What voltage is too high?
#53944
02/18/08 07:31 PM
02/18/08 07:31 PM
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Joined: Jul 2003
Posts: 1,869
Carmichael, CA
NotEnufGarage
OP
top fuel
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OP
top fuel
Joined: Jul 2003
Posts: 1,869
Carmichael, CA
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I think I'm having a charging system issue in my Li'l Red Express. It's measuring 14.8V - 15.0V at the battery. I've tried 3 different regulators (2 new), 2 different alternators (original and a 100A chrome that I had laying around) and 2 different batteries.
I have the ammeter bypassed (red and black tied together and insulated behind gauges) and I have a direct feed from the alternator to the starter relay battery post to minimize current running through the bulkhead connectors. Also, the headlights are on relays.
With the engine idling around 750RPM, I'm getting 14.8 - 15 at the alternator. The red field wire measures 14.4V and the light green measures between 8.8 - 9.2V. When I disconnect either field wire the alternator battery post measures about 12.4V.
I've check the voltages at the igition switch connector and they're all around 14.5V. Same on the bulkhead connector.
Is 15V too high, or should I just live with it? I always thought 13.8 - 14.1V was what I should be getting.
Any suggestions?
Thanks!
'70 Charger FE5 Daytona Clone 451/727/D60
'70 Challenger FM3 440/833/3.55SG
'79 Ramcharger SE 360
'89 Shelby Dakota
‘06 PT Cruiser GT Convertible
‘07 Charger R/T Daytona
‘10 Ram 1500 ST Crew Cab
Yes, I'm a Dodge Boy. Verstehen?
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Re: What voltage is too high?
[Re: NotEnufGarage]
#53948
02/18/08 08:19 PM
02/18/08 08:19 PM
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Joined: Dec 2003
Posts: 5,314
Carstairs, Alberta, Canada
dave571
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master
Joined: Dec 2003
Posts: 5,314
Carstairs, Alberta, Canada
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I wouldn't be afraid to run 14.8 , but it is a tad high. Looking at your voltage readngs, you see 14.5 in a lot of places, except at the battery. What is likely going on, is that there is a voltage drop (resistance) between the ignition switch, and the voltage reg. The reg thinks it is regulating at 14.5, because that is what it is seeing. But in reality the voltage on the system is higher. You can go digging through the 30 year old harness for the drop(or likely multiple drops of around .1 or .2 each). You may find them. OR What I normally do when I get a car like this, is I use the existing voltage supply/ign wire on the regulator to turn on a relay that is wired to direct battery voltage(straight to the positive terminal of the battery). Then the regulator sees actual system voltage, instead of the dropped down voltage through the harness. Takes about half an hour to wire up, and cost less than 10 bucks. Hope this helps 
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Re: What voltage is too high?
[Re: dave571]
#53949
02/18/08 08:23 PM
02/18/08 08:23 PM
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Joined: Jan 2004
Posts: 27,347
Today? Who Knows?
1_WILD_RT
Management Trainee
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Management Trainee
Joined: Jan 2004
Posts: 27,347
Today? Who Knows?
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Quote:
I wouldn't be afraid to run 14.8 , but it is a tad high.
Looking at your voltage readngs, you see 14.5 in a lot of places, except at the battery.
What is likely going on, is that there is a voltage drop (resistance) between the ignition switch, and the voltage reg. The reg thinks it is regulating at 14.5, because that is what it is seeing. But in reality the voltage on the system is higher.
You can go digging through the 30 year old harness for the drop(or likely multiple drops of around .1 or .2 each). You may find them.
OR
What I normally do when I get a car like this, is I use the existing voltage supply/ign wire on the regulator to turn on a relay that is wired to direct battery voltage(straight to the positive terminal of the battery). Then the regulator sees actual system voltage, instead of the dropped down voltage through the harness.
Takes about half an hour to wire up, and cost less than 10 bucks.
Hope this helps
Good shortcut.. 
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Re: What voltage is too high?
[Re: dave571]
#53950
02/18/08 08:41 PM
02/18/08 08:41 PM
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Joined: Jul 2003
Posts: 1,869
Carmichael, CA
NotEnufGarage
OP
top fuel
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OP
top fuel
Joined: Jul 2003
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Carmichael, CA
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Thanks.. I'll be heading out to find a relay shortly.
'70 Charger FE5 Daytona Clone 451/727/D60
'70 Challenger FM3 440/833/3.55SG
'79 Ramcharger SE 360
'89 Shelby Dakota
‘06 PT Cruiser GT Convertible
‘07 Charger R/T Daytona
‘10 Ram 1500 ST Crew Cab
Yes, I'm a Dodge Boy. Verstehen?
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Re: What voltage is too high?
[Re: dave571]
#53952
02/18/08 08:54 PM
02/18/08 08:54 PM
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Joined: Nov 2004
Posts: 25,050
Texas
GoodysGotaCuda
5.7L Hemi, 6spd
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5.7L Hemi, 6spd
Joined: Nov 2004
Posts: 25,050
Texas
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Quote:
What I normally do when I get a car like this, is I use the existing voltage supply/ign wire on the regulator to turn on a relay that is wired to direct battery voltage(straight to the positive terminal of the battery). Then the regulator sees actual system voltage, instead of the dropped down voltage through the harness.
Thats exactly how my v/r is wired up as well. Except its to my starter relay since my batt is in the trunk.Alt output feeds directly to the batt back there
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Re: What voltage is too high?
[Re: NotEnufGarage]
#53956
02/21/08 05:05 PM
02/21/08 05:05 PM
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Joined: Jul 2003
Posts: 1,869
Carmichael, CA
NotEnufGarage
OP
top fuel
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OP
top fuel
Joined: Jul 2003
Posts: 1,869
Carmichael, CA
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I think this is what I really want, right?
Ignition triggers relay which passes battery voltage to regulator and red field wire on Alternator.
'70 Charger FE5 Daytona Clone 451/727/D60
'70 Challenger FM3 440/833/3.55SG
'79 Ramcharger SE 360
'89 Shelby Dakota
‘06 PT Cruiser GT Convertible
‘07 Charger R/T Daytona
‘10 Ram 1500 ST Crew Cab
Yes, I'm a Dodge Boy. Verstehen?
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Re: What voltage is too high?
[Re: 1_WILD_RT]
#53959
02/21/08 11:26 PM
02/21/08 11:26 PM
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Joined: Jan 2003
Posts: 5,439
So Cal
Sinitro
master
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master
Joined: Jan 2003
Posts: 5,439
So Cal
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The amp guage, wiring harness & bulkhead connections can/will pose some issues with age... But the basic premise is when Mopar invented their electrical systems it wasn't designed to handle loads up to 125 Amps.. Maybe up to 60-70 Amps but not double... A beefy subwoofer amplifier can draw 100 Amps, Then next add... Electric fuel pump.. Electric fans.. MSD box.. Turn ON the lites.. Nuff said.. 
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Re: What voltage is too high?
[Re: NotEnufGarage]
#53960
02/22/08 02:37 AM
02/22/08 02:37 AM
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Joined: Dec 2003
Posts: 5,314
Carstairs, Alberta, Canada
dave571
master
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master
Joined: Dec 2003
Posts: 5,314
Carstairs, Alberta, Canada
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The second one would be right with the 70 and up style reg. Then the reg sees actual battery voltage when the key is on. not the reduced voltage through the bulkhead etc. The red wire on the alt doesn't have to be from the same source. It only has to be a positve voltage source, that is on with the key. It doesn't need to be as exact.. The green wire is the ground, and that is how the field output is controlled (on the ground side for 70 up) The voltage on the positive side of the field connections is not crucial. It needs voltage, but the ground is applied to increase alt output. It will simply ground less or more as needed with a lower or higher voltage positive source The point of the mod, is Only that the regulator knows what the actual voltage is, when controlling the ground side. Not to improve the positive connection to the alt itself.
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Re: What voltage is too high?
[Re: Exit1965]
#53963
08/31/08 08:45 PM
08/31/08 08:45 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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Quote:
I was considering doing the relay mod mentioned, then did a quick measurement. With the key in the ON position, I get 12.66 volts across the battery terminals, and 12.60 volts from the IGN side of the (electronic, pre 70) voltage regulator to ground (neg bat terminal). Is the .06 drop anything to worry about, e.g. would it adversely affect charging?
no. thats very small
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