Intermittent amperage spike causing engine aural warning
- Thread starter gras747
- Start date
airguy
Well-Known Member
Might not be the shunt causing the problem. The alternator could be sensing a "low" voltage on the system and trying to put out maximum effort to bring the voltage up - is your alternator internally or externally regulated?
There is an external VR that I replaced that seems to have fixed the generator light that was flickering on at low RPM's. But the intermittent amperage spike seems to be unrelated. I believe the redline on the ammeter is minus 22 because it flashes for 2 or 3 seconds, enough time to see it before it goes back to the normal range.
jakej
Well-Known Member
Maybe you have too many electrics on (too much 'load') when at low rpm? Some aircraft systems do not output enough power to overcome the 'loads' 
The anomely does not occur at low RPM. It only happens inflight and just for a few seconds. The ammeter drops to the bottom of the scale and hits the red line (approx. -22 amps), then sets off the engine alarm which can be silenced with the silence button that pops up. Within 2 or 3 seconds after the alarm goes off, whether you silence it or not, the amps reading returns to normal and the warning goes away. Catastrohy averted. It does get your attention. What the...
Marc_J._Zeitlin
Active Member
So in order to determine what might be going on, the first question to ask is "What is the Ammeter Measuring"? There are usually three possibilities:
- Alternator Output
- Bus Current Usage
- Battery Current In/Out (sans starter current)
Personally, I'm partial to setting up an ammeter for configuration (3), but most aircraft are setup for (1) or (2).
airguy
Well-Known Member
The fact that it only happens in flight points to vibration as a root cause - likely to be a loose connection somewhere. Pull a set of user data and go look at the reading for the ammeter in there, see if that gives you any kind of clue.
It could be a false indication (like a connection to the shunt, or in the EMS) or it could be a real short somewhere that is pulling a lot of current - does your voltage stay level/steady during the event?
It could be a false indication (like a connection to the shunt, or in the EMS) or it could be a real short somewhere that is pulling a lot of current - does your voltage stay level/steady during the event?
I've just flown again with no issues after thoroughly buffing the contacts on the shunt and re-applying the DeoxIT liquid. Your question of what the ammeter is actually measuring puzzles me and so far I don't have access to a Flight Design CTLS schematic. I suspect that it is showing bus current usage because the normal reading is a minus 8 or 9 amps.
Marc_J._Zeitlin
Active Member
You didn't say how often this happens or how regularly, but if after cleaning/buffing it stopped happening, then you may have found the root cause.
Well, if it was alternator output, that would USUALLY show up as a positive number (but not always - depends completely on configuration). If it was battery current, then it would (when the battery has recharged after starting) show up as 0 - 1A, as it would be only trickle charging the battery. So you're PROBABLY correct that it's showing your bus usage (although I'd reconfigure it to show it as a positive #, but that's just me).
Do you know how to re-configure for a positive reading? That makes more sense to me.
Marc_J._Zeitlin
Active Member
The easiest way it to swap the two sensor leads on the shunt. Assuming you're reading BUS usage, you can't ever get current coming OUT of the bus, so the polarity can't ever change.