For the voltmeter conversion crowd

[Old Sparky]

What shunt? Up to 74/75 allmost all ammeters where full load Without any shunt. The shunted ammeters began on earliers 70s on C bodies, 75 on B and 76 on A bodies... then of course the rest which were new bodies... F, M etc... And all shunts run down the hood from factory.

Dunno on trucks.

The shunted systems used a diff ammeter with a coil mounted inside to move the needlee, but the full load don't get this coil. Just the internal brass path and a magnet.

All ammeters have a shunt somewhere even moving iron meters. Some are outside some are inside, but usually d'arsonval movements have the outside type. Long ago moving iron meters were common. I have seen thousands of ammeters and never one without a shunt or equivalent somewhere in the circuit.

 

[72RoadrunnerGTX]

The ammeter in question here does not contain or use any kind of electrical shunt anywhere in this circuit. Simple brass buss sandwiched to a permanent magnet. No moving coils or electromagnets to burn out or otherwise fail. Needle responds to changes in the magnet field as influenced by current flow through the buss.

 

[Old Sparky]

The ammeter in question here does not contain or use any kind of electrical shunt anywhere in this circuit. Simple brass buss sandwiched to a permanent magnet. No moving coils or electromagnets to burn out or otherwise fail. Needle responds to changes in the magnet field as influenced by current flow through the buss.


View attachment 1179861

That is a moving iron meter movement. The shunt is the brass bar.
It is used a lot in High current measurement. All tho not as accurate as others it will suffice. That kind of movement requires overly large conductors in respect to other methods..... As a side note that particular method is not as reliable as some others either.

 

[72RoadrunnerGTX]

Have to disagree on the description of this bus a shunt, does not fit the technical description of an electrical shunt device in this case.

“In electronics, a shunt is a device that creates a low-resistance path for electric current, to allow it to pass around another point in the circuit.[1] The origin of the term is in the verb 'to shunt' meaning to turn away or follow a different path.”

 

[Old Sparky]

Have to disagree on the description of this bus a shunt, does not fit the technical description of an electrical shunt device in this case.

“In electronics, a shunt is a device that creates a low-resistance path for electric current, to allow it to pass around another point in the circuit.[1] The origin of the term is in the verb 'to shunt' meaning to turn away or follow a different path.”

Yes that is true. But point of view is very variable as to what can or cannot be classified as a shunt in electrical circuits. In your picture what is on the other side of the black insulator between the terminals and the face plate of the meter

 

[Nacho-RT74]

Wherever the shunt therm can be discussed ( myself have called "shunt" the brass path built into the ammeter just for simplicity ) there is NO WAY to move that "shunt" outside the ammeter, let's say or imagine for a minute it could be moved to the engine bay as suggested, because that will make unnoperative the gauge. It means in fact to destroy the amm itself. That's the ONLY PATH available for the charging system on the full load ammeter system.

And any other path parallel to this kind of ammeter will make a virtual bypass to it, because the small ammount of load this ammeter will get won't be able to move the magnetic field to move the needle, hence the reason why is a full load ammeter

 

[Nacho-RT74]

Chrysler already created ( on the bodies and years specified previouslly) a shunted system but these ammeters are way diff than the full loads. And they look like this

F and M body with a voltimeter warning light built in system

Of course not everyone get that voltimeter warning light system.

These Charging system already gets as mentioned an external shunt or path, which is a resistor wire between alt and starter relay, and between the ends of this shunt two 18 gauge wires feed this ammeter. Other wire usually on 10 gauge is spliced into the alt wire just right before the shunt gets inside the cab to feed the main splice in cab and spreaded to all around.

Now compare with the plain full load ammeter in a side view for easier comparison

Now, explain to me HOW TO MOVE the buss bar ( what you are calling "shunt" ) outside the gauge without destroy or become unnoperative the gauge itself ?

