Alternator power always pulling

[Huemann]

I've been trying to solve an issue on my truck, 1989 Ford Ranger XLT 2.3l Manual Transmission, and I've just found myself confused. I believed I found a short, I took the negative cable off and with my multimeter reading mA put the ground on the post and the positive on the cable. Got a reading of 3.4 something.

Went through the process of pulling fuses, found it was the alternator power, and narrowed it down to the alternator itself. I read that if the alternator has a short in it, there would be smoke, obvious visible signs, and I haven't had any problems, truck is mostly running fine.

I'm wondering if this is a normal reading. The way my truck is wired, the positive battery cable runs to the starter relay, with the same post holding the power to the power distributor box. There's nothing stopping the alternator from pulling power. Thought I had my starter relay wired wrong but I confirmed it with my wiring diagram.

If this is normal, wouldn't this drain the battery? It's not been dead for me.

Attached files of the wiring diagram, and a closeup of the starter relay wiring. The RED/LT BLU goes to the ignition switch, and the second connection (No color, it's black) coming off the input of the switch goes to power the power distributor box.

 

[ericbphoto]

Ok. Let's start from the beginning.

Are you having an actual problem? Is the battery draining fast and giving you problems? Why were you checking it in the first place.

"3.4 something" doesn't tell us anything. If it's 3.4 Milliamps, that's fine. If it's 3.4 amps, that's bad. If it's 3.4 gallons, you're using the wrong meter.

Regarding the starter relay; the red/lt blue wire brings 12 volts FROM the ignition switch to energize the relay coil and close a set of contacts to send power to the starter motor via the black wire. Black IS a color. In most automotive 12volt circuits, it is used as a ground wire. In this particular case, it carries 12volts to the starter motor solenoid when the stater relay is energized.

A relay is simply a remotely operated switch that is turned on and off by an electromagnetic coil.

 

[Huemann]

Ok. Let's start from the beginning.

Are you having an actual problem? Is the battery draining fast and giving you problems? Why were you checking it in the first place.

"3.4 something" doesn't tell us anything. If it's 3.4 Milliamps, that's fine. If it's 3.4 amps, that's bad. If it's 3.4 gallons, you're using the wrong meter.

Regarding the starter relay; the red/lt blue wire brings 12 volts FROM the ignition switch to energize the relay coil and close a set of contacts to send power to the starter motor via the black wire. Black IS a color. In most automotive 12volt circuits, it is used as a ground wire. In this particular case, it carries 12volts to the starter motor solenoid when the stater relay is energized.

A relay is simply a remotely operated switch that is turned on and off by an electromagnetic coil.

Thank you for your response.

Yes, I'm having an issue when the temperature gets low (Something like 30-40F) I lose power in the system gradually until I lose blinkers, radio, headlights. The battery gauge in my dash shows this process. Depending on the temperature this can last anywhere from 5 minutes to an hour if I'm driving. In the pursuit of diagnosing this problem I was searching for shorts. The temperature today is high enough that the problem isn't present. (We'll see about tomorrow)

I have replaced the battery and the alternator, cleaned and tested all grounds.

Just checked to be sure and I believe it is reading 3.01 milliamps. (Picture attached)

I've been using a Chilton manual to learn about repairs. In it it doesn't mention a starter motor or solenoid. It has a small section on the starter relay, which is fender mounted and receives directly from the positive terminal on the battery, and sends a ground to the frame, and power to the power distributor box. (This is referenced in the wiring diagrams as 'starter relay') When I looked up the part number e9tf-11450-aa (motorcraft) I found most people referencing it as the starter solenoid or starter motor.

Best I could figure those were all referencing the same part.

The wire in the wiring diagram running from what is listed as my starter relay to the power distribution box doesn't have color listed, on my truck it is black.

 

[SenorNoob]

That's 3ma which is normal.

I'd suspect loose connection somewhere. (Maybe something shrinking away from a connection when cold?) Or perhaps the alternator drive belt slipping when cold.

It's really weird for electrical to be temperature related except for causing marginal batteries to die.

 

[alwaysFlOoReD]

I had a serpentine belt idler pulley disintegrate. I had no electric when the belt slipped. Only noticed the cause when I went under the hood while the truck was running because the belt was stationary. Most times the belt was turning and producing power...

 

[Huemann]

That's 3ma which is normal.

I'd suspect loose connection somewhere. (Maybe something shrinking away from a connection when cold?) Or perhaps the alternator drive belt slipping when cold.

It's really weird for electrical to be temperature related except for causing marginal batteries to die.

That's very good to know. In my manual it has a sections on charging system troubleshooting. It gave me the test I was using to check for shorts, and said if the test light lights, you have a short. I switched to my multimeter and that's when I found my reading, thought I had a short.

Been giving it a good look over for loose connectors and the like, I'll keep looking.

I had a serpentine belt idler pulley disintegrate. I had no electric when the belt slipped. Only noticed the cause when I went under the hood while the truck was running because the belt was stationary. Most times the belt was turning and producing power...

