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After a few years in the driveway.
I put my 74 in the shop.
He got it running so I could take it to the dyno.
After a week in the driveway, the batt went dead.
I recharged the Batt and started the car.
The Ammeter showed the batt discharging while running.
So today I started the car and put the volt meter on my 140 amp alternator.
The alternator was putting out 14.75 volts.
So why is my Batt not charging?
Elect is not my strong suit!
I need some help!
My 130 amp alternater was too much for my amp gauge and fried the gauge. I install a volt gauge per wiring instructions...now the battery recei es 14.5 volts when needed/13.0 volts normally.
With car running at say 1,500 RPM - measure voltage at alternator output, and again at batt terminals. Are the readings the same ??? (Bottom line, you're looking for a bad / high resistance connection- could be on either the positive or the ground side.) Then repeat with headlights on, blower fan on high, and any other significant electrical load you can find turned on. It's OK for the alternator output voltage to drop by 0.1 - 0.2 Volts - but not much more than that.
While certainly not common - it's not unheard of for a brand new battery to be NG.
You might also want to run the car a while, shut it off, then disconnect the battery. Leave it sit for a week- reconnect the battery and see if it starts up. You could have a parasitic current draw that is killing the battery. The other way to check for that is to disconnect the battery and put a DC current meter between the disconnected wire and the battery terminal - ideally - you should see less than 25mA of current draw (25 thousandths of an amp).
I'd check for parasitic current draw- the clock draws about 37mA- If its low 50mA- then I'd take the battery to get checked.
If it's as high as 2A- then on the pre-75 the culprit is usually the horn relay. If the horn doesn't work- that's usually a sign.
Here's how to measure-
You have to disconnect the battery-
Do the left configuration first- ONLY use the right side configuration after you have determined the draw is lower than 200mA...otherwise you'll blow a fuse.
A picture is worth a thousand words...even more if you are a slow typer!!!
Before I started the car, I was getting 14.7 through the alternator.
Is the leak coming back from the Batt through the Alt?
It spent a few years as yard art, I expect a few problems!
But everything worked before getting parked.
Before I started the car, I was getting 14.7 through the alternator.
Is the leak coming back from the Batt through the Alt?
It spent a few years as yard art, I expect a few problems!
But everything worked before getting parked.
R
Think of you alternator as income- the battery as a bank account.
Everything is connected to your battery.
A parasitic draw is like you wife buying stuff all night on Amazon - draining your bank account as you are not working to replace the money she just spent.
The alternator will NOT fry your ammeter. That's not how the system is set up. I've had a 140 amp CS-144 in my car for over a decade.
Get the car started and take a reading at the battery terminals. Report that. If the alternator out put is NOT reaching the battery it means nothing that it's reading 14+ volts at the alternator. If the voltage at the battery is not reading above standby battery voltage when the car is running, then the alternator output is not reaching it.
The running voltage at the battery is satisfactory, then my initial suspicion is that your "new" battery is faulted. You could get it load tested at the local parts place to check that.
Last edited by carriljc; Aug 17, 2021 at 12:22 AM.
The alternator itself can be the source of the current draw, if one of the diodes has failed. I think this was the case recently for someone. The tests outlined above will show that, too, as long as it is one of the circuits you selectively remove.
Clean the area good where the battery Negative cable bolts o the frame under the car...it can look o.k., but have a layer of rust/corrosiog between the battery eyelet and the frame causing the battery. I removed the original charging wire per members and installed a 10 ga. wire to/from my alternator + .
Where did you measure output? Take the reading at the battery. If it's good, then take an amp draw reading when the vehicle is off. Anything higher than 50 milliamps is an issue. If you measure a draw, you can pull fuses one at a time to see it it affect the draw. I would start with disconnecting the output terminal of the alternator.
Was the engine running when you took those measurements? You also have a 1 volt drop from the alternator to the battery.....not good. I would say 1/2 volt is the max allowable. Check you connections and condition of your battery terminals
Last edited by Mrvettenick; Aug 19, 2021 at 04:00 PM.
Forum: Thanks for all the suggestions.
I'm still not sure what the problem is?
Leaving the ign off, I measured the alt and got 14.8 v.
Then I measured the Batt and got 13.8 v.
Now what?
Ahhhh - Actual Data.... GOOD !!!
So - Now we need to determine if the problem is on the Pos side or the Ground side.
To do this - with the car running - place the Voltmeter pos lead on the alternator output stud and the neg lead on the battery pos terminal. What is that reading ??? IT should be less than 1/4 Volt. Now - do the same with one lead on the Alternator case (a good clean spot), and the battery neg terminal. This should be less than 1/4 volt as well.
Basically - from what it sounds like - you have one (or more) corroded, or high resistance connections in your electrical supply system. It could be alternator output, alternator ground, Starter Connections, Battery connections, Main chassis ground, engine ground(s). Just go through - disassemble each one - sand all connections to bare metal, and reassemble. Placing a bit of Petroleum Jelly (a.k.a Vaseline) over the connections after tightening them is NOT a bad idea !!!
Charging problems?
