Help with 12V DC PNP Sensor and SSR Relay circuit

Thread Starter

Fortel

Joined Nov 3, 2020
13
Did you de-burr the holes that you used to mount the SSR?

Did you use thermal grease?

The general reccommendation for mounting is to use a Bellville washer. https://www.mcmaster.com/belleville-spring-washers
I did deburr the holes. The SSR's are mounted on a sheet of aluminum. Screws go through the mounting holes, through the aluminum sheet, and into locking nut plates which are flush riveted to the aluminum. I didn't use the thermal grease- thought about that, but the mfr's installation sheet didn't mention it. I don't imagine heat will be much of a problem for these SSRs in this application. At most, one will operate for about 10 seconds to run the motor and pressurize the "up" hydraulic side. The other SSR will do the same thing at the end of a flight, running a shorter duration to pressurize the "down" side. So, very light, infrequent use.

Still, I'll go back and see if I can find where I might have missed the need for the thermal grease, and will use it if called for.

Thanks!

Peter
 

Thread Starter

Fortel

Joined Nov 3, 2020
13
Okay!

Circling back to report success, and close out this thread.

Thanks everyone for your help, and especially, a big, big, big thank you to Sghioto.

Adding the diode and capacitor in front of the pole at the SPDT switch worked. The Sensors operate as expected, and the solid state relays work correctly- the pump motor runs in the direction it's commanded based on the switch and sensors.

Still not totally clear on how this fixed it, and will need to study that a bit. (I tried just the diode before starting this thread- no joy.) But adding the diode along with the capacitor clearly was the answer.

So, I'm very happy, and grateful.

Thanks again,

Peter
 

sghioto

Joined Dec 31, 2017
5,380
Congrats, your welcome.
Still not totally clear on how this fixed it
The way it works is the capacitor is charged at appx 12 volts when power is connected to the SPDT switch. When the motor kicks in and the battery voltage drops the voltage on the capacitor starts to discharge but slow enough to still provide enough voltage to keep the pressure sensor activated while the battery is recovering. The diode provides the isolation by only allowing the capacitor to discharge through the pressure sensors. Without the diode the capacitor will rapidly discharge to the same voltage as the battery. Hope this makes sense.
 
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