[C2] Current Draw Problem
Thread Starter
Burning Brakes
Joined: Nov 2017
Posts: 780
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From: Redneck Riviera, FL
Current Draw Problem
67 sb coupe with ac. i managed to leave the key in the accessory position and my battery went dead in about a day and a half so i checked for current draw. with the ignition off i'm seeing less than a 100 ma, in the on position about 5 amps which seems to be about right. with the switch in the accessory position 2.5-3 amps. this seems like a lot. afaik, there's nothing drawing current but the electronic clock. pulled all the fuses one at a time and still have the draw. with the alternator completely disconnected there is a .55 amp draw, with just the blue/yellow (field?) disconnected there is also a .55 amp draw. but with just the red wire disconnected there is still a 2.55 amp draw. surely this isn't normal. guess i should also mention that the oem regulator was replaced with the solid state version at some point in the past. from everything i've read here (especially 65GGvert) it sounds like it might be a diode problem. i don't know how long it's been like this, this is the first time i've left the key in the accessory position. could use some feedback before i start pulling what's left of my hair out. thanks.
Race Director
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From: northern california
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When the ignition switch is in the ACC position, the gauges are powered up. They are what drained your battery.
Been there, done that with my '63.
Been there, done that with my '63.
Melting Slicks
Joined: May 2001
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From: Dadeville AL
In 1979 I had my 1963 Corvette shipped from the US to Germany where I was stationed. The battery was fully charged when it started the trip. It was absolutely dead on arrival four weeks later. No doubt the person who drove the car onto the ship moved the key to the far left (ACC) position thinking it was off as on most cars of that era. As an aside, it was a six hour drive from the port to my home in Germany and I didn't shut off the engine until I got home. The BATT gauge was pegged to +40 for more than four hours at 70 MPH.
Burning Brakes
Joined: Mar 2008
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From: Magnolia Texas
As I recall, in the ACC position, the voltage regulator is still powered. With the engine off, but key on (or ACC?) the regulator (if powered) will see the battery voltage as being low and apply current to the field winding in the alternator. I think what you are seeing for current draw to the alternator is about normal for the field.
Steve
Steve
Thread Starter
Burning Brakes
Joined: Nov 2017
Posts: 780
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From: Redneck Riviera, FL
hi jim, fwiw, i pulled all the fuses from the fuse block including one labeled gauges.
steve, i guess that's the question, is the ignition switch supposed to be sending power to the field in the accessory position. wonder if there's any way to find out? but you're right, after your post i did a little more research and a 3 or more amp draw at the field terminal is normal. i was surprise it was that much. still wondering about the 1/2 amp draw even with the alternator completely disconnected. apparently something else that is unfused is being powered from the switch accessory position. oh well, i guess i just need to make sure i leave the switch in the off position and maybe this would be a good time to install a battery disconnect switch and remember to use it.
thanks again to all who contributed to this thread.
steve, i guess that's the question, is the ignition switch supposed to be sending power to the field in the accessory position. wonder if there's any way to find out? but you're right, after your post i did a little more research and a 3 or more amp draw at the field terminal is normal. i was surprise it was that much. still wondering about the 1/2 amp draw even with the alternator completely disconnected. apparently something else that is unfused is being powered from the switch accessory position. oh well, i guess i just need to make sure i leave the switch in the off position and maybe this would be a good time to install a battery disconnect switch and remember to use it.
thanks again to all who contributed to this thread.
Last edited by 3154tm; Nov 28, 2020 at 07:35 PM.
Burning Brakes
Joined: Mar 2008
Posts: 859
Likes: 53
From: Magnolia Texas
It's easy to test if you have a voltmeter or a test light. Just check the alternator field terminal with the key off and then in the ON and ACC position. If I remember correctly, I discovered at one point that the field is energized in the ACC position but I'm not positive. Reviewing the schematic would tell you as well but the meter or test light would be easier.
Steve
Steve
Thread Starter
Burning Brakes
Joined: Nov 2017
Posts: 780
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From: Redneck Riviera, FL
steve, i've been checking this at the battery and with the switch in the acc position and the field terminal connected it's definitely drawing current, around 2.5 - 3 amps. i guess i just found it odd that the field would be energized when the switch wasn't in the on position. that's why i just assumed i had a problem. wonder why it's needed?
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Burning Brakes
Joined: Mar 2008
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From: Magnolia Texas
Boy, now you're REALLY making me think.... I looked at the schematic and I believe the regulator comes off the same buss that runs the windshield wipers. That buss is hot in ACC and thus, so is the alternator field. I seem to remember I thought about putting a relay in that line so I could run the radio without the extra draw of the alternator but I never got around to doing it. I am surprised they did it that way, I would have expected it to come of the ignition side of the switch but I guess it doesn't.
