Dash Battery Light Stays Lit

[sonny]

I have a 1995 L35 and the Battery light on the dash stays lit . Thought it was my 10 year old battery ( I always had to put the charger on the battery prior to starting the tractor ) So I bought a new heavy duty battery and installed today.

Well light is still on - any thoughts ?

 

[kc8fbl]

Is the light from a bad battery or the charging system not charging properly?

 

[Bulldog]

Sounds like the charging system to me.

 

[sonny]

Yep I think it might be the charging system, as the light has stayed on after installing a brand new fully charged battery.

Any thoughts on what and how to check out the charging system ? Belt is tight , ground looks good , everything is clamped down and tight .

Best way to check an alternator ?

 

[Bulldog]

If you have a load tester it will check the charging system as well. If not check it with a volt meter. If you don't have either of these you can poor man check it with a screw driver. While the engine is running lay a screw driver against the back of the alternator. If it's charging it will hold the driver like a magnet, if not it won't hold it. If you try this method be sure to stay away from belts, fan, and ect!!!

Multimeters are real cheap and that would be the easiest to use and much safer than the driver method.

The battery light tells you when the charging system has failed, not when the battery is dead. Even with a weak battery as long as the charging system works the light should be off.

 

[birddogger]

Make sure connections at the alternator are clean and tight and also at the regulator. It only takes 1 wire with some corrosion to shut off the alternator.

 

[kc8fbl]

Does it have an internal regulator or an external voltage regulator?

 

[motorhead]

Saving money by not buying a battery is going to cost you a lot more for charging system parts.
Running a poor or dead battery puts a lot more load or shorts out the charging system.
Working on equipment and cars for over 45 years this is one point I try to stress to my clients.
Sorry for being so direct.
Start the tractor and put a volt meter across the battery. Should read at least 13 or more volts if it is charging.
If your tractor has the permanent magnet style alternator, chances are that the solid state regulator is bad.

 

[sonny]

Saving money by not buying a battery is going to cost you a lot more for charging system parts.
Running a poor or dead battery puts a lot more load or shorts out the charging system.
Working on equipment and cars for over 45 years this is one point I try to stress to my clients.
Sorry for being so direct.
Start the tractor and put a volt meter across the battery. Should read at least 13 or more volts if it is charging.
If your tractor has the permanent magnet style alternator, chances are that the solid state regulator is bad.

Started tractor , checked battery with meter - got 12.41 voltage ,
Check Alternator all connections are tight and look clean. Tried the metal - magnetic test and could not get my metal to stick anywhere on the Alternator - Maybe the light is just stuck?

 

[birddogger]

Without a wiring schematic or trouble shooting guide; before you start throwing parts at it I'd start with a look at the brushes in the alternator. Maybe one is gummed up with dust and chaff, breaking contact.

 

[Bulldog]

You should have more than 12.41 volts while it's running. I would pull it off and take it to a local alternator shop and let them put it on a machine.

 

[dmanlyr]

Yes, you should have more than 12v on a fully charged battery. You should see about 13.5 to 13.7v or so when running. 13.0 or so at rest, fully charged, room temp.

Each cell in a wet acid storage cell as used in our equipment should be at approx 2.2v fully charged. Therefore a six cell "12v" battery is not really a "12v" battery (people like to round things off, but that can cause confusion. I imagine that someone started rounding off 2.2v to 2.0v and then it just snowballed from there as more and more cells were added!) but instead truly a approx 13.2v battery fully charged. Same with a three cell "6v" battery - it is really a 6.6v battery.

Note I said lead acid. The throw away dry cell batteries commony used are 1.5v per cell, and the common rechargable replacement for the throw away batteries are commonly 1.3-1.4v per cell. Newer technology batteries also have differing outputs per cell.

The way the light normaly works is this is what supply the power to the field initialy upon starting. This power comes from the key switch when in the on position, thru the light and then to the field side of the alternator. Of course you do not get a full 12v as you are going thru the "resistance" of the light element. This does not matter as you are only applying enough voltage to generate a initial magnetic field, and once the alternator starts putting out, it self excites. You can initialy excite a alternator with a 9v dry cell for that matter!

The reason it is a light is so that power does not back feed thru the light to key switch, preventing you from shutting the engine off once started and the alternator is charging. While there may be enough power thru the light to initialize/excite the alternator in one direction, there is not enough in the other direction thru the light to keep the fuel solinoid on. (or the ignition in your car)

Pretty sneaky really. A inexpensive light does the work of a diode, PLUS alerts the operator if the alternator is not working. Of course it is pretty dumb, as it does not know if it is the regulator or alternator, or both that are not working properly, just that the alternator is not charging.

Ok, so why does the light go out then when the alternator is charging? Because you have relativly equal power on both sides, IE battery voltage on one side, alternator voltage on the side, so there is no voltage difference. No potential. Hence no power flows thru the light bulb element. Remember, the light is not technicaly grounded in the normal sense that say a headlight would be.

Sometimes though, the light will glow dimly. Why? Well that is due to corroded or undersize wire. Basicly all of the alternators output is not going directly over to the battery, so you have a feed also going thru the light, thru the key switch and then to the battery. This slight feed keeps the light dimly lit.

Hope this helps!

David

 

[ipz2222]

damanlyr,,, really goood info..

 

[sonny]

Yes, you should have more than 12v on a fully charged battery. You should see about 13.5 to 13.7v or so when running. 13.0 or so at rest, fully charged, room temp.

