Ammeter to Voltmeter Conversion

theguruat12

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So, I had seen somewhere over on FTE there was a guy who does this, and I decided I would try it myself, since I had an extra cluster full of gauges I picked up to have spares. I bought a Cen-Tech analog voltmeter from Harbor Freight for $8, and went to work.

The only tools I used were a Dremel, a soldering iron, and screwdrivers/pliers. Total cost for this would be a $5 junkyard gauge (Probably 10 of them in the one yard I go to here) and the $8 gauge from Harbour Freight.

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The idea is to swap a voltmeter interior into your ammeter, because I have seen people simply cut a voltmeter into the cluster where the ammeter goes, and it looks OKAY, but I really wanted to keep the stock cluster look.

First, I took the face off of the ammeter, I had to use a screwdriver to [carefully] open the plastic tabs that held it onto the gauge body.

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Then I bent open the tabs on the back that hold the actual gauge guts into the body.

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Next, I removed the ammeter itself (the posts just pull out of the plastic insulator) and snipped the wires off of the lead posts (tried to desolder them, but it's not solder holding them on, or I didn't have enough heat. This turned out to be a benefit because I had something to solder to when I installed the new guts). I snipped the needle off of the ammeter with scissors to put onto the new gauge.

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This picture shows the entire Cen-Tech voltmeter disassembled in order on my desk. The only thing I used from this was the main part of the gauge (in the cylinder).

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Next, I took the metal cylinder off. There are two magnets (that CAN NOT be reversed otherwise the gauge will be off by 180 degrees) that were shoved in between the case and the electromagnet assembly. I just wrapped a piece of Scotch tape around the whole thing to hold them on there after I took off the cylinder. I used a cutting wheel to remove the needle from the needle hub, since I wanted it to look perfectly stock, and use the original needle.

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Finally, getting down to the actual modding. I used a sanding wheel to trim the legs down a bit, and a bit off the face of the gauge needle hub. This is because the gauge as it sat would be compressed by the instrument cluster front piece, and wouldn't allow the hub to turn.

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I soldered new wires to the electromagnet assembly and to the lead posts. Lead posts pushed back in, and the electromagnet assembly is in the ammeter case. I just cut up a hipolymer pencil eraser and used the pieces to wedge the assembly where it needed to be.

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I used a cutting wheel to trim the metal posts at the top, since they interfered with the ammeter face going back on the case.

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The voltmeter hub was too far up to go through the ammeter face hole, so I used a sanding wheel to notch it a bit for fitment. I tested it with the trim on to make sure I wasn't cutting where I would be able to see it when the trim was one.

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Here is a picture of the face back on, the hub trimmed, and it ready to be assembled.

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I used a soldering iron to melt a few lips in the back of the face to hold it onto the case. This appears to be what the factory did when they attached it, and it was easy, so that's how I held it on. Then, I took my old ammeter needle, and very carefully lined it up and glued it on with modeling cement.

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The cement is drying as I type this. I don't have my truck in Albuquerque with me, so I can't just drop it in for a test, but I know that the middle bar SHOULD be 12 volts. From my measurements, the D bar should be 10 volts, and the C bar should be 14 volts.

I'll test this as soon as I can to see how well it came out and how accurate it is. As it sits, the needle will travel WAY further to each side of the gauge than the other gauges, so I may add two pegs to keep it looking the same as the others when it's off. This would reduce the gauge's range to about 9.5 volts to 14.5 volts. But, the way I see it, if my voltage drops below the center mark when I'm driving, there's a problem, and I'll know it. I just like the idea of having a useful gauge and keeping it looking perfectly stock. I'll be repainting the needles on all of my gauges with the fluorescent orange from HiPo Parts to get rid of the classic faded/not faded line on them.

I'd love to hear any feedback any of you have to offer! I'm really happy with how it looks for only spending $13 and a few hours of detail work on it.
 
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theguruat12

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Ammeter measures current, and does not work correctly if you upgrade the alternator to a 3g, as I'm planning on doing later this year. A voltmeter measures voltage. The factoury ammeters are pretty lame, they hardly ever move, whilst a voltmeter will tell me how much voltage the alternator is putting out.
 

laserjock

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Very nice. I didn't realize the older trucks had ammeters in them. Didn't remember that. In general all the ammeter would tell you is if the system is charging (c) or discharging (d). Hardly see such a thing now except on tractors.


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Wyreth

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Well done sir!

