Bouncing voltage guage at idle

[keymonkey]

I just replaced my guage volt regulator, my alternator and voltage regulator, as well as both vbelts. After the alternator and vbelts I took my 74 out for a test drive and at idle now the voltage dash guage bounces around 0. Never did ot before with just the voltage regulator change. It only happens at idle. Meter reads 14.6v across the battery at idle without variation. At a loss. Brand new alternator.... possibly bad?

 

[DirtDonk]

Hey there keymonkey.
Just to be sure, are you still running the original ammeter, or is it a replacement voltmeter?
You said zero, so I’m assuming an ammeter because it has 60A plus in one direction, 60A negative in the other direction, and zero in the middle.
What does it do when you first fire it up in the morning? Does it rise to about 20 or 30 amps positive for a few moments and then slowly go down to near zero?

And another thing you can do to test is, with everything off, tap the gauge cluster cover and dash in the area with your finger and see if the needle moves on its own.
It may just be an old tired gauge that is bouncing on its own.

 

[spap]

They after market voltmeters to fit our gauge pod do bounce a lot but will show the positive volts

 

[Johnnyb]

If it's an ammeter, it reads charge or load. I take the bouncing around 0 to be a good sign that it's working. After you start it, or run the battery down a little bit with the headlights (not too much! 10-15 min should be good), the ammeter should move to + (charge) for a few minutes while the alternator replenishes the battery.
The problem with the stock ammeter is that it requires a shunt, passing the entire charge (draw) current behind the gauge itself, and limiting the capacity of the alternator or creating a fire hazard.
If it's a voltmeter (I think there are volt meter replacements for the stock ford ammeter, but not sure) it reads system voltage. 12.6 is a nominal (engine off or slow idle) battery full indicator. Most times with the engine running or driving, it should read about 13.6. Anything less than 11.3 and your battery is toast and will never recharge properly.

THX,
-JB

 

[keymonkey]

Hey there keymonkey.
Just to be sure, are you still running the original ammeter, or is it a replacement voltmeter?
You said zero, so I’m assuming an ammeter because it has 60A plus in one direction, 60A negative in the other direction, and zero in the middle.
What does it do when you first fire it up in the morning? Does it rise to about 20 or 30 amps positive for a few moments and then slowly go down to near zero?

And another thing you can do to test is, with everything off, tap the gauge cluster cover and dash in the area with your finger and see if the needle moves on its own.
It may just be an old tired gauge that is bouncing on its own.

Does not wobble when tapped. Jumps up to 20-30 for a second or two on cold start, then settles to zero and is stable. After a mile or so of driving, when sitting at idle the needle bounces around 0.

 

[keymonkey]

Could be the draw off of my aftermarket stereo, but it never read a draw before the new alternator and certainly never bounced.

 

[cldonley]

Could just mean that you have some new parts and are now getting more accurate indications than before. As long as it is bouncing on plus side of zero for an ammeter, you're good. Have you changed any other components? Lights, for isntance?

 

[keymonkey]

Could just mean that you have some new parts and are now getting more accurate indications than before. As long as it is bouncing on plus side of zero for an ammeter, you're good. Have you changed any other components? Lights, for isntance?

It bounces back and forth above and below the 0 like a inconsistent draw for a fraction of a second that the new alternator recharges instantly like a sine wave. The fact that it does not happen immediately on cold start, makes me think it is a faulty part somewhere that hates heat. The order of parts replaced was dash voltage regulator(no bounce), Under hood voltage regulator (no bounce), Alternator and v-belts (bounce at idle). Lots of coincidental things go wrong with these trucks given that mine is almost all original. Perhaps the added voltage of the new higher powered alternator is simply driving the slightly faulty but not shot ammeter to show wacky readings.

 

[cldonley]

It bounces back and forth above and below the 0 like a inconsistent draw for a fraction of a second that the new alternator recharges instantly like a sine wave. The fact that it does not happen immediately on cold start, makes me think it is a faulty part somewhere that hates heat. The order of parts replaced was dash voltage regulator(no bounce), Under hood voltage regulator (no bounce), Alternator and v-belts (bounce at idle). Lots of coincidental things go wrong with these trucks given that mine is almost all original. Perhaps the added voltage of the new higher powered alternator is simply driving the slightly faulty but not shot ammeter to show wacky readings.

That's plausible. Could also be a loose wire, or something providing a pulsating draw, although I can't imagine what that would be. Is the new voltage regulator mechanical or solid state? Could be a slight delay with contact points in a mechanical regulator, but that's just a poke in the dark.