Each cell in a wet acid storage cell as used in our equipment should be at approx 2.2v fully charged. Therefore a six cell "12v" battery is not really a "12v" battery (people like to round things off, but that can cause confusion. I imagine that someone started rounding off 2.2v to 2.0v and then it just snowballed from there as more and more cells were added!) but instead truly a approx 13.2v battery fully charged. Same with a three cell "6v" battery - it is really a 6.6v battery.

Note I said lead acid. The throw away dry cell batteries commony used are 1.5v per cell, and the common rechargable replacement for the throw away batteries are commonly 1.3-1.4v per cell. Newer technology batteries also have differing outputs per cell.

The way the light normaly works is this is what supply the power to the field initialy upon starting. This power comes from the key switch when in the on position, thru the light and then to the field side of the alternator. Of course you do not get a full 12v as you are going thru the "resistance" of the light element. This does not matter as you are only applying enough voltage to generate a initial magnetic field, and once the alternator starts putting out, it self excites. You can initialy excite a alternator with a 9v dry cell for that matter!

The reason it is a light is so that power does not back feed thru the light to key switch, preventing you from shutting the engine off once started and the alternator is charging. While there may be enough power thru the light to initialize/excite the alternator in one direction, there is not enough in the other direction thru the light to keep the fuel solinoid on. (or the ignition in your car)

Pretty sneaky really. A inexpensive light does the work of a diode, PLUS alerts the operator if the alternator is not working. Of course it is pretty dumb, as it does not know if it is the regulator or alternator, or both that are not working properly, just that the alternator is not charging.

Ok, so why does the light go out then when the alternator is charging? Because you have relativly equal power on both sides, IE battery voltage on one side, alternator voltage on the side, so there is no voltage difference. No potential. Hence no power flows thru the light bulb element. Remember, the light is not technicaly grounded in the normal sense that say a headlight would be.

Sometimes though, the light will glow dimly. Why? Well that is due to corroded or undersize wire. Basicly all of the alternators output is not going directly over to the battery, so you have a feed also going thru the light, thru the key switch and then to the battery. This slight feed keeps the light dimly lit.

Hope this helps!

David

Well on my tractor the light never goes out , and it never dims - stays brightly lit. In the spring I will pull the alternator and have new brushes installed. Until I will test voltage and when it drops below ? I will just slow charge my new battery

 

[dmanlyr]

Well on my tractor the light never goes out , and it never dims - stays brightly lit. In the spring I will pull the alternator and have new brushes installed. Until I will test voltage and when it drops below ? I will just slow charge my new battery

It would be possible that if the wire from the alt to the light were to somhow become cut, and then found a ground, that would cause the light to stay on all the time, in this case it would be working like any other light.

But it is more likely that the alt simply is not charging. Just verify this with a volt meter, you should see about 13.5v - 13.7v, perhaps even as high as 13.9v or so with the engine above idle speed AND the battery charged. This would be considered the "float" voltage where the volt regulator cuts back on the field voltage, which reduces the magnatism and thereby the output. This is how the battery is kept from being overcharged.

If anyone is interested, a disscussion on low output or less than rated output even with a fully functioning voltage regulator could be added as well.

David

 

[birddogger]

It dawned on me (after a good dose of chocolate brownies) there's a fuse to protect the alternator and regulator if the battery shorts out. I have no idea where it is but lurking somewhere. The part book show a rather standard fuse block with from 3 to 8 fuses.

 

[dmanlyr]

It dawned on me (after a good dose of chocolate brownies) there's a fuse to protect the alternator and regulator if the battery shorts out. I have no idea where it is but lurking somewhere. The part book show a rather standard fuse block with from 3 to 8 fuses.

Those are normally high amperage fuses (or fusable links) that are not in the normal fuse block. many times thet are mounted directly off the main battery terminal on the starter motor. Note that NO fuse protects the starter motor, it is ditrect wired and if it shorts, the post on the post on the starter will melt, the main battery cables will melt or the battery will explode from the quickly generated heat. Just like arc welding, but uncontrolled!

So these fuses or fusable links are there for protection of the alternator should it develope a internal ground, or the high amperage wiring to the alternator shortes to ground. Either case would shunt the full battery amperage to ground at that point of failure and heat things up pretty quick.

Whie I do not have the exact wiring diagram in front of me, but traditionaly there are two ways these fuses (or fusable links) are wired.

First, only one is used, could be either type, and this protects the alternator and wiring as well as the wire feeding the main fuse block. On this type, if it is blown or open, then you do not have any battery potential at the main fuse block as well as the BAT terminal on the alternator. To recap, you would also not have any battery potential to the key switch with this type.

Second way they are traditionaly wired is to use two fuses or two fusable links, one to protect the alternator and its wiring, the second only protects the main fuse block, and by expention, power to the key switch. With a failure of the alternator fuse, you would see battery potential at the main fuse block, but no potential at the BAT terminal on the alternator.

2 mins with a voltmeter would slueth out if either of these fuse(s) or fusable link(s) is blown or open.

Your voltage regulator is normaly protected by a fuse in the main fuse block, and this fuse may be shared with the key power, or not. There is no need to have a high amperage fuse for the voltage regulator on a alternator because it does not see high amperage.

Food for thought. Can't do much testing though without a voltmeter, or at worse, a 12v test light.

David

 

[manofaus]

what is the voltage of the battery when it is disconnected? What happens to the voltage as you increase the revs?

 

[Bulldog]

Sonny posted earlier that it was 12.41 volts with the engine running and that was on the new battery.

 

[manofaus]

If your battery in weak, voltage will increase with revs as you output in amps goes up.


Just a note to make sure that the globe that is in the dash is the right wattage too. As mentioned you may not get the desired exciting voltage for the alternator if it is incorrect.