I need help with multimeter battery/alt testing

[NRAninja]

I need help verifying the voltage readings on a car battery. I'm trying to figure out if I just had bad batteries or if the alternator is killing them. I want to make sure everything is OK so I don't kill a new battery.

Background info: Car with the potential issue is 1999 Toyota Avalon 180K. I had a 5 year old battery that wouldn't start after sitting for a few weeks. Took it out and saw fluid in the plastic holder tray that bubbled and fizzed up when i poured baking soda/water on it. Probably safe to say that that battery was done. I got a new battery from Advance (with the $40 off coupon of course

), put it in the 2008 highlander, and took the OEM highlander bat and put it in the Avalon. Drove it a few times over a few days, ran fine. Sat for a week and it was dead as a doornail, but I saw the map light switch was in the ON position

Since that bat is also 5+ years old I'm just going to write it off. I took a known good 6 month old battery from our other vehicle, put it in the avalon, and got various voltage readings. I'm not 100% sure what the voltage is supposed to be under different loads.

Here are the readings:
Car not running, no dome lights on (

) - steady 12.6v
Car running on idle (750rpm) - readings jumps between 13.99 - 14.08
Runing on idle, highbeams, dome light, radio, defroster, air conditioner full blast, hazard lights - jumps between 12.28 - 12.35ish depending on when the radiator fan clicks on

Do those readings indicate normal alt/battery function? Do I need to have someone rev the engine to a higher RPM to get an accurate reading? The car starts right up and runs fine like it always has. The battery light on the dash doesn't come on when driving and it didn't come on during the testing. I don't hear any unusual noise from the alternator and the alternator belt is only a couple of years / 30K old. Is there anything else I should check or can I put a new battery in it and be good to go?

 

[trooper001]

That full load reading is too low for my liking. Should be around 13+ volts at the minimum. At the reported voltage you are getting at load, the battery isnt getting the ample... amps and volts to charge itself. I suspect a bad alternator. May need to get it load tested to get a definite answer.

 

[147_Grain]

Originally Posted By: NRAninja
[Vehicle] sat for a week and it was dead as a doornail, but I saw the map light switch was in the ON position

^

There's your problem. Electrical system is likely fine.

Drive the vehicle more often, after a week......check the battery tie-down, electrical connections clamps, and then retest the voltage.

 

[JHZR2]

Full load too low. Id want to see a current draw by running the meter in the ammeter function. Low load looks just fine.

The question is if you have higher than normal parasitic draw. Perhaps a bad diode in the alternator...

 

[cat843]

I think things are fine. Your alternator is not going to put out a lot at 750 RPM. But it should at 2500 RPM.

Try loading it up and run it at a nice steady 2500 RPM while you check the voltage.

A carbon pile load tester is better as you can set the load to what you want.

 

[Chris142]

We are just guessing without an ammeter.

 

[Dave Sherman]

Originally Posted By: JHZR2
Full load too low. Id want to see a current draw by running the meter in the ammeter function. Low load looks just fine.

The question is if you have higher than normal parasitic draw. Perhaps a bad diode in the alternator...


Average multimeters only go up to 10-20 amps, and would require opening the battery lead to use them, which creates problems such as how to bypass the ammeter while starting the car to avoid frying the multimeter with the hundreds of amps the starter takes. He would need a clip-on DC ammeter that can measure up to 100 amps or more to measure the current.

The voltage under load looks low, but he would have to run the engine at 2000-3000 RPM to really gauge whether the alternator is functioning properly. If it can't keep things at 13 volts or more at that speed with all the accessories (lights, fog lights, defroster, air conditioning, radio, heated seats, wipers, etc.) on then it's very suspect.

 

[SHOZ]

You can't expect the alt to put out full voltage at idle. Raise the engine speed to at least 1500 rpm with an large electrical load. It should be above 14v.

 

[Chris142]

Volltage does not mean it's charging correctly. Need an ammeter.

 

[GSCJR]

You require an AVR machine to check the health of your battery and charging system accurately. I also recommend checking the parasidic draw level.

 

[SHOZ]

When the car is off and the battery fully charged you should have ~12.4 VOC with a rested battery. Start the engine and it should read above 14V until it replenishes the capacity that was drained when running the starter.

Some read higher say up to 14.5v.

But with a load on the alt, engine alone anymore can be 50a, turn on the lights, AC rear defrost radio heater fan on hi. Rev the motor to 1500 rpms and if you have over 14v you are good to go.

 

[NRAninja]

Thanks for the replies!
I went by Autozone and they connected a tester to it. The battery test passed and said it had 638 CCA (battery says 585 cca on the label). A charging system test was done with the car running and that came back as "passed" as well.

