General > General Technical Chat
Any expertise here on the Honda Dual-Mode Charging System?
Peabody:
Honda autos have something called the Dual-Mode charging system, which sets the alternator at 14.4V when heavy electrical loads are present, but drops it back to 12.4V otherwise. The 12.4 V level leaves the battery only partially charged - about 60-70% - and I assume the thinking is that so long as it will still start the car, there's no point wasting gasoline keeping it charged any higher than that. Unfortunately, a partially charged lead-acid battery will soon sulfate up and fail. I had to replace the battery on my 2012 Civic twice over about five years. So any benefit Honda gets from quoting high MPG numbers is paid for by the customer having to buy a new battery much more frequently than necessary, now at $150 a pop.
So I've taken to driving with the headlights on, even during the day. That keeps the battery charged. But I was hoping to find a way to defeat the Honda system, and keep the alternator at 14.4V as God intended, so I won't have to waste gasoline on the headlights.
Earlier models (Civic 8th gen) could be hacked with the "ELD bypass", which consisted of strategically inserting an 820-ohm resistor into the Electronic Load Detector circuit in the fuse box, but apparently this no longer works on 9th gen and later cars. I was thinking of simply hacking the alternator, but it is now controlled over CAN bus, so that doesn't seem promising.
Well, I was hoping to find someone who had solved this problem, or maybe a Honda engineer who could offer a solution.
bdunham7:
I can't think of a hack that wouldn't have unwanted side effects. The ECU controls the alternator field directly, IIRC, and any tampering with the ELD to fool it will likely trigger fault codes and warning lights. But I think headlights are the best solution anyway--studies show that daytime headlights reduce accidents slightly and the amount of energy needed to run them is pretty small, probably less than the power that will go into the additional charging of the battery.
If you still want to change it, you need something like FlashPro to go into the ECU and simply turn the option off.
amyk:
Something like https://www.backyardmechanic.org/how-to-build-a-external-voltage-regulator-for-dodge-jeep-chrysler/ ?
Peabody:
FlashPro is $695, which is completely out of the question.
nali:
Interesting, I too drive a 9th Gen Civic and I hadn't heard about that. So I took mine for a run this morning and as you say 12.4V. Then I had a thought and checked the ECON mode which was on... turned it off and went for another short drive and guess what, the battery was at 15V!
So, it appears to be one of the subtle effects of ECON mode (which AIUI also backs off the aircon and changes the throttle map at least while on cruise control, not sure about normal driving).
Have you tried civinfo.com which is a pretty good repository for Civic nerds?
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