4 ms·

Another neat trick in the same ballpark (but not involving a potato :-p) is to create a 220v to 110v adapter with a "resistance bridge". Plugging two (hopefull

Another neat trick in the same ballpark (but not involving a potato :-p) is to create a 220v to 110v adapter with a "resistance bridge". Plugging two (hopefully pretty equal resistance) incandescent lights in series, each lamp should have a 110v potential difference... say: A ----(60W lamp)-- B --(60W lamp)----- C By plugging A and C "cables" to a 220V electrical outlet, one should be able to grab 110V from either A-B or B-C :-) (assuming both lamps have about the same resistance). Most electronic devices work with a wide range of input voltage any way, so it doesn't have to be extremely precise.

cfn 4y ago
Should work but don't plug the 110v equipment until the lights are totally on. The initial rush current will cause higher voltages for a split second that may damage it.
unnouinceput 4y ago
If the light that is in parallel with the circuit you are trying to power up malfunctions, you going to be in for a nasty surprise. This method, ignoring the fact that you're wasting at least 120W in plus, is also quite unreliable.
Denvercoder9 4y ago
You want to be very careful about what kind of equipment you power like this. If it has resistance that's substantial compared to the resistance of the lamps, the voltage divider won't be a neat 50:50 anymore and you'll get more than 110 V.
- kimburgess 4y ago
  That's why you use two potato halves instead of light bulbs. You can calibrate the wire distances to create the exact relative resistance for the divider to function to spec with the load.
ilyt 4y ago
Oh god please fucking dont
comboy 4y ago
This is a bad idea on multiple levels. Do not do this.
dtgriscom 4y ago
Among the many reasons this is a bad idea: the "hot" resistance of an incandescent bulb is many times the "cold" resistance. For example, [0] finds that a 110V 40W bulb is 24Ω when cold, but 360Ω when hot. Why does this matter? Let's put two of these bulbs in series, one of them hot and the other cold, and run 220V through them. The total resistance will be 384Ω, so the current will be V/R, or 0.57A. The hot bulb will have IR volts across it, or 206V; the cold bulb will have 14V. Bingo: your voltage divider is way, way off. Even better, putting 200+ volts across a 110V bulb will blow it (power would be IV, or 117W), and you've got either nothing or 220V. Now, you won't be starting with one bulb hot and the other cold, but the two bulbs won't be exactly equal. The one with the higher resistance will be hotter than the other one; can you be sure that the imbalance won't slowly get larger and larger? [0]: https://electronics.stackexchange.com/questions/571836/why-does-my-120v-40w-lightbulb-only-have-26-ohms-across-it https://electronics.stackexchange.com/questions/571836/why-d...
emmanueloga_ 4y ago
Haha so controversial :-p I did not say it was a good idea, just a neat trick. I actually _had_ to do this once, when I forgot a 220v to 110v adapter for a wireless microphone, for a wedding, in an hard to access location [1], and there was just no time to go get a transformer from anywhere else :-) Luckily, the whole "setup" did not turn into fire for the 30 minutes or so that the mic was needed and the wedding speech could actually happen without anyone needing to scream :-) 1: https://en.wikipedia.org/wiki/Tigre,_Buenos_Aires https://en.wikipedia.org/wiki/Tigre,_Buenos_Aires

cfn 4y ago

Should work but don't plug the 110v equipment until the lights are totally on. The initial rush current will cause higher voltages for a split second that may damage it.

unnouinceput 4y ago

If the light that is in parallel with the circuit you are trying to power up malfunctions, you going to be in for a nasty surprise. This method, ignoring the fact that you're wasting at least 120W in plus, is also quite unreliable.

Denvercoder9 4y ago

You want to be very careful about what kind of equipment you power like this. If it has resistance that's substantial compared to the resistance of the lamps, the voltage divider won't be a neat 50:50 anymore and you'll get more than 110 V.

kimburgess 4y ago
That's why you use two potato halves instead of light bulbs. You can calibrate the wire distances to create the exact relative resistance for the divider to function to spec with the load.

ilyt 4y ago

Oh god please fucking dont

comboy 4y ago

This is a bad idea on multiple levels. Do not do this.

dtgriscom 4y ago

Among the many reasons this is a bad idea: the "hot" resistance of an incandescent bulb is many times the "cold" resistance. For example, [0] finds that a 110V 40W bulb is 24Ω when cold, but 360Ω when hot. Why does this matter? Let's put two of these bulbs in series, one of them hot and the other cold, and run 220V through them. The total resistance will be 384Ω, so the current will be V/R, or 0.57A. The hot bulb will have IR volts across it, or 206V; the cold bulb will have 14V. Bingo: your voltage divider is way, way off. Even better, putting 200+ volts across a 110V bulb will blow it (power would be IV, or 117W), and you've got either nothing or 220V. Now, you won't be starting with one bulb hot and the other cold, but the two bulbs won't be exactly equal. The one with the higher resistance will be hotter than the other one; can you be sure that the imbalance won't slowly get larger and larger? [0]: https://electronics.stackexchange.com/questions/571836/why-does-my-120v-40w-lightbulb-only-have-26-ohms-across-it https://electronics.stackexchange.com/questions/571836/why-d...

emmanueloga_ 4y ago

Haha so controversial :-p I did not say it was a good idea, just a neat trick. I actually _had_ to do this once, when I forgot a 220v to 110v adapter for a wireless microphone, for a wedding, in an hard to access location [1], and there was just no time to go get a transformer from anywhere else :-) Luckily, the whole "setup" did not turn into fire for the 30 minutes or so that the mic was needