Replaced alt. still not charging the battery. | Ford Explorer Forums - Serious Explorations

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Replaced alt. still not charging the battery.

superedge88

Well-Known Member
Joined
October 7, 2004
Messages
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City, State
Minnesota
Year, Model & Trim Level
99 Mountaineer 5.0L
My battery was not being charged, the other morning I had to jump start it to get it to the mechanic (for a leaky antifreeze issue) The mechanic told me that the alternator was bad. I replaced the alternator, but still no charging at all. I looked through my chiltons manual, but got no where. I started following the + wire that comes from the alternator and goes to the battery. I found a junction box where there is a 175 amp fuse. I tested the fuse and I get no continuity across it (it isn't one of those clear fuses but kind of an ANL style fuse) Of course I found this fuse after I already took the alternator out to go back and have checker test. I did have checker test the newer one and the old one, both are fine, but they would not let me return the new one I had just bought from them last night. So I am unsure if all I have to replace is this 175 amp fuse, or if there is another possibility that I am not thinking of? Since I also have had problems with my antifreeze leak, I haven't been to work in 3 days! I have to get this vehicle operational, I have changed alternators out before, and I have never had this much trouble before.
 



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the wires maybe shot. Check all points with a voltmeter.
 






I'll do continuity and voltage tests throughout both negative and positive wires.
 






check to make sure that you are getting 12v IN on your alternator.... referred to as the "A SIDE". This "turns on" the regulator and causes 12v + to go out on the "Bside". If you aren't getting the 12vin either the fuse is bad or the lead which goes to your start relay (at least in 96) is no good .... ultimately this goes back to your battery.
 












Get a voltmeter and first make sure you have a minimum of 12.6volts at the stud on the back of your alternator.

If you do, then start the Ex and measure voltage at the same stud on the back of the alt. If there is voltage present above 13.2volts then your alt is fine and you have a problem elsewhere. Replace that 175amp maxi-fuse and with your Ex running, check your voltage at the battery. It should be no less than 13.2v.

You'll then want to verify that you have the same voltage at the junction box as you do at the back of the alt.

Remember, a fully charged battery must have a minimum of 12.6volts and the alternator should have no less than 13.2volts or you have something wrong.
 






What's funny is that I sat in the Advance Auto parking lot and changed out 3 alternators before giving up. Took it to a local Mr. Alternator and they couldn't figure it out. Finaly once of the gurues came in and said check the fuse.

A freaking fuse was keeping the alternator from charging the battery. Change the fuse out. That is probably all it is. I keep spare fuses like crazy now.
 






Did you check the battery to make sure it doesnt have a bad cell. I had a chevy citation that use to eat alternators every couple months. I even bought a new battery right after i changed the Alt the first time. After the third alt i said screw it and took the battery back to NAPA and found out that my new battery had a bad cell. Problem solved.
 






orange_exploder said:
Did you check the battery to make sure it doesnt have a bad cell. I had a chevy citation that use to eat alternators every couple months. I even bought a new battery right after i changed the Alt the first time. After the third alt i said screw it and took the battery back to NAPA and found out that my new battery had a bad cell. Problem solved.

I changed out the 175 amp fuse, works like a charm. Thanks guys!
 






I have a similar problem, but with a non-similar solution.

The other day, the charging system decided to quit on me. Car runs, but everything is running off the battery. I know this because it dies after a period of time and a voltmeter shows me 12.6 or lower depending on how long the engine has been running or if the lights are on or not. I have to manually charge the battery to get it back up. I pulled the alternator, autozone says its bad. I get a new one thinking, duh, this WILL fix it. No, it didn't, I still have the same problem. I tested all fuses that I think are related (175amp and the 30amp #14) under the hood, still nothing. I get battery voltage at the b+ alternator post, so I know I have continuity. My guess is that I'm not getting the voltage needed on the A side of the alternator. (My understanding is that this voltage is required to "enable" charging from the alternator) Can anybody tell me what the voltages should be on the small wires going to the alternator? I can't find this info anywhere!