The plot thickens though. I followed the parasitic draw test procedure in this video http://www.youtube.com/watch?v=KF1gijj03_0
With the multimeter on the DC10A setting, the reading was .573. Not 5.73, but .573
Is that a 573 milliamp draw? Eric said anything over 50 is bad. Should I start pulling fuses like in the video?

 

[SHOZ]

Yes that is 535 ma or just over 1/2 an amp and it is enough to drain the battery over a week or so.

I would guess most cars use around half that for keep alive memory.

I had a Taurus that had the parasitic draw. Was pulling about 3/4 amp all the time. Traced it to the heater controls radio pod.

Beware that some cars will take 15 minutes or so to fully time out on some circuits. There will be higher current draw at rest with the key off until these timeout.

So you need to hook up the amp meter with the car off, then cycle the key to see what the reading changes to. You can monitor this and see the amps draw drop as the circuits time out and shut off. Then you will be at your stable reading.

Opening the door often triggers a time circuit. So I would kill the interior light circuit first and then leave the door open. Just be sure you know what the amp draw is with the door open and closed. It will take a couple time outs to figure this out.

After that it's just pulling fuses and knowing what is on the circuits.

 

[Vikas]

It is extremely difficult to measure parasitic draw. You have to wait until all the systems in the car "go to sleep" That could be be anywhere from half an hour or more. since your interior light was on, it drained the battery.

with the voltmeter just monitor the voltage. as long as the running (car engine running) is higher than resting battery voltage (car engine off) your batter is being charged. Auto parts store has given clean bill of health for your battery and alternator. Your previous draw was because of the interior light.

Just drive normally and if you start having problems again, then start measuring the leakage current.

 

[SHOZ]

It's been my experience with Fords (90's) that a new alternator will put out 14.4 volts. As the alternator wears down the voltage will start to drop. When it gets below 13.6v max it is time to change it.

In my Hyundai's with ECU controlled regulator it runs at 14v.

And like said above if you can monitor the voltage while driving that's all you need to know.

 

[NRAninja]

I did the parasitic draw test again after the car had been sitting overnight and got .018. I got the same reading on our Sienna from the same vintage so it looks like I'll be good to go with a new battery and not leaving the dome light on.

Originally Posted By: SHOZ
It's been my experience with Fords (90's) that a new alternator will put out 14.4 volts. As the alternator wears down the voltage will start to drop. When it gets below 13.6v max it is time to change it.


Yeah I think the alternator in the Avalon isn't putting out the same juice after all these years. We have a 2001 Sienna with the same engine/alternator but 90K less miles and the volts are .15 or so higher under various conditions.

 

[meep]

all of the readings up top look good to me.
thats a big load at idle, voltage ok under load at idle rpm.
wouldn't hurt to test voltage of same load at 1500 rpm as posted above.
parasitic of 0.018 is excellent. right in the pocket. anything over 0.03 is considered a bit wasteful. Any parasitic that is over 0.1 is a Problem.
and yes, newer cars with ECUs/TCUs/BCMs that run self-tests after turn-off's are a pain to check. I've seen 0.5-0.6A draw during those cycles on a couple.

(I'm the one that gets pulled outside to "look" at someone's car...)

 

[1 FMF]

Originally Posted By: NRAninja

Here are the readings:
Car running on idle (750rpm) - readings jumps between 13.99 - 14.08
Runing on idle, highbeams, dome light, radio, defroster, air conditioner full blast, hazard lights - jumps between 12.28 - 12.35ish depending on when the radiator fan clicks on
Do those readings indicate normal alt/battery function?


this is a symptom of a bad diode in the voltage regulator of the alternator.
the bouncing voltage readings are due to having the flashing hazard lights. just run the headlights and hvac blower, you should have a constant voltage above 13.0.
cars don't get built with undersized alternators where they cannot output enough power to run normal accessories at idle. after 10+ years and 180k miles, it would be uncommon for the alternator to not have one blown diode especially if it's seen many hot days in stop and go traffic.

 

[TechnoLoGs]

Not to threadjack, but I tested my readings the other day.

Battery resting voltage: 12.6V
(turned car on)
Voltage measured a idle: 14.35V
Within 30 seconds: 14.4V

Is mine a good system?

 

[andyd]

Yah, Both systems sound OK to me. The regulator on the 90 amp Bosch is rated at 14.3. It will maintain the battery , but it was not designed to recharge it. With an engine rated at 128 hp, you dont want to spend it on charging a battery. The alt on the Ranger will actually charge a dead battery. Keep up on the belt driving it too.