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Atti2d

Quick question - Solid state Relay

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Are solid state relays suitable for use in controlling a pump motor... such as a swimming pool pump? I have a 1HP pump (about 25A @ 115Vac???) that needs to be activated by a typical household appliance timer that is rated at 15A max.
I figured the best way to do this is via a relay... a contactor... or a solid-state relay, the latter of which I have a number onhand with acceptable load handling capabilities. I just don't know if there is some aspect of the solid state mechanism that makes them unusable in this application. Thx for any help.
Dan

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There are some solid state relays that at rated at 25A or 40A. If you find a relay of that amperage everything will work nice.

Check this as a reference: http://www.aeonelectric.com/aeon%20electric/ssr/ssr.htm

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Also notice that most common solid state relays, are made to handle ONLY RESISTIVE LOADS, not inductive (like as a motor). Else they burn...
There are specific type of solid state relays to handle that kind of loads. Seek for them. :)

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EMF from the motor is what usually causes a problem in solid state relays when used in this application. You should have no problem if you find a relay that is rated at twice the volt/amp rating of your motor and use diodes to protect it from the EMF. You need these diodes anyway. EMF will cause other problems for you as well. When you see special relays for motor use, they usually are the type with protection built in such as internal diodes. This makes them more expensive.
MP

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Yes, but this is not a solid state relay, as the title of this thread says... ??? ???


This is a Solid State Relay because it switches a larger load on and off without the use of metal contacts on the output.

What does Solid State mean in your mind?
Solid State in my mind means not mechanical

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Yes, this is solid state. It is just not a relay. I think it is a good circuit to achieve the same goal. Many times someone will refer to the term relay as a switching method instead of an actual device. This is a vey good circuit and I for one will add it to my library. I have been thinking of some changes on my swimming pool pump circuit as well. Thanks! :D
MP

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What does Solid State mean in your mind?
Solid State in my mind means not mechanical


I agree with this: "Solid State in my mind means not mechanical" but the schematic, can't be called "a solid state relay":

As you know, relays offer isolation between the relay contacts and the coil. Also, you can control (on-off) any kind of voltages/currents, with indepedent voltage on coil.
A solid state relay (the component, not substitutes) does all this, because it has a diode as coil, and photosensitive thyristors/triacs as relay contacts (for example, with 5VDC as control voltage, you can do 220VAC on-off control).
None of the above conditions met by the schematic posted above, so I couldn't call it "a solid state relay". Anyway, it does it's job! ;)

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