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alternator check

Hello 1948jr,

Using a volt meter at the battery will tell you if the generator is charging properly. Making sparks fly? Not the way!!!!!

Guido.
 
More people than not will scream that the disconnect/re-connect transient voltages will kill the alternator's VR..........why don't you try it & let us all know how it goes? :twisted:
P.S. be sure to tell us which alternator survived or smoked.
 
This is on a mf 265 tractor I was told to unhook battery cable and if alt. is bad tractor will die.I was wondering which cable to unhook or does it matter?
 
I agree with Guido. If I suspect a problem I test battery voltage without it running, then start and check voltage with it running. This should show you if the alt. Is working.
 
Unhooking a battery cable while running is a very good way to let the smoke out of the alternator plus if you happen to be holding the cable in one hand and have your other hand on the tractor it is a good way to hurt your self or even kill you. When you pull a battery cable off the alternator sees a dead battery so it goes to max volts and max amps and can put out over 90 volts and 35 plus amps which is way more then it takes to kill a person. Did that test back when I was in the navy and will not and have not done that ever since. VERY good way to have to replace the alternator
 
An alternator could put out 100 volts or more if fully energized, the battery dampens this out, take the battery out and you can blow things up.
 
Guido,
What's wrong with sparks?? Just kidding, but I have seen some people, Bubba, with jumper cables do the spark test to see if it working. Same with the old manual battery chargers.

I always use a voltmeter. One time the voltmeter lied to me, so after using a voltmeter on 120, 240vac I do the spark test. Scared the crap out of SIL, a big snap and breaker popped. So, what's wrong with spark test???

I wired my Farmall C alternator so both control wires going to alternator goes through the ignition switch. If I turn the key off, removing power going to the control wires, alternator will still continue to produce 12v. I have to pull the kill switch to mag to turn tractor off.

geo
 
Hello Geo-TH, In


I told him the right way. Disconnecting one of the battery cables WILL prove if the generator is charging.
Nothing else will happen, BTDT,

Guido.
 
Do you and your family a favor and don't try it. I am not a fan of harbor freight tools but they sell a tester for about six Dallas that will test the state of the battery and then once the tractor is running tells the amount of charging.
 
If the tractor is a diesel and does not have an electric fuel solenoid or fuel pump then hypothetically completely removing the battery and alternator/generator still will not cause the engine to quit.
 
Neither! Unless you want to kill the alternator. To test an alternator, get a GOOD volt meter. Observe nominal battery voltage for a reference when it's not running. Then start the engine and bring it up to a fast idle and observe again. It should be pushing over 14v or 1.5-2v more than reference. If it's doing that... start turning all of your electrical loads on and see if it still maintains 1.5v over reference. If it's doing that... you don't have a problem. If it isn't doing that, start looking for loose belts, bad connections or ultimately a bad regulator or slip rings in the alternator. Usually you find a marginal alt will only push 13.6 or something like that... so it sort of charges but not enough to keep the battery up. A dud will do absolutely nothing. The marginal may also keep up if you're not using any electrical loads but fall behind when the lights are turned on, etc.

Rod
 
Don't pull either cable, you [u:47e5ef0c67]might[/u:47e5ef0c67] ruin the Alt.
As others have said do the non running / running DC voltage test.
Also when running set your voltmeter to AC and check at the battery, if more than 1-2 volts AC you might have a problem.
 
Easy way to check it if you don't have a voltmeter, with the engine running,take a flat bladed screwdriver and hold it against the rear bearing. If the alt is charging the magnetic field will "hold" the screwdriver to the rear bearing housing.
 
You never want to disconnect either battery cable when the alternator is charging. Reason #1 is the alternator needs to sense that load and battery voltage. Reason #2 is the alternator is hooked to the battery terminal on the starter and this is the same terminal all other power comes from. So if the alternator doesn't sense battery voltage it will send high voltage out to all the accessories from the starter terminal thus burning out all lights and other accessories. This was done years ago by fools. Putting a screwdriver by the rear bearing and check for magnetism isn't a good check either. There's magnetism there when the alternator isn't running. Best is to check with a vold meter.

The only time I disconnect a battery cable to check things is when I check for a drain on the battery with engine off. I disconnect the positive cable and hook my battery charger red lead to the positive battery post and then the black negative lead to the battery cable. I then turn my charger on and check if it draws any amps. If it does measure amp flow with everything turned off then I have a drain.
 
