Solid State Relays, DC or AC?

Other Hardware General Electronics
1

Hi everyone, I've got a bunch of these as I needed some SSRs.

http://www.aliexpress.com/item/10pcs-lot-SIP-1A05-SIP-1A05-DIP4-reed-relay-5V-Voltage-Hot-Sales-Free-shipping/32524948181.html

When I put 12v, to be switched, on the load pins without even connecting anything to the coil pins 12v goes right though.

Could it be that they're AC type and not DC type?

Thank you.

2

It is a reed relay, not a SSR. The load terminals are 1 and 7 (the two outside terminals). It is normally open. Put a meter on 1 and 7 and test. The put 5 VDC on pins 3 and 5 and test 1 and 7 again.

3

+1,

plus what current are you intending to switch with those reeds, they are typically used for small data signals and can that model is quoted as 500ma maximum, which for regular use means more like 300ma to be long lived.

4

I see, thank you.

Maximum current at the moment is 500mA but could be up to 1.5A.

Are these better? http://www.aliexpress.com/item/Solid-state-relay-normally-open-GJ-5FA-L-220V-DC-control-DC-DC-DC-5A/32223850240.html?spm=2114.01010208.3.114.b95d6y&ws_ab_test=searchweb201556_7,searchweb201602_1_301_10034_507_10032_508_10020_10017_10005_10006_10021_10022_401_10018_10019,searchweb201603_9&btsid=b876fff3-f694-471f-b99a-4589f7aa8837

Or shall I just use optocouplers? If optocouplers which one?

Thank you.

5

Those SSRs will do you job, though they are expensive.

An opto-coupler is just that, something that usually isolates two small signals, a SSR contains an opto coupler along with a power output stage for either AC or DC.

What would be better if you could say what you are switching on or off, as that can affect the choice of device ?

For 12 DC at up to 2 Amps a simple logic level Mosfet is all thats needed for some applications.
A FDP7030BL is a common low cost device in a TO220 package

6

Cost is not an issue that much.

I am switching a 7" LCD on an off which powers up with 12v DC and takes 500mA current. Another LCD (12") takes around 1.2A. I have tried with a MOSFET STP16NF06 but it gets extremely hot.

Thank you.

7

That STP mosfet has an On resistance ten times higher than the FDP7030 that I have used.

I have had the 7030 passing nearly 2A at 12v and without a heatsink, the tab just gets warm.

Its just a case of using the right part for the job, many mosfet circuits on the web of are the older generations with a relatively high On resistance and not really suitable for being fully driven by the Arduinos 5v outputs.

There are now a good few of Logic Level mosfets out there with very low RDS(on) <10 milli ohms, just check the datasheets if you cannot find a 7030 locally.

8

I ordered these:http://www.aliexpress.com/item/Solid-state-relay-normally-open-GJ-5FA-L-220V-DC-control-DC-DC-DC-5A/32223850240.html?spm=2114.01010208.3.114.b95d6y&ws_ab_test=searchweb201556_7,searchweb201602_1_301_10034_507_10032_508_10020_10017_10005_10006_10021_10022_401_10018_10019,searchweb201603_9&btsid=b876fff3-f694-471f-b99a-4589f7aa8837

They work as expected. They're great!