Ok guys.... 87 base, have had a draw since I bought it last year... got into it this morning.... here the data:
test light shows draw, meter says 0.075 draw.. what I have done:
Pulled all fuses and relays in panel and behind DIC
unplugged radio
disconnected alternator and starter
pulled fusible links off stud behind battery
had battery tested- shows good
none of this changed my test light or meter reading... same draw on meter....
it takes about 3-4 days of sitting to pull it down enough to need to be charged before it will start.
I can’t think of anything else to check... I’m open to any ideas or suggestions
thanks

 

Is that draw in amps or volts?

 

Most modern cars draw some power while they are just sitting to some extent. It sounds like you isolated pretty much everything. It varies from Corvette to Corvette but is usually around .035 to .045 amps if I am not mistaken. Does your Corvette have any aftermarket conversions parts or performance parts. How about alarm systems?

How old is the battery? What brand? Is it a flooded lead acid battery or something special like a Gelled battery or a Tubular battery?

As soon as a battery is manufactured it has a Self-Discharge Rate. This discharge rate increases as the battery ages. As a battery cycles it tends to shed a little lead from the plates and this falls to the bottom of the cell. As the lead that has been shed moves around with the motion of an automobile it can make a short inside the battery. This short if minor could be a drain and increase the self discharge rate, if it is a bad short it would start making heat and eventually cause the battery to rupture or even explode.

Has the battery been maintained? When I ask this I am asking if you checked the electrolyte inside the battery recently? A battery with low electrolyte will frequently loose the plate area above the electrolyte to oxidation and this will cause a decrease in capacity. I have seen many batteries put on "Slow Chargers" that were charged to the point of boiling away virtually all the electrolyte. I used one and it killed a brand new Interstate battery in three months. The battery was run dry by a constant charge of ~1 amp. It was hard to dish out another $160 for a new battery after my saving money on the $20 no-name slow charger at harbor freight. If your battery tender does not recognize that the battery is full, it will boil it dry.

Not to sound dumb but how did you determine the load? First I use a meter that measures up to 10 amps. I disconnect the battery negative wire and then put the meters leads in between the battery Negative post and the battery Negative Cable connector. With the meter set to measure amperage I then measure the drain with both leads attached. I would start at a specific time and record battery voltage and current drain. Do this every 10 minutes for a while and see if it changes at all.
If I was doing this myself I would put a Current Shunt in place allowing me to monitor the drain very accurately. How do you do it with a test light?

The battery was tested? How?

My idea of battery maintenance is to remove the battery from the Corvette for the winter months and put it on a workbench in my garage. I wipe it down and clean the outer surfaces. Then I open the access holes allowing me to see the electrolyte and verify it is at the proper level. If it is Low I would add Distilled water and then connect it to a charger. The charger needs to be able to completely charge the battery and make it boil away (Gassing) and then the charger is shut down and the battery is charged once a week to keep it full by a timer. The charger I use is designed to have four stages of charging and it does an amazing job. Before going back into the Corvette I wipe it down, clean the posts and check the electrolyte once again. Then I clean the battery connectors and re-install the battery and bolt it down. I then put battery grease on the tops of the connectors and the exposed post areas. This keeps oxygen away from it and ensures a better connection for your Corvette.

With everything you described being disconnected the problem is likely the battery. In my garage I would pull it out and test it specifically. I would watch it for a couple days making measurements and recording them. I suspect your battery might test okay and still have a higher than normal self-discharge. Like mentioned earlier your "Drain" is a bit higher than normal but might be okay.

Best regards,
Chris

 

My alternator was draining my battery overnight. My guess was bad diodes or something keeping the charging circuit open. I replaced it and haven't had a problem since. I ended up going through three brand new batteries until I figured out what was causing it. Luckily the batteries were under warranty and I'm glad they replaced it that many times within a couple weeks. It wasn't just draining the batteies, it was killing them.

I still have the old alternator, just haven't taken it apart yet to have a look inside to see what was going on with it.

 

Good tip! I hadn't considered this possibility and I've got a rebuilt alternator! Thanks.

