The Stovebolt Site Forums The Shop Area The Electrical Bay 12v battery drain need some advice

I have a 59 Apache with a 327 sb. The engine has been converted to a serpentine belt system off a 95 chevy truck. When I picked up the truck the engine had been rebuilt and the PO had started to install a easy wire universal harness in the truck. I found that the battery has a 12v current draw on it with everything turned off. So I decided to go and pull all the wires loose and basically start from scratch with the harness. I had all the wires pulled except the battery positive lead from the starter and the starter wire and the alternator power wire and sxciter wire.. I checked and found that there still was a current draw of 12v. I disconnected the wires from the alternator and found that there was NO draw from the battery. So I figured the alternator was bad and went and picked up a new alternator. But after installing the new alternator I still had a current draw. I checked the alternator by seeing if there was continuity between the alternator power post and the alternators case and there was. So I carried the alternator back thinking I just got a bad alternator. But when I went to Advance auto I carried my volt meter to check the next alternator and it had the smae issue with the alternator's power post showing continuity with it's case. So I figured this was normal for this type of Alternator. I carried the alternator home and hooked the alternator's wires back but this time I set the alternator on a piece of cardboard to insulate it from the engine block. I checked again for a battery draw and there was no draw. I then put the alternator in it;s bracket and checked for a draw and there was a 12v draw showing again. I then decided to check for continutiy between the positive battery cable and negative battery cable (with the cables off the battery). And there was continuity between the positive and negative cables. This 12v battery drain is driving my crazy trying to find its source. If anyone has had this same problem I could sure use the help to figure this out.

When you say 12V current draw that has me a bit confused. Current is measured in Amps where Volts are a potential difference between two points. Can you be a bit more specific on where you are taking your readings? You will and should have 12V betwen the BATT post of the ALT and the NEG of the battery. I am assuming you have a one wire ALT?

I have the positive battery terminal connected to the battery. I have the negative battery cable disconnected. I run my voltmeter from the negative battery cable to the negative battery post. This is where I see there is a 12v drain from the battery. The alternator is a 2 wire, a exciter wire and the power post wire. So there should be continutiy from the alts power post to it's casing? When I disconnect the power wire from the alt I get no reading. Only when i have the power wire connected to the alt do I get a 12v reading. As far as i can tyell the alt is draining the battery. But I have exchanged the alt 2xs and had the second alt tested before I left the store and it tested working. The PO has the battery mounted inside the cab behind the seats. he also has the battery cable zip tied to the fuel line. I checked the battery cable to make sure it was not grounding to the line but found nothing wrong. I'm also going to change the cable being zip tied to the fuel line, don't like that set up. Also is there suppose to be continuity between the positive and negative battery cables? And is there suppose to be continuity between the alt power post and it's case? thanks for any help

What is the amperage draw of the parasitic drain? It's not uncommon to have a few milliamps of current draw through the voltage regulator. If you've got much more than 1/10 amp (100 MA) that's too much. It would take several weeks to draw the battery down enough to give a starting problem with the tiny parasitic drain of the voltage regulator. Until you get a measurement of parasitic current draw, not voltage, this discussion is meaningless.
Jerry

Jerry

all I have is a voltmeter that measures ac/dc volts. The meter is showing 12 DC being pulled off the battery. My main question is should there be contin uity between the pos and neg battery cables. And should there be continuity between the alts hot post and the alts case, thanks

It's impossible to measure continuity with a voltmeter. Even if a digital voltmeter gives you some sort of reading, it will be worthless. You either need an ohmmeter or a DC milli-amp meter. Ohmmeters work on circuits WITHOUT a battery connected, and measure resistance. For the test you're attempting, an ohmmeter is almost worthless.

If you've got the usual type of digital multimeter, it will have a scale measured in milli-amps that can be connected in series with the battery cable to measure parasitic drain. Connect the test leads to the meter in the proper location to measure "amps" and disconnect one battery cable. Connect one meter lead to the battery post, and the other one to the cable. If there is any current flow at all, it should be less than 1/10 ampere, which translates to 100 milli-amps.
Jerry

Do you have a diode in line on you're exciter wire? There needs to be a diode only letting current flow from the ig. switch to the alternator on a two wire alternator.Also you should have the exciter wire so there is only power to the alternator when the ig.switch is in the engine run pos.

Jim Carter sells the wire with a diode in line or you can just go to a Radio shack and tell them what you're doing and install the diode in line.

Pete

The diode I'm using (for the last 4 years,) is a 1N4003, Radio Shack # 276-1102. I'm told any similar diode will work fine. Good luck!

Pete52 and 40casey,

THANK YOU VERY VERY MUICH for the help that fixed the problem. man I was going crazy trying to figure out the problem. I pulled the whole wiring harness and re installed it and still had the same issue until I put the diode inline. I did not have this problem with my 50 chevy truck that has a sbc 400 but the 50 truck was not using this type of alternator. So I have leraned that alternators that are used with a computer set up vehicle are made differntly then the older style made alternators used And there was showing a full 12v draw off the battery not mili amps. Now the 12v draw is gone.