Recommended alternator charging voltage

[RF_Burns]

So, on the way (still in the driveway) to take to coach in for transmission problems, the GEN light is on. Get out the voltmeter and I have near zero
volts at the input to the isolator. So I start the Onan and let the combiner do its job feeding power to the engine. I tell the shop to replace the
alternator, but I'll keep the old one to repair and keep as a spare.

So when the coach is fixed and ready to roll, I picked up the coach and head back home. Its raining so I pull ON the headlights and flip ON the
electric wipers. I see from the corner of my eye an orange light coming ON in the DigiPanel. Focusing on it, its the battery voltage flipping from
Orange/Green to Orange only with the intermittent wipers. So I know my battery voltage is less than optimum.

Back home I check the voltage at the input of the isolator = 13.3 and output = 12.6V. So I check the output of the alternator is 14.5V. More tests
show the alternator output is pretty much constant at about 14.5V even though the voltage sense is only 12.6-12.8V.

I repaired my old alternator (bad diode trio) and also replace the regulator with the same as is in it, a Transpro D101HD 14.8v. So I swap the old
alternator back in. Now I get 15.6v at the isolator input and 14.8V at the isolator output. I checked the output of the alternator and its 16.5V, so
I have about 0.8V IR loss in the alternator wire. I turn the headlights ON and it jumps to a loss of 1.2V. Checking the resistance per foot of #10
wire, that works out to about 100Amps, which I know cannot be right. So I decide to replace the alternator output wire. I used the old wire as a
fish and found 2 junctions in the old wire. The new wire shows a loss of 0.2V which works out to 25Amp from the alternator which makes more sense.

I opened the new alternator and found it had a D689 regulator. A quick Google shows it to be a 14.5V one-wire regulator. The sense wire connection is
a DUMMY! So be aware these things look the same, but what is inside may not be right. Even with the new wire... 14.5V - 0.8V (under load isolator
loss measured 0.85V) - 0.2V (wiring loss) = 13.5V which is not enough to fully charge unless on a long trip.

SO, my question is... the D101HD regulator in my old alternator is 14.8V, so with voltage feedback it will try to keep the voltage at the battery at
14.8V approx. I think this is a bit high, but is the same regulator that was in it since 2008. I'm wondering if it should be maybe 14.3V. Or do the
new regulators ramp the voltage down over time?

What say yea?

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

 

[terry1]

You fixed the problem with the new charge wire. Making up for the resistance in the old wire is blew the diodes. What is the reading at the fully
charged battery with the engine running now? Looks like it's going to be 14.0>>14.1 volts, which is a little low, but with no electric fuel injection
system on the vehicle you really don't need the 14.3 volts normal on modern vehicles.
--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.

 

[Ken B]

The rule has always been 13.8 to 14.2 to charge lead acid automotive batteries. Some regulators allowed variance to this depending on ambient
temperature sensed at the alternator. On more modern cars the BCM varies the voltage even more and considers other factors. So some mechanics quote
higher and lower numbers they have observed. 14.8 is definitely too high after going through the .7 or .8 drop at the isolator. It is great short
term when initially charging a cold battery.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

 

[RF_Burns]

Terry,
I put the old (repaired) alternator back in so it has a working V-sense input. It had a Transpro D101HD regulator in it which I replaced with a new
one, same part number (14.8V HD A-circuit). So with the V-sense input, the feedback voltage will cause the alternator to increase its output to
overcome any voltage losses (output wire & Isolator). So my battery is seeing ~ 14.8V from the alternator.

I do have EFI using a Rochester TB and EBL ECM

Ken,
Looking through the Transpro Buyers Guild, there are plenty of voltage regulators that appear from the photo to fit the 27SI100 alternator. I do see
some at 14.2V which would be more appropriate. Looking at their 24V regulators most seem to be 27.5V which divided in half = 13.75V, so maybe the
lower voltage in that case for engines running for long times continually would make sense.

Its not really a buyers guild since you can't search by alternator model, voltage etc. Its just a PDF grouped by alternator manufacturer.

I pulled up an EBL data log from last fall and it recorded the battery voltage at ~13.8V. Maybe they changed the specs on the D101HD regulator?

