60 Amp Ammeter?

[kingbee]

Does anyone know if there's a 60 amp ammeter THAT WILL FIT IN OUR INSTRUMENT PANEL?

[P.S.]

Question- In what instance would you ever charge or discharge at 60 amps, or for any length of time?

[Jim/GA]

I agree with P.S., it is difficult to imagine that situation. I don't think the stock wiring can even handle 60 amps for very long.

If the car is wired anything close to the stock setup, the ammeter only shows the current flowing in or out of the battery, not the total current coming out of the generator or alternator. So you can have a 55 amp alternator (to power all your accessories) and still never see more than 20 or 30 amps on the ammeter (usually much less).

[Mitch//pa]

here is a 50 thats in mine

[kingbee]

Wow Mitch, do you have any idea where that came from?

[kingbee]

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My air conditioning alone draws 30 amps, so currently it's not powered through the ammeter. (12 volt system) Add to that 150 watts of driving lights, plus headlights and you can see where a 30 amp ammeter is inadequate.

This is for my Town Sedan, not the roadster in my avitar.

[Mitch//pa]

pm sent

[Purdy Swoft]

Jim/TX is right on. I've run a sixty amp alternator on our coupe for nearly 20 years and only use a thirty amp ammeter. I use the original type wiring harness with no problems on my daughters coupe with a 60 amp alternator and my roadster that runs 12 volt on the original generator. The voltage regulator prevents overcharge and it will only charge enough to keep the battery charged. I use the Fun Projects voltage regulator with the model A generator and the 60 amp alternator has a built in regulator. If the regulator functions properly you should be good to go.

[Mike V. Florida]

30 Amps for a A/C fan?

[BRENT in 10-uh-C]

Originally Posted by Mike V. Florida

30 Amps for a A/C fan?

That is an unreal amount of draw for an A/C blower for sure!!

[kingbee]

Not really excessive. There's the evaporator blower inside the car, the condensor fan mounted under the rear of the car, and the compressor clutch = 30 amps.

[P.S.]

30 amps x 14 volts (while car is running and battery charging) = 420 watts. That is excessive.

150 watts for running lights isn't excessive though.

Either way, this doesn't answer your original question, very sorry about that.

[Jim/GA]

Originally Posted by kingbee

Not really excessive. There's the evaporator blower inside the car, the condensor fan mounted under the rear of the car, and the compressor clutch = 30 amps.

I have this same situation (even have the driving lights).

I split the power feed for my A/C to reduce the draw through the ammeter. I took power for the inside fan and driving lights directly from the alternator and I took power for the outside condenser fan and the compressor clutch from the battery cable post on the starter switch.

It all works without pegging a 30 amp ammeter. (You can't use a 20 amp meter, though.)

It took me a bit of thinking to make this all work out. I was headed down the "60 amp ammeter" path at first myself. That's a lot of power, requires heavy wire.

[Tom Wesenberg]

Jim, the only problem now is that it's hard to know what charge is going into the battery, because at some times most of the indicated amps are flowing to other circuits.

[P.S.]

Yea, but as long as the meter says there is current going into the battery, so what? The whole purpose of the ammeter was to show whether or not you were draining the battery. No?

[Tom Wesenberg]

Originally Posted by P.S.

Yea, but as long as the meter says there is current going into the battery, so what? The whole purpose of the ammeter was to show whether or not you were draining the battery. No?

Yes, but you don't want to be overcharging the battery, which a good ammeter can show.

[BRENT in 10-uh-C]

[QUOTE=Tom Wesenberg;579779]Yes, but you don't want to be overcharging the battery, which a good ammeter can show. ...or a good voltage regulator can prevent!! [/QUOTE]


Sure by now we have all assumed the vehicle is equipped with an alternator to generate the necessary amperage. I suppose it is also assumed this vehicle has modifications that sort of remove it from being placed in fine-point competition at the next Model-A meet, so if we can all see the alternator with the hood closed, hear the "whirring" of the Condensor fan, and see the A/C unit hanging under the dash, why not just add an Aristocrat style instrument panel to the dash and place a temperature gauge on one side, and an ampmeter on the other size.

Heck, if someone wants to be really 'trick', take the lens off of each gauge and take them to a trophy shop with laser engraver capability. Then have whatever logo & numbers you feel suits the era engraved on the faceplate after it has been painted with a flat black finish. Now it matches the ammeter and the speedo faceplate.

[kingbee]

Jim/TX, you may know my vehicle, as you live in Houston. I purchased this vehicle about 3 months ago and brought it to northern Illinois. It seems to be a very solid, but older restoration, drives very well, but has a very faint engine knock. I'm putting in an inserted touring engine, Mitchell transmission and overdrive. Also repainting the hood and front fenders.

[Kurt in NJ]

Another way to use the original ammeter for higher amperage is to add a shunt(an xtra wire between the ammeter terminals), by choosing different wire for the shunt the reading can be double, or even triple the indicated reading.

[MikeK]

There are two ways to wire an automobile ammeter. 1) Total output, with the meter in series directly with the output stud of the gen/alt. That would require a 60A meter for a 60A source. 2) The way Ford, and almost all cars wire and use them- only in the path between the battery and the electrical sys, NOT between the alt and sys.

The Ford wiring method requires only a 20A meter for any size car battery and alternator, even if you use a 300A Diesel rig alt. Unless you get a jump start with a 90% dead battery, you will NEVER push over 20A into the battery because the voltage regulator would never give you enough EMF (V) to do it. A big floor model charge/boost starter that may show 50A into a battery is delivering ~17.5 volts. (half that on a 6V batt) Your VR always keeps it at less than 15V. That 90% dead battery will only draw ~30 amps with a 15V source, and only for a few minutes. If you have a 6V 10SI convert alternator with the dreaded, too 'hot' 7.8V regulator, it will push 35A into a 90% down group one 6V wet battery for about five minutes.

Now here is one situation where cheapass 'ole Henry helps out. The ammeter in an A is NOT a sensitive D'Arsonval or 'taut-band' design with a moving coil of hair fine wire. The pointer is moved by induced reverse EMF into a non-magnetic pointer. It works just like a speedometer, but the pointer is centered so it can go both ways. Instead of a spinning magnet (speedo) the variable magnetic element is the brass shunt strip inside a wire ring magnet. You can put 30+ amps through it with the needle pinned and do no damage! That's exactly what happens when you have a short and see the ammeter needle pinned down past -20. Fix it, no damage. The worst that could happen with a huge instant 100A jolt would be to slam the needle hard enough to bend it, an easy fix. If you took it apart and glued in needle travel retarder you could slam it back and forth with amperage all day with no ill effect. Try that with a quality D'Arsonval or 'taut-band' meter and you'll be out $100+ in a flash! Thanks, Henry for being so cheap. You made it bulletproof.

The 30A jobs sold by vendors are the same delightfully cheapass (and inaccurate!) design. Just use a stiffer needle spring or bend the field sensitivity tabs on the needle to recalibrate it for 30A at the travel limit.

Side note#1- ALL aftermarket auto ammeters are of that cheap design that make them immune to extreme over amperage EXCEPT ONE. LINK It is made to fit a '19-'25 Model T. I'd love to get one and put it in an A meter case!

Side note#2- The notion that an alternator requires a bigger ammeter is a great myth to perpetuate if you are a PARTS SALESMAN.