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Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
so im doing my science fair project on Magnetohydrodynamics and how different magnetic field locations and strengths affects the movement of the water.
So i can test that, but how do i measure the speed of the water? My only idea is food coloring from 1 point to another, and that seems unreliable.
Another question, I have a 16v 4.5A laptop power adapter. The adapter has short circuit portection and someone here said it would only work with >4 ohms of resistance. On another project, im using NaOH for an electrolysis cell, and i have maybe 2 ohms of resistance. without increasing the resistance, is there any way i can "bypass" the short circuit protection and maybe do something so it limits the current drawn by the cell?
Registered Member #51
Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263
16v into 2 ohms will pull 8a. Bypassing the shortcircuit protection will only cause it to blow a fuse or melt. Try moving the electrodes further apart, use a power supply that can handle the current, or use a lower voltage power supply. Try a real ATX smps, they can easily do 10a at 12v and can be hacked for anywhere from 5v to 20v.
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
i had an ATX Power supply, im guessing i didnt have a minimum load so the thing melted inside. Im getting another one soon, do you think 20 ohms (2x 10W resistors in seris)across the 5v line will be enough as a load?
EDIT: i got some parts from the supply, how can i find the inductance of one of the inductors? its a powder iron core. One film cap(?) says F 1.0k MD 250v
Registered Member #1107
Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792
i use a 10 ohm 10 watt wirewound from radioshack and it works just fine. i heatsinked it to the case and it barely gets warm so i suggest trying that 1st
Registered Member #567
Joined: Tue Mar 06 2007, 10:55AM
Location: Singapore
Posts: 147
To measure the water speed, try picking up a cheap anemometer (One with the cups sticking out) and push the cups into the water. Try not to get anything else wet.
Registered Member #16
Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554
You could quite easily brew up a little waterwheel that could measure water speed. Use a LED an phototransistor to detect the speed of the wheel in RPM, then do some quick math to determine forward speed of the water. So long as you make the wheel very light, it should be pretty accurate.
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Science Fair/Power supply
