Testing battery/alternator?

audiobliss

A friend has a '97 Accord 4-cyl that won't start. It's totally dead. However, it jumped just fine off my car. We took it to Advanced Auto to have them test it, and they concluded the battery and alternator are bad. We were going to buy a new alternator and replace it there in the parking lot, but due to funds will be waiting 'til Thursday to do this. Since that decision was made I've learned that Advanced Auto is not always right with their diagnosis and went out and bought a cheap multimeter to see if I could determine what's wrong for sure before buying something unnecessarily.

How should I go about this? The simplest thing seems to me is to check the voltage output AT the alternator with the car running, and also check the voltage at the battery, to make sure there's nothing messed up with the wiring.

What kind of readings should I expect? The battery is totally shot, so how will that alter my diagnosing?

BTW, the car ran for about 10 minutes or so to the store after jumping and didn't die. Is that testament enough that the alternator's fine? Should I just unhook the battery after jumping it to see if the alternator's any good?

I don't know if it means anything, but I watched the guy as he tested the alternator (just connected his doodad to the battery with the car running), and saw it reported ~14V. When he said the alternator's bad, I asked why, and he said because he was reading less than 30A.

I'm a bit over my pay grade here, which is embarrassing since this is really so simple, but I would really appreciate any input/advice you could throw my way.

Thanks!!


Oh, and if we end up replacing the alternator: This is a non-EX, meaning it has an 80A alternator. The EX has a 90A alternator, and it costs less. Is there any difference? Should we just get the 90A EX alternator? I'm also going to look into finding a place to just rebuild the current alternator if it turns out it's a dud.

treitz3

Replace the battery.

exalted512

I think your buddy's car needs a new car.
-Cody

audiobliss

Replacing the battery makes great sense, but if it's the alternator that's bad, then the battery should still be fine, and there's no surplus money to replace things unnecessarily.

audiobliss

thanks, cody...you're a life saver

exalted512

audiobliss wrote: »

Replacing the battery makes great sense, but if it's the alternator that's bad, then the battery should still be fine, and there's no surplus money to replace things unnecessarily.

a car runs off the alternator, it is started by the battery.

If the car does not start, your battery is drained (possibly bad). If the car runs after started, then the alternator is working.

Butttttttt, that still doesnt mean the alternator is working correctly.

Best solution:
Take the money you would spend on battery/alternator, invest it here:
https://www.winthevettes.com/OrderTickets.aspx
-Cody

WesKParker

I've never seen one of the "doodads" in action. But i'm pretty sure to measure current (amps) you have to have the meter inline with the cable between the alternator and the battery. So if didn't take the cable off the battery, then he didn't read amps. Also, even if he did this, he'd only be measuring the draw of electrical system off the alternator, and not necessarily the max capability of the alternator. Also, i assume the car was idling when he measured the current off the alternator, in which case the alternator would not be at full output anyways, as the output increases with engine speed.

So, first off, i'd try charging the battery, if you haven't done that yet, then replacing the battery if it won't keep a charge. Which is entirely possible, especially if you left the battery dead for any amount of time.

As far as the 80amp vs 90amp alternators. You should check with people who know hondas pretty well before you try using the other alternator. The pulley on the two could be different sizes, they could have different sized mounts. either of these would put you in a position where you needed a different sized belt, which i imagine is a hassle you'd prefer not deal with

sucks2beme

Just pull both, and take them somewhere else to test. It doesn't take long.
A standard meter will tell you if it's dead, but not if either device is not
up to par. Load testing is the only way to go. Or we could go on and on for two weeks in this thread beating it to death. Get your hands dirty and get them out and tested.

nadams

There's two separate tests that an auto parts store will run. Both use the same machine. First, they'll hook the leads up to the battery and test it under load with the car off. This tells you if the battery is good. But, make note - if the battery is drained, or even low, there's no way to test it. Also, a drained battery can make an alternator test bad, but a bad alternator that's not charging the battery will obviously leave it drained.

The second test uses an inductive load to check the amperage capabilites of the alternator. There is no need for them to remove any cables to do this, they just hook the inductive clamp over the positive battery cable. The first part of this test will have the car at idle. It'll put the load on the alternator and check output. The second part of the test has the car run up to 2000rpms, and then puts the load on it, to get an idea of the nominal output of the alternator.

I've seen cars that were running fine come in and fail both tests. If the alternator is weak, and the battery is dead, when you test the load on the alternator, the car will usually stall out due to lack of power to the electrical system.

My suggestion? Take the battery out, and take it back to Advanced/Autozone. Have them charge it, and then do a load test out of the car. That's the only way you're going to be able to tell if the battery is good... to charge it outside of the car. If the battery is good, take it home, reinstall it, and take the car back for the alternator test.

