Ask an Expert: Electromagnet

[lfeneque]

Hi. I am making a science fair project with my daughter. The projects is about the strength of electromagnet. We made it and it works, but we try to replace the 6 volts battery by a inverter ( 120v(ac) to 12v(dc) of 1.5 amps). It does not work. Then we try with another inverter ( 18V(dc) of 2.5amps output) and it does not work. I want to know, why the project work with the 6 volts battery and do not works with the inverters that has a greater DC output?

[bfinio]

Hi lfeneque,

How are you connecting the electromagnet to the adapters? Did you cut and strip the adapter's cable so you could attach alligator clips to the two wires separately?

If you did that and it still doesn't work, my best guess would be that the adapters have some sort of built in short-circuit protection. The electromagnets have very low resistance (just a few ohms) so the adapters might automatically shut off when you connect them. That's just a guess though. If you want to test the magnets with higher voltages, you could buy more 6V lantern batteries and connect them in series. You should be able to get more batteries at a hardware store, they are also available from Jameco Electronics:

https://www.jameco.com/z/4R25-EV-Evergr ... 83699.html

Hope that helps,

Ben

[rmarz]

lfeneque - Ben had some good observations about the short circuit protection. If you have a multimeter, you might check to see what the current drain is when you used the 6 volt battery. It may be above the output of the Inverters. Are you sure the 12 and 18 volt sources are truly inverters or just transformer power adapters? If you have that multimeter, measure the output voltage of the inverters at 'no load' and with the electromagnet connected. Does it show any voltage when connected to the electromagnet?

Rick Marz