10 replies to this topic

[nick217]

How do i wire one of these up in my mini sprite?

Edited by nick217, 05 August 2010 - 07:22 PM.

[dklawson]

Generally you don't use an ammeter.

Ammeters were much more common and safe in the days of generators/dynamos where the charging current seldom exceeded 20 Amps. Even a tiny alternator will typically produce 35 Amps, most produce more than that.

The problem is your ammeter needs to be sized to work with the maximum output of the alternator and the wires to/from the ammeter also need to be sized to support that current. Those wires have to pass through the firewall to reach the gauge. That requires special care to make sure there is no chance the wires will fret or chafe and come into contact with the metal car body.

Voltmeters are much safer and easier to install. In most cases they can tell you as much about the condition of your charging system.

[nick217]

I gather that so i would not run a live heavey amped cable through the interior.

So i would like to use it to see what amps all the internal components are using like radio & heater + most of the lights ie headlights too cheers. how would i do this?

[nick217]

Anybody i need something to do tomorrow

[Barman]

Surely an Ammeter is just a voltage device that reads the voltage ( +'ve or -'ve) across a 'shunt' or resistor through which the main current passes...?

The full load doesn't actually pass thorough the meter...

I'd have thought it would be possible to read the voltage 'remotely' (without the current passing through the bulkhead) but I guess that would depend on the design of each individual manufacturers device...

Not that helps very much without having the instructions from the Smiths device - don't they have a web site with installation instructions?

[Pooky]

I had an ammeter once. It needed to be connected in series between the starter solenoid and alternator. Scary having those big cables running up to the dash. It doesn't do anything anyway! Mine just sat at 0 most of the time. I disconnected it.

[dklawson]

Surely an Ammeter is just a voltage device that reads the voltage ( +'ve or -'ve) across a 'shunt' or resistor through which the main current passes...?

The full load doesn't actually pass thorough the meter...

Were we talking about a LARGE Ammeter you would be correct. There ARE shunt type Ammeters and shunt type meters do read the voltage drop across a heavy duty resistor. However, these gauge are typically heavy duty and are the ones rated for well over 100 Amps. They cost a LOT more. Quality ones in the U.S. will run well over $150 when new (including the shunt which typically is purchased separately). MOST people who ask about Ammeters are talking about the 52mm in-dash gauges that swing between -30 to +30 Amps. They measure full current flow, NOT a voltage drop.

See this web page which lists several common Ammeters made by VDO:
http://www.egauges.c...A...ion&Units=E
Note the 30-0-30 Ammeter requires no shunt, nor do the 60-0-60 or the 100-0-100. (They measure current directly, all the current flows through them.) The 150-0-150 Ammeter DOES require a shunt.

Here's a link explaining why a volt meter is better/safer:
http://www.egauges.c...eterammeter.htm

I reluctantly provide the following link on how to install an Ammeter:
http://www.egauges.c...515-012-154.pdf

[nick217]

Its alright guy's i now put an ampmeter into the lighting circuit so it measures the Load on the lighting circuit.
The main reason is so i know if i left the headlights on during the day or left the side lights on when parking the car .

NExt job will be a volt meter which will just hook off the switched radio feed

[Barman]

Surely an Ammeter is just a voltage device that reads the voltage ( +'ve or -'ve) across a 'shunt' or resistor through which the main current passes...?

The full load doesn't actually pass thorough the meter...

Were we talking about a LARGE Ammeter you would be correct. There ARE shunt type Ammeters and shunt type meters do read the voltage drop across a heavy duty resistor. However, these gauge are typically heavy duty and are the ones rated for well over 100 Amps. They cost a LOT more. Quality ones in the U.S. will run well over $150 when new (including the shunt which typically is purchased separately). MOST people who ask about Ammeters are talking about the 52mm in-dash gauges that swing between -30 to +30 Amps. They measure full current flow, NOT a voltage drop.

See this web page which lists several common Ammeters made by VDO:
http://www.egauges.c...A...ion&Units=E
Note the 30-0-30 Ammeter requires no shunt, nor do the 60-0-60 or the 100-0-100. (They measure current directly, all the current flows through them.) The 150-0-150 Ammeter DOES require a shunt.

Here's a link explaining why a volt meter is better/safer:
http://www.egauges.c...eterammeter.htm

I reluctantly provide the following link on how to install an Ammeter:
http://www.egauges.c...515-012-154.pdf

Being slightly pedantic...

The meter itself is a voltage device - you can't get a 'current' meter...

If an ammeter requires the full current to pass through it then it must have an internal 'shunt' that the meter reads the voltage across.

[AndyMiniMad.]

Surely an Ammeter is just a voltage device that reads the voltage ( +'ve or -'ve) across a 'shunt' or resistor through which the main current passes...?

The full load doesn't actually pass thorough the meter...

Were we talking about a LARGE Ammeter you would be correct. There ARE shunt type Ammeters and shunt type meters do read the voltage drop across a heavy duty resistor. However, these gauge are typically heavy duty and are the ones rated for well over 100 Amps. They cost a LOT more. Quality ones in the U.S. will run well over $150 when new (including the shunt which typically is purchased separately). MOST people who ask about Ammeters are talking about the 52mm in-dash gauges that swing between -30 to +30 Amps. They measure full current flow, NOT a voltage drop.

See this web page which lists several common Ammeters made by VDO:
http://www.egauges.c...A...ion&Units=E
Note the 30-0-30 Ammeter requires no shunt, nor do the 60-0-60 or the 100-0-100. (They measure current directly, all the current flows through them.) The 150-0-150 Ammeter DOES require a shunt.

Here's a link explaining why a volt meter is better/safer:
http://www.egauges.c...eterammeter.htm

I reluctantly provide the following link on how to install an Ammeter:
http://www.egauges.c...515-012-154.pdf

Being slightly pedantic...

The meter itself is a voltage device - you can't get a 'current' meter...

If an ammeter requires the full current to pass through it then it must have an internal 'shunt' that the meter reads the voltage across.

Sorry to but in here but an ammeter does not read voltage because it is not conected to a +ve and -ve. just a +ve. it is connected in series with the +ve supply from the altenator to the battery. Well mine is anyway. Works fine and measures the current drawn by each device as you switch things on. Its a 52mm Smiths guage.

[dklawson]

Being slightly pedantic...

The meter itself is a voltage device - you can't get a 'current' meter...

If an ammeter requires the full current to pass through it then it must have an internal 'shunt' that the meter reads the voltage across.

You are not being pedantic at all.
However the non-shunt-type ammeters may be more correctly thought of as a galvanometer. There is as you stated a conductor carrying the current through the gauge, however, there is no volt-meter connected to each end of that conductor to measure voltage drop. Instead, the magnetic field created by the flowing current deflects the needle directly.

As for there not being a device that measures current.... The most basic current measurement is introduced to physics students at the college level. The equipment involves two parallel conductors passing the current for one circuit. The current flows "up" on conductor and "down/back" the second conductor. The second conductor is mounted on a balance beam. The magnetic fields created by the current flowing in opposite directions parallel to each other creates a force between the two conductors. A simple weight scale (balance beam) technique is used to measure that force. This experimental example of a current meter is used to confirm the SI definition/units for an Ampere. A more modern application of this technique is to wind wire around a ferrite toroid and mount that in proximity to an analog Hall Effect sensor. The current flowing through the coiled wire produces a magnetic field which is in turn measured by the Hall Effect sensor. Strictly speaking you are correct that you are not measuring the current directly, you are measuring the magnetic field produced by the flowing current. That is also what is going on inside an Ammeter that does not have an external shunt.