Understanding today’s charging circuitry and what to
The other day an 08’ Ford F250 showed up at my door
with the charge light blaring away on the dash. My shop,
being an electrical shop this type of repair is just another
repair, just another day. Charging systems are a common
repair too, but on a 08’ things aren’t exactly like they
use to be when it comes to the charging systems.
Opening the hood revealed an even bigger disaster.
Something was seriously wrong with the components
under the hood. At first glance it seemed just to be a
new alternator. But further inspection lead to an
astonishing find. It wasn’t the original style alternator
that was in the truck. It was in fact an older style
externally regulated alternator system. Still a Ford
system but definitely not what this truck originally came with.
Curious to see what kind of output this system was producing I hooked up a volt meter to the battery. It showed a perfect voltage output (14. + Volt output) but there was no doubt it was a complete homemade setup. The voltage regulator (external) was bolted to the right side ground distribution post and the “I” wire to the regulator was stuck into the under hood fuse box with a spade terminal. (Shoved would have been a better way to put it.)
The problem was the dash indicator was still glowing even with a good output. Whoever had put in this charging system had a pretty good idea on how to make an older external regulated system charge but apparently knew nothing about the more modern “computer-driven” systems.
What should you know about computer-driven charging systems;
First off, today’s regulators can read temperature, that’s right, they know how hot it is and or how cold it can get. These temperature changes can vary the voltage settings and output of the alternator.
Typically the “set” voltage (a predetermined voltage level pre-set in the regulator) is higher in cold temperatures than in the warmer times of the year. This allows for a more even battery recharge in the winter and reduces the chance of overcharging in the hot summer months. More importantly, the charge indicator on the dash isn’t directly connected to the alternator as was the case with the older externally regulated systems. Today, the CAN system (Controller Adaptable Network) monitors and distributes the needed signals to the different components in the vehicle.
In today’s cars the PCM is the direct link to the alternator by sending out a signal and telling the alternator “it’s time to turn on” once the alternator begins to create voltage an output electrical signal is sent thru the stator windings. This voltage signal is sent back to the PCM as a feedback signal (typically half the battery voltage) this “signal” in turn travels down the wiring and the CAN buss line to the IC (instrument cluster) and this “return” signal is what turns off the charge indicator light. (Some will call it “canceling” the signal at the IC)
All this time the battery sense circuit is comparing the set voltage internal to the regulator and controls the generator field current to maintain correct alternator output.
So as you can tell there is a lot more going on then what there was in the past charging systems. Along with all this other information being passed back and forth between the PCM and the alternator the PCM can also tell to you “the tech” certain codes that can help determine how to make the proper repair.
In the case of the 08 F250 there was a code B1317 (battery voltage high). The reason for that code was that they had taken the (yellow) PCM wire and tied it to the “I” wire of the external regulator. As the truck was started the light would go off for about 10 or 20 seconds, just enough time for the PCM to recognize that the return signal from its “yellow” wire at the alternator, was a lot higher than its pre-set voltage.
My best solution was to install the correct parts and connectors and start all over again. Which by the way… worked just like it was designed to. Charge light went out, and output voltage was now being controlled by the internal regulator and monitored by the PCM.
The nice thing was there were no ill effects to the PCM so there was no need in replacing it or any other components. But I’m sure that the owner of this truck will think twice before having somebody yank out his alternator again…
As always progress and new innovated components seem to be hard to understand or wonder what “they” (the engineers) were thinking when they designed these things. But it’s what’s out there and I don’t think it’s going to change to a simpler system for the benefit of simplicity… but change it will, you can count on that. Right now it may seem a little confusing, but in time even this system will become old and simple. It’s just a matter of learning and understanding these new concepts. In this business you can count on one thing… change.
Learning how these new systems work is as important as the repairs themselves… the systems of the past were good, the new systems may have some differences from the old but I’m sure there is a good reason for it all, it could be for more even charging under different conditions, it could be for load requirements, and probably a few other reasons that are all important… but one thing is for sure… the past systems are the past. As a modern tech in these modern automotive times there is one thing to remember:
Keep Charging Forward.