Dino AMMETER upgrade

HOw about this one??

Motor Mart (MoMa's)
Rework Smith guages
10853 Magnolia Blvd
North Hollywood, Ca
(818) 980-8642

 

Albuquerque, New Mexico
I do not have her number at home but will post it when I get to the shop in the AM. She has done all of my gauge repair for better than 25 yrs now. The last 3 Dino AMP gauges she did for me have been perfect in every respect. Make it a point to get it done when the car is down for the winter or repairs, before it burns up. Two melted Dino gauges this summer so far.
Margaret and I were speaking one day and she mentioned that she thought she had the final fix for the low oil pressure readings. I had a Dino in for major service and the dash was pulled back for the AMP gauge repair so I sent her the sender and the gauge for her research. I have not spoken with her on this front since then but I suspect she has that delt with as well.

Dave

 

Last Try.

Mo-Ma
1321 2nd Street Southwest
Albuquerque, NM 87102
(505) 766-6661

 

I have not experienced the Amp gauge meltdown (3 Dinos, 50 years combined usage). I have recently experienced substantial heat arising from the amp gauge while rebuilding my car. During testing of the engine and new wiring harness, I happen to touch the amp gauge to find it quite warm. The two brass nuts holding the 8 gauge main bus ring contacts were not snug. I tightened carefully (brass, after all), and the temperature dropped substantially.

During starting or significant charging one will see 40 amps passing across those lugs. Loose nuts will lead to significant contact resistance. I suggest that a good cleaning with wire brush or sandpaper of nuts and ring connectors, and proper tightening will solve the problem.

Finally, I have opened my amp gauge. There is no shunt resistor.

Jim S.

 

Dave - a true amp gauge contains nothing but a coil of heavy gauge wire that creates a magnetic field proportional to the current flowing through it. The needle moves under the force of the field. Hence, an amp meter is a short circuit through near-zero resistance wire. The full amperage runs through the gauge, and if there is a bad solder joint, loose contact, etc., then heat will be created (much like a toaster).

As you imply, the direction of current flow is more important to us than the quantity of amperes, as is true with oil pressure. I suspect that both the amp meter and oil pressure system provide +/- 50 percent accuracy at best. But who cares? If I really want to know if my oil pressure is low because of a failed crank-journal bearing, I have bigger problems. Hence, the call for idiot lights. Is it charging...or isn't? That's about all we can tell with these gauges.

Jim

 

"

 

Right you are, Dave - Electrical Engineering (Carnegie Tech undergraduate- before it was Mellon) and M.I.T. graduate, then on to medical school and then on to business school. All that education and I still can't afford a 575 F1.

Those gauges do need a slap on the dash to wake them up. I use them merely to tell me that everything is qualitatively correct. Rev the engine, amps go up and oil pressure goes up. Temperature goes up until thermostat opens, then temperature goes down. Long hill climb and temp goes up, coast down hill and temp goes down. Numbers are not important. Better than an idiot light, not as good as real transducers and gauges.

Italians, remember, check their pasta by throwing it against the wall!

Jim S.

 

Italians, remember, check their pasta by throwing it against the wall!

Jim S.

Only in american movies

Pasta is too good to waste

 

Synchro - I suspect Margaret is replacing the magnetic coil with heavier gauge wire. Since I have replaced my wiring harness, my fans, lights, and fog lights are running better and brighter, but in so doing, are drawing more amperes. Hence, the battery is both discharging and charging at higher amperage. I am consistently seeing +/- 40 amps. This means that 40 amps or more are running through the brass lugs on the amp gauge and through the coil in the amp gauge. Scary, but when properly installed (tight lug nuts) it should be okay.

That said, there is a safety margin in redesigning the magnetic coil to carry more current. With appropriate calibration, the function will be the same.

Jim S.

 

Does running AC play a part in this? And would making sure that all contacts were clean and tight prevent sparks fires and what have you? Is the upgrade needed or just a good idea?

 

Dignini - The original design is sound. Entropy, however, drives everything towards randomness.

Now, addressing the ammeter. As a bit of background, remember that ALL electrical current going to and from the battery passes through the ammeter. Hence, if you see that you are discharging at a traffic light, with fans going, headlights on, windshield wipers waving, etc., and the ammeter reads minus 40 amps, then the battery is delivering 40 amps to the main electrical bus (through the ammeter). When charging, the same can be said.

If the ring connectors on the two large red wires connected to the ammeter are loose, the contact resistance will be high and a great deal of heat will be generated (I squared R losses). I have not heard of any Dino electrical fires owing to ammeter meltdown. Could happen, but hasn't as yet.

A good policy would be to periodically remove the instrument panel and check the torque on these two brass studs - nuts. I strongly encourage everyone to disconnect the ground terminal of the battery before loosening the instrument panel. If you touch one of the red ammeter wires to ground you will 1) ruin the ammeter and 2) stain your underwear.

If the ammeter is properly connected, I believe everyone is safe. I have not changed mine, if that says anything.

One point of interest. If you are discharging 40 amperes at the stop light (again, everything possible pulling current), then the ammeter is telling you that you require 40 amps to supply the loads. Now you pull away from the light and you charge at 30 amps for a few minutes to recharge the battery. Your alternator must supply the 40 amps of the existing load PLUS the 30 amps going to the battery, or 70 amps. This current is flowing from the alternator through the firewall fuse panel to the battery and main bus. The point is, the alternator must be able to supply not only the load demands, but the load demands PLUS the batter-charging current.

Tighten the brass nuts on the ammeter. Have fun. By the way, I installed a ground breaker switch in front of the spare tire well, with a stainless steel 1/16 inch cable leading back to locate under the driver dash near my left leg air vent. I can pull the cable to disconnect the battery.

Jim S.

 

Thanks taking the time to explain. I know little of electronics, but a friend of mine struggled for three hours under a desk tring to set up a computer prototype he was working on. He finally got it working and instead of being elated he just mumbled f****** connections. That was a good lesson for me. Now I clean and use Stabilant 22.