Let's talk DP Alternators!

I see what you mean. With the diode based isolator you have to have the sense wire so it can see the voltage of the chassis batteries beyond the isolator.

This would be why the "one wire hookup" type of alternators should be avoided in these applications.

vacuumbed wrote:
The isolator is a Cole Hersee. It's blue anodized with fins. I'm guessing it's diode based. It's part number 48160.

Then you will want an external sense wire for the regulator (whether built in or external regulator).

Do this test. Put engine at 1000 RPM. Check voltage at alternator (if accessible-- if not at center lug of isolator where wire comes in from alternator.

Now, check at the chassis battery lug of the isolator. Bottom line-- you want the battery to see close to 14 VDC with engine running, NOT 14- .7= 13.2 VDC.

The isolator is a Cole Hersee. It's blue anodized with fins. I'm guessing it's diode based. It's part number 48160.

If you have a diode-based isolator, you definitely want an external regulator, as you can connect the sense wire to the chassis battery side of the isolator and thus provide the batteries with full voltage rather than full voltage less .7 VDC.

If a solenoid based or manual isolator switch, internal regulation is just fine as there is no significant voltage drop from alternator to battery.

As far as I can tell all the connections are good.

I determined that I have a HEHR Powerline alternator modem 25-12 with a rating of 190 amps. It uses an external regulator based on the Ford style, but I've been told they are no the same.

The HEHR version of this regulator is a bit pricey, like $175-$275. :E

I may just keep the Motorcraft regulator on there. I still wouldn't mind finding a different alternator setup that will fit, with an internal regulator.

x2 on Leece and bought out west to ship to the east. Went this route as reliable and what is most used in resue/fire apps. Only reason had to replace was originally coach was brought from OR to CA thru a massive snow storm and appeared that the corrosion took it's toll. We don't travel in salt but if we do, wash down and when under to do a grease job, always inspecting to ensure touch up any parts needing attention from rust. Not that I have to, but a great way to lear where/what/how pcs/parts are located/work.

The Hehr Power line is an upgrade. This is a high quality Alt. that is used on fire and rescue units! Going to a leece or Delco would be a downgrade!

Moisheh

My motorhome originally had a Hehr alternator that crapped out for the PO, it was replaced with a high dollar Leece Neville and that crapped out on me and I replaced it with a cheap Delco 22SI. That is working fine for 4 years now.

We too had Leese Neville alternators on all of our Fire Trucks. Most were 400 amp units. And in the last batch we ordered just prior to my retirement, those rigs came in with "Two", 200 amp units on them. That was different for sure.
Anyway, as for their history, yes we had quite a few fail but, one thing you have to realize is the electrical demand of an alternator in a Fire Truck. Just a bit more than your average motor home.

As for the OP and his fluctuations, I've seen that more than once in my life. Haven't seen it lately and almost forgot that it existed until I read his original post. Wolf seems to have a handle on the possible cause. Sorry, I can't be much help here. I never did know how to cure it even way back when I used to see it more often.
Scott

Along with what Wolfe stated, check to see if you have any AC on your alt output.