Unusual electrical issue

H

hal stclair

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Mar 26, 2013
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I just ran into an interesting issue on our Thanksgiving trip. After replacing a NEW alternator under warranty after little over 1000 miles, I was
afraid the replacement was going bad 5000 miles later. The voltage would drop to 11.9 volts and randomly jump to 14+ at times. While observing -12
volts a semi truck passed and the voltage popped up to 14+ and seemed to drop as soon as the big rig passed. I noticed the same effect when going
under an overpass. It then hit me-the solar panels (280 watts worth) are wired to the house battery bank and the alternator sense wire is attached to
the same point on the isolator. It seems the voltage from the panels is making the alternator reduce output thinking the battery voltage is satisfied.
Guess I'll have to install a relay to open the PV circuit when the ignition is energized. Who'd of thunk that would happen? It's always something to
keep the gray matter going on these GMC's.
Hal
--
1977 Royale 101348,

1977 Royale 101586, Diesel powered,

1975 Eleganza II, 101230,

1974 Eagle Bus 45',w/slideout,

Rio Rancho, NM
 
Nothing like the sudden realization that we have just outsmarted ourselves.
Keeps me humbler than I would otherwise be. Guess I ain't alone. (Grin)
Jim Hupy
Salem, Or
78 GMC ROYALE 403

On Wed, Nov 28, 2018, 10:09 PM Hal StClair
wrote:

> I just ran into an interesting issue on our Thanksgiving trip. After
> replacing a NEW alternator under warranty after little over 1000 miles, I
> was
> afraid the replacement was going bad 5000 miles later. The voltage would
> drop to 11.9 volts and randomly jump to 14+ at times. While observing -12
> volts a semi truck passed and the voltage popped up to 14+ and seemed to
> drop as soon as the big rig passed. I noticed the same effect when going
> under an overpass. It then hit me-the solar panels (280 watts worth) are
> wired to the house battery bank and the alternator sense wire is attached to
> the same point on the isolator. It seems the voltage from the panels is
> making the alternator reduce output thinking the battery voltage is
> satisfied.
> Guess I'll have to install a relay to open the PV circuit when the
> ignition is energized. Who'd of thunk that would happen? It's always
> something to
> keep the gray matter going on these GMC's.
> Hal
> --
> 1977 Royale 101348,
>
> 1977 Royale 101586, Diesel powered,
>
> 1975 Eleganza II, 101230,
>
> 1974 Eagle Bus 45',w/slideout,
>
> Rio Rancho, NM
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Try moving the sense line to the engine battery side of the isolator.

> Nothing like the sudden realization that we have just outsmarted ourselves.
> Keeps me humbler than I would otherwise be. Guess I ain't alone. (Grin)
> Jim Hupy
> Salem, Or
> 78 GMC ROYALE 403
>
> On Wed, Nov 28, 2018, 10:09 PM Hal StClair

>
> > I just ran into an interesting issue on our Thanksgiving trip. After
> > replacing a NEW alternator under warranty after little over 1000 miles, I
> > was
> > afraid the replacement was going bad 5000 miles later. The voltage would
> > drop to 11.9 volts and randomly jump to 14+ at times. While observing -12
> > volts a semi truck passed and the voltage popped up to 14+ and seemed to
> > drop as soon as the big rig passed. I noticed the same effect when going
> > under an overpass. It then hit me-the solar panels (280 watts worth) are
> > wired to the house battery bank and the alternator sense wire is
> attached to
> > the same point on the isolator. It seems the voltage from the panels is
> > making the alternator reduce output thinking the battery voltage is
> > satisfied.
> > Guess I'll have to install a relay to open the PV circuit when the
> > ignition is energized. Who'd of thunk that would happen? It's always
> > something to
> > keep the gray matter going on these GMC's.
> > Hal
> > --
> > 1977 Royale 101348,
> >
> > 1977 Royale 101586, Diesel powered,
> >
> > 1975 Eleganza II, 101230,
> >
> > 1974 Eagle Bus 45',w/slideout,
> >
> > Rio Rancho, NM
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--

*John Phillips*
 
I agree with Johnd01, the alternator voltage sense line should be on the engine battery side of the isolator. The 77/78 chassis wiring diagram shows
the voltage sense line connected at the horn relay/buzzer power connection. That puts it after the fusible link after the battery junction block.

