Battery Charging Question

[Jeffrey S.]

The battery gauge (ammeter) on my '69 has always been very sensitive in that it jumps around when the brakes are applied, the turnsignal is on, or the heater a/c blower goes on. Usually, at startup, the ammeter needle pegs to 40 and within a minute or so gets to 0. This evening I went for a ride down Woodward and the needle pegged at 40 but took an extraordinariy long time to slowly get toward 0. It never got there. I was driving for almost 1 hour. I always keep a Battery Minder on when the car is parked in the garage and the battery has a disconnect. The battery is just 3 years old (Delco). When the engine is off the ammeter is at 0. Any thoughts? As always, thanks form your advise.
Jeff

[Rich G.]

Re: Battery Charging Question

Start by measuring the voltage at the battery with the car not running and then with it at an rpm approximately what you cruise at.
A no load reading should be in the 12.3 to 13 or so with the car off for a fully charged battery. When the car is running you should see around 14. If it’s high, like 15 you have a regulator/alternator issue. Another thing to do is measure the voltage with the car off and your charger connected. It should give you an idea of the correct charging voltage.

Next step would be to go to a shop with more sophisticated diagnosis tools. Also have a load test done on the battery

I have the opposite issue in my 66. The ammeter hardly moves so I do a voltage check every so often to satisfy myself that things are working.

[Jeffrey S.]

Re: Battery Charging Question

Rich,
Thanks for the response. I will do the tests that you suggest later today and report back. I don't mind that the gauge is real jumpy- it shows minute changes. It just never stays on the charging side so long. Maybe a bad cell in the battery? When I replaced the battery 3 years ago, the battery minder showed a full charge and I got stranded at a fuel pump after getting gas and had to be towed. Maybe it's the same thing.
Jeff

[Mark E.]

Re: Battery Charging Question

My approach would be to install a new battery to eliminate it as a problem. At 3 years it's at the backside of its life anyway.

[Bill B.]

Re: Battery Charging Question

Jeffrey,

From your description of over sensitivity (turn signal, brake lights, et al) , I believe the ammeter gauge itself might be the issue. (Might be best to rule out the battery as the cause first). The instrument gauge is basically a voltmeter that is shunted with a very low resistance shunt (approx. 0.1 ohms of resistance as an example) across the terminals internal to the unit. (at least that is what the 1970's was ... internal shunt). If the shunt has an internal poor connection, it makes for a higher resistance, therefore more sensitive to current measurement. (so instead of measuring + and - 40 Amps, the gauge might be indicting + and - 4 Amps full scale, as an example.) I've seen some units with an external shunt across the terminals on the backside of the gauge, but can't recall what years those were.

Bill B. (retired Electrical Engineer)

[Jeffrey S.]

Re: Battery Charging Question

Bill,
Thanks for the information. Of course the gauge could be bad and that might be the next step.
Mark, it is sad that a battery would only last 3 years. I have put approximately 400 miles on the car in that time.
Jeff

[Mark E.]

Re: Battery Charging Question

Bill,
Thanks for the information. Of course the gauge could be bad and that might be the next step.
Mark, it is sad that a battery would only last 3 years. I have put approximately 400 miles on the car in that time.
Jeff

Others may know more about batteries, but its life isn't a function of miles but rather long periods of discharge, charge cycles and heat cycles. I just replaced the 7 year old battery in my '70. It had fewer than 600 miles, was slow charged (2A) at least once per month and disconnected when not used. It cranked the engine but I could tell it was getting weak.

I replace batteries on our daily drivers every 3-4 years no matter how they seem. Cheap insurance from a common cause of being stranded.

[David M.]

Re: Battery Charging Question

Load test the battery.
Verify both ends of both battery cables are clean & tight. Verify the big battery type ground cable is present clean & tight on the passenger side engine mount.
50+ year old battery cables should be replaced IMO.

Buy one of these. It will load test and voltage test static & running VDC.

https://www.amazon.com/Schumacher-BT...89052226&psc=1

[Jeffrey S.]

Re: Battery Charging Question

I just went to the car and did a simple voltage test to see if the voltage regulator was doing its job. I started it up and the needle moved to the +40 position as it always does. Before I could back out of the garage and down the driveway the needle was at 0. With the engine warm and running I got 14.63 volts. Engine off 13.8. This was with a cheap Harbor Freight multimeter so I take the numbers with a grain of salt. So it appears that all is working well. It still does not mean that the battery is up to par. When cold the engine spun very well and started right up (thank you non-ethanol gas). I will take the battery to get a load test on it when I can but for now all's well.
Thanks for all your help!
Jeff