I'll see if I can get a regulator from the shop that rebuilt the replacement with one closer to 14V

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

 

[d c *mac* macdonald]

Bruce, I don't believe your battery should be receiving 14.8 Volts
as that would be a good way to greatly shorten its life!

If your isolator is working properly, it should drop .6 to .7 Volts
which should provide 14.2 to 14.1 Volts to the battery for a short
while after you run the starter.

You can check the isolator out by measuring the voltage between
the alternator and the output to the battery. If you don't measure
.6 to .7 Volts there, your isolator is kaput!

D C "Mac" Macdonald
Amateur Radio K2GKK
Since 30 November '53
USAF and FAA, Retired
Member GMCMI & Classics
Oklahoma City, OK
"The Money Pit"
TZE166V101966
'76 ex-Palm Beach
k2gkk + hotmail dot com
________________________________
From: Gmclist on behalf of Bruce Hislop via Gmclist
Sent: Monday, September 14, 2020 07:08
To: gmclist
Cc: Bruce Hislop
Subject: Re: [GMCnet] Recommended alternator charging voltage

Terry,
I put the old (repaired) alternator back in so it has a working V-sense input. It had a Transpro D101HD regulator in it which I replaced with a new
one, same part number (14.8V HD A-circuit). So with the V-sense input, the feedback voltage will cause the alternator to increase its output to
overcome any voltage losses (output wire & Isolator). So my battery is seeing ~ 14.8V from the alternator.

I do have EFI using a Rochester TB and EBL ECM

Ken,
Looking through the Transpro Buyers Guild, there are plenty of voltage regulators that appear from the photo to fit the 27SI100 alternator. I do see
some at 14.2V which would be more appropriate. Looking at their 24V regulators most seem to be 27.5V which divided in half = 13.75V, so maybe the
lower voltage in that case for engines running for long times continually would make sense.

Its not really a buyers guild since you can't search by alternator model, voltage etc. Its just a PDF grouped by alternator manufacturer.

I pulled up an EBL data log from last fall and it recorded the battery voltage at ~13.8V. Maybe they changed the specs on the D101HD regulator?

I'll see if I can get a regulator from the shop that rebuilt the replacement with one closer to 14V

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

 

[RF_Burns]

Mac,
The issue is the alternator receives a feedback voltage from after the isolator. So its internal regulator adjusts its output voltage to see 14.8V
coming back to it. This feedback voltage is tapped from the power wire going to the Ignition switch according to the chassis wiring diagram.

I could move the voltage feedback source to the center terminal of the isolator at which time it would act as you suggest and the isolator would drop
the 0.7V and leave me with a more appropriate 14.1V. However it would then not compensate for voltage losses in wiring after that. Headlights with
dim, heater fan would slow with varying load conditions.

The old regulator with the same part number seemed to be set to 13.8V. The lowest I can find in their catalog now is 14.2V

If I find a regulator with the appropriate voltage, I'll post it on here and send the part number to Kim Weeks to be included in the parts exchange.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

 

[d c *mac* macdonald]

In my opinion, the rest of the systems in your coach
are designed to work at the ~ 14 Volt level. One would
hope that the wiring chosen by engineers would be of
sufficient size to minimize expected voltage drops for
expected currents.

Over voltage will shorten the lifespan of ALL devices
that are receiving that voltage.

Clean connections at EVERY junction are mandatory for
optimum performance.

D C "Mac" Macdonald
Amateur Radio K2GKK
Since 30 November '53
USAF and FAA, Retired
Member GMCMI & Classics
Oklahoma City, OK
"The Money Pit"
TZE166V101966
'76 ex-Palm Beach
k2gkk + hotmail dot com

________________________________
From: Gmclist on behalf of Bruce Hislop via Gmclist
Sent: Monday, September 14, 2020 07:48
To: gmclist
Cc: Bruce Hislop
Subject: Re: [GMCnet] Recommended alternator charging voltage

Mac,
The issue is the alternator receives a feedback voltage from after the isolator. So its internal regulator adjusts its output voltage to see 14.8V
coming back to it. This feedback voltage is tapped from the power wire going to the Ignition switch according to the chassis wiring diagram.

