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  #1 (permalink)  
Old 07-25-2012, 12:42 PM
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Default Is my alternator overcharging my battery?

Well, I got stranded by the Cobra yesterday, battery went bad (checked on a load-reading machine, verified the battery would not hold a load).

I had noticed that there were a few things "fishy", for lack of a better term. For example, the needle "voltage" gauge would jump by 1 or 2 volts every time the turn signal flashed, and other electrical items weren't working very well, like the fuel gauge.

I pulled the battery when I got home, charged it until the charger could no longer deliver 2 amps, and tried to start the engine. Click, click, click...sounded just like the relay does when a Ford starter is bad. Next I started working on grounds around the car, found all but one to be very tight, and then tightened that one up.

I had a recently purchased but unused 375 CCA battery sitting around, so I topped off the charge and put it in. The Cobra roared to life, the fuel gauge now works, there is no wavering on the Voltage gauge (the ammeter is not working...a job for when the dash comes out), and the charging rate with no lights, no fan, just the engine running runs above 14 volts, not quite 15. When I turn on the large Spal puller fan, the voltage meter drops below 14, but only slightly. With the previous battery the charging voltage was rarely at 14 and dropped to 12 as soon as the fan was turned on.

If it matters, fuel filter is a Mallory Series 140 Comp Filter and the fuel pump is a Mallory series 110 Comp Pump. Naturally, the pump runs any time the switch is turned to a setting that energizes the electrical system.

My concern is that I might be overcharging the battery. The one that failed was a Bosch unit, still looked to be in great shape although it was probably at least 4 years old, maybe more (the battery was in the Cobra when I bought it).

I didn't have the alternator checked for output, but can if anyone thinks that my battery failure might have resulted from overcharging.

If there is one thing I have learned about our component cars, it is to check the grounds anytime ANY issue arrises....I must admit the needle on the voltage gauge is much more stable now than before (no falling and rising with the turn signals), that might be the result of my ground-tightening efforts, or it might be because the battery I just put in the trunk is in better shape than the old Bosch unit.

Any advice????

TIA for whatever help you can provide!

Cheers!

Dugly
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  #2 (permalink)  
Old 07-25-2012, 01:02 PM
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I didn't see anything in your description that made me think of anything more than a four year old battery that had come to its natural end.
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  #3 (permalink)  
Old 07-25-2012, 01:02 PM
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Quote:
Originally Posted by YerDugliness View Post
...the charging rate with no lights, no fan, just the engine running runs above 14 volts, not quite 15. When I turn on the large Spal puller fan, the voltage meter drops below 14, but only slightly. With the previous battery the charging voltage was rarely at 14 and dropped to 12 as soon as the fan was turned on.
Sounds normal to me. I run 14.7v at idle with nothing running, it drops if I throw the fans on, but if I rev the engine up a little bit to speed the alternator up, it returns to normal. Now, I have the old 60 amp Ford alternator. My SPAL puller draws 18 to 21 amps, the pushers (when I use them) draws a little under 10, the MSD draws 1 amp per thousand RPM, and the headlights draw (if I recall) about 10 amps. That's all I have on my car that draws anything over 1 amp. Some guys have much more and a 60 amp alternator just won't cut it.
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  #4 (permalink)  
Old 07-25-2012, 01:09 PM
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Quick check for an alternator is output voltage. Should be between 13.75 and 14.25 volts. depending on load. ie a 50 amp alternator should maintain that voltage at full 50amp load. beyond 50 amps the voltage will drop off.
Sounds like your voltmeter is reading a little high with the new battery. Might want to check it's accuracy with a known good multimeter.
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Old 07-25-2012, 02:48 PM
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Ammeter is not working?????????????????????????
main current flow between battery and system should be thru ammeter-------------
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  #6 (permalink)  
Old 07-25-2012, 03:50 PM
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Quote:
Originally Posted by Jerry Clayton View Post
Ammeter is not working?????????????????????????
main current flow between battery and system should be thru ammeter-------------
Yes, I know....have not had the dash off to see if there is even a wire to it. I have never seen it move from the central "0" position.

The battery is trunk mounted, so it should not be an impossible routing issue.

I know there are a few various wires exiting the firewall into the engine compartment that are cut off and terminated with electricial tape...perhaps one of those is the wire to the ammeter? Will find out when the dash comes out...a project for the winter down months.

Cheers!

Doug
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Old 07-25-2012, 04:16 PM
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I would never use an ammeter anyways, change it for a volt meter.
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Old 07-25-2012, 04:35 PM
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Quote:
Originally Posted by CHANMADD View Post
I would never use an ammeter anyways, change it for a volt meter.
The voltage meter works fine...checked it against a VOM, it's right on..14.5 volts. Sadly, there is no function to check the amperes on the VOM, though .

Given the choice, I would rather fill the hole occupied by the ammeter with an oil temperature gauge, or a fuel pressure gauge, they appear to be standard VDO gauges.

I do notice that the new battery, despite having only slightly over 50% of the CCA of the original battery, starts the car better...when I would try to start the engine with the older battery it seemed like it was trying to get it spinning but having trouble...very much like having the timing advanced too far. The "newer" battery has never displayed that behavior, just spins the engine like a champ

When the Bosch battery went belly-up, it went all at once , SO glad it failed here in the town where I live and not as I was on the highway to the place where I spend weekends...110 miles away, one way, and I have to drive right through the center of Houston, TX's downtown area...that would have been a real PITA to get stranded there!!

I think Tommy hit the nail on the head:

Quote:
Originally Posted by Tommy View Post
I didn't see anything in your description that made me think of anything more than a four year old battery that had come to its natural end.
Cheers!

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  #9 (permalink)  
Old 07-25-2012, 06:13 PM
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It sounds like your battery went open circuit. Check the cells. If one of them is dry, you have a bad cell. If you jump start a car with an open circuit battery, It can make an alternator run away to 17 volts and destroy many things. Some ammeters a wired to stay on zero, some to show how much charge goes into the battery, depending on the load.
A volt meter is a better way of knowing what the system is doing, and if the alternator stops working, it'll give you a countdown to when the engine will quit. I really like optima batteries. No fumes, will hold a charge for 6 months or more, 800cca. solid construction. Quickest way to check for earth problems is a test light. From the centre of the battery neg post to the block, try to crank, if light comes on, bad earth, also from pos, to starter solenoid bolt, if light comes on, a bad connection. Keep touching along the connections, until light goes out is where the fault is.
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Old 07-25-2012, 06:49 PM
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Just to echo what's already been said. All of this sounds like a battery that has gone to a normal death. The last two or three batteries I've replaced in my daily drivers have all been in hot weather, with no warning, and could not be jump started. They all died catastrophically and instantly!
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