What the? Battery drain found...
11-24-2013, 02:08 PM
#1
Instructor
Thread Starter
What the? Battery drain found...
I finally had time to chase down the battery drain that has been haunting my 69 427/390 since reassembling it this summer.
My test showed I was draining about 77 milliamperes with everything off. This is too much, even if this was a modern car with a couple of computers.
I started with the alternator since I had installed a new one and thought it might be the problem. Turns out the exciter wire at the alternator did have something to do with the drain. I disconnected the harness under the steering column thinking the ignition switch might be the cause but had no change.
I checked the continuity with the loose exciter wire at the alternator with the chassis ground and sure enough, I had some flow. It wasn't a direct short, but made some sense with ohm's law. The resistance was measuring about 175 ohms which at 12.6 volts would be 72ma.
So I referenced the wiring diagram and see where the exciter switched ignition wire also (and only) powers the radio. I pulled the radio fuse and my drain usage dropped almost to zero ma. I remove the side panel to study the harness around the radio (original) thinking there was a worn place on the wire and that it was rubbing the chassis. But looked ok. By chance, I reached over and turned the **** of the radio. I switched off the radio and my drain went away!!!
I turned the radio back on and the milliamperes jumped back into the 70s but no sound comes out of the radio?
Clearly, the alternator is allowing 12v to flow from the hot battery connector, through the alternator, to the exciter wire, and then it is grounding through some resistance inside the radio!
Side note: when running, the alternator charges 14v and the radio works as well as a factory 69 radio can.
So, as long as I turn off the radio when shutting off the car, my battery will be good for restart. But it shouldn't be this way!
Thoughts?
My test showed I was draining about 77 milliamperes with everything off. This is too much, even if this was a modern car with a couple of computers.
I started with the alternator since I had installed a new one and thought it might be the problem. Turns out the exciter wire at the alternator did have something to do with the drain. I disconnected the harness under the steering column thinking the ignition switch might be the cause but had no change.
I checked the continuity with the loose exciter wire at the alternator with the chassis ground and sure enough, I had some flow. It wasn't a direct short, but made some sense with ohm's law. The resistance was measuring about 175 ohms which at 12.6 volts would be 72ma.
So I referenced the wiring diagram and see where the exciter switched ignition wire also (and only) powers the radio. I pulled the radio fuse and my drain usage dropped almost to zero ma. I remove the side panel to study the harness around the radio (original) thinking there was a worn place on the wire and that it was rubbing the chassis. But looked ok. By chance, I reached over and turned the **** of the radio. I switched off the radio and my drain went away!!!
I turned the radio back on and the milliamperes jumped back into the 70s but no sound comes out of the radio?
Clearly, the alternator is allowing 12v to flow from the hot battery connector, through the alternator, to the exciter wire, and then it is grounding through some resistance inside the radio!
Side note: when running, the alternator charges 14v and the radio works as well as a factory 69 radio can.
So, as long as I turn off the radio when shutting off the car, my battery will be good for restart. But it shouldn't be this way!
Thoughts?
11-24-2013, 03:59 PM
#4
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11-24-2013, 05:25 PM
#5
Le Mans Master
For example, if I am seeing battery drain, what are Procedures/Steps 1, 2, 3 and how do I do it in terms that are relevant to the C3 (in my case 1980 L48) and that a 'shade tree mechanic' can understand (yours truly).
Great info and thanks for sharing!
11-24-2013, 10:17 PM
#8
Instructor
Thread Starter
'75 -
That's part of the confusion.
There's not enough power at the yellow wire to "run" the radio with the key off.
Questions:
Does the exciter wire connect to either of the 12v positive wires at the alternator? In other words, what components inside the alternator are in between the 12v heavy or sensing wire and the exciter wire?
I do feel something is amiss inside the radio. If I directly short the 12v heavy cable to the exciter wire (removing the alternator), I still have the same drain (of course when the radio switch is on).
If I place the test light on the radio fuse, I can't see it glow because the power drain (current) is so low.
That's part of the confusion.
There's not enough power at the yellow wire to "run" the radio with the key off.
Questions:
Does the exciter wire connect to either of the 12v positive wires at the alternator? In other words, what components inside the alternator are in between the 12v heavy or sensing wire and the exciter wire?
I do feel something is amiss inside the radio. If I directly short the 12v heavy cable to the exciter wire (removing the alternator), I still have the same drain (of course when the radio switch is on).
If I place the test light on the radio fuse, I can't see it glow because the power drain (current) is so low.
11-24-2013, 10:33 PM
#9
Safety Car
Battery drain is a simple process of pulling fuses and checking the volt meter, 99% of the time that will locate your issue.
11-25-2013, 12:46 AM
#10
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Details on the type of alternator and exactly which wire you are referring to would help. A diode on the wire going to the alternator would likely fix it but the alternator may simply be defective.
11-25-2013, 05:58 AM
#11
Burning Brakes
'75 -
That's part of the confusion.
There's not enough power at the yellow wire to "run" the radio with the key off.
