| Understanding alternator [message #280444] |
Sun, 21 June 2015 14:21  |
appie
Messages: 902
Registered: April 2013
Location: denmark
Karma: 2
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Senior Member |
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My favoret hobby: trying to understand all the bits and pieces of my gmc
I have this idear that the alternator is not charging my house batterie as good as should be. I had this feeling for a long time
I have a smart combiner cyrix. And I just installed a victron bm 700 batterie monitor
The batteri was down 60Ah when I started the engine. House batteries were charged initially with 18 A. On idle. Then I drove of had my light on and drove for 2 hours. That only charged my house batteries with 10 Ah
Now I try to understand what happens with the alternator. It has the sensor to the + distribution point. Now does the alternator stop charging when the starter batteri reaches a certain voltage ? Thus not charging the house batterie? Or is there just to little left with lights on etc to charge the house? No aircon, no invertor running. Fridge on 12 volts
Does a alternator loose power when it gets old?
Is a100 A alternator a straight swap ?
Thank you
Appie
eleganza 76 "Olga" now sadly sold
6 wheel discbrake
Quadrabags
Springfield stage 2 462 olds
Manny tranny
( pictures at http://www.gmcmhphotos.com/photos/g6489-olga.html
Fulltiming in Europe july 2014 til july 2016
Denmark
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| Re: Understanding alternator [message #280448 is a reply to message #280444] |
Sun, 21 June 2015 14:48  |
A Hamilto
Messages: 4508
Registered: April 2011
Karma: 39
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Senior Member |
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appie wrote on Sun, 21 June 2015 14:21My favoret hobby: trying to understand all the bits and pieces of my gmc
I have this idear that the alternator is not charging my house batterie as good as should be. I had this feeling for a long time
I have a smart combiner cyrix. And I just installed a victron bm 700 batterie monitor
The batteri was down 60Ah when I started the engine. House batteries were charged initially with 18 A. On idle. Then I drove of had my light on and drove for 2 hours. That only charged my house batteries with 10 Ah
Now I try to understand what happens with the alternator. It has the sensor to the + distribution point. Now does the alternator stop charging when the starter batteri reaches a certain voltage ? Thus not charging the house batterie? Or is there just to little left with lights on etc to charge the house? No aircon, no invertor running. Fridge on 12 volts
Does a alternator loose power when it gets old?
Is a100 A alternator a straight swap?
Thank you The OEM isolator should charge better than that if working. Think of it this way. The alternator is sensing the chassis battery after the 0.7V drop across the diode in the isolator. The house battery SHOULD be at the identical voltage. They both see the same voltage, so if the house battery is more discharged than the chassis battery, more of the alternator current should flow into it than is flowing into the chassis battery, and it SHOULD get to the same voltage as the chassis battery.
I don't know if 2 hours is enough to charge it, but I would think it should be better than what you are describing...
Alternators normally fail pretty hard, not gradually getting "weak". Corroded and loose connectors are your enemy.
I know nothing about combiners, but maybe they limit the current more than the OEM isolator (the only current limit in the OEM system is the alternator itself).
I think the right 100A alternator is a direct bolt-in, but there might be different electrical connectors involved. I was looking at bigger alternators at one time, and I found it is possible to acquire up to 300A alternators that will bolt up, the complication was that at some point the electrical connector had to be changed out.
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| Re: Understanding alternator [message #280452 is a reply to message #280444] |
Sun, 21 June 2015 15:12 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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The 100 amp alternator is a direct bolt in for the OEM 80 amp alternator.
If you are running an isolator the alternator will run around 14.5 to 15.2 volts INTO the isolator and 13.8 to 14.2 out of the isolator and at BOTH batteries. If you are running a combiner you will see 13.8 to 14.2 at the alternator and at both batteries.
The rate that the batteries charge is NOT determined by the alternator. It is determined by the batteries themselves as long as the battery terminal voltage is in the 13.8 to 14.2 range. If the voltage is low under higher amperage loads, I would first check the alternator belt to see if it is slipping.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Understanding alternator [message #280453 is a reply to message #280452] |
Sun, 21 June 2015 15:37 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Lenze, the alternator output current goes from the output lug to the center
tap on the isolator. The diodes extract a .5 to.7 volt toll for their part
in the system. So, if your charge voltage from the alternator is 14.7
volts, by the time it exits the Isolator toll booth, it is less than that
by .5 to.7 volts. That is the amount of voltage delivered a short distance
away to the engine battery. If your house battery(s) are as close as the
engine battery, their charge voltage will be very close to what the engine
battery receives. If they are located 25 feet away in the generator
compartment, there will be a further voltage drop depending upon the
resistance of the conductors that carry the voltage to the rear of the
coach. A wet cell battery in an ideal state of charge has the potential of
2.2 volts per cell. 2.2 x 6 = 13.2 volts. You will very seldom see that
voltage because of a variety of conditions. As the charging voltage enters
the battery, the voltage needs to exceed that ideal state, or no electrons
will flow. That is why the output voltage of the alternator has to exceed
the ideal state, plus enough extra to overcome the resistance in the
circuit. That force is known as Counter electro motive force, or CEMF for
short. Amps don't mean much when charging is concerned. One ampere of
current is equal to 1 billion billion electrons per second of time flowing
at the rate of 186,000 miles per second. When you start your GMC and draw
300 amps of current for 15 seconds, that number of electrons have to be
replaced by the alternator to get the battery back to ideal state. Simple,
no? Electricity 101 dismissed for the day.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Sun, Jun 21, 2015 at 1:12 PM, Ken Burton wrote:
> The 100 amp alternator is a direct bolt in for the OEM 80 amp alternator.
>
> If you are running an isolator the alternator will run around 14.5 to 15.2
> volts INTO the isolator and 13.8 to 14.2 out of the isolator and at BOTH
> batteries. If you are running a combiner you will see 13.8 to 14.2 at the
> alternator and at both batteries.
>
> The rate that the batteries charge is NOT determined by the alternator.
> It is determined by the batteries themselves as long as the battery terminal
> voltage is in the 13.8 to 14.2 range. If the voltage is low under higher
> amperage loads, I would first check the alternator belt to see if it is
> slipping.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
> _______________________________________________
> GMCnet mailing list
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| Re: [GMCnet] Understanding alternator [message #280456 is a reply to message #280444] |
Sun, 21 June 2015 16:07 |
Daniel Starks
Messages: 20
Registered: April 2015
Karma: 0
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Junior Member |
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One step at a time. The cyrix unit connects the two batteries together
with a relay so there should be no voltage difference between them. If a
load on either battery drags the combined voltage down, the relay opens
so that the load will not discharge both batteries. If the voltage on
either battery increases enough to indicate it is being charged, the
cyrix unit connects them back together again.
Notice that connecting them together results in immediately bringing
them to the same voltage, often by discharging one battery into the
other. This can show a high charge rate for the lower voltage battery.
The alternator should be putting out about 14 volts, unless this voltage
is being limited because of high charge current. So if you measure 14
volts the charger is doing it's job.
Batteries that are well discharged have a low voltage, this causes the
charger to deliver a lot of current. As the battery voltage rises, the
charge process takes longer. This is not a problem, just a fact of
life.
Two hours of driving giving 10AH is 5 amps per hour, or just plain 5A
charging rate. If the house battery is almost fully charged this is
quite reasonable.
Bottom line, if the alternator can maintain 14 volts it is doing fine.
The batteries are just not that hungry.
Daniel
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of
lenze middelberg
Sent: Sunday, June 21, 2015 1:21 PM
To: gmclist@temp.gmcnet.org
Subject: [GMCnet] Understanding alternator
My favoret hobby: trying to understand all the bits and pieces of my
gmc
I have this idear that the alternator is not charging my house batterie
as good as should be. I had this feeling for a long time I have a smart
combiner cyrix. And I just installed a victron bm 700 batterie monitor
The batteri was down 60Ah when I started the engine. House batteries
were charged initially with 18 A. On idle. Then I drove of had my light
on and drove for 2 hours. That only charged my house batteries with 10
Ah
Now I try to understand what happens with the alternator. It has the
sensor to the + distribution point. Now does the alternator stop
charging when
the starter batteri reaches a certain voltage ? Thus not charging the
house batterie? Or is there just to little left with lights on etc to
charge
the house? No aircon, no invertor running. Fridge on 12 volts
Does a alternator loose power when it gets old?
Is a100 A alternator a straight swap ?
Thank you
--
Appie
eleganza 76 "Olga" ( pictures at
http://www.gmcmhphotos.com/photos/g6489-olga.html
Fulltiming in Europe since july 1 2014
Denmark
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| Re: Understanding alternator [message #280468 is a reply to message #280444] |
Sun, 21 June 2015 20:12 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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This situation is why I have two (2) ammeters in my coach, one for each battery. I've a solar charging system for the house battery, so at startup I expect to see very little current headed for it, but substantial to the chassis battery for about a minute which tapers off as the starting energy is replaced. I am so seldom away from either a running engine or shore power that the house battery has little to do. It keeps the icebox going at fuel stops is about the extent of it.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: Understanding alternator [message #280474 is a reply to message #280444] |
Mon, 22 June 2015 08:32 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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I would disconnect the combiner, set your meter to 00.0scale and run engine at fast idle. Cold you should have 14.20 at the outer 2 isolator terminals. The center will read about .7 higher. As things heat up in the engine compartment voltage will taper down to 13.8 or so to the battery as the regulator senses voltage and corrects for temperature. I would also meter at both batteries to check for voltage drop due to poor connections. Once you prove the isolator is 100% you can add the combiner across it. There is SOME slight voltage drop across the isolator at higher Ampere drawns due to the series current limiting of it's wire leads to protect the relay. This may vary with size rating and Mfg. The sense is on the engine batt side. More current will flow to the battery side needing more charge demand at that voltage.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Understanding alternator [message #280478 is a reply to message #280477] |
Mon, 22 June 2015 08:41 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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Read here
Link might help😀
http://gmc49ers.blogspot.com/2014/03/check-your-battery-system-through-your.html
On Monday, June 22, 2015, gene Fisher wrote:
> Or
> Read here !
>
> On Monday, June 22, 2015, John R. Lebetski > wrote:
>
>> I would disconnect the combiner, set your meter to 00.0scale and run
>> engine at fast idle. Cold you should have 14.20 at the outer 2 isolator
>> terminals. The center will read about .7 higher. As things heat up in
>> the engine compartment voltage will taper down to 13.8 or so to the battery
>> as
>> the regulator senses voltage and corrects for temperature. I would also
>> meter at both batteries to check for voltage drop due to poor connections.
>> Once you prove the isolator is 100% you can add the combiner across it.
>> There is SOME slight voltage drop across the isolator at higher Ampere
>> drawns
>> due to the series current limiting of it's wire leads to protect the
>> relay. This may vary with size rating and Mfg. The sense is on the engine
>> batt
>> side. More current will flow to the battery side needing more charge
>> demand at that voltage.
>> --
>> John Lebetski
>> Woodstock, IL
>> 77 Eleganza II
>> Source America First
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>
>
>
> --
> Gene Fisher -- 74-23,77PB/ore/ca
> “Give a man a fish; you have fed him for today --- give him a URL and
> -------
> http://gmcmotorhome.info/
> Alternator Protection Cable
> http://gmcmotorhome.info/APC.html
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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