Steve
Steve
Thread Starter
Burning Brakes
Joined: Nov 2017
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From: Redneck Riviera, FL
yeah, i guess i could see the wiper and washer being powered with the switch in the acc as well as in the ignition position but it doesn't seem to make any sense that the alt field would need to be hot if the engine isn't running. at least with the wipers, if you leave the switch in acc, you don't drain the battery if they're not actually on.
Burning Brakes
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From: Magnolia Texas
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Dan
8th Gear
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From: Indy
response to Kellsdad:
Not sure 40 + amps is normal current draw even if the battery is fully discharged, especially while driving. Seems high to me. Ironically I have the same issue (40 + amps) while at idle with a fully charged battery. Not sure what the problem is. Do you find that this is normal for your car? I also have a 67 coupe.
Not sure 40 + amps is normal current draw even if the battery is fully discharged, especially while driving. Seems high to me. Ironically I have the same issue (40 + amps) while at idle with a fully charged battery. Not sure what the problem is. Do you find that this is normal for your car? I also have a 67 coupe.
Last edited by Chiz; Dec 3, 2020 at 05:24 PM.
Melting Slicks
Joined: May 2001
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From: Dadeville AL
Chiz - It was normal for my car and it showed no ill effects after the battery was fully recharged. ...And for the record, the BATT gauge is not calibrated in amps. Those numbers just indicate the magnitude of current flow to (+) or from (-) the battery (e.g., 20 is more than 10). But the BATT gauge is not a true ammeter in spite of it being called that in some documents.
If your battery is fully charged, it is not normal to see full deflection on the BATT gauge. I would suspect a faulty gauge or possibly a problem with the charging system. You can start to diagnose the problem by checking the voltage at the battery when OFF, at idle, and at higher RPM. Then start a new thread with your question and results.
If your battery is fully charged, it is not normal to see full deflection on the BATT gauge. I would suspect a faulty gauge or possibly a problem with the charging system. You can start to diagnose the problem by checking the voltage at the battery when OFF, at idle, and at higher RPM. Then start a new thread with your question and results.
Last edited by kellsdad; Dec 3, 2020 at 07:01 PM.
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If your battery is in good health, fully charged and your charging system delivers 13.8-14.2 +/- volts I would not worry about what the indicator indicates. However the connections at both ends of said indicator should be checked for cleanliness and tightness.
Dan
Last edited by dplotkin; Dec 3, 2020 at 07:47 PM.
8th Gear
Joined: Dec 2020
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From: Indy
Chiz - It was normal for my car and it showed no ill effects after the battery was fully recharged. ...And for the record, the BATT gauge is not calibrated in amps. Those numbers just indicate the magnitude of current flow to (+) or from (-) the battery (e.g., 20 is more than 10). But the BATT gauge is not a true ammeter in spite of it being called that in some documents.
If your battery is fully charged, it is not normal to see full deflection on the BATT gauge. I would suspect a faulty gauge or possibly a problem with the charging system. You can start to diagnose the problem by checking the voltage at the battery when OFF, at idle, and at higher RPM. Then start a new thread with your question and results.
If your battery is fully charged, it is not normal to see full deflection on the BATT gauge. I would suspect a faulty gauge or possibly a problem with the charging system. You can start to diagnose the problem by checking the voltage at the battery when OFF, at idle, and at higher RPM. Then start a new thread with your question and results.
Burning Brakes
Joined: Mar 2008
Posts: 859
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From: Magnolia Texas
The "battery meter" measures the voltage drop across the wire from the horn relay to the starter solenoid. Many high current applications (outside automotive() do essentially the same thing ... that is, they measure a voltage drop across a shunt (the wire from the relay to the solenoid) and present the result as "amps". The main difference is that our meters are not really calibrated but they are reading a voltage drop across a resistance which is current.
BTW, as I recall, I believe about 1.5 volts across the meter results in full scale deflection. For a deeper understanding of the "science" look up Ohm's Law. I=E/R
BTW, as I recall, I believe about 1.5 volts across the meter results in full scale deflection. For a deeper understanding of the "science" look up Ohm's Law. I=E/R
Last edited by 67*427; Dec 4, 2020 at 10:55 AM.
Le Mans Master
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The "battery meter" measures the voltage drop across the wire from the horn relay to the starter solenoid. Many high current applications (outside automotive() do essentially the same thing ... that is, they measure a voltage drop across a shunt (the wire from the relay to the solenoid) and present the result as "amps". The main difference is that our meters are not really calibrated but they are reading a voltage drop across a resistance which is current.
BTW, as I recall, I believe about 1.5 volts across the meter results in full scale deflection.
BTW, as I recall, I believe about 1.5 volts across the meter results in full scale deflection.
You can substitute a $20+/- electronic regulator from the auto parts store and see if that improved needle movement. A sticking mechanical regulator can cause this.
Dan
Last edited by dplotkin; Dec 4, 2020 at 10:22 AM.