Actually, this is what I plan on doing for all my factory gauges, with the addition of changing faces for water temp and oil press. Thanks for giving a very clear picture of what it will actually entail.
 

NTOLERANCE

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whilst a voltmeter will tell me how much voltage the alternator is putting out.

Im not trying to pick a fight but his is untrue

A volt meter is going to measure voltage where ever you take the measurements from. If youre at the fuse box it will take it from there if youre at the key switch it will take the reading from there.
While i appreciate your quality and detailed work here, you havent posted where youre getting your voltage signals from (that i see). And since these diesels need little electricity to run, if your alternator quits in the middle of the day, average voltage in your system will remain relatively high untill it dropps off slowly.
You could pull voltage from the alternator out put but again if the alternator fails, the battery is going to keep the voltage up for some time. Especially considering we typically have big dual batteries

If you really want to know when your alternator fails in he shortest amount of time, a WORKING ammeter is the best choice.

That being said, im being picky in regards to my comments, and for the most part, a volt meter is fine.

I prefer an ammeter.
 

theguruat12

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I'd prefer both if I could have them, but I didn't want to resize a new shunt for the ammeter. I definitely agree with you as far as having a good ammeter.


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icanfixall

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I suppose this is not going to work on my 1989 truck because it appears I have a votmeter in it with the numbers of volts on the gauge face..
 

theguruat12

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I suppose this is not going to work on my 1989 truck because it appears I have a votmeter in it with the numbers of volts on the gauge face..

I debated trying to swap in a voltmeter from the later trucks, but I decided to try to keep it looking perfectly stock. I wish I had a stock voltmeter, it would make a 3g conversion so much more satisfying. I hate the idea of one of my gauges doing nothing, even if it wasn't all that useful to begin with.
 

franklin2

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Im not trying to pick a fight but his is untrue

A volt meter is going to measure voltage where ever you take the measurements from. If youre at the fuse box it will take it from there if youre at the key switch it will take the reading from there.
While i appreciate your quality and detailed work here, you havent posted where youre getting your voltage signals from (that i see). And since these diesels need little electricity to run, if your alternator quits in the middle of the day, average voltage in your system will remain relatively high untill it dropps off slowly.
You could pull voltage from the alternator out put but again if the alternator fails, the battery is going to keep the voltage up for some time. Especially considering we typically have big dual batteries

If you really want to know when your alternator fails in he shortest amount of time, a WORKING ammeter is the best choice.

That being said, im being picky in regards to my comments, and for the most part, a volt meter is fine.

I prefer an ammeter.

You do not want your voltmeter on the alternator or the battery, it does draw current and would be a drain. Voltmeters work fine, the later trucks use them, they are tied in the system up behind the dash, and they will indicate the alternator not working, though I think the best combo is the voltmeter AND the idiot light. Truth be known, the idiot light is the best indicator over both the ammeter and the voltmeter. It's either working or it's not, and a red light in the dash will get your attention much quicker than a needle in a gauge.

The best setup I ever had was a battery monitor Sears used to sell. It mounted under the dash and had about 5 or 6 led's in it. Green ones lit when everything was ok, red ones for undercharge and orange ones for overcharge.
 

theguruat12

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You do not want your voltmeter on the alternator or the battery, it does draw current and would be a drain. Voltmeters work fine, the later trucks use them, they are tied in the system up behind the dash, and they will indicate the alternator not working, though I think the best combo is the voltmeter AND the idiot light. Truth be known, the idiot light is the best indicator over both the ammeter and the voltmeter. It's either working or it's not, and a red light in the dash will get your attention much quicker than a needle in a gauge.

The best setup I ever had was a battery monitor Sears used to sell. It mounted under the dash and had about 5 or 6 led's in it. Green ones lit when everything was ok, red ones for undercharge and orange ones for overcharge.

I'm going to add the charge idiot light with the 3g when I install it, it's super simple to add. Probably in the upper-left dash light spot where there's an EMISSIONS light not hooked up to anything.
 

oregon96psd

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Ammeter measures current, and does not work correctly if you upgrade the alternator to a 3g, as I'm planning on doing later this year. A voltmeter measures voltage. The factoury ammeters are pretty lame, they hardly ever move, whilst a voltmeter will tell me how much voltage the alternator is putting out.

If your interested when i get out of the oilfield and get home i can show you how to make it work with the 3g swap, mine goes almost to the full discharge side then slowly comes back as the glow plugs warm up, then shoots back over to the charge side when started, slowly coming back to little charge as the batteries recover, just like it should.
 
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