absorption and Float charging. If you set your alternator regulator to 14.7 volts, the house batteries will likely see no more than 14.4 volts due to the much longer wire runs. If the gels are seeing a little too much you could adjust the regulator accordingly.

I wonder if Foretravel dialed down the voltage from the alternator to protect the Optima AGM batteries originally installed. I never see that high a voltage while driving. If they did dial it down, the original GEL house batteries would not have been charged at their fastest rate, but would have also been protected from overcharging.

My 1988 Winebago had a three position boost switch, one position was "boost" to momentarily tie the house batteries to the chassis DC system for starting, one position was "normal" to sit them together only when the engine was running, and one position was "off" to keep the alternator from charging the house batteries at all. Not a bad system, except for the momentary part of the boost switch.

Re: alternator bad or isolator

Reply #48 – September 11, 2014, 08:43:20 pm

Other mere FYI. On my '98 the sense wire does NOT go to the isolator nor does it go to the battery terminal. According to wiring diagrams (which I looked briefly at), it appears to go to a + connection somewhere on the remote start relay panel. I haven't traced the exact spot yet.

Also, my '98 must have a self exciting alternator, because when the engine is first started, the voltage will not go up at idle until engine goes above 1000rpm. Once it self excites, it will charge at idle.

I have sitting in my "box of stuff to install" a Yandina combiner that I am going to install in place of the OEM isolator. I'll leave the isolator in place and just move the wires over.

Combiner 160 Sheet

Re: alternator bad or isolator

Reply #49 – September 11, 2014, 10:29:01 pm

Correct. Moving the sense wire from the relay panel to the isolator block is the mod that I just did. I learned about it towards the beginning of this forum topic. The sense wire used to go to a terminal on the relay panel that shares duty with the AC compressor, creating a potential for voltage fluctuation that can affect alternator output. Moving the wire eliminates this problem by giving the alternator a more accurate battery voltage reading. It's an easy change to make by simply abandoning the old wire, capping and tying it off, and running a new wire to the chassis battery post on the isolator.

Quote from: krush – September 11, 2014, 08:43:20 pm

Other mere FYI. On my '98 the sense wire does NOT go to the isolator nor does it go to the battery terminal. According to wiring diagrams (which I looked briefly at), it appears to go to a + connection somewhere on the remote start relay panel. I haven't traced the exact spot yet.

Combiner 160 Sheet

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