 

To all the above.., car is driven weekly usually unless it’s raining or bad weather, while it’s in the garage it’s always on a higher end charger/maintainer because of the draw. The charger is automatic and switches to float when the battery is fully charged. My charger displays charging volts and float volts so I can monitor state. It’s a maint free wet cell, so can’t check water. It was purchased and installed about 12 months ago. It was removed from car after it charged overnight and taken to a parts store and tested with a load tester.
the test method for the draw was almost exactly as written above, neg cable unhooked, meter between cable and post. To test with my test light I had neg cable unhooked, test light clamped to neg post and probe to neg cable. Test light was illuminated and never went out while unhooking everything I described in my earlier post.
I have had the battery unhooked from the car for 5 days, with my meter monitoring voltage and it has fallen from 12.75 to 12.60 over the 5 days while no load on the battery.
I may test battery again in its current state of charge to see what the results are now.

 

Did you try singing a lullaby to make sure the body control module goes nighty night?

Sorry Im feeling a little punchy this morning

In all seriousness.. this is a great example of needing the right tools. With the right tools and accessories for the tool you could pull each fuse, and splice in a current draw meter to pinpoint this. Ideally, a scope which will monitor over time and the proper cables to punch in. You would need a DC current "probe". This can all be had for under $180 if you have a laptop. Not ideally a DC current meter with proper cables to punch into where your fuses go. A scope will help you immensely if you plan to keep an old car in the corral.

As I think was mentioned the vette does draw some when asleep... I just keep a good charger on the car that has a float mode on it so my battery doesnt get destroyed. Float mode is critical for battery life. I built an adapter that connects to the hood light cable so its easy to connect (I leave my hood lights disconnected).

This is the charger I chose.. I didnt like buying a non usa device but I couldnt find one that did float mode specifically for under $100. Some may do float mode and not indicate so but that doesnt help me choose a charger.


I do not believe that the thing does 10amp but I dont care about that.. It does have a built-in fan to cool the regulator so its a well thought out design. I think its russian made actually. They probably stole the design from the CIA.

As far as a cheap scope search for my thread concerning oscilloscopes. Aw hell, here you go:

 

Have battery tested with a digital battery tester, most auto parts stores should have one. Many times they will pick up a weak cell, where other types will pass the battery as good.

 

go buy a ''CTEK'' charger/tender,,

leave it on the system

 

Sorry i didnt see this post.. you can ignore my "contribution"

 

Hello again vyper202,

When they make a flooded lead acid battery "Maintenance Free" you should be able to get access to the electrolyte anyway. I have seen stickers covering the holes and other tricks by the manufacturers to hide the access points. I have not found a "Maintenance Free" battery yet that I could not get into and check the electrolyte. The manufacturers know that the battery will use water but choose to seal the case as much as they can to get people to replace the battery instead of filling the electrolyte with Distilled water. Battery companies are in the business of selling batteries. Look for any way to open the top of the cells, it might be a large block that covers three cells that needs a screwdriver to pry the cover off. Before trying to pop the covers off PLEASE wear Eye protection of some sort, the electrolyte can blind you if it gets in your eyes.

A large percentage of flooded lead acid batteries have Antimony in them to make the cast plates harder and last longer. The problem is that antimony is poison to a battery and the more they use the shorter the life of the battery. Higher antimony also requires more electrolyte refills as the battery will be thirsty. They try to use as much of this antimony as they can without influencing the life of the product or making it a very thirsty battery.

When I buy a new battery I will charge it up completely BEFORE installing it in my Corvette. It is even better to form the battery a bit more by discharging it of 80% of it's rated capacity and charging it to 110%. I do this using an automated system in my garage using a small electronic load that pulls a specified current regardless of the voltage. Battery companies do this as part of the forming of the battery. My past experience has taught me that this will ensure full capacity of the battery to be available. Most cars never charge their battery completely and batteries will suffer and have a shorter life due to this fact.

Batteries were part of my job, I tested them and verified the charging algorithms allowing us to fully charge the products used in a particular job. I have tested hundreds of batteries and seen some amazing stuff along the way. I also know which companies tell you the facts and who makes up the facts as they need them.

It sounds like you have done a good job of isolating your battery. What brand battery is it? I know the type of load testers they use at auto parts stores and they are okay for basic testing but I have seen batteries tested with that type of clamp on load tester pass the load test and fail the discharge test. The electrolyte stores the energy and sometimes even that gets stratified inside the tight confines of a battery case. I have seen stratified batteries on Corvettes that use a Battery Tender and what happens is the electrolyte unevenly wears the plates down. This is why a good solid charge where a battery starts gassing is really helpful as it helps circulate the electrolyte and get it evenly charged. I have never seen a properly functioning charging system in an automobile make the batteries gas. In stationary batteries it is done often as they are aware of the potential for stratification and the loss of capacity. The best way to prevent stratification is to drive the Corvette with the battery installed for a short period.

