Cheaper Relay

[CyrexCore2k]

Hello all.

I'm trying to use a 3.3v DC digital signal to complete a circuit running 26v AC. I managed to find this guy which I think fulfills that purpose:

http://www.drillspot.com/products/455298/Crydom_D2425_Solid_State_Relay

I'm just curious if there's a cheaper alternative. I know there are other relay types besides solid state but I don't understand the terminology the other categories use so I'm not sure how to find an equivalent unit of a different (and hopefully cheaper) design.

Any info would be appreciated!

 

[NickS]

There are plenty of cheaper alternatives but how cheap depends on a few more pieces of information.
(1) Do you know how much current you will be drawing @ 26VAC?
(2)Do you know what the current rating for your 3.3V digital signal is?
(3)Do you have access to the 3.3V rail to gain up the drive of the digital signal?

 

[CyrexCore2k]

There are plenty of cheaper alternatives but how cheap depends on a few more pieces of information.
(1) Do you know how much current you will be drawing @ 26VAC?
(2)Do you know what the current rating for your 3.3V digital signal is?
(3)Do you have access to the 3.3V rail to gain up the drive of the digital signal?

1) Enough to power a lawn sprinkler valve solenoid. I don't know exactly.
2) It's a digital circuit so I think less than one amp?
3) No.

 

[(*steve*)]

Possibly *way* less than 1A I would suspect. Maybe only several thousandths of that.

This is really pretty key information. without it we could suggest something completely wrong. So what is this device or source of signal. We may be able to estimate a little better.

A possible option is a solid state relay, but I couldn't be certain if you have enough signal to drive one.

edit: *snap* a solid state relay is suggested. Go here and search for "SSR". Hopefully the postage won't kill you.

 

[NickS]

Here are some options for non SS options LINK

Here are some SS options LINK

Assuming your digital source can drive them. Like steve said without knowing the specs of the digital source these may not work.

 

[CyrexCore2k]

The signal goes up to 500 mA per:
http://www.smileymicros.com/index.php?module=pagemaster&PAGE_user_op=view_page&PAGE_id=31

I have to use the 3.3v output because the signal needs to go through some registers and such per my design.

I'm not sure how much current a small solenoid takes and I'm not really sure how to find out without a current tester.

 

[(*steve*)]

Are you talking about the current available from the logic signal, or the current from the 3.3V supply (that you claimed no access to)?

In any case, I believe you shouldn't be drawing more than 100mA unless you alter settings in the eeprom to identify it as a high power device.

You could use a transistor to switch a relay. I'd still recommend a relay (mechanical or SS).

 

[CyrexCore2k]

I really like the price tag of this relay from the site you recommended Steve:

http://www.futurlec.com/Relays/SSR10A.shtml

But it looks like it's operating voltage is 48VAC to 280VAC. I think it's odd that there's a minimum voltage for these things to operate. Why do they need a minimum operating voltage?