1.6A Parasitic Battery Drain - And Then NOT?

[ZTatZAU]

Hello All,

 

It's been a while since I've posted anything here but I'm looking for a little insight and/or suggestions from anyone who may have been down this path before.

 

My 1975 LeSabre Custom Convertible is not a daily driver but rather only an occasional driver for special occasions when the weather is suitable.  When parked, I regularly rotate a 1.5 Amp Battery Minder between the Buick and a couple of other vehicles to keep the batteries up.

 

With kids and grandkids in town a couple of weekends ago, I took the Buick out for some local top down rides with no problems whatsoever.  I then put the top back up and parked the car in the garage.  Then early this week, before hooking up the battery tender, I measured the battery voltage and was surprised to find the battery was completely dead at 0.11 V.

 

Fortunately, I was able to nurse the battery back up to full charge with a variety of chargers and charging rates and then hooked up the 1.5 A battery tender.  The next day, my 12.6 V battery was down to only 10.5 V or so.  Further investigation revealed 1.6 - 1.7A parasitic drain on the battery with everything turned off; that the 1.5 A battery minder couldn't quite keep up with.

 

Before starting a full blown diagnostic routine of pulling and replacing fuses one-at-a-time to locate the source of the parasitic drain,  I got the battery back up to 12.6 V and started the car.  It may be important to mention that, according to my Buick Service Manual, 1975 was the first year for a certain new type of alternator and I have found that after starting the alternator does not come "on-line" without revving the engine a few times after which the alternator comes on-line and works just fine from idle RPMs on up, with measured battery voltage remaining constant at about 14.5 Volts regardless of load.

 

So after going through this routine, I shut everything down and found the 1.6 Amp parasitic drain had disappeared with an at rest battery drain of only 0.11 Amps which seems to be normal.

 

Having taken no further diagnostic or corrective steps, beyond what I've described above, I'm hoping someone can explain or at least take a stab at what may have been causing the 1.6 A parasitic drain that seemingly has corrected itself?

 

Any ideas, hunches, or guesses will be much appreciated.

 

ZT

[Ben Bruce aka First Born]

ZT, I believe the alternator is faulty.  I had one on a 1957 Cadillac that was doing the same thing.  Remove the wire from the alternator, all ok. Replace same and drain returned. Something about a transistor or diode that was failing in a closed position. Most rare, according to the auto electric shop. 

 

  Ben

[ZTatZAU]

Thanks Ben!  I appreciate your reply and sharing your experience.

Do you recall if your parasitic drain was about 1.6 A too?

[ZTatZAU]

Well, it appears I spoke too soon.  After running the car as described above and seeing only a 0.11 A drain after shutting it off, I went back out to the shop a few minutes ago, to see the 1.6 Amp parasitic drain has returned.  As per Ben's post, I tried disconnecting the two wire plug on the top of the alternator and it had no effect on the 1.6 Amp drain.

 

So, unless anyone else has a different suggestion, I will proceed with pulling and replacing fuses to see if I can isolate the problem circuit.

 

ZT

[usnavystgc]

Does the radio on the car work?  I know that seems a crazy question but bear with me.  If the radio doesn't work but is turned on, there may be some electronics in it drawing a drain from the battery.  You'll never know it's turned on because it "doesn't work".  Check to see if the radio is turned on.  If it is, turn it off and see if that fixes your issue.

[ZTatZAU]

Thanks for your reply Phil.  Yes the radio and retractable antenna both work.  With the key OFF, turning radio ON or OFF does not affect the 1.6 A parasitic drain.

 

ZT

[Ben Bruce aka First Born]

 

 Dome light, glove box light, trunk light.

 

  Ben

[ZTatZAU]

No dome light in my ragtop!  Only foot lights and under dash lights; they all turn off as they should with the doors closed.  Glove box was actually the first thing I checked, as that little bulb got me once before in the past.  I have confirmed the glove box light is not on.  I haven't checked the trunk light as I haven't been in the trunk in quite a while.  But I will make sure the trunk light is not lit.

 

ZT

[ZTatZAU]

Trunk light (and the license plate lights at the aft end of the trunk lid) both turn off when the trunk lid is closed... so that's not the culprit!   However, when I pushed the fore and aft electric seat switch back and forth a couple of times and let the switch return to the neutral position, the 1.6A parasitic drain disappeared once again.

 

Battery is now fully charged at 12.9V which I expect will drop off to 12.5 or 12.6 volts with the charger disconnected.  I will monitor the situation to see what happens over time (over night) and report back.

 

Thanks for all the replies!  ZT

[EmTee]

Might be time to pull fuses one at a time and test across the contacts with an ammeter.

[MRJBUICK]

more than likely you have a clock 

most clocks of this vintage work sometimes at best

see if there is a fuse for the clock if so pull it and see if that changes things

if it is you have to see if there is anything else on that circuit and if so you would have to unplug the clock

i would also consider putting in a battery disconnect, takes away all the headaches

Marty

[ZTatZAU]

13 hours ago, EmTee said:

Might be time to pull fuses one at a time and test across the contacts with an ammeter.