--
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
 
Moving the sense wire would eliminate the problem but I'm not willing to sacrifice the battery capacity loss the .6 volt loss the isolator creates. We
do quite a bit of off grid camping an need all the battery we can get. I think a simple relay will make it all better :p . But thanks for the
suggestions.
Hal
--
1977 Royale 101348,

1977 Royale 101586, Diesel powered,

1975 Eleganza II, 101230,

1974 Eagle Bus 45',w/slideout,

Rio Rancho, NM
 
The 0.6volt drop should be the same for both sides of the isolator and if
you think your house batteries are lower than the engine battery you could
turn the relay on between the batteries.

On Thu, Nov 29, 2018 at 8:28 AM Hal StClair
wrote:

> Moving the sense wire would eliminate the problem but I'm not willing to
> sacrifice the battery capacity loss the .6 volt loss the isolator creates.
> We
> do quite a bit of off grid camping an need all the battery we can get. I
> think a simple relay will make it all better :p . But thanks for the
> suggestions.
> Hal
> --
> 1977 Royale 101348,
>
> 1977 Royale 101586, Diesel powered,
>
> 1975 Eleganza II, 101230,
>
> 1974 Eagle Bus 45',w/slideout,
>
> Rio Rancho, NM
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--

*John Phillips*
 
How about moving the sense wire and add a combiner with the isolator?
--
1977 Kingsley 455 as stock as it gets except lots of Ragusa parts
 
If you connect the sensor wire to one side of the isolator it is connected directly to the battery and does not go through a diode so they is no voltage loss. Your alternator charge does go through a diode but the voltage regulator steps up the voltage to provide the voltage at the battery that the sensor circuit demands.

Emery Stora
77 Kingsley
Frederick, CO

>
> How about moving the sense wire and add a combiner with the isolator?
> --
> 1977 Kingsley 455 as stock as it gets except lots of Ragusa parts
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Combining the batteries with the combiner switch didn't make the alternator charge as it still saw the PV voltage. I doubt using a combiner would work
as it accomplishes the same task as the manual switch. The relay would be a much less expensive alternative I'd guess.
Hal
--
1977 Royale 101348,

1977 Royale 101586, Diesel powered,

1975 Eleganza II, 101230,

1974 Eagle Bus 45',w/slideout,

Rio Rancho, NM
 
Hal,
Using the combiner will allow charging of both House and Chassis batteries from either alternator or solar cells automatically.

The alternator voltage sense is a feed-back to the alternator of the battery voltage. The 0.7V drop across the isolator is a non-issue because the
voltage sense line tells the alternator to increase its voltage to offset this loss. There is also a voltage drop in the main wire from the alternator
to the isolator which at high currents may be more than the isolator drop. Again the voltage sense line will compensate for this.

If the solar is outputting more voltage than the alternator's regulator is internally set for, then through its voltage sense line it will back off
its charging rate. Between the two sources I would suspect they would come to a load sharing state depending on how much the solar is producing.
Depending on your solar controller, it should start with a high rate of charge, then back off to a float voltage.

The alternator's regulator is not smart at all. It is set for a float rate voltage but being current limited by the engine speed and the alternator's
internal resistance. This should not be an issue though since your solar controller will back off to a float voltage and with the load of the engine
accessories, I doubt if it will get to its full voltage without the help of the engine alternator.

Just my shade-tree ex farm-boy mechanic with 40 years experience in public safety communications & electronics keeping systems alive at all costs
during power outages through backup and redundant automatic fallback systems... way of seeing things.

But I could be all wrong.

