Battery light illuminates! - Diesel Forum

Cowboy1985 · 03-12-2006, 06:41 PM

THe battery light suddently illuminated and stays that way while driving, but the voltmeter reads normal voltage and such!
Anyone have some ideas ?

9ENGEL · 03-12-2006, 07:31 PM

Greetings!

You can't really trust the factory voltmeter, so get a multimeter and check at the battery with it running.

Mine did the same thing, new alternator, problem solved.

Good luck

tim94f250 · 03-12-2006, 07:37 PM

That light should only illuminate when the charge at the alternator falls below the normal operating range. Tim

AMMODYTE · 03-12-2006, 08:15 PM

Technically, it a "problem."

In reality, a Voltmeter at the Battery terminals is the recommended course of action.

My truck used to be an Ambulance in its former life. It has dual batteries and a Leece-Neville Alternator rated at 260 Amps. During a load test, it blew a diode inside the Alternator, and it "only" tested 130 Amps. (under load)

Now 130 Amps is just fine for my application, I probably need about half THAT capacity. I won't replace my Alternator until it fails to perform its duty. The only disadvantage is that my "BATT" light is on. But my VOLTMETER and my AMMETER say that everything is normal!

Maybe I can "fix" the problem with a piece of Black electrical tape?

AMMO

tjgriffin · 03-12-2006, 08:30 PM

mine does the same thing, no problems with it so far.

OkieGringo · 03-12-2006, 08:31 PM

Try to tighten the Alternator belt and check the Alt Belt Mod in my signature. Loosen the vac pump and tighten the alt belt, then retighten the vac pump. OkieG

Cowboy1985 · 03-13-2006, 12:21 PM

I should mention that my alternator and my regulator are brand new not long ago!
I got readings from the battery.. everything seems to be a-ok except from the battery light that is glowing!

9ENGEL · 03-13-2006, 01:33 PM

What was the reading at the battery? Was that reading with all electrical accesories on, lights, blower on high, etc?

Cowboy1985 · 03-13-2006, 06:22 PM

I have found the problem, was just a wire... so now what happened was the TC that caved i think! always something aint it ?

wheeze · 03-13-2006, 10:43 PM

It usually means a flakey diode in the alternator housing, or if your uing an external regulator a bad diode in the regulator. If you are using a battery isolator the proble could be caused by a flakey diode in the isolator.

The fastest way to check for this is to turn the vechile off, and disconnect the positive battery terminal. Place a current meter in series with the battery where you come off the battery terminal, into the ampmeter/voltmeter, and then into the battery cable.

You should have less then 50 mA of current draw with the engine off, but whatever you do you should not try to start the engine as you will at least blow the fuse in your VOM and in some cases could seriously damage the unit or recieve a serious burn.

The diodes are a lot cheaper to replace than an entrire alterator, and with a diesel engine you should always keeps some of these on hand.

You can also check the tempature of the housing of the alternator after the engine has been off for a few hours, or overnight. A flakey alternator diode(s) will pass current, and will remain warm/hot to the touch until it drains the battery. If you have a really bad alternator it will be so hot that you will burn your hand.

Another way to check if your alternator has started to flake out is to tune your vechile radio to an area of the AM radio band where there are no stations when you have the key on, and the engine off. Then, while listenign to the radio, start your engine. If the noise you hear in the speakers is loud, or if the noise changes in frequnecy as you rev your engine you may have a diode problem.

If you have a diesel engine the alternators and batteries can really take a beating, which means we have to really keep an eye on the electrical system.

A wise diesel operator will add a couple of extra guages to their instrument panel to see what i going where, always keep a quality DIGITAL volt ohmmeter in their tool box to find what are causing the guages to be unhappy.

I installed two shunts between glow plug relay and the glow plug harness so that I know when the glow plug are on line, and by using two shunts/meters I can see if one of the glow plugs go bad. I use a dual movement ampmeter/voltmeter to save space.

I have also found it helpful to put a shunt in series with the starter cable to see how much current the starter is drawing to detect if the starter is getting funky, or to judge just how the cold is effecting the oil/engine. I've been able to catch there bad starters using this method over the years.

I have a similar shunt on the alternator to measure the current coming off the alternator. Since I run dual alternators I merely use a dual movement meter and dual shunts.

You can help protect your truck by putting an a "battery saver" that will totally diconnect the battery if the voltage drops due to some kind of a phantom load, or leaving your lights turned on, etc. If your alternator diode(s) get nasty you will pop the easily reset battery saver instead of kiling your battery.

If you find a single faulty diode in an alternator you should replace all of them (a full set of diode for a 215 amp alternator costs under 10 bucks).

For a couple of buck you can also install a couple of alternator diodes between the battery and alternator B+ cable. You will usually blow one of these easy to access diodes instead of the ones INSIDE the alternator. I attach mine to the shunt.

tjgriffin · 03-14-2006, 01:24 AM

damn prolly one of the best and most articulate posts i have seen here yet sir, thank you for that.

Greenie · 03-14-2006, 05:31 AM

The battery light came on for me on a trip once - I cleaned the contacts on the plug connector on the alternator and the light went out and stayed out.