Battery Keeps Draining
Fleet Owner
Joined: Aug 2001
Posts: 29,941
Likes: 46
From: Drummonds, TN USA
Further test method - begin pulling fuses one at a time, when the drain stops - that's the circuit.
If it's still draining with all fuses out, disconnect your main alternator wire (the big red one). If the drain stops - you have a bad diode rectifier in the alternator. This is best done with a meter set on the 20 volt scale! A FULL 12 volt drain is one thing, some alternators or other circuits will draw 3 or 4 volts, which is usually only a small amount of current, and normal.
If the drain is still there - unplug the connection to the cigarette lighter(s). They often corrode inside, and are normally hard wired with no fuses.
Look for anything that uses un-fused (direct battery connection - such as the starter relay) that is in the system. You'll need the wiring diagram for this.
(Hint: Trace all wires that run directly from the battery positive with a red highlighter on your wiring diagram, following them until you come to a fuse, fusable link, or an electrical unit. That makes for a good "Always HOT" diagram)
~Wolf
If it's still draining with all fuses out, disconnect your main alternator wire (the big red one). If the drain stops - you have a bad diode rectifier in the alternator. This is best done with a meter set on the 20 volt scale! A FULL 12 volt drain is one thing, some alternators or other circuits will draw 3 or 4 volts, which is usually only a small amount of current, and normal.
If the drain is still there - unplug the connection to the cigarette lighter(s). They often corrode inside, and are normally hard wired with no fuses.
Look for anything that uses un-fused (direct battery connection - such as the starter relay) that is in the system. You'll need the wiring diagram for this.
(Hint: Trace all wires that run directly from the battery positive with a red highlighter on your wiring diagram, following them until you come to a fuse, fusable link, or an electrical unit. That makes for a good "Always HOT" diagram)
~Wolf
Elder User
Joined: Nov 2006
Posts: 726
Likes: 0
1978 Lincoln
Well, my uncle's '78 Lincoln started draining its battery. I never thought much of that battery, it always looked too small for cranking a 460 and it did have a hard time in the dead of winter, failing to start the engine several times last winter.
So Unc. started having problems a few weeks ago and claimed the car wouldn't start after sitting for more than a day or so. We just thought that skimpy battery was giving up. But the guy at NAPA said it looked low on charge, but OK when he tested it. Unc. wanted the "right sized" battery and I figured a bigger one would do him a better job. Parts counter guy said the book called for a battery nearly double the cranking amps of the previous battery.
Well, we took both batteries home and I went to install the new battery in the old hawg Lincoln. Soon as I put the negative clamp on the post I knew Unc. had a problem. I don't even have to bother with the trouble light test. It's throwing a nice blue spark every time it makes or breaks contact.
Nothing we can control is on. When the contact is made (juice on) or broken (juice off) I can hear a solenoid or relay making and breaking contact. I have felt each flasher and relay plugged into the fuse block and they don't seem to be the culprits. The noise is in that general area, but seems to be behind or below somehow. I'm not extremely familiar with a Lincoln, but I'm afraid I am going to become better acquainted as time goes on.
Does anyone have any ideas for the next round of investigation? I guess I'll be pulling fuses next, huh?
So Unc. started having problems a few weeks ago and claimed the car wouldn't start after sitting for more than a day or so. We just thought that skimpy battery was giving up. But the guy at NAPA said it looked low on charge, but OK when he tested it. Unc. wanted the "right sized" battery and I figured a bigger one would do him a better job. Parts counter guy said the book called for a battery nearly double the cranking amps of the previous battery.
Well, we took both batteries home and I went to install the new battery in the old hawg Lincoln. Soon as I put the negative clamp on the post I knew Unc. had a problem. I don't even have to bother with the trouble light test. It's throwing a nice blue spark every time it makes or breaks contact.
Nothing we can control is on. When the contact is made (juice on) or broken (juice off) I can hear a solenoid or relay making and breaking contact. I have felt each flasher and relay plugged into the fuse block and they don't seem to be the culprits. The noise is in that general area, but seems to be behind or below somehow. I'm not extremely familiar with a Lincoln, but I'm afraid I am going to become better acquainted as time goes on.
Does anyone have any ideas for the next round of investigation? I guess I'll be pulling fuses next, huh?
Senior User
Joined: Dec 2007
Posts: 104
Likes: 0
This may help some with there problems and tells a great deal.
Voltage test first:
Measure the voltage at the alternator output post and case with heavy electrical loads on (lights, fan, etc.) after five minutes at idle, note.