--
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
 
The alternator is " slightly smart" in that all GM alternators are temperature compensating. Fine Voltage trim is inverse to internal regulator temp,
which is an emulation of expected battery temp as weather effects both.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
The solar voltage must be higher than the alternators regulator's set point because it won't charge when sunlight hits the panels directly. The two
sources may come to balance eventually but the engine batteries not being charged until that happens certainly doesn't create a warm fuzzy feeling. I
was reading less than 12 volts during this condition on the engine side. I guess I'm confused with your reference of the voltage drop being a non
issue-if the sense wire is on the engine bank, the house is going to be charged at the reduced rate. The house bank can't get to max voltage in any
reasonable length of time at the reduced charge rate. The sense line is only reading the bank it's connected to for compensation, not the second bank.
What am I missing here?
Hal

> Hal,
> Using the combiner will allow charging of both House and Chassis batteries from either alternator or solar cells automatically.
>
> The alternator voltage sense is a feed-back to the alternator of the battery voltage. The 0.7V drop across the isolator is a non-issue because
> the voltage sense line tells the alternator to increase its voltage to offset this loss. There is also a voltage drop in the main wire from the
> alternator to the isolator which at high currents may be more than the isolator drop. Again the voltage sense line will compensate for this.
>
> If the solar is outputting more voltage than the alternator's regulator is internally set for, then through its voltage sense line it will back
> off its charging rate. Between the two sources I would suspect they would come to a load sharing state depending on how much the solar is producing.
> Depending on your solar controller, it should start with a high rate of charge, then back off to a float voltage.
>
> The alternator's regulator is not smart at all. It is set for a float rate voltage but being current limited by the engine speed and the
> alternator's internal resistance. This should not be an issue though since your solar controller will back off to a float voltage and with the load
> of the engine accessories, I doubt if it will get to its full voltage without the help of the engine alternator.
>
> Just my shade-tree ex farm-boy mechanic with 40 years experience in public safety communications & electronics keeping systems alive at all costs
> during power outages through backup and redundant automatic fallback systems... way of seeing things.
>
> But I could be all wrong.

--
1977 Royale 101348,

1977 Royale 101586, Diesel powered,

1975 Eleganza II, 101230,

1974 Eagle Bus 45',w/slideout,

Rio Rancho, NM
 
"I guess I'm confused with your reference of the voltage drop being a non issue-if the sense wire is on the engine bank, the house is going to be
charged at the reduced rate. The house bank can't get to max voltage in any reasonable length of time at the reduced charge rate. The sense line is
only reading the bank it's connected to for compensation, not the second bank. What am I missing here?"

Hal, the situation you describe could only occur if the ENGINE battery were being charged from another source, the way your house battery is now.
Otherwise, the alternator will work to provide ~14.5V PLUS the 0.6V drop to the center terminal of the isolator. Unless there's a problem (open
diode) in the isolator, this should send ~14.5V to BOTH output terminals, and therefore all the charge the system is capable of supplying.
I'm thinking this may all be moot for your house battery, as your solar panels must have it MORE than fully charged (ie: OVER 14.5V) to cause your
alternator regulator (when sensing the same point your panels are feeding) to cut alternator output to essentially nothing. Do you have a functioning
voltage regulator on your solar system? Are you sure the isolator is good?
Remember, the alternator's regulator controls ONLY voltage, unlike with the old generator vehicles. Alternators are self-limitting for current.

HTH,
Rick Staples
--
Rick Staples, '75 Eleganza, Johnstown, CO

"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien
 
The alternator will charge the lower voltage battery no matter which side
the sense line is tied to.
You need a charge controller for the solar to be safe.

