Car trouble: battery or alternator?

[gerti]

OK, I am confused. Tuesday evening the car wouldn't start, battery low (4 month old Die Hard). So I brought the battery in, they charged and tested it and claimed it was fine.

My wife took two short trips with the car (dark and cold, so lights and heater were used). Afterwards the battery voltage was actually slightly higher. So it seems the alternator is doing something.

Then I used an amp meter to check the current, to see if there maybe was anything drawing current in the car when off. All I got was 0.3 mA (clock I presume), nothing that should drain the battery.

At this point I think the alternator might not be providing enough current. Is that something they can easily check at the shop?

[jking]

Did they put a load on it when they tested it? If they didn't the test doesn't tell you much.

[LCHIEN]

I think most auto parts stores can check an alternator for function. Of course you have to pull it and bring it in.

A quick indication would be When the engine is running, lights and fans running, and the alternator is charging the battery (might have to race the motor a bit higher than idling RPMS) the voltage should be at least 13.5 to 14 volts. If the alternator is not charging the battery then the voltage will be more like 12 volts.

[gerti]

They supposedly load-tested the battery.

Loring, thanks for the tips, I'll try that voltage test tomorrow.

[mpc]

Regular car batteries do not like a "deep discharge." That typically reduces their capacity considerably even though they may charge to normal voltage. The "load test" in theory tests the capacity but that's only if they let it run for quite some time. Also, I've seen car batteries get drained, take a charge (after a jump-start), and work normally for weeks or months. Then, one night without warning, it just does nothing. Higher cost "deep cycle" batteries (usually used in RVs and marine applications) are built to withstand deep discharges without injury and are a good idea for folks that tend to forget to turn off headlights and whatnot.

Simple tests that can be done at home:
1: think a battery is low on voltage or capacity? With the engine OFF, turn the ignition key ON and turn on the headlights. If they're reasonably bright the voltage is close to the proper 12 volts. Leave the lights on for ten minutes... they shouldn't dim much during that time. If they do, the battery capacity is low. If you see the lights starting to dim, turn them off and turn the key OFF quickly before draining the battery so much that it can't start the car again!

2: if the battery passes the 10 minute headlights test, leave them ON and try to start the engine. Once the engine starts watch the headlight brightness again. They should be a little brighter than they were with the engine OFF --> the alternator is now charging the battery and the car voltage is in the 13-14 volt range as Loring noted. If they're really bright - brighter than you remember as "normal" - then the voltage regulator (used to be a separate module attached somewhere near the engine, on almost all cars now though it's inside the alternator) is shorted out and the car is getting hit with 16 volts or so. That'll damage the battery (overcharge), will shorten light bulb life, and may stress the electronics in the vehicle. Get the regulator replaced ASAP in this case.

3: drive the vehicle for half an hour or so to fully warm up the engine bay - not just the engine. On a cold winter day/night, you may have to drive a while longer. Most alternators & voltage regulators are pretty temperature sensitive so, when hot, the charge voltage will reduce. On problem regulators a hot regulator may not even reach 12 volts, let alone the 13-14 volt normal range. So shut the engine off and repeat steps #1 & 2 again - the 10 minute headlight test and engine start test. If the regulator is temperature sensitive the headlights won't brighten after starting the engine.

Typical things that kill batteries overnight:
1: alternators with shorted internal diodes (diode = one way valve for electricity, several are used inside alternators to convert alternating current into the output direct current) can act like a short circuit when the engine is OFF.

2: dome lights, trunk lights, etc. left on or stuck ON from bad control switches. Power antenna motors, power door locks, basically anything with electrical motors that have bad controllers or busted controls switches will suck a battery down over a night or two. Hear any motor whirring sounds or plastic gear grinding/snapping/popping? Many recent cars with oodles of electronics & alarms have hood and trunk "closed" sensors activated by rubber bumps on the hood/trunk lid. If those rubber pieces are missing then the sensor switches will constantly indicate "hood open" or "trunk open" which can make the car electronics a) not arm the factory alarm and b) keep the high-power stereo + navigation system either ON or in STANDBY rather than having it fully power down. You'll typically find 2 rubber bumpers on the hood or trunk lid near the corners opposite the hinges; or on the vehicle bodywork where those corners would otherwise hit. The rubber bumper that I'm describing is NOT one of those two; typically it's located mid-way between the hinge and one of those main bumpers. There will be an electrical button switch (or rubber boot protected button switch) in the vehicle bodywork where this rubber bumper hits.

