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the ammeter isn't worth much as a diagnostic tool. I have had an alternator fail and the slight discharge the ignition system pulls wasn't enough to get my attention. And if I'm going to install a 3G alternator I can't make the ammeter any more sensitive in order to see the slight discharge or the gauge will peg when the battery is being charged.
Good point about the slight needle deflection being 50% less if modified, making an ammeter even more useless for catching an alternator failure. How about removing the ammeter altogether and installing a Pez dispenser? It would pretty much give you the same amount of useful information, plus you'd have some candy treats.
The shunt is a very low ohm resistor, and all of the current goes through it save for the very, very small amount that goes through the ammeter itself. And a longer shunt means more resistance, so that means the ammeter is more sensitive.
I guess I'm not getting it.
In post 262 you said "parallel" which is product over sum, isn't it?
With two equal resistors the value would be half, and the wattage double, no?
I'm not sure of the ammeter shunts value..
By chance were you ever a designer for McDonnell-Douglas?
No, but I used their software - Dynal and Strudal - dynamic and static load analysis.
Originally Posted by ArdWrknTrk
I guess I'm not getting it.
In post 262 you said "parallel" which is product over sum, isn't it?
With two equal resistors the value would be half, and the wattage double, no?
I'm not sure of the ammeter shunts value..
Yes. And while that would work it would effectively cut the sensitivity in half and the slight deflection when the alternator dies would be even less noticeable. Obviously, now that I think about it, not useful.
Basically, we have a gauge that needs to be very sensitive on the discharge side to show when the alternator fails, but insensitive on the charging side, especially when a 3G is installed, or it will peg. Maybe a diode could be used in parallel with the shunt so that when charging there is less voltage drop. However, most diodes have a .7 volt drop across them when conducting and that may be more than the ammeter needs to peg.
Originally Posted by FuzzFace2
Ok here's the wrench, where is the vacuum gauge going??
Dave ----
The AFR meter will, at least for a while, replace the Autometer tach and it has a vacuum gauge built in. But, isn't a vacuum gauge on a 460 pretty much like an ammeter?
The AFR meter will, at least for a while, replace the Autometer tach and it has a vacuum gauge built in. But, isn't a vacuum gauge on a 460 pretty much like an ammeter?
I guess it would be
What ARF meter is that that has a vac gauge in it?
If I ever get my truck on the road I would like to get a AFR and if it has vac good.
Dave ----
Gary, I think this is why oems use a simple charge indicator lamp...
Yep. Simple and yet effective. Hmmm, I have an idiot light cluster, so what if I swap that in to replace the ammeter? Does the 3G work with an idiot light? Obviously it would take some requiring, but no biggee.
It'll get a 3G, eventually. But not right away as there are lots of other more important things to do, like replace the front main seal, get the fuel gauge working, replace the exhaust, etc.
Has anyone tried the factory ammeter gauge with a 3G alternator to see how it works? Personally I have no plans to upgrade charging as the factory setup works for me and I no longer have ammeters in either truck. I am just curious. It keeps getting mentioned about pegging the needle with a higher output alternator but I didn't think full current ever went through the ammeter, it was just acting as a voltage drop indicator with low current. Maybe I'm misunderstanding its function. Would it also depend on how the new alternator is wired? I put a 100 amp 1 wire alternator in my mustang, removing the regulator and harness, and there was no impact on the factory ammeter. It worked just as poorly as before.
Hmmm, I have an idiot light cluster, so what if I swap that in to replace the ammeter? Does the 3G work with an idiot light? Obviously it would take some rewiring
It works because before starting the bulb is sending power through the excite wire into the alternator.
when the engine starts there is power on both sides of the bulb and it goes out.
This works with my 3G.
Brad,
There are many anecdotes of 3G current melting the ammeter and boiling the insulation right off the shunt wire.
The harness in a 45A truck was never meant to pass three times the current.
I never had a 1G in my truck, so never experienced this.
I think my plan needs to be to use an idiot light for both the oil pressure and ammeter since I'll have the aftermarket voltmeter and oil pressure gauges. That way there's no true duplication. I just need to figure out whether to use an idiot light PCB and hardwire the tach, or use a gauge PCB and hardwire the idiot lights.
Last edited by Gary Lewis; Jan 28, 2017 at 06:37 PM.
Reason: Fix stupid mistakes.
Put an LED in the oil pressure idiot light and tie the negative side to the bottom side of the oil pressure switch shown below - perhaps at C143. And tie the positive site to a 12v source. With the engine off or low oil pressure the relay's coil will pull enough current to light the LED w/o pulling the relay in. But with the engine running and good oil pressure the switch will be closed and both sides of the LED will be at 12v so the LED will be out.
Tie the choke's power to the fuel pump relay so the choke is only heated when the engine is running.
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But, isn't a vacuum gauge on a 460 pretty much like an ammeter? 
