Alternator question

[Richard]

I have a JCB and when I first got it, needed to have the alternator rebuilt. Fine & dandy....

Some $$ later, all is fine however, over the 9 years or so of ownership, I've ALWAYS had a dying battery problem and have simply created the habit of putting it on the charger or buying a new battery

Presuming it was losing some power even with the key turned off, I installed some kind of "guillitine" switch on my negative battery terminal to totally remove the battery from the system when the machine is not being used. I've now created the habit of closing the switch when I get on the machine and opening the circuit when I get off.

No big deal.

Several weeks ago I had need to work in the middle of night...so I turned my headlights on and they were dim. That intrigued me. I charged the battery and forgot about it.

Tonight, I was again, working in the early dark and realized lights would be beneficial so turned them on....and they were bright.

Intrigued, I reached forward and lifted the switch to the battery, totally taking the battery out of the system and now relying on the alternator.

Of course, my lights died immediately.

Implication to me is my alternator is now bad and might have been for several years.

My question is.... (since I have had the alternator off a couple years ago for ANOTHER rebuild....and they told me my alternator was ok) could there be anything else that would kill the lights with this battery terminal disconnected?

What this is telling me is it's my battery alone that is powering my lights and a couple weeks ago, as my battery was on a lower charge, my lights dimmed when, had my alternator been charging (or something else not been getting in the way?) my battery should have been charging and then powering the lights at worst....or, at best, the lights SHOULD be working off my alternator.

Any thoughts?

 

[CharlieS]

a simple test on the alternator, with a fully charged good battery and ignition off. bat. voltage should be in the neighborhood of 12 - 12.25 volts. with the tractor running, slightly more than that, depending on the charging system 12.5 to 13.2 or so.
If the Alt. tests ok, as you indicated a repair shop confirmed, next suspect would be voltage regulator.

With the battery isolated from the charging system, i doubt if lights will run on alt. only, generally speaking even with a bad battery, the battery is needed for system stailization. While the battery will not accept a charge, the charge still passes through.
Eventually battery voltage drops so low it will not excite the alternater fields, thus the current from the alternater does no good.

Alternators put out AC voltage which is converted to DC, and regulated by the voltage regulator, so current is fed from the alt, through the regulator, to the battery and fed to electrical loads.
One other possibility to check is for loose connections, cracked/damaged wires. either or both will create (sometimes intermittant) resistance causing what appears to be a low voltage issue.
Hooking a test light in series with a disconnected neg. batt. cable will indicate any "leaks" in the system. If the test light lights up, there is a leak somewhere, anything from a bad switch to a hairline crack in a wire comewhere.

Lastly be sure to check water level in the batt. and top off with distilled water if needed and recharge.

 

[schmism]

check your wires.

multi wire alternators need an "energizing circuit" to "turn it on" if you will.... if thats not hooked up right then the alternator will not output regardless of weather or not there is anything physically wrong with it.

if everything seems hooked up right, then ya id take it off and have it tested.

 

[hawkeye08]

Unless you have added a bunch of lights, your alternator will run lights fine without battery (otherwise you would always end up with dead battery whenever you used your lights). In fact, your alternator should be capable of not only running all your lights, but also recharge your battery at the same time (restoring the charge that starting the tractor used).

 

[sjb]

In most cases even a good alternator will not produce any current without a battery connected. Since the output of the alternator is rectified AC, the voltage will drop as the AC changes direction. When this happens, the current through the field coil stops, and the alternator stops creating any voltage. As was previously mentioned, the battery is needed to smooth out the rectified AC keeping the field current flowing.

A generator will work just fine without a battery.

Stan

 

[Transit]

You guys are off base. The alternator output is 13.8 to 14.2 volts. How does the alternator know how to maintain this voltage to keep the battery charged? Simply put, the regulator has the smarts to compare the actual battery voltage to a reference voltage and decide to feed current to the alternator Rotor field. Battery voltage less than 14 v, turn on the rotor current till the battery reaches 14 v, at 14 + volts turn the rotor field current off. The battery voltage slowly sinks to less than 14 v and the cycle is repeated. If your tractor is equipped with a ammeter you will see the needle wiggle as the rotor current is switched on-off.

 

[sjb]

You guys are off base. The alternator output is 13.8 to 14.2 volts. How does the alternator know how to maintain this voltage to keep the battery charged? Simply put, the regulator has the smarts to compare the actual battery voltage to a reference voltage and decide to feed current to the alternator Rotor field. Battery voltage less than 14 v, turn on the rotor current till the battery reaches 14 v, at 14 + volts turn the rotor field current off. The battery voltage slowly sinks to less than 14 v and the cycle is repeated. If your tractor is equipped with a ammeter you will see the needle wiggle as the rotor current is switched on-off.