I'll keep an eye on that. Replaced the belts a couple months ago, and everything looks fine, one pulley is a little wobbly, I'll keep checking it.

Today it's not cold enough for the problem to appear, everything is running fine temp is supposed to go down this week and I'll be up late to catch it.

If anyone has any insight on what to investigate to diagnose this, it's appreciated.

 

[ericbphoto]

Check voltage at the battery, engine off. Check again, engine running.(just after starting. Check again after engine has been running 5 minutes or more.

Your description really sounds like a bad alternator - not putting out rated voltage& amps. Could also be a loose connection somewhere. I know you said new alternator. But, these days, it's not uncommon to get a bad one right out of the box.

 

[RonD]

Usable battery is 12.3volts to 12.8volts key off and after sitting over night, so test BEFORE you start engine
12.8v is a newer battery
12.5v is 3 year old battery
12.3v is 5 to 6 year old battery and time to shop for battery sales

After startup battery voltage should be 13.5v to 14.8volts
14.8v for quick recharge
13.5-13.9volts after 5minutes or so of running
Under 13.5volts is a failed alternator
Dimming lights at idle is a failing alternator

If a battery drains/dies after sitting overnight or a few days then it can be "self draining" thats a normal way batteries end their life, but can happen to newer batteries
Drive vehicle, assuming alternator is working
Park it and disconnect one battery cable
Check battery voltage after 3 hours, write it down
Check it again after 8 to 24 hours, should be exactly the same each time
If its going down battery has an internal short, "self draining", replace it

 

[Huemann]

Check voltage at the battery, engine off. Check again, engine running.(just after starting. Check again after engine has been running 5 minutes or more.

Your description really sounds like a bad alternator - not putting out rated voltage& amps. Could also be a loose connection somewhere. I know you said new alternator. But, these days, it's not uncommon to get a bad one right out of the box.

Usable battery is 12.3volts to 12.8volts key off and after sitting over night, so test BEFORE you start engine
12.8v is a newer battery
12.5v is 3 year old battery
12.3v is 5 to 6 year old battery and time to shop for battery sales

After startup battery voltage should be 13.5v to 14.8volts
14.8v for quick recharge
13.5-13.9volts after 5minutes or so of running
Under 13.5volts is a failed alternator
Dimming lights at idle is a failing alternator

If a battery drains/dies after sitting overnight or a few days then it can be "self draining" thats a normal way batteries end their life, but can happen to newer batteries
Drive vehicle, assuming alternator is working
Park it and disconnect one battery cable
Check battery voltage after 3 hours, write it down
Check it again after 8 to 24 hours, should be exactly the same each time
If its going down battery has an internal short, "self draining", replace it

I have never found the battery dead after sitting for a while in the past, but this battery is new of three weeks.

Did as you suggested yesterday and today.
Without starting, it had been sitting a few days, the battery read: 12.71V
After I started it, it was: 14.38V

After five minutes of idling: 14.33V

After twenty minutes of driving: 13.24V

Took off the positive cable and tested it at 3:30PM (Right after driving): 13.21
6:30PM (Significant temperature drop outside): 12.80
9:30PM: 12.78
Come the next morning 9:00AM : 12.76
And just now : 12:76 / 14:40 running

My analysis is that my alternator may be failing, despite being replaced, evidenced by the 13.24V reading after twenty minutes of driving. Seems the drop in the battery was due to temparature as it stabilized.

Interested in more experienced opinions.

Are there other things which could go wrong that would prevent the alternator from charging the system that I should look into before replacing it again?

Any opinions on heet? A friend suggested it, but I've heard others say you shouldn't put any additives in your fuel system.

Thanks for the help!

 

[RonD]

Yes, it reads like one of the three Fields in the alternator is bad, it happens even with new alternators

The 3 Field Coils are in the case of the alternator
The Rotor is the part that spins

The voltage regulator controls the voltage in the rotor, 7 to 9volts to create a magnetic field around the spinning rotor
Each Field coil in the alternators case generates AC voltage from this spinning magnetic field
The higher the rotors voltage the higher the AC voltage

Each Field coil has a pair of diodes that convert the AC to DC Volts, and the DC Volts are sent out on B+ terminal to vehicle' 12volt system

Rotors limited voltage of 7 to 9v is so it can't produce more than 15volts, over that and battery and electronics could be damaged

But just after startup 14.8volts would be normal, so yours was a bit low
And it should never drop below 13.5v at idle
Both of these would be a sign that alternator has a bad field


Alternators ability to produce voltage/AMPs is based on RPM, at idle RPM, 650-800, an alternator can only generate 60% of its rating, so 80amp alternator could only generate 48amps
With engine at 1,600rpm most can do 100% rating

Most vehicles need 40-50amps max, so 48amp at idle is fine
But if a Field failed then you only have 32amps, 2/3rd's of rating at idle
So voltage drop below 13.5v at warm engine idle

Its not hurting anything, common sign of this is dimming lights at idle, especially if heater fan is on high
No, dimming lights at idle is not normal, lol, I read that often