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How to test if your alternator and voltage regulator is good?

meanwire

Jr. Member
Joined
Nov 14, 2010
Messages
135
Loc.
Central Oregon
I'm in the process trying to figure out why my battery is drawing power when the Bronco is shut off and draining the battery. I'm trying to do a process of elimination, so I'm wondering how I would go about finding if my alternator or voltage regulator is any good. Any way of testing these things? Thank you and have a Happy New Years!
?:?
 

camomog

Full Member
Joined
Sep 10, 2008
Messages
254
Loc.
Reno, Nv.
A old hot rod trick for the alternater is to have the motor running, on the back of the alternater is a bump in the middle were the bushing is, take a flat blade screw driver and if that area is magnetic then the alternator is charging. Good luck
 

Vragor

Jr. Member
Joined
Jul 22, 2010
Messages
149
Loc.
Colorado Springs
Easiest thing I've found is to drive to Advance Auto, Checker, Etc, and ask them to bring out their charging system tester. It's free and easy and pretty accurate.

You can remove the alternator and have it spin tested in most shops as well.
 
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meanwire

meanwire

Jr. Member
Joined
Nov 14, 2010
Messages
135
Loc.
Central Oregon
One thing I've noticed is that the alternator gauge reads 0 but bounces to maybe 25. The needle bounces real fast and hard to read but more 0 than anything. Don't know if the gauge is inaccurate of defective is this normal with Early Broncos?
 

aduff68

New Member
Joined
Feb 22, 2005
Messages
10
Needle Bounce

Needle bounce:

Short answer: It's not you its one of the lovely tics of our beloved beasts. and that bouncing is letting you know that its doing its job and reading voltage draw/gain and how hard its working.

Redundant long answer: I remember when i first got my bronco ~6 years ago it did the same thing. There used to be a good thread on why it does it, dont know if its here anymore. All i know is that, like referenced in the old thread, mine is the same. The higher the direction of the bounce into either the positive or negative side, the more the battery is being charged or drained. Its easy to see once you know you have a good charged battery in there. watch it when everything is off, it should be bouncing close to the zero. Then, while at idle, start turning things on and you will see it go into the nagative farther with each accessory activated. Bring the rpms up and you will see it start to bounce (hopefully) into the positive side. My alternator has been "bad" ever since i got my ol bronc'. It doesnt really start charging until i get into the 2k rpm range (even then it is minimal-i seriously need a new starter, lol). With my highbeams, wipers, and radio on even at the higher RPMs on the autobahn or e-way it wont keep up, (the yellow top altima really pays for itself in this rare situation). The next morning i just drive in 2nd at town road speeds (with everything off) during my short drive to work and let her charge back up. Once i learned how to read and manage the voltage meter, i've never run my altima down again after the first year.

On the other ?:

If you dont already, you should always keep a spare voltage regulator, ignition control module, and starter solenoid with the required tools on hand (in the vehicle). They are notorous for going out at the worst times. I've had some last 2+years and other only last a few months. When i was stateside the guys at advance auto and auto zone were really good about honoring the warrenties the units come with.

As far as testing them, if i remember right, i think the spares from ac delco come with a wiring diagram and how to test the part on a piece of paper in the box. maybe others do as well.

I know my voltage regulator is going when the needle stops bouncing and stays flat or moves slowly instead of like its on speed.

When my ignition control module starts going my truck starts acting like it has a clogged fuel filter or like a cold carb in the winter. Then, it progress to cutting out in low power situations (ie, abruptly releasing the accelorator during aggressive maneuvers or coasting down a hill) and not wanting to restart for a bit afterward, eventually progessing to not starting at all. After checking my fuel filter, cap and rotor, ignition solenoid, and wires, it usually always is the module. (-funny, almost missed a new years eve hunt for this very reason yesterday. Cut out in the middle of nowhere halfway between my and my buddies place :eek:)

The starter solenoid i've never had to replace on mine, but i've seen it happen to enough of my other bronco friends. it's a small part and easy to just add to the other two.

I've given more than one of these to bronco brothers when in need. ;D

A little long i know, Hope this helps though, :D
 

markperry

Bronco Guru
Joined
May 8, 2009
Messages
4,175
Loosen the positive terminal of your battery, start the engine and while the motor is running pull the positive terminal off, if it stays running the alternator is charging the system, if it dies it's a bad alternator! This method is not recommended by most, but I have never ruined an alternator by doing it?
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,821
Loosen the positive terminal of your battery, start the engine and while the motor is running pull the positive terminal off, if it stays running the alternator is charging the system, if it dies it's a bad alternator! This method is not recommended by most, but I have never ruined an alternator by doing it?

The battery is what absorbs the spikes in the eletrical system. Unhook it and you can fry stuff. I have generally been lucky when having battery cables fall off stuff didn't die. But there are better ways to test stuff.

As stated, most parts stores will do a free test. on or off the car. The off car is better at finding problems I feel. Since you are chasing a dieing battery with the car off (which most of the above are neglecting) then you should find your drain and not dwell on the charge.

First, charge the battery.
Second, unhook the cable for a night where the battery is drawn down.
Third, hook up the cable and try to start the truck.
No start, it is the battery. Does start, you have a draw that is sucking juice out of the battery.

Now to find a current draw.
Get a test light (get one with a normal incandecent bulb, none of the new fancy LED stuff). unhook the battery cable (ground side recomended). Attach one end of the test light to the disconnected battery terminal
Attach the other to the disconnected battery cable.
The light should be on showing a load (by lighting the bulb)
Disconnect stuff until the light goes out. Whatever is powering the light is drainging the battery. It is save to plug and unplug stuff with the test light in place. Worst thing is if you short out the light will just go full bright. Common things to try;
voltage regulator
Main charge feed off the alternator
Aftermarket radio
Aftermarket ignition
Aftermarket anything eletrical
Ignition switch
etc.