While the above is true what exactly does it have to do with this thread? And how exactly am I "off base".

The original poster asked for reasons that his lights went out with the battery disconnected. I gave him one, the alternator needs a battery in the circuit.

 

[J_J]

Rotor Assembly. The rotor assembly consists of a rotor shaft, a winding
around an iron core, two pole pieces, and slip rings. The rotor is pressed
into the core. Six-fingered, malleable, iron pole pieces are pressed onto the
shaft against each end of the winding core. They are placed so that the
fingers mesh but do not touch. When direct current is passed through the
field coil winding, the fingers become alternately north and south poles. A
slip ring assembly is pressed on to the rear end of the rotor shaft and
connected to the two ends of the field winding.

Two brushes are held against the slip rings by springs, usually mounted in
plastic brush holders that support the brushes and prevent brush sticking.
Each brush is connected into the circuit by a flexible copper lead wire. The
brushes ride on the slip rings and are connected through a switch to the
battery. When the switch is closed, current from the battery passes through
one brush, through the slip ring, and then through the field winding. After
leaving the field winding, current flows through the other slip ring and brush
before returning to the battery through the ground return path. The flow of
electrical energy through the field winding, called field current, creates the
magnetic field for the rotor.

 

[Transit]

Yes JJ and the HP taken from the engine is converted to electrical energy. The OP needs to check to see if all the events are taking place.
Bad alt = no charge
Bad reg = no charge
Sense line to reg open = no charge
Broken weirs to alt rotor ckt = no charge

 

[sjb]

Did either of you even bother to read the original post?

The issue is whether the alternator can be expected to continue to produce current when the battery is removed with the engine running.

 

[J_J]

The field has to have the current flow from the battery to generate the field for the stator.

 

[Soundguy]

Did either of you even bother to read the original post?

The issue is whether the alternator can be expected to continue to produce current when the battery is removed with the engine running.

Probably not.

I'd also like to point out that the 2nd fastest way I know to KILL an alternator is to unload it while it is turning.. I.. disconnect the battery.

that said.. to the OP what alt model are we dealing with?

that will help with diagnosis.

soundguy

 

[Soundguy]

The field has to have the current flow from the battery to generate the field for the stator.

not always. you can get 1 wire regulators that will bootstrap their own field current once the alternator is spinning fast enough. same principle as an old a or b circuit genny and external reg.. residual magnetism in it's field pieces generates small current on armature.. which is fed to field.... etc..

I don't prefer 1 wire setups like that.. they usually require something ridiculess like 1800 rpm to self excite... plus they typically cost more. I much prefer the ulti wire alts that have an excite circuit, and external voltage sense.

soundguy

 

[crazyal]

I just want to second the warning that disconnecting your battery while your engine is running can harm your diodes inside the rectifier. The best way is to turn the key on, measure the battery voltage with a good multimeter(before starting the engine) and then after starting the engine. You should see an increase in voltage with the engine running.

 

[Richard]

Sorry late in getting back.

What type alternator? I don't really know. I CAN say (as useless as I know this is going to be) it "LOOKS" like a typical General Motors style that I might have had on my 1971 442. I don't recall if the regulator is integrated or not.

I'll do the voltage check thing this weekend. As for possibly hurting a diode or two by lifting the battery switch while running.... too late :ashamed:

However, it was done after this problem (annoyance) has persisted so if I blew anything, I probably only added to an existing problem. What really stinks is the only place I know of to take it is probalby 30 miles from work... AWAY from the direction where I live and I already drive 25 miles to work.

yeesh....

Interestingly, my rear work lights (flood lights mounted on the top of the cab for backhoe use) stopped working maybe 2 years ago. I've been wondering if the switch is bad since the fuses seem to be ok.

Maybe this will be a good excuse to run some of those problems down as well. It sure is nice having the rear floodlights every now & then.

 

[Soundguy]

post a pic of the alternator, especially back, and of any connectors on it. note any writing, especially at the connector locations.

soundguy

 

[J_J]

Soundguy is right. Maybe this will help.

FIELD EXCITATION

When a dc voltage is applied to the field windings of a dc generator, current flows through the windings and sets up a steady magnetic field. This is called FIELD EXCITATION.

This excitation voltage can be produced by the generator itself or it can be supplied by an outside source, such as a battery. A generator that supplies its own field excitation is called a SELF-EXCITED GENERATOR. Self-excitation is possible only if the field pole pieces have retained a slight amount of permanent magnetism, called RESIDUAL MAGNETISM. When the generator starts rotating, the weak residual magnetism causes a small voltage to be generated in the armature. This small voltage applied to the field coils causes a small field current. Although small, this field current strengthens the magnetic field and allows the armature to generate a higher voltage. The higher voltage increases the field strength, and so on. This process continues until the output voltage reaches the rated output of the generator.