i want to be able to switch off a 240V (Europe) appliance with my Arduino Pro Micro. The current switch is a 15A rated switch so i'm going to assume that is going to be needed to switch the appliance on or off(although i'm pretty sure that it will never even see over 1A...).
Thing is, when the Arduino loses power i still want to be able to normally power on the appliance and therefor my idea for a Solid State Relay solution will be somewhat useless since those are "normally open". Is there any way to use a phototriac SSR in a configuration where i end up with a normally open setup? I really want to use an SSR because i want to get rid of the mechanical sounds and interference.
Exactly. The appliance should work regardless of wether the Arduino does. However the Arduino should be able to power down the appliance. Normally i'd just interrupt one of the leads from the original switch with a relay and wire it up over the normally closed pin. The problem with SSR's in this case is that most SSR's are normally open which means that the SSR has to be powered (or in other words the Arduino operational) for the appliance to work at all.
(very rough, just got started with the program and can't find half the parts...)
However, if you consider the same schematic but with the SSR normally open you'd have a useless machine should the Arduino ever be powered off or defective. I need an override of sorts in that case.
the SSR is a solid state device and requires power in order to allow power to pass.
so, the SSR requires power. if you take the device power as the power supply, you are assured that when the device has power, the SSR has power.
just put a resistor in front of a transistor. the base to the arduino, with a pulldown
connect the 5v of the SSR too the resistor, between the resistor and the transistor, and as long as there is power to the resistor, there is power to the ssr.
when the transistor base goes high, it pulls the resistor leg to ground and the SSR has no signal and will change state to the open condition.
alas, you cannot account for every possibility, a solar flare of sufficient magnitude could cause the power utility to loose control and shut power off to the grid in your area. the battery backup on the unit, could run too long and deplete the charge and the power to your device is lost,
dave-in-nj:
the SSR is a solid state device and requires power in order to allow power to pass.
so, the SSR requires power. if you take the device power as the power supply, you are assured that when the device has power, the SSR has power.
just put a resistor in front of a transistor. the base to the arduino, with a pulldown
connect the 5v of the SSR too the resistor, between the resistor and the transistor, and as long as there is power to the resistor, there is power to the ssr.
when the transistor base goes high, it pulls the resistor leg to ground and the SSR has no signal and will change state to the open condition.
alas, you cannot account for every possibility, a solar flare of sufficient magnitude could cause the power utility to loose control and shut power off to the grid in your area. the battery backup on the unit, could run too long and deplete the charge and the power to your device is lost,
I don't intend to cover every base, not by a long shot. What i want to prevent is that, when the Arduino for some reason dies, i end up with a useless appliance. In other words i'd have to be able to bypass it.
I have thought about just powering the SSR with the available 240V powersupply but wouldn't really be a solution since i'd still have to be able to interrupt the 240V powersupply that switches the SSR, which is essentially the same problem.
I want to use a Phototriac SSR to keep the Arduino powersupply completely separated from the 240V powersupply in the appliance itself otherwise i'd just use a simple mechanical relay with both NO and NC connections and be done with it.
nicoverduin:
I checked RS here and there do exist NC SSR's. Hoewever... you can buy many many many Arduino's for that price :).
I know they exist, but they are quite expensive indeed which is why i'm looking into other ways to achieve the same result
I want to use a Phototriac SSR to keep the Arduino powersupply completely separated from the 240V powersupply in the appliance itself otherwise i'd just use a simple mechanical relay with both NO and NC connections and be done with it.
Don't see why you can't just utilize a 5vdc electro-mechanical relay as it has both the galvanic isolation and normally closed mode you require. The standard Dc relay is a viable device often ignored for no good reason.
I want to use a Phototriac SSR to keep the Arduino powersupply completely separated from the 240V powersupply in the appliance itself otherwise i'd just use a simple mechanical relay with both NO and NC connections and be done with it.
Don't see why you can't just utilize a 5vdc electro-mechanical relay as it has both the galvanic isolation and normally closed mode you require. The standard Dc relay is a viable device often ignored for no good reason.
I need to keep electric interference to a minimum and as an added benefit a SSR doesn't "Click".
Use an Arduino output to pull a transistor low that keeps another SSR off. If the Arduino signal fails, the transistor goes high, turning the second SSR on, and bypassing the first SSR.
I want to use a Phototriac SSR to keep the Arduino powersupply completely separated from the 240V powersupply in the appliance itself otherwise i'd just use a simple mechanical relay with both NO and NC connections and be done with it.
Don't see why you can't just utilize a 5vdc electro-mechanical relay as it has both the galvanic isolation and normally closed mode you require. The standard Dc relay is a viable device often ignored for no good reason.
I need to keep electric interference to a minimum and as an added benefit a SSR doesn't "Click".
Household AC power already has 'electrical interference' from all the other household AC loads turning on and off at random times, a relay won't add enough to matter. As far as clicking sound there are ways to deal with that by simple mounting and packing methods as well as selecting relays that don't click to begin with. For example for AC loads of 1 amp or less there are DC reed relays that don't make a sound detectable by human hearing in ambient conditions.
So far you haven't convinced me that a DC relay is still not the best/simplest/cheapest solution.
a prebuilt, SSR (ie one you're not making yourself using a TRIAC) should already have an optoisolater for the low voltage DC side to switch the 240/120ac side right?.
so as already suggested, use transistors to keep the SSR normally closed.
cjdelphi:
a prebuilt, SSR (ie one you're not making yourself using a TRIAC) should already have an optoisolater for the low voltage DC side to switch the 240/120ac side right?.
so as already suggested, use transistors to keep the SSR normally closed.
But such a transistor stage requires a DC current source and because of the user's requirement that the SSR conducts even if the arduino is powered off requires more components to derive this DC current source from the AC load voltage. So more components needed which also removes the galvanic isolation from the load AC and the arduino controlled transistor stage.
So if a DC relay doesn't appeal how about just a simple SPST switch wired across the SSR output terminals. That would allow one to 'override' the off condition when the arduino is powered off, but you still want the AC load powered on in that condition.
cjdelphi:
a prebuilt, SSR (ie one you're not making yourself using a TRIAC) should already have an optoisolater for the low voltage DC side to switch the 240/120ac side right?.
so as already suggested, use transistors to keep the SSR normally closed.
But such a transistor stage requires a DC current source and because of the user's requirement that the SSR conducts even if the arduino is powered off requires more components to derive this DC current source from the AC load voltage. So more components needed which also removes the galvanic isolation from the load AC and the arduino controlled transistor stage.
So if a DC relay doesn't appeal how about just a simple SPST switch wired across the SSR output terminals. That would allow one to 'override' the off condition when the arduino is powered off, but you still want the AC load powered on in that condition.
You're actually quite right. Thing is, i expect the Arduino's powersource to fail far sooner than the arduino itself. If only the Arduino fails it surely would work to constantly trigger the SSR and to merely use the Arduino to interrupt the power to the SSR and thus the appliance. But like you said, if the powersource to the Arduino fails (too) the SSR will default to an open state.
I haven't put in my order for my SSR's yet but i intend to combine both solutions. I will trigger the SSR's constantly and then merely interrupt with the arduino and the use an override switch over the SSR's output terminals as well. That way i'm safe if the Arduino fails or if its powersource cuts out.
Check bottom of page 1 on this datasheet for more part numbers.
If used is acceptable, they're US $2.95 here on eBay. Edit: oops - don't forget to save one for C44Supra