 

[Old Sparky]

Chrysler already created ( on the bodies and years specified previouslly) a shunted system but these ammeters are way diff than the full loads. And they look like this

F and M body with a voltimeter warning light built in system

View attachment 1179916

Of course not everyone get that voltimeter warning light system.

These Charging system already gets as mentioned an external shunt or path, which is a resistor wire between alt and starter relay, and between the ends of this shunt two 18 gauge wires feed this ammeter. Other wire usually on 10 gauge is spliced into the alt wire just right before the shunt gets inside the cab to feed the main splice in cab and spreaded to all around.

Now compare with the plain full load ammeter in a side view for easier comparison

View attachment 1179917

Now, explain to me HOW TO MOVE the buss bar ( what you are calling "shunt" ) outside the gauge without destroy or become unnoperative the gauge itself

HI...not all shunts are external necessarily. A shunt is where the current is measured by what ever means has been employed.

 

[Nacho-RT74]

Whatever! Is not posible to make what you said on these ammeters without destroy or bypass the amm.

Here is another example of a Mopar amm ( 75/78 B body ) designed for a shunted system. A basic one without a voltage warning system.

The coil creates or amplifies the magnetic field to move the needle with just afew miliamperes when a shunt was installed on these cars.

Since the gap between studs is the same we could try to install one of this ammeters into an earlier full load system and become our cars into a shunted system. I have thought on that back in 2008 or so for my car ( that's when I got a dirty cheap NOS M body amm, the one pictured on the earlier reply... that's in fact my own hand ) just needing to get a matching indexing ammeter ( needle pointing up or down ) and aprox same sweep and ratious, replacing face, trimming here and there to match deepness into cluster... BUT we don't know how much is the shunt resistor value to get the right reading on amm. So that's when my project stalled.

Mostly sure the best bid to proceed with this conversion successfully would be try to get the shunt from the same donor car the ammeter came out. In my case, an M body harness with the shunt. But I decided to left at a side the project for more important things

 

[Old Sparky]

Whatever! Is not posible to make what you said on these ammeters without destroy or bypass the amm.

Here is another example of a Mopar amm ( 75/78 B body ) designed for a shunted system. A basic one without a voltage warning system.

View attachment 1179918

The coil creates or amplifies the magnetic field to move the needle with just afew volts/miliamperes when a shunt was installed on these cars.

Since the gap between studs is the same we could try to install one of this ammeters into an earlier full load system and become our cars into a shunted system. I have thought on that back in 2008 or so for my car ( that's when I got a dirty cheap NOS M body amm, the one pictured on the earlier reply... that's in fact my own hand ) just needing to get a matching indexing ammeter ( needle pointing up or down ) and aprox same sweep and ratious, replacing face, trimming here and there to match deepness into cluster... BUT we don't know how much is the shunt resistor value to get the right reading on amm. So that's when my project stalled.

Mostly sure the best bid to proceed with this conversion successfully would be try to get the shunt from the same donor car the ammeter came out. In my case, an M body harness with the shunt. But I decided to left at a side the project for more important things

Hi....by testing the new one to find out what is the full scale current draw you can use ohms law to find out what value the shunt should be. Then you can go to the local electronics shop and purchase a resistor of the right resistance and wattage to use as a shunt. You do not need any special part from the donor car all you need is the specs or do the calculation. To find the full scale current of the new ammeter all you need is a good multi-meter and a variable supply.
Another point is that the ammeter you pictured does not really measure amps it measures the voltage that the current flowing through the shunt creates. Once again ohms law is in effect.

 

[Nacho-RT74]

Agreed! I would need to build up a testing bench with known vaules of resistors, bulbs with known specs could work and check the gauge variations. A regular multitester by itself doesn't work. Is simple but not so simple.

The deal with the M body amm is it says C and D, and I'm not really sure if is +/-40 or 60 amps. I think is 60 amps scale.

