Mopar Action article

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I am not sure, but it would take some work to use one of the other gauges...

All the "other" gauges are actually just voltage gauges, they measure the voltage coming from the sensor (oil pressure, fuel level, temp). It is theoretically possible to convert one of these gauges to read raw voltage between 8-16 volts.

It would be a matter of using a resistor divider or something else to convert the voltage range the gauge reads (0-5 v, lets say) to 8-16 volts.

It would take some engineering / work to work out the details to make it work... but it MIGHT be possible

Although it might be possible, aren't the other gauges damped to some degree by the heating of the resistor wire that constitutes the needle movement? I'm thinking that the slow response time of a gauge like that would make it pretty useless as a voltmeter. Voltmeters are much more useful when you can read instantly when the voltage drops or rises depending on load/alternator output at idle, etc.

Just my $.02.

The water temp and oil pressure gauges are simply 5V gauges, so any of these could be used but a dropping resistor will be needed to reduce the 12V to 5V. The rite way to do it would be to change the respective meter artwork to be a voltage scale like 8V to 15V using the fonts of the original gauges..

Sean @ Redline gauges can do this nicely, just remember to tap into a switched 12V line..

Here is the link to Redline..

www.redlinegaugeworks.com

Just my $0.01...

Posted By: That AMC Guy

Re: Mopar Action article - 02/27/10 03:42 AM

It's my understanding that they don't sense voltage so much as they actually measure resistance. Don't forget, they are powered by a (more or less) constant 5 volts. The variable factor in their operation is the resistance to ground. Each gauge is calibrated to a specific range of resistance. Essentially, what they are is Ohmmeters.

So, I don't really think you could convert one to measure volts.

Posted By: Sinitro

Re: Mopar Action article - 02/27/10 03:46 AM

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It's my understanding that they don't sense voltage so much as they actually measure resistance. Don't forget, they are powered by a (more or less) constant 5 volts. The variable factor in their operation is the resistance to ground. Each gauge is calibrated to a specific range of resistance. Essentially, what they are is Ohmmeters.

So, I don't really think you could convert one to measure volts.

Incorrect..
The gauges are voltmeters, and by changing the resistance revises the amount of swing of the meter by decreasing the incoming voltage...

Just my $0.01..

Posted By: @#$%&*!

Re: Mopar Action article - 03/01/10 12:37 AM

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...The Painless tech advised that it would be dangerous to continue to use the gauge, as he stated it was 40 year old technology...

More like 140-year old technology, and a technology that's still used today. It sounds like that "tech" was trying to sell you something. The problem is tired old riveted connections and ammeters that put out a lot more than the 40-60 amps the gauges were designed for. Swapping in a WT or OP gauge could work but getting it to read accurate numbers would be tough. If all you needed to know is whether you were above or below 12-14 volts then it wouldn't be that tough. The gauges are usually about 12-15 ohms while the sending units are about the same at minimum resistance and around 80 ohms at maximum resistance. If I remember right the sending units are around 30 ohms at mid-gauge and if we assume the IVR output is 5 volts then the gauge would see about 1.7volts at mid gauge. At maximum reading the voltage across the gauge would be about 2.5volts and this is then about the maximum you should put on the gauge based on the assumptions above. Now all you have to do is design a voltage divider to generate about 2.5@15 volts and/or 1.7@12.5volts. It looks like 6 or 7:1 will do. Of course some testing will be necessary. I've found the IVR to actually put out over 6 volts effectively in back to back comparison with a solid-state regulator.

Posted By: 70duster340

Re: Mopar Action article - 03/01/10 01:27 AM

So Dragstripper, are you saying that, if all the connections are clean and in good working order, that using the stock ammeter is not a danger to the wiring harness nor the car?

Posted By: denfireguy

Re: Mopar Action article - 03/01/10 02:58 AM

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Can you possibly expand on that, 6T6Cuda?

I am trying to, if possible, keep my ammeter functional. The Painless tech advised that it would be dangerous to continue to use the gauge, as he stated it was 40 year old technology. I want to keep all my gauges in the rallye dash functional, and if possible, convert the ammeter to a voltmeter. I really do not want to have another gauge hanging outside of the dash if at all possible. Unless you or somebody here can suggest another location for the voltmeter?

