Batteries draining while running - Light on - Diesel Forum

imrich · 11-19-2009, 12:16 PM

03 7.3 I replaced the alt and batteries last month old alt burned up. I think my current problem caused it. My battery light is staying on longer and longer each week. It is taking 15 to 20 minutes of driving until it goes off but as much as 40 mins. I tested the alt and it was putting out 40 amps. Could it be glow plugs staying on? The light will go out after a while but will flicker on an off. Sometimes just touching the throttle will make it go off.

BTBBT · 11-19-2009, 05:44 PM

The light shouldn't stay on because the glow plugs are on. I've been going through this on my truck right now too. You've measured the aperage output of your alternator, but the light measures the voltage. It's not putting out the proper voltage if your little light is coming on. If your old alternator blew up (wow, I'd hate to see what it looked like) then how is all your wiring? Sounds like you've got a few wires in there that aren't doing their job.

One thing I would suggest is that you run a 6 or 4 gage wire from the stud on the back of the alternator directly to the battery. The other thing you need to check is the other 3 wires going to the alternator.

Let us know what you find out.

imrich · 11-19-2009, 07:23 PM

The alternator tested out fine, actually took it into a shop. Checked and cleaned all wires. Once the light finally goes out it charges the batteries like normal.
When driving with the batt light on the lights are very dim. When the batt light goes off there is a dramatic increase in about of light from the headlights. The problem does not seem to be dependent on RPM at all.

**techkdb** · 11-19-2009, 09:33 PM

Pulley, Tensioner, Belt

Powerstrokin400 · 11-20-2009, 12:25 AM

Quote:

Originally Posted by imrich

03 7.3 I replaced the alt and batteries last month old alt burned up. I think my current problem caused it. My battery light is staying on longer and longer each week. It is taking 15 to 20 minutes of driving until it goes off but as much as 40 mins. I tested the alt and it was putting out 40 amps. Could it be glow plugs staying on? The light will go out after a while but will flicker on an off. Sometimes just touching the throttle will make it go off.

40 AMPS seems really low, do you have the Heavy Duty Towing Package? I may be wrong, but if memory serves me correct, when I replaced my alternator with a NEW "Ford" alternator for Heavy Duty Towing Package, it was a 130 AMP alternator. My truck came with the HD Tow Pkg. What was your battery voltage? You need 12V to run, & 12.5V is full battery charge, and a minimum of 13.5V is needed from your alternator (with all your lights & accessories on) to charge a battery. CK Pulleys & tensioner....that's cheap & easy to check.

HighwayPrisoner · 11-20-2009, 12:47 AM

What is the voltage reading off the back of the alternaor? A weak tensioner can cause the alternator not to charge properly, if a 6 ga or larger wire is run from the alternator to the pass side battery, use an in line fuse, in case of a voltage spike.

BTBBT · 11-20-2009, 05:05 PM

Your stating that there is a significant increase in the voltage at a certain point is this: the glowplug circuit is turning off and the charging circuit is now allowed to charge at it's full capacity. Yes, the glow plugs will stay on for a while after the engine is started.

That said, you should still be able to maintain 11+ volts while the glow plugs are on which should NOT set the light to come on. If you cannot, then there is something wrong. If the shop is telling you the alternator is good, and the wires are good, then definitely check your belt and tensioner.

Placing a fuse in a new line is a good idea, but it will not protect from voltage spikes. Fuses are an over-current protective device, they don't have anything to do with voltage. Most fuses are rated at a couple hundred volts allowing them to be used for either DC or AC where they can see 120+ volts. On a 12volt DC system you would want a voltage spike protection of only +/-5volts. IF you want to protect your batteries from a voltage spike then you need to install a Regulator which will keep the voltage from going over a certain limit but will allow current to pass at will. There really isn't much of a need for that on our trucks as there is a Regulator built into the alternator. The fuse would protect the batteries if an alternator would happen to short circuit or if you are like me and pull the alternator off the engine without removing the wires to work on something and it shorts out as it touches something it should.

CPUNeck · 11-21-2009, 09:52 AM

Quote:

The fuse would protect the batteries if an alternator would happen to short circuit or if you are like me and pull the alternator off the engine without removing the wires to work on something and it shorts out as it touches something it should.

Ha, I thought I was the only one to do that

OP, why not confirm what your "phantom" load is. When you first start your truck, ensure the Glow Plug Relay (GPR) is passing voltage to the GP's. Then when you suddenly get the extra juice, pull over and check that GPR again. There should be no voltage passing between the big lugs.

Could be a couple possibilities; 1) Your GPR is bad, and sticking or leaking, 2) The feed cable on the rear of your alternator is corroded (check behind the wire jacket, especially if on the bad alt there was evidence of burning/charring, 3) Corrosion at the battery terminals. Again, check behind the connector, the corrosion can travel up the wire.

All in all, with the described symptoms, sounds like a reproducible event, point to the GP system. I'd start there... hope that's a start. Oh and on the belt tension, there are visible indicators on the tensioner that indicate when it is out of service limits, so you shouldn't have to do an actual deflection test of the belt.