Use of solid state relays (SSR)

[jraef]

Ok, so if I got this straight.

The SSR have a leakage current when they are off and a voltage drop when they are on.

Am I right in assuming that if I want to have two SSR contacts in series, I want a low voltage drop so that I have enough voltage left for my load?

And it's always better to have a SSR with low leakage current? So that I don't trigger more sensitive inputs on a PLC for example? In other words it's not bad to have a low leakage current even if I don't need it to be?

I have found a relay from Crydom: http://www.crydom.com/en/products/catalog/e_d_dc.pdf

Load: 5A
Voltage drop: 0.3V
Leakage current: 20uA

I think this would suit me pretty good in all my areas.
For the most part my relays will go to indication lights (Allen Bradley 800F series LED), for controlling 24VDC contactors (with low consumptions coils and diode) and to a LOGO module from siemens.

Am I on the right track here?

You are now.
Personally, I think DC SSRs are a little too "finicky" for my taste. They are much more susceptible to false operation from noise, unlike relays. For me, there has to be a very compelling reason to add that risk factor, such as a very high duty cycle or very high speed switching. But you have to respond to your request, so that's what I would do too.

 

[rQx]

You are now.
Personally, I think DC SSRs are a little too "finicky" for my taste. They are much more susceptible to false operation from noise, unlike relays. For me, there has to be a very compelling reason to add that risk factor, such as a very high duty cycle or very high speed switching. But you have to respond to your request, so that's what I would do too.

I agree, we have had this cabinet design for years and years and never had problem with it. I think the cabinet is for Chevron in USA, maybe they have some strict paperwork they have to fullfill.

 

[jraef]

We do a lot of work for Chevron, I've never seen a spec like that. More likely someone's personal pet peeve.

 

[rQx]

We do a lot of work for Chevron, I've never seen a spec like that. More likely someone's personal pet peeve.

Hm, then maybe I can ask them more specific as to why they don't wan't any regular relays or mechanical level sensors etc. Maybe if I get in contact with the right person, the specs can be withdrawn. Thanks alot for pointing that out!

 

[just the cowboy]

how about a smart relay

How about a smart relay unit ??? It can be changed in the front panel, has eeprom for fast swaps, and is solid state, and has NO or NC. IT IS NOT A PLC!

 

[rQx]

How about a smart relay unit ??? It can be changed in the front panel, has eeprom for fast swaps, and is solid state, and has NO or NC. IT IS NOT A PLC!

They don't want any PLC or Smart relay unit. We usually supply with a LOGO from siemens but they didn't want that either :/