The Amp Gauge

[BlueRooster]

Can someone explain in detail how this little bugger functions? How I can decipher what it is telling me?

AND why a volt meter is better, and how to hook it up?

My battery did not fare too well over winter this year and it takes and holds a charge, but if it sits for 2+ weeks it becomes too weak to start the car. So I am trying to learn a little more about the charging system this year.

Thanks Guys.

[Tommy]

Wikipedia has good info on how various gauges work. But the water analogy helps a lot of people better understand electrical matters. Electricity involves the flow of elctrons along wires sort of like water flowing through pipes. The amount of water flowing through a pipe (watts for electricity) is determined by the pressure (voltage) and the size of the pipe (amperage). In a car, the battery is like a reservoir of pressure that can be used to push electrons through the electrical system. When the engine is started, the alternator acts like an electron pump to push electrons into the system. When the alternator produces more pressure (voltage) than the battery, it forces electrons back into the battery, recharging it.

An ammeter measures the flow of electrons along a pathway. If it is wired between the battery and alternator, it will indicate whether electrons are flowing into or out of the battery. The amount of electricity flowing into or out of the battery can indicate the state of charge of the battery and the effectiveness of the charging system.

A voltmeter indicates the voltage (electrical pressure) on a pathway. Since most car batteries charge to around 13 volts, a voltmeter on a fully charged car battery should read near that level. When the engine is running, the charging system should produce more than 13 volts to power the car and recharge the battery. By monitoring the voltmeter before and after the engine is started, you can judge the condition of both your battery and your charging system.

I personally perfer the voltmeter over the ammeter.

[Woodz428]

The main reason that voltmeters have taken the place of ammeters in most cases now days is a liability problem the MFG. would prefer to avoid. While I have never experienced it personally, an ammeter can short out an cause a potential fire. All the current to the car and from the alternator are fed through the ammeter, so however much amperage is in the battery can possibly create a safety issue. A voltmeter on the other hand pulls a reading off a line with no circuit running through it. I have never had an ammeter fail to that degree, and wouldn't want it to. I did have the wiring in an old Morris I bought melt the wiring insulation and then the oil pressure line. It was an aftermarket adaption, pretty standard type thing at the time, and was wired with too small wiring. I do prefer voltmeters for the reason stated in an earlier post. I think they give a better indication of the system condition.

Oddly enough when I looked at your location, Morristown ,NJ., THAT'S the place that my Morris melted it's wires to the gauge....how weird. Had some great times there.

[patrickt]

Originally Posted by Woodz428

While I have never experienced it personally, an ammeter can short out an cause a potential fire.

I had that happen; not in my Cobra, but in my Datsun 2000 roadster. I hit a speed bump at a not too high speed and the ammeter in the dashboard shorted out, fried everything, small fire, lots of smoke, of course it resulted in a tow home. It really does happen.

[Bill Wells]

wow, great info ....even I can understand it now and I am NOT a techie .

now, for the short version :

1. get a new battery

2. live with the amp gauge til it quits , or change it to voltmeter.

Bill

[jerry w]

You should be able to find a voltmeter that fits the same size hole in your dashboard as the ammeter. It is usually only three wires to connect.

How old is your battery? They do not last forever. MIght be a good investment. A battery charges when the voltage on the dash voltmeter is reading about 14.5 volts or higher. A 12 volt battery actually should read 14 volts when fully charged.

Just for the record:

Voltage = Electro-motive force.

Amperage = quantity of electricity in the form of moving electons (current) this is different than charge (Coulombs)

Wattage = Electrical power. In D.C. applications Watts = Volts X Amps

A.C. applications Watts = amperage squared X Ohms

Regards,

[Velox]

Here's how the Smiths voltmeter looks in the SPF dash (I also changed over to an electric oil pressure gauge)

[BlueRooster]

So at -0- all is balanced. So it should always be at 0 or +, because a negative would mean the battery is putting out more pressure than the alternator? Which would indicate a bad alternator or grounding problem?

