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Parasitic draw?

7

77volvo242

Member
Joined
Nov 14, 2020
Location
California
My ?77 242 has not been starting after a few days of not driving it. Hooked up a multimeter and saw the battery voltage was dropping +/- .2 volts in 24 hours. For example, after being fully charged to 12.6 volts, the next day it would be down to 12.4 or so.

I then did a parasitic draw test on the battery like here: https://www.wikihow.com/Find-a-Parasitic-Battery-Drain

However, I?m not detecting any draw whatsoever.

I replaced the battery and still see the same voltage drop.

Any ideas how else to find the culprit?
 
Well, 12.6v is not a fully charged battery. Also a drop over night of .2v is perfectly normal. I would suspect that your alternator is not charging the battery. Sometimes when they fail they only put out around 12v which is enough to run the car but not enough to fully charge the battery. A theoretical fully charged battery would be at 13.2v. But usually the high 12v like 12.9 or 13v is what you'll see with a full charge after sitting a bit.
 
Sorry I should have clarified that. The new battery I just put in charged to 12.88v or so (didn?t go on a long drive so not sure if it?s totally charged). Multimeter reads 14v with engine running.

There is a basic alpine single din stereo. It doesn?t appear to have power with key in off position.

.2v is normal drop overnight? I?m seeing this continuously so after 3 or 4 days there isn?t enough voltage to start the engine.
 
You need to check for the draw with a low range current meter. Something like the 200 milliamp range would do. Even a basic stereo like your Alpine should have presets that need at least 10-20 milliamps to keep the memory. If the draw is more than that, then that is your issue.
 
I use a special tool to do parasitic battery drains. It is just a cutoff switch. You connect your meter, THEN open the switch. That way, there is less of a chance of the draw going away and a misdiag. (compared to just disconnecting the cable and then connecting a meter). I use a Fluke 87 V.
 
Yeah even on the 200mA setting I get 00.0 reading doing the parasitic draw test. And yet the battery voltage continues to drop. That?s why I?m so confused on how to begin addressing it.
 
Long ago and far away I had responsibility for a dozen or so battery strings that consisted of a total of about 200 individual 12v cells.

A lead/acid battery has a nominal, fully charged, voltage potential of 12.6v. Float chargers should float at that rate and charge at 13.6v.

Dropping even 0.6v off float is not at all unusual. A better measure is where the battery drops under load. Turn on the headlights. Battery voltage will drop to somewhere about 12.0v and stay there for minutes or hours. That is an expected normal.

Automotive problems occur when a battery under starter load drops voltage below 10.0v. That is the point that the electronics begin to do funny things like not starting. I have a car that does exactly that.

Almost any auto parts store will do a load test on your battery for free. That will produce a number related to the engineered specification of the cold cranking amps of the battery under test. Just replaced a battery that tested at 150 CCA at a 850 CCA spec while still starting the engine reliability. At some point the battery will fail that 10.0v electronics requirement and the engine will not start.
 
Did the 77 have the delayed overhead interior light function? Perhaps not enough to brighten the bulb but still draw current? Remove the bulb and check again. Radio was mentioned. Remove fuse and check again ( overnight).
 
77volvo242 said:
Yeah even on the 200mA setting I get 00.0 reading doing the parasitic draw test. And yet the battery voltage continues to drop. That’s why I’m so confused on how to begin addressing it.
Click to expand...

I've never seen 0.00 draw. Clock, ECU, stereo memory has to add up to something more than 0.
Like ZVOLV said- you need to hook up the meter before removing the battery terminal. Make sure your meter's fuse is not blown (turn on the dome light and see if anything is registering on the meter).
 
If you don't have a switch, you can just use a jumper wire. Connect a jumper wire to a disconnected cable terminal and the battery terminal, connect the meter, then remove the jumper wire. It's tricky to connect to the big battery post. I recommend you buy a $5 cutoff switch and slam a couple screws into each side for meter connections. https://www.amazon.com/LotFancy-Bat...MTXXY9M/ref=pd_lpo_2?pd_rd_i=B07MTXXY9M&psc=1

The Fluke 87 also has a Min/Max feature that records the peak and low readings. You can leave it on the vehicle overnight.

Just because a battery is new doesn't mean it is any good.


Do you have your meter leads in the correct position? You have to put the positive lead to AMPS. Not the hole/connection for VOLTS .
 
77volvo242 said:
Yeah even on the 200mA setting I get 00.0 reading doing the parasitic draw test. And yet the battery voltage continues to drop. That?s why I?m so confused on how to begin addressing it.
Click to expand...


Then you are not testing it right (blown fuse on meter?).

Near EVERY car has a certain amount of parasitic draw.
 
Thanks for all the advice. Will try the headlights for 20 minutes and also confirm multimeter hooked Up correctly and report back.
 
Yeah on a old car like this, I would expect about a 5-7 milliamp draw normally.

And buy a switch for $5 and put a post/screw into each side of the switch to clip leads onto. On a modern car with auto headlights, alarms, etc you WILL blow the fuse in your meter if you simply put it in between a disconnected cable and the terminal.
 
Another thing I have experienced is alternator failure after getting hot. Make sure that you not only test the alternator voltage on the battery when running. But be sure to check it again after the alternator is hot and the car is fully up to temp. About 20 minutes or so of running.
 
77volvo242 said:
Sorry I should have clarified that. The new battery I just put in charged to 12.88v or so (didn?t go on a long drive so not sure if it?s totally charged). Multimeter reads 14v with engine running.

There is a basic alpine single din stereo. It doesn?t appear to have power with key in off position.

.2v is normal drop overnight? I?m seeing this continuously so after 3 or 4 days there isn?t enough voltage to start the engine.
Click to expand...

Try shutting the radio off with the source button and see if the battery stays up. If the display shows anything when the ignition is shut off the radio is still turned on.
 
another test you can do: measure the battery voltage, temporary disconnect battery for safety, then disconnect the alternator from the battery. (TAPE OFF the wires that you disconnect!), reconnect the battery, measure the voltage the next morning. Voltage the same as the day before? Then there might be a faulty diode inside the alternator. That faulty diode can cause/create an electrical path through which the battery can drain.
 
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