I replaced my alternator on my 2000 3.0 back in May at 93K. Now I may or may not have a problem.

I noticed last night with the lights on and fans on at idle the dash lights would dim and volts gage would lower a little bit but well in range. I accelerate and everything normal. The head lights do not seem to dim though. In the past I never saw the gage move even while the old alternator was failing.

I did some tests this morning and all indicate all is good, but is it. BTW the new alternator is a Duracrap.

Battery volts: 12.6

Voltage at battery with engine running at idle: 13.1

Voltage at battery with engine running at idle with lights and fans on: 12.0

I know I should have done tests at 1500 RPMs as well. Any thoughts!

Like I said before I never saw the dash lights dim at idle nor seen the volt meter drop.

 

With the engine running, you should be between 13.5 and 14.5 Volts. Run the engine and turn on all electrical accessories(radio, wipers, blower motor, rear defrost) and monitor voltage. Anything under 13.5V is bad. Also check for a slipping Serpentine belt. That could cause under charging.

 

Belt is fine as well as tension. I'll just take it back and get another as I have lifetime warranty. I just hope I won't have a lifetime of changing these every 6 months.

 

Some of the rebuilt Alternators don't last very long at all. All they basically do is repack them with new bushings and clean them up, and back on the shelve.

 

Just a question. Was your battery all charged up when you put in the alt?

I have read in a few places that a low batt can put a strain on the new alt -- making it fail early,

I've never seen this issue myself, but I have often read about it.

I will say that I've never liked brands that start out with 'Dura' . They always seem to be low end brands trying to convince you that they're better.

ford2go

 

Battery had to be jump started after replacing alternator. Have not had any problems with battery since. battery is 4 years old, Die Hard.

 

Start your engine and pull the positive batery cable off, if the engine dies, you need another autozone special, if it stays running, the alt is ok. This an old trick that has never failed me when testing an alt. Rebult alt and starters are **** to failure unlike the factory originals. I worked in an auto parts store as a teenager, sometimes thier good and sometimes not so good, luck of the drawl.

 

Two things
1. You may have damaged your alt slightly because the batt was down when you first installed it. As mentioned, I've never experienced it myself, but I'm sure that it does happen.
2. Many FTE members say never to pull a batt cable when the engine is running. It causes a voltage spike that can damage things. I don't think that it's as large a spike as some say, but it can damage things.

The safest way to check alts/ batts is with voltage checks.

I looked up some stuff. At idle, the batt should be 13.10 or so with all of the stuff running. Put on the brakes as well. You show 12 v -- the battery is actually discharging when you're stopped at a light. This will eventually do in the batt.


As for the battery
If you charge your battery, then turn on the headlights for 15 sec or so, it should read at least 12.4. That's a 75% charge.

Also watch the volts while you're starting it. In moderate weather, it shouldn't go below 11 v -- if that. Minnesota cold will take it down to 10v

There are a lot more checks, but I think that you have a marginal alt. It is worth the effort to see if the battery is still OK.

ford2go

 

I've done it for years without any problems other than telling me my alt is bad. Too many worry warts around here. I may not try it on the newest of cars as they do crazy things even when the battery is low. However the ranger is still pretty much old school, at least up to my 04. They do have voltage regulators. It's a sure fire way to tell if your alt is bad and easy to do unless you listen to the naysayers on here, which in this case don't know what thier talking about.

 

The alternator should not be used as a battery charger for a dead, or badly discharged battery. Doing so, won't do the alternator or battery any favors, or cause them to last longer.

The alternators voltage regulator will sense the batteries voltage as being low & dump AMPS into the battery, trying to QUICKLY bring it back up to full charge.

SO, if the battery is in a deep state of discharge, those AMPS of charge current over an extended period of time, will cause the alternator & battery to over heat.

The altenator isn't designed to put out MUCHO AMPS, over a long period of time & the battery isn't desiged to be recharged that way either, so the big current flow, will cause it to heat up too & the plates won't appreciate that & if they get hot enough, can warp, shed plate material & short out.

In extreem cases of really deep discharge & a really high recharge current for extended periods, the electrolyte will boil out & the level can drop enough to expose the cells plate material & oxidation of the plate material will render it & the battery useless.

All the high current & boiling of the electrolyte can cause the plates to warp & shed material & that can cause them to short out.

So basicaly nothing is to be gained by trying to force a quick charge of a battery.

In general, recharge a battey at the same rate it was discharged. A 4 to 6 amp hour rate is about right. So when we buy a new battery, it's best to bring it home & charge it slowly, with a battery charger, designed to slowly bring it up to a full charge.
A charger that'll do it in at least three steps is a good idea.

Pulling the B+ cable from a running engine isn't good practice.

It sure can cause electrical system problems with the alternators voltage regulator, the vehicles computer & other turned on solid state devices.

The battery provides sort of a filter function for the electrical system, to absorb voltage spikes & voltage ripple from the alternator, so disconnecting the alternator from a running engine isn't being nice to the electronic things online, nor to the alternators voltage regulator, which is designed to operate with the battery load in place.

Azu, before you pull the alternator. why not consider running this ride by your favorite autoparts store, for a no cost, in vehicle, electrical system load test check up, via their portable electrical system tester.

It can properly check all your rides electrical system components, in the vehicle, in place as they are used, with the engine running. This way you'll get ALL the electrical system checked out, including the battery cables & their connections.

It kinda sounds like the alternator isn't handeling a load well, but it could be high resistance battery cable connections, or bad cables, or a faulty alternator voltage regulator, anyway the tester should be able to sniff the culprit out.

Let us know how it goes.

 

That's a lot of info. I will try to swing by Autozone, which is where I bought the alt, this weekend.

The volts just seem to bottom out when at idle under load from lights and fans.I believe battery is 4-5 years old so the old alt could have taken the battery on a slow terminal death. I'll post back with what they find.

 

Went to Autozone and had it tested. They said battery wasn't holding a load. I figure battery is almost 4 years old and 50K miles on it. I get new battery and tests show slight improvement but voltage still dips under load. I'll just pull alt out when I have a chance and swap for another one, unless someone has any ideas something I overlooked.

New stats:


Battery volts: 12.8

Voltage at battery with engine running at idle: 13.5

Voltage at battery with engine running at idle with lights and fans on: 12.2

Voltage at battery with engine running at approx 1500: 14.0

Voltage at battery with engine running at approx 1500 rpms with lights and fans on: 13.5

 

Well the numbers look better, almost normal, but with the lights on at idle the alternators output looks a little low to me.

Seems to me it should be able to handle the lights load at idle better & it seems to be doing it's thing at higher rpm ok.

What did they say about the alternators output, at idle under load?????

 

No. Do not do that. That may have worked on carbed vehicles, but you run the risk of toasting parts of your electrical system by doing that.

 

To the OP - That sounds about right. I think your truck has a 95 amp alternator. If you have any extra things, such as an electric fan conversion, additional lights, etc then you will not have enough juice at idle. At cruise the alternator is outputting enough to satisfy the demand.