Starter woes

nigelspeedy · #1 03-28-2016, 11:14 AM

I have a weird thing happening with my RV-8. It has an IO-360 engine and a Skytech starter motor. I used Lamar solid state relays for the master and starter circuits. I have the VPX-PRO and Dynon Skyview system. The aircraft has about 140 hours since new and to date the system has worked great.

On the weekend in flight with RPM of 2500 I started to get an intermittent 'starter engaged' indication on the Dynon engine display. This is a read of voltage on the starter motor side of the starter relay. Luckily the VPX disables the start circuit above 600 RPM. It did not sound like the starter was being activated. I wired the starter annunciator as per the instructions i.e. down stream of the start relay, so it would seem that the VPX was detecting some voltage on the starter side of the relay even though the relay should have been closed/off. When I view the VPX page on the Skyview the start circuit does not show as being activated when the 'starter engaged' widget indication comes on.

I landed and shut down. On the ground with the master still on the starter engaged widget did not come on and the starter did not intermittently engage. When I tried to restart the engine it would not crank.

I looked at the starter switch wiring and when I checked with a multi meter at the starter relay the switch appeared to be operating normally. The starter relay had good voltage on the input side and when the starter switch was depressed good voltage on the output side and also at the input to the starter itself.

When the starter button was pressed the starter made a low buzz or hum but the drive was not engaging. The starter motor and solenoid were warm but about what I expected having just shut the engine down. I could not detect any brown electrical smell.

After taking the starter off and hooking it directly to a battery it ran just fine. Reinstalled and it worked fine but I am still getting the intermittent 'starter engaged' indications.

Long story but the questions are:

1. Could the VPX be inadvertently activating the start circuit above 600 RPM?

2. Could the solid state relay be intermittently activating without the starter button being pressed or the VPX activating it?

3. Could a failure mode of the starter or starter solenoid be causing the 'starter engaged' indication and subsequent issues with not cranking?

Thanks for any ideas.
Cheers
Nigel

JonJay · #2 03-28-2016, 12:25 PM

I would be focusing on your Solid State Starter Relay. If it is partially failing, it could be throwing stuff on the line that the Dynon is picking up.
Do you have access to an Oscilloscope? It would be readily apparent on the waveform measured on the output side of the Relay. If not, see if you can measure any AC voltage on the circuit when the Relay is OFF. If you see any AC voltage, that could point to a SSR partial, or total, failure.

dynonsupport · #3 03-28-2016, 12:42 PM

What voltage threshold do you have on the SkyView for counting this as "engaged"? If you have this at a low voltage you may just be seeing some leakage current.

nigelspeedy · #4 03-28-2016, 09:46 PM

G'day Dynon,

I just spent some time playing at the hanger and could not find a way to adjust the voltage threshold for this widget. If I am missing something please let me know.

Cheers

Nigel

nigelspeedy · #5 03-28-2016, 09:48 PM

To add to my drama as I pulled the starter off this afternoon I noticed that two teeth were missing on the flywheel ring gear. Not happy.

With the master on and the starter off there is about 0.5 volts on the output terminal of the solid state starter relay.

lr172 · #6 03-28-2016, 10:08 PM

Quote:

Originally Posted by nigelspeedy

With the master on and the starter off there is about 0.5 volts on the output terminal of the solid state starter relay.

I have never used a large SS relay (I don't recall the low amperage ones having any voltage present on the NO lead). I would think this is a sign of a failing relay, which seems to be the most likely cause of your symptoms.

Larry

nigelspeedy · #7 03-30-2016, 11:35 PM

So it turns out that a characteristic of the Lamar Super Switch solid state relay is that the voltage at the output terminal will 'float' up to the voltage of the input terminal unless the output terminal is grounded.

So if I have the battery master off I have battery voltage at the input and at the output of the master relay I have about 2.7 volts. The same voltage is at the input of the starter relay. Under the same conditions I have 0.5 volts at the output of the starter relay.

Turn on the battery master there is battery volts at the input and output of the battery relay and also at the input of the starter relay. Even though the starter is not engaged there is also 12+ volts at the output of the starter relay when the heavy gage wire is disconnected from the starter. The VPX sees this voltage and reports it as the starter is engaged. Interestingly if you take a small piece of 22 gage wire and ground the starter lead you might think this would create a shower of sparks and some smoke but no, the voltage at the output of the starter relay just drops to zero. No current to be seen. For a mech eng this is pfm. So I think the intermittent starter engaged in flight on the VPX was a fault in the Sketch starter solenoid that did not ground. As a result the starter relay output floated up to the input voltage and the VPX reported this as starter engaged. This would probably explain why the next time I went to start the solenoid would not work and the starter motor did not engage. Starter has gone off for a rebuild and i will report back on what they find.

Cheers

Nige

krw5927 · #8 03-31-2016, 07:02 AM

I'd be inclined to try a 10k ohm pull-down resistor on the output of that solid state starter relay. Just a small crummy ol' resistor from your local electronics shop, between the output and ground.

Airdog77 · #9 01-30-2018, 05:53 PM

I know it's been a couple of years since you reported on this Nigel, but I too have a Lamar Super Switch SS relay that I plan on using for my starter contactor. Can I ask how this turned out?

Are you still using the Super Switch and did you continue using the 22 AWG ground wire on the starter lead? Also, does it matter where on the starter lead you place the ground? Finally, do you think I diode on the ground lead would help? (I've seen LED lights linked to higher voltage components use this setup to protect the LED from getting fried).

Thanks!
Wade