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Thread: Phidgets Relay board for a Lamp?

  1. #1
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    Phidgets Relay board for a Lamp?

    Hello,


    http://www.trossenrobotics.com/store...lay-Board.aspx

    Can I use this Phidgets Relay to sitch on and off a 40 watt lamp that I plug into the wall? Would this be safe or even possible?

    Thanks!

  2. #2

    Re: Phidgets Relay board for a Lamp?

    Quote Originally Posted by Husko View Post
    Hello,


    http://www.trossenrobotics.com/store...lay-Board.aspx

    Can I use this Phidgets Relay to sitch on and off a 40 watt lamp that I plug into the wall? Would this be safe or even possible?

    Thanks!
    Based on Ohm's law (watts = volts * amps), and the spec, that relay should have no problem controlling a 40 Watt bulb at 120 volts as it's rated for 1200 watts. That said, if you have to ask, you need to be VERY careful working with high current/voltage electricity as it can KILL YOU.

    What you might want to do is get one of those surge protectors with a switch and hook the relay up to the switch contacts. That way you've got something you can work with that you can then plug the light into.

    I have some of those phidget relay boards and their contacts are somewhat close together so they are difficult to get higher gauge wire into. What I ended up doing was hooking the output of that relay into the coil end of one of those high-current relays from Radio Shack and then used the high-current relay to control the switch on the surge protector. The relay allowed me to use the crimp-on spade connectors, which were very convenient. Incidentally, I used this setup to control a floor sump pump.
    We suspected that an agreement with humans would prove impossible to maintain. You are erratic, conflicted, disorganised. Every decision is debated, every action questioned. Every individual entitled to their own small opinion. You lack harmony, cohesion, greatness. It will be your undoing.

  3. Re: Phidgets Relay board for a Lamp?

    Phidgets Inc. is currently shipping the 1014 with 12-24 Gauge terminal blocks. You should not need wire larger than 12 Gauge to wire up a 40 watt bulb. The 3051 is still using 16-26 Gauge terminal blocks - a little small for household mains wiring.

    Chester

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    Re: Phidgets Relay board for a Lamp?

    I'd say that 16G is fine for a 40 watt bulb with almost any reasonable length run - make SURE you have a working breaker or fuse close to the source. I wouldn't go larger than 14 gauge as some over-inventive inspector would make me tear it out - they don't like my propensity for overbuilding in the building code.

    700 circular mills/amp rule would give us 3.7A for 16G power transmission - it's HYPER conservative. It only gives us 6A for 14G where Code gives us 15A for 14G (@ 120v) - so even with the excessively conservative 700 circular mills/amp rule, our [email protected] light bulb is a happy camper at 16G.

    Choice of stranded raises this, excessive distance lowers it. 16G resistance is about 4Ohms/1000ft as memory serves. So quick back-of-the-napkin calculation says that we'd have a voltage drop of 0.5v over a 20ft run with a 3A load at 120v, so if we were getting a clean 120v (we won't be) from the supply, we'd end-up with 119.5vAC at the lamp, and at almost 2600 circular mils, we'd be happy enough.

    [edit: Note copper wire assumed]
    Last edited by Adrenalynn; 08-26-2008 at 01:17 PM.
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    Re: Phidgets Relay board for a Lamp?

    Quote Originally Posted by Hephaistos View Post
    Based on Ohm's law (watts = volts * amps), and the spec, that relay should have no problem controlling a 40 Watt bulb at 120 volts as it's rated for 1200 watts. That said, if you have to ask, you need to be VERY careful working with high current/voltage electricity as it can KILL YOU.
    Just a question. It's mostly the high current (amps) that kill you right? Because some TAZERS have 50 000 volts in them and (often) don't kill you. But you could die with a 24 volts circuit passing more amps. Does it work just with the current or wattage?

    You will be fine with a light bulb 16G usualy. Couldn't you use those fluorocompacts with only like 15 watts. Could save you electricity

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    Re: Phidgets Relay board for a Lamp?

    The general rule of thumb is "Volts Jolt, Mils Kill". So your assumption there is correct HOWEVER there are notable exceptions. Voltage through the chest can cause the heart to defibrillate (sp?) even at a pretty low current.

