3
$\begingroup$

I have a T206H and The POH says:

Current indication (AMPS) for both the main and standby batteries is provided at the bottom of the EIS bar (along the left margin of the MFD or PFD), labeled M BATT S. Main battery current is numerically displayed below the M. Main battery current greater than -1.5 amps is shown in white. Standby battery current is displayed numerically below the S. A positive current value (shown in white) indicates that the battery is charging. A negative current value (shown in amber) indicates that the battery is discharging. In the event the alternator is not functioning or the electrical load exceeds the output of the alternator, the main battery ammeter indicates the main battery discharge rate.

The part that confuses me is the one that says:

Main battery current greater than -1.5 amps is shown in white.

Does that means that when the number is negative but greater than -1.5 it is OK, because it is in white?

And after 40 minutes of flight in normal daytime operations I have a -1.0 in the M BATT amps but the M BUS volts remain 28.3. What does this mean?

$\endgroup$
3
$\begingroup$

You've actually answered your own question back there:

A negative current value (shown in amber) indicates that the battery is discharging. In the event the alternator is not functioning or the electrical load exceeds the output of the alternator, the main battery ammeter indicates the main battery discharge rate

The 28.3 Volts reading is the electric energy charge supplied by the aircraft alternator (60-Amp alternator is standard and a 95-amp one is optional) through the main bus, whereas the M amp reading is what's happening to the main battery. In the situation you've described, you've got so many electrically-powered systems running, that the alternator, though operating normally, is unable to supply them all, so additional power is drawn from the battery.

The 206 PIM states that the Main battery Ammeter is color-coded white for values greater than -1.5 Amps, meaning that Cessna is not concerned with battery drains of 1.5 Amps or less (i.e. readings between -1.5 and 0). If the discharge rate is greater than 1.5 Amps (reading lower than -1.5), then the reading will be color-coded yellow. See below for an example of this.

enter image description here

$\endgroup$
  • $\begingroup$ Ok. I understand that the reading of the ammeter between 0 and -1.5 is considered by cessna of no concer if i am using much more load than The alternator output. But the thing is that I was not. It was day time, no light on but the bacon, no AP, dead-reckoning flight, and still -1. $\endgroup$ – Mark David Maduro Guerra Jun 26 '15 at 1:04
  • $\begingroup$ Ok. I understand that the reading of the ammeter between 0 and -1.5 is considered by cessna of no concer if i am using much more load than The alternator output. But the thing is that I was not. It was day time, no light on but the bacon, no AP, dead-reckoning flight, and still -1.0 on the M Batt Amps. I have checked the lamar MCU, I try a new battery, I checked the alternator but still -1.0. What else do you suggest? $\endgroup$ – Mark David Maduro Guerra Jun 26 '15 at 1:13
  • $\begingroup$ @MarkDavidMaduroGuerra - that sounds like a tricky one; from what you've described, the alternator should be more than capable of handling the load, but, for whatever reason, the battery was still discharging. For electrical gremlins like that, I'd take her to an A&P for a look. Things that might cause something like to happen could include an alternator that's no longer up to scratch, a battery that might not be adequately isolated and is finding a pathway to drain to somewhere, maybe even a faulty sensor or software glitch giving erroneous readings in the cockpit. $\endgroup$ – habu Jun 26 '15 at 1:35
  • $\begingroup$ Thanks habu. I will take Her to a Cessna servises center. This is draving me crazy. I am suspecting the amperage sensor. I will conecte a hand tester to compare its reading and the PFD ammeter reading. $\endgroup$ – Mark David Maduro Guerra Jun 26 '15 at 3:38
  • $\begingroup$ @MarkDavidMaduroGuerra - good luck, and, when you find out, come back here and let us know what it was. $\endgroup$ – habu Jun 26 '15 at 3:44

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.