Since this is a family board, all I can say is Bull. The technology is as old as Ohm's Law but its application is totally current (pun intended). I am sitting near a brand new Generac diesel emergency power back up system. The DC charging is through an AMMETER, there is no voltmeter. Why? According to the factory rep, a voltmeter can only tell you if it reads low, the battery is dead. Nothing else. An ammeter can tell you if the alternator is providing current, how much current is being drawn by the engine and accessories and if the battery is in good shape.
Painless is trying to sell stuff by scaring people. Any wiring system can be dangerous if not maintained. The bulkhead connector is a weak link and needs to be looked at all times. But the technology is sound and still in use in professional if not painless applications.
One other thing to remember, the cop cars and taxis with the high current alternators in the Satellite and Fury series ran the wire from the fusible link through a grommet in the firewall with no connectors to the ammeter, bypassing the bulkhead connector. But they still used the ammeter. They used radios that drew 30 Amps on transmit, more than any modern electronics I know of.
Craig

Posted By: 70duster340

Re: Mopar Action article - 03/01/10 05:15 PM

Very interesting, Craig. I appreciate the response. You bring up a lot of good points. I do intend to keep my ammeter in use, but am just not sure how to wire it in since I have added the new fuse block. I decided to install the new fuse block since I didn't like how the old glass type fuse block looked, and here where I am located, those types of fuses are becoming scarce. I thought that applying new technology would be a good idea. I am just now trying to figure (with NachoRT74's help) how to wire in the ammeter.

Thanks again, and I do really appreciate all the comments!!!

Posted By: John_Kunkel

Re: Mopar Action article - 03/01/10 09:04 PM

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According to the factory rep, a voltmeter can only tell you if it reads low, the battery is dead. Nothing else. An ammeter can tell you if the alternator is providing current, how much current is being drawn by the engine and accessories and if the battery is in good shape.

Why do you need to know how much current is being drawn by the system? A voltmeter will tell you the system voltage, if the system voltage is above the battery's "engine off" voltage the battery is being charged.

Ask that generator tech if their ammeter is a shunt type, the shunt type ammeter doesn't run the full system amperage through the meter, lots different than the factory ones that do.

Posted By: denfireguy

Re: Mopar Action article - 03/01/10 10:52 PM

Judging by the number 8 cables, I would say that it is not shunt driven.
I have often wondered about calibrating a voltmeter to the current drop across the alternator lead to use it as a shunt. The wire should have around .01 ohms from end to end. Then you could have the best of both worlds.
Craig

Posted By: Supercuda

Re: Mopar Action article - 03/02/10 01:13 AM

There is substantial misinformation about ammeters.

ALL an ammeter reads is current to, or from, the battery. NOTHING else. If you have a 120A alternator and you are pumping 120A into the battery you have substantially more problems than a "40 year old" ammeter to worry about.

If you put in a thumping sound system and you wire it on the battery side of the ammeter then you need to step away from the soldering iron cause you are over your head.

Voltmeters and ammeters measure two different things in an electrical system. To use the water flow example, it's like a pressure guage (voltmeter) and a flow guage (ammeter). Both have their places and an ammeter will tell you things a voltmeter won't.

For example, if you have both hooked up and your voltmeter shows a nice 13.8V but your ammeter shows 75A being pushed into the battery you have a problem, one a voltmeter will not show.

Another issue with a voltmeter is that it is buffered, to an extent, by the battery. When the alternator dies your voltmeter will still show battery voltage as it drops (rate of drop depends on the load), an ammeter will an instantaneous discharge.

The factory draws almost all the electrical load (except the starter) from the alternator side of the ammeter. One should never draw a load from the battery side of the ammeter, except for the battery obviously. Then it really doesn't matter how many amps your pulling cause none of the load passed thru the ammeter unless the charging system isn't working (engine off, for example).

Posted By: @#$%&*!

Re: Mopar Action article - 03/02/10 01:19 AM

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Why do you need to know how much current is being drawn by the system? A voltmeter will tell you the system voltage, if the system voltage is above the battery's "engine off" voltage the battery is being charged.

A voltmeter tells you the voltage 'state' of the system while the ammeter tells you what is actually happening right now, charge or discharge. If your charging system dies you might not know it for a while with a voltmeter while the ammeter tells you immediately that it's not charging.

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So Dragstripper, are you saying that, if all the connections are clean and in good working order, that using the stock ammeter is not a danger to the wiring harness nor the car?

All of my cars are still stock in the ammeter department. The problem is that some of the internal connections aren't easily maintained and as the metals oxidize over the years the resistance of the connections go up. Resistance and high current generates heat. You could troubleshoot the system by exercising the charging system and then feeling the various connections for high temps, carefully! Any instrument rebuilder worth using will set you up and have your gauges working as good as new. I've never been a fan of the charging system current going through those light-duty bulkhead connectors but mine are all still hooked up that way, except for the bracket car which is totally custom.

