Ammeter schematic and possible reuse

[clarkoh]

I am in the process of a modern upgrade on a 1948 B pickup.  It is now sitting on a shortened 2000 Ram frame and has the Ram driveline and a 4 cylinder Cummins.  My question relates to reusing the stock Ammeter.  I had the gauge cluster rebuilt and would like to use those gauges on the truck.  The water and oil are mechanical, no problem.  Is there a way to use the ammeter to register charging/ discharging?  I am not using any of the original wiring.  How did it know what was happening with the generator/battery ?  Is there a shunt somewhere in the old truck wiring?  Or did current pass through the meter to indicate direction and amplitude?  A schematic of that section of the wiring would be of great assistance.  Thanks.

[Plymouthy Adams]

the older systems are not shunted but direct read....most folks like to use a voltmeter instead of the amp gauge with an alternator...the alternators usually will put out current above the gauge's scale....the period of time that alternator was used and the onset of voltmeters, ma mopar used a shunted amp meter that just read some indication and direction...not anything close to accurate.

you can read on the internet as there are a number of articles written on installing shunts to use with the vintage gauges...

[clarkoh]

Thanks.  Sounds like a plan.  

What wire is routed through the ammeter to allow direct readings?

[Plymouthy Adams]

hard call for color and gauge without looking at the schematic...if you do not have the book with the wiring, you may find it here posted by someone doing a search..be sure you are at top of forum and not within this thread when searching.   Maybe some one has it handy to post again.  The amp meter is a common tie point for some power distribution and usually the battery supply wire from the volt regulator is the wire you inquire....

[clarkoh]

Thanks.  Good information.

[DJ194950]

2 hours ago, clarkoh said:

Thanks.  Sounds like a plan.  

What wire is routed through the ammeter to allow direct readings?

Originally one terminal post of the amp gauge had the battery and the generator output wire on it. That is what amps are available to be used. The other post had all the things connected to it that Used (drew) amps. the total flow of amps(electrons) either was toward the battery (more amps going than be used) or the amps being used was higher than being made by the generator to the battery.

The amp gauge wired correctly would show a slight change indicated when the battery was being charged in normal use or a discharge of the battery if the draw was higher that the generator output.

Hope all that makes sense, clarkoh. 

DJ

 

Edited July 26, 2017 by DJ194950

[clarkoh]

Thanks. Perfect explanation. 

I am guessing that it has a shunt inside, through which most of the current flows, minus a small percentage for the meter movement.  I looked across the ammeter terminals with my Fluke meter and it appears to be a short circuit, which makes sense.  I get the same 0.3 ohm reading as I get putting the meter leads together.  Now I am not sure if I can install a shunt in the B+ lead and expect the voltage drop across the shunt to show up as enough to show a deflection in the ammeter??  Anyone ever make this work? 

In theory, I need to wire the ammeter in the main feed to the ignition switch, fuse  box/ charging lead and that would use the circuit as originally intended.  But, I am reluctant to create a single point of failure.  Unless I wire a panic/bypass switch across it, just in case.

[Plymouthy Adams]

on another forum years ago I read of folks put two identical amp meters parallel to each other (but IN SERIES TO the circuit, a must) and see but 1/2 of the indicated on the dash gauge shown and the other half on the hidden gauge..the hidden gauge could be NOT SO Hidden if you wish to install under the hood for quick look see while servicing your vehicle...

[Andydodge]

My 1940 Dodge has had a 318 Poly since 1973 using a Lucas 12 volt alternator of approx. 50amps, at least that's what I think it is, as its been there since the mid 70's and am pretty sure it wasn't much more than that, anyway the car uses the original stock instruments, mechanical water & oil gauges, stock fuel gauge with a resistor and stock ammeter.....it just reads amps, I havn't told it that the car is 12 volts but after 44yrs I think that it realises that somethings been changed..........lol........but it doesn't complain..........I completely rewired the car in the late 70's also.............everything works fine..........Andyd   

[medium_jon]

4 hours ago, Andydodge said:

I havn't told it that the car is 12 volts but after 44yrs I think that it realises that somethings been changed.......

Too funny @Andydodge

[Andydodge]

Yeh, well when I went to look at the car the guy selling it came to the door, "Yeh man?"........"I rang about the Dodge"........."Ah yeh, you mean Sebastion, man, the car man"........."Err, yeh?".........."he's round the corner man".......so off we went around the corner and yes indeed, there was the car, err.Sebastion as it was called.....so after we, mainly my Dad, beat the price down from $40.00 to $15.00, he, I mean it was mine........so I have to be a little delicate when discussing its more personal things.............lol.............regards, andyd. 

[clarkoh]

Great stuff.  Thanks for the responses. 

Opened it up for pictures.  The brass horseshoe piece conducts the current.  The steel piece that looks like a crab is a permanent magnet, which is isolated from the current carrying piece.  The brass piece with the meter movement has a small coil on the movement, which is influenced by the current passing by in the horseshoe piece.  Simple, not too accurate, but will provide a slightly larger clue than an idiot light. Once it is bolted together, the permanent magnet holds the meter to its zero point, until the flow of current creates deflection.  I just have to be careful not to exceed the current carrying capacity of the little piece of brass!

Just have to determine which of the battery powered leads to intercept to show charge vs. discharge.