Test Alternator by unhooking the battery NOPE, NOPE ANNND NOPE (FAIL)

Recently while glancing over a few unrelated and useless topics out of boredom I came across an article describing various methods on how to test batteries and Alternators. The test which caught my attention was when testing if an Alternator is working to disconnect the battery terminal and if the car keeps running the alternator is good…….

Its on a High traffic Website so I thought it was a little silly, Maybe its just really a stupid ass click bait site with half assed Data.

Battery test breakdown

Back in 1956 vehicular charging systems were built pretty simplistic and grandpas old school method of disconnecting the battery to test the Alternator was a fine and dandy way to see what the issue was. I even seen some of the old boys run around in their old trucks without a battery at all having no issues other than if the truck quit they better have a plan! But its not 1956 anymore and the modern and high tech vehicles of today are a little bit different, and the cause and effect relationship has changed with it.

The modern charging system was advanced to a higher level due to all the complex systems added to modern cars like various power sensitive CAN control modules, infotainment centers and electrically assisted driving systems which require a more filtered and steady power flow to decrease the probability of failure. These more complex battery and charging systems were fitted with Battery Control Modules, Ammeters, and power filtration that in the past were more than likely to be found only on high tech server systems or maybe the occasional solar array.

And then little johnny disconnected the terminal to see if the car would die……..

So lets break down why you DON’T DO THAT

If you take a closer look at a 2016 Ford F150 wiring diagram (Green Circle….Look at the Green Circle) you can see that the entire electrical system funnels directly to the battery from everything, power from the generator passes through the Ammeter that tell the Battery Control Module whats going on, passes through a big ass fuse and into the battery, There is also a separate positive coming off the fuse on its own fuse that goes DIRECTLY TO THE STEERING SYSTEM! This SOLO Positive wire keeps you from losing power steering in the event of a power failure or if your battery goes full retard when your doing 90 on the freeway.

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2016 F150 battery diagram

Starter motor, Power steering control module, Battery Monitoring system, Battery Junction box, Body control module and generator all have their very own HOT wire from the battery!

So If we disconnect the positive wire where does all the power go?



DC power which likes to act abit like water and its pretty lazy finds an easy path that offers the least amount of resistance. Being disconnected from the battery made the entire ground system disappear so lazy ass 14 Volts looks around and finds a random wire or a body ground to get all its electrons from, After all, Power flows from the ground to the positive so you basically remove the systems ability to create solid electron flow.

So lets look really hard at the diagram and take a wild guess where or what the power wants to do…………

First the giant capacitor (The Battery is just a voltage source and a big slow capacitor….so basically a filter circuit for the Alternator…..) that was acting like a big awesome power filter is missing, So gobs of dirty unfiltered power is working its way around and getting into everything disrupting the various sensitive Modules and electronics.

The Battery current sensor connected to the Battery ground goes full retard because it detected a lack of any current and sends some HOLY SHIT BATMAN! Commands to the body control module to cut power to everything so the main control systems don’t lose power, It might even just kill everything to protect itself…Just a guess… I haven’t looked into what kind of protective commands are going on between the ECM, BCM and the battery control module as of yet.

If the truck happens to still be running (more than likely not) Power from the Generator starts looking for an alternate ground (Power Control systems dropped the reference signal by now and the Alternator is probably not doing a damn thing) and if it finds one that fits the bill for its laziness (closest ground with the least resistance) It will use that ground for its electron source. So if the starter positive cable or maybe a random Module has a ground that seems to look like a good idea Lazy ass DC voltage takes the path and dumps whatever Amperage looks like a good idea into the ground creating more chaos and fun so DC can chill on the couch again.

But looking at the full diagram it looks like the truck will just……. die, Not having proper power paths for the Battery control to measure what is going on. and no source for DC power other than a Generator that gets its commands from a module.

Maybe we can take a closer look later on and figure out what can get damaged when little johnny disconnects the battery terminal.