Installing a ammeter in my car

[scottmandue]

There is a useless cubby in the dash right under the radio where two gauges will fit perfectly.

I want to install a voltmeter, no big deal just one wire to the chassis and one to any positive I can find under the dash (cigarette lighter etc.).

Well, wouldn't it be cool to have a ammeter next to the voltmeter so I could check on my charging system?

However they say to do this properly all the current for the car has to be run through the ammeter thus you have to interrupt the positive from the battery and run large gauge wires.

But then someone suggested I can do this by interrupting (wiring the ammeter in series) with the ground off the battery.

In theory it sounds like it would work, current in equal current out, right?

Thanks!

[jyl]

The battery ground wire is also large gauge, though.

I think a voltmeter tells you if you're charging, just fine. 13+ volts = charging.

I don't see what use an ammeter is. See here
Auto Meter

Why not a cylinder head temp (CHT) sensor, if air cooled?

[jyl]

Another thing I have on my 911 which is fun, is a TPM tire pressure monitor.

[red-beard]

Originally Posted by scottmandue

There is a useless cubby in the dash right under the radio where two gauges will fit perfectly.

I want to install a voltmeter, no big deal just one wire to the chassis and one to any positive I can find under the dash (cigarette lighter etc.).

Well, wouldn't it be cool to have a ammeter next to the voltmeter so I could check on my charging system?

However they say to do this properly all the current for the car has to be run through the ammeter thus you have to interrupt the positive from the battery and run large gauge wires.

But then someone suggested I can do this by interrupting (wiring the ammeter in series) with the ground off the battery.

In theory it sounds like it would work, current in equal current out, right?

Thanks!

No. You put a shunt in the circuit you want to measure, then you are measuring the voltage drop across the shunt. This is proportional to the current and what the meter displays.

[scottmandue]

Originally Posted by jyl

Another thing I have on my 911 which is fun, is a TPM tire pressure monitor.

This is for the Miata (so not air cooled)

Have TPM on the Hyundai but while cool want to keep the Miata low tech (says the guy who just install a bluetooth radio into the Miata )

Already has a speedo, tach, water temp, oil presure, gas gauge... want a voltmeter... just not sure what to add to ballance the dash.

DDMWorks Miata Radio Surrounds

[jyl]

Egt?

[Esel Mann]

Another possible way to achieve safer (but more expensive) current measurement is to utilize a current sensor and matched meter/display. I would not recommend a shunt for current sensing in this application either. The charging system at the battery utilizes the same chassis ground as everything else. In order to measure what the charging system is providing, it is necessary to perform the current sensing on the hot side, specifically the wire which comes from the alternator and connects at the battery. If you use a shunt, it will be necessary to add in protection of the 2 wires which go between the shunt and the meter/display. Reason being they are hot. Another possible way around this is to utilize an electrically isolated current sensor, say something which utilizes the hall-effect. In doing so, the wires going between the sensor and meter/display are isolated from the charging path so the danger of a hot wire of high amperage is minimized.

[scottmandue]

Thank you everyone...

I guess I will just go with a voltmeter and skip the ammeter.

They do have a digital volt/ammeter that may not use a shunt on Amazon but I like the old school look of the round gauges.

[dad911]

Originally Posted by red-beard

No. You put a shunt in the circuit you want to measure, then you are measuring the voltage drop across the shunt. This is proportional to the current and what the meter displays.

Don't necessarily need a shunt. There are sensors like this one that can read DC current without interrupting the circuit CSLA2CF Board Mount Current Sensors | Mouser but require a custom electronics/display.

[red-beard]

I put ammeters into charge control panels all the time. Currents measured are in the 100 to 200 amps in the neighborhood of 24-32VDC. The simplest way is to use a shunt and matched meter. And yes, I used inline fuses from the shunt to the meter. The current is next to nothing, so I use 1/2 amp quick acting fuses. And yes, you fuse both sides.

I prefer shunts since it allows me to put the measurement where I want and the meter where I want.

[EarlyPorsche]

Install a stoichiometer! You weld a bung into your exhaust for an o2 sensor and then you can read how rich/lean your engine is running at different throttle positions/loads.