Eletrical work can be time consuming and mental, but rarely hard. Worst part is trying to see what can't be seen. Thus you cheat and add the test light so you can see something.
 

hotrodtim68

Contributor
Full Member
Joined
Nov 6, 2010
Messages
306
Good Information

Hey Guys, this a vey informative post . Thank you for the information, especially for me; one with basic electical knowledge.:eek:
 

Steve83

Bronco Guru
Joined
Jul 16, 2003
Messages
8,976
Loc.
Memphis, TN, USA, Earth, Milky Way
...I have never ruined an alternator by doing it?
The alternator isn't what you're risking. It's any modern electronics, like CD changer, GPS, iPhone, EFI PCM...

Simply grounding the F terminal (on any alternator system that has one) will force the alternator to its max output at that RPM (1500-2K is enough). That's the safe way to test one at home, but don't ground it for more than a few seconds, and ONLY if the battery is connected. A voltmeter should jump to ~15V and climb if the alternator is good. This test bypasses the voltage regulator, so you CAN have a good alt with a bad (internal, external, or remote) regulator.

 

jw0747

Contributor
Bronco Guru
Joined
Nov 22, 2006
Messages
2,434
Loc.
San Antonio, TX
Easiest thing I've found is to drive to Advance Auto, Checker, Etc, and ask them to bring out their charging system tester. It's free and easy and pretty accurate.

Wow! all things considered, this is the best advice on this thread.
 

tn_dave_73

New Member
Joined
Dec 26, 2010
Messages
14
Loc.
Knoxville
well, if mine was drawing juice when it wasn't running,first i would pull the hot battery(pronounced ba-tree) cable off. Then if you touch the battery cable end to the battery post you should see a tiny arc which indicates something is drawing current.Note: make sure everything is off. Then start disconnecting things(like alternator, voltage regulator, elect. ignition, etc.) one at a time and rechecking to see if the little arc goes away. This is a shadetree way to do it but has worked for me
 
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meanwire

meanwire

Jr. Member
Joined
Nov 14, 2010
Messages
135
Loc.
Central Oregon
So my ALT needle is jumping from 0-30 charge, I guess that's normal from you guys are telling me. I went for a 40 mile drive today and noticed that the needle settles down and holds steady at 0 when I'm out on the open road, is this ok?
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,821
So my ALT needle is jumping from 0-30 charge, I guess that's normal from you guys are telling me. I went for a 40 mile drive today and noticed that the needle settles down and holds steady at 0 when I'm out on the open road, is this ok?

Yep, sounds normal and correct.

the charge bit is the recovery from starting the engine. Then once the battery is topped off it will go to 0 stating the battery is neither recieving or loosing any eletricity.
 

markperry

Bronco Guru
Joined
May 8, 2009
Messages
4,175
Loosen the positive terminal of your battery, start the engine and while the motor is running pull the positive terminal off, if it stays running the alternator is charging the system, if it dies it's a bad alternator! This method is not recommended by most, but I have never ruined an alternator by doing it?

Shadetree;D But seriously these guy's will tell you the correct way to check things, my way has worked for me but it is shadetree!
 

Steve83

Bronco Guru
Joined
Jul 16, 2003
Messages
8,976
Loc.
Memphis, TN, USA, Earth, Milky Way
...a tiny arc which indicates something is drawing current.
Unless you know how much it's drawing, and how long it's drawing it, that test is useless. If you have anything with memory (like a clock or a radio or a PCM...), or anything with a capacitor (like an ignition system, an alternator, an amplifier...), then there will be a current surge when the voltage jumps (like when you connect the battery). So just looking at that little arc only says you're completing a circuit - you can't look at a spark and tell how much current or voltage caused it.

USE A METER to measure current.

To find the drain on a circuit, pull the fuse & install a low-current incandescent light (like a 194 bulb) in its place. Then start disconnecting things on that circuit. When the light goes out, you just disconnected the draw.
 

blubuckaroo

Grease Monkey
Joined
Jun 11, 2007
Messages
11,795
Loc.
Ridgefield WA
I just put a voltmeter across the battery terminals and check the voltage with the engine shut off. It should be 12.5 to 13 volts. Then start the engine and check voltage again. It should be 13.5 to 14 volts with the engine idling. If not, the alternator isnt doing anything.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,821
I just put a voltmeter across the battery terminals and check the voltage with the engine shut off. It should be 12.5 to 13 volts. Then start the engine and check voltage again. It should be 13.5 to 14 volts with the engine idling. If not, the alternator isnt doing anything.

His problem is a drain with the engine off. that test won't tell you about a problem there.
 

tn_dave_73

New Member
Joined
Dec 26, 2010
Messages
14
Loc.
Knoxville
I did say that was a shadetree way to do it. If everything is off there will be no current draw, so no arc. done it, know it works, but yes there is a better way if you have the time and stuff and want to do it. Growing up didn't have a lot of stuff to work with like i do now much less a bunch of fancy electronics:)
 
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meanwire

meanwire

Jr. Member
Joined
Nov 14, 2010
Messages
135
Loc.
Central Oregon
I want to THANK you all for your help, without your help I'd be lost. After much reading all of your advice I was able to fix the problem. The draw ended up being a bad voltage regulator. Again THANK YOU!!!;D
 
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