Hello, Wrenchers and special greetings to the silicon gurus to whom I address these questions about solid state relays.
A client wants a gizmo to connect grid "AC In" to their inverter/charger when the battery voltage is low...resembling the LBX function on the good ol' Trace SW inverter. The grid power would feed into a 120/240 Magnum inverter/charger which is rated for 30 amps pass through on each hot leg. I may use a solid state relay for the heavy lifting: double-pole, single-throw, normally open...with DC for the control voltage. Using a voltage controlled switch, I'll send battery DC to the SSR when the battery voltage goes too low for too long; then I'll remove that DC trigger when the battery voltage recovers. Question 1: Are SSR's suitable for the variety of loads (including motors) that this circuit might carry? Question 2: Should the SSR be massively over-rated relative to the expected load (as with typical electronic design practice)? McMaster-Carr stocks solid state relays with built in heat sinks; model 7456K43 is published for 30 amps @ 230 volts AC. If protected with a 30 amp double-pole breaker, would this relay suffice long term or would it instead produce expensive smoke? (Let's assume free air conditions around the heat sink and a 90 degree F ambient temperature.) Question 3: Should I instead bump up to model 7456K44 with a 50 amp rating for this 30 amp pass through situation? I like the idea of no moving parts/no arcs/no clunks compared to a mechanical power relay, but I also want no customer callbacks. High speed switching (pulse width modulation) is not one of our requirements, so... Question 4: ...is it bad strategy to even consider using an SSR for this application? Thanks in advance, Mick Abraham, Proprietor www.abrahamsolar.com Voice: 970-731-4675
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