BACK IN STOCK AND UPDATED PRODUCT – Powerswitch tail 2
BACK IN STOCK AND UPDATED PRODUCT – Powerswitch tail 2! The Power Switch Tail II is a smart alternative to slicing apart power cords to wire up your own relays. Its a compact 120V 3-pronged extension cord, with a relay board embedded in the middle. Connect to the relay using two screw terminals and activate by providing a 3 to 12V signal (3mA current draw at 3V, 30mA at 12V). The relay can switch 15 Amp resistive loads such as heaters, small skillets, lights, etc. An LED indicator above the terminals will help you with debugging.
Ideal for people making their own controllable lights, SMT reflow plates, boilers or heaters, coffee roasters, home automation projects, etc.
New! The Power Switch Tail II now is opto-isolated so you don’t need a transistor or protection diode. The input acts like an LED so its safe for use with any microcontroller or logic pin.
Please note, this is a safer alternative to wiring up your own relays but still requires common sense and knowledge of electrical circuits. Stay within the rated limit of the relay and de-rate properly when not using resistive loads. Do not leave DIY electrical projects unattended or where they can get wet! This product is intended to be used by advanced hobbyists who are comfortable working with power supplies.
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Is there also going to be a 230V EU version? That would be awesome!
This is a handy-dandy device for a lot of projects, and I am happy to see the upgrades.
Unfortunately, the design mis-applies MOV transient surge protectors. MOVs are designed to soak up transients generated when inductive loads switch off, so that relay contacts don’t get burned. The MOV in this device will do a swell job of that until…
…something makes the MOV short-out. In fact, MOVs often fail shorted, and if that were to happen here, you would lose control of the load and not be able to shut it off. The MOV may also flame-out as it tries to conduct the load current. Hopefully the case is made of a self-extinguishing polymer.
In short, don’t do that. MOVs and TVS diodes should only be tied across loads, never switching elements.
What are the chances of a problem happening with this product? Hard to say, but this is something that falls under the category of “Good Design Practices.”
I hope the designer takes my comments in the spirit of caring that I intended.
@daniel – this is good feedback, have you sent this along to the product’s designer? if you need their contact info let us know!
Thanks, LadyAda- I have just sent it. Thanks for the suggestion.
By the way, I am in the process of adapting some of my engineering guidelines that I have developed over the last 25+ years for use by Hobby Enthusiasts. I have lots and lots of material on the best way to drive big nasty electrical loads with small-signal electronic devices. It will soon be posted on my Blog. Stay tuned!
Oh, one more thing-
Incandescent lamps are well-known relay-killers, because cold tungsten filaments have a cold resistance roughly 1/10th of their resistance at operating temperature. Even though the filament warms up within a few 10s of milliseconds, that is plenty of time to weld the contacts shut. A great workaround for that is to use an Inrush Current Limiter element, a component that resembles an MOV, but is actually a ruggedized NTC thermistor.
For more info: http://www.ge-mcs.com/download/temperature/920_325a.pdf
By the way- a properly rated ICL will greatly extend the life of incandescent bulbs by reducing the thermal shock on the filament at turn-on (which is when most bulbs fail). Anectdotally, I used one of these in a halogen drafting lamp that uses very expensive bulbs. Afterwards, my bulbs lasted me at least 5 times longer!
@Daniel: as someone interested in building his own home automation system by replacing all the light switches in his home with relays and buttons, I look forward to your insight!
Wouldnt it be great if it also provided 5V power for the DiY board you might add…