Ammeter doesn’t hold charge

[RyanB]

A few nights ago I was flying a cross-country and the ammeter began to show a discharge. Ended up making it home on battery power just fine.

The mechanic on field installed a new alternator + hardware. When it was finished I went to start it and upon flicking the ALT on, the ammeter showed a strong charging indication and then it started declining to basically zero within a few seconds and holds there or maybe just ever so slightly above.

My question is, why would it show a stronger charge upon turning the ALT on, then quickly decline and remain at zero or slightly above? As I understand it, the ammeter is supposed to read zero under normal conditions, but shouldn’t it show a steady charge?

 

[Capt. Geoffrey Thorpe]

Battery was low and it took a lot of current until it charged up - current then tapered off.

Current flow into a fully charged battery is low enough to not really show up on the typically numb aircraft ammeter.

 

[RyanB]

Battery was low and it took a lot of current until it charged up - current then tapered off.

Current flow into a fully charged battery is low enough to not really show up on the typically numb aircraft ammeter.

Makes sense, thanks!

So as long as it’s not indicating a discharge, a zero reading is okay?

 

[Gary Ward]

A few nights ago I was flying a cross-country and the ammeter began to show a discharge. Ended up making it home on battery power just fine.

The mechanic on field installed a new alternator + hardware. When it was finished I went to start it and upon flicking the ALT on, the ammeter showed a strong charging indication and then it started declining to basically zero within a few seconds and holds there or maybe just ever so slightly above.

My question is, why would it show a stronger charge upon turning the ALT on, then quickly decline and remain at zero or slightly above? As I understand it, the ammeter is supposed to read zero under normal conditions, but shouldn’t it show a steady charge?

I guess you didn't learn to drive in a older car with a amp meter?

What your describing sounds normal to me.

 

[RyanB]

I guess you didn't learn to drive in a older car with a amp meter?

What your describing sounds normal to me.

Nope I didn’t. I suppose I figured it should show a steady charge of some 13.5 or so.

 

[Bill]

Ammeter will show you a problem before the voltage gauge shows low voltage. If the ammeter ever swings into the negative, shed electrical load and find a place to land.

 

[RyanB]

If the ammeter ever swings into the negative, shed electrical load and find a place to land.

Yeah for sure. Sunday night I was between here and Marietta when the alternator decided to puke. Had a pretty hefty discharge going on but felt close enough to continue back to base. Of course I figure if it’s going to fail, it’ll be at night when it’s under the heaviest load.

 

[Bill]

Yeah for sure. Sunday night I was between here and Marietta when the alternator decided to puke. Had a pretty hefty discharge going on but felt close enough to continue back to base. Of course I figure if it’s going to fail, it’ll be at night when it’s under the heaviest load.

My alternator out was at night, and the lights went out on short final.

 

[RyanB]

My alternator out was at night, and the lights went out on short final.

Eek!

 

[Capt. Geoffrey Thorpe]

So as long as it’s not indicating a discharge, a zero reading is okay?

Yup.

 

[Bill]

Eek!

The zots did last long enough to get to the diversion airport, get the gear down without having to use the emergency gear extension, and got the PCL lit up. The battery just didn't quite make it to touchdown.

 

[Bell206]

Nope I didn’t. I suppose I figured it should show a steady charge of some 13.5 or so.

Perhaps when it catches up on the battery load turn on your lights, etc and check to see if the meter reacts.

 

[Bill]

Perhaps when it catches up on the battery load turn on your lights, etc and check to see if the meter reacts.

That is part of my runup, kick on the pitot heat, watch the ammeter momentarily dip and then rise back to ~0.

 

[Dan Thomas]

My alternator out was at night, and the lights went out on short final.

This is the reason the aircraft manufacturers have a 500-hur alternator brush inspection in their inspection checksheets. It seems that most owners are running them (and vacuum pumps and magnetos) to failure, and failures they will get.

 

[Bill]

This is the reason the aircraft manufacturers have a 500-hur alternator brush inspection in their inspection checksheets. It seems that most owners are running them (and vacuum pumps and magnetos) to failure, and failures they will get.

While that can certainly happen, this one was a new alternator where the cable out of the alternator had a bad crimp at the terminal lug. The fixing shop said the installing shop did a bad job on the crimp.

 

[Jim K]

Hang on guys, @RyanB has a Piper. Piper wired the ammeter to display the output of the alternator, not the battery. A Piper will never show a negative reading. If the ammeter reads zero you're either using no electricity, or the alternator has ceased operating. The check is to switch the pitot heat on and make sure the ammeter reading increases. In our archer, the avionics only draw a couple amps, so a reading near zero is not unusual.

 

[Dana]

Nope I didn’t. I suppose I figured it should show a steady charge of some 13.5 or so.

13.5 is the voltage the alternator is putting out, which should be essentially constant. An ammeter measures the current actually going into (or out of) the battery, which varies with the state of charge.

 

[idahoflier]

Hang on guys, @RyanB has a Piper. Piper wired the ammeter to display the output of the alternator, not the battery. A Piper will never show a negative reading. If the ammeter reads zero you're either using no electricity, or the alternator has ceased operating. The check is to switch the pitot heat on and make sure the ammeter reading increases. In our archer, the avionics only draw a couple amps, so a reading near zero is not unusual.

True, if we're talking about a loadmeter and not an ammeter...

