amp gauge behavior

[Moriarty]

I mentioned in another thread that I noticed some odd behavior with my amp gauge. I took a video here:

https://drive.google.com/file/d/1wVp...w?usp=drivesdk

Right at the beginning, you can see the meter goes from zero to pegged (+) directly proportional to rpm.

I've got a volt meter attached to the battery to see its charging and cut to that shortly after, but my wires weren't long enough to capture both in a single shot. Didn't see anything particularly odd there. I had put the battery on the charger for a bit before capturing this just to make sure the battery wasn't just low.

Then after turning off the engine, it occurred to me to hold the rpms for a bit to see if things settled down. However, this time when I went to test everything seemed to be working as expected.

Does this seem like a short somewhere? Voltage regulator going bad?

I guess I need to get some longer wires for the volt meter so I can see them both at the same time.

Side question: My amp gauge reads "Smith" but this is clearly just a sticker on the face. Any idea what the story is there?

EDIT: Oh.. also no longer centers on zero. I wonder if that's from pegging. I'm pretty sure it used to be properly centered, but never paid much attention. I think I would have remembered if it had been off though previously.

And yes, I should just do the volt meter modification. Before doing that, I'd like to sort out whatever else is going on to cause this.

[patrickt]

Well I saw it. Your amp gauge says you're pushing 60 amps and your volts gauge says you're pushing 14.6v at the max (which is ok). If I had to bet, I'd say your amp gauge is just plain wrong. I would test it by putting an inductive amp meter around the positive cable at the battery and have a helper read out your amp readings from that gauge while you watch the Smiths. If the ammeter has a normal reading (25 amps or less, I'd say) then put the ammeter on the charging wire at the alternator and repeat the test. If you get the same result while the Smiths is saying 60, then the Smiths meter is faulty and should be replaced. But if either of the two tests with the inductive ammeter show 60 amps, then we'll take a step back and think.

[patrickt]

And the reason why you have to put the ammeter on the wire coming out of the alternator (unless the ammeter reads 60+ amps right at the battery, then you know something is wrong) is because there's the slim chance that you have a transient short to ground on the wire going to the battery on the battery side of the Smiths. If you put the ammeter on the wire to the battery after that short, you won't catch the high reading because the current is running straight to ground and not to the battery. But you will catch the reading if you put the ammeter at the wire right at the alternator. Now, I really don't think you have a transient fault because 14.6v at, say, 40 amps, is almost 600 watts. That's a lot of heat (half of your typical blow drier, in fact). I think you'd see smoke, and it would probably stay shorting, not just go away. But, you have to check.

[Gaz64]

Originally Posted by Moriarty

I mentioned in another thread that I noticed some odd behavior with my amp gauge. I took a video here:

https://drive.google.com/file/d/1wVp...w?usp=drivesdk

Right at the beginning, you can see the meter goes from zero to pegged (+) directly proportional to rpm.

I've got a volt meter attached to the battery to see its charging and cut to that shortly after, but my wires weren't long enough to capture both in a single shot. Didn't see anything particularly odd there. I had put the battery on the charger for a bit before capturing this just to make sure the battery wasn't just low.

Then after turning off the engine, it occurred to me to hold the rpms for a bit to see if things settled down. However, this time when I went to test everything seemed to be working as expected.

Does this seem like a short somewhere? Voltage regulator going bad?

I guess I need to get some longer wires for the volt meter so I can see them both at the same time.

Side question: My amp gauge reads "Smith" but this is clearly just a sticker on the face. Any idea what the story is there?

EDIT: Oh.. also no longer centers on zero. I wonder if that's from pegging. I'm pretty sure it used to be properly centered, but never paid much attention. I think I would have remembered if it had been off though previously.

And yes, I should just do the volt meter modification. Before doing that, I'd like to sort out whatever else is going on to cause this.

Certainly an issue, hopefully not a partial to ground. The gauge looks faulty to me. It also does say "Smiths", but looks like a sticker.

[Anthony]

Well, what is the amperage rating of your alternator?

[patrickt]

... and you can't rely on the fact that your volt meter never goes over 14.6 volts to mean that your system does not have a short. For example, my little Gen 1 AC Delco alternator puts out a whopping 60 amps at its peak. If I had a resistive short of around 45 amps worth, my alternator could probably serve that up, along with an extra 15 amps to keep the car running normally, and my voltage readings would still be around 14 volts or so. Now, that example, and your unlikely, but possible, example of a resistive short that has just the right amount of resistance, and doesn't burn itself up, but still produces the watts to create just the right load, is unlikely. It's more likely that the crappy Smiths gauge is just reading wrong. But you have to check. You have to honestly, truthfully, and authoritatively know exactly how much current is coming out of your alternator and where it's going. This is not a tough case -- you just have to take the measurements in a couple of places and you'll know for sure. But you really do have to measure amperage, not voltage.

[DanEC]

Have you checked all you connection at the alternator, alt gage, starter relay, etc to be sure they are good and snug tight? I bring this up only because I somehow managed to catch the ring terminal on the big red wire to the alternator on the lip of the insulator when I made my connection. The plastic insulator eventually gave way leaving the ring connector on the post but very loose. I noticed my gage starting to act jumpy. I looked around under the hood and spotted that a couple inches of the red wires insulation was melted along with the insulator on the case post and in general it looked like an arc welder had been struck in there a few times. I had to get a new red wire from ERA and open up the harness to replace it and re-wrap it. Also needed a new alternator as the insulation around the case post was all melted.

