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.