How many amps does an amp gauge pull?

[4123]

This may have already been covered but I'll be darned if I can find it anywhere. I want to wire in an automotive type charge/discharge analog amp gauge, in series, between the positive post and the DC workings of the trailer. My question is, is there an amp draw when the amp meter is at rest (zero)? Also, when its giving a reading, plus or minus, is there an additional amp draw on the system?

[planovet]

How many amps would an amp gauge pull if an amp gauge could pull amps? Say that 3 times real fast! (sorry Ron)

[Steve_Cox]

There is enough draw from a wired in analog meter that you might want put a momentary toggle or push button switch in series with the meter to be used when you want to read the meter. There is also the induction type analog meter that has an external coil that slips over the wire you want to meter, it uses no power when no power is being used

[depatty]

If you're speaking of the shunt style ammeter like that has two connections on the back and a zero center meter then:

There is no current draw (from the meter) when the meter is at it's center or rest point.
The current drain from the meter is in the micro or milli amps when reading a charge or discharge. The meter is actually a voltage meter that is reading the voltage drop across a known resistance in the form of a piece of metal or wire (the shunt).

See http://bluesea.com/productspecs/8254 for the specs on the Blue Sea 8254 DC Zero Center Micro Ammeter.

According to their info on this meter: The Meter Current is 1 Milliampere at full scale and the External Shunt drops 50 Millivolts at meter full scale

Note that these values are only for this particular meter.

HTH
Dave

[Dale M.]

For all practical purposes in the whole scheme of life, it is so small that it will probably never have any effect on what makes the world turn.......


Dale

[Steve_Cox]

I prefer to use an analog 0-15 DC volt meter myself to determine the battery state of charge rather than the ammeter showing the discharge rate.
I used a digital multi-meter on each current drawing item that was to be mounted in my camper so I could size the fuses accordingly. I can't see the need past that to watch an ammeter.

[vrooom3440]

Automotive ammeters are a series device, thus there is NO current draw by the meter itself. In use there may be a very slight inconsequential voltage drop but that is about it. Remember that these used to be wired into many cars. If they ran the battery down on their own they would not have been there.

They have been phased out in favor of the voltage gauge due to the length of high power wiring required in an automotive setup. It is also true that most of the diagnostic capability (the reason we use gauges in the first place) provided by an ammeter can be provided just as well by a voltmeter. Plus a few diagnostic capabilities not provided by the ammeter.

Voltmeters are a different beastie as they are connected in parallel and thus DO consume some very small amount of current. Which is why they are wired "ignition hot" in automotive systems.

[Larwyn]

Analog "ammeters" and "voltmeters" are actually all ammeters. The external circuitry and meter face scale are what makes it indicate amps, volts, etc.

http://www.electronics-tutorials.com/test-equip/meters.htm

[depatty]

Analog "ammeters" and "voltmeters" are actually all ammeters. The external circuitry and meter face scale are what makes it indicate amps, volts, etc.

http://www.electronics-tutorials.com/test-equip/meters.htm

I stand corrected.
Boy that page takes me back a lotta years. Seems like that stuff was in the basic electronics course right after basic ac/dc way back when.

Good link Larwyn! Got it bookmarked now. They have a page on shunts http://www.electronics-tutorials.com/test-equip/meter-shunt.htm that is quite informative/helpful too.

[4123]

I think that a DC analog charge/discharge amp meter will tell you when your battery is fully charged. That is, if you have been parked for an extended time and want to charge your battery using your tow vehicles regulated charge system, when the battery is fully charged the gauge will read 'zero' and you can turn the motor off. Is it so?

[Dale M.]

I think that a DC analog charge/discharge amp meter will tell you when your battery is fully charged. That is, if you have been parked for an extended time and want to charge your battery using your tow vehicles regulated charge system, when the battery is fully charged the gauge will read 'zero' and you can turn the motor off. Is it so?

A ammeter will only tell you when battery voltage has matched charger voltage... As as battery voltage matches charge voltage current flow diminishes....

IF charger voltage is low, then battery MAY NOT reach full charge. Only voltage reading will indicate FULL charge....

Dale

[wlooper89]

Reading this thread I became curious about the amp draw of a voltmeter. The draw of ammeters was said to be 1 mA earlier in the thread. That really is negligible unless the meter is using a backlight.

My voltmeter is a digital type made by a company named Cyberdyne. Trivia buffs may recall it is also the name of a fictional company that created robots in the "Terminator" movie series.

Using a multi-meter tester it turns out that the current draw of my voltmeter is 100 mA including the LED display, fully 100 times the draw of an ammeter. I am curious as to how this would compare with an analog voltmeter, but I do not have one of those. I expect that an analog ammeter would use much less current without the LED display. My voltmeter will use one ampere hour from the battery or power source in ten hours. Fortunately the voltmeter selector switch has a center off position. I have also added an on-off switch for the ammeter backlights.

Bill