Alternator Generating High Voltage

[swebster]

It's been a really long time since I've posted here. Feels like an old pair of Jeans

Chasing a charging issue lately and have run into a situation where the Alternator is putting out 40+ volts at 1200 - 1500 RPM. Even higher at 2000 RPM.

Here is what has been done so far:

Alternator is a 12V 150 AMP Lestek. Took it into the shop this week for a bench test, totally dead so I had it rebuilt. New brushes, stator, bearings, etc. Bench tested AOK.

Replaced original voltage regulator (Echlin) with a NAPA Echlin VR-428 (Ford replacement)

Checked, double checked and triple checked all of the wiring which is setup as follows:


Alternator BAT to Solenoid/Battery Junction
Alternator GRD to ground shared by Voltage Regulator
Alternator FLD to "F" on Voltage Regulator
Alternator STA (unused)

Voltage Regulator A+ from Battery/Ignition
Voltage Regulator S from Ignition
Voltage Regulator F from Alternator F
Voltage Regulator I (unused - no ignition light on my 34%)

Test Results Ignition Off

VR A - 12.05v
VR S - 9.83v
VR F - 11.7v
Alt BAT - 4.2v

Test Result Ignition On

VR A - 12.03v
VR S - 9.79v
VR F - 11.68v
Alt BAT - 3.37v

Test Results Engine On (1200 RPM)

VR A - 11.9v
VR S - 9.65v
VR F - 11.58v
Alt BAT 57.3v

I've run the same tests with the Alternator output separated from the battery isolater as well just to rule out an open or short in there.

So, I'm looking for any additional tests, things to check, etc. As always, any advice is appreciated.

[dadstoy]

Hi Steve. Good to see you are still out there! I just replaced my alternator as well.

I'm curious why you are running an external regulator? Don't all modern alternators have their own built in regulator?

[swebster]

Still here

The Lestek alternators are a high amperage alternator for low RPM use on RV's, Boats, etc. and therefore use a heavy duty external voltage regulator. It's a bit old school for sure, but it's a common setup in RVs running these alternators.

I thought about replacing it with a "normal" Chevy alternator but would loose the high amp/low RPM features.

FWIW - anyone with a Lestek, the company was bought out by Penntex and they offer cross reference replacements (Alternator Cross Reference)

[72 tradewind]

The last time I saw this, the charge wire from the alt to the battery positive terminal was burned open...Do you show 40 volts at the battery? You should have no more than 14.8ish. If is only 12v -ish the wire is open from the alt to the battery. P.S. while the engine is running....

[swebster]

I show approx +/- 12v at the battery in all three scenarios (ign Off, ign On, Engine On). I should add, the battery has not been charging (which is what led to this process of testing, rebuilding and replacement)

Sounds like I need to start tracing the battery wiring. Any tips?

On Edit - The Battery was also newly replaced

[Keyair]

Welcome back Swebster!
I have read your posts with interest going back years... like Brad, you guys forged the path us newcomers are widening!

Mine has some charging issues too, and has the Ford Voltage Regulator mounted on the radiator support, so I will be interested to follow your diagnosis!

[bkahler]

Originally Posted by dadstoy

Hi Steve. Good to see you are still out there! I just replaced my alternator as well.

I'm curious why you are running an external regulator? Don't all modern alternators have their own built in regulator?

Dean, while dismantling the 345 I found that it also had a Lestek alternator with external voltage regulator. It's a 105 amp output alternator. At the time I found it I was wondering why it had an external regulator so I'm glad Steve was able to clear that up for me.

I just might have to use it on the Argosy.

By the way, welcome back Steve!

Brad

[swebster]

Originally Posted by 72 tradewind

The last time I saw this, the charge wire from the alt to the battery positive terminal was burned open...Do you show 40 volts at the battery? You should have no more than 14.8ish. If is only 12v -ish the wire is open from the alt to the battery. P.S. while the engine is running....

Bingo. Found the open in the Battery Isolator. Bypassing the isolator gives me 14.3v - 15v at the battery while running. Thanks guys, it's been a while since I've needed to post here but as usual I got some sage advice within minutes.

Time to order a replacement isolator.

[Keyair]

Good news!
Is that the one mounted on top of the engine, close the alternator?

[swebster]

Well on mine the isolator is mounted on the "firewall", drivers side. It's a blue finned solid state isolator. Pulling the old one out it appears it's under-rated for the higher amperage alternator...betting this was the cause of many a battery and charging problem over the years.

Looks like this one but dirty



Found a replacement online rated for 160 amps for $66.

[swebster]

Keyair, I think you might be referring to the solenoid mounted to the alternator bracket. I replaced about five of those in rapid succession (vibration + heat = bad)....finally dumped the Chevy solenoid and went with a Ford that I mounted on the frame. Have not had any issues with than in years.

[PeterH-350LE]

Hi Steven, welcome back. I returned after a few years away myself. I sold my 79 bought Dennis's 345 in May and have been working on it since. Did you decide to keep your 345, I saw it up for sale not long ago.

[swebster]

Thanks Peter. Yeah, we've certainly been under utilizing the 345 the last couple of years. May re-list it, not really sure at this point. Frankly, the selling process was a bit frustrating. Lot's of tire kickers, time wasters and dreamers. At some point it's not worth selling it as I could get back into it and enjoy every second of it. Just balancing working on the Airstream against working on everything else.

Gotta say, really nice to jump back on air forums and feel like it's only been a few days since I last posted. Such a great group here.

[crazeevw]

Steve,
Which amperage isolator did you end up purchasing? As well, where did you find such a great price?
Thanks, Derek

[swebster]

Derek,
Here are a few: Sure Power 160 Amp Dual RV Battery Isolator