My multimeter reads about 13.4 to 13.9 and I have an optima red which is about 2 and a half years old. I think the battery has life left in it still. Its the gauge that confuses me.

Every now and again the fuel pump will click and get quiet. The gauge does a hard flicker back to 0 or below then the pump will slowly get noisier and as it does this the gauge goes back to normal. This cycle always happens...always did from day one. I stopped being concerned about it years ago, I just want to understand whats happening.

[jerry w]

Not to be critical of your multimeter, but not knowing the brand or quality, it could be slightly inaccurate. That said, 13.9 volts sounds reasonable for charging. Your Optima battery most likely is good.

I do not know what is going on with your fuel pump? Maybe someone else with a similar set-up will see this thread and offer some advice

Regards,

[Blas]

Dane,
I have a name somewhere of who to contact to get a Voltmeter that matches the Smiths gauges exactly...The graphics are all done for the gauge face...PM me if I don't post it by Monday night (in case I forget when I get home)
Blas

[Blas]

I spoke with Chuck at "Gauge Guys" (search the Internet) He confirmed that he has Voltmeters in stock to match our instruments. BUT: When I asked about the problem with the dimness of the instruments in general, he said that they were in fact quite bright. A 2.2V bulb is standard he said, and as we spoke more on the issue, there came a comment from him in passing about the newer style electronic instruments are quite bright....The Voltmeter is a newer style gauge and that would mean it much brighter than all the other "Older" style gauges most of us have in our cars. We then spoke about bulbs, and switching to a highter wattage bulb. He said that everything is metal in the instruments - not plastic - heat should not be a factor....(???? the clear side "windows" are plasic ????) that being said, I guess we need to run some tests on bulb wattage vs melting....He also mentioned something about the newer design has colored sleeves available...
And by the way, there is a notation on the wiring diagrams I have available for the SPF cars as to the source of this gauge - I knew I put it somewhere the info wouldn't get lost....(a shameless plug for the wiring diagrams....sorry)


Here is the contact info for them:
APT Instruments International Inc
9632 Humboldt Ave S
Bloomington MN 55431
PHONE 952-881-7095

[BlueRooster]

Thanks Blas. I have been thinking of getting one the diagrams. I'll reach out to you.

But, the gauge itself. How do you interpret what it is telling you? If it is not on -0-, but closer to either pole, what is it telling you?

[Blas]

I guess I would ask why you want to replace it...Are you having a specific problem with your car?
With your particular series car#, I would be more concerned with installation of a main fuse in the line from the ammeter to the power tap on the starter solenoid...80Amp should do fine if you have a stock setup....PM me if you need directions....

[Rick Parker]

I am not fully versed on the circuitry of a SPF however unless you are attempting to monitor the voltage in lieu of amperage, you could install a fusable link or a manually resetable circuit breaker in a main leg from the solenoid? ERA circuitry uses a circuit breaker between the 12 V feed from the post on the solenoid and Amp gauge. Last year on the way to the WSCB I discovered a bad voltage regulator (old type with points & coils) that was sticking and when ever the key was shut off the circuit breaker would "Pop", rendering the entire electrical system dead. It was doing its job.

[dbn04]

blue rooster,
i had a similar problem not long ago, for several months the gauge was playing up, and the fuel pump would not sound right, but it kept starting and running,then it sat for a few weeks and would not start, changed battery,(3years old) and then 3 weeks later dead, i checked with multimeter at the alternator 13.9 volts and at the battery was 12 volts, starting tracing back and it ended up being a loose nut on the starter motor, not a lot just enough to not get full contact, all works good now.

[BlueRooster]

Blas- No specific problem, just the fuel pump/amp gauge thing mentioned above. I really want to know how to read the gauge. When it is closer to either pole +or- what is happening ? Bad alternator, bad ground, bad battery?

AND, if it isnt a good indicator of anything, maybe, I should changeover to the Voltmeter. Thats all.