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96 850 Testing for battery drain

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
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JimBee
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96 850 Testing for battery drain

Post by JimBee » Sat Jun 01, 2019 4:14 pm

Key off, multi-meter on the 10 amp setting, I'm getting fuse readings that range around -.17 to -.35, but settle at -.22—except for #12 (stop lights) that settles at -.15. The battery does drain really fast (over night can lose 2 or more volts). Apparently those readings suggest the whole system is energized far beyond the 50 milliamps recommended. True?

What should I check next?

Afterthought: Could it be the key switch, even with the key out? Engine starts and runs okay. Headlights and signals work correctly.



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Re: 96 850 Testing for battery drain

Post by abscate » Sat Jun 01, 2019 6:29 pm

Get all lights off and put the ammeter I; the ground circuit in series. Remove ground cable and measure current flowing. Should be under 50 mA


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Re: 96 850 Testing for battery drain

Post by tardcart » Sat Jun 01, 2019 6:59 pm

you couldn't have those draws on every fuse. There is a large flash voltage upon initial contact when you put the battery cable on that then goes to only enough to make the light blink on the stereo/alarm and memory on the computer. Are you pretty sure its not just a bad cell in the battery? If you had another battery to swap in i'de do that. next Ide disconnect the computer and see if when hooked up in the morning there was still loss of voltage over night. Its pretty hard to measure mA with a less than 200 dollar meter. but over night loss is easy to measure. so every night pull another fuse. also its helpful to place a small light bulb like a dash bulb between the neg terminal and removed ground and observe as you pull fuses .



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Re: 96 850 Testing for battery drain

Post by JimBee » Sat Jun 01, 2019 8:23 pm

I'm testing like abscate suggests, negative cable off battery post, meter set to the 10 amp position with its leads connected between negative battery post and negative cable. The car has been parked for a week with the battery disconnected so no part of the system should be energized. I've had this car for a while, have driven it very little over the last couple of years. Other batteries have likewise drained.

So what I'm measuring is circuit demand, not current, true?

So that brings me back to the key switch question: If there is a closed contact in the switch that should be open with the key off and out, then couldn't that act like a "key on" condition that would trace through all the fuses to ground?

One other clue. When I touched the meter lead to battery ground with some of the fuses out (one at a time), the alarm emitted a short beep. Thinking back, the driver's side door might not have been closed tightly. I know that if I connect the battery with the door open the alarm will sound until I lock and unlock the door with the key. What's interesting is that some how the alarm got a little jolt when I was measuring amp draw.

Tomorrow, I'll double check, making sure the doors are all closed.



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Re: 96 850 Testing for battery drain

Post by abscate » Sun Jun 02, 2019 3:18 am

Each time you check your current draw, you are reconnecting your battery, so the alarm is doing a reset.

Try pulling the plug of the ignition switch with the ammeter in circuit to see if the current draw falls, perhaps?
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Re: 96 850 Testing for battery drain

Post by JimBee » Sun Jun 02, 2019 6:06 pm

All of today's measurements taken on the 10 amp multimeter setting. The glove box lamp did turn out to be part of the draw.
All fuses installed:
Glove box:
open, lamp on, reading is .22 on 10 amp setting, so 2.2 amp draw. Fixed.
closed, lamp off, reading is .1 (1 amp draw)

Fuse 15 out:
car door open, 1.3
car door closed .1 (so 1 amp draw).

Fuse 15 (and all other fuses) in:
car door open, 1.84 (half amp difference from fuse 15 out).
car door closed, .1

I also tried some of these measurements with the the key switch unplugged—that didn't seem to make any difference.

So it looks like I'm down to .1 x 10 = 1.0 amp draw, still way higher than the spec'd 50 mA.

I think tomorrow's test will be pull fuses 1-10, test; pull 11-18, test; and keep pulling until I find a big decrease, then replace in that span until it goes back up.



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Re: 96 850 Testing for battery drain

Post by tardcart » Sun Jun 02, 2019 6:58 pm

just because you are on the 10 amp setting doesn't mean you divide by ten. the ten amp setting is just the max the meter will take with out blowing the fuse or burning up.( I think). if so, you are .1 that's 100mA only twice 50mA which is fine? Put a elec light tester to a ground and to neg, and then remove neg terminal and see how bright it glows. if its dim you are using nothing. don't make the initial contact to ground with the light tester and cable off as it may burn it out. dont turn anything on either as it will fry the light. best to use small bulb on alligator clips disposable.



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Re: 96 850 Testing for battery drain

Post by DeadEric » Sun Jun 02, 2019 9:26 pm

Sounds like you have a parasitic draw. JimBee is correct, anything after the decimal is mA. If it's been a constant issue your battery could be weak beyond repair. As long as it holds some charge you should try to find the draw before you replace it.

The key to ruling out parasitic draw is finding the circuit that has the draw. The easiest way (for me) to find the circuit is...

Key out, doors closed (or make the car think they are closed) and all lights out.

Using a DVOM check the DC volts between the fuse pins. The little metal things on the top of the fuse, black on one side red on the other.

If the meter reads 0.0 volts DC, it's not active. If it has a reading, the fuse has power running thru it. Mark the fuse and check all of them until you know what fuse numbers are active.

Once you know the active fuse circuits, you can narrow down the fuses that should and shouldn't have power with wiring diagrams and power distribution diagrams.

If you want to go full nerd (as I always do) you can take your findings and go to this website and convert them to amps.

https://www.powerprobe.com/fuse-voltage-drop-charts

Lastly,
I have access to Mitchell wiring diagrams at work. They aren't factory diagrams and sometimes lacking in important details. However, I'm always happy to check things for people (when I remember and as time permits) and report what I find.
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Re: 96 850 Testing for battery drain

Post by JimBee » Sun Jun 02, 2019 10:00 pm

Cool. I hadn't seen a chart like that before.

I have noticed that the fuses have a bit of metal revealed on each side of the top, so I'll put the meter on those tomorrow and see what I come up with.



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Re: 96 850 Testing for battery drain

Post by JimBee » Mon Jun 03, 2019 9:24 pm

I checked voltage at the fuse box on all the circuits—ignition off.
Found significant (close to battery) voltage at: 5, 6, 12, 13. Very slight amounts at: 14, 23, 24, 26.
I had a jiffy fix for the glove box lamp—one of those very small caliper nipple caps stuck on the end of the switch post, it fell off and I lost it. The idea is workable though. How about a short section of plastic straw with a gob of super glue in the end to extend the length of the post a few mm?
The #15 fuse supplies 4 different circuits. The glove box lamp on that fuse is the main draw, but there still appears to be ~ 30% more draw on that one than there should be.



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