alternator/ battery dead

farmer boy

Well-known Member
I have 1998 Toyota Camry. While driving the battery will die. The car will act funny, run rough when it's like this. The battery will drain slowly when left sitting.
Replaced the battery, no more slowly dying but the car still drains down when driving.
I started the car and put a good fluke amp clamp on the alternator output wire. It will run the blower on high, and the brights at idle. Reads about 52 amps on the display.
Increasing the rpm will not bring the number up.
If you 'dead head' all the power windows, it will climb to about 70 amps, if you increase rpms if will climb to 95 amps. The alternator acts like it's working perfectly when cold, but not working when hot. Will alternator's output decrease to nothing when hot if it's bad.?
 
With the engine off put your amp clamp on one of the battery cables and see what reading you get. If it has a 10, 15, 20, or 30 amp drain I would start pulling out the fuse that rates with the reading on your amp clamp.
 
You can have all the amps in the world but if say the volts are only 6 then it will not charge the battery no matter what. You need to check what the voltage if of the battery when fully charged and then with it running.
 
Did you also check the the output when it was hot? Is there anything else on when driving that could drain it? I would pull fuses of any thing that could draw a lot of amps and see if output increases.I once owned a bike that did not charge when hot-you may be on to it there. Mark
 
Describe the symptom from "still drains down while driving" does it not start after a certain amount of driving? If so what is the battery voltage at that point while attempting to start it? The starter and battery may both be bad. Are you the owner of the car or is it someone else's and we are missing some of the symptoms? Part of the reason I ask that is yes the alternator could lose its charging ability when hot, but if you were personally driving the car at that point I think you would be able to figure out the alt charge had dropped off.
 
After you drive so far(20mi), the system voltage will be low. If you turn the fan to high, the radio will cut right out(after about 20 miles). It will not restart after this. The battery is brand new. The old battery was slowly draining down. Was probably 5 years old. After the symptoms continued(with the new battery installed), we moved the battery to another car that we've been driving instead, and the battery does fine in there. The whole thing reeks of a bad alternator, but testing it cold, it acts like it's working perfectly. I'll have to test it while hot with the amp clamp tied under the hood(remote display). THE BATTERY LIGHT COMES ON when all of this is going on.
Screams alternator, but I would rather diagnose the issue then put a $150 alternator on it, hoping it will fix it.
 
I had the SAME thing happen with a fairly new Ford pickup a couple of months back. Alternator worked fine when cold, crapped out after about the same 20 minutes.

Would work just fine again after cooling off.

Replaced the alternator, and all is well.

That's the first time I've encountered that, as usually once an alternator dies ONCE that's the end of it.
 
Read the charging volts across the battery terminals. Should see 14 volts or better. If the belt isn't broken, you probably need an alternator. My neighbor had that problem and she took the car to a battery warehouse. They told her nothing wrong with battery and her car probably needed to go the dealer. She called the
dealer and wanted $100.00 just to check it.

I took my multimeter along with some veggies from my garden. Told her unlatch the hood and start
the engine. I only saw 12 volts on my meter and told her she needed an alternator. She had it fixed nearby. Hal
 
Whut he said...

I would suspect a worn brush along with a well worn slip ring on the rotor... It will come and go it just happen to be in the go mode when you checked it... Are something else in the alt is going open...

I will commend ya on your diagnosis you proved the alt could get down and dirty... Some don't know there amps/arse from there volts/head and are confused as ell as well as confuse others...

The only thing I question is from what I can gather toys used a 80 are 90 amp alt... Make sure your battery cable connections are clean and in good health...
 
(quoted from post at 20:38:21 01/25/15)
52 amps with the blower and lights only on is way too high. :

"Replaced the battery, no more slowly dying but the car still drains down when driving.
I started the car and put a good fluke amp clamp on the alternator output wire. It will run the blower on high, and the brights at idle. Reads about 52 amps on the display."

First we don't know the bat state of charge... I assume he just started it so the alt is working above what it takes to keep it running and trying to recharge the bat

Blower on high possible 15/20 amp draw
All lights 10amps
Fuel pump and engine management 12 amps

My numbers may be high so I will round them off.

The alt would have to put out 38 amps just to keep it running and not using any of the storage capacities of the bat... At this time the alt is charging the bat at 14 amps... All this at IDLE

It would have been a flag if the amp readings were not at least what the draw was on the battery at the time of his test... After you start it up it runs off the alt not the bat...

Alt amp out put fully loaded should be within 10% of the rated amp out put... I normally go 50 amps with a load tester and see them be right at there rating and sometimes a little more... Most of the time you have to throttle the engine up but I have seen them reach the 10% range at idle... I think he was about there when he deadheaded his windows are what ever he did...

Modern alts a little dynamo's that's why you should charge the battery if you replace them are you chance over working it from the get go... He did provide good info tho its not normally seen from the general public... He proved the alt was capable of what it was designed for... If it had a dash mounted voltmeter he would have seen when the alt went off circuit... I do wonder why his charge light did not come on...

His last question

"Will alternator's output decrease to nothing when hot if it's bad.?"

That's a two sided question depending on how you read it are take it... Of course the answer is YES... If its running it should output more than is being taking out... If not you are using your storage capacity up till its depleted...
 

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