3: a battery that is somewhat discharged (sitting in the car with the lights ON or stereo ON for a long while with the engine OFF) will be more sensitive to outside temperatures. On a cold winter night a half-charged battery will get "injured" from cold weather far more easily than a fully charged battery. Storing a battery that's not 100% charged on a cold cement floor is a good way to turn that stored battery into a dud.

4: CHARGE/BATTERY light on the dash display burned out... the voltage regulator gets its power feed through this light. With the ignition key ON but the engine OFF the light should be ON. If not, check the light, fuses, and on some cars the "fusible links" (wires that act like slow burning fuses, typically inverted "U" shapes in a plastic box in the engine bay).

5: water level inside the battery too low. Even the so-called "sealed" or "maintenance free" batteries can loose water. Carefully pop the caps off (splashes can lead to burns so wear gloves, keep your face out of the way and/or protected) and look at the water level. It should cover the metal plates, add DISTILLED water (grocery stores sell it) if necessary. Re-install the caps, then charge the battery/start the engine. Also, if the metal plates don't look clean and/or are not parallel metal strips the battery is contaminated.

Loose/sloppy/corroded battery connections will introduce a lot of resistance. So a perfectly healthy battery won't be able to deliver full amps to the vehicle yet will test okay on a voltmeter and battery load tester. Look at the battery connections... then follow the fat wires. The black one will usually go to the chassis so verify that end is clean & tight. It'll also go to the engine block somewhere... check that end too. The fat red wire will usually go directly to the starter motor or to a solenoid (=a big relay) that feeds the starter motor.

There are alternator testers available that do not require removing the alternator from the vehicle. My local NAPA has a small unit they carry to your car in the parking lot; this tests the basic output voltage and the "ripple" voltage - excessive ripple voltage indicates issues with one or more diodes inside the alternator. Alternators are 3-phase AC generators so one phase can be shorted out, or two phases can be open, and you'll still get some net battery charge capability. Ripple measurement will identify these diode/phase problems.

Most of the time the problem is the battery itself. Especially if it's been discharged enough to need a jump start, recharge, etc.

mpc

[cabinetman]

I would first take the battery in to have it checked before doing anything with the alternator. I had the same problem...charged the battery, showed 13.5 V, but wouldn't start the car after one or two tries. You could have a bad cell or two, that an auto parts store could determine. A new battery solved my problem.

.

[Slik Geek]

3:
Most alternators & voltage regulators are pretty temperature sensitive so, when hot, the charge voltage will reduce. On problem regulators a hot regulator may not even reach 12 volts, let alone the 13-14 volt normal range. So shut the engine off and repeat steps #1 & 2 again - the 10 minute headlight test and engine start test. If the regulator is temperature sensitive the headlights won't brighten after starting the engine.
mpc

mpc provides good testing tips (particularly if you don't have a way of measuring the battery voltage). One thing should be clarified so that somebody doesn't improperly conclude that their voltage regulator is bad when it is operating properly.

Most alternator/voltage regulators should be temperature compensated - in other words, they are intentionally "temperature sensitive". This is required to properly charge a lead-acid battery over a wide temperature range because the battery voltage itself varies with temperature.

Battery voltage increases as the temperature decreases, so for a given level of charge, the battery voltage will be higher at cold temperatures and lower at hot temperatures.

One other note, battery capacity is significantly impacted by the battery temperature. The colder the battery, the lower its capacity. In extremely cold temperatures (-30F and colder), the battery capacity drops to very low levels.

The bottom line is this: if you perform these tests during extreme temperatures (hot or cold), you'll get different results than you might during "comfortable" temperature conditions.

[jking]

OK, I am confused. Tuesday evening the car wouldn't start, battery low (4 month old Die Hard). So I brought the battery in, they charged and tested it and claimed it was fine.

My wife took two short trips with the car (dark and cold, so lights and heater were used). Afterwards the battery voltage was actually slightly higher. So it seems the alternator is doing something.

Then I used an amp meter to check the current, to see if there maybe was anything drawing current in the car when off. All I got was 0.3 mA (clock I presume), nothing that should drain the battery.

At this point I think the alternator might not be providing enough current. Is that something they can easily check at the shop?

Have you had any problems with the battery since Sears charged it? Is it possible headlights or interior lights were left on the first time? Maybe a door didn't get shut tight? It's also a good idea to have someone other than Sears check the battery as a second opinion. I had a battery issue a couple of years ago (two years old Die Hard) & I had to have Sears check it more than once before they were able to get it tested properly.

