110v mains switching questions

Hi,

I was trying to use some parts from an old toaster oven for a new project but have had to go back to basic controls as a more simple approach.

I need to switch a 110vac heating element that measures as 31-Ohms, which if my calculations are correct, comes to 390W.

I also need to switch an AC/Cap-start motor that shows "110v -- 100-Watts"

I am thinking two relays, but, both may be switching on and off up to 5+ times a minute and I am wondering if a mechanical relay is OK or should I go with SSR?

I'd like to stay with mechanical as I can use normal 2-relay (10A - 120vac) board. The double version of this... https://www.addicore.com/Single-Channel-Relay-Module-p/ad317.htm

I haven't found anything similar that has SSRs at a reasonable cost.

What kind of cycle-reliability can I expect from mechanical relays v SSR?

MODS! The forum posting-restrictions suck. I just tried to edit some spelling mistakes and now told to wait five minutes. That restriction is OK with individual post, but surely not editing to correct mistakes? I have made 59-valid posts so obviously not a spammer.

As an inductive load, the motor (off) will arc the relay's contacts and so it has a short life. You can add MOV's or X capacitor say 47nF across the relay's contacts to extend their life. The contact arcing can also make enough EMI to crash your MCU.

Resistive loads like a heater you can get 100,000 cycles from a mechanical relay.

For rapid-cycling applications I suggest using Fotek SSR's, they are under $5 on eBay.

There are lots of fake (unsafe?) Fotek's on eBay alas, you should be careful out there.

prairiemystic: As an inductive load, the motor (off) will arc the relay's contacts... Resistive loads like a heater you can get 100,000 cycles from a mechanical relay.

Great, thanks for the explanation, it helps a great in understanding why one appoch is better than the other.

Looking at the an old toaster oven board that explains why they had a relay for the heating elements and electronic switching (SCR or whatever) for the motor.

I am thinking two relays, but, both may be switching on and off up to 5+ times a minute and I am wondering if a mechanical relay is OK or should I go with SSR?

A relay will exceed 100,000 cycles in just less than 2 weeks. I would go with a SSR from a reliable source that's random turn-on type. You'll need to add a RC snubber or a 150VAC rated MOV.

Selecting a Solid State Relay or a Solid State Contactor for start/stop control of an AC motor