 

[RyanB]

13.5 is the voltage the alternator is putting out, which should be essentially constant. An ammeter measures the current actually going into (or out of) the battery, which varies with the state of charge.

Ah, thanks for the clarification!

 

[NealRomeoGolf]

This is the reason the aircraft manufacturers have a 500-hur alternator brush inspection in their inspection checksheets. It seems that most owners are running them (and vacuum pumps and magnetos) to failure, and failures they will get.

Or some of us proactively change theirs and the redone one they get fails in 50 hours. Sigh.

 

[Dan Thomas]

Hang on guys, @RyanB has a Piper. Piper wired the ammeter to display the output of the alternator, not the battery. A Piper will never show a negative reading. If the ammeter reads zero you're either using no electricity, or the alternator has ceased operating. The check is to switch the pitot heat on and make sure the ammeter reading increases. In our archer, the avionics only draw a couple amps, so a reading near zero is not unusual.

I believe Ryan has an Archer, and starting with serial number 28-8390001 they had ammeters instead of loadmeters. Ryan said his ammeter showed a discharge. Must be an ammeter.

 

[Dan Thomas]

Or some of us proactively change theirs and the redone one they get fails in 50 hours. Sigh.

Yes, there are some places that can't get it right. Kelly's alternators were horrible for years, maybe still are (now Hartzell). They couldn't seem to understand that the rear alternator bearing needs very little grease. They'd fill the thing and it would squeeze out when the shaft went in, and get thrown all over the brushes and slip rings and fail the alternator. I did many, many alternator internal inspections and never had one fail.

 

[NealRomeoGolf]

Yes, there are some places that can't get it right. Kelly's alternators were horrible for years, maybe still are (now Hartzell). They couldn't seem to understand that the rear alternator bearing needs very little grease. They'd fill the thing and it would squeeze out when the shaft went in, and get thrown all over the brushes and slip rings and fail the alternator. I did many, many alternator internal inspections and never had one fail.

Mine was done by Falcon. Now mine is a Hartzell so I hope it lasts longer. Don't get me started on the crap warranty that Spruce sells with them. Grumble, grumble.

 

[Jim K]

I believe Ryan has an Archer, and starting with serial number 28-8390001 they had ammeters instead of loadmeters. Ryan said his ammeter showed a discharge. Must be an ammeter.

From the "what do you fly" thread:

1963 PA28-180

Also, the club archer I'm familiar with has a load meter; it's a '98. I THINK the POH refers to it as an "ammeter", but I'd have to check.

 

[Jim K]

Yep, they call it an "ammeter"

 

[RyanB]

I believe Ryan has an Archer, and starting with serial number 28-8390001 they had ammeters instead of loadmeters. Ryan said his ammeter showed a discharge. Must be an ammeter.

That is usually the airplane in question. In this case, it’s a 1963 Cherokee 180.

 

[Der Fliegermeister]

Any attention paid to the voltage regulator yet?

 

[Domenick]

Ammeter vs. Load Meter: https://gsmis.org/load-meter-vs-ammeter/

A typical ammeter features a pointing needle initially sitting the value Zero (in the center). It also features negative numbers on the left and positive numbers on the right.

When the needle points to a negative number, it tells you that more electricity is leaving out of the battery that it’s getting in. If it points to a positive number, it means the battery is charging (i.e., more electricity is getting into the battery that it’s being used).

A loadmeter refers to a current meter used in the electrical systems of aircrafts to indicate the amount of current being produced by the generator or alternator. In other words, a loadmeter shows the load (in amperes) being placed on the alternator by all the plane electrical components, including the battery. ...

A typical loadmeter has a scale beginning with zero. Its needle moves to reflect the total percentage of load being placed by electrical components on the electrical system’s generating capacity.

 

[Ed Haywood]

Loadmeter vs Ammeter should be obvious from looking at the scale ... Loadmeter does not have a negative range:



Indications suggesting problems should be addressed in the emergency procedures section of the AFM or POH.

To the OPs question, yes perfectly correct. One of my personal starting checklist items is to watch my Ammeter do exactly that. I learned this the hard way after an in-flight Ammeter failure at night left me trying to get enough power to turn on PCL at my landing site. After that, I put more effort into understanding my electrical system.

Analog ammeters can be tough to read because the scale is so large. Us old guys gotta squint hard to tell the difference between zero and plus/minus 2 amps.

I'm going to install a Voltmeter next to my Ammeter. I think the 2 together make it easier to monitor and troubleshoot the system.

 

[kshaw]

If the battery was seriously discharged, I would test it for any degradation.

 

[Skip Miller]

@Ed Haywood

Loadmeter vs Ammeter should be obvious from looking at the scale ... Loadmeter does not have a negative range:

View attachment 102369

This is not universally true. I was crew on a Hatteras yacht that had a load meter setup except the indicators were +60 amps/-60 amps meters, which never showed negative numbers because they were functioning as load meters. -Skip

 

[Timbeck2]

I'm going to install a Voltmeter next to my Ammeter. I think the 2 together make it easier to monitor and troubleshoot the system.

I got rid of the ammeter and installed this in it's place. Much mo bettah.

 

[Bill]

I'm going to install a Voltmeter next to my Ammeter. I think the 2 together make it easier to monitor and troubleshoot the system.

We have both in our plane, but the ammeter is on the far left side of the panel and the volt meter is on the far right lol.