2nd Gen gauge voltage to amperage relationship

[hemi68charger]

Hey gang..
I know the voltage limiter mechanically "averages" the 12v DC from the electrical system to approximately 5v... My question is does the amperage matter? I'm thinking of buying a bench 3-30v power supply with 1 amp output for testing of my gauges.... I'm also getting a decade resistor box.........

Thanks..
Troy

[71_deputy]

amps is the draw from the device when it is working. yours is a 1 amp output- thats good, mot sure but the guages don't draw very much current.

they gat their power fom the acc fuse- 20 amps. guages may draw less thans 1/2 amp when they work give or take.  so your power supply will be fine. gauges need about 5 volts but actually almost need 5.7 volts  from my testing to be most accurate.

John Mac

[Chatt69chgr]

The amperage matters in the respect that if the instrument panel drew more than 1 amp, then your power supply wouldn't be adequate for testing.  Like 71deputy says, the instrument panel probably doesn't draw much current overall.  You could easily measure the current gong to it by pulling the 12 volt wire going to the 3 terminal voltage limiter and using an inline ammeter to see what the current is.  I would definitely replace the electromechanical nightmare voltage limiter with a solid state voltage regulator.  The place in Washington that Shakey mentioned that plates the rockers on rocker switches sells these built right into the case of the old voltage limiters.  Pretty neat--around $30.  Using one of these will stop the instrument needles from wavering around due to voltage fluctuations.  A previous post on here describes the exact resistance values needed to test each of the gauges. 

I think that the ammeter could be rewired as a voltmeter using the same movement.  I havn't spent the time to look into this but it is considered a much better indicator of the health of the charging system than the ammeter.  Everybody but Chrysler got rid of the ammeter.  Chrysler finally did.  All the current in the car goes thru the bulkhead connector and these fry on a regular basis.   

[hemi68charger]

The amperage matters in the respect that if the instrument panel drew more than 1 amp, then your power supply wouldn't be adequate for testing.  Like 71deputy says, the instrument panel probably doesn't draw much current overall.  You could easily measure the current gong to it by pulling the 12 volt wire going to the 3 terminal voltage limiter and using an inline ammeter to see what the current is.  I would definitely replace the electromechanical nightmare voltage limiter with a solid state voltage regulator.  The place in Washington that Shakey mentioned that plates the rockers on rocker switches sells these built right into the case of the old voltage limiters.  Pretty neat--around $30.  Using one of these will stop the instrument needles from wavering around due to voltage fluctuations.  A previous post on here describes the exact resistance values needed to test each of the gauges. 

I think that the ammeter could be rewired as a voltmeter using the same movement.  I havn't spent the time to look into this but it is considered a much better indicator of the health of the charging system than the ammeter.  Everybody but Chrysler got rid of the ammeter.  Chrysler finally did.  All the current in the car goes thru the bulkhead connector and these fry on a regular basis.   

Thanks... Do you know the website Shakey knows about? Sounds interesting, especially if I can purchase it already done. That would eliminate me having to find a 5v bench power supply, I could use a simple 12v charger as long as it had low amperage... I will be sending my amp. gauge off to redline to do the amp-2-volt conversion soon for my C500.........

Troy

[Chatt69chgr]

http://www.gcartrim.com/index.html

I had never heard of this place until Shakey came up with it. 

[Plumcrazy]

Just go to Radio Shack and buy a #7804 voltage limiter and build your own 5v supply for less than $10.
Just build an external version of this setup.

http://www.martinihenry.com/temp/instrumentreg/instrumentreg.html

[Dennis K]

Are you going to use the factory gauge regulator, or a solid state 5v regulator? Either way, the easiest way to test the gauges would be to leave your instrument panel together, us a 12v supply or a car battery connected to the pin on the instrument panel that normally has the ignition voltage going to it, and use your decade box set to the correct resistance and test each gauge individually by connecting it to the pin for each sending unit and the ground screw on the circuit board. If you are interested in using a 7805 regulator, there is a much easier way than the magazine articles tell you to do it. I'll take a pic of how I did mine and post it later. To answer your original question, yes, 1 amp is enough to power the gauges, even if you do all 3 at a time.

[Chatt69chgr]

I believe the correct 3 terminal voltage regulator would be the 7805 but Plumcrazy is correct that your could purchase the necessary parts for under $10.  I looked up the 7805 and it is capable of 1A output at 5-volts with a 12-volt input.  Just thought that some might want the convenience of the packaged unit in the original MOPAR voltage limiter case.  They have two versions:  one that plugs in like the original and the other that has wires.  You send in your old one and they send you the solid state version for $29.95.  I am not sure if the 7805 has a current limited output but if it doesn't you would want to be careful to not short the 5 volt lead to ground or it would probably burn the IC real fast.  But I do know that the 7805 has been around a long time and is a very good integrated circuit.

[Dennis K]

Ok, here's how I did mine. I drilled and tapped a #6-32 screw hole in the back of the instrument panel. I had my panel apart at the time, if the speedometer were still in it I would have drilled the hole somewhere else to avoid getting drill shavings in the speedometer housing. Then I clipped the middle lead off the regulator and mounted it using a #6-32 x 1/4" machine screw with a little heat sink grease on the back of it. Mounting it this way eliminates the need for a ground wire and the heat sink, since you're using the panel housing as the heat sink. Then I soldered the 2 wires on, one on the 12v input, and the other on the 5v output. I used a capacitor on the input just because I happened to have one, but capacitors are not necessary on the newer 7805 regulators, they are not nearly as sensitive to voltage spikes and noise as they used to be.

[Plumcrazy]

Ok, here's how I did mine. I drilled and tapped a #6-32 screw hole in the back of the instrument panel.

I used the hole where the factory capacitor attached to the housing to mount the regulator.  Just had to open the hole a little for the screw to fit through the regulator.

What I did do completly different from everybody else was take the male pins out of a couple old houshold extension cords and use them to plug the wires into the circuit board.  I wanted something I could easily remove if I wanted to.

[70 Charger RT]

Troy.  I just had some 7805 regulators on ebay for $5.  Did you want one?  It includes a box and heatsink too.  See this link http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=001&sspagename=STRK%3AMESO%3AIT&viewitem=&item=110082432793&rd=1&rd=1  Anyone else need one?  I have 24 left.  I can reduce the shipping to around $5.

[Doc MoPar]

Posted by: Chatt69chgr

http://www.gcartrim.com/index.html

I had never heard of this place until Shakey came up with it. 

That site is great!!! and they have really reasonable prices.  I've seen repro stuff on the net and e-bay for twice what these guys sell it for.

I bookmarked that one!!  Thanks guys this site is awsome.

[hemi68charger]

What's attached to the 12v feed and ground? A capacitor? I'm not good with electronics.... In the learning phase.......

[71_deputy]

red stuff is red silcone to hold the cap in place.

left lead of reg is +12 volts
centre is ground but top metal tab is ground as well so the screw to the back of the dash grounds the tab
right side is for the + 5 volts out to the gauges.

John Mac

[Dennis K]

Troy, yes, that's a capacitor. It's really not necessary with the quality of the modern ICs, but I happened to have one laying around so I put it on. The red stuff is silicone RTV. I believe the one I put on is a 10 microfarad 35v cap, but I can't tell anymore because the label is stuck down in the RTV.