[JimD]

All seem like pretty good comments. I will add two I did not notice. Lots of short trips, especially in cold weather, can drain a battery. If this is the vehicles normal use, you might want to invest in a trickle charger.

Harbor Freight sells a tester that will load test the battery and also tell you if the alternator is putting out correct voltage for about $20. Seemed like a good investment to me so I bought one. It is very easy to use. You do not need to disconnect the battery.

Jim

[cabinetman]

Maybe clean and check the battery connections (both ends of each). They need good contact.

.

[jseklund]

Good advice above - and yes, if you pull the alternator you can bring it into an auto parts store and they can test it for you. Depending on the car you have this could be a 15 minute job or a 3 hour job. I've done it on trucks in 15 minutes, but my Audi requires the removal of the front bumper and everything to get it out....

Have you had any problems since you charged it? You mention it was low and wouldn't start, then charged it, but then you never mention you had another problem...maybe you're looking for the "problem" as preventative care, but it was something like mention above - headlights left on, a door not shut, etc.

Another thing to check is the fuses. Maybe something is shorting, continued to draw juice while the car was off, and the fuse blew (which is why you only get 0.3mA now and haven't had any problems).

If you are worried about the car leaving you stranded with a dead battery, I suggest a jump-starter from Wal-Mart. You can get a very decent one for around $60. Don't get the smallest one - go big. I have one of these and you would be suprised at how many times I've used it on my own cars, family cars, friend's cars, strangers cars in parking lots, etc.

[woodturner]

I think most auto parts stores can check an alternator for function. Of course you have to pull it and bring it in.

Both Autozone and Advance Auto will test the battery and charging system for free. The alternator does not have to be removed from the car - they use an inductive pickup to measure the alternator current.

As a recall, Autozone's tester gives a printout with detailed results for both the battery and charging system.

[woodturner]

OK, I am confused. Tuesday evening the car wouldn't start, battery low (4 month old Die Hard). So I brought the battery in, they charged and tested it and claimed it was fine.

How did the terminals look? Corrosion on the terminals could cause the problems you experienced. Was the battery actually "low" when you brought it in? How long did they charge it?

If it was corrosion on the terminals, you probably fixed it when you removed and re-installed the battery.

[d_meister]

JimD makes a good point about cumulative loss of charge over time with short runs and high electrical loads. One thing that contributes to that is an improperly tensioned alternator belt. It doesn't have to squeal to be loose enough to cause insufficient charging.
I would also add a caution about battery testing. It's surprisingly rare to get a good battery test, even from "professionals. First, a battery can't be properly tested unless it's fully charged. All discharged batteries will fail a load test, so be careful with that Harbor Freight tester (not that it's a bad tool, though). A battery is discharged at 11.8 volts and fully charged at 12.6 after the 13.2 volt surface charge has dissipated.
The most accurate method for testing batteries is to measure the specific gravity of each cell with a hydrometer when the battery is fully charged. Unfortunately, almost all automotive batteries are sealed, these days, so the load test is just about all there is.
General battery info:
http://en.wikipedia.org/wiki/Automotive_battery
Good battery and testing info:
http://www.batterystuff.com/kb/artic...-basics.html#6
Hope this helps!

[gerti]

Thanks everybody for the detailed infos!

I tried the car this morning, with lights, fans etc all on full, the voltage at the battery was 14.3V, so it seems the alternator works fine.

As mentioned the current with the car off is around 0.3 mA (actually after the battery was disconnected for a while the current starts out at around 30 mA and goes down to 0.3 mA after a while, probably capacitors charging and car electronics running cold start checks).

The battery connectors are in pristine condition.

The battery was down to 9.6 V when I brought it into Sears. They charged it for 5 hours, but it wasn't fully charged at that point but I was in the neighborhood so I picked it up anyway. Car has been driven twice for short routes since, voltage was slightly higher after than before.

The usage patterns for that car have not changed in years. Even in below zero we never had a problem before, right now it is around freezing. As mentioned that battery is basically new (4 month old Die Hard Gold).

I triple checked all lights, even ran the camera phone video in the glove box to make sure the light in there turns off ;-)

No third-party gizmos connected to the car either.

My money is on the battery. I'll see if I can have it checked at a local Autozone or Advance Auto as suggested.

I really appreciate all the help, thanks guys!