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| Is 16 volts from alternator at start up too high? [message #238116] |
Thu, 30 January 2014 13:42  |
Otterwan
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After sitting for awhile I started up the Twinkie II. With the engine idling high the alternator was putting out between 16- 16.5 volts. After it warmed up it settled in around 14.7 at idle, which is more what I would expect. The batteries are on a maintainer so they were fully charge before starting.
This voltage at startup seems a bit high to me. Should I be concerned?
And yes, I do have the APC installed ;o)
1977 Birchaven, Lynnwood WA - "We may not be able to stop all evil in the world, but I know that how we treat one another is entirely up to us."
[Updated on: Thu, 30 January 2014 17:03] Report message to a moderator |
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| Re: Is 16 volts from alternator at start up too high? [message #238145 is a reply to message #238129] |
Thu, 30 January 2014 17:11  |
Ken Burton
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Registered: January 2004
Location: Hebron, Indiana
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It is my opinion that reconnecting the house battery will not fix your issue. It may mask it by initially loading down the alternator so it can not go that high .
For an alternator to go that high, you have one of two problems 1. The regulator is defective or 2. The sense line going to the alternator is sensing low voltage and the alternator is trying to make up for the low sensed voltage.
I would not ignore this symptom after reconnecting the house battery(s) as I believe it can only get worse.
I would immediately install an APC if you do not have one. I would move the voltmeter to the alternator sense line and see how it is acting when you first start the MH cold. If you have two voltmeters I would leave the first one where it is to observe when it is failing and watch the sense line with a second line.
When starting cold I would remove as much load from the alternator as possible (heater fan, lights, house battery, etc.) The alternator should regulate it's voltage under all loads. If it is not doing it, then go looking for the problem because next time it might be 30 or 40 volts.
I had a regulator go bad one time in an airplane while flying home a night. I do not when it started to but near Milwaukee it finally boiled the battery dry and really went way over voltage. It blew every light that was on in the plane and fried two radios. I ended up flying home down the Chicago lake front with no lights, no radios, and only a flash light to see the remaining operating instruments.
After fixing all of the damage, I installed a crowbar circuit on the alternator set to 15 volts. If the voltage ever reached 15 volts, it fired an SCR which took out the circuit breaker in the alternator field and shut down the alternator.
On a GMC the failure can cause similar problems to anything that is turned on at the time. I know of one guy the burned up a 12 volt refrigerator and a few house light bulbs with a similar failure. Of course we all know about burning the dash wiring with similar failures.
Find the problem and fix it BEFORE it gets worse.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Is 16 volts from alternator at start up too high? [message #238147 is a reply to message #238145] |
Thu, 30 January 2014 17:31 |
Otterwan
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Thanks Ken. I'll check again tomorrow, but the house battery shouldn't have been applying a load as it is new and was fully charged using a battery minder. It makes sense to me that if the isolator see nothing (and perceives it as a low or dead battery) the alternator would work really had to charge it.
1977 Birchaven, Lynnwood WA - "We may not be able to stop all evil in the world, but I know that how we treat one another is entirely up to us."
[Updated on: Thu, 30 January 2014 17:34] Report message to a moderator |
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| Re: Is 16 volts from alternator at start up too high? [message #238154 is a reply to message #238116] |
Thu, 30 January 2014 17:59 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
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Where are you metering? If at center of isolator and it's very cold out It's probably ok. GM regulators emulate battery temp to adjust set point and it is cold out. Remeter at outside terminal after it warms up a bit and 14.2 would be nice gor a value.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Is 16 volts from alternator at start up too high? [message #238167 is a reply to message #238147] |
Thu, 30 January 2014 22:08 |
Ken Burton
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The isolator is nothing more than two diodes. It has no ability to sense anything. If the voltage is higher on one side (the center terminal) than on the other sides (top and bottom terminals) it will allow current to flow. That is it. It has no intelligence and does not sensing for the alternator.
If the initial voltage is high I would suspect sense line and the circuit to the regulator built into the alternator. This includes the engine side of the isolator, the fusible link, and any connection in the circuit from the the isolator on to the sense to the sense line. It You have not given us the reading onthe upper and lower terminals of the isolator but at 16 volts in they should be 15.3 out. That is a bit much to be putting in to any 12 volt device. Usually most excess voltage is absorbed by the battery for the short term. After that anything over 14.4 will gas (boil) the battery.
It is true that some / most GM regulators do temperature compensate. I closely monitor the voltage on my Colorado which has no regulator but is instead is computer controlled by the BCM. Cold at -15 it will make the alternator to go as high as 14.4 volts. As the under hood temperature warms up, the BCM cuts the voltage back to 13.8 to 14.0. In 100 degree weather I have seen it cut the voltage down as low as 13.4. Keep in mind that it is much hotter than that under the hood. Honda on many of their smaller engine models, computer control the alternator by adding something called an ELD (Electronic Load Detector). They reduce the voltage based on temperature and also even sooner when the computer thinks the battery is charged. They do this to enhance gas mileage. While the GMC alternator is not computer controlled, it is temperature compensated and should follow a similar voltage curve based on temperature.
So until you do some additional problem determination by looking at the voltages on the load side of isolator and the sense line, I would keep a close eye on that alternator output. Something is changing with temperature. There is a good chance it is the isolator, regulator, or fusible link, and that the problem, in my opinion, will get worse over time.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Is 16 volts from alternator at start up too high? [message #238251 is a reply to message #238167] |
Fri, 31 January 2014 17:27 |
Otterwan
Messages: 946
Registered: July 2013
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| Ken Burton wrote on Thu, 30 January 2014 20:08 |
The isolator is nothing more than two diodes. It has no ability to sense anything. If the voltage is higher on one side (the center terminal) than on the other sides (top and bottom terminals) it will allow current to flow. That is it. It has no intelligence and does not sensing for the alternator.
If the initial voltage is high I would suspect sense line and the circuit to the regulator built into the alternator. This includes the engine side of the isolator, the fusible link, and any connection in the circuit from the the isolator on to the sense to the sense line. It You have not given us the reading onthe upper and lower terminals of the isolator but at 16 volts in they should be 15.3 out. That is a bit much to be putting in to any 12 volt device. Usually most excess voltage is absorbed by the battery for the short term. After that anything over 14.4 will gas (boil) the battery.
It is true that some / most GM regulators do temperature compensate. I closely monitor the voltage on my Colorado which has no regulator but is instead is computer controlled by the BCM. Cold at -15 it will make the alternator to go as high as 14.4 volts. As the under hood temperature warms up, the BCM cuts the voltage back to 13.8 to 14.0. In 100 degree weather I have seen it cut the voltage down as low as 13.4. Keep in mind that it is much hotter than that under the hood. Honda on many of their smaller engine models, computer control the alternator by adding something called an ELD (Electronic Load Detector). They reduce the voltage based on temperature and also even sooner when the computer thinks the battery is charged. They do this to enhance gas mileage. While the GMC alternator is not computer controlled, it is temperature compensated and should follow a similar voltage curve based on temperature.
So until you do some additional problem determination by looking at the voltages on the load side of isolator and the sense line, I would keep a close eye on that alternator output. Something is changing with temperature. There is a good chance it is the isolator, regulator, or fusible link, and that the problem, in my opinion, will get worse over time.
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Ken, took your advice. Pulled the alternator, ran it over to NAPA, at 2500 RPM they got 18.2 volts! So new alternator ordered, install tomorrow, back on the road in less than 24 hours. Thanks again for the advice - Dave
1977 Birchaven, Lynnwood WA - "We may not be able to stop all evil in the world, but I know that how we treat one another is entirely up to us."
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| Re: [GMCnet] Is 16 volts from alternator at start up too high? [message #238261 is a reply to message #238251] |
Fri, 31 January 2014 18:02 |
Mr ERFisher
Messages: 7117
Registered: August 2005
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Should get rebuilt not from maps
FREE WIFI @ Mickey D
On Jan 31, 2014, at 3:27 PM, David Orders <dao@oarsllc.com> wrote:
>
>
> Ken Burton wrote on Thu, 30 January 2014 20:08
>> The isolator is nothing more than two diodes. It has no ability to sense anything. If the voltage is higher on one side (the center terminal) than on the other sides (top and bottom terminals) it will allow current to flow. That is it. It has no intelligence and does not sensing for the alternator.
>>
>> If the initial voltage is high I would suspect sense line and the circuit to the regulator built into the alternator. This includes the engine side of the isolator, the fusible link, and any connection in the circuit from the the isolator on to the sense to the sense line. It You have not given us the reading onthe upper and lower terminals of the isolator but at 16 volts in they should be 15.3 out. That is a bit much to be putting in to any 12 volt device. Usually most excess voltage is absorbed by the battery for the short term. After that anything over 14.4 will gas (boil) the battery.
>>
>> It is true that some / most GM regulators do temperature compensate. I closely monitor the voltage on my Colorado which has no regulator but is instead is computer controlled by the BCM. Cold at -15 it will make the alternator to go as high as 14.4 volts. As the under hood temperature warms up, the BCM cuts the voltage back to 13.8 to 14.0. In 100 degree weather I have seen it cut the voltage down as low as 13.4. Keep in mind that it is much hotter than that under the hood. Honda on many of their smaller engine models, computer control the alternator by adding something called an ELD (Electronic Load Detector). They reduce the voltage based on temperature and also even sooner when the computer thinks the battery is charged. They do this to enhance gas mileage. While the GMC alternator is not computer controlled, it is temperature compensated and should follow a similar voltage curve based on temperature.
>>
>> So until you do some additional problem determination by looking at the voltages on the load side of isolator and the sense line, I would keep a close eye on that alternator output. Something is changing with temperature. There is a good chance it is the isolator, regulator, or fusible link, and that the problem, in my opinion, will get worse over time.
>
>
> Ken, took your advice. Pulled the alternator, ran it over to NAPA, at 2500 RPM they got 18.2 volts! So new alternator ordered, install tomorrow, back on the road in less than 24 hours. Thanks again for the advice - Dave
> --
> 1976 Royale "Twinkie II", 1978 Palm Beach with front end fire. Lynnwood WA - "We may not be able to stop all evil in the world, but I know that how we treat one another is entirely up to us."
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| Re: Is 16 volts from alternator at start up too high? [message #238266 is a reply to message #238251] |
Fri, 31 January 2014 18:30 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
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I'm happy that you found it before it burned up something. I do not know if you ever said it or not, but if you do now have an APC on that alternator, now is a great time to install it.
I wish I had caught you before you got the new alternator. I would have suggested that you get the 100 amp Cadillac one. It looks the same as yours only they put 100 amp windings in it rather than the 80 amp ones.
I replaced mine with a 100 amp one not because it was bad but because I had an engine fire and the insurance company was paying for it.
Also I do not know the warranty period on NAPA ones but the AutoZone warranty is lifetime. I never expect to need to use it but if I ever need another one there are AutoZones everywhere.
I disassembled the new one I got form AZ and everything inside was new. I think the only thing they reused during the rebuild was the case. Also at the time I had AZ swap the single pulley on the front for a double one.
These are all just ideas. What you did was also fine.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Is 16 volts from alternator at start up too high? [message #238269 is a reply to message #238266] |
Fri, 31 January 2014 18:37 |
Otterwan
Messages: 946
Registered: July 2013
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I've had the APC for quite some time. The NAPA 13-4022 80 amp has all new parts (not just the bad ones) and a lifetime guarantee. I'm happy with that for now.
1977 Birchaven, Lynnwood WA - "We may not be able to stop all evil in the world, but I know that how we treat one another is entirely up to us."
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| Re: Is 16 volts from alternator at start up too high? [message #238278 is a reply to message #238266] |
Fri, 31 January 2014 19:10 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
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| Ken Burton wrote on Fri, 31 January 2014 17:30 |
I'm happy that you found it before it burned up something. I do not know if you ever said it or not, but if you do now have an APC on that alternator, now is a great time to install it.
I wish I had caught you before you got the new alternator. I would have suggested that you get the 100 amp Cadillac one. It looks the same as yours only they put 100 amp windings in it rather than the 80 amp ones.
I replaced mine with a 100 amp one not because it was bad but because I had an engine fire and the insurance company was paying for it.
Also I do not know the warranty period on NAPA ones but the AutoZone warranty is lifetime. I never expect to need to use it but if I ever need another one there are AutoZones everywhere.
I disassembled the new one I got form AZ and everything inside was new. I think the only thing they reused during the rebuild was the case. Also at the time I had AZ swap the single pulley on the front for a double one.
These are all just ideas. What you did was also fine.
