Low and High current alarms

[Dave Ceddia]

I recently bought a 2008 CTLS and flew it home from Oregon to NH. During the first ~2.5hr leg, I got a "low current" alarm a couple times on the EMS. It lasted for a few seconds each time, along with a blinking Engine light, and then went away. I spoke to Roger about it, and he suggested tightening the battery terminals, which I did - and that appeared to fix it! I flew the rest of the way without incident. It was a wonderful trip.

Yesterday, the problem came back with a vengeance. Now it's fluctuating between a low AND a high current alarm. The Amps reading will spike up to +24 or drop to -15, and it's much more frequent. Meanwhile the voltage is pretty steady around 13.1 to 13.4. Here's a ~1min video of it happening. This is right after startup. (after this, I tried turning avionics master off, and that didn't change the fluctuations)

I checked the battery terminals again, and tightening had no effect this time.

I checked the connections going into the voltage regulator, just pulling and pushing on those wires, and they all seemed solid. The ground cable that goes to the VR also seemed solid. I didn't pull that big connector, just tugged on the wires with it in place, and made sure the big connector was seated well.

With the engine running, I pulled the Generator breaker, and in that state the amperage fluctuation disappeared. I think that makes sense since it was just drawing down the battery at that point... maybe that helps rule something out but I'm not sure what!

I'm also not sure if the battery could be the culprit? It has 25/Mar/11 stamped on it so it's over 12 years old at this point. The plane came with a spare battery which also has 25/Mar/11 stamped on it, but I'm tempted to try swapping it out just to see if that makes a difference.

So my main theories are the battery, some loose connection somewhere, or the voltage regulator. Does anyone have any suggestions for what to check next?

[Anticept]

Turn off the alarms on the Ammeter. Long story short: rotax engines are so electrically noisy that these dynon units have trouble compensating. They were designed before Rotax rocketed in popularity; the first firmware revisions didn't even have a rotax option.

Make sure the software is updated on your unit, that you have a good battery, that your capacitor in your electrical system is good (or replace with the bigger kemet 100k ALS40A104KF025), clean terminals.

[Tom Baker]

Alarms or not that is a pretty big swing, and not normal. With that kind of age on the battery, my recommendation would get a new one regardless. If that doesn't fix it clean all of the plugs and connectors on the voltage regulator, including the ground. If there is still an issue then the regulator. I have had to replace several regulators around that age. 

Another regulator tell tale sign is the generator light being on at low RPM's during warm up.

[Dave Ceddia]

That seems like a good plan, I’ll start with the battery. I haven’t seen the generator light come on at all, and despite being a 2008 it only has about 310 hours on it, but I don’t know if the regulator failing would be wear-related or age-related.

[Dave Ceddia]

Just wanted to drop an update here. I replaced the battery with a new PC310 and ran the engine on the ground for about 5 minutes, and didn't see any wild current swings. And today I took it around the pattern a few times, and it still looked good. No more low or high alarms, and they were happening a few per minute before.

I do still see the current swinging as wide as -8 to +8 or so, but that seems about in line with what it was doing back before the low/high alarms started happening. I imagine it's charging the battery, letting it discharge for a bit, then charging again. Certainly not the smoothest control loop I've ever seen, but hopefully good enough.