If the battery is bad, get a new one, take it home, reinstall it, and take the car back for the alternator test. If, in either case, the car still fails the alternator good/bad test, ask the parts-swapper to explain why.

As for the difference between the ex/non-ex alternators... as was pointed out above, there could be several things different on it, or there could be no difference at all except for the amperage. I know a lot of domestic vehicles will come up with several amperage ratings to choose from, usually from cheapest/lowest quality to most expensive/best quality.

Good luck, and let us know how you made out.

nadams

sucks2beme wrote: »

Just pull both, and take them somewhere else to test. It doesn't take long.
A standard meter will tell you if it's dead, but not if either device is not
up to par. Load testing is the only way to go. Or we could go on and on for two weeks in this thread beating it to death. Get your hands dirty and get them out and tested.

Just an FYI - if the alternator is out of the vehicle, they likely won't perform a load test. When I worked at Autozone, our in-store tester could only check voltage/diode/rectifier performance, not actually put a load on it. The only load tester we had was the one for in-car tests.

Batteries can be load tested in, or out, of the vehicle.

Fireman32

If you dont feel comforatable with the test they did take it somewhere else. If the alternator is bad it will kill the battery pretty quick. Please the battery on a trickle charge and then see how the car starts.

[Deleted User]

You could also jump start the car, and while the engine is running, disconnect the battery. If the engine still runs, the battery is bad, if the engine stops, the alternator is bad. Hope this helps.

Halen

george daniel

halenhoang wrote: »

You could also jump start the car, and while the engine is running, disconnect the battery. If the engine still runs, the battery is bad, if the engine stops, the alternator is bad. Hope this helps.

Halen

Yep,, thats exactly what I've been told,, while running,disconnect the battery from the mix,,car dies,it's the alt. Curious to know what you find.Good luck.

nadams

halenhoang wrote: »

You could also jump start the car, and while the engine is running, disconnect the battery. If the engine still runs, the battery is bad, if the engine stops, the alternator is bad. Hope this helps.

Halen

Bad bad BAD BAD idea on modern fuel-injected computer-controlled cars. You will be lucky if you don't fry the ECU.

This was okay, and standard practice for troubleshooting, back when car electrical systems were just there to fire plugs and run lighting. Now, it's a VERY bad idea.

george daniel

nadams wrote: »

Bad bad BAD BAD idea on modern fuel-injected computer-controlled cars. You will be lucky if you don't fry the ECU.

This was okay, and standard practice for troubleshooting, back when car electrical systems were just there to fire plugs and run lighting. Now, it's a VERY bad idea.

Hmm, did not know that,, I have a 2000 Honda accord,, guy tried to sell me an alt,,so I did the battery disconnect thing, car ran,, replaced battery, good to go,,fortunately nothing got fried.I do know that they ECU's are very expemsive though.As an afterthought, while running I only removed the negative cable from the battery, the engine continued to run,so I replaced the battery. Good luck.

sucks2beme

nadams wrote: »

Just an FYI - if the alternator is out of the vehicle, they likely won't perform a load test. When I worked at Autozone, our in-store tester could only check voltage/diode/rectifier performance, not actually put a load on it. The only load tester we had was the one for in-car tests.

Batteries can be load tested in, or out, of the vehicle.

I've got a battery load tester. Worth every penny.
I've got a clamp on auto ampmeter. Not real accurate, but it gives a
pretty good idea. I used to have an inline shunt and meter set up, but that is long gone.
Other parts places have a load test for out of car testing.
I try to stay out of both Autozone and PEP boys.
The local O'reilly store can load test out of vehicle.
Either way, on a 13 year old car, I wouldn't hesitate a moment to change
both. Far better than walking.

doggie750

I was in your shoes before so I pulled and tested the alt and battery. The battery was good but the alt was 50-50. 2 out of 4 tests, the load tester indicated it was good. Replaced the alt, got a refurbished for a lifetime warranty.

audiobliss

Thanks for the input, guys. We took the battery out, had AutoZone charge it, and they proclaimed it dead. So, we bought a new battery from WalMart, popped it in, and it's running fine. I read about 12.8V just the battery, and with the car running it was about 13.5V. So, I'm betting the alternator's just fine, but I'm going to try to check the voltage on the battery a few times over the next few days just to make sure it's not getting drained too much.

nadams

Take the car back to AutoZone and have them check the Alternator again, just to be sure. Wouldn't want it to leave him sit again. Voltage isn't everything when it comes to the alternator. That just means the regulator's still good...

audiobliss

nadams wrote: »

Take the car back to AutoZone and have them check the Alternator again, just to be sure. Wouldn't want it to leave him sit again. Voltage isn't everything when it comes to the alternator. That just means the regulator's still good...

Good point. I had meant to do that but forgot. Will have to make a point to do it tomorrow. Thanks for the reminder!