 

[Old Sparky]

Agreed! I would need to build up a testing bench with known vaules of resistors, bulbs with known specs could work and check the gauge variations. A regular multitester by itself doesn't work. Is simple but not so simple.

The deal with the M body amm is it says C and D, and I'm not really sure if is +/-40 or 60 amps. I think is 60 amps scale.

You don't need a lot of equipment. Just a good volt or multi-meter to measure how many volts to full scale on the unknown meter. That is the amount of volts you want to see across the shunt at the rated full current draw. next you calculate how many ohms of resistance that you will need to produce that amount of voltage at the current you want to show on the meter at full scale considering that 12 volts will be a constant in the circuit.

 

[Old Sparky]

You don't need a lot of equipment. Just a good volt or multi-meter to measure how many volts to full scale on the unknown meter. That is the amount of volts you want to see across the shunt at the rated full current draw. next you calculate how many ohms of resistance that you will need to produce that amount of voltage at the current you want to show on the meter at full scale considering that 12 volts will be a constant in the circuit.

If the meter does not show an actual quantity it is much easier to settle for chg or dischg then solving the problem is quite simple.

 

[Nacho-RT74]

The ammeter doesn't show the scale but doesn't meant it doesn't have a scale according on how wide or hard it moves. The A bodies full load amms and 68-70 B bodies with rallye cluster get a +/-40 amps scale... 71/74 B bodies doesn't get a scale, just D and C but I know they are +/-40 scale. There are 71/74 Standard cluster amms available on +/-60 and 80 scale and these are numbered.

So if we know the scale still on a non "scaled" ammeter we will know when amm is on half reading to one or the other side we are charging or discharging half of the scale... 30 amps if 60 amps, etc...

Shunts from car harnesses have being tested ( per my request ) in the past and the Readings were close to 0 ohms. So a GOOD tester with a nice small scales needs to be used.

How many volts to get full scaled the ammeter? Buddy, the ammeter won't move feeding with volts if you don't apply a load after the ammeter ( which will read discharge of course ). And having these ammeters you can't use ANY load rate, because could burn it out.

Remember an ammeter doesn't work feeding with - and + on a parallel circuit but in series between the source and the load sucker. And on shunted sistem it gets in parallel with the shunt but not with the source.

Sure maths can be made but needs also to be carefull of the specs of the devices to be used and being into the handling rate for the amm.

 

[kbfallon]

I don't claim to know much about this part of the electrical system BUT it seems to me that a lot of us are upgrading to higher output alternators to handle such things as EFI, etc. In my opinion that should require heavier gauge wiring AND you want to keep as little current as possible going into the passenger compartment - using relays near the high current components. So this pretty much eliminates using the ammeter.

Having various in-depth chats with Nacho, and some experience on my end (not near what he has) I rank this guy high up there on knowledge. This topic can be found on the forum; likely hundreds of posts, some are mine; more questions than answers, lol. The amp gauge discussion and my reading on it, was not good design running the wires through the BH. Of course, what vehicle mfg designs their products to last multiple decades. I got a good glance viewing my skanked BH I replaced much later than I should have. Meanwhile was coached by Nacho on safer ways to run/connect the amp gauge wires, being kind enough to do so, bypassing the BH. Too bad that this particular routing (bypassing the BH) was only done on special vehicles like police cars as was the case with my ride.

The Police Special models also ran Alot Higher Amperage Alternators.....

 

[Old Sparky]

The ammeter doesn't show the scale but doesn't meant it doesn't have a scale according on how wide or hard it moves. The A bodies full load amms and 68-70 B bodies with rallye cluster get a +/-40 amps scale... 71/74 B bodies doesn't get a scale, just D and C but I know they are +/-40 scale. There are 71/74 Standard cluster amms available on +/-60 and 80 scale and these are numbered.

So if we know the scale still on a non "scaled" ammeter we will know when amm is on half reading to one or the other side we are charging or discharging half of the scale... 30 amps if 60 amps, etc...

