ammeter gauge

[EDREIZIG]

Long story short, in addition to some of the standard gauges that I'll be installing, I had a space for a spare one (fifth). Two will replace the ashtray and the other three will sit above the ashtray. It's a bit packed, but oh well...

I was thinking on what to choose for that last one and decided on the ammeter. Really old cars used to have it and these days it's rare, so I figured, why not, it's cool...

The mandate though was to NOT hook it up like a standard ammeter would dictate in series since I didn't want to change any wiring and it had to match all my gauges, so had to be VDO Vision, which added some very nice constraints to the project.

This turned out in quite a cool, custom, electronics project. If anyone's interested, I can share more info.

[dogsbark26]

I'm interested!

I am no electronics genius but have wanted an ammeter in my car for a while now. Not voltmeter (worthless) but ammeter. So ammeters need a huge wire cause they run all the current being drawn by the circuit. OR install with a shunt. I wish someone could help me understand a shunt.

Let's see pics. Please share installation / wiring details. Woo hoo! Finally someone who installed an ammeter.

[george graves]

A shunt is a low low value resistor that is calibrated to some degree, and can handle a large amount of current. But, it's really just a resistor.

This is over simplifying things but... - every circuit must make full path, from voltage source and back again. Like this:



So - where it says "Vin" - pretend that's your battery. And where it says R1, that would be the "load" of all of you're car's electronics (fuel pump, your dash lights, everything - just imagine them all grouped together) That's what R1 is..........So R2 would be where you would install a "shunt" - you would place it in "series" with everything else (well, that's not always true - but anyways - it's one of the major flaws with an ammeter)...........So, if you know the value of R2, and then measure the voltage across it(Vout), you can know what the current through it is. Just with Voltage = amp X ohms. Mix that equation up a bit and you get amps = volts/ohms. And bingo - now you know the amps that is flowing through the circuit.

Not voltmeter (worthless) but ammeter.

Well, here the kicker. It's almost not worth it to know how much current your car is using.

An ammeter won't tell you the condition of you battery before you start the car. So...you'll be looking at that ammeter, thinking all is good - meanwhile you battery is dieing and it at 10-11 volts or something, but your ammeter will be tell you "all is good here! I'm still delivering current!" And what that current value is, isn't really useful information. It will only tell you one of two things. The battery is being supplied with current, or it's being robbed of current - that's really it.

It won't tell you if your alternator is delivering the voltage needed to keep the battery charged, and what you battery voltage is before starting - that's a much more useful value IMHO.

Plus there are other issues. Since the "shunt" is in series with the car's electrical load - all of the current the car is using must pass through the shunt (some gauges don't use a external shunt - they build it in to the gauge - but it's still there) - and that can be a lot of energy. And where you have a lot of electrical energy - you have a lot of heat - and the chance for things to go wrong.

The hot rod guys stop installing aftermarket ammeters when the build quality went south - even on the brand name ones, and it started burning down their cars.

If you want to install an ammeter - go ahead, but you better know what you're doing, and it's worthless without first knowing what voltage the car is at.

[dogsbark26]

Wow George, good, interesting, informative post. Thank you.

Will take further questions to PM so not hijacking this guy's thread.