Attn: wiring guys. Tracing voltage draw...

[Mustang John]

I have a slight voltage draw that is slowly draining dead the battery on the 89 5.0. over 3-6 days.

I disconnect the positive and put a DVM in series between the pos terminal of the batt and the pos cable and see no mA draw, I do see about a 1.5v dc draw, that slowly settles to around .5v over a couple minutes. IF I open a door, it goes to 0volts, soon as the door is closed, it goes back to .5 or so...

I was thinking alarm sys, but since the fuses are well up in the dash, I was being lazy and not pulling them yet. However, it is not armed at the time of the test.

Am I even doing this test correctly?

Any other ways to look the system over?

Thanks!!!!!!!

 

[MrKwik]

The way I check is to use the DVM in series like you are but you need to set it to amps not volts. If you have an escessive draw, you will see it there. I have had ford alternators develop some kind of internal short before so while Im in there I would unplug the alt and see if the draw goes away. Then hook the battery back up and go to the fusebox. Pull each fuse and look for a draw across the terminals in the box. When you find the draw, you will at least know what circuit is the culpret. From there is just tedious tracing everything on that circuit. You will need to wedge something in the door to kill the domelight when checking the fusebox so that you dont see a false reading.

 

[Mustang John]

Yeah, that's what I was doing basically, pulling fuses etc with the meter connected. Initially, I did try mA setting and no draw (0.0) which I thought was weird as the ECM should draw at least a little. I better try again and make sure.

Just in the Volt setting is where I saw the reading.

I've had the alternator do what you mentioned in mustangs before, so the was the first culprit as well.

The car keeps drawing down the battery sitting over the winter. I killed a new Odyssey battery by it discharging it and me nuking the battery with a big rolling charger too much (ouch), and now I killed what should have been a good older Optima I had in my truck. So, now I have a new Optima, and need to make sure I don't kill it (bought a smart charger/maintainer). Less likely it will go dead as I drive it a lot in the summer, but, now is the time to tidy the loose ends on this beast.

Thanks for your input!

 

[Gravel]

Optima's hate to sit dead for any amount of time and it’s near impossible to get them back up...

I have a couple of racers that sit over the winter and have found that just the ecu, and other trace draws will take it down... I now either leave a trickle charger on them or I disconnect the batteries.. Got tired of replacing Optima's.....

 

[Mustang John]

Ahhh... I wasn't sure whether I had killed the Optima by leaving a 2 amp charger on it for a couple days, or now, I'll guess it just sat dead too long too many times, at which point it just quit recovering. I just don't see a major draw that would kill a "good" battery in a few days.

I definitely smoked the Odyssey bat when it went dead with a large amp charger. Umm, oops.. The Optima, I was sorta wondering about. Good to know.

I bought a little Schumacher 1.5amp "smart maintainer" charger. I hope that won't screw it up. It says it won't.

Thanks for the input!

 

[gt90stang]

Hi,

Connect your current meter between the battery terminal and cable, then check for current (you stated 0 amps). Now open the car door and you should see about an amp or so if your dome light works. Maybe you blew the protection fuse in the meter which is usually 2 amps depending on meter. If it takes 5 days to drain then an approximation of the current you are looking for is:

current in amps = Battery amp hour rating / hours to drain

This is a very non-linear function and is an approximation YMMV...yada yada yada.

Oh yeah, sometimes the drain is inside the battery due to the plates flaking and it builds up until the flakes short between the plates.

Good Luck, Don

 

[Mustang John]

I have a typical DVM that has mA scale on it. That should be appropriate for this I believe?

Of course, I left my decent one at work in my cart. Bleh...

Thanks for reading and commenting, good stuff! I'll check the fuse if I see no draw... Didn't think of that...

 

[HISSIN50]

John, i have nothing productive to add, but i have one thought. i assume your alarm is not armed normally (for many hours of the day while not driving it each day or days on end)????
alarm installers are real anal about not having more than about 300 mA draw while armed (usually one relay worth- starter kill relay is not normally energized unless someone tries to start it). but some folks run a relay off the starter kill trigger output (usually orange) to run additional LED's and such (using a relay to not overload the .5 amp circuit). just a thought. (i know your alarm is off for testing, but was not sure how often it is on w/o being driven).

between the anemic charging system, little draws like radio memory, alarm memory, ECU memory and all, it is easy to deplete a battery substantially over a few days.
that is just what came to mind.
good luck, John.

 

[Mustang John]

Actually, when the car is sitting for a couple days, it is in my garage and the alarm is off.

This car is pretty well off for charging. 130 amp alt, Optima battery grounded to the block on one terminal, and to the frame on the other terminal. All battery cables are 0 gauge welding cable and battery is still in the engine compartment.

Gotta get my good meter from work and have at it this week.

Thanks!