Shunts from car harnesses have being tested ( per my request ) in the past and the Readings were close to 0 ohms. So a GOOD tester with a nice small scales needs to be used.

How many volts to get full scaled the ammeter? Buddy, the ammeter won't move feeding with volts if you don't apply a load after the ammeter ( which will read discharge of course ). And having these ammeters you can't use ANY load rate, because could burn it out.

Remember an ammeter doesn't work feeding with - and + on a parallel circuit but in series between the source and the load sucker. And on shunted sistem it gets in parallel with the shunt but not with the source.

Sure maths can be made but needs also to be carefull of the specs of the devices to be used and being into the handling rate for the amm.

The ammeter you showed...the newest one Will read with voltage applied if done properly and yes the shunt will be less than 1 ohm but more than 0. It will take very little voltage to move that meter,,,,micro or millivolts. The old style inline will not move with voltage that is correct it is a different design. The shunt you need would be in the milliohm range I would guess.

 

[Old Sparky]

The ammeter you showed...the newest one Will read with voltage applied if done properly and yes the shunt will be less than 1 ohm but more than 0. It will take very little voltage to move that meter,,,,micro or millivolts. The old style inline will move with voltage. Don't forget that without a voltage there will be no current flow. The shunt you need would be in the milliohm range I would guess.[/QUOTE

 

[RJRENTON]

DC Shunts are usually calibrated in milli volts; the ammeter connected to the shunt will read the millivolts on a calibrated scale in amps. For example: a calibrated 50 mv shunt measuring say, 100 amps DC will show at 25 mv = 50 amps or any proportional amount. The meter scale will show 100 amps which equals the 50 mv provided by the shunt. Its the resistance of the shunt and the milli volt drop it produces with current flowing thru the shunt. Ohms Law applies: E = I x R. Calibrated shunts are used with DC current measurement; AC current is typically measured using current transformers.
BOB RENTON

 

[Old Sparky]

DC Shunts are usually calibrated in milli volts; the ammeter connected to the shunt will read the millivolts on a calibrated scale in amps. For example: a calibrated 50 mv shunt measuring say, 100 amps DC will show at 25 mv = 50 amps or any proportional amount. The meter scale will show 100 amps which equals the 50 mv provided by the shunt. Its the resistance of the shunt and the milli volt drop it produces with current flowing thru the shunt. Ohms Law applies: E = I x R. Calibrated shunts are used with DC current measurement; AC current is typically measured using current transformers.
BOB RENTON

Was trying to purvey that very thing without getting to technical. One thing tho shunts are calibrated in OHMS not milli volts. It is impossible to calibrate in volts as they change with the current thru the resistance which of course changes the movement of the meter.

DC Shunts are usually calibrated in milli volts; the ammeter connected to the shunt will read the millivolts on a calibrated scale in amps. For example: a calibrated 50 mv shunt measuring say, 100 amps DC will show at 25 mv = 50 amps or any proportional amount. The meter scale will show 100 amps which equals the 50 mv provided by the shunt. Its the resistance of the shunt and the milli volt drop it produces with current flowing thru the shunt. Ohms Law applies: E = I x R. Calibrated shunts are used with DC current measurement; AC current is typically measured using current transformers.

 

[Nacho-RT74]

Sure, as I mentioned needs to be made with known specs of the tools to the testing, so is simple but not THAT simple with just any tester around. Not even just a good one. Need more than just the tester. On this case the ammeter doesn't need to be calibrated per se but backwards, the shunt value needed to be known and used with this ammeter.

I didn't have the patiente back in the days to proceed, so got stuck with the stock old system ( upgraded ) and make this later, since is not just guess the shunt value needed but also wiring mods. I didn't want to sacrifice the stock ammeter either, but 8 years later got a damaged ammeter which I can use the face to proceed with the conversion someday in the future. Including the voltage pilot light feature with the M body ammeter