Measure the voltage right at the battery posts not the connections at the same time, note.
The difference between the two should be less than .3 volts. If the voltage difference is greater than check the charging circuit wiring and connections, you might need to upgrade wire size if that is the problem. Getting the voltage close to zero is the goal here.
The older alternators will have a output voltage around 13.8 volts, the newer alternators greater than 14 volts. The newer lower maintenance batteries of the last twenty years require the higher 14+ volts to insure there long life.
The above test will tell you more in ten minutes than anything else you can do. It is better to test first then attack the problem to prevent wasted time and parts. Once you touch anything with wiring you do not know if you fixed the problem or made it worse.
This test will tell you if the alternator is producing the correct output voltage or if the wiring is at fault for poor connections in the charging circuit. This is very quick to do and should always be the first test when having electrical charging issues with voltage problems on any system.
If the voltage is low in the entire charging system check these:
alternator/regulator
alternator light/gauge and wiring
belt slipping
shorted battery
To test for current drain with the key off a test light or current meter inserted in series with the battery at the battery connection. Just remember some devices use current all the time, a clock for example. Pull one fuse at a time to find the circuit leaking.
There is a misconception that a larger alternator rating will charge more but this is not really true. The maximum output rating of an alternator is only produced at very high RPM's. Most of the time the engine is at lower RPM's and many alternators of lower rated maximum outputs will produce more power at lower RPM's. The output of a alternator is greatly reduced at the lower RPM's. There are spec sheets for alternator output to fit the best condition. If most of the driving is at lower RPM and there is a lot of non-stock electrical devices to power you can slightly decrease the alternator pulley size to increase it's RPM and produce much more power. Most alternators are rated for 10 to 12 thousand RPM maximum. Remember that increasing the RPM though will lower the life of the alternator somewhat.
The only way to fully test the output of any alternator is to run a proper test to look for shorted windings, open or leaking diodes, bad brushes, etc. and this can only be done at a good shop. For the most part though if the voltage is proper than the system is most likely ok.
Hope this helps someone, I see at great deal of info on charging systems going around that is not correct.<!-- / message --><!-- one sig per page -->
Voltage test first:
Measure the voltage at the alternator output post and case with heavy electrical loads on (lights, fan, etc.) after five minutes at idle, note.
Measure the voltage right at the battery posts not the connections at the same time, note.
The difference between the two should be less than .3 volts. If the voltage difference is greater than check the charging circuit wiring and connections, you might need to upgrade wire size if that is the problem. Getting the voltage close to zero is the goal here.
The older alternators will have a output voltage around 13.8 volts, the newer alternators greater than 14 volts. The newer lower maintenance batteries of the last twenty years require the higher 14+ volts to insure there long life.
The above test will tell you more in ten minutes than anything else you can do. It is better to test first then attack the problem to prevent wasted time and parts. Once you touch anything with wiring you do not know if you fixed the problem or made it worse.
This test will tell you if the alternator is producing the correct output voltage or if the wiring is at fault for poor connections in the charging circuit. This is very quick to do and should always be the first test when having electrical charging issues with voltage problems on any system.
If the voltage is low in the entire charging system check these:
alternator/regulator
alternator light/gauge and wiring
belt slipping
shorted battery
To test for current drain with the key off a test light or current meter inserted in series with the battery at the battery connection. Just remember some devices use current all the time, a clock for example. Pull one fuse at a time to find the circuit leaking.
There is a misconception that a larger alternator rating will charge more but this is not really true. The maximum output rating of an alternator is only produced at very high RPM's. Most of the time the engine is at lower RPM's and many alternators of lower rated maximum outputs will produce more power at lower RPM's. The output of a alternator is greatly reduced at the lower RPM's. There are spec sheets for alternator output to fit the best condition. If most of the driving is at lower RPM and there is a lot of non-stock electrical devices to power you can slightly decrease the alternator pulley size to increase it's RPM and produce much more power. Most alternators are rated for 10 to 12 thousand RPM maximum. Remember that increasing the RPM though will lower the life of the alternator somewhat.
The only way to fully test the output of any alternator is to run a proper test to look for shorted windings, open or leaking diodes, bad brushes, etc. and this can only be done at a good shop. For the most part though if the voltage is proper than the system is most likely ok.
Hope this helps someone, I see at great deal of info on charging systems going around that is not correct.<!-- / message --><!-- one sig per page -->
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