What Is 1987 S4 Normal Battery Load With Ignition Key Out?
01-25-2005, 09:30 AM
#31
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John;
You are indeed right. My early 90s GMC pickup has NEVER failed to crank (and start) in over 13 years of abuse...and this includes long periods of inactivity in sub-zero weather. The ignition switch is in essence a battery disconnect in this vehicle. Indeed the original battery just died a month ago...the alternator was replaced on the assumption it was failing when it was a dead battery cell all along!
There is no doubt that a 1/2amp constant drain will kill a 500amp battery in less than 6 weeks...and that "modern" vehicles seems to have more "stuff" that cause these drains. Guess it's the price we pay for all the fancy gadgets! This is just one more indication as to how "modern" the 928 is...while we think of it as 70s or 80s technology (a la my pickup), it is closer to 21st century stuff.
I find myself charging the battery in my late model Audi S4 and Dodge Caravan about 1/2 way through the long winter season, just to ensure I don't get caught out in the cold. I do mostly city driving with short trips...lots of electrical drains and only a short time to recharge the battery. I find most of the time that the batteries are only 1/2 full (so to speak). You know, take out 20amps put back 18...over time the battery just runs low. Sort of like my bank account at Xmas season!
For all these reasons, I think a battery maintainer is essential equipment in a seasonal or "Sunday drivin'" vehicle. That, some basic battery maintenance and reasonable investigation to ensure there is not some major electrical issue.
BTW:
My 928 battery went dead last summer twice...both times for the same reason: the rear window defogger relay. It seems to turn off, but actually does not -even when the ignition is shut down. WallyP wrote about this some time and noted that a simple ignition cycle will kick the relay out again. As ususal, he was 100% right. Something to keep in mind if the rw defogger is used infrequently!
Regards,
SteveCo in St. John's
You are indeed right. My early 90s GMC pickup has NEVER failed to crank (and start) in over 13 years of abuse...and this includes long periods of inactivity in sub-zero weather. The ignition switch is in essence a battery disconnect in this vehicle. Indeed the original battery just died a month ago...the alternator was replaced on the assumption it was failing when it was a dead battery cell all along!
There is no doubt that a 1/2amp constant drain will kill a 500amp battery in less than 6 weeks...and that "modern" vehicles seems to have more "stuff" that cause these drains. Guess it's the price we pay for all the fancy gadgets! This is just one more indication as to how "modern" the 928 is...while we think of it as 70s or 80s technology (a la my pickup), it is closer to 21st century stuff.
I find myself charging the battery in my late model Audi S4 and Dodge Caravan about 1/2 way through the long winter season, just to ensure I don't get caught out in the cold. I do mostly city driving with short trips...lots of electrical drains and only a short time to recharge the battery. I find most of the time that the batteries are only 1/2 full (so to speak). You know, take out 20amps put back 18...over time the battery just runs low. Sort of like my bank account at Xmas season!
For all these reasons, I think a battery maintainer is essential equipment in a seasonal or "Sunday drivin'" vehicle. That, some basic battery maintenance and reasonable investigation to ensure there is not some major electrical issue.
BTW:
My 928 battery went dead last summer twice...both times for the same reason: the rear window defogger relay. It seems to turn off, but actually does not -even when the ignition is shut down. WallyP wrote about this some time and noted that a simple ignition cycle will kick the relay out again. As ususal, he was 100% right. Something to keep in mind if the rw defogger is used infrequently!
Regards,
SteveCo in St. John's
01-27-2005, 03:24 PM
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H John (Speake),
You were right. The Cooling Fan Control Unit keeps drawing current after ignition key is out. After 1 hour of testing, the current draw did drop from 100 mA to 20 mA. Thanks John. It looks like there is there that 45 min timer to keep fans alive in case of hot spots occured.
The lesson is: test your current draw right. When one is not careful, one can measure 580 mA draw on a healthy system drawing only 20mA:
1) testing with hatchback open and all interior lights OFF (400 mA for doors red safety lights),
2) testing inside the car without cycling doors open and close (80 mA for a relay that energized when Ignition Key is rotated to 1st position and drops out only after one exits the car - doors are open and closed), and
3) testing withing 45 min after ignition key is pulled out (80 mA for Cooling fan Control Unit).
Thanks everybody. It looks like 5 weeks was simply too long to start the engine, even with 20 mA draw.
You were right. The Cooling Fan Control Unit keeps drawing current after ignition key is out. After 1 hour of testing, the current draw did drop from 100 mA to 20 mA. Thanks John. It looks like there is there that 45 min timer to keep fans alive in case of hot spots occured.
The lesson is: test your current draw right. When one is not careful, one can measure 580 mA draw on a healthy system drawing only 20mA:
1) testing with hatchback open and all interior lights OFF (400 mA for doors red safety lights),
2) testing inside the car without cycling doors open and close (80 mA for a relay that energized when Ignition Key is rotated to 1st position and drops out only after one exits the car - doors are open and closed), and
3) testing withing 45 min after ignition key is pulled out (80 mA for Cooling fan Control Unit).
Thanks everybody. It looks like 5 weeks was simply too long to start the engine, even with 20 mA draw.
01-27-2005, 07:33 PM
#33
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Oh well, at least we understand the system better now ! Good work !
20mA/H = 0.5A/H per day. = 3.5A/H per week = 17.5A/H over 5 weeks.
Assuming the battery was in a reasonable state of charge initially, it should have lasted OK, but the unknown is the rate of self discharge I believe as a battery gets older, the debris that falls off the plates starts to short plates out, accelerating this self discharge.. this is just my theory.
20mA/H = 0.5A/H per day. = 3.5A/H per week = 17.5A/H over 5 weeks.
Assuming the battery was in a reasonable state of charge initially, it should have lasted OK, but the unknown is the rate of self discharge I believe as a battery gets older, the debris that falls off the plates starts to short plates out, accelerating this self discharge.. this is just my theory.