On Fri, Nov 30, 2018 at 11:13 PM Richard H Staples
wrote:

> "I guess I'm confused with your reference of the voltage drop being a non
> issue-if the sense wire is on the engine bank, the house is going to be
> charged at the reduced rate. The house bank can't get to max voltage in
> any reasonable length of time at the reduced charge rate. The sense line is
> only reading the bank it's connected to for compensation, not the second
> bank. What am I missing here?"
>
> Hal, the situation you describe could only occur if the ENGINE battery
> were being charged from another source, the way your house battery is now.
> Otherwise, the alternator will work to provide ~14.5V PLUS the 0.6V drop
> to the center terminal of the isolator. Unless there's a problem (open
> diode) in the isolator, this should send ~14.5V to BOTH output terminals,
> and therefore all the charge the system is capable of supplying.
> I'm thinking this may all be moot for your house battery, as your solar
> panels must have it MORE than fully charged (ie: OVER 14.5V) to cause your
> alternator regulator (when sensing the same point your panels are feeding)
> to cut alternator output to essentially nothing. Do you have a functioning
> voltage regulator on your solar system? Are you sure the isolator is good?
> Remember, the alternator's regulator controls ONLY voltage, unlike with
> the old generator vehicles. Alternators are self-limitting for current.
>
> HTH,
> Rick Staples
> --
> Rick Staples, '75 Eleganza, Johnstown, CO
>
> "Advice is a dangerous gift, even from the Wise to the Wise, and all paths
> may run ill." -Tolkien
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--

*John Phillips*
 
Put the sense line back where it belongs on the engine side and be done with it. The sense line is simply to tell the alternator to raise or lower
the voltage to make up for any loss in the circuit (including the isolator loss). There is not need for added combiners, relays, etc.

You are worrying about and trying to engineer around something that is not a problem to start with.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
> Put the sense line back where it belongs on the engine side and be done with it. The sense line is simply to tell the alternator to raise or
> lower the voltage to make up for any loss in the circuit (including the isolator loss). There is not need for added combiners, relays, etc.
>
> You are worrying about and trying to engineer around something that is not a problem to start with.

Hal,

I am completely inline with KenB on this, and if you want to stop worrying about it, after you put the alternators sense lead back where it should be,
then move the pick-up point for you system voltmeter to where it should really be and that would be the main engine system supply line anywhere.
First thought would be the downstream side of the fusible link. Now it will be reading the system and that is really all you should be concerned
with.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
As long as current is generated it will go to the lower voltage battery. If
the chassis battery voltage is less than the regulator setpoint current
will be generated.

> > Put the sense line back where it belongs on the engine side and be done
> with it. The sense line is simply to tell the alternator to raise or
> > lower the voltage to make up for any loss in the circuit (including the
> isolator loss). There is not need for added combiners, relays, etc.
> >
> > You are worrying about and trying to engineer around something that is
> not a problem to start with.
>
> Hal,
>
> I am completely inline with KenB on this, and if you want to stop worrying
> about it, after you put the alternators sense lead back where it should be,
> then move the pick-up point for you system voltmeter to where it should
> really be and that would be the main engine system supply line anywhere.
> First thought would be the downstream side of the fusible link. Now it
> will be reading the system and that is really all you should be concerned
> with.
>
> Matt
> --
> Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> Electronically Controlled Quiet Engine Cooling Fan
> OE Rear Drum Brakes with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--

*John Phillips*
 
There is no consensus on which is the 'right' side of the isolator to place the sense wire, especially in the water vessel world as Matt must surely
be aware. Some of us prefer to get the most out of our batteries and charging at the correct rates is a must for this to happen. Trojan specs 14.8
volts for bulk charging where most all solar chargers have default settings of 14.4 volts as an example. I use a Blue Sky MPPT solar charge controller
that is programmable and so set. The 160 amp alternator 's sense wire is doing just what it's designed to do and throttling back the charge when
sensing the solar voltage of 14.8. Interrupting the solar voltage at the sense wire will permit everything to work as designed. A simple relay will
accomplish this, not a big deal.
Oh, and thanks for the youtube Electricity 101. Guess I missed something in my 40 years in the trade.Blush
Hal
--
1977 Royale 101348,

1977 Royale 101586, Diesel powered,

1975 Eleganza II, 101230,

1974 Eagle Bus 45',w/slideout,

Rio Rancho, NM
 
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