1976 amp gauge, what should it read?

[chicknnhead]

this is the amp gauge rolling down the road at 60mph
changed out voltage regulator.
I checked the battery and the alternator with volt gauge, they read just as they should.
at idle it reads just above 0

just wondering do I have a problem or that is where they are supposed to read?



with the lights on

[UK-Winnie]

I wouldn't worry too much they are not particularly accurate or well calibrated. 

I took one to bits and all they are is a tiny magnet (like a little sausage) fixed to the base of the needle and lined up against a thick brass conductor. 

As the current flows along the conductor it creates a field around it and the magnet responds by swinging the needle one way or the other.  Holding it in my hand I noticed the needle even moved a bit if I turned round (I'm guessing due to the earth's magnetic field).

[DaveVA78Chieftain]

Highest amperage is right after you start the engine in order to restore the energy used to start the engine.  After 10 minutes or so it normally drops back to a much lower amps because the alternator is only outputting that amperage need to run the engine and current loads (lights, heater, wipers, etc.).
If you have a dual battery switch in DUAL position or a diode battery isolator, then amperage may be higher until the "coach" battery system is charged up.
The amperage level depends on battery condition and how many loads you have ON. 
The gauge in that year chassis uses a "shunt" (a short section of wire) to measure amperage so almost no current is actually going through the gauge itself.

Dave

[chicknnhead]

thanks for both the responses

Dave, the pics were takin about 15 mins into my drive on the interstate, will still another 30 mins to go on the drive.
both the chassis battery and both coach batteries(tied together in series) checked out 14.2 while running.

nothing changed after 45 drive

this was during the day, now lights on(except for the demo pic) or wipers etc.

I'm starting to lean towards gauge being off

[DaveVA78Chieftain]

With voltage sensing regulation, like used on a automotive charging system, the regulator outputs the amount of amperage needed to maintain the target voltage (i.e 14.2VDC).  That could be 3 amps or 40 amps.  In both cases the voltage would be 14.2VDC.  14.2VDC does indicate the system is producing energy as it is supposed to.  You just do not know what amperage it is putting out at that voltage.  I suspect you are ok though.  Only way to know for sure is to measure with an amp gauge.  Myself, I use a DC clamp on meter to verify what it is going on.

Dave

[chicknnhead]

yeah good point, maybe this weekend i'll dig out the multi meter and see what the amperage is at the guage

[DaveVA78Chieftain]

Hope your multimeter can read > 10 amps DC.  Thats why I use this:

http://www.sears.com/craftsman-digital-clamp-on-ammeter/p-03482369000P

I have never seen a better deal on a AC AND DC clamp meter

Dave

[UK-Winnie]

 
The gauge in that year chassis uses a "shunt" (a short section of wire) to measure amperage so almost no current is actually going through the gauge itself.

Dave

You're too good Dave - the one I stripped was a bit earlier than that - seems they went to a shunt in '75 

Even so I don't expect they were a lot more accurate.

[UK-Winnie]

With voltage sensing regulation, like used on a automotive charging system, the regulator outputs the amount of amperage needed to maintain the target voltage .......
Dave

Don't want to start an argument but shouldn't that be - the regulator maintains the target voltage and the resistance of the ancillaries/battery etc. then dictates the amperage.

I mean like as in I=V/R   

[DaveVA78Chieftain]

Don't want to start an argument but shouldn't that be - the regulator maintains the target voltage and the resistance of the ancillaries/battery etc. then dictates the amperage.

I mean like as in I=V/R   

LOL - Yes that is correct however, the vast majority of members here have no clue what you are referring to so, I typically keep the discussions here at a very low understandable level.   The important information is:
1) The regulator maintains a target voltage (13.8VDC to 14.4VDC)
2) It controls the alternator amperage output in order to maintain that target voltage in response to system load needs.  More loads, more current required.

Most anyone can understand it when worded that way.  The electronics theory behind it in this case is not the important information.

Dave

[DaveVA78Chieftain]

You're too good Dave - the one I stripped was a bit earlier than that - seems they went to a shunt in '75 

Even so I don't expect they were a lot more accurate.

Originally Dodge routed all current through a dash mounted amp gauge.  When the gauge failed, a frequent occurrence, all voltage to the vehicle was lost.  Dodge changed to the shunt style amp gauge across all body styles in the mid 70's because of that.   That removed a high current path (battery charging current) from inside the passenger area.

Dave

[UK-Winnie]

When the gauge failed, a frequent occurrence, all voltage to the vehicle was lost.

And an even more serious failure mode after 40 odd years is a small resistance can build up at the terminals so the high current makes them get very hot and sometimes even cause a fire. 

That's why I removed the one I was talking about - I reconfigured it as a volt meter (go on ask me how I did it).

Steve

[Oz]

I just don't believe that... you're going to have to tell me how you did it....

 

[UK-Winnie]

LOL - did this on my 'cuda about 4 years ago and it's still working fine.

I took out the brass conductor and replaced it with a 12v electro-magnet from a small relay.  Then I glued a tiny magnet on the opposite side (I got it from a butterfly fridge magnet).  I wired the electro-magnet between earth and the ignition feed.

So - after a bit of physical adjustment and adding resistors to the circuit - with power off the fridge magnet pulls the magnet on the needle to read at the "D" end of the scale.  With the ignition on the electro-magnet matches the fridge magnet so the needle goes to the middle.  And with the motor running the electro-magnet overcomes the fridge magnet slightly and the needle moves a little way into the "C" side of the scale.

I also had to glue in a little rubber stop because otherwise the gauge magnet got too close to the fridge magnet and got stuck there.

I've got some photos of when I was doing it somewhere I'll try and dig them out.

[UK-Winnie]

Here you go - ameter and electro-magnet:

[UK-Winnie]

Electro magnet fitted and in the second photo powered on - you can see the gauge has swung over

[UK-Winnie]

Actually I think the one swung over is power off as the fridge magnet is pulling it over - here's one where you can see the fridge magnet - it's that little grey disc at the top

[UK-Winnie]

And here are some of it working under different conditions - off, ignition on and finally with motor idling

[UK-Winnie]

Actually looking at those now I realise I didn't take out the brass conducter, I just disconnected it.

Anyway, not bad eh ?

[DaveVA78Chieftain]

Cool.  Scaling?  Most of the modern dash meters are roughly scaled to 8VDC to 16VDC.

I know, sheesh, he is a slave driver!

Dave

[UK-Winnie]

Cool.  Scaling?  Most of the modern dash meters are roughly scaled to 8VDC to 16VDC.

I know, sheesh, he is a slave driver!

Dave

I played around with the resistors and the distance of the electro-magnet and got it as good as I could without going too silly over it.

As far as I had the kit on hand to test it the whole scale seems to run from about 5v to about 18v so the movement around the important middle area is not as well scaled as it could be.  The center spot must be around 13v because it registers a little below the center with ign. on and not running.  Switch the lights etc. on and you can see it drop a little more.   

When driving it is usually a small but noticeable way right of center.  If I got a serious over-voltage I'm sure that would show up quite clearly, so all in all it's not too bad - good enough for me anyway.

[UK-Winnie]

Someone cropped my pics - thanks whoever you are.

[Oz]

... cropped, reduced file size, and enhanced for better viewing.  That's a little bit of what I do.  Thank you for noticing.