Solid state relays

krtw said:

I wanted to replace the noisy mechanical relay in my house furnace with an SSR. However I can't figure out how to wire the SSR. I understand the mechanical relay and how its wired. There are 6 terminals, Two are the +/- output voltage going to the blower motor, Two are the +/- input of the relay (line voltage) and two are the coil terminals (coil voltage activates the relay). On all the SSRs I have seen there are only 4 terminals, labled input and output. Some of the SSRs are calling the input the "coil" voltage so i can only assume that is the activating signal, and if so where does the actual input go for the line voltage?

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krtw said:

There are 6 terminals,

Two are the +/- output voltage going to the blower motor,
These are the relay contacts that close to start the blower.

Two are the +/- input of the relay (line voltage) and
These two could be the supply to the relay coil, one of which is switched by these two below.?

two are the coil terminals (coil voltage activates the relay).
Are these two connected to the manual On/Off switch.?

On all the SSRs I have seen there are only 4 terminals, labled input
The input is the control voltage that switches the SSR, there are range of control voltages, eg: 3 to30Vdc, 3 to 30Vac and 90 to 280Vac.

and output. Some of the SSRs are calling the input the "coil" voltage so i can only assume that is the activating signal, and if so where does the actual input go for the line voltage?
The LINE wire of the mains is connected to the Output terminals, which is switched by the SSR

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johnsmith123 said:

Eric can you post any links or schematic that would work in the circuit above? Any part numbers for a SSR that would also work in the above circuit?

This is interesting, I would also like to know as I have a few devices that use a mechanical relay.

I have used opto-isolators on low voltage circuits but nothing involving 120VAC.

Your input is always appreciated and well respected.

Best Regards

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ericgibbs said:

hi John,
Is the 90v thry 280V 'ac' control input type you are interested in using.?

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johnsmith123 said:

it would be 110 - 120VAC.

thanks

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johnsmith123 said:

WOW!

very expensive!! (see the attachment)

I was just curious on how to (for example) control a 120VAC appliance with a 3 to 5V microcontroller without using a mechanical relay.

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hi,
The replacement of a mech relay with a SSR is not a direct swop.

The SSR expects on the Input a Control voltage. Which would be switched by a remote manual or automatic switch closing.

The SSR only switches one wire of the mains wires, usually the LINE wire.

Do you follow OK.?

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krtw said:

Thanks for the help. If the input is the control voltage then where would the line voltage connect to? The input for the crydom SSRs is labled -/+, terminals 1-2.....the only terminals left are the ouput terminals 3-4. If I can't figure this out I will try to find a quieter mechanical relay, or just shield the one I have to reduce/elliminate the noise it makes.
Thanks again.

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