Measuring current

JayDubya · Posted: Fri Aug 27, 2004 6:49 pm Post subject: Measuring current

My sister has a 96 grand prix with an aftermarket radio. She has been having electrical problems and a few of my mechanic buddies and I think it is drawing too much current ( 50milliAmp parasitic draw and it should be around 19mA) We thought we had it fixed but its having the same problems again
Problem: I am unable to get the tool that sits in the line by the battery that is supposed to allow you to connect in series. How would you guys go about measuring the draw of current when the car is off?

Since I'm pretty sure that the radio is the problem, I have decided to take out the fuse and use the multimeter (in series) to measure the radio's parasitic draw.
I will then put in a second radio and do the same thing.

Does this sound like the best way to go about this? I don't want to spend $50 for a tool I will only use once or twice. Any suggestions, Weaz, SS, 2Old, Nate, Stang, . . . I'll go out on a limb here . . . TH?

Thanks fellas!
_________________
JayDubya aka JW Jay JD ^> ﺵ

Google · Sponsor

Silicon Skum · Posted: Fri Aug 27, 2004 7:34 pm Post subject:

Actually i did a course on 'Autotronics' recently

Yeah using the multi in series between the positve terminal of the battery and the car ( battery disconected and multi bridgeing the battery + terminal and terminal connector) will allow you to measure the current draw (BE CAREFULL if there is a ECU on the car, could be corrupted or damaged if disconnected too long!). Make sure you don't switch anything else on in the car (lights, ignition etc) you could damage the multi if it pulls more than about 10A.

You should also check the line from the radio to the positive feed (the backup) between the radio and its terminal (the un-switched feed) in the cockpit of the car as the ECU , clock etc will add to the total current draw. This will give a clearer picture of the current drain.

What exactly are the "problem" with the electrics? battery draing too quickly?

SS

ToggleHead · TWEAKGURU Joined: 03 Mar 2004 Posts: 4360 Location: Jersey

yeah share more on the problem......thanks for the insult btw,.....=P

i would have a similar thing as SS but in a much less coherent way.......like.....the apsrt about series and multimeters....=P

You sure this isnt a voltage regulator problem....this has been know to happen withthese cars....a friend has one and her windows are slow beacause of that....but she has a stock radio.....share more
_________________

JayDubya · Posted: Fri Aug 27, 2004 8:48 pm Post subject:

Well, I thought it was a voltage regulator too. The thing is that the radio is just plain drawing too much parasitically.

I know there isn't a short anywhere but the car refuses to start all the time and yes, the battery does drain once and a while. It is a new battery.

Hopefully the new radio will help. I just thought of a new thing . . . I could splice in a fuse in one of the leads of my multimeter. That way if something goes wrong, hopefully the fuse will blow instead of the multimeter

I hate the way current has to be measured in series

_________________
JayDubya aka JW Jay JD ^> ﺵ

Silicon Skum · Posted: Fri Aug 27, 2004 9:18 pm Post subject:

A 50MA current draw should not cause the battery to loose so much power, it would be fine for about a week of standing before the care would have trouble starting.

I think this problem lies in the charging circuit. check the altenator and regulator. Also check the ground connections (you would'nt belive how often this is overlooked!).

I would check to see what current draw is being pulled from the battery when the car is running (do not run without the battery connected, you'll blow the altenator!) there may be some other device that is pulling way too much power.

Most likely, it an earth connection problem or altenator / regulator.
Check the condition and resistance across the main positive cable to the battery, this may be corroded or poorly connected.

SS

JayDubya · Posted: Fri Aug 27, 2004 10:09 pm Post subject:

Sorry I didn't say so earlier, but we have checked EVERYTHING and it has been pretty much narrowed down to the radio. In this case, I figured a 50mA draw would leave the battery dead in 2 or 3 days. Maybe a week is right. I tend to be a little on the safe side of my guesses.

I am just trying to see if it is without a doubt, the radio that is causing this problem and I am just trying to find the safest way to do this . . . for all things considered.

Thank you for the advice! It is very much appreciated!
_________________
JayDubya aka JW Jay JD ^> ﺵ

2old2care · Posted: Fri Aug 27, 2004 10:12 pm Post subject:

Agreed with SS....NOTan auto tronics guru, but done a bit of ....troubleshooting in my time. Let's see 50 mA times let's say 720 hours (1 month) = 36Ah That's nothing to a car battery, a lead cell loses nearly that much in internal leakage.
Prolly not getting charged all the way...whats the voltage on the battery in the morning after its sat all night vs. the voltage at idle vs. the voltage at 2500rpm? That may tell you a bunch more.
_________________
.
Liquid-Cooled Q9450 and an EeePC
.