I could move the voltage feedback source to the center terminal of the isolator at which time it would act as you suggest and the isolator would drop
the 0.7V and leave me with a more appropriate 14.1V. However it would then not compensate for voltage losses in wiring after that. Headlights with
dim, heater fan would slow with varying load conditions.

The old regulator with the same part number seemed to be set to 13.8V. The lowest I can find in their catalog now is 14.2V

If I find a regulator with the appropriate voltage, I'll post it on here and send the part number to Kim Weeks to be included in the parts exchange.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

 

[Jim Hupy]

Here is the real scoop.In a scientifically perfect world, a lead acid
battery should, with a perfect specific gravity in the electrolyte, have
2.2 volts per cell, times 6 cells, or 13.2 volts. But, this world ain't
perfect. And batteries are not either, and there is resistance in
conductors and loads. So an expected voltage of 12.8 volts is more
reasonable. There is a term used to describe charging systems. It is known
as "Counter electromotive force" In order to encourage electrons to flow
through a conductor into a storage battery, that CEMF must be exceeded. So,
to charge a battery that has 12.8 volts, you must use a higher voltage than
that. Industry commonly uses 13.8 volts minimum to overcome CEMF. So
regulators have a low limit near 13.8 volts. High limits usually are 1 volt
higher, or 14.8 volts.
Of course, if there are high resistances in the charging circuit, this
might not be a high enough limit to overcome those resistances. So they
fudge the high limit up a bit higher be .5 volts or so. That might be 15.3
volts, but for a very short time. Batteries do not like charging voltages
that high for very long.
That's enough low voltage 101 for today. Chew on this for enough time
for it to digest.
Jim Hupy
Salem, Oregon

On Mon, Sep 14, 2020, 5:57 AM D C _Mac_ Macdonald via Gmclist <

> In my opinion, the rest of the systems in your coach
> are designed to work at the ~ 14 Volt level. One would
> hope that the wiring chosen by engineers would be of
> sufficient size to minimize expected voltage drops for
> expected currents.
>
> Over voltage will shorten the lifespan of ALL devices
> that are receiving that voltage.
>
> Clean connections at EVERY junction are mandatory for
> optimum performance.
>
> D C "Mac" Macdonald
> Amateur Radio K2GKK
> Since 30 November '53
> USAF and FAA, Retired
> Member GMCMI & Classics
> Oklahoma City, OK
> "The Money Pit"
> TZE166V101966
> '76 ex-Palm Beach
> k2gkk + hotmail dot com
>
>
>
> ________________________________
> From: Gmclist on behalf of Bruce Hislop
> via Gmclist
> Sent: Monday, September 14, 2020 07:48
> To: gmclist
> Cc: Bruce Hislop
> Subject: Re: [GMCnet] Recommended alternator charging voltage
>
> Mac,
> The issue is the alternator receives a feedback voltage from after the
> isolator. So its internal regulator adjusts its output voltage to see 14.8V
> coming back to it. This feedback voltage is tapped from the power wire
> going to the Ignition switch according to the chassis wiring diagram.
>
> I could move the voltage feedback source to the center terminal of the
> isolator at which time it would act as you suggest and the isolator would
> drop
> the 0.7V and leave me with a more appropriate 14.1V. However it would
> then not compensate for voltage losses in wiring after that. Headlights with
> dim, heater fan would slow with varying load conditions.
>
> The old regulator with the same part number seemed to be set to 13.8V.
> The lowest I can find in their catalog now is 14.2V
>
> If I find a regulator with the appropriate voltage, I'll post it on here
> and send the part number to Kim Weeks to be included in the parts exchange.
>
> --
> Bruce Hislop
> ON Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> My Staff says I never listen to them, or something like that
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[Ken B]

> In my opinion, the rest of the systems in your coach
> are designed to work at the ~ 14 Volt level. One would
> hope that the wiring chosen by engineers would be of
> sufficient size to minimize expected voltage drops for
> expected currents.
>
> Over voltage will shorten the lifespan of ALL devices
> that are receiving that voltage.

The wiring design is far from ideal. The biggest drop is the fusible link and almost everything on the engine side except the starter runs through
it.

--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana