11.5V = Dead Cell?

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DartGTDan

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My buddy has had an electrical problem with his '63 Dodge 440 (383 engine) for quite some time. He says the car "blows" voltage regulators when he turns the headlights ON. He has tried multiple mechanical & electronic voltage regulators (with a known good ground). The alternator has been bench tested "good". He has replaced the under hood wiring (harnesses from Evans wiring). He has added a volt gauge (spliced into the ignition "run" side of the ballast resistor) and with the engine running it reads 11.5 volts.

Will a dead, or dying, battery cell limit the voltage to the 11.5 volts?
 
No, just the opposite. If a battery is weak or dying, it will cause the charging system to put out "all it can" to keep up.
 
Get into a service manual, that is maybe go to MyMopar and download the 67 manual, and in section 8, electrical, pay attention to the procedure to measure alternator field current. I'm thinking the rotor is partially shorted, drawing too much current.

One of the first things you should do is either swap in a known good battery, or yank out the one in there and charge it on a good charger, then let it set for at least an hour and have it load tested with a carbon pile tester.
 
This is the same roundabout way I'm getting on with another guy here on the Forum who wants to shoot his alternator LOL he's killed the battery several times and now is blaming the alternator for not running correctly.. did he thoroughly charge his battery and verify it was a good battery before he hooked the alternator up to it or did he jump start it and then let the alternator charge its brains out until it was dead again ..
He's slow to post so I'm being patient..
 
My battery with a dead cell would read 10 volts sitting on the bench after being charged.
I thought it was my battery charger not working correctly. But it wound up being a dead cell in the battery
 
Agree.
Before testing the system, you have to start out with a known good and fully charged battery.
Otherwise you can get some misleading diagnosis.
 
Each cell carry's 2 volts. Cars can sometimes get by all summer with a dead cell until that 1st cold morning where it then fails.That's when most people buy batteries.
I agree with Post #6
 
My buddy has had an electrical problem with his '63 Dodge 440 (383 engine) for quite some time. He says the car "blows" voltage regulators when he turns the headlights ON. He has tried multiple mechanical & electronic voltage regulators (with a known good ground). The alternator has been bench tested "good". He has replaced the under hood wiring (harnesses from Evans wiring). He has added a volt gauge (spliced into the ignition "run" side of the ballast resistor) and with the engine running it reads 11.5 volts.

Will a dead, or dying, battery cell limit the voltage to the 11.5 volts?

i AINT NO ELEC. EXPERT , BUT MY RIG WOULDNT RUN RIGHT AT THAT LOW OF VOLTAGE , FINALLY JUST QUIT .
 
New cars will run on 10 Volts and quit if 9 or under.

I don't know about that. Every Dodge I've had the last few years, as soon as the alternator quits it won't idle. I've run the battery dead on one, and after jumpering it, it STILL would not idle or run correctly for several minutes even with the alternator online
 
This is the same roundabout way I'm getting on with another guy here on the Forum who wants to shoot his alternator LOL he's killed the battery several times and now is blaming the alternator for not running correctly.. did he thoroughly charge his battery and verify it was a good battery before he hooked the alternator up to it or did he jump start it and then let the alternator charge its brains out until it was dead again ..
He's slow to post so I'm being patient..
Electrical problems can drive you crazy. Other people's electrical problems can drive you completely nuts! :lol:
 
Each cell of a healthy battery puts out 2.1 volts. 12.6 total. 11.5 sounds like it is just discharged. Its funny how so many folks have electrical/charging system issues and never fully charge the battery and do a system check. The battery is the first place to start.
 
No, just the opposite. If a battery is weak or dying, it will cause the charging system to put out "all it can" to keep up.
My Charger was pushing THIS type of voltage when I had a bad battery:
Ginger 105.JPG


Check out this chart:

Bttery.jpg
 
My Silverado is always 14+ on the "ammeter" This morning I had to jump it and on the way to work it was high 14's, but the inverter connected in the lighter (power jack) often sees down to 11.2V and alarms.
 
My Silverado is always 14+ on the "ammeter" This morning I had to jump it and on the way to work it was high 14's, but the inverter connected in the lighter (power jack) often sees down to 11.2V and alarms.
Actually, you meant "Voltmeter".
 
Thanks for the replies. Today my buddy installed a new battery, and said it's still running at 11.5 Volts. He's had enough and is taking it to a shop tomorrow.
 
My Charger was pushing THIS type of voltage when I had a bad battery:
View attachment 1715573501

Check out this chart:

View attachment 1715573503
That chart is ballpark correct for voltage across the battery when its not being charged or discharged, and there is no surface charge.

What your battery charger does is provide power at some voltage above the battery's internal voltage. For a given state of charge, the greater the voltage difference the greater the current flow.
Different chargers work in different ways but a charger that can provide 14.6 Volts to a discharged battery will be providing lots of current.
Providing power to recharge a battery in the 14 Volt range is basically what the car's alternator does.
The ammeter will show how much current the battery is drawing.
When a battery is fully recharged, less than a 0.1 amp will flow when connected to charger or alternator at 14.6 Volts.
In this post is a photo sequence of moderately discharged battery being charged.
Charging Battery with Alternator - Warning

He has added a volt gauge (spliced into the ignition "run" side of the ballast resistor) and with the engine running it reads 11.5 volts.

Will a dead, or dying, battery cell limit the voltage to the 11.5 volts?

The problem is that he's not measuring battery voltage. He's measuring voltage between his splice and whatever ground he's using.
To guestimate the battery state of charge he needs to measure the voltage across the battery when its not in use or being charged.
To do it more exactly should measure the acid in each cell (if it has caps) or put it on a load tester. But to solve his mystery start with the voltage.

He says the car "blows" voltage regulators when he turns the headlights ON.
If the voltage the regulator is seeing is 11.5, then it will most likely continuously "full field" the rotor.
My guess is there are poor connections in this circuits. And/or something may be miswired.
If the voltmeter in the dash was in addition to the ammeter, looking at the ammeter will reveal much more of the story.
 
My Charger was pushing THIS type of voltage when I had a bad battery:
View attachment 1715573501

Check out this chart:

View attachment 1715573503
Ya, anytime the charging voltage is that high check your battery. State of charge, electrolyte level, and load test. Even corroded cable ends can cause issues as well as a bad ground (battery cable ground or regulator case to firewall ground)
 
Aftermarket in dash volt meter. Was voltage verified with a good multimeter? Just a point to ponder.
 
The voltage alone doesn't tell anything about the charge rate.
 
You can theorize all you want but the steps are fairly simple unless there is some convoluted intermittent that is difficult to run down

1...Charge and test the battery and or sub a known good battery

2...If the system voltage does not come up to normal then you know you have a charging problem Troubleshoot that

3...On factory "ish" wired Mopars, you have the charge path and the field path. You have the components, the alternator, the VR. Just check them all out. The charge path on stock Mopars is ALWAYS suspect, because of the bulkhead connector and ammeter. Ten seconds with a voltmeter will give you the answer. Running, charging, one probe on alternator output othe probe on battery PLUS, if there is over 1 or 2 volts difference, there is a poor REALLY poor connection someplace

4...The VR MUST be grounded to the battery NEG. It MUST see "same as battery" voltage to the sensing terminal (IGN in Mopars) with no voltage drop

5...The VR must be good that is functional. It is fairly rare for a solid state regulator to regulate "wrongly." They usually either fail or work. But this is not ALWAYS the case. What you do is, you eliminate as "much else" as you can (battery, wiring / voltage drop, connections) and if the charging voltage is wrong, you gamble and replace the VR

6...The alternator must put out rated current. There are lots of little glitches here, like partial shorts in the stator, or rotor, or one or two bad diodes, or bad brushes, etc. BUT THE bottom line is, replace it with a good rebuilt or good used or good new alternator and move on

7...On highly modified cars especially with trunk mount battery, etc, suspect everything and anything and ask yourself "did it ever work correctly?" Repeat 1-6. NEVER assume terminals are good connections. I've found bad molded terminals in fairly new (we are talking the seventies here) Mopars at the molded ammeter terminals, and down at the solenoid wire---vibrated until it broke internally. Looked great on the outside of the wire.
 
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^^^This^^^^ I think we're in agreement.

All I'm pointing out is the 11.5 Volts was measured at location that tells nothing about the battery.
Nor does it really tell us much about the alternator even though the engine was running.
It would only be useful in conjuction with other voltage measurements.

Any diagnoses needs to start with step 1 in the above post.
 
Measure the voltage at the battery, then turn on the headlights. If the voltage drops below 11vdc there abouts, you have a bad cell, maybe shorted. But do not blame your alternator.

If the battery is bad, you ahould still read 12 vd or there abouts. Once you put a load on the battery, that will let you know its status
 
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