    Volts = Current * Resistance [Ohms law] - the resistance of the skin denotes the amount of current that will be drawn at a given voltage.

    It's also worth noting that even a stun gun can be fatal in many instances (see defib above), even as simply as causing a fatal fall when "the volts jolt".

    The upshot though is to just simply treat every live circuit as if touching things you shouldn't be touching will be fatal. RF can up that anty. It can reach out and bite you quite a distance. I have a nasty scar from when I was a kid building my first LASER power supply. Just a little black mark at the tip of my finger and a little black mark where my palm was touching ground. It burnt a path all the way along the bone and my hand was useless for more than three months. I still have numbness and some limited range of motion 25+ years later. Note to self: That big read guard on the high voltage probe behind which is the handle is there for a reason - a reason other than to inconvenience you.

    Don't mess around with stuff you aren't MORE than certain of - and remember the "rule" my daddy taught me: "One hand for the circuit, one hand for the pocket." Presumably keeping current from traveling across the heart. That said - as note: RF can still getcha.
    Last edited by Adrenalynn; 08-26-2008 at 02:33 PM.
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  7. #7

    Re: Phidgets Relay board for a Lamp?

    Quote Originally Posted by sam View Post
    Just a question. It's mostly the high current (amps) that kill you right? Because some TAZERS have 50 000 volts in them and (often) don't kill you. But you could die with a 24 volts circuit passing more amps. Does it work just with the current or wattage?
    It's really the amps that kill you. However, amps and volts are inextricably bound together by Ohm's Law. Since the human body is essentially a fixed resistence, it's really a combination of volts and amps that come into play most of the time. However, lots of other factors can potentially determine whether or not someone experiences a lethal shock (length of shock, environmental factors such as humidity).

    It only takes about 100ma to stop the heart. I believe the resistence of someone with dry skin is around 100K ohms. At this, 120 volts isn't enough to kill you. Add some moisture however and your resistence can drop down to 1K ohms, which would be a problem.

    OSHA has a decent site that discusses the affects of electricty on the human body. Check it out here:

    http://www.osha.gov/SLTC/etools/cons...eccurrent.html
    We suspected that an agreement with humans would prove impossible to maintain. You are erratic, conflicted, disorganised. Every decision is debated, every action questioned. Every individual entitled to their own small opinion. You lack harmony, cohesion, greatness. It will be your undoing.

  8. #8

    Re: Phidgets Relay board for a Lamp?

    Quote Originally Posted by Adrenalynn View Post
    Don't mess around with stuff you aren't MORE than certain of - and remember the "rule" my daddy taught me: "One hand for the circuit, one hand for the pocket." Presumably keeping current from traveling across the heart. That said - as note: RF can still getcha.
    Excellent pieces of advice. Incidentally, my dad gave the same advice. Interesting how that works!
    We suspected that an agreement with humans would prove impossible to maintain. You are erratic, conflicted, disorganised. Every decision is debated, every action questioned. Every individual entitled to their own small opinion. You lack harmony, cohesion, greatness. It will be your undoing.

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    Re: Phidgets Relay board for a Lamp?

    Incidentally, men can generally withstand more of a shock than women can prior to fatality. A woman's skin resistance tends to be lower...

    It's also interesting to see how the body's resistance changes in the daily cycle. I was doing an experiment detecting REM sleep (and subsequently lucid dreaming state) using galvanic skin resistance (GSR) - my results are posted on another forum - but anyway... Even in sleep my skin resistance varied from ~80kohms up to about 3M ohms using my loosely calibrated probes. I was more interested in the window than in the actual value, but the point being that it varied by a quarter magnitude. (My circuit was properly multiply isolated btw)

    [note that the probes themselves added resistance and there was no conductive gel involved. Typically skin is about 1k-150k in resistance]
    Last edited by Adrenalynn; 08-26-2008 at 03:01 PM.
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    Re: Phidgets Relay board for a Lamp?

    Quote Originally Posted by Hephaistos View Post
    Excellent pieces of advice. Incidentally, my dad gave the same advice. Interesting how that works!
    Fascinating! I'd never heard anyone else use it... Where are you from, if I may ask?
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