JayDubya · Posted: Fri Aug 27, 2004 10:20 pm Post subject:

I'll test the voltages too. I can't do so right now b/c the car is 200miles away. Hopefully tomorrow we can get some answers to some of the questions.
_________________
JayDubya aka JW Jay JD ^> ﺵ

2old2care · Posted: Fri Aug 27, 2004 10:22 pm Post subject:

tomorrow....I'll pop in a time or two...it's a g/f, weekend though...
_________________
.
Liquid-Cooled Q9450 and an EeePC
.

JayDubya · Posted: Fri Aug 27, 2004 10:50 pm Post subject:

I appreciate the help!
_________________
JayDubya aka JW Jay JD ^> ﺵ

Silicon Skum · Posted: Sat Aug 28, 2004 6:32 am Post subject:

I would say the fault is in the charging cicuit, OR it *may* be in the starting circuit, i.e is the motor cranking over fine, but not firing. could be that the coil is not getting enough voltage (would depend on the coil type, resisted ballast etc). If the car is not cranking at all / poorly, could it be the connections from the battery to the starter? checked the solenoid?

If you have checked the regulator and altenator then I would place my bet on the problem being with the earth strap, this whole thing just screams poor grounding! you can never have enough money, good luck or good grounding

If that earth strap from the engine block is a poor connection the altenator will be trying to ground to any available point (accelerator cable, brackets etc)
Try replacing the earth strap if it is frayed or looks corroded (even if it *looks* alright it could still be at fault -replace it anyhow it's a cheap part), I replaced mine with a heavy gauge earth strap for a large truck (it's 5 times longer and thicker than the standard, never had a problem since).

SS

JayDubya · Posted: Sat Aug 28, 2004 7:00 am Post subject:

More things to check out . . . thanks guys
_________________
JayDubya aka JW Jay JD ^> ﺵ

[KoG]^weaZel · Posted: Sat Aug 28, 2004 10:52 am Post subject:

Jay,
Most multimeters (DVOMs) will have internal fuses for protection. At least all the Fluke and radio shack meters that I have used have them.

Now on to the car. When you disconnect the positive terminal and place the DVOM inline there what is the reading? And what is the reading at the radio?
What kind of condition are the batter cables in? Have you load tested the battery? If so what were your findings there? And when you test the battery you need to make sure to test the draw when the starter is engaged too. Then once the car is started you need to test the amperage and voltage output of the alternator. Oh and what is the voltage in the battery at rest?

I dont know how much of this stuff you have already done I just want to cover all the bases. Because this problem sounds like something I had happen to me with a battery just not holding a charge for very long. And when the battery was tested it looked alright. So I would trickle charge the battery and it would be good for the better part of a week. But as the time went along the jeep would crank slower and slower. At first I was think it was the alternator, but once the battery was replaced everything was fine and has been since.
_________________
I tweaked and it tweaked back! So I Tweaked some more!

"Barney is like the Michael Jackson of PBS." - James Tybeerious

ToggleHead · TWEAKGURU Joined: 03 Mar 2004 Posts: 4360 Location: Jersey

what about the brushes in the alternator.......i know you said you checked all this and all but its possible there may be an internal problem caused some where......

and not meaning to be a jerk but are you sure its (radio) installed right......ive had problems with grounds bridging circuits and causing simliar issues.....

i had a '73 fury with a 360 under the hood.....that every time i stepped on the brake, the ignition fuse would blow....the car would shut off....and all battery connection would be dead.....certainly....trying to turn, brake, or do much of anything behind the wheel of a 2.5 ton car at 45 miles an hour with no power ANYTHING, and worse....power steering that wasnt WORKING (we all know manual steering is easier than broken power...=P) didnt go over too well.......
i found a very simple fix to this though........i cut the head off od a bolt and replaced the fuse with it........

real safe huh???

=]
_________________

Silicon Skum · Posted: Sat Aug 28, 2004 1:06 pm Post subject:

2old2care · Posted: Sat Aug 28, 2004 2:58 pm Post subject:

JayDubya · Posted: Sun Aug 29, 2004 12:26 am Post subject:

Yeah, I'd love to see TH blow up

Anyway, when the car is in a dead state the battery produces ~12.65v. When started and idling, about 14.45v and ditto @ 2500rpm . . . or therabouts (I had to guesstimate b/c i couldn't watch the tach and open the throttle body at the same time whilst watching the multimeter.

