Weird voltage drop help! (Video)

[fmedina]

 

[WalledSonic]

PCM controlled alternator

EDIT: This is very common with car manufacturers these days.  Most cars produced now have a regulator that is based on engine speed, battery SOC, current draws throughout the system, fuel efficiency, etc.  For some cars (like my Sonic), there is no solution at this time without having a 'check engine' light.

[fmedina]

3 minutes ago, WalledSonic said:

PCM controlled alternator

Ha! Just looked it up. Told ya I ain't no alt expert. Thanks for that. So... How can I bypass this? Or is that not recommended. I was about to go to pick n pull and see if I could swap it out. But I'm guessing I'd run in to the same situation. 

[fmedina]

So here's what I found just in case someone else is wondering...

 

"Honda’s Dual Mode Charging System
For many years Honda and Acura have utilized a dual mode charging system to increase fuel efficiency and to 
decrease the drag on the engine when starting. The two modes can accomplish as much as 10% load reduction on the 
engine by allowing the Electric Control Module (ECM) to determine charging rates based on information gathered 
from an Electric Load Detector (ELD) and various other sensors. 
During heavy electrical or mechanical loads (i.e., if the AC clutch 
is engaged), the ECM will set the charging voltage to 14.4-14.9V 
(high output mode); during startup and light electrical load 
conditions, the ECM will set the charging voltage to 12.4-12.9V
(low output mode). In the latter case this anomaly might cause a 
technician to try to diagnose a low charge problem, although it is 
normal to have 12.5-12.7 charging voltage when the parameters 
are met.
This might confuse most technicians because it takes more than 
12.6 volts to charge a battery. However, while in the low output
mode, the alternator is not actually “charging” the battery but it is 
just holding the battery voltage at 12.5-12.7 volts. The main draw 
on the battery occurs during startup and after the battery has been 
charged there is no need to keep the voltage higher than what the 
vehicle needs. After the battery has been charged most of the 
current is drawn from the alternator as illustrated in figure 1. 
Thus, this system increases efficiency by charging the battery 
only when needed."

[fmedina]

This explains exactly what I'm experiencing. Ok I feel better. So it's normal lol but bummer I can't get the full 14.4 constantly. Would a high output alt act the same way?

 

"The C circuit is responsible for controlling the charge mode. The voltage regulator sends a voltage to the ECM 
through the C circuit. Depending on the charging systems needs, the ECM either holds the voltage high to signal the 
high output mode, or it pulls the voltage low to signal the low output mode. When the circuit C voltage is pulled low 
by the ECM: the charging voltage at the battery will range from 12.4-12.9V. The ECM uses the low output mode
when the engine is starting or if all of the following parameters are met: 
electrical Load below 15 Amps (varies with vehicle), 
vehicle speed between 10-45 mph or at idle while in drive, 
engine speed below 3,000 rpm, 
coolant temperature above 167°F (75°C), 
A/C Switch Off
intake air temperature above 68°F (20°C)."

[WalledSonic]

Keep your current draw high so the alt stays on (system banging all the time) haha

1 minute ago, fmedina said:

electrical Load below 15 Amps (varies with vehicle), 

Reach out to all the alternator manufacturers, some of them have solutions that are vehicle dependent.  I'm waiting on Dan at US Alternators to release his PCM Module that works with my car.