On 02/01/14 17:45, newshound wrote:
On 02/01/2014 07:27, Adrian Brentnall wrote:
On 01/01/2014 16:31, Andy Burns wrote:
Adrian Brentnall wrote:
I'd rather not go the fully electronic route with a solid state relay
for the final device - I rather like things that go 'clunk' grin.

Dad used solid state relays on his kiln controller, instead of going
"clunk", the specialist fuses that protect the relays liked to go "fot"
unfortunately they were more expensive than the relays themselves.

I think he did eventually find a previous owner had incorrectly wired
the elements, and now it's reliable.


HI Andy
Thanks for your comments. I've always been a bit wary of high-power
semiconductors protected by expensive fuses. Many years ago at
university we used a big homebrew lighting rig, and when the explosive
fuses blew in that (which they did fairly often, with a 'crack' like a
gunshot and a bright purple flash), they often took out the triacs as
well...

I'm sure that ssr's should be more reliable, but the luddite in me likes
an electro-mechanical device - if for not other reason that you can hear
it working...

I built a controller for a small brewery "hot liquor tank", basically
four 3 kW immersion heaters. I used octal base relays (notionally
adequately specced) in the first version but they didn't last all that
long. Solid state ones have been fine.

Non inductive loads like heaters is the one case where I WOULD use SSRs
without hesitation.

The fuses will not protect the SSRS but they will stop the wiring
catching fire.

SSRS fail short circuit though,so its important to have a full
mechanical DP isolator behind them for fault repair purposes.


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