On cars they tell us to leave the headlights on for 10 minutes and then check the voltage. Using a Min-Max feature I attach the meter to the battery and start the Engine. The battery should not go below 11 volts even after 10 minutes of headlights on. If it does I would consider replacing it....

Harbor freight has a tool that will plug into a fuse holder and show the current flowing thru the circuit. They are inexpensive and very helpful to have in your tool box. For me the most important tool is a higher end Fluke Multi-meter which is extremely accurate and easy to use. There is another tool called a Power Probe, these are very useful working on virtually anything with a battery in it. With the power probe you can test most of the components of your Corvette. I bought mine in a large kit with a ton of accessories on Amazon.

 

CTM, since you are a pro, I would expect you to use the proper terminology. The word power is related to Watts. The HF tool measures Amps, not Watts. In addition, the HF tool cannot register less than 0.1 Amps (100 mA), which may be misleading on low current circuits. Seeing 0.0 Amps on the HF tool does NOT mean there is no current flow in the circuit.

 

Couldn't you do the same thing with a digital voltmeter that also measures amps?

 

Yes
You can't measure current draw using a test light or a volt meter.

It's not complicated to measure current which is in amps. Just get a decent multi meter that measures amps and connect it in series with either of the battery terminals and read the current.

No fancy or expensive equipment is needed just a good digital multimeter.

On my 94 I use the 10 Amp scale even though my final current reading is 30ma. Reason for this is that when first connected, interior lights come on when first connected and draw about 5 amps. After about 15 seconds the CCM cycles off the lights and current drops to its normal steady state current draw of 30ma. That’s why I can't use a lower scale to measure when first connected

On the 87 not sure how the body control modules works. I would start on a higher scale and see what it does. If there's no high current draw when first connected, then you can use a lower scale if desired.

 

Since you are getting a current draw with the fuses out it must be a circuit that is hot all the time or a circuit not fused by one of the fuses you pulled. If you have a FSM look in the wiring diagram section. Circuits that are hot all the time are marked as such. Some circuits have a fuse link in the wiring so you will have to test them individually. As you are finding out, electrical problems are a real bear to find!

 

I have to agree with the above comment. Maybe you did not go far enough and need to pull fuse links. Although it feels like you missed something or there is bad initial data.

How did you disconnect the alternator. Did you remove the heavy cable with the nut on it? (rather than a connector)

 

Mine pulls 3.9 amps when the interior lights come on, thru my meter connection... yes I know how to use a Fluke...lol

Since you are getting a current draw with the fuses out it must be a circuit that is hot all the time or a circuit not fused by one of the fuses you pulled. If you have a FSM look in the wiring diagram section. Circuits that are hot all the time are marked as such. Some circuits have a fuse link in the wiring so you will have to test them individually. As you are finding out, electrical problems are a real bear to find!
I believe I have checked all the fusible links, for continuity and draw... but never hurts to check again...

I have to agree with the above comment. Maybe you did not go far enough and need to pull fuse links. Although it feels like you missed something or there is bad initial data.
How did you disconnect the alternator. Did you remove the heavy cable with the nut on it? (rather than a connector)
I disconnected the internal regulator plug and the 12V supply cable... it was completely isolated...

 

With the alternator disconnected, did you check it for bad diodes? I forget the procedure but I'm sure if you google it you will find the procedure somewhere or someone on here will chime in. The diodes convert the AC current the alternator produces to DC current the battery needs. Diodes will only let current flow one way but if one goes bad it will slowly drain the battery.

 

So it sounds like you have been pretty detailed in your troubleshooting and with completely disconnecting the alternator would eliminate that also. Most power that says "always hot" comes thru some kind of fuse or fuse link. Basically everything should be always fused which would be normal design. The only items not fused would be the alternator and starter. Can't think of anything else offhand. Did you ever look at the car in total darkness to look for a light on somewhere.

Look at where the 12 volt battery lead goes and splits off to for corrosion. It could be a high resistance short to ground in any of those places like under fuseable link blocks or any major power connector.

 

I have not measured the Parasitic battery draw on my 95 vett yet.
Your unknown number "0.075" I will assume is AMPs coming out of the positive battery lead going into the car.

Assumptions:
Voltage 12.6 vdc, Current 0.075 amps, equals 0.945 watts.
That’s less that 1 watt per hour.

If these number are valid then:
#1. Your Parasitic leak is very low, and is nothing to worry about.
#2. You have a bad battery or Your measurements are wrong.

Try using a Digital Volt / Current meter (must support 10 Amps)