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EMS-220 issue?

Bill Boyd

Well Known Member
15 hours into phase one with a full Advanced Panel setup and dual alternators, Dynon shunt monitoring their combined output current...

Last week my Red Cube suddenly stopped registering in the middle of the day's flight tests. Visual inspection of the wiring at the cube shows no apparent damage - ok, I was thinking of moving it out of the tunnel anyway; replacing the Cube with a new one is my opportunity to relocate it. Meanwhile the plane runs fine without fuel flow monitoring so the test program soldiers on while I decide how to address the flow transducer failure...

Today in flight I get an aural warning "Check amperage!" The displayed amperage is typically about 25-30 with lights and full avionics load, but now I'm seeing single digits, dithering. Bus voltage rock steady at 14.2 under load. Now the alternator output is back to reading 25A... Now it's minus 9A... Back to positives... Down to zero, then negative... All the while the voltage is steady at 14.2V. I ignore the warnings and complete my test cards, land with the alternator output showing the nominal 25 amps or so.

Now I'm thinking back over the day's events - earlier I had an EGT probe (that I just replaced) read "---" for a few minutes, then revert to indicating normally ever since. Strange. Multiple electrical instrumentation anomalies that all have the EMS-220 in common. Tomorrow I'm going to do my RV yoga and crawl up in there to remove, inspect and re-seat the D-sub plugs on the EMS-220. Anyone else with Dynon/Advanced gear faced anomalies like this? My understanding of the basic electrical architecture is that it's not possible for the battery to push current into the alternator outputs (negative amperage reading), so the negative values I'm seeing would only be possible if the EMS/EFIS is somehow intermittently losing its reference to the amperage shunt offset/calibration values stored in the software. There's no way the battery could maintain 14.2V if the alternators were both dropping offline every few seconds, so I know they're not actually doing that.

Very curious what manner of wonkiness inside the EMS-220 could give readouts like this, and if it's somehow related to the sudden loss of my red cube readout the week prior. Input from any electron-herding guru's welcome!
 
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Bill,

A few thoughts:
- As you state, stepping back and looking for a common fault that could be causing all these indication errors would also be my first step. It could well be the EMS module itself, or a wiring issue in the harness to it or the connectors at the EMS. As this is a new problem, perhaps something happened - such as firewall harness penetration chafing.
- The simple way to isolate the problem is to swap out the EMS module with a known good one. Dynon might be able to help here if you don’t have anyone near that has one you can borrow.
- I installed or help install five full SkyView systems - none had an shunt for amperage reading. Voltage is the far better indication of what is going on and I view the shunt as a clunky, adding unnecessary big connection points, leftover from 1950 cars when amp meters were used because voltmeters where too expensive.

If your Phase 1 area supports, drop into VA42 and perhaps a second set of eyes will be of assistance.

Carl
 
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Agree on the shunt. Voltage tells the tale. It was part of a bundle from Dynon early in my build and I probably would have been as well off leaving it out from a reliability standpoint.

I will check wires today. I wish I was closer to your field but it's outside my test area. For that matter, so are any avionics shops that can to a transponder cert or prop balance :rolleyes:
 
Removing and reinserting the D-sub in the EMS-220 changed none of my issues. And I now have dancing CHT values in flight that are changing impossibly fast on a couple cylinders. I suppose that's an indication of impending probe failure after just a dozen hours. One of my EGT probes went T.U. in less than two.

It just occurred to me that the two wires presently going through the FW to the shunt can be repurposed as V+ and signal leads for the Red Cube when I move it forward of the firewall, with a ground to the FWF forest-of-tabs. Voila - firewall penetration issue solved. No new holes, no need to thread wire through cured FireBlock silicone. Useless ammeter shunt gone, new wires from starter solenoid to the alternators will eliminate splices and associated reliability concerns. Win-win. Love it when a plan come$ together.
 
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FWIW, your symptoms are typical of bad connections, especially if you use "crimped" connectors and terminals. I had the AMPS display bouncing all over the place and found one small wire on the shunt was not making good contact inside the crimped terminal. I also had the same issues with EGT and CHT values until I replaced all the terminals and spade connectors with these much better ones.

:cool:
 
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The EMS plug that comes with the engine sensor kit is supplied with very long leads. The only builder connections should be at the sensor. There should not be any issues at the plug. I would concentrate on those connections. It doesn’t make sense that a large number of brand new sensors are defective.

Look at the ground side of the problem devices.

You might rerun the system setup wizard that detects the devices on the network, a long shot but easy.

Advanced support should be your next call. They usually do a very quick turn on their devices.
 
Correct, Bruce - no builder-made connections except at the junction with the probes themselves. Advanced seemed not at all surprised that an EGT probe failed within a few hours of ground run time before first flight! They offered an upgrade to a more expensive probe that came with an actual warranty, but having had 20 years and 950 hours of perfect service in my 6A from the same style of probe, I opted to consider this a fluke and replace with same type.

Galin, I like the look of those connectors. (Not the price so much, but at this point if it relieves the aggravation it's well-spent). Thanks for the tip. I may try these in the tunnel on my red cube before replacing it as T. U.
 
The Advanced/Dynon probes have a warranty and yes your probes are under warranty, I will be looking for the person that told you otherwise. I suspect your problem is with the connection to the probe and not the actual probe.

The amp reading is actually important and gives you a lot information. I have the audible warning set to 8 amps in my RV-10, if the amperage drops under 8 amps I get an immediate warning. If you see a change in the normal amperage use you can start looking for the problem.

You should verify that you installed the shunt after the alternator output circuit breaker. If the shunt is on the other side and you pulled the breaker with the engine running the SV-EMS shunt circuit could be damaged from the alternator spikes.

Rob Hickman
Advanced Flight Systems
 
Galin, I like the look of those connectors. (Not the price so much, but at this point if it relieves the aggravation it's well-spent). Thanks for the tip. I may try these in the tunnel on my red cube before replacing it as T. U.

But in the overall scheme of things the significantly increased reliability of these are well worth the $1.28 they cost. BTW if you buy them make sure you get a 3/64" (0.050) hex driver, which is not normally available at your local hardware store. You can buy a pack of 10 on-line for about $2.50.

:cool:
 
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Bill, My electrical experience a few hundred hours ago :
1. Clean the shunt connections. They carry micro-amps and can easily give bad indications if grimy or a tiny bit corroded. I now clean at annual.
2. I switched my EGT & CHT connectors to Omega brand. Theyre specifically made for this and each is made of a different metal. $3.50 ea.
3. Doubt it’s the EMS box. I thought the same at 50 hours, 3 years after purchase from Dynon. I now have a spare on the shelf. Changing it did not fix anything.

Keep us posted.
 
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