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Topic: Another alternator question (Read 934 times) previous topic - next topic

Another alternator question

The small, disconnected wire at my isolator is connected to a terminal labled "R" at the alternator. Is this the sense connection for the alternator? ...and where does it connect at the isolator.

Jim
1992 ORED, 36', White w/Stripe decal(getting old)
Cummings 8'3 Mechanical, 182561kmi. 3299hrs.
Build #4062

Re: Another alternator question

Reply #1 –
Jim,

If you can tell us the brand and model number of your alternator, it would be helpful.  Or post a photo of the back of the alternator, showing the connection points.  The different alternator brands are not always consistent in the way they mark the connection points.

Don't want to give out any bad info.
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: Another alternator question

Reply #2 –
Gotta wait til it comes back from the shop...

Jim
1992 ORED, 36', White w/Stripe decal(getting old)
Cummings 8'3 Mechanical, 182561kmi. 3299hrs.
Build #4062

Re: Another alternator question

Reply #3 –
Finally managed to get info back in my sig.

Jim
1992 ORED, 36', White w/Stripe decal(getting old)
Cummings 8'3 Mechanical, 182561kmi. 3299hrs.
Build #4062

Re: Another alternator question

Reply #4 –
Quote from: jimsizemore –
Gotta wait til it comes back from the shop...

Jim
Its a Delco Remy #'s - 8600310, 24S1 or Si, M18P14B  I don't know which is model #...
12v, 160W
1992 ORED, 36', White w/Stripe decal(getting old)
Cummings 8'3 Mechanical, 182561kmi. 3299hrs.
Build #4062

Re: Another alternator question

Reply #5 –
Start by verifying that the alternator is properly wired.

Go to: Alternators by Model Family | Delco Remy

Click on "Installation Instructions".
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: Another alternator question

Reply #6 –
Brett - I still don't know what the terminal labeled R is for. The shop told me the alternator ischarging and all they did was hook  battery up to it and spun it. we checked the disconnected wire hanging' at the isolator before we took  the alternator off and measured only a few tenths of voltage. does this R terminal need to be connected to the isolater before the alternator will excite? The shop said all they did was hook up the battery? and spin it.I still don't want to hook that wire to that center post until I know what I'm doing! Why do so many folks just want to know HOW to do and not concern them selves  with WHAT they're doing??  AND what should the voltage at that center post be with it not hooked to the alternator?

Jim
1992 ORED, 36', White w/Stripe decal(getting old)
Cummings 8'3 Mechanical, 182561kmi. 3299hrs.
Build #4062

Re: Another alternator question

Reply #7 –
I did not read far enough down in Delco install instructions. I did and they answered my ? about the R...

Jim
1992 ORED, 36', White w/Stripe decal(getting old)
Cummings 8'3 Mechanical, 182561kmi. 3299hrs.
Build #4062

Re: Another alternator question

Reply #8 –
Quote from: jimsizemore –
AND what should the voltage at that center post be with it not hooked to the alternator?
Jim,

That is a excellent question, and one which has been discussed in depth on this Forum.  I know because I had the exact same question when we bought our coach.  I, also, had to straighten out some wiring problems with our alternator, and came up with the isolator "center post voltage" question while analyzing the alternator performance.

I will post a link below to that old thread.  But to save you time, I will tell you what I decided after much discussion and measuring.  If you have the coach batteries hooked to one of the outside posts, and the start batteries hooked to the other outside post, under perfectly ideal theoretical conditions you should not read any voltage on the center post.  However, I found out in the real world that is not necessarily true.  Although the diodes in the isolator are supposed to only allow current flow in one direction, they can actually allow a little "leakage" in the other direction.  The way this shows up on the isolator is a voltage reading on the center post when there is nothing connected to it.  You can read this voltage with a sensitive multimeter, but if you connect a 12 volt test light from the isolator center post to ground, you will probably find, as I did, that it will not light.  What this means to me is there is "voltage" on the center post, but no amperage.  Keep in mind that I was a English major, so my technical expertise can be questionable.

Anyway, even though my isolator (which is the 25 year old original factory equipment) does show "phantom" voltage on the center post, this does not seem to affect its function in any measurable way.  It performs exactly as designed, by protecting the start battery bank from discharge even when the coach batteries are heavily discharged.  Also, both banks charge correctly off the alternator when the engine is running.  Based on those facts, I decided to retain my old OEM isolator and let it do its thing, in spite of the voltage on the center post.  But that's just me...

Here is the link to my "isolator" thread from 4 years ago. 8)

Bad 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: Another alternator question

Reply #9 –
If the isolator is actually working and nothing is connected to the center post voltage to ground should be essentially zero.

Diode isolators fail or leak as Chuck points out.  They also cause a voltage drop of 0.7 to 1.0 volts from the center post to the start battery post or house battery post across the diode.  With these isolators alternator voltage gets turned up on the LN alternators to account for the voltage loss so that at your start batteries you will see 13.6 +/- that you want.

There are a selection of zero voltage drop isolators available.  This one is 200 amp capable for two battery banks for under $120.  Zero voltage drop.

Victron Argofet Battery Isolator

It can supply the excite voltage to the LN that it needs.

Sterling makes a smart zero voltage drop isolator that actively manages charge distribution based on need.  Also available from Bay Marine Supply.
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: Another alternator question

Reply #10 –
Quote from: jimsizemore –
I did not read far enough down in Delco install instructions. I did and they answered my ? about the R...

Jim
I continued reading and it said the R terminal is NOT the sense connection so do not hook it to battery...it identified that terminal as a place to hook a relay and said it was optional(I think it is to drive an idiot lite or indicator of some sort. We reinstalled the alternator(after looking at Delco instructions. The alternator that the shop said we could charge our battery with and the voltage did not change at the positive post. The kids left for south carolina a couple hours ago with a couple charged batteries along with them. Keep your fingers crossed for them. Thanks.

When they get back, the alternator goes back to the shop.

Jim
1992 ORED, 36', White w/Stripe decal(getting old)
Cummings 8'3 Mechanical, 182561kmi. 3299hrs.
Build #4062

Re: Another alternator question

Reply #11 –
I believe you have it correct Jim as I read what you did.  Alternator Plus to the center post of the isolator, Alternator Neg to a solid ground point.  S post on the Delco to a start battery plus point.  It will work without the S post connection but not as efficiently.  The output volts will be .5 volts less.  Batteries charge faster with a remote sense wire.
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: Another alternator question

Reply #12 –
Roger - I think it makes sense that, whoever installed the Delco alternator, knew what they were doing and left that small red wire, going to the isolator hanging loose on purpose? My coach started to Columbia, SC after dark last nite. They carried a couple good batteries with them and my honda 2000 generator. My grandson(at Shaw AFB will be living in it for couple months, so unless he works on it, I will have to wait 'till it comes back home). Thanks for your(and everyones concern.

Jim
1992 ORED, 36', White w/Stripe decal(getting old)
Cummings 8'3 Mechanical, 182561kmi. 3299hrs.
Build #4062

Re: Another alternator question

Reply #13 –
Just answered a call from son & they have made the trip and all went well...

Jim
1992 ORED, 36', White w/Stripe decal(getting old)
Cummings 8'3 Mechanical, 182561kmi. 3299hrs.
Build #4062