 

[keymonkey]

That's plausible. Could also be a loose wire, or something providing a pulsating draw, although I can't imagine what that would be. Is the new voltage regulator mechanical or solid state? Could be a slight delay with contact points in a mechanical regulator, but that's just a poke in the dark.

All are solid state from Tom's. Frankly after troubleshooting my dead battery issue across all voltage regulators to an alternator that inconsistently charged when warm, causing my yellow top battery to burn out a cell and not charge properly... I might just live with the warm bounce as long as the damn thing fires up every time I turn the key! It does cause an itch in my brain though.

 

[ssray]

I can chip in on ^^^. (cldonley) The old mechanical regulators could have those tendencies. Been years since I messed with one, but we used to clean the contact points or play with spring tension in them. Could be a combination of things. New parts these days aren’t always the quality we used to have.

PS. I see you have solid state!

 

[cldonley]

All are solid state from Tom's. Frankly after troubleshooting my dead battery issue across all voltage regulators to an alternator that inconsistently charged when warm, causing my yellow top battery to burn out a cell and not charge properly... I might just live with the warm bounce as long as the damn thing fires up every time I turn the key! It does cause an itch in my brain though.

I hate those itches. Our airplanes have so many flashing lights and charging capacitors that ammeter dance is pretty normal for me!

 

[keymonkey]

I can chip in on ^^^. (cldonley) The old mechanical regulators could have those tendencies. Been years since I messed with one, but we used to clean the contact points or play with spring tension in them. Could be a combination of things. New parts these days aren’t always the quality we used to have.

PS. I see you have solid state!

Exactly. Original alternator dies after 48 years of reliable service, new alternator causes issue on first start. I'm loathed to swap out any of the parts on this thing for new. 48 year old power steering pump is probably next, but I'm hoping it is so simple it just works forever!

 

[DirtDonk]

Perhaps the added voltage of the new higher powered alternator is simply driving the slightly faulty but not shot ammeter to show wacky readings.

Not sure how that would cause anything, but stranger things have happened with charging systems for sure!
The higher amp rating of the alternator (what was your old one, and what is the new one?) should not change normal charging. Even a 500 amp alternator only puts out as many amps as needed. So if the system calls for 11 amps, that's all that's going through the system.
Is it a different type of alternator altogether? If so, what type and output is it? Still has an external regulator? If so then it's probably 65a or less. Correct?

The instrument regulator has no direct effect on the ammeter since it is on a separate system. Only works with the gas, pressure and temp gauges.
It's possible that it's creating some kind of weirdness on it's own of course, but it's such a low amp draw kind of part I would hardly think it would register on the ammeter.

Paul

 

[DirtDonk]

The problem with the stock ammeter is that it requires a shunt, passing the entire charge (draw) current behind the gauge itself, and limiting the capacity of the alternator or creating a fire hazard.

You might have your terminology mixed. While out alternators are still limited to a certain amp level, it's the wire gauge, not the ammeter itself that limits the capacity.
Our stock ammeters do not use a shunt. They are an inductive type, using an "indirect" reading from the loop on the back that the charge wire passes through.

A shunt is different, where only a small sample of the total current passes through smaller wires out to the instrument. Keeping all the main current under the hood where it belongs. Instead, the shunt type interprets this signal and makes the needle read a (hopefully) accurate recreation of that current flow.

The real fire hazards with regard to ammeter use comes from the very common "direct-reading" type, where the charge wire is attached directly to the back of the gauge. If all ammeters had been of the type our Broncos had, there would likely have been far fewer dash fires in other cars and trucks over the years.
The direct reading type can become a fire waiting to happen right at the gauge itself. While an inductive type like used in Early Broncos cannot cause a fire even if the gauge itself fails. Only a direct failure of the wire under the dash would have that type of effect.

Either of those two types can be a fire hazard however, if something happens to cause your alternator to output it's full capacity for too long, or if you install a too-big alternator and circumstances cause it to put out more current than the 12 feet or so of 10ga wire can handle.
No matter what the cause though, a failure of the charge wire is capable of causing a lot of grief.

Another often overlooked (but luckily rarely a problem) area of hazard is built up resistance in the charge wire. Which means taking care to be sure that all three connectors, including the big inline connector near the ammeter, remain clean, tight and corrosion free for their lives.

Paul

 

[keymonkey]

Not sure how that would cause anything, but stranger things have happened with charging systems for sure!
The higher amp rating of the alternator (what was your old one, and what is the new one?) should not change normal charging. Even a 500 amp alternator only puts out as many amps as needed. So if the system calls for 11 amps, that's all that's going through the system.
Is it a different type of alternator altogether? If so, what type and output is it? Still has an external regulator? If so then it's probably 65a or less. Correct?