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I've been using the 100 amp Autozone unit as well but haven't had quite as good luck as you have. I think I am on my 3rd (possibly 4th) unit but am still a satisfied customer. It's easy enough to replace and there are never any questions. The last time (a few months ago) I did have to hunt for one in stock, so I think they are becoming somewhat obsolete. I suspect my 2 battery banks that need charging after boondocking, may be increasing the load factor more than usual. Regardless it's a good alternative.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: Is 16 volts from alternator at start up too high? [message #238314 is a reply to message #238278] |
Fri, 31 January 2014 22:11 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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| Bob de Kruyff wrote on Fri, 31 January 2014 19:10 |
I've been using the 100 amp Autozone unit as well but haven't had quite as good luck as you have. I think I am on my 3rd (possibly 4th) unit but am still a satisfied customer. It's easy enough to replace and there are never any questions. The last time (a few months ago) I did have to hunt for one in stock, so I think they are becoming somewhat obsolete. I suspect my 2 battery banks that need charging after boondocking, may be increasing the load factor more than usual. Regardless it's a good alternative.
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Dan also had some problems with AutoZone alternators. He went through a couple of them.
I think it was those apple computers that he is using causing the problems.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Is 16 volts from alternator at start up too high? [message #238319 is a reply to message #238278] |
Fri, 31 January 2014 23:18 |
sgltrac
Messages: 2797
Registered: April 2011
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If you go to a 100 amp alternator make sure you have a 100 amp isolator or you might burn up the isolator and then the alternator. Think that's what I did. Happy the alt had lifetime warranty.
Todd Sullivan
Sully
77 royale
Seattle
> On Jan 31, 2014, at 5:10 PM, Bob de Kruyff <NEXT2POOL@AOL.COM> wrote:
>
>
>
> Ken Burton wrote on Fri, 31 January 2014 17:30
>> I'm happy that you found it before it burned up something. I do not know if you ever said it or not, but if you do now have an APC on that alternator, now is a great time to install it.
>>
>> I wish I had caught you before you got the new alternator. I would have suggested that you get the 100 amp Cadillac one. It looks the same as yours only they put 100 amp windings in it rather than the 80 amp ones.
>>
>> I replaced mine with a 100 amp one not because it was bad but because I had an engine fire and the insurance company was paying for it.
>>
>> Also I do not know the warranty period on NAPA ones but the AutoZone warranty is lifetime. I never expect to need to use it but if I ever need another one there are AutoZones everywhere.
>>
>> I disassembled the new one I got form AZ and everything inside was new. I think the only thing they reused during the rebuild was the case. Also at the time I had AZ swap the single pulley on the front for a double one.
>>
>> These are all just ideas. What you did was also fine.
>
>
> I've been using the 100 amp Autozone unit as well but haven't had quite as good luck as you have. I think I am on my 3rd (possibly 4th) unit but am still a satisfied customer. It's easy enough to replace and there are never any questions. The last time (a few months ago) I did have to hunt for one in stock, so I think they are becoming somewhat obsolete. I suspect my 2 battery banks that need charging after boondocking, may be increasing the load factor more than usual. Regardless it's a good alternative.
> --
> Bob de Kruyff
> 78 Eleganza
> Chandler, AZ
> _______________________________________________
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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| Re: Is 16 volts from alternator at start up too high? [message #238332 is a reply to message #238251] |
Sat, 01 February 2014 04:35 |
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Loffen
Messages: 1087
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Location: Norway
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| Otterwan wrote on Sat, 01 February 2014 00:27 |
Ken, took your advice. Pulled the alternator, ran it over to NAPA, at 2500 RPM they got 18.2 volts! So new alternator ordered, install tomorrow, back on the road in less than 24 hours. Thanks again for the advice - Dave
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Why order a new one ? it is pretty easy to rebuild it, you get complete rebuild kits for $ 25-30.
If you still have the old one, I would have given it a try, nice weekend project and you would have a good spare on the shelf.
1973 23' # 1848 Sky Blue Glacier called Baby Blue and a 1973 26'-3 # 1460 Parrot green Seqouia Known as the Big Green,
And sold my 1973 26'-2 # 581 White Canyon lands under the name Dobbelt trøbbel
in Norway
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| Re: [GMCnet] Is 16 volts from alternator at start up too high? [message #238355 is a reply to message #238319] |
Sat, 01 February 2014 09:24 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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""If you go to a 100 amp alternator make sure you have a 100 amp isolator or you might burn up the isolator and then the alternator. Think that's what I did. Happy the alt had lifetime warranty.
Todd Sullivan
Sully
77 royale
Seattle
""
Good point.
No isolator here. I use a relay powered by the run side of the ignition to connect the banks when the engine is running.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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