Thanks EmTee, and "Yes", that would have been my next approach; but it looks like I've jumped that shark for now.  I'm fairly certain that my electric seat control was causing the battery drain.  Once I cycled the seat position switches last evening, the parasitic drain disappeared and has not returned as of another check this morning.  😊

 

As expected, once off the charger last evening, the battery drifted down to its usual 12.6V and currently remains at that level.

16 minutes ago, MRJBUICK said:

more than likely you have a clock 

most clocks of this vintage work sometimes at best

see if there is a fuse for the clock if so pull it and see if that changes things

if it is you have to see if there is anything else on that circuit and if so you would have to unplug the clock

i would also consider putting in a battery disconnect, takes away all the headaches

Marty

Thanks Marty!  Yes, I do have an electronic clock that hasn't worked in years; but that has never previously caused any battery drain problems.  As stated above, I'm fairly certain that something was stuck in my electric seat control and once the switches were cycled, there was no more parasitic drain.

 

I am however, intrigued by your suggestion of a battery disconnect to avoid such problems in the future.  What sort of "battery disconnect switch" would you recommend?

ZT

[Ben Bruce aka First Born]

Glad you found it, ZT.    Your battery is easily accessible, I believe?  I would just remove the NEG cable from the battery post.  Cheaper and more reliable than any disconnect I have seen.  

 

  Ben

[ZTatZAU]

25 minutes ago, Ben Bruce aka First Born said:

Glad you found it, ZT.    Your battery is easily accessible, I believe?  I would just remove the NEG cable from the battery post.  Cheaper and more reliable than any disconnect I have seen.  

 

  Ben

Thanks Ben!  And your take on disconnecting the battery makes perfect sense.  I was just curious as to what Marty had in mind.

ZT

[NTX5467]

A bit of a definition issue . . . 1.6A is NOT a parasitic draw, but a MINOR draw that needs to be fixed.  "Parasitic draws" are usually measured in milliamps, not full amps.

 

For example, when the '86 Corvettes came out, the dealers got a letter instructing them to fully charge the battery when they first received the cars from the assembly plant.  The batteries in such new cars are usually only 60% charged, so they needed a complete full charge to start with, before they were put on the lot for display and/or sale.  The new factory alarm system had enough parasitic draw to make that newly-charged battery "dead" in about 30 days.  Sooner if the battery was not fully charged.

 

If a diode in the alternator goes bad, the alternator will not fully charge the battery, due to the alternator's lower output.  The diodes chop off the bottom part of the voltage sine wave produced by the alternator, such that only positive voltage comes from the alternator.  ONE failed diode lets voltage go both directions.

 

Alarm systems and electronic-tune radios are two "normal" parasitic draw producers.  The radio has a "memory wire" that gets voltage all of the time, even when the radio is turned "off" manually.  This allows the internal clock to work as well as keep the owner's station pre-sets in memory all of the time, too.

 

You might limit your investigations to systems whcih are "live" all of the time.  Headlights, brake lights, courtesy lights, trunk lights (whether controlled by a normal switch or a mercury switch, power door locks, and other things which will operate with the ignition key "Off", for example.  Plus, of course, if the radio is a later-model electronic tune unit.

 

Rather than just a bad electrical item, it could ALSO be a chaffed power feed wire, too.

 

Just some thoughts.  Please keep us posted on your progress.

NTX5467

 

 

[ZTatZAU]

2 hours ago, NTX5467 said:

A bit of a definition issue . . . 1.6A is NOT a parasitic draw, but a MINOR draw that needs to be fixed.  "Parasitic draws" are usually measured in milliamps, not full amps....

You might limit your investigations to systems whcih ...

Please keep us posted on your progress.

NTX5467

Thanks for your reply and the technical info you provided NTX...  But apparently, you missed my reply to EmTee  above...

 

"I'm fairly certain that my electric seat control was causing the battery drain.  Once I cycled the seat position switches last evening, the parasitic drain disappeared and has not returned as of another check this morning."  😊

 

At least for now, all seems to be good!  ZT

[Century Eight]

ZT, There are a lot of good comments here, but the easy fix is a battery shutoff switch for a number of reasons.  They are very inexpensive , a few years back, $10-$30, depending on the type you get.  When I put a new clock in my 70 Chevelle, the batt was dead in about a week.  When I put my sons 86 Corvette into storage, it was dead in about two weeks, certainly because of all the electronics.  

 

The cutoff switch can stop this draw, and when a car is put into dead storage, the car will start right up after a six month slumber.  I like that when my cars are in a garage with no power and I don’t  have to stretch an extension cord out to the barn to charge them up.  Works just as well with my six volt Buicks and their long skinny batteries. There are a couple of types, one that screws on and on an another one is a knife switch depending on how much clearance you have.

 

 The big thing is that with all these old cars under one roof,  and their old wiring, and electronics, I dont worry about one of them catching themselves on fire with a stuck horn relay or something and taking the whole barn down.  Are you storing your old flivver in an attached garage?  That is even worse.  About once a year, I read about a barn fire and a lost collection.  That’s just not for me.