Ammeters and Airworthiness

[FlyingAggie]

Can anyone tell me if a non-operational ammeter would be considered an airworthiness issue and cause the a/c to "fail" its annual inspection?  The ammeter in the engine gage cluster is not working in the a/c I am considering buying.  This in in a 231 with gages at the top of the left side panel.  How difficult is it to replace the gage cluster?  Does the glare shield lift off, giving easy access to the gage cluster?

Alan

[Cruiser]

In addition to the requirements of FAR Part 91.205, look very carefully at the Limitations section of the POH. If anything in that section requires the measurement of amps then it is considered a requirement for airworthiness unless otherwise stated there. (i.e. the following are not required but......) If it is NOT listed in the POH then it is not a limitation for flight.

[jlunseth]

I am not going to chime in on the airworthiness issue, but rather on the need for a working ammeter in a 231.  The 231 has a mediocre alternator system design.  It is a direct drive, and the gearing of the drive unit is such that no matter what size alternator you have, the charging system does not work very well at low engine speeds (such as at idle or during taxi).  The stock alternator is a 70 amp, and there is or was an 80 amp kit available, but the A&P's that know Mooneys will tell you the alternator size is irrelevant to this issue.  The stock strobes and landing lights have a big draw.  So night pattern operations where the engine is operating at idle for extended periods and these lights are on can lead to a discharged battery.  The annunciator panel will tell you that the battery is discharging, but I would want a working ammeter if I were you, and I would also want a voltmeter.  There are aftermarket units that are switchable between amps and volts.  Unless you have something installed above the strip of engine gauges, they are accessible with the glare shield off.  Maybe not convenient, but there is nothing there blocking access. 

A good alternate is an engine analyzer that reads amps and/or volts.  Must be STC'd to be primary though, to satisfy airworthiness concerns.  For example, an EDM 700 is not STC'd as primary, the 711 is STC'd. 

[hansel]

I agree with jlunseth that you should have a working ammeter regardless of airworthiness concerns. If you're not ready to shell out the cost of a full blown engine monitor (which is a great investment btw), you could opt for a stand alone, STC'd, primary voltmeter/ammeter combo like this from Aerospace logic... 

http://www.200series.com/site/dbload.asp?PageId=PROD&Level=5&Inst=VA-100-K60

Fits in one of your 2.25" diameter displays to the left of your primary instruments (if you have the space). Also, installation of an ammeter should be a piece of cake for your mechanic since there's no complex probes/wiring that needs to be completed. Mine was less than $500 out the door (with instrument and labor).

[Immelman]

You should aso check the Mooney TCDS, which for some models specifies required equiptment in addition to 91.205 requirements. This varies by model.

And I second having an ammeter, or at least some other means of showing a discharge. I have an EI combination ammeter/volt meter which was a legal replacement for the 6-pack cluster gauge ammeter. It has a yellow light that comes on when current is flowing out of the battery.

Also, my engine monitor (jpi 700) can be set up to alarm at high and low voltages.. so I put 12.8 (or something) as the low voltage limit so that it will alarm me if the alternator drops off line and I am running on battery voltage.

[FlyingAggie]

jlunseth,

The aircraft is actually a 231 that has undergone the Trophy 262 conversion, so it has two alternators.  It also equipped with a JPI 700.  The seller says he feels comfortable with flying with the volatge readings from the JPI as well as the panel docked GPSmap. 

The aircraft passed it's last annual apparently without a problem, but I would like a working ammeter.  A voltmeter will only tell you that you have a problem when the lights begin to dim, but the ammeter will give you more insight into the health of the electric system.

I take it the only option for fixing the ammeter is to have the entire gauge cluster overhauled because there is no OEM source for the unit?   Also it must be is pretty expensive.  I noticed that Craig McGregor (mooniac58) removed the cluster entirely and installed an EDM930 and another 262 owner has offered to sell me his gauge cluster because he did the same thing when installed a Xerion Auracle.  Gee, I haven't even bought the plane yet and I am already finding things to upgrade!!!!

Has anyone had their gauge cluster overhauled, if so how much did it cost and who does it?

Alan

Quote: jlunseth

I am not going to chime in on the airworthiness issue, but rather on the need for a working ammeter in a 231.  The 231 has a mediocre alternator system design.  It is a direct drive, and the gearing of the drive unit is such that no matter what size alternator you have, the charging system does not work very well at low engine speeds (such as at idle or during taxi).  The stock alternator is a 70 amp, and there is or was an 80 amp kit available, but the A&P's that know Mooneys will tell you the alternator size is irrelevant to this issue.  The stock strobes and landing lights have a big draw.  So night pattern operations where the engine is operating at idle for extended periods and these lights are on can lead to a discharged battery.  The annunciator panel will tell you that the battery is discharging, but I would want a working ammeter if I were you, and I would also want a voltmeter.  There are aftermarket units that are switchable between amps and volts.  Unless you have something installed above the strip of engine gauges, they are accessible with the glare shield off.  Maybe not convenient, but there is nothing there blocking access. 

A good alternate is an engine analyzer that reads amps and/or volts.  Must be STC'd to be primary though, to satisfy airworthiness concerns.  For example, an EDM 700 is not STC'd as primary, the 711 is STC'd. 

[FlyingAggie]

Eric,

The a/c is equipped with a JPI700.

The Aerospace Logic gauge  is a nice looking instrument.  The a/c has separate OAT gauge and clock on the left side of the panel, so I could replace those with this dual OAT/Clock from the same vendor (http://www.200series.com/site/dbload.asp?PageId=PROD&Level=5&Inst=CT1-F) freeing up a spot to put the dual volt/amp meter.  So that would be a 1 amu solution.

Alan

Quote: hansel

I agree with jlunseth that you should have a working ammeter regardless of airworthiness concerns. If you're not ready to shell out the cost of a full blown engine monitor (which is a great investment btw), you could opt for a stand alone, STC'd, primary voltmeter/ammeter combo like this from Aerospace logic... 

http://www.200series.com/site/dbload.asp?PageId=PROD&Level=5&Inst=VA-100-K60

Fits in one of your 2.25" diameter displays to the left of your primary instruments (if you have the space). Also, installation of an ammeter should be a piece of cake for your mechanic since there's no complex probes/wiring that needs to be completed. Mine was less than $500 out the door (with instrument and labor).

[N9937c]

you might check the 2 very small fuses that are on the bottom of the curcuit breaker panel

they are under  a little thimble shaped cap. made by LITTLEFUSE and you will fell like you have been screwed when you have to replace them. there are 2 of them one + and one-.

[danb35]

Quote: FlyingAggie

[FlyingAggie]

Quote: N9937c

you might check the 2 very small fuses that are on the bottom of the curcuit breaker panel

they are under  a little thimble shaped cap. made by LITTLEFUSE and you will fell like you have been screwed when you have to replace them. there are 2 of them one + and one-.

[FlyingAggie]

Quote: danb35

[danb35]

Quote: FlyingAggie

The additonal insight comes from knowing the direction of current into the battery in addition to knowing the bus voltage.