t3chiman Senior Member Joined: 26 Dec 2011 Posts: 20 Location: Chicago Expertise: I love coffee
Espresso: Cuadra Grinder: hand Drip: Brazen
Posted Sun Jun 23, 2013, 12:35pm Subject: Adding SSR to Cuadra, notes and experiences Sec 3/7
The part The Omron G3NA 220B has been recommended on coffeegeek a few times. It is rated at 20A, so is reassuring at first blush in a 10A application. But, uh-oh, that 20A spec is for a fully heatsinked part in 40C ambient. Omron's recommended heat sink is ridiculously oversized for internal mounting in a Cuadra. Omron helpfully offers a temperature derating curve for nonheatsinked operation: 4A up to 80C. And we are near a boiler, operating at 1 bar; that's 100C. Are we doomed?
We are not doomed Existing field reports are reassuring. The part will work fine if you get it on the far side of a barrier to that boiler tank. Bolt the SSR to Cuadra's steel frame to use it as a heat sink. And use the water reservoir as a moderator for ambient temperature. Seems reasonable: get in a sufficiently derated part, and mount it in spot protected from temperature extremes. That's what I did.
The water reservoir gets in the way Expose the unit's internals by, first, popping off the side panels, then, the curvy rear panel. Note that the screw at the rear base of the Cuadra is a different size than the others (why?). After taking the SSR in hand, and trialling some mounting spots on the interior of the Cuadra, a couple of mounting locations suggest themselves. One is on the rear steel brackets that position the water reservoir inside the unit. It's a long way from the boiler back there, good and cool. Another is on the side frame, higher up but still protected from high temperatures by the bulk of the water reservoir. Ultimately, I chose the latter. (pic 3) I reasoned that there is some virtue in keeping new wiring short, and the side frame is a bit sturdier steel, so acts as a better heat sink. But realize that no matter what you do, you will be fiddling with the water reservoir or its supports: it's a tight fit to begin with, and when you add more stuff around it, it's even tighter.
Screwing it in I didn't agonize over mounting fasteners. I had some M4 hardware handy; M4 x 10mm SHCS; worked fine. Lockwashers are probably overkill, but I had some. I bent some sheet aluminum to serve as heatsink and splashguard. Added a touch of heatsink compound, snugged things up, and that was that.
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