That test only tells you that the alternator has been excited it does not tell you it is in fact charging. I can in fact be magnetized but yet not be charging due to diode problems or other such thing
 
" So if the alternator doesn't sense battery voltage it will send high voltage out to all the accessories from the starter terminal thus burning out all lights and other accessories." come on man, it will sense its own output and regulate accordingly, battery or no battery. Where do people come up with all this crap?
 
Hello 1948jr

I just ask Billy Bob, and he said remove the negative cable quickly. If the generator is charging the engine will keep running. Shut the engine off before reconnecting the cable. Worked for him. I would use a free Harbor Freight volt meter,

Guido.
 

Do what Rod says. Unhooking an ALTERNATOR will fry it. Unhooking an GENERATOR may or may not cause issues. Either way, a volt or amp meter is the easy, safe, least cost way to do it.
 
I use a tester similar to this one. Not terribly expensive and simple to use and read.
http://cdn.wonderfulengineering.com/wp-content/uploads/2016/08/Best-Car-Battery-Testers-8.jpg
 
OH really?? you need to do a little research before you ask where some of us come up with such crap. If a charging system doesn't
read battery state of charge how does it regulate what current to put out???? Da!

The battery is the only thing that keeps a generator from putting out infinity voltage in a charging system that still use generators.

Just try disconnecting a battery cable sometime and you'll see who's talkin crap!!!
 
(quoted from post at 23:22:56 05/18/17) OH really?? you need to do a little research before you ask where some of us come up with such crap. If a charging system doesn't
read battery state of charge how does it regulate what current to put out???? Da!

The battery is the only thing that keeps a generator from putting out infinity voltage in a charging system that still use generators.

Just try disconnecting a battery cable sometime and you'll see who's talkin crap!!!
Click to expand...
ello??? This thread is about ALTERNATORS, NOT generators!
 
" Without a battery in the circuit the charging system
senses high resistance ..." Sir! There is NOTHING in the charging system (generator or alternator) that senses resistance.
 
JMOR, after this post I have nothing else to say. But I do want to ask and I hope you can explain it. If there is nothing in a
charging system that senses resistance (as you say). What causes the voltage regulator to back down on the charge??? It's monitoring
something and that something is battery state of charge. Resistance changes in a battery as it's used and as it's charged. The more
resistance is senses the higher the voltage is put out. Am I wrong???
 
(quoted from post at 13:43:05 05/19/17) JMOR, after this post I have nothing else to say. But I do want to ask and I hope you can explain it. If there is nothing in a
charging system that senses resistance (as you say). What causes the voltage regulator to back down on the charge??? It's monitoring
something and that something is battery state of charge. Resistance changes in a battery as it's used and as it's charged. The more
resistance is senses the higher the voltage is put out. Am I wrong???
Click to expand...
he voltage is the quantity being sensed by the voltage sensing coil inside the voltage regulator. That function is accomplished inside the solid state VR using a voltage comparator, comparing the alternator output voltage (which is the same as battery voltage, via common connection) to the reference voltage inside the VR. Both ultimately control the field current of alternator or generator, which in turn controls the final output. Alternator VRs do not have a current regulation function, whereas most generator VRs do have a separate current regulating function implemented by a winding of heavy wire carrying armature output current to battery & loads which opens and closes a set of contacts controlling field current. Those contacts are in series with the voltage regulating field control contacts, such that either too much current or too much voltage will cut back field current & thus output.


Voltage, not resistance control.
 
(quoted from post at 14:08:01 05/19/17)
(quoted from post at 13:43:05 05/19/17) JMOR, after this post I have nothing else to say. But I do want to ask and I hope you can explain it. If there is nothing in a
charging system that senses resistance (as you say). What causes the voltage regulator to back down on the charge??? It's monitoring
something and that something is battery state of charge. Resistance changes in a battery as it's used and as it's charged. The more
resistance is senses the higher the voltage is put out. Am I wrong???
Click to expand...
he voltage is the quantity being sensed by the voltage sensing coil inside the voltage regulator. That function is accomplished inside the solid state VR using a voltage comparator, comparing the alternator output voltage (which is the same as battery voltage, via common connection) to the reference voltage inside the VR. Both ultimately control the field current of alternator or generator, which in turn controls the final output. Alternator VRs do not have a current regulation function, whereas most generator VRs do have a separate current regulating function implemented by a winding of heavy wire carrying armature output current to battery & loads which opens and closes a set of contacts controlling field current. Those contacts are in series with the voltage regulating field control contacts, such that either too much current or too much voltage will cut back field current & thus output.


Voltage, not resistance control.
Click to expand...

P.S. A battery's internal resistance goes down as it becomes more fully charged, as it's voltage rises.
 
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