Thanks!
 






check your solenoid for the starter. even thuogh it starts find can still cause a no charge situation. I have seen this more than once.
 






I have never seen that 175A fuse blown. It would scare me to death to think about what could blow that.
 






I have never seen that 175A fuse blown. It would scare me to death to think about what could blow that.

I've seen it smoked once or twice. Usually caused by someone working on the vehicle with it running and accidentally shorting the positive terminal on the alternator to ground with a wrench or screwdriver...(been there, done that...d'oh!!)
 






Swapped out bad alternator with a new one. tested out fine. Left it over night, now battery is completely dead. I mean completely dead. (1.5V)

Any ideas???
 






I have a 1996 F150 that keep blowing that 175Amp fuse leading to the alternator. When that happens the alternator isn't charging. When i jump the two leads together the alternator starts to charge again. So i replace the fuse, but only to find that it'll last about a month or so, then the same fuse will blow again. I have checked battery voltage and it measures 12.8v when the motor is off, then when i fire up the truck the charge rate is 14.2v. It appears to blow this fuse out when the alternator stops charging. Is it possible that the diodes in the regulator malfunction and then it put a shot of AC thru the fuse taking it out. Nothing else on that truck has a wire heavy enough to take out that fuse other than the alternator putting out AC or am i wrong. Please help.
 






Charging?

check your solenoid for the starter. even thuogh it starts find can still cause a no charge situation. I have seen this more than once.

In reading all of these posts I see that no one has mentioned cleaning the battery posts and clamps. I realize that it's basic but, I've seen many starting and charging problems cured by cleaning the terminals at the battery.

Mel
 






Those items were the first thing a person would check. Oh by the way, i've been a mechanic for 25 years, but didn't run into this much on the F150. I am not a ford mechanic so they have features there, that don't apply to other manufacturers, but the solenoid and the starter draw was checked. As long as the truck is charging there isn't a problem of any kind. It's just when that fuse blows you can check the alternator and it no longer puts out 14.2 volts. It's not putting out anything. However, as soon as i jump those links together that attach to the fuse, it starts charging again. Hence, install another new 175amp fuse and drive away. this could be good for a month or so, then it returns. I have checked wiring from the rear of that truck including accellery plug in (re for trailers), all the way up the chassis, and that includes the wires on top of the fuel tank. Yet, to know avail. This one has me stumped.
 






Blown megafuse is usually a short in the alternator...

When I bought my current Ford Explorer, ther was no voltage to the rear terminal...Checked the megafuse and it was blown...So I pulled the alternator and had it checked and sure enough it had a dead short to ground internally...

I had a spare alternator from a Ranger v8 conversion so I changed the case to use the Explorer mounting lugs and had it tested...It was charging just fine so I mounted the alternator into the Explorer...Changed the megafuse and it has been happy ever since...Charging voltage is 14-14.5v and all circuits are happy...

If your alternator is intermittantly charging then blowing the megafuse, I would test the wiring at the alternator to see if it might be touching the case or body somewhere or the diodes/rectifier bridge inside for movement...Make sure the case bolts are tight and it can't shift a little bit...A little movement is all it might take to ground out an internal connection...

If there was a dead short to blow the fuse, it would still be there after the fuse is blown and not start charging when you connect the terminals...
 






I recently found myself in need of a jump as the the battery was dead and I figured it might be the alternator.As it turned out my NEW sears diehard was a die easy.I had it tested and found out it was defective. Glad I didn't jump in and replace the alternator.
The tech at sears told me they get a lot of bad battery's back. Paid $110.00 and when I brought it back I noticed a little sticker on it that said made in Mexico. So much for Diehard,Americas best battery as there advertisement says.
Yes ,the alternator regulater must see 12 volt for it to work.
 



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I'm not sure if it's been mentioned yet, but there's also a small fuse n the power dist box for the alt in some years.
 






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