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Topic: Solid state relays (Read 1 time) previous topic - next topic

kerimil

Hi,
I'd like to completely isolate logic circuit (arduino) from the devices controlled by it.

I know I can use ULN2803A IC and it almost cuts it as far as its rating is concerned (correct me if I am wrong, but it contains eight Darlington Drivers and each of these can provide up to 0.5A, right ? though I understand it's the max rating and it might require some extra cooling), but I've seen some SSRs and they come with terminal blocks on both sides and are completely ready made.

So I am wondering if there are things that combine several SSRs into one package (let say 4 or more) and have terminal blocks on both sides?
Just to clarify, I don't want to use AC just DC and all I need is 50-70V and 1A max.


Grumpy_Mike

#1
Sep 16, 2010, 02:32 pm Last Edit: Sep 16, 2010, 02:32 pm by Grumpy_Mike Reason: 1
Quote
though I understand it's the max rating and it might require some extra cooling)

No it is actually imposable to run this chip with all the outputs switching their maximum simultaneously.
See:-
http://www.thebox.myzen.co.uk/Tutorial/Power.html

http://
http://www.thebox.myzen.co.uk/Tutorial/Power_Examples.html


For true isolation you need an opto isolator something which DC SSRs have built in.

kerimil

I do know that ULN2803A does not isolate the two circuits. I mentioned it a sort of example of what I want - one module or IC with several 'channels'. Yeah, maybe it was a bit confusing - sorry.

I've seen some IC that combine 4 or 6 of optoisolators but they normally can't be used directly to power anything that requires, let say 50V and 0.5A.
Of course, I could combine them with ULN2803A or relays to have a board that both isolates the two circuits and can power most output devices directly.

I suspect that most SSRs do more less the same thing and some of them come as ready made modules with terminal blocks. Sure, I could combine a few of them but are there any that combine a few SSRs in one single unit ?

Grumpy_Mike

Quote
are there any that combine a few SSRs in one single unit


Not that I have come across.

novice

Hi kerimil,

keep the solution simple.  Use multiple SSRs.

kerimil

yeah, that's probably the best idea. But it would be could if someone created a sort of SSR shield - hmm not a bad idea huh ?  :)

I've seen some I/O modules used in industrial PCAs that do pretty much what I mentioned, plus they work 'both' ways (so they are not only for outputs but also inputs). Unfortunately they are quite expensive

Grumpy_Mike

Quote
But it would be could if someone created a sort of SSR shield

problem with that is that most SSRs are larger than the arduino itself due to the heat sink they are on. The other problem is that again most SSRs are of the AC type and you wouldn't want your arduino that close to the mains.

kerimil

#7
Sep 17, 2010, 12:52 pm Last Edit: Sep 17, 2010, 12:59 pm by kerimil Reason: 1
well if we are talking about SSRs for higher currents and AC they are relatively large but there are smaller ones too

http://sklep.avt.pl/photo/_pdf/JGX40F.pdf
(I've seen smaller than this one)



It would be great if I could find an IC that can handle a little bit higher current than this one, maybe 0.5A max
http://sklep.avt.pl/photo/_pdf/LAA110.pdf

Ohh and yeah I am aware that smaller ICs won't be able to dissipate heat if under max load. I know that 50V @ 0.5A = 25W, multiply that by the number of outputs and you can use it for heating  ;)

But if it can handle, let say 4-5 times as much as arduino and isolates the two circuits then it seems worth it


kerimil

yeah, thx

I am new to this stuff so it's not that I know every IC that exists. Though, I knew that there must be something like that.

Grumpy_Mike

Quote
am new to this stuff so it's not that I know every IC that exists


Hey I am not new (over 40 years at it) and I don't know a fraction of what is out there. I hadn't even seen these chips until I found them for you. The trick is knowing how to look, best of luck with that.  ;)

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