The Stovebolt Site Forums The Shop Area The Electrical Bay Battery drain

Help, please. I changed over to 12 volts with a GM single wire alternator patched into the old wire loom and still using the ampmeter rather than a volt meter. Now if the truck is not started and run every day, in two days the battery needs to be re-charged. The ampmeter shows charging after the initial throttle blip to "excite" the alternator, but something's not right. How do I fix this? TIA

Oldbones,

First of all, when you shut it down, does the ammeter show "Zero" or a slight discharge?(Should read Zero; cead-center)
If this is difficult to determine, try this: with the engine off, disconnect the positive battery cable, and touch it back onto the battery post, repeating several times, watching and listening for a small spark.(this may be easier to detect in a darkened garage, or after dark)
If you get a spark, something indeed is draining the battery, and the next thing I would try is disconnecting the wire from the alternator and trying that battery-post thing again; perhaps your alternator is faulty, and draining the battery.

Other possibilities include stoplight switches; I had this problem with a '62 Falcon, and after a legnthy and frustrating search, I discovered that the stoplight switch had "shorted" just enough to drain the battery over several days of non-use, but not enough to make the tail lights glow visibly. I discovered this when my hand brushed against the brakelight switch on the master cylinder, and it burned my hand, it was so hot!

Check other switches such as the ignition, heater,and headlight switch to make sure that when they're "off" , they're really off, and not "bleeding current" out of the battery.

You say you "patched" this alternator into the old harness; did you leave the old regulator in place? If so,did you use any of the terminals as "tie points", and if so, did you connect the alternator to the "Battery" terminal or the "Armature"
terminal?
Perhaps the old regulator is "grounded"?

Start at the battery, and one at a time, disconnect stuff along the way until you eliminate the current drain.

Good luck!

I've had more than one one-wire alternator do this. Try e-mailing Randy, the moderator of this board. He is our all-knowing wiring guru, and should have a solution for you. Randy has a business, Fifth Ave. Auto in Clay Center, KS and he specializes in antique auto electrics.

If you get a spark and rule out the Alternator & wiring go to the fuse panel. Pulling 1 fuse at a time will usually Identify the offending circuit. Do this AFTER checking the alternator as outlined in the previous post. I see about 4-5 alternator draw problems a month and 99% are the alt itself.
Good luck
Brad

better than a spark test: do a voltage drop reading........
Disconnect negative battery cable. Connect the red lead of an ANALOG voltmeter to the negative cable, the black lead to the negative terminal (on battery). Should read less than 2 volts, more if you have modern stereo with memory or clock, alarms,...

Sparking across a battery is always dangerous!

one more thing: Did you buy one of those cheap "lifetime warranty" crap alternators? ALWAYS buy a quality decent new or reman piece. Some remans are sent to Mexico for cleaning and Krylon and shipped back. Same goes for starters.

best of luck!

Johhny,

Yeah, you're right about sparks around a battery (forgot about that Hydrogen gas thing) :o

Guess I should put out my cigar too! :rolleyes:

Frank

Seems a waste of a good cigar. Just hand it to your kid to hold.

.

I realize that this is an old post, but I’m experiencing this problem on my ’53 3100 (converted to 12V with an alternator) and I want to try this troubleshooting suggestion.

But I’m not sure I understand it correctly. It sounds like you’re putting the voltmeter in series with the battery. I thought you always measured voltage drop in parallel. Maybe that’s not a problem if it’s only a couple of volts, but what’s that going to do to my meter (digital not analog) if it’s a higher voltage or high current?

"Johnny" hasn't made a post since September 2005, so I'll assume he isn't going to answer you. Using a voltmeter for a parasitic drain test is an exercise in frustration- - - -you won't get any useful results. Most multimeters have a "milliamps" function. Some of them will carry up to 10 amps without overloading. Disconnect one of the battery terminals- - -doesn't matter which one, and connect the amps function of the multimeter in series with the cable and the battery post. A current flow of more than 100 milliamps (1/10 amp) is a problem. Start disconnecting circuits one at a time until you find the drain. I'm going to guess the most likely culprit is the rectifier assembly in the alternator. Disconnect the big charging lead at the alternator, and watch the parasitic drain drop to a fraction of its former amount!
Jerry

53ChevyTruck,
I too think that is not a valid voltage check although it does have merit. Instead of a volt meter I use a test light. The one that I use looks like a ice pick with a lamp in the handle. Just a few bucks at your FAPS. Put in series as suggested. If the lamp glows you have a drain. The brighter the lamp, the greater the drain. Start pulling fuses or disconnecting wires till the bulb goes dark. Only thing to remember is devices that have memory will draw current, as stated, so lamp will never go totally dark. I found a leaking diode in my alternator this way.

Up till about 1989 when the cars just had a feed when the key was off because to keep the clock running, station preset, ECM memory. If you had less then about 9.6 to 10.5 volts you did not have a drain.

So at the dealership we would roll the Sun Bat 9 or was it a 6 or a 13. I don't remember. Though I have a BST 5. We would disconnect a bat cable and put the analog meter in series. When we saw bat voltage we knew something was on or there was a short to ground. It was usually a glove box, hood light, or trunk light staying on.

Once the cars went to more complex computers, added BCM's, etc, the voltage readings were to close to bat voltage to use the old analog volt meters for a battery drain quick test.

So we then had to use digital multi meters.

However using a old time analog voltmeter to measure a parasitic drain was essentially using the volt meter hooked up in series as if it was an amp meter. Combination of the meter was rugged enough and the parasitic load current flow was low enough that it was possible to check to see if there was a drain causing the battery to go dead.

Also shops back then rarely had an analog amp meter that would read milliamps so they improvised.

So if I had an old time analog volt meter, and pre 1981 auto and suspected a parasitic drain I would not hesitate to still test for it that way.

Problem with using a test light for a parasitic drain is that unless you have a test light made back in the 1960's or before is that the newer bulbs draw less current and there can be enough of a drain to make the battery go dead but not see the filament glow.

However a true voltage drop test is using a voltmeter that will read voltage below .1 volt. And it is measuring the voltage drop in parallel not in series as above when removing a battery cable.

Two weeks ago my Jeep would not crank. I measured a series of voltage drops with my multi meter. I put one lead on the negative bat post and the other lead on the bat cable clamp, then from neg clamp to neg cable. I did the same with the positive side. Initially I was getting voltage drops of .1 v.

That told me the contacts were all good without having to remove anything to verify there was no corrosion.

Until I measured the voltage drop across the pos cable terminal end and the pos cable. That v drop was .6 volts.

I then took the metal strap off and removed the positive cable from the terminal and there I saw build up of crud between the terminal and the cable.

Point is without that excessive voltage drop there was no visual corrosion on the cable terminal or in the exposed bit of wire of the positive battery cable. Even the bat posts to cable terminals looked clean.

32vid, If one wishes to measure low current in a circuit but doesn't have a meter that reads that low, here is a trick we electronics guys use.
For example, say you have a 1 milliamperes (0.001 amp) drain. Install a 1000 ohm resistor in series with your circuit. Using the voltmeter you will read 1.0 volt across the resistor, E=IxR.

Great tip. Jeffrey

A trick I've used for the inductive ammeter on a Sun VAT-40 for low current measurement is to make up a 10X multiplier by wrapping 10 loops of wire around a thin slice of plastic pipe and securing the loops with zip ties. When the inductive current clamp is placed over the looped wire, a 1 amp current flow reads out as 10 amps on the meter.
Jerry

Thanks for the update. I couldn't see where a voltage reading would show anything.