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Discussion Starter #1 (Edited)
Time for a another bit of tinkering :D.

Before I start, I'll just say that I know this isn't necessary and I know some people may not like altering their cabin, but it is very cheap and is an interesting little project that's quick and easy to do for those that do ;).
When I was growing up, I seemed to remember that many cars had voltmeters in them (my bro's mini's for instance) but as cars have become more reliable, they have gradually disappeared from cabins. I myself thought that it would be nice to have the good ol' voltmeter back in the car, and seeing as it is very easy to do, decided to install it.



Firstly, buy a digital voltmeter from eBay that has a range at least from 10-16v.
The first one I chose was a spot on orange colour and cost £3 but that stopped working after a day! I then bought this one as I was happy enough with red and it has a 5 digit readout.
The voltmeter you buy may have only 2 wires, but it may have three, with the third one being the measuring wire (the other two being +ve and -ve for the meter's power). In which case, you'll have to solder the +ve and measuring wires together (as you're measuring the batt/alt that is powering the device).
So first I extended the wiring, combined the +v and measuring wires (red and yellow) and heatshrinked accordingly.



I then removed the panel with the cigarette lighter. This was easy and involves first removing the panel above which is clipped in (same as removing it in order to remove the radio fixing screw), and then unclip the panel toward you:



Then I unplugged the lighter socket and took the panel inside for a bit of dremelling in order to cut out a square the size of the meter. Remember to buy a voltmeter off eBay that includes the bezel so that it will fit flush into the panel you choose (this voltmeter cost me about £4 inc. deliv).

Once fitted, I reassembled the two panels and connected the -ve to ground (any good earthed screw) and +ve/Msr to an Acc +ve feed (mine was via the fuse box). Works really well and not too bright (some eBay items are blindingly bright, choose a display that is a bit dimmer).


Acc on, no radio:




Acc on, radio on:




Car running (alternator on):





For placement, I wanted somewhere in line of sight whilst also being fairly unobtrusive and out of the way...plus it's easy to get to.

It does also have some uses in that with the acc on (and nothing else on) after the car has been off for 1 hour, you can see the state of charge of the battery:

12.6v = 100% charged
12.4v = 75% charged
12.2v = 50% charged
12.0v = 25% charged
11.8v = nearly dead, may have trouble starting

^^^rough figures for the average battery. Plus, you can see if you have alternator issues or load issues on the car (alternator should give roughly 14.2 - 14.8v at full load with everything on, any less and it may be a be having problems supplying the current you need).

So a nice, cheap, easy, mod that is quick to do and fairly unobtrusive :).
 

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Discussion Starter #2
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 :).
 
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