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Topic: 130A alternator & 100A isolator (Read 969 times) previous topic - next topic

130A alternator & 100A isolator

Problem with two different rated units?
Seven years ago we had our 100 Amp alternator fail while in Texas. The only replacement the shop had was a 130 Amp unit.
Price was right. Need was there. Ignorance was bliss. So went ahead, not knowing there was this thing called an isolator that separated the two batteries.
So, now that I finally realized that I have this mismatched charging systems, is this what is causing my coach battery charge level to go down and the dash gauge to read only 12.5 volts now?
Has the isolator finally failed?
Yesterday I removed the alternator and checked the brushes. They look like new, about 3/4" long. Bearings are good. Spins smooth and quietly.

Re: 130A alternator & 100A isolator

Reply #1 –
The diode-based isolator is easy to test/diagnose:

With engine running above idle (say 1,100 RPM) check with your digital voltmeter between good chassis ground and:

Center lug coming from the alternator B+ terminal.  Should be in the mid 14's VDC

Each of the side lugs (one going to each battery bank).  Should be about .7 VDC lower than the center one and should reflect what you saw before the failure-- generally in the 13.5-14 VDC range. Yes, if it reads 12.5, then either the alternator is not supplying proper voltage (see test above) OR the isolator is not conveying this voltage to the two lugs connected to the two battery banks.

While I agree that the isolator should be speced with the same rating as the alternator, unless charge rate exceeds isolator rating (i.e. batteries very deeply discharged when engine started) amps would likely not exceed isolator specs.

Said another way, the mismatch in specs does not necessarily suggest the issue.  But DOES suggest testing.

Re: 130A alternator & 100A isolator

Reply #2 –
Thanks Brett.
Unfortunately the alternator is already out of the coach and on my tool box.
Real Pain in the derriere to put in and remove, as I have to crawl up under the bed and lay on my stomach just to access the alternator.
Putting it in and then back out (twice if it is bad) just to test the output is a whole bunch of work. How about if I take the alternator somewhere where they can bench test it for output?
Then I can take the wires off the isolator and check it for function?

Re: 130A alternator & 100A isolator

Reply #3 –
Norm,

Yes, take the alternator in to be tested.

If good, reinstall-- it has been eliminated as the cause of your low voltage.

Then do the isolator test above.

Re: 130A alternator & 100A isolator

Reply #4 –
I'll take the alternator for bench check today.
After the sun gets on the west side of the coach I will take the wires off the isolator and check it . Our coach faces south so it gets quite hot on the east side in the morning and the glare off the white paint blinds.

Re: 130A alternator & 100A isolator

Reply #5 –
I just went back and looked at the pics. of your voltage regulator.  That regulator is non adjustable and has a set point of 14.2.  It is possible that the regulator has failed.  Those are about $20 if it is just the regulator. Having a shop test the alternator is a good staring point. You need to check the sense wire for good connection and it seems like (on your year coach) there is a fuse under your dash that feeds the alternator. Look and see if you have this fuse and give it a check.

Mike

Re: 130A alternator & 100A isolator

Reply #6 –
Went looking for the inline fuse. None, and none indicated on any of my schematics.
Strange, as there isn't even any indication of the "external excite" wire to the alternator on my schematics

Re: 130A alternator & 100A isolator

Reply #7 –
There are 3 optional voltage regulators for the alternator: single voltage, 3-step adjustable voltages (can only change before installing), variable voltage (can adjust any time with alternator installed). We prefer the adjustable and keep the output on the low side to protect our GEL & also RedTop AGM battery banks.

As Brett noted, isolator likely never saw over 100 amps & if so for only a moment, so isolator rating differences are ok, but isolator age could be issue.

Re: 130A alternator & 100A isolator

Reply #8 –
Quote from: nitehawk –
Strange, as there isn't even any indication of the "external excite" wire to the alternator on my schematics
Are you talking about a "excite" wire, or about a "sense" wire?  Two different things.

If there is only one small gauge wire connected to your alternator, I suspect it is a "sense" wire.  Should be connected (either directly or indirectly) to the START battery positive post, or to the START battery post on the isolator.

If you have two small wires connected to alternator, the second one would be the "excite" wire.  Should be connected to a "HOT with ignition switch ON" terminal somewhere in the engine bay.

Re: 130A alternator & 100A isolator

Reply #9 –
One wire (red) goes into a protective cover along with the large cable on the right side/rear of the alternator.

Re: 130A alternator & 100A isolator

Reply #10 –
Quote from: nitehawk –
One wire (red) goes into a protective cover along with the large cable on the right side/rear of the alternator.
Check that wire, now, while the alternator is out of the coach.

If it is hot all the time, it is a "sense" wire.  Should read pretty dang close to same voltage as start battery.

If it is not hot unless the ignition switch is on, it is a "excite" wire.

Re: 130A alternator & 100A isolator

Reply #11 –
Isolator is isolated--all wires off. So can't test anything other than the isolator itself. Batteries have "POS" cables off the batteries.
Strange setup. The left post has two heavy gauge wires with red covering. The center post has one  heavy gauge red wire. The right post has one heavy gauge red wire and two small gauge red wires.

AND THE MYSTERY DEEPENS!!!

Re: 130A alternator & 100A isolator

Reply #12 –
Do a search on DUVAC. Unless the alternator has been modified for DUVAC it is not going to work with your isolator.

Re: 130A alternator & 100A isolator

Reply #13 –
Ain't going with Duvac. Getting this existing system working...$$$$$$$$$$$$$$$$$$$$

Re: 130A alternator & 100A isolator

Reply #14 –
Latest chapter: I removed ALL the electrical cables from the isolator.
Then proceeded to check the diode(s) with my trusty HF Centech Digital Multimeter.
With the dial pointer pointing at the arrow/plus function I got the following readings:
Plus (+) clamp on alternator post and minus (-) clamp on left post Multimeter reads 4.9-5.0
Minus (-) clamp on alternator post and plus (+) clamp on left post Multimeter reads 1
Plus (+) clamp on alternator post and minus (-) clamp on right post Multimeter reads 4.9-5.0
Minus  (-) clamp on alternator post and plus (+) clamp on right post Multimeter reads 1
So, based on this my isolator is still good?
A bit of "pretty" lime green corrosion on the ends of the wire insulating, by the wire ends.
Next project is to clean all connections and then reassemble.
Alternator shop is closed today so tomorrow we go there.

Re: 130A alternator & 100A isolator

Reply #15 –
Hawk,if you can,maybe a good idea to take isolator off and take to shop.

Re: 130A alternator & 100A isolator

Reply #16 –
Dave, you do like to see me work, don't you?
The isolator 1/4" hex head bolts, (4) of them, are under the floor, forward of the engine compartment, mounted on welded strips on the frame.
I will have to crawl under the coach, half sit up, and then blindly feel for the bolt heads.
I will have the alternator checked first.
(Call the Canopy Factory. I'm curious as to whether they are still in business.)

Re: 130A alternator & 100A isolator

Reply #17 –
Quote from: nitehawk –
Ain't going with Duvac. Getting this existing system working...$$$$$$$$$$$$$$$$$$$$
Alternator plus isolator IS  duvac. Anyhow, good luck.

Re: 130A alternator & 100A isolator

Reply #18 –
Just got back from having the alternator tested.
Conclusion? "Das is Kaput" Zero output.
Maybe regulator or stator. Should have it done by next Monday.
Oh, by the way, we originally bought this alternator from the original shop here in town. The guy we dealt with even knew the guy we bought the alternator from.

Re: 130A alternator & 100A isolator

Reply #19 –
Rebuilder just called.
Regulator is/was bad.
Bench test, regulator replaced, bench test again=$85 + tax.
Not bad, considering I get confirmation as to what was bad, seeing as I have neither the knowledge or equipment to determine what was bad.
Merely substituting/swapping parts goes against my principles.