Newsgroups: sci.electronics.design,sci.electronics.misc
Subject: Re: SSR Problem.
References: <[email protected]>
"B. Woods"  writes:

> I'm completely frstrated with an SSR design I'm working on. I'm hoping
> someone can tell me what I'm missing.
> 
> Facts:
>     I'm working with a Potter & Brumfield SSR-240D50.

I have not worked with this specific SSR but I can give some 
general advice related to SSRs.

>     I'm trying to switch a simple resistive heating coil that comes out at a
> little over 4 amps at 124V.
> 
> Initially I had this hooked to a pin on my printer port. I have other, much
> smaller, SSR's that I run this way. For some of my tests I put a 9volt
> battery across the drive lines.
> 
> Wiring:
>     I have, quite literally, an electrical cord that I spliced the SSR into.
> One side of the cut is on pin 1, the other side is on pin 2 (which are
> labeled 120/240vac).
> 
> Observations:
>     Whenever the cord is plugged in I read 124v at the plugged. There isn't
> enough current to drive anything, but there is energy. This concerns me.

A small leakeage like this through SSR is quite typical. 
Theare are various technical reasons (leake through the 
conducting triac / SCR pair inside SSR, leakage caused by snubber network 
in SSR, possibly current taken by zero voltage swithing logic etc.)

Some leakage is a feature of SSR that you need to live with.

> Tests/Result:
>     LPT: First test was totally dead.
>     LPT: Second test I plugged in a light bulb, worked perfect for many
> cycles.
>     LPT: OK, I hooked up my heating coil... dead.
>     9V Batt.: Back to the light bulb... works (here I'm pretty frustrated)
>     LPT: Hook it back up to my heating coil... Works!!!
>     LPT: Do some tuning on my code that drives the device, run it again...
> Works intermittently, once turned off it wouldn't always come back on.
> 
>     Dismantle, hook drive lines directly to 9 volts... Dead
>     Never works again.
> 
> (Step 10 - Hit the newsgroups at www.deja.com, find little of value, deicde
> to post)
> 
> Can anyone see what I'm missing? I have similar designs running on 3amp SSR.
> Is it possible that I have a bad SSR.

Possible reasons could be that you have bad SSR, you have used 
it improperly or your parallel port does not give enough current 
to reliably control the SSR (quite propable reason).

> Here is the spec sheet for the SSR:
> http://www.steveneng.com/Tech_Support/PDFs/37SOLID.PDF

I read the datasheet briefly. 
It said "leakage current max 5 mA rms at 240V rms". 
So there can be quite considerable leakage and relay still OK. 

The input parameters says for DC control models:
" 3-32V DC on zero V turn on models, 3.5-26V DC on Random T turn on models"
" Current 15 mA @ 5V DC max." 
The data sheet does no list the miminum needed current. 

One test to check if the control from pralel port 
is enopugh for SSR: 
Wire the SSR to paralel port. Turn it on through software.
Measure the voltage on the SSR input connectors. 
Check that the voltage there is within the input voltage 
limits of the SSR you use. 
If the volrage is below minimum listed voltage, then the parallel 
port does not give enough drive power to reliably operate the SSR.

>    bwoods114charter(dot)

I reply to both newsgroup and mail.

> Thanks,
> Brad
> 
> 
> 

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/