The old radio drew over 25 milliamps for a parasitic draw. The new radio is only drawing 1.67mA now.
From the battery, There was a draw of 49mA but that is now down to 15.3mA.
I just cleaned all the battery terminals and connectors now as well as checking ALL the grounds humanly possible. With any luck it should be good to go now.

I love you guys and i'll have a few more stones for each one of ya

_________________
JayDubya aka JW Jay JD ^> ﺵ

Silicon Skum · Posted: Sun Aug 29, 2004 10:03 am Post subject:

good luck! <keeps fingers crossed and strokes lucky rabbit foot and wears his lucky T-shirt>

That battery sounds low to me, should be around 13.8V the 14.45V frrom the altenator sounds ok. Did you check for fluid level in he battery?
Also have you checked for an AC ripple yet?

You might need to drop a few battery "cleaning" tablets in that thing, sounds like the plates have have furred up due to the low charge state and boiling while the little charge left is dumped on to the starter. If you can visually check, see if any of the plates are warped, there may be an internal short on one of the cells. Once a car battery goes flat, thats usually the end of it's usefull life.

Untill last year the battery in my car was 15years old (my car is only 13) and never had a problem, mind you the battery for the Mini was taken from my old Merc (mercedes benz 200), the battery would'nt start the Merc any more, but the mini will start on 9V as long as there is enough current to turn the starter

Lasted for years until the batery lead arced onto the frame and boiled the battery up.

So now I have the newer model of the same battery and uped the alt to a 50A model from a Ford Escort. Sweet.

SS

[KoG]^weaZel · Posted: Sun Aug 29, 2004 10:29 am Post subject:

WOW 15 years!!! That is a loooooong time for a battery to last. Here in Arizona we are lucky to get 2 years out of a quality wet cell battery. You might get 3 if you are lucky. The dry cells, like the optima brand do tend to last quite a bit longer. I had one that lasted 8 years.

The resting voltage of your sister's battery is in the normal range. I think that you went in the right direction with the radio. But the battery should be able to hold that much of a draw for longer. With that in mind I have a question. How often is this car driven? and when it is driven how long of a trip?
_________________
I tweaked and it tweaked back! So I Tweaked some more!

"Barney is like the Michael Jackson of PBS." - James Tybeerious

2old2care · Posted: Sun Aug 29, 2004 4:46 pm Post subject:

Resting voltage is okay, but are you still getting that >14V after a run to the store or such? If so...your not holding the charge right or something. All warm, and charged the voltage should settle down to somewhere like 13-14 volts. If it always stays high like that all the time it will "overcharge" the battery, not good either.
_________________
.
Liquid-Cooled Q9450 and an EeePC
.

JayDubya · Posted: Sun Aug 29, 2004 8:40 pm Post subject:

Its a new battery load tested and all . . . we know its good.

The battery usually doesn't have alot of time to charge during its trips. Usually it takes at least 2-10 minute drives back and forth from school each day and sometimes it will take a 15 minute drive to other parts of town.
Great point on the charge times, Nathan. The times are barely adaquate to make up for the time it spends draining.

It could be that the radio is drawing from an already lower storage of potential.

I managed to clean all the battery cables and ground connections as well as resistance testing all the cables too. Everything checks out fine and hopefully it was just the radio . . . I know it doesn't all add up and it really does sound like a bad ground but hopefully the dremel found some good metal to keep everything peachy.

Did I mention I love you guys

_________________
JayDubya aka JW Jay JD ^> ﺵ

[TN] Nathan · ALMIGHTY PWNER! Joined: 14 Feb 2002 Posts: 7406

We need some numbers.

Get a multimeter and give us these voltages from the car.

Battery voltage with car running = ?
Battery votage when car not running = ?
Battery voltage when post are removed from the battery and it is by itself?
_________________
Owner & Administrator
www.Tweaknews.net
www.Pocketbookpinch.com

JayDubya · Posted: Sun Aug 29, 2004 10:43 pm Post subject:

Car running is about 14.45v
car not running is about 12.65v
battery disconnected is about 12.7v

All of these seem to be well within good ranges.
I'm just hoping the new cd player and all the wire/grounding cleaning helped.
Time will tell.
_________________
JayDubya aka JW Jay JD ^> ﺵ

[TN] Nathan · ALMIGHTY PWNER! Joined: 14 Feb 2002 Posts: 7406

Those voltages are perfect.
_________________
Owner & Administrator
www.Tweaknews.net
www.Pocketbookpinch.com

[KoG]^weaZel · Posted: Mon Aug 30, 2004 12:08 pm Post subject: