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I seem to be having a problem with something electrical or have some sort of drain on the battery while it’s sitting. I took the voltage measurement on the battery posts with the car off. It was 12.29 volts. From what I hear, the battery should be 12.6 volts. I have taken voltage measurements with the car off for over 24 hours, and while car is hot. The voltage is the same whether cold or hot. So, the voltage is 12.2. But, when I disconnect the battery the battery voltage goes immediately to 12.6 volts. So, that led me to thinking it was a battery drain problem. Well I had that battery tested, and it was a good battery. Also, about 4 months ago, I replaced the alternator because it had failed the test at Autozone and Advance Auto. And I went ahead and bought a brand new battery. So the battery is 3 days old. I tested for battery drain, alternator output, and did voltage drop tests on the cables. I did these tests before and after replacing the alternator and the battery. The test results from the old alternator and old battery are the same with the new alternator and battery. So, a little more about the voltage output test….. The voltage while running with no load was 15.1 volts. The output with everything on was 11.8 volts. Then with everything on I raised the rpm to 2500 rpms and voltage went to 13.8 volts. Keep in mind these results were the same with the new and old alternator and battery. The voltage drop tests were good on both positive and negative cables. The battery drain test was done 3 times. I waited for 40 minutes each time to make sure the “car was asleep” and all 3 times there was only a 0.4 amp draw. I believe this to be acceptable. So, why would the battery voltage be 12.2 volts with the battery hooked up to car and when disconnected from the car it immediately goes to 12.6 volts?
Some more info and questions… I had the whole starting and charging system test at Advance Auto with their testing machine. They found no problems whatsoever. But, when I took the alternator in by itself later that day, they tested it with a machine just for the alternator and it failed. I had it tested a few times there and at Autozone and the alternator failed every time. So, why would everything be fine with the alternator being tested on the car versus testing the alternator seperately and it failed? Also, why is the low alternator output under load and the battery drain test exactly the same between the old and new alternator and battery? And why is it that the battery voltage goes from 12.2 volts hooked up to 12.6 volts disconnected with the old and new alternator and battery? I was thinking maybe the voltage regulator, but it is pcm controlled.
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[b]There are 5 things that I would suggest that you do.
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1) Check to see if there are any Service Bulletins out for your 2000 Tarus. Sometimes the information found in it can lead you to the direct cause of the problem.2) Locate the system that is at fault. In your case it’s the Electrical System.
3) Test all of the components inside of your electrical system. Find out what is the acceptable condition of each part by comparing it to data that you can find from the manufacturer. Check fuses, wires and just about anything that runs off the battery.
4) Replace the components that are not functioning properly.
5) This option can be EXPENSIVE. Get an updated Service Manual on your vehicle from the dealer and look for what they say as it relates to your electrical system.
I have learned that you can’t know it all. However if you use the check ” Component by Component” procedure + research from Service Manuals and Service Bulletins you will eliminate the problem.
Ok I found out what is draining the battery when the car is off. It’s the alternator fuse. It’s a 30 amp fuse in the engine compartment fuse box. My question….Why and how is the alternator draining the battery? Also, how do I go about troubleshooting this problem? Thanks for the feedback!
[quote=”Plasmide56″ post=49982][video]http://www.youtube.com/watch?v=KF1gijj03_0[/video][/quote]
++++1 🙂
I’ve already found the drain. It’s the alternator. From what I am hearing it’s probably a bad diode in the alternator. The thing is this very same thing happened to the old alternator. Is there anything in particular that can kill alternator diodes? And until I get another alternator, can I just go ahead and take out the 30 amp fuse to the alternator so it doesn’t drain the battery overnight?
I read the link above. My mega amp fuse is good. The alternator charges the battery when the car is on. It’s only that when the car is off that the alternator is killing the battery. I will do a definite check to make sure the diode is dead tomorrow morning. My question is why is my car killing alternator diodes?
It is possable to get a bad part new out of the box but I would check the switch wires going to the alternator, good chance the wire is damaged and lightly shorting, check inside the fuse box too, I have seen problems there before. If you disconnect the plug on the alternator and the draw goes away then it is likely the alternator is faulty, if it draws unplugged then it is definitely in wiring.
I bought a cheap alternator from ebay. I thought it would be ok since it was new and not rebuilt. I should’ve just bought an OEM one. I took out the 30 amp fuse that went to the alternator and the battery still drained overnight. I think, though, that the alternator can still backflow current back to the battery even with that fuse out. But, I think if I disconnect the alternator connector overnight, it would not drain the battery anymore. I will disconnect the alternator tonight and check the battery voltage in the morning and see if the drain is gone.
Anyways, I can tell something’s wrong with my car because the new alternator whines as did the old one. Every time I check the battery in the morning, it’s 12.20 volts, and that was with both the old and new battery. The lights dim alot, like when it’s at night and I am rolling the window up, they dim alot. The car will still run and everything and it will charge perfectly at anything above idle. But, when it’s at idle, it doesn’t charge worth a crap and at night the battery drains. Never has the battery drained so much, though, that I couldn’t start it in the morning.
Ok I did some tests this morning….
i tested the battery voltage before starting the car (battery had some surface charge). It was 12.6 volts. I then started the car and it was 13.99 volts between the battery posts. I then turned all accessories on, with car running. It was 14.00 volts. I then raised the RPM’s with engine loaded and got 14 volts again.
I testing for leaking amps. With the engine off, I disconnected the positive feed to the alternator. I placed the DVOM on amp scale and place leads between the alternator terminal and the wire. I got 0 amps.
I did a diode check by setting DVOM on diode. I put the positive lead of meter on the alternator terminal and the negative lead to alternator case. I got no reading this way. I then switched the leads and got 375. I think this means that the diode is good???
I then checked the ripple voltage. From what I read, this also checks for bad diodes… I set meter to the 200ACV scale. I put the negative lead of meter to chassis ground (I did this test twice, I used the negative battery post the second time and got the same results). I put the positive lead of meter on the battery terminal on the back of the alternator. I got 30.5 ACV. From what I hear that measurement is supposed to be around 0.5 VAC. So, is this test conclusive enough to say that I have a bad diode in the alternator?
Really you problem is the alternator. Personally I did not buy car part from ebay because It’s hard to have an warranty. You can buy a new one from local store, because electricity is a major issue as a coolant issue. The part store will give you an warranty and will reduce the cost of the new one. Or, you can try to find an alternator electrician to fix you alternator, but It’s will take feww day. It’s up to you.
If you had a bad diode the alternator would not charge. +1 on buying ebay parts. Your repairs are only as good as the parts you use. That said, you need to do the parasitic draw test at the battery, not the alternator. If you find a draw and suspect the alternator, disconnect it and check for a drop in amps. If you don’t have an amp draw above 50miliamps then don’t worry about it, you don’t have a significant amp draw to cause the battery to drain. If it’s above 50miliamps then pull fuses till the amp draw stops. Don’t overcomplicate your testing, just focus on the results.
Don’t ignore the elephant in the room. The FIRST thing to check with any charging issue like this is the battery. Checking the surface charge is not enough. You MUST do a load test or conductance test on the battery to accurately test it.
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