what component should I use for controlling on/off high power device
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Andrew Cowan
Senior Member
Most people on here will say that if you have to ask that question, stay away from mains electricity. It CAN kill you - best to pick another project.
The answer is a relay (for on off control of a non inductive device) - either a mechanical relay (simplest) (switch the relay with a transistor), or a solid state relay (connect the relay striaght to the PICAXE).
How much experience do you have with mains electricity? If you don't know anything about relays, I really recommend you start simple (12V max), and not with mains voltage.
A
The answer is a relay (for on off control of a non inductive device) - either a mechanical relay (simplest) (switch the relay with a transistor), or a solid state relay (connect the relay striaght to the PICAXE).
How much experience do you have with mains electricity? If you don't know anything about relays, I really recommend you start simple (12V max), and not with mains voltage.
A
westaust55
Moderator
Nothwithstanding Andrew's comments, some additional information may help.
Being Auckland, presume the heater is single phase 240V? Is this the case (or 415V 3 phase?)
What is the power/current rating?
What other purpose will the pICAE 18X have?
monitor temperature (via DS18B20)? or does the heater have a thermostat?
What tells the 18X when to turn the heater on and off?
What if the heater falls over?
Safety is an issue here as well as having someone not experienced/qualified working with mains voltage.
Will this "Device" be mounted on the heater or where?
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hippy
Ex-Staff (retired)
First you'd have to consult your local laws to see if such a homebuilt contraption is permisable, then you might consult your household insurance to see if it invalidates your cover, and then you'd see what local 'wiring regulations' dictate has to be done.
What is permissible and legal depends on local legislation, whether permanently wired or a plug-in unit, used at home or in a place where the public may be.
If you are going to do it the best way is probably a two pole mechanical relay of adequate rating switching both live and neutral with suitable fusing, correctly rated wiring, and proper earthing.
Your main concern should be safety, In isolating the electronics and everything externally from the live mains.
What is permissible and legal depends on local legislation, whether permanently wired or a plug-in unit, used at home or in a place where the public may be.
If you are going to do it the best way is probably a two pole mechanical relay of adequate rating switching both live and neutral with suitable fusing, correctly rated wiring, and proper earthing.
Your main concern should be safety, In isolating the electronics and everything externally from the live mains.
krypton_john
Senior Member
It would be nice if someone manufactured a power controller that had all the dangerous bits inside and just had a connector for a ttl control exposed. It would just have a standard power plug on one side and a socket on the other.
There's probably lots of these around. X10 comes to mind. Perfectly safe.
There's probably lots of these around. X10 comes to mind. Perfectly safe.
Andrew Cowan
Senior Member
Economatics used to make a mains relay. Sealed box, very safe. However, pricey at £70.
I'm sure plenty do exist.
A
I'm sure plenty do exist.
A
Bah, all you need is an optoisolated triac, just keep your fingers off the wires. 
220V is nasty, once I almost got the final zap from it, after surviving, 60VDC, 120VAC, 480VAC and a shot of about 8000V from a video camera. The 220 was the worst. It locks you in and you can't let go.
220V is nasty, once I almost got the final zap from it, after surviving, 60VDC, 120VAC, 480VAC and a shot of about 8000V from a video camera. The 220 was the worst. It locks you in and you can't let go.
The X10 collection includes a universal module that can be switched to detect either low voltage DC or a contact closure. The signal it sends (via the AC mains) can operate a light or appliance controller. Everything except the sensor terminals is enclosed and all the AC is connected via standard plug-in connectors (whatever your national standard uses). (I've even connected a DC output wallwart across the end-of-cycle buzzer on a clothes dryer to trigger a universal module and operate a chime elsewhere in the house.)
Not as cheap as the $15US 240volt 20amp SSR, but safer for those who manage to get both hands on AC, I've only been shocked by AC mains once, when working on an AC and DC powered two-way radio that had a wiring error on the power connector which did not affect 12volt DC operation but did put 120volts on the chassis when connected to AC. Bumping the radio case with my elbow as I picked up the coax from a grounded antenna put AC from fingertips to elbow on that arm. I still remember how much it hurt...
I've used X10 controllers for a long time and find them better than 95% reliable (occasionally a wireless switch fails to operate a module, but it's usually the batteries in the wireless switch).
John
Not as cheap as the $15US 240volt 20amp SSR, but safer for those who manage to get both hands on AC, I've only been shocked by AC mains once, when working on an AC and DC powered two-way radio that had a wiring error on the power connector which did not affect 12volt DC operation but did put 120volts on the chassis when connected to AC. Bumping the radio case with my elbow as I picked up the coax from a grounded antenna put AC from fingertips to elbow on that arm. I still remember how much it hurt...
I've used X10 controllers for a long time and find them better than 95% reliable (occasionally a wireless switch fails to operate a module, but it's usually the batteries in the wireless switch).
John
krypton_john
Senior Member
As a child I once stick my finger into a light socket and got a zap.
No ill effects that I know of ... <twitch, twitch>
Probably lucky that there was no decent current path from my finger to ground via my heart or brain though.
No ill effects that I know of ... <twitch, twitch>
Probably lucky that there was no decent current path from my finger to ground via my heart or brain though.