Change original Temperature gauge to Alternator gauge

[SA69mach 39]

thanks. Midlife.

[Midlife 814]

There's no guaranty that this will work...just using my knowledge/experience and a hunch, so be careful!

[1969_Mach1 333]

Since the ammeter is a sensitive voltmeter, reading a very small voltage different between two points of the wire it is spliced into, will adding a resistor to one side of the gauge possibly skew the needle too far to one side.  Thus, the needle will never be centered.

[danno 128]

I am sorry, I have been out of the loop on this.  There is a wire from the starter solenoid to the fuseblock that supplies 12 volts for most things in the car to work from. Th resistor would need to be added in this wire, at the starter solenoid. I have some calculations on it at home, I will get them tonight and reply tomorrow.

[1969_Mach1 333]

It has been a while since I rewired my engine compartment.  It seems to me it is not a good idea to add a resistor to a wire that feeds power to most of the car?  I think the ammeter is what it is and there may be some negative side effects to make it work better.  I still believe if your goal is a better functioning gauge have it converted to a volt meter.

[Guillaume69 150]

^^ +1

[Midlife 814]

Oh, I don't think anyone intended to add a resistor wire to the main power feed, only to the two lines that go to the ammeter within the underdash harness.

[SA69mach 39]

The goal is to make the amp meter more sensitive. To give an obvious visual indication of charge rate or drain. As they are the oem gauges are useless in practical terms.

I will have to think it through and then try some of the suggestions. The answer may be in the gauge's internals. The operating range needs to be halved, at least.

[TheRktmn 15]

Not much to the internals, it is a simple meter consisting of copper wire wrapped around a loop. The ammeters I bench test here are VERY responsive. I hook 12V to one side and a sealed beam to the other. The pointer pegs in the direction of flow. I think the problem is not in the meter but in the wiring to it.

[SA69mach 39]

Are the ammeters on the 69 and 70 printed circuit boards receiving 12 volts or 5 volts? I assumed the IVF supplied all the gauges, but could be wrong about the ammeter.

 

I don't mind checking wiring, but the printed boards don't make it easy.

[TheRktmn 15]

The ammeter is battery voltage. Only the Fuel, Oil and Temperature gauges use the regulated voltage.

[det0326 179]

Are the ammeters on the 69 and 70 printed circuit boards receiving 12 volts or 5 volts? I assumed the IVF supplied all the gauges, but could be wrong about the ammeter.

 

I don't mind checking wiring, but the printed boards don't make it easy.

Neither 12 or 5 really. The ammeter really has nothing to do with voltage it is designed to measure current flow and in what direction. 

[danno 128]

I have  a solution I want someone to try.  I will start by running some calculations by you. The calcultions could be too much for some of you, but in case you want to know, this is the way it works.  The ampmeter requires 0.6 volts to move it to the first mark, and 0.7 volts to move it to the second mark.  That is the first problem,it is not linear.  It takes a lot of voltage to move it a little, then not as much to move it the rest. So let's work with 0.7 volts full scale.

 

The factory lights on high beam take 14.6 amps. The heater fan on high is 8 amps. So if we assume 30 amps load on the battery  with a lot of things on, and the motor off. We want this 30 amps to make the meter go full scale. Full scale on the ampmeter is 0.7volts.   Resistance = volts/amps, so R= 0.7/30, or 0.023 ohms. You have maybe 0.003 ohms in the existing wire in your car, so you need to add a 0.02 ohm resistor.

 

It is a fact that all wire, even copper, has resistance in it. So we can just use a section of wire as the resistor.

 

The easiest way to see if this works is to add a short section of standard #14 wire you use in your house. It is 0.0025 ohms per foot, so you need about 8 feet of it. What someone needs to try ( my car is in storage for the winter or I would do it) is to get a 8 foot length of #14 wire, and add it to what you have in your car now. Then turn on your high beams, with the motor off, and you should see the ampmeter move to about the first mark on the discharge side.

 

What you have to do is add this wire between the starter solenoid and where the big black ( or Blk/Yellow in some cars) wire connects. So it is in series with the big black wire. Disconnect the big back wire from the solenoid and  connect one end of the 8 feet of #14 wire to the screw terminal on the solenoid. Connect the other end of the #14 wire to the ring terminal on the end of that big black wire.

 

This is a real simple test to see what happens.  We will start with this and see what happens.  It could be we will need a longer section of wire, and we will also have to adjust it if you have heavy loads like halogen lights, electric radiator fan, and large amplifiers on your car radio.

