Fun with Voltage
 

Hello all,

Since I breathed life back into my 4runner via some neurosurgery, I have been noticing some odd readings from my torque pro app in regards to voltage. My charging voltage is staying steady at 12.6 volts.........no matter the RPM. 1000, 2000, 3000 all read the same 12.5 to 12.6 voltage range. Im not sure what would cause that. I know there are a million alternator threads, trust me, I read a lots of them. But none mentioned steady voltage at all RPMs. During my 3 month diagnostic process, the 4runner never left its parking spot. I sanded all the grounding point I could find. The battery ground wire was upgraded last year to a much heavier gauge than the stock wire. I also cranked the engine at least 50 times during that 3 month period. I was impressed the battery still had enough charge to start the engine that last time. Could this be a voltage regulator or brush problem? It looks like the Voltage regulator is just $50 shy of the price for a new OEM alternator. Thoughts?

Thanks, -Z

Sounds like it is time to break out the multimeter.

You'll need to figure out where the voltage drop is coming from. Start with the actual battery voltage (ground clipped on battery), then the output of the alternator, then check various spots on the chassis vs. the ground post, etc.

If the brushes are bad (in my experience) you will get the 'charge' lights on the dash at least some of the time.

-Charlie

Im getting 12.94 volts with the engine off at the battery. 13.89 volts idling at the battery. Voltage increased to 13.91 at 3000 RPM. So how am I losing an entire volt at the OBDII port?

Well, if you decide to replace the brushes in your alternator, @infamousRNR and I have a video for you.

<iframe width="560" height="315" src="https://www.youtube.com/embed/71_kBhg6_-A" frameborder="0" allowfullscreen></iframe>

I wouldn't trust an app on my phone compared to a readout on my Fluke. Furthermore, I have a Scanguage 2 and the the values you put in to get the correct output and addresses from the ECU can be changed thus changing the readout. I did this to acquire a proper AFR reading from the front sensor of my Cali emissions 4Runner. Some have said that the OBD2 reading is a direct voltage reading somehow from the charging system but I don't buy that.

On a side note, I did @mtbtim brush replacement using his video and I caught mine JUST in time. 182,000 miles. They were completely worn down to where they were just barely riding on the shaft. One of the easier repairs I've done on my Runner. Thank's Tim.
I don't think this is your problem though.

I did re watch that video to see if you had replaced the voltage regulator but as soon as I saw the price I knew it wasnt happening. For $50 more you could get a whole new OEM alternater. The brushes are cheap enough that I may have to add them to my list when im back in the states this Christmas.

Your charging system is probably fine. I missed the part where you said you were using Torque Pro. Torque Pro with my rig shows around 12.6-12.8 volts as well. When I check the charging system via a multimeter at the battery, I'm reading between 13.8-14.3 volts.

Torque Pro does not deliver an accurate number for volts but it can still be useful since we know what it reads when the charging system is working appropriately.

Hey John, you're welcome and Sean and I are happy it helped you out.

Either way it still doesn't increase the voltage when the engine is at a higher rpm

Sent from my SM-G930T using Tapatalk

Sounds prefect. ~14.5V when very cold (below freezing), ~14.2V when cool/cold and ~13.9V when warm/hot are the numbers you are looking for at the battery. The alternator regulator adjusts for temperature.

-Charlie

Oh, I always thought it fluctuated with the rpm. Glad to know it's working.

Sent from my SM-G930T using Tapatalk

I have always wondered about this. I have seen mine drop when hot and driving around the desert. Never gets hot enough to drop the voltage here at home.

It can drop a bit at idle with high loads (turn on your lights, fog lights, brake lights, maybe some aux lights, fan on high, etc. and it will drop). Once it can produce enough current/power, it will regulate to the correct voltage, which is temperature dependent.

Cold vs. hot batteries take charge differently. Cold temps = more voltage needed to 'add' power back into the battery. 14.5+ volts at high summer temps will fry a battery, but barely charge it below freezing.

http://www.tekrispower.com/pdfs/xant...20Charging.pdf

-Charlie