Need some help with a bit of electronics...

[The Grim Ninja]

Connect the top two pins of the IC. [by the little circle on the chip and pin across from it].

That should result in "ON" forever. Or until the wire melts or the USB port deactivates.

[PeterB]

Hi guys, I actually may already have the chromel wire. The problem for me is going to be that with the length and gauge I need, I might have to go fairly high on the voltage. Is there a way to figure out how hot it'll get, as a function of those two parameters?

Edit: I looked and what I found is that I have wire in the range of 18-30 gauge. I'm thinking I'll need more than a 9V...

[space-time]

Dude, 9V can make it red hot, you need much less than that. You don't want to boil these little creatures, do you? Just test and start with low voltage. Take it slow and go from there. Be brave, experiment, you are a Scientist! You don't need us to guide you step by step, or you're going to have to list us as co-authors.

[Filliam H. Muffman]

PeterB wrote:
Hi guys, I actually may already have the chromel wire. The problem for me is going to be that with the length and gauge I need, I might have to go fairly high on the voltage. Is there a way to figure out how hot it'll get, as a function of those two parameters?

Edit: I looked and what I found is that I have wire in the range of 18-30 gauge. I'm thinking I'll need more than a 9V...

What are you planning to use as a power supply? If it has enough power/amps, a 5V power supply should be more than enough if you have a wide selection of wire available.

If the lighter ran off of USB, a similar size and length wire should work with less than 5V (most devices are designed to run at 3.6V or a little less, which is why 3.6V LiON batteries are so popular). If you have a different wire that is longer or a smaller diameter, there is a chance it would need over 7V.

The chart I linked has Ohms/ft for different size wires. Assuming 5V, and guessing 1W will be more than enough power, that says the wire should be 25 Ohms* (Resistance=Voltage²/Power). 12 inches of 36 gauge would be 27 Ohms. If that is "too long", you can coil it around a toothpick to make it a more compact heat source. Cutting the length in half will double the power, so just under 6 inches of 36 gauge would be 2W.

You can figure out power, resistance, voltage, current using an electrical formula circle.

Please remember that the wire won't glow in water, so if you take it out and apply too much voltage, it might burn up.

Edit: * this is a guess since I haven't played around with nichrome wire in 35 years.

[space-time]

guys, keep in mind that he wants to put these in a solution and those worms should still be alive! he tried to do this with other means (he's still working on that) and he wants a small temperature difference (I can't remember details from previous discussions, but let's say for the safe of argument, about 10F). Now this wire GLOWS in air, and in water it will stay cooler of course, but it may still be too much. he simply needs to get an adjustable power supply, and start at 0V and increase slowly until he sees the worms being deflected when looking under microscope. also this will happen in a very thin layer of water, more like a 2D experiment. I am afraid that all our calculations will be way off, and the only proper way to do it is to try it under microscope with various wire diameters, always starting at 0V and ramping up slowly.

[PeterB]

s-t is correct, except that it won't be in solution. The wire will likely be suspended in the air, some distance above a semisolid surface, where the animals will hopefully avoid the wire. As you all are saying, I'm sure I'll have to determine this empirically; I just need some idea of where (ballpark) to start, as far as voltages, lengths, and gauges of wire are concerned. The problem in my case is that if the wire is too thin, it's unlikely to keep its shape or position, so it needs to be a bit thicker and longer, which I assume means the voltage will also need to be higher. Oh, but on the other hand -- I may not need that much heat.

[Filliam H. Muffman]

PeterB wrote:
s-t is correct, except that it won't be in solution. The wire will likely be suspended in the air, some distance above a semisolid surface, where the animals will hopefully avoid the wire. As you all are saying, I'm sure I'll have to determine this empirically; I just need some idea of where (ballpark) to start, as far as voltages, lengths, and gauges of wire are concerned. The problem in my case is that if the wire is too thin, it's unlikely to keep its shape or position, so it needs to be a bit thicker and longer, which I assume means the voltage will also need to be higher. Oh, but on the other hand -- I may not need that much heat.

Voltage is not really anything to worry about. With a selection of wire available, current and power are the main variables to worry about for something like this. Thin wire can be wound around many types of non-conductive supports, as long as it doesn't get hot enough to burn or melt the support. A coil of 36 gauge wire should be reasonably rigid when it's supported at the ends, as long as you aren't heat cycling it high enough to make it glow yellow.

Another option is to use a small incandescent nightlight. Plug the nightlight into an inline dimmer then to an extension cord. The biggest problem might be that it will be hard to control to the exact heat output needed. The ones listed are only sold online, but a decent local hardware store should have something comparable.