Solid state master relay on an experimental

[Dana]

If the battery is behind the cockpit as it was in my Hatz, running everything from a master solenoid near the battery (mine was next to my seat) makes sense as it allows you to isolate that long heavy cable running from the battery to the starter solenoid. If the battery is up front, I think it'd be better to have the starter circuit not run through the master solenoid. In that case you'd want the starter solenoid coil fed by the master so you can't crank the engine with the master off.

[mmarien]

My original design was to have the battery behind the pilot. It was too close to the magnetometer so I moved it up to the firewall. I have a bunch of expensive 4 AWD cable left over from that change.

I guess the original question on this thread was about solid state relays. I have some solid state relays that I bought off Amazon. I used a pair for the pitch trim. These are only good for 10A but use an optocoupler for switching so they are faster then mechanical relays. They also are smaller and lighter than regular Bosch type relays. Plus no moving parts.

[Eric Page]

I have some solid state relays that I bought off Amazon.

This makes my point. Those "solid state relays" from Amazon aren't SSRs at all; they're standard electro-mechanical relays. I'm sure they work fine for the application, but whoever put them in that two-relay module lied about it on Amazon.

Here's the manufacturer's website listing for the relays, and here's the datasheet.

[mmarien]

Ah. So I didn't get what I ordered at all. This is the Amazon page:

https://www.amazon.ca/dp/B085N49S79?...title_0_0&th=1

[Eric Page]

No, I think you did; the listing doesn't mention SSRs.

The optocouplers on the board's input are there to provide electrical isolation between the control signals and the switched circuits. That's only important if you use the board to switch high voltage, but it doesn't hurt anything in a low voltage application. It's kind of a belt-and-suspenders design, as the relays provide 1,500V of isolation by themselves.

The relay switching speed isn't affected, but the relays close in 10mS and open in 5mS -- significantly faster than human perception -- so it doesn't really matter.

Looks like a good choice despite the confusion, and $45 cheaper than a similar board at Aircraft Spruce.

[Aerowerk]

Sonex is using a SSR in their high wing. It's in the story here:
https://www.sonexaircraft.com/highwing-update-040725/

The Sonex team is also experimenting with the use of a solid-state master relay, saving weight, eliminating moving parts, and reducing relay power consumption to a maximum of 13mA (0.013 Amps). The solid-state relay is performing great so-far and we’ll continue to monitor its performance as we begin engine runs and start flying.

I would not be surprised if they offer it for sale on the Sonex Web store if it works out.