Adding an Ammeter

[Editor_Reid]

The ejector seat, I would assume that's on the passenger side!

D'oh! Lucas strikes again - it's on the passenger side ... of RHD cars.

 

[Patrick67BJ8]

The ejector seat, I would assume that's on the passenger side!

Of course!

 

[John Turney]

The ejector seat, I would assume that's on the passenger side!

Not necessarily:

 

[bdcvg]

The small square headed one?

Yes I think it was square

 

[tahoe healey]

Best "size" fuse for the ammeter in line wiring? Please specify British (Lucas) or American (Buss). I have a 50 amp British in now just for trial wiring purpose, but I think it might not blow when it would need to.

 

[Michael Oritt]

TH--

The purpose of the fuse is simply to prevent a dead short should the hot wire ground on the chassis or dash.
50 amps is way too much and you might as well be using a nail--Find out how much current the instrument draws and let that be your guide.

 

[John Turney]

Best "size" fuse for the ammeter in line wiring? Please specify British (Lucas) or American (Buss). I have a 50 amp British in now just for trial wiring purpose, but I think it might not blow when it would need to.

If all the current is going through the ammeter, 50 amps (British) would be proper, as the horn fuse is 50 amps (British).

 

[Michael Oritt]

John--

You're 100% right and I'm 100% wrong--somewhere in my enfeebled mind I forgot we were talking about total current being drawn, not that of the ammeter..

 

[Lotuswins]

TH--

The purpose of the fuse is simply to prevent a dead short should the hot wire ground on the chassis or dash.
50 amps is way too much and you might as well be using a nail--Find out how much current the instrument draws and let that be your guide.

Sorry but the purpose of the fuse is to protect the wiring, not the load on the end. We size it to the load the wire will support to prevent overheating the insulation, which when melted the copper can come in contact with ground (short) or other copper wiring having melted into their insulation causing failure of the loom.
Note that with vehicle wiring fuse sizes are substantially greater than with, say, house wiring. This is because the higher voltage will heat the wire faster/higher temperature as Power = Voltage squared divided by resistance, and Power is what does the heating....

You can find wire current capability charts on line for automotive wiring but for the most part the insulation is rated pretty low compared to other applications, I would expect a 60C rating for most automotive. Make sure the chart is for 12vdc application.

Jerry Rude, PE

 

[Michael Oritt]

Sorry but the purpose of the fuse is to protect the wiring, not the load on the end. We size it to the load the wire will support to prevent overheating the insulation, which when melted the copper can come in contact with ground (short) or other copper wiring having melted into their insulation causing failure of the loom.
Note that with vehicle wiring fuse sizes are substantially greater than with, say, house wiring. This is because the higher voltage will heat the wire faster/higher temperature as Power = Voltage squared divided by resistance, and Power is what does the heating....

You can find wire current capability charts on line for automotive wiring but for the most part the insulation is rated pretty low compared to other applications, I would expect a 60C rating for most automotive. Make sure the chart is for 12vdc application.

Jerry Rude, PE

Jerry--

See post #48--I have already confessed my sins--Mea culpa. BTW I thought one could determine DC amperage by dividing the watts by the volts. Am I wrong here as well?

As long as we are still on this topic can someone explain how a shunt is wired and how it apparently prevents the passage of high current by or through it.

 

[Lotuswins]

Jerry--

See post #48--I have already confessed my sins--Mea culpa. BTW I thought one could determine DC amperage by dividing the watts by the volts. Am I wrong here as well?

As long as we are still on this topic can someone explain how a shunt is wired and how it apparently prevents the passage of high current by or through it.

Hi Michael,

Yes, I saw and the response was for 'others' who might have been misled....sorry for the confusion. Ohms law is I = E x R, and the derivative P = I squared x R or P = E squared divided by R. So yes you are wrong on that account.

A meter movement works on a very small amount of current, and generally there are shunts involved when large amounts of current are involved. The shunt flows all the current, and the movement taps into the shunt such that a ratio is designed into the combination of shunt and meter. So think of the shunt as a resistor with multiple taps along its length. The movement connects to those taps in parallel so that the voltage generated along the length of the shunt will give sufficient voltage to deflect the movement the appropriate amount proportional to the total current being passed.

The ammeters I've so far disassembled in this hobby (Lucas) have the shunt as a solid link of copper wire. The movement doesn't actually connect with the shunt but the distance is close enough for the magnetic field surrounding the copper to influence the meter movement and give the proper deflection. A very delicate adjustment to get the distance between the two correct. I can't imagine the accuracy is that good, but that isn't really necessary for something like an automobile system.

I hope this helps?

Jerry

 

[Lotuswins]

Best "size" fuse for the ammeter in line wiring? Please specify British (Lucas) or American (Buss). I have a 50 amp British in now just for trial wiring purpose, but I think it might not blow when it would need to.

The older classics I've had experience with hadn't ever had fuses in the ammeter circuits. The most common size of wire that I've seen is 10 AWG which will pass much more current than 50 amps safely. But since the British fuse sizes will blow at approximately 1/2 the size of an American fuse it may not be adequate, but testing will ensure if it is sufficient. Most modern autos have fused links which act like a fuse but replacement is more involved. I don't know what wire size you have in your added system so can't speculate as the right fuse size to protect its insulation but you can find charts on line as I've just mentioned. I think on my healey I used an 80 amp american fused link and so far its been okay with a toyota alternator out of a celica.

I'm not sure if everyone knows how the fuses of British and American manufacture differ in rating?? The British rating is where the fuse will blow at that amperage within a certain amount of time. The American system rating is that the fuse will carry that current for an indefinite length of time, at least that is what I recall. A specific fuse by a specific manufacture will have a curve derived from testing that shows current versus time and the line on the graph indicates the point at where the fuse should melt (blow).

ahh. too much theory...sorry.

jerry

 

[Michael Oritt]

Hi Michael,

Yes, I saw and the response was for 'others' who might have been misled....sorry for the confusion. Ohms law is I = E x R, and the derivative P = I squared x R or P = E squared divided by R. So yes you are wrong on that account.

A meter movement works on a very small amount of current, and generally there are shunts involved when large amounts of current are involved. The shunt flows all the current, and the movement taps into the shunt such that a ratio is designed into the combination of shunt and meter. So think of the shunt as a resistor with multiple taps along its length. The movement connects to those taps in parallel so that the voltage generated along the length of the shunt will give sufficient voltage to deflect the movement the appropriate amount proportional to the total current being passed.

The ammeters I've so far disassembled in this hobby (Lucas) have the shunt as a solid link of copper wire. The movement doesn't actually connect with the shunt but the distance is close enough for the magnetic field surrounding the copper to influence the meter movement and give the proper deflection. A very delicate adjustment to get the distance between the two correct. I can't imagine the accuracy is that good, but that isn't really necessary for something like an automobile system.

I hope this helps?

Jerry

Jerry--

My interest in this topic is intellectual as I have no plans to add an ammeter to my 100. As I think I said earlier in the string, later Healeys are better laid out to add additional instruents whereas the dash of 100--with its graceful iteration of the car's side profile--has little room for extra instrumentation (unless hung underneath). I do have a voltmeter installed on the right side in front of the passenger and I feel it gives me enough information re the real-time condition of my electrical system.

Back to the calculate of ampere load, if my understanding is incorrect (dividing watts by volts to get amps) then I am certainly in good company.
Here's some info from an online site that seems to say what I believe to be the formula:

How to convert Watts to Amps
Watts / Volts = Amps. 4160 Watts / 208 Volts = 20 Amps. ...
Amps. Amps measure the flow of electricity as an electric current. ...
Volts. Volts are the measurement used to determine how much force is needed to cause the electric current to flow. ...
Watts.

Is there a difference between AC and DC? Where am I going wrong?

 

[Lotuswins]

Jerry--

My interest in this topic is intellectual as I have no plans to add an ammeter to my 100. As I think I said earlier in the string, later Healeys are better laid out to add additional instruents whereas the dash of 100--with its graceful iteration of the car's side profile--has little room for extra instrumentation (unless hung underneath). I do have a voltmeter installed on the right side in front of the passenger and I feel it gives me enough information re the real-time condition of my electrical system.

Back to the calculate of ampere load, if my understanding is incorrect (dividing watts by volts to get amps) then I am certainly in good company.
Here's some info from an online site that seems to say what I believe to be the formula:

How to convert Watts to Amps
Watts / Volts = Amps. 4160 Watts / 208 Volts = 20 Amps. ...
Amps. Amps measure the flow of electricity as an electric current. ...
Volts. Volts are the measurement used to determine how much force is needed to cause the electric current to flow. ...
Watts.

Is there a difference between AC and DC? Where am I going wrong?

You got me! Brain fart I guess…getting old!!

P = I x E of course….what was I thinking?
AC vs DC? Well yes, of course but calcs on this basic level are similar if you remember with AC you are dealing in RMS (Root, Mean, Square). RMS is what your AC meter reads. A good instruction manual, and the one I was initially trained on, is the Naval Electricians Training Manual. > 1969 Bureau Of Naval Personnel NAVPERS 10086-B Basic Electricity Navy Manual | eBay <
sorry for the brain fart.
jerry

 

[petnatcar]

I tried to find any articles dealing with the issue but couldn’t find anything.
I’m going to add an ammeter to my Austin Healey 100-6. Can anyone recommend the best way to accomplish this?
Regards
Roger

I had an Ammeter in my car for years but didn't like the idea that they drew such a high current so I replaced it with a Volt Meter.
When I removed the gauge I noticed the wires had turned black about an inch down the insulation from where they were attached to the back of the gauge !!! I feel safer now.
Bouna fortuna,
Peter C.

 

[tahoe healey]

What gauge wire had you used? Ten gauge wire all the way on mine. I've had one for 18 years without a problem. I just recently re-wired many things under the dash (relays and fuses for fog lights) and now I get significant indication of charge when I accelerate which I hadn't noticed before. But I had never paid attention before. Wires don't seem hot to the touch.

 

[Michael Oritt]

I had an Ammeter in my car for years but didn't like the idea that they drew such a high current so I replaced it with a Volt Meter.
When I removed the gauge I noticed the wires had turned black about an inch down the insulation from where they were attached to the back of the gauge !!! I feel safer now.
Bouna fortuna,
Peter C.

 

[Michael Oritt]

That must have been a difficult car to drive.

 

[DrEntropy]

FWIW-The Voltmeter will tell you the battery voltage by just turning the ignition Key, typically 12.4 VDC. Once started the voltage should rise to 13.7-14.7 VDC approximately. This shows that the Generator or Alternator is producing enought voltage to power all of the electrical systems and charge the battery. If the voltage goes below 12.4 volts or above 15 volts there is a problem with the voltage regulator or generator/alternator.

The Ammeter will just tell you which way the current is flowing and not the voltage.

I know it's JUST an old MGB, but I made a console to add a period correct looking voltmeter and clock. The voltmeter gives enough feedback to know what's going on with the electrical system. This car ('65 MGB roadster) was converted to negative ground and an alternator.

 

[Bristol401]

If you’re putting an ammeter in a car that wasn’t designed for one….. you really need to change a lot in the wiring loom. An ammeter needs the charging system on one terminal And much of the ‘discharging’ stuff connected to the other terminal. A voltmeter is sooo much easier to install.