A quick addition about the voltages.
I found out a few odd things with the voltages today that I thought was worth sharing.
If I have a full electrical load, the voltage from the alternator isn't really affected too much (stays at about 14.4v-14.5v) i.e., even with the A/C, Radio, Headlights on, etc, the alternator when stationary shows a 14.4ish voltage.
However, when the fans kick in the voltage drops to around 14.2v briefly whilst the fans are running, and then back to 14.4ish when they turn off (you can hear them clearly).
I then noticed that when I drive and move off, the voltage drops to about 12.5v regardless of load applied
, i.e. it doesn't matter what is or isn't running, start moving and the voltage quickly drops to 12.5ish volts.
So if I then stop at the lights, it goes back to 14.4ish until I start driving again.
This is regardless of any other electrical load so the only variable seems to be that I'm moving. I noticed it at each traffic light today consistently where the same thing kept happening.
When I turn the car on in the morning the battery is at about 11.6-11.7v but has no problem
starting the car (the battery is the stock one and is only 3yrs old and I only killed it once when doing my stereo install). It's worth noting that after sitting for a week or more on the driveway, it still starts up fine. It also always starts up fine in winter.
Therefore I'm happy that the battery, alternator, tension of alternator belt and grounds are all fine, but couldn't get my head around this weird voltage drop on motion nor on the fact that at 11.6v, the battery should need jumping going by the chart above but it never has problems starting the car.
N.B. The voltmeter itself has a drop of about 0.06v c.f. "direct measurement" due to the length of lead I used to wire it up (quite long) so I know it's fairly accurate and these are fairly true readings.
So after looking around t'internets, I found that others had almost identical issues (not only the voltage drops on movement but also the low cranking voltage apparently being fine to start the car) and I finally found the answer to the former q.
The alternator in the Jazz has it's output directly controlled by the ECU and is NOT meant to ALWAYS put out 14.4v+. The Honda's use Electric Load Distribution which works as follows:
The powertrain control module accepts an input from the ELD. The ELD senses current on the 50A ignition wire in the engine fuse box. The ELD gives information to the PCM with a DC voltage between 1.1-5 VDC. The higher the number, the lower the load, and vice versa. So when the sensing voltage stays above 2.5-2.8 VDC, the PCM tells the alternator to turn off. The voltage drops to the battery float voltage, and your fuel mileage goes up. This trick saves you fuel, but you lose alternator power. When the ELD sensing voltage decreases to around 2.1 VDC or lower, this tells the PWM that the ignition load is high, so the alternator kicks back on to full output and your voltage increases to >14 VDC.
So the ELD circuit varies the alternator output based on electrical load, and tries to actively improve mpg by cutting the alternator output whilst in motion if not needed.
It begs the question, "is that enough to charge the battery then?" but apparently it must be although I can't quite get my head around how (it should logically provide virtually no charging current at all if it keeps doing this).
I also still can't quite figure out how you can start the car with such apparent low voltages, but as I said, it starts fine in any weather with no problems.
So if you do this mod and find the voltage dropping when in motion, it's Honda's ECU and ELD system working as they're designed to, NOT a problem with the car