Very long shot for you to find something similar but thought I would mention it.

[Moriarty]

Okay, $80 later and a trip to Lowes and I'm now a proud new owner of a DC inductive amp meter (the cheaper units only measured AC).

I'm seeing similar behavior at both the battery and alternator.
https://drive.google.com/file/d/1A5S...w?usp=drivesdk

I ran the lights for a couple minutes to drop the battery voltage first. Amperage runs high and steady until the battery comes back up to ~14.5V, then starts to wiggle (the meter doesn't show this as clearly as the amp gauge). I am seeing about 55A @ 3000 rpm. After the battery charged, I dropped to about 1500 rpm where the meter in the video reads ~40A. This mostly held steady on the dash gauge, though I expect it would start bouncing again if I waited long enough. Didn't want to fry anything though.

So, if I have a 60A alternator, is this expected behavior? Or maybe I have a 100A alt w/ 40A load?

Patrick, above you suggested I should not expect to see more than 25A and your math has me scared a bit. I haven't yet seen any evidence of shorting or smoking.

About a year and a half ago, I did have a short under the dash where some previous owner rewired the amp connection through a lower spec connector which had melted. Bob from ERA sent me a new fat black connector to use in its stead and that's been working well since. I'll have to get a scope under there and see if anything strange is going on.

[ERA 626]

after reading several scary stories about electrical fires in cobras started by running all that current through a gauge with small wire connectors I decided to replace my amp gauge with a volt gauge... Smith starting making volt gauges recently and they are made to order. I just ordered one. I have a BRAND new "lucas" amp gauge if any one wants it... The gauge Moriarty is clearly a knock of with a smith sticker on it. The original 427 cars had LUCAS amp meters. I have a BRAND NEW Lucas for sale...

[patrickt]

Originally Posted by Moriarty

I am seeing about 55A @ 3000 rpm.

I watched the vid, and 55 amps is going somewhere. Let me make sure I understand though that the behavior is the same when measured at the battery and the alternator. If that inductive gauge is clamped right at the positive terminal of the battery cable and it's measuring 55 amps when you rev, then the current is going in to the battery and is not shorting out somewhere upstream. Let's check the easy stuff first. Maybe there's a bad connection on the battery terminals. Take them apart, clean them up, tighten them down good, and repeat the test. If the results are the same, pull the battery out and put a known-to-be-good battery in, maybe from one of your daily drivers, and retest.

[Moriarty]

New battery. Old one was dropping to zero volts on start, while the new one stays above 10V.

I think the inductive multimeter amp readings are behaving as expected now? Spiking up to 35A on startup (too high still?), but settles down to around 20A pretty quickly. Or should that be going to zero after the battery is topped off?

Similar readings at battery and alternator.

Amp gauge in dash is still pegging 60+ while ammeter reads ~35A.
Here's a video capturing both the output of the alternator and the dash gauge (sync'd up the videos the best I could):
https://drive.google.com/file/d/1Re0...w?usp=drivesdk

Occasionally (as captured at the start of this video), when the dash gauge spikes to 60, the multimeter reading drops out. Does this indicate a short somewhere? Or maybe the meter is having trouble reading the poorly smoothed DC current coming out of the alternator? Voltage regulator starting to die?

Seems like I should definitely replace the dash amp gauge. Still not clear if there's another issue here. Thanks for all the help!

[patrickt]

With a fresh battery, it should settle down to close to zero pretty quickly after you start up, unless you really had to crank a lot. Maybe a minute or less of 20 amps is ok. You're not going to be able to spot leaking AC from the alternator unless you have an oscilloscope. But I wouldn't worry about that right now. And if your voltage stays under 14.7 volts, then I wouldn't touch the voltage regulator. Now, I will tell you that my Smiths ammeter, with the engine off, reports -60 amps when I turn on all my fans, and I know for a fact that they're only pulling 34 amps. But my amp gauge doesn't shake like yours. I think you probably just have an amp gauge that is getting a little flaky.

[jhv48]

Faulty voltage regulator?

[patrickt]

Originally Posted by jhv48

Faulty voltage regulator?

No, because you consistently see the correct voltage value (13 to 14.7 volts) when you measure it. Now, if you saw 20 volts on the gauge, that would be a bad voltage regulator, but yours is just fine.

[jhv48]

Faulty voltage regulator?

[strictlypersonl]

I doubt whether anything is wrong. Voltage regulators are built to create maximum charging voltage when they are cold. This one may be slightly on the high side, but it looks like it calms down quickly.
One of the reasons they don't include ammeters on late model cars is they sometimes spook the driver...
The era of the 40A alternator was over in 1968.

[patrickt]

Originally Posted by strictlypersonl

I doubt whether anything is wrong. Voltage regulators are built to create maximum charging voltage when they are cold. This one may be slightly on the high side, but it looks like it calms down quickly.
One of the reasons they don't include ammeters on late model cars is they sometimes spook the driver...
The era of the 40A alternator was over in 1968.

I agree with that.

[tdc]

My 64 pick up always had a jumpy ammeter gauge. I replaced the 56 year old voltage regulator with new and repaired a loose connection at the S terminal. The gauge is now steady and reads normal. I suppose the loose connection might have been the issue.