Best Way To Disconnect An Amp Meter?

I have a 1971 Renegade with the original amp and OP gauges, both still working. The P.O. installed a volt meter that is working. I want to disconnect the amp meter. I am not going to remove the amp meter I just want to avoid the fire potential that I have read about with amp meters.
What is the best/safest way to disconnect it?

 

I have a drawing -



Top is before, below is after. This is specific to my '82, but the idea is the same. Bulkhead is the firewall penetration connector. The wire labeled 14 ga is an '82 factory fusible link. The fusible links protect the rest of the car from the battery in case of a wreck or other disaster.

Electrically, the ammeter acts like splice; in this case if you just removed it, you'd have no connection the dash and lights.

 

The fire danger , if any, has nothing to do with the ampmeter itself. It is the fact that the circuit it monitors carries the full amperage used by the entire vehicle, and often is unfused. Thus damage to that wire anywhere on its path could result in a significant short circuit. That applies meter or no meter.

[EDIT. See post # 5 below}

 

Maybe the round CJ ammeters are better in this respect. The ammeters used in the J-trucks and Wagoneers actually catch fire in the dash. I attribute this to the shunt in the meter aging and increasing resistance. The regulator only reads the battery voltage, and any voltage drop between the alternator and the battery is added to the output voltage of the alternator. The alternator increase current output to raise the voltage. Suggest that added current causes more heat in the ammeter, which raises the shunt temperature and its resistance, adding more current.

 

Oh. I never had an ammeter with an alternator. Sounds like another reason for me prefer generators...

 

Maybe. I don't know how a generator regulates versus an alternator. Both use some kind of regulator to change the current output based on the battery voltage, but generators don't have semiconductor components.

 

And most alternator vehicles use voltmeters, not ammeters.

I suspect generators are somewhat self-limiting. My '34 Ford regulates the maximum output by how far one rotates the "three-brush" assembly relative to the field coils. I set it higher at night when I need the headlights!

No ammeter fires.

 

I don't understand? One tells Volts, the other tells Amps, what is the problem? A short would cause a problem with either one, right? I have a 10 SI alternator no my Jeep with an amp meter like everyone else had in the old days, yes you have to Goose it start it charging, once you get it charging there is no problem? As soon as I give it the gas you can see the meter go up to what the amp meter is putting out.

 

Simply put. the ammeter sits directly between the battery and the rest of the load (minus the starter). It monitors whether the system is charging + (pushing electricity into the battery) or discharging - (power is flowing out of the battery and into the system).
This is a source of potential issues since all the voltage flows through the meter.

A volt meter simply reads existing voltage in the system.

Take the + and - sides of the ammeter and connect then together with a small nut/bolt and hit the joint with some tape or shrink wrap is the easiest.
Or
Splice/solder the two together and insulate the joint.

Insure your voltmeter is wired to the accessory side of the key. Meters left "on" continuously can drain the battery over time.

 

I think the main problem is the distance between the charge terminal of the alternator and the battery. Any resistance along that distance will make a voltage drop between the alternator and the battery, proportional to the resistance and the charge current.

The regulator determines how much current to make by sensing the voltage at the battery. This is direct to the battery, with no cables and ammeter between. The voltage across the battery is held at a constant, say 14 volts. This includes the battery electrochemical potential of 12.6 volts and the internal resistance of the battery to ground.

The load (current demand) increases, and the regulator responds by juicing up the field of the alternator to make more current. When the demand and supply equal, the voltage goes back to the ideal 14 volts.

The regulator sees the battery voltage at the battery, not at the charge cable connection to the alternator. Any resistance in the charge cable reduces the supply current: turned into heat by the resistance in the ammeter and charge cable. The regulator increases the juice to the field to compensate.

With more current, the ammeter gets hotter. Resistance increases as the temperature increase; the alternator increases the current to compensate. This is positive feedback ... not good.

(A little speculation here). The regulator is also a feedback system. It tries to achieve the set point of 14 volts by feedback. Any feedback system with finite gain can only approach the set point, not match it exactly. I suspect any ammeter heating is fine as long as its gain does not exceed the regulator voltage feedback gain. Add a tiny amount more resistance, and the charge current increases a little... at some point the regulator says "meh, good enough" and all is stable.

This is why the short wire direct to the battery is better than the long wire through the gauge, with all its extra connections. The wire has resistance gain just like the ammeter, but it's pfff. Nothing. The regulator gain is so much higher than the wire's gain that you never see it.

One final comment - never connect an alternator capable of 60 amps charging to an ammeter that's not capable of handling at least 60 amps. The original ammeters in these Jeeps were like +/- 30 amps? You can't buy a 30 amp alternator any more; they are all replaced by alternators with much higher ratings.

 

Yet the last one I bought came with a warning that my new alternator could be ruined if I attempted to charge a dead battery.

W. T. F. ?

Another vote for The Good Old Days.

 

Undoubtedly true. But were they not at one time "designed" to do better?

"Design" can also be to reduce cost, weight, or whatever the Head Office thinks is more profitable.

 

Yep. Seems clear. Maybe the OEM ones do.

 

Thanks For explaining that, Howard and Term8ted, it makes Sense to me a little more now. I have little more now, I have never had much experience with DC ecstaticity, or AC for that matter. Rick

 

I learned that in auto shop class 40+ years ago, it's not a new thing.

 

Could a dead battery be a shorted battery? Charging into a dead short would seem ill advised. Unless shorted, these batteries have internal resistance which would be current limiting to some extent.

I'd suspect it's unusual for a battery to be completely discharged in normal service. You can imagine case with a parasitic drain and sitting for months, but most cars don't sit unattended long enough for the battery to be completely depleted. No start happens well before zero volts.