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Judging by the number 8 cables, I would say that it is not shunt driven.
I have often wondered about calibrating a voltmeter to the current drop across the alternator lead to use it as a shunt. The wire should have around .01 ohms from end to end. Then you could have the best of both worlds.
Craig

You could certainly sever the factory ammeter internally and run modest gage wires to a section of the circuit elsewhere as long as the resistance between the connection points of the new wires is precisely the same as the internal resistance of the factory ammeter. That's basically what a shunt setup is. Maybe a section of fusible link calibrated to simulate the resistance of the factory ammeter, keeping the charging current under the hood, straight from the alternator to the battery.

Cory

Posted By: ahy

Re: Mopar Action article - 03/02/10 01:41 AM

I did the ammeter to voltmeter conversion on a Challenger ralley dash... or more precisly I had a shop do it. They set it up so the needle was just about centered at normal charged battery voltage - around 12.5 volts. Higher voltage went the the charge side and lower voltage went to the discharge side.

It has been a very useful instrument; At a glance when running if the needle is a bit to the left of center, all is well. If its centered or to the right that means problems. I won't get into the debate on which is better, ammeter or voltmeter, but I can say this setup has worked well for me. Keeping the ammeter wasn't really an option for me due to heavy non-stock electrical loads and the requirement for a bigger alternator.

That said, I've delt with problems on stock MOPAR's with the standard setup and am glad to get away from it. The heavily loaded charge wire on the bulkhead connector especially.

Posted By: 70duster340

Re: Mopar Action article - 03/02/10 03:10 AM

Hmmm, lots of good debate going on here!

Posted By: Supercuda

Re: Mopar Action article - 03/02/10 03:36 AM

There is no debate. Ammeters, in stock applications, work one way. All else is misinformation.

Posted By: denfireguy

Re: Mopar Action article - 03/02/10 02:31 PM

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I did the ammeter to voltmeter conversion on a Challenger ralley dash... or more precisly I had a shop do it. They set it up so the needle was just about centered at normal charged battery voltage - around 12.5 volts. Higher voltage went the the charge side and lower voltage went to the discharge side.

It has been a very useful instrument; At a glance when running if the needle is a bit to the left of center, all is well. If its centered or to the right that means problems. I won't get into the debate on which is better, ammeter or voltmeter, but I can say this setup has worked well for me. Keeping the ammeter wasn't really an option for me due to heavy non-stock electrical loads and the requirement for a bigger alternator.

That said, I've delt with problems on stock MOPAR's with the standard setup and am glad to get away from it. The heavily loaded charge wire on the bulkhead connector especially.

I agree that a heavily loaded bulkhead connector is bad news. See the above post about police and taxi versions. Not a lot of us are running overhead lights and a Federal Q siren so that should not be an issue. The 30 amp two ways are also history. Halogen headlights draw less current than the old tungsten lamps. All in all, current loads in cars have dropped. GPS, car stereo, CB, and dvd player only add around 5 or ten amps total to current draw.
I worked for 4 years in the '70s for a city fleet management shop with a fleet of 85 Plymouth police cars and battalion chief cars. I took care of the radios, sirens, radar, Vascar and consoles. I wound up doing lots of charging systems since the mechanics always blamed the electronics for all electrical issues. The ammeter system was never an issue. A lot of that is because none of them was more than 5 years old so the oxidation had not set in.
To keep my 'Cuda in shape, I just drop the radio out of the dash (two bolts, one nut and the antenna connector). Laying on the floor I can see the ammeter connections. I back off the nuts with a nut driver then retighten them. I do this as part of every oil change. Five minutes of work but good insurance. The bulkhead connector is packed with dielectric grease to keep water and green cancer away. The seals are available from Detroit Muscle and have been replaced. Dielectic grease also helps hold the gasket in place when mounting the connector from the inside.
Craig

Posted By: 70duster340

Re: Mopar Action article - 03/02/10 02:46 PM

Thanks, Craig. I intend to keep the stock ammeter working, I'm just not sure right now how to wire it in. When I installed the Painless fuse block, it effectively did away with the ammeter. The red power wire from the bulkhead connector is not routed to the fuse block, as is the black wire from the alternator. I just need to figure out how to wire in the ammeter. I thought it was a good idea to install the fuse block, as the stock fuse block was looking a bit suspect. And, where I live, the glass type fuses are becoming more difficult to find. This fuse block includes the horn relay, and flashers for both the turn signals and the emergency flashers, among many other things.