Hope You can Help - I own a 68FB 350 conv. recently Purchased. all runs fine except what I am finding is that the battery seems to discharge albeit very slowly over a period of time. appox 1/10 a volt every 3 days.
The problem is that this discharge seems to happen irrespective wether I drive it or not. In testing it appears that my alternator is charging as when I test the Battery while the car is on I am registering approx 13.5+ on my voltmeter...The problem is that the battery does not seem to recharge.
The only way I can charge the battery is to put it onto a charger and then it takes it reaches full charge and then discharges again over time. The battery is only 6 months old. Is it possible that the alternator while showing it is charging really isnt? Can it be something else? Can the alternator be bad? Is there something else? A voltage regulator? Again, it appears to be charging but the Battery does not seem to re-charge.
Any help or advice would be appreciated.

Thank you,

Lee

Sounds like you could have a small voltage drain. Have you tried disconnecting the battery and seeing if the voltage still drops?? If it holds a charge then batt. is fine (its only 6 months old but could be NFG.). If batt is OK then you need to track down the drain. Methodically try to remove one electrical component at a time by pulling a fuse and see if it stops the drain. Have you ever used the Amp setting on a voltmeter? It will tell you if you are drawing amps from the battery.

Here is a wild one: check the water in the battery. I had a battery once I had to add water to periodically, but that was when the car sat more that it was run.

Any advice on using the Amp setting would very much be appreciated....Thank You and I Truly Appreciate it.

Lee

Thanks Mike...Yes I checked that too.

Lee

OK on the bottom of my voltmeter is 3 places to put my 2 leads. On mine the center is always the ground black. If the red lead is in the right hole then I can test for voltage & Ohms resistance. When in the left hole the red lead can now test for Amps. In the pic I set the dial to read 10 Amps (max). I can't crank the engine or even run the headlites as its too many Amps. But it is useful to find a small electrical drain. Now I unhook the pos. battery cable and move it over and hold the black lead on my voltmeter to the + batt. post and the red to my + battery cable which is not touching the batt post. This puts the voltmeter in series with the + battery post & + battery cable. If there isn't any drain the voltmeter will read 0.00 and thats not the problem. If there is a reading (even 0.1 of an amp.) you have a small drain & you should see it on the voltmeter. Now go through your electrical system one circuit at a time and remove a fuse and check the voltmeter. The voltmeter will go to zero when you have found it (if thats your problem). then you need to figure out why. Bad headlite switch, or a short or ???

The problem you're describing could be a result of several root-causes. The fellas have already hit on 2 of them, but I'll summarize just for fun:

1. Battery de-charging on its own
2. High resistance short somewhere
3. Charging system not doing its job

Ruling out #1 is easiest by just swapping in another (known, good) battery. I'm concerned that your current battery may already be in a state where it's not holding a charge so it could skew your results by just disconnecting it.

Possibility #2 was covered beautifully by ragtop above. With his excellent instructions, you will be able to do a high-level diagnosis of your various circuits to determine if one of them is the culprit. You'll need to get super-acquainted with your multi-meter to home in on the precise circuit as the fuse-panel trick will only reduce it down to several smaller suspects.

Which leaves option #3. If your charging system isn't working at capacity, this could have the effect of "draining" your battery with use. An easy test is to start the car, and then remove the positive terminal while the engine is running. If you notice any change in operation (like the lights dimming or the engine stopping), your charging system is suspect. You can have your alternator tested easy enough, for example.

Best of luck in your diagnosis.

Well said Tom.

He said in his first post that he had 13.5+ volts when the car is on (i can assume that means running), that sounds to me like the charging system is working OK, what do you think? What should he see for volts when he runs the engine and removes the + batt cable? I've never actually done that.

Probably not a good idea to remove cables while the engine is running...you can check output of the alternator at the stud on the back of it. 13.5 volts is on the LOW end of acceptable charging, 13.8 - 14.5 is the range I'd like to see. On the higher end if the battery is discharged. With the symptoms described, i'd suspect the regulator, assuming he still has the external set-up. Fully charging the battery and leaving it disconnected for about a week and checking voltage it shouldn't be lower than 12.6 volts...that's a fully charged battery. If it's anywhere near 12.0 volts, it is probably bad...wouldn't be the first new bad battery sold. Anywho, hard to say without the car in front of me...let us know what happens.

I said it was a "simple" test...one that was discussed in 9th grade auto shop (in 1977). Is your concern, Herr Doktor, getting a jolt from said test or something more interesting? I've used this test more than once to prove a charging system wasn't working. In those cases, the engine died, proving that the battery was keeping the engine running (a bad thing obviously). The opposite is also true: if removing the battery terminal has no effect, your charging system is "working".

And yes, Ragtop, I totally missed the point about the 13.5 volts...read too quickly. My wife accuses me all the time of not paying attention. I think it's adult attention deficit disorder.

That would certainly imply a working charging system, but the Doctor's advice about measuring from the Alternator is the better test.

I'm leaning towards the high-resistance short which would drain the battery when not in use. I like Ragtop's test to verify this.

You Guys( ALL) are great!!!!

Thank You all for your advice and More Impotantly I wish you all a very Happy Thanksgiving....I will keep you up to date as I dig further into this all.

Best Regards,

Lee

With the risk of sounding totally foolish....What does the Voltage regulator do? can the alternator be working but the regulator not? what are the signs of that?

Lee

It regulates the voltage. The voltage fluctuates coming from the alternator. If you have a good re-builder in your area I would just take in the alternator for a checkup/rebuild. Do not go to those places that just supply alternators to trade-in. You rarely have to replace the entire alternator because all the parts are replaceable. You want to look for Auto-Electric companies in your area. The brushes might need replacing or a simple diode has failed. Bring your voltage regulator in as well for a checkup. It may not solve 100% of the problem but it's good preventive maintenance.

Get a quote before they do any work and just bring them the parts. It should any take less than 15 mins for them to discover what is wrong with the alternator and regulator. If they need hr(s) they are ripping you off.

Thank You very Miuch...Happy Holiday.

Lee

On an internally regulated alternator (two side by side blades for field leads on side of alternator case), removing either positive or negative battery cable under load can kill the diode. If the diode fries, the alternator will not charge the battery. The diode is replaceable by an alternator repair facility.

If you have an internally regulated alternator, including one wire design, on your '68, be sure that the factory voltage regulator connection is properly bypassed.

Photos of your alternator's connections would help to see what you are working with.