Questions:
Does the exciter wire connect to either of the 12v positive wires at the alternator? In other words, what components inside the alternator are in between the 12v heavy or sensing wire and the exciter wire?
I do feel something is amiss inside the radio. If I directly short the 12v heavy cable to the exciter wire (removing the alternator), I still have the same drain (of course when the radio switch is on).
If I place the test light on the radio fuse, I can't see it glow because the power drain (current) is so low.
That's part of the confusion.
There's not enough power at the yellow wire to "run" the radio with the key off.
Questions:
Does the exciter wire connect to either of the 12v positive wires at the alternator? In other words, what components inside the alternator are in between the 12v heavy or sensing wire and the exciter wire?
I do feel something is amiss inside the radio. If I directly short the 12v heavy cable to the exciter wire (removing the alternator), I still have the same drain (of course when the radio switch is on).
If I place the test light on the radio fuse, I can't see it glow because the power drain (current) is so low.
Also, any chance that you turned the key all the way back to the "ACC" position ("off" position is one click before the "acc" postion)? In that case the radio should have power.
11-25-2013, 07:23 AM
#12
Instructor
Thread Starter
Lionelhutz - standard three wire alternator. I've tried to be very clear about which alternator wires I'm discussing.
Exciter wire - the smaller, brown and white, switched
Sensor wire - medium red direct to battery
12v heavy - largest heavy 12v cable
Danish Shark - the brown ignition switched wire goes also to the fuse panel and provides power to the yellow radio 12v source wire. The panel lights system wiring is gray.
Exciter wire - the smaller, brown and white, switched
Sensor wire - medium red direct to battery
12v heavy - largest heavy 12v cable
Danish Shark - the brown ignition switched wire goes also to the fuse panel and provides power to the yellow radio 12v source wire. The panel lights system wiring is gray.
11-25-2013, 07:29 AM
#13
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The brown wire should go through the charging light before it goes to the radio or anything else. Also, it should not have power with the key off so if you're seeing power on it back fed from the alternator then the alternator is bad.
11-25-2013, 08:41 AM
#14
Instructor
Thread Starter
Lionelhutz - 69s dont have a charging light.
This is my third alternator. I absolutely thought it was the alternator several times. The alternator shop was getting tired of seeing me.
This is my third alternator. I absolutely thought it was the alternator several times. The alternator shop was getting tired of seeing me.
11-25-2013, 10:45 AM
#16
Instructor
Thread Starter
No resistance in the field or exciter wire is necessary.
The purpose if the bulb us only to let the user know if the alternator has stopped charging.
It does this because the failed alternator field square wave pattern drops and stays at 0v when not charging so the bulb lights up.
The purpose if the bulb us only to let the user know if the alternator has stopped charging.
It does this because the failed alternator field square wave pattern drops and stays at 0v when not charging so the bulb lights up.
11-25-2013, 11:05 AM
#17
Instructor
Thread Starter
I just called the radio repair shop Corvette Radio and Repair, the guy who worked on my radio.
He confirmed with me i gave a leaking diode inside the radio. He basically said the radio can operate between 10.xx and 14 volts and if the power is too low it wont work. He said a leaking diode, radio switched on, and slight power coming from the alternator would drain a battery.
He confirmed with me i gave a leaking diode inside the radio. He basically said the radio can operate between 10.xx and 14 volts and if the power is too low it wont work. He said a leaking diode, radio switched on, and slight power coming from the alternator would drain a battery.
11-25-2013, 11:20 AM
#18
Team Owner
On my '72, the old alt had no markings on the case, so bear with me on this description....looking from the back of the alternator, the two pin regulator connector, like the replacements from the parts house will have a RED and White wire on them, most of the old wiring is shot due to vibration, and so the connectors changed out, the old wiring color codes were all unreadable in my car....SO....
of the two wires going to the regulator, the one that is MOST CLOCKWISE should always be hot with battery voltage it is the Red wire....
with the ignition off, the white wire should have NO voltage on it...and connected to the harness of course, obviously there is voltage on it with engine running, but the regulator is trying to ground it, which would light a dash/idiot light IF there was one, but like stated there is a resistor wire instead.....
with the ignition ON but engine not running, the two wires will both have 12 volts on them when unplugged from the alt....
IF the two wires are reversed, it is possible to blow the regulator, but maybe not every time....
Radio power should be on a brown wire, and switched on/off with ignition....
of the two wires going to the regulator, the one that is MOST CLOCKWISE should always be hot with battery voltage it is the Red wire....
with the ignition off, the white wire should have NO voltage on it...and connected to the harness of course, obviously there is voltage on it with engine running, but the regulator is trying to ground it, which would light a dash/idiot light IF there was one, but like stated there is a resistor wire instead.....
with the ignition ON but engine not running, the two wires will both have 12 volts on them when unplugged from the alt....
IF the two wires are reversed, it is possible to blow the regulator, but maybe not every time....
Radio power should be on a brown wire, and switched on/off with ignition....
Last edited by mrvette; 11-25-2013 at 11:22 AM.