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Semicton
08-25-2008, 06:13 PM
Hello,


http://www.trossenrobotics.com/store/p/3204-Dual-Relay-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!

Hephaistos
08-25-2008, 07:56 PM
Hello,


http://www.trossenrobotics.com/store/p/3204-Dual-Relay-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.

fitchett
08-26-2008, 01:00 PM
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

Adrenalynn
08-26-2008, 01:14 PM
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]

sam
08-26-2008, 02:13 PM
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 :tongue:

Adrenalynn
08-26-2008, 02:31 PM
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.

Hephaistos
08-26-2008, 02:38 PM
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/construction/electrical_incidents/eleccurrent.html

Hephaistos
08-26-2008, 02:43 PM
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!

Adrenalynn
08-26-2008, 02:59 PM
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]

Adrenalynn
08-26-2008, 03:00 PM
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?

Semicton
08-26-2008, 04:53 PM
Interesting replies everyone. Me and my boss where talking about voltage vs. amps today earlier at work. Specifically how the electrons move. We work as programmers at a power company and we asked a line Foreman to actually describe the rate or flow of electrons(amps) because we could not understand the real difference between the two. He didn't have an answer either. After only a little bit of research We concluded that Voltage is the potential flow of elections between a positive source and a negative source. Is this correct? We concluded that amps are the rate of elections passing from a negative to positive source. is this correct?

We still don't truly understand so we tried to visualize it and for example a 9 volt battery will always have the same voltage of 9 volts. And if you took a wire from the positive and wired it to the negative, the rate of which the electrons are passing over the wire from the positive to the negative is the amps? So, Will a wiring up any 9 volt battery will always have a set amount of amps determined by the resistance of the wire itself?

I'm sure this is all wrong but it was the best we could come up with. Because How is it that a high voltage source could only contain a few amps.. or more amps for that matter.

heheh I'm rambling. But a good answer would be great! We rambled on most of the day for fun and threw ideas out in the air. The line format did explain that 110 with water can kill you flat, but he could not explain why. But It's interesting to know the reason is that water decreases your resistance because it creates a better contact from the source to your body and it's own water..... I think....

Oh and I almost forgot, The flow of electrons is actually from the negative to positive becuase elections are a negative charge, right?

sam
08-26-2008, 07:23 PM
Interesting replies everyone. Me and my boss where talking about voltage vs. amps today earlier at work. Specifically how the elections move. We work as programmers at a power company and we asked a line Foreman to actually describe the rate or flow of elections(amps) because we could not understand the real difference between the two. He didn't have an answer either. After only a little bit of research We concluded that Voltage is the potential flow of elections between a positive source and a negative source. Is this correct? We concluded that amps are the rate of elections passing from a negative to positive source. is this correct?

We still don't truly understand so we tried to visualize it and for example a 9 volt battery will always have the same voltage of 9 volts. And if you took a wire from the positive and wired it to the negative, the rate of which the electrons are passing over the wire from the positive to the negative is the amps? So, Will a wiring up any 9 volt battery will always have a set amount of amps determined by the resistance of the wire itself?

I'm sure this is all wrong but it was the best we could come up with. Because How is it that a high voltage source could only contain a few amps.. or more amps for that matter.

heheh I'm rambling. But a good answer would be great! We rambled on most of the day for fun and threw ideas out in the air. The line format did explain that 110 with water can kill you flat, but he could not explain why. But It's interesting to know the reason is that water decreases your resistance because it creates a better contact from the source to your body and it's own water..... I think....

Oh and I almost forgot, The flow of electrons is actually from the negative to positive becuase elections are a negative charge, right?

Right, Negative to positive. That confused a lot of people in my class :tongue:. We usualy (well, in my class) don't talk about this, don't need too.

Volt is always been pretty vague for me. By what my teacher was trying to explain to me, I understood what volts were better than him. :sad: I good explanation would be pretty nice.

Semicton
08-27-2008, 06:07 AM
I found a couple videos that helped me understand


http://www.youtube.com/watch?v=1xPjES-sHwg

http://www.youtube.com/watch?v=YGvu9iqjJq4

sam
08-27-2008, 06:54 AM
That first video help me quite a bit to understand what a volt is. Forgot it was a J/C.

Ahhh, electricity.

ooops
08-27-2008, 08:48 AM
Not to over simplify things but the garden hose analogy works pretty well:
Volts would be the pressure of the water and amps would be the volume of the water. They are both separate yet tied together. If you increase the pressure on the hose (by sticking your thumb over the end) but not the volume of water flowing through it you increased the voltage but not the amperage. If you remove your thumb and turn the spicket up higher more water comes out but at a lower pressure so you have increased amperage and lowered voltage. So, if want more volume and can't increase the pressure we would get a bigger hose. Conversely, if we increase the pressure we can flow the same amount of water through a smaller hose.
No how does that help???
In the case of a water pump ... no analogy a real water pump ... the last one I looked at was 110/220 volts capable. It drew 9 amps at 120v and 5 amps at 220v (from memory). The total wattage was the same and the total mechanical force was the same but we had an option of which voltage to use. Now one step further, the wire size requirements for the higher 220 voltage was smaller than the wire size requirement for the 110 voltage, which for me would seem counter intuitive until we remember that we are increasing the "pressure" in our water hose analogy by changing the voltage from 110v to 220v so at the higher "pressure" (voltage) we can use a smaller hose (wire) to flow the same amount of "juice".
Hopefully that helps someone somewhere with understanding the voltage/amperage relationship ... it helps me:)

Electricity
08-27-2008, 11:57 AM
Ahhh, electricity.

Yes?




:D


That first video helped me a bit too. Electricity has always been a bit confusing to me aswell. Maybe I need to do some introvert thinking.