Three most useful gauges?

[Red]

I'd say oil pressure and a voltmeter. Ammeter not so much since you have wire the ammeter in series with the cars electrical system requiring the usage of some heavy gauge wire. There is a fire hazard as that cable will be carrying your cars entire electrical load

[ttoyoda]

I'd say oil pressure and a voltmeter. Ammeter not so much since you have wire the ammeter in series with the cars electrical system requiring the usage of some heavy gauge wire. There is a fire hazard as that cable will be carrying your cars entire electrical load

There is no need to cut into the cable. You can use a hall effect amp meter sensor that goes over the alternator cable. Another way that works is to hook a millivolt meter up so that one terminal on the mv meter is connected to the alternator cable at the Alternator end. The other terminal of the mv meter is connected to the alternator cable at the battery end. The flow of current thru the cable to the alternator creates a small voltage difference between the two ends, and you can meausure this and calibrate it for acutal amps.
In other words, the cable from alternator to battery acts as a shunt.
Nice job for an Arduino
Here is an example to show the idea of the hall effect sensor, this one is too big and too expensive, but much smaller and cheaper ones are available
http://www.alliedelec.com/Search/Pro...DESC=RSS-100-A

[JJW]

Are there any off the shelf remote-sender ammeters for auto use?

(although the arduino idea is attractive. I've been looking for an excuse to play with one.)

[MetroMPG]

Originally Posted by ttoyoda

Amps absolutely, and here is why.

ttoyoda, what a well reasoned post. I was going to chime in to say "voltmeter" until I read that.

Very nicely explained - thanks.

And this coming from an EV driver.

[Red]

Originally Posted by ttoyoda

I'd say oil pressure and a voltmeter. Ammeter not so much since you have wire the ammeter in series with the cars electrical system requiring the usage of some heavy gauge wire. There is a fire hazard as that cable will be carrying your cars entire electrical load

There is no need to cut into the cable. You can use a hall effect amp meter sensor that goes over the alternator cable. Another way that works is to hook a millivolt meter up so that one terminal on the mv meter is connected to the alternator cable at the Alternator end. The other terminal of the mv meter is connected to the alternator cable at the battery end. The flow of current thru the cable to the alternator creates a small voltage difference between the two ends, and you can meausure this and calibrate it for acutal amps.
In other words, the cable from alternator to battery acts as a shunt.
Nice job for an Arduino
Here is an example to show the idea of the hall effect sensor, this one is too big and too expensive, but much smaller and cheaper ones are available
http://www.alliedelec.com/Search/Pro...DESC=RSS-100-A

Cool didn't know about that, wonder how well that would work if hooked up to say an IMA cable?

[ttoyoda]

ttoyoda, what a well reasoned post. I was going to chime in to say "voltmeter" until I read that.
Very nicely explained - thanks.
And this coming from an EV driver.

Thank you. Unfortunately for me almost everything I have learned has come from some sort of (usually repeated) near-miss or disaster, large or small. Like the time I touched an electric fence in the dark twice, because I could not believe it had shocked me the first time. Only once in a while do I have an opportunity to learn from someone ELSES disaster, e.g. why I don't want power windows.


Are there any off the shelf remote-sender ammeters for auto use?

I have never seen one, (being cheap) I just use the mv meter and the alternator cable as a shunt. If you are going to use a moving coil meter, then a (center zero if you want to read discharges, means different hookup) meter movement that is about a microamp full scale has a reasonable internal resistance to give a reading directly, but if you are going to try that then start off by putting resistors in line with the meter movement to make sure you do not peg the needle right off the bat.
Ideally, the connection to the alternator cable would be to the crimped lug just away from where the threaded stud goes thru the terminal hole, so that changes in the resistance of the contact at the terminals do not have any effect on the results. I am usually lazy and just use big ring terminals, use the threaded stud with the meter ring terminal on last.

[Dust]

Wanted to bring this back up, and see about a fourth gauge. Already have a boost/vac, and I am looking at a water temp and oil pressure. The boost may go on the column, and three in a DIN pod. What should the 4th be?

[Joseph Davis]

Originally Posted by ttoyoda

Amps absolutely, and here is why.

Eventually, the battery will start to fail. Often, it will fail by shorting out one cell out of the 6. That means it is now a nominal 10 volt battery instead of a nominal 12 volt battery, BUT the fully charged voltage might be 11.8 or 11.9 so you will not notice it on the voltmeter.

When the battery cell fails, the alternator is going to try REAL hard to charge the battery,

Meh, if/when that happens your battery completely dies overnight and you get another battery. No ammeter is needed.

I'm really not a big fan of a thousand and one gauges. I tune cars for a living and see an endless procession of cars with pillar pods full of crap information I could do without. Oil pressure so I can verify engine condition (oil pressure switch set to kill ignition if it drops too low at WOT), boost/vac, and maybe wideband AFR. Or maybe not.

Honestly, all of the cars I've tuned that made it on TV or ran notoriously strong, and reliably, have no wideband. It's a great diagnostic or tuning tool, but in the hands of someone less than an experienced technician it's too much information and a distraction.

[Ptero]

Jason, you can keep your scangauges and tachometers, my most valuable instrument is this bird, mounted on the cowl of my Smart car. All this $4 flowerpot bird has to do to tell me everything I need to know about hypermiling is just to flap its set of spring-loaded wings in a particular way.

This is how it works. When the wings are extended, like they are in this picture, I get the best mileage. At highway speed they fold up into a tight V. In a cross wind, one will fold upwards and the other will lay out flat, pointing in the direction of the wind. In a good tailwind, the wings lay out like in the photo sometimes up to 40 mph. On the highway, I'll get behind a line of trucks or cars and the wings will flap, indicating turbulence and reduced drag. If you dare, pulling up close to a truck will cause the wings to drop down, indicating that you are in the low pressure pocket behind the truck. Naughty bird!

Don't you hate it when you spend hundreds of dollars on instruments and some weirdo goes by you at 65 mpg with a stupid bird on his hood and a speedometer and a couple of idiot lights in his dash? Life ain't fair!

[RH77]

Originally Posted by Ptero

Jason, you can keep your scangauges and tachometers, my most valuable instrument is this bird, mouted on the cowl of my Smart car. All this $4 flowerpot bird has to do to tell me everything I need to know about hypermiling is just to flap its set of spring-loaded wings in a particular way.

Perfect! After driving 50 miles home in a 25 MPH / Gusting to 40 MPH headwind today, I looked for flags or trees for an indicator. This (or a ribbon) gives you the perfect airspeed and direction. Brilliant!

In all seriousness, I'm worried about the battery. It's 6-7 years old, cranks slowly in cold weather, and could be taxing the alternator. I've often hit hard road bumps or rural/gravel road vibration in typical operation. There's a pull like the A/C engaging, which I'm convinced is the alternator draw.

An Ammeter would be ideal. Installing one seems to be a challenge (and a new batt -- is it too early???). It still starts!

RH77