Solid State Relays and EMI

On Mon, 26 Jul 2004 08:46:27 -0700, Jim Thompson


Mercury-wetted?
It's OT gents.
RL
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Which brings up the age-old question: Just how {anal-retentive, deliberately wrong} can one be on Usenet before crossing the line into "troll"?
--
William Smith
ComputerSmiths Consulting, Inc. www.compusmiths.com
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"David Harper" ...

What type _exactly_? URL?

Not if it's a mains load switching type with a triac or thyristor output, they have no "R-off", they are either ON or OFF.

SSR's with an optocoupler inside are easily triggered by RF voltages occurring between in-and output. You might try adding a ceramic Y-rated capacitor (470pF ... 1nF should do), between the ground on the input (optocoupler) side and the supply pin on the output (contact) side, as short a connection as possible. Also one over the output pins. **** Warning **** this may solve the problem but will add leakage current between controller and mains. Check you stay on the safe side!
Another test could be just the 1nF Y-rated cap over the output (less likely to help).This does not introduce leakage to the controller ground, just some extra OFF-state current in the load.
Regards, Arie de Muynck
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snipped-for-privacy@gmail.com (David Harper) wrote in message

With the turn-on time being ten times the turn-off time, I don't expect that false turn-on will be a result of LED emitter modulation at the interfering frequency.
Fet structures usually have a hefty input capacitance; the coupling capacitance to the gate is piddling by comparison.
Biggest coupling capacitance that could produce false gate turn-on is from the two drains. Is there a fairly large amplitude of RF voltage present there? These thinga are really only isolators at low frequency or DC, unless a voltage close to at least 1/10 their rating exists when 'off'.
RL
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snipped-for-privacy@magma.ca (R.Legg) wrote in message

OK, but I've seen SSRs used at broadcast transmitter sites running many kilowatts of RF with no problems. SSRs are like Rank telecines. When you see it 'misbehave' don't assume it isn't being 'told' to do it. GG
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David Harper wrote:

1. It's very likely. In my classes, I've been taught that EMI can bugger up the proper working of just about any circuit, so it should always be taken into consideration. 2. Er, I think it's a simple matter of induced current in the line giving false hi signals. 3. First thing I'd do is make absolutely sure your relay coil is grounded rather than floating when in the "off" state. Being assured of that, if the problem persists, you might want to try a simple RC band-elimination filter. If you do not have it handy, I can give you the formula to determine the R and C values.
I apologize in advance if your electronics knowledge is more advanced than mine and I've just wasted your time.
- NR
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