The instrument regulator has no direct effect on the ammeter since it is on a separate system. Only works with the gas, pressure and temp gauges.
It's possible that it's creating some kind of weirdness on it's own of course, but it's such a low amp draw kind of part I would hardly think it would register on the ammeter.

Paul

Old one was original so I think it was 60 Amp. The new one is a 74 amp external regulator from Summit PWM-7078.

 

[cldonley]

75 amps has the potential to smoke your ammeter. Shouldn't, unless you have a bunch of high amp stuff operating simultaneously. Just be aware. Can also be an issue for your 48 year old wiring.

 

[DirtDonk]

Nice. Back when I upgraded mine there weren't many stock size (small 1G) versions over 60a, and I was always having trouble with the bearings wearing out first anyway.
So I went to a larger (large 1G) 70a factory replacement instead. Would have gone with the one you did if I'd seen it probably, but glad i went to the large case 1G anyway.

All the more reason however, to double/triple-check your stock Black and Black w/yellow charge wire through it's entire run.
Make sure the connection at the back of the alternator is clean, rust free and tight. Make especially certain that the connection at the starter relay is clean, rust free and tight. Then check under the dash and make sure that the "bullet" style connector near the ammeter is good and tight.
Might even consider separating the two halves to see if the wire and the contacts are in good shape still. If even a tiny bit rusty, clean them up before putting them back together. Maybe even us a light layer of di-electric or electric grease to make sure they stay rust-free.
But I would only bother with the grease if you find rust to begin with. The contacts were originally galvanized or plated with something, so it takes a bit of wear and tear to bugger them up.
But it still happens!

Paul

 

[DirtDonk]

75 amps has the potential to smoke your ammeter.

What exactly would happen with this inductive meter? Can the needle be forced too far? There really isn't any electrical current passing through the gauge, so I'm wondering if it is even possible for the ammeter to burn up.
Other, direct-reading types, yes I'm sure that would happen. But one of ours? Not sure.
I'm not a gauge specialist by any means, but that's what it seems like to me anyway. No current, no electrical connection, no way for it to smoke.
Or am I not understanding an inductive meter correctly?

Curious because I've always imagined running an up-sized wire of about 8ga or so from the firewall and through the gauge. Just to keep an ammeter and still handle the current of a 3G without burning up the wiring.
Wasn't worried about the gauge itself, but as you pointed out, the 40-50+ year old wiring is always a question mark.

As another point, the folks at Centech rate their charge wire for 100a maximum. It's the same 10ga wiring, but it's done slightly different and obviously using new, high-quality wire as well.
I would not try to put 100a through a stock setup, but it makes me feel better knowing the Centech can handle the 100a load if needed.

Paul

 

[cldonley]

What exactly would happen with this inductive meter? Can the needle be forced too far? There really isn't any electrical current passing through the gauge, so I'm wondering if it is even possible for the ammeter to burn up.
Other, direct-reading types, yes I'm sure that would happen. But one of ours? Not sure.
I'm not a gauge specialist by any means, but that's what it seems like to me anyway. No current, no electrical connection, no way for it to smoke.
Or am I not understanding an inductive meter correctly?

Curious because I've always imagined running an up-sized wire of about 8ga or so from the firewall and through the gauge. Just to keep an ammeter and still handle the current of a 3G without burning up the wiring.
Wasn't worried about the gauge itself, but as you pointed out, the 40-50+ year old wiring is always a question mark.

As another point, the folks at Centech rate their charge wire for 100a maximum. It's the same 10ga wiring, but it's done slightly different and obviously using new, high-quality wire as well.
I would not try to put 100a through a stock setup, but it makes me feel better knowing the Centech can handle the 100a load if needed.

Paul

First, I didn’t see this for a while after you wrote it, then, I started to question myself, because I’ve seen ammeters fry before but had to reassess the why of it. So I did a bit of research and here’s what I think I think.

Back in the day in airplanes we often had direct reading ammeters mounted In the instrument panel (in line, from generator or alternator to main bus), mostly Piper aircraft as I recall, 50s and early 60s models. These could fry generally due to a runaway alternator or generator (voltage regulator problems) or old, faulty wiring. Piper built aircraft with aluminum wire for a period of time to save weight, which led to an Airworthiness Directive, which is like a vehicle recall only It’s mandatory to comply with or your airplane. Is grounded (or you get fined and lose your license for flying it) You can’t even buy those ammeters any more. If you need to replace one in those old airplanes you’ll need an FAA approved substitute. These airplanes were built when we were sending fuel through the cockpit to operate mechanical fuel pressure and flow rate meters, and oil for oil pressure and temperature.

I think an induction ammeter, if it were to fry, would be due to fault within the ammeter rather than due to an over current situation.