 

Someone try this and report back.

[Midlife 814]

Danno:

I like your suggestion: it makes sense.

 

The Ford system uses the difference in resistance between a 16 and a 10 gauge wire of approximately 3 feet or so; I don't believe there is enough difference there to make up your 0.02 ohms.  The internal DC resistance of wire is very sensitive to the gauge of individual strands and the number of strands that make up the insulated wire as well. 

 

The two points of measurement are the first OEM splice behind the starter solenoid and a second splice on the main power line where the alternator ties into the main power line.  Yes, yes, I know...the alternator attaches directly to the starter solenoid as well, but there's another junction further down the main power line.

[danno 128]

Midlife, you ar right. It is the internal resistance of the wire that Ford tried to use as a voltage drop for the ampmeter.  You know what I am talking about with the splices.  One is under the radiator on the drivers side of the car, but I did not realize there is another splice by the solenoid.  If there is, then the wire needs to be cut, and nobody likes to to that, even me. If that splice is on the bolt on the + side of the solenoid, than it can be done.  The splice locations could also be different in a 1970, I am not sure.  Can you confirm the location of the splice by the solenoid?

 

You are right, the aternator power output does not connect to the battery, solenoid, or the regulator.  It connects to that magic point under the radiator.

 

Also keep in mind that this is all different in cars with a factory tach, just in case any of you are reading this.

[danno 128]

Midlife, my calculations for the resistance were 3 feet of 10 gauge at 1mohm/foot, and 8 feet of 14 gauge at  2.5mohm per foot.

[det0326 179]

Midlife, my calculations for the resistance were 3 feet of 10 gauge at 1mohm/foot, and 8 feet of 14 gauge at  2.5mohm per foot.

Hello Danno

 

 

The experiment you want to do I can't help with because my car is all apart.

How ever I do have the gauge out and if you need any thing checked I don't mind 

taking it apart for a visual If you need anything from the inside.

i don't plan on using an Amp gauge when I reassemble the car anyway so if it

is damaged no sweat.

 

Dave 

[Midlife 814]

Each splice for the two ammeter lines are on the side away from the starter solenoid.  The OEM splice is a large molded junction that is cylindrical in shape.  You can feel the splice through the tape---sorta like a snake that has swallowed a large rodent.

 

One needs a micro-ohm-meter to measure the resistance (and thus the difference in resistance), and those machines cost hundreds of $$.  Those machines actually measure seimens (the inverse of resistance).  I don't even have one, but have used them at work. 

[danno 128]

I could borrow a micro ohm meter from work, but if the sense wires both go to molded junctions or splices, then my idea of adding wire will not easily work. For it to work, you would need to cut the wires.

 

Dave, thanks for your offer. I have a spare ampmeter as well stored above my garage. I dont know why, as worthless as they are, but I have it just in case.

 

I have an circuit that I put together to amplify the signal that the existing wires in the car have, to make the existing ampmeter work better.  I just need to test it. It amplifies the 0.002 volts the ampmeter sees when the lights are on to be 0.6 volts, so the meter will move.  It is complicated, though, to get it to move the meter in 2 directions and not consume any power when the car and all electrical things in it are off. I will bet there would be others who would want one of these. No wires to cut, just fasten it to the back of the ampmeter.

[Midlife 814]

Here's some old data I collected circa 2000 using a D-cell battery at 1.565V.

1/16 of gauge deflection required 13.3 ohms, yielding 0.118 amps

1/8: 7.3 ohms, 0.24 amps

1/4: 2.8 ohms, 0.559 amps

3/8: 2.2 ohms, 0.711 amps

1/2 deflection: 1.8 ohms, 0.869 amps

 

I believe the gauge is truly an ammeter, not a voltmeter.  If true, this gives you an idea of the DC current that flows through those two ammeter wires.  Note that it is somewhat non-linear.

[danno 128]

I suppose that technically it is an ampmeter, you are right. It needs more amps than the wire connections supply.  When I ran the test, I was measuring the voltage, and it is of course directly related to the current.   This is not over yet, I will revive this post when I get my car out of storage in April and can do some more tests.  I want to see if my voltage amplifier is a workable idea. I want to see my ampmeter work like it is supposed to, without any modifcations to the wiring.

 

By the way, I even tried rewinding the coils in an ampmeter.  I doubled the amount of turns of wire, using a smaller wire. That really did not help much.