32 amp gauge -- sort of

rbullockv8

rbullockv8

Senior Member
I haven't been able to find a 30 amp or even a 20 amp gauge with the wiring posts for my 32 Ford (the one I have is a 20 amp with pass through loop). I'm running a 60 amp alternator, and it pegs the gauge momentarily when it initially spins up. Then it drops to about 12-15 amps.

So I was playing around just to see what I could do with a repo Model A ammeter. It's slightly smaller than the '32, and it slips completely through the dash hole. I needed a way to mount it in the dash.

I carefully removed the bezel from my 32 and found that the Model A gauge fit perfectly inside against the glass. I fashioned a bracket out of 1/8" ABS that wraps across the back of the gauge between the wiring posts--heated it with a heat gun and bent it around, drilled holes, and put screws through it to fit the back of the dash.

Came out pretty good. Although there is double glass, you can't tell by looking.

The only problem is the screw-on nuts on the wiring posts tend to come loose. I've tried single and double star washers, but no matter how tight I make the furled nuts, they come loose with a push of the wire connector. I'll have to try standard lock washers tomorrow.

Also, took the truck out for a tour of the neighborhood. New tires, torqued rear axle nuts, etc. Time to try it out. I'm posting a link, so we'll see if this works: https://flic.kr/p/QmmHp3.
 

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Rich,

I solved my problem by running a jumper wire across the two terminals at the back of the amp gauge. I think it was 10 gauge wire but it has been 20 years. Part of the current goes through the amp gauge and the rest around it through the jumper wire. The gauge reads low but you can't have everything. Everything looks like it belongs there from the front seat.

Charlie Stephens
 
1 I agree with Charlie about shunting your meter to increase it's amperage range. If you want to know where you stand with the shunt, you can use an additional known calibration ammeter to learn the new amperage amount which the shunt has given the original meter. Then remove it once you are satisfied. This can be done outside the car if necessary as a bench test.

2. If you find an external resistor which works, great. If you find an external wire for use as a shunt, you can start with a longish wire and gradually shorten it to decrease the shunt value, thus increasing the ammeter range.

3. Re the loose-ish posts as I understand the problem. As long as the internal connection is ok, simply double-nut the external connection with a nut above and below the external connection by locking the two nuts against each other. Similarly, if the problem is fastening the post against the internals, use the double nut system to establish a grip on the post for turning it without fear of damaging the threads.
 
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Hi Rich,

Your truck is looking great!

I read this last night and was going to suggest the double nuts but Paul beat me to it I see. You could also used a starred lock washer between the two nuts which which gives a little more space for tightening and provides even more locking resistance.

Glenn
 
If it is coming loose that easily, I would guess the wrong size nut. There are several small nut sizes that are very similar and that will interchange.
 
RE: Shunt Wire: Really good idea - never thought about that. I have a 40 amp converted generator and it will peg the needle on my 32 gauge upon start up.

Will that eventually damage the gauge (opinions?), or should I go ahead and try to 'shunt' method to take some of the amps out of it.

Nice RPU - not many of those around, what type of engine are you running in it? Drop us some pictures on this thread.
 
In the helicopters I maintain, the manufactures use either a calibrated shunt wire (calibrated by length and gauge of the bypass wire) or they use an actual shunt assembly that is taylor made for the voltage and amperage capacity of the system. The shunt assemblies are available from several sources. If your 12-volt 60-amp system will need something to drain off the excess amperage if it ever exceeds 30-amps otherwise it can damage the amp meter. The original Model A amp meter was only 20-amp so that one must be from something else. I know the repro meters for model A cars are crap. They basically won't work at all compared to an original. The Ford tractors may have used a 30-amp.

Just to add: The split type lock washers will work much better than any type of star lock.
 
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rotorwrench said:
In the helicopters I maintain, the manufactures use either a calibrated shunt wire (calibrated by length and gauge of the bypass wire) or they use an actual shunt assembly that is taylor made for the voltage and amperage capacity of the system. The shunt assemblies are available from several sources. If your 12-volt 60-amp system will need something to drain off the excess amperage if it ever exceeds 30-amps otherwise it can damage the amp meter. The original Model A amp meter was only 20-amp so that one must be from something else. I know the repro meters for model A cars are crap. They basically won't work at all compared to an original. The Ford tractors may have used a 30-amp.

Just to add: The split type lock washers will work much better than any type of star lock.
Click to expand...

Thanks. As mentioned above, do you know if the momentary ******* of the needle will hurt the overall performance of these gauges or permanently throw off their readings? It only pegs when the alternator spins up to speed, then the gauge immediately drops to the 10-15 range. I suppose that's due to the alternator's self-regulating feature. The needle is centered when the engine is off. Even with the headlights on and turn signal on, the amp gauge reads steady in the 15 range, so the alternator's regulator is working.
 
rbullockv8 said:
Thanks. As mentioned above, do you know if the momentary ******* of the needle will hurt the overall performance of these gauges or permanently throw off their readings?
Click to expand...

The amp meter would normally only show a small deflection if nothing but the engine is running until you turn on the lights or some other large current draw. It is normal for an alternator to put out a large surge after start up to replace the heavy draw that took place to start the engine but does drop rapidly as the battery charge is replenished.

Since I can't see the construction of your meter, I can't really tell whether it would be damaged or not. If it is the same construction as other model A type repros I have seen, it likely won't hurt it since they are not a very sensitive type of unit. I believe the originals were D'Arsonval type meters and have very fine windings on the rocking electromagnet inside. The repros don't even have an electromagnet in them so there isn't much that can damage them.

As long as it functions to let you know that you either have a charge or a discharge then it should be fine for your purposes.
 
Hey Rotorwrench and Gang, much appreciate the input - believe I'll try a 10 gauge shunt wire and see what happens. I'd like to NOT burn up my original 32 amp gauge - it only goes to 20 amps.
 
BTW, the motor is a Model B, rebuilt over ten years ago by Phil Andrews in Ojai. Full-pressure oiling, insert bearings, oil filter. Couldn't get my Zenith carb to stop leaking all over my garage floor, so I went with a Macs new Tillotson. Doesn't leak and seems to run fine. Standard 3-speed transmission. Rear end rebuilt with 3.56 gears (was 4.11). Most of this was done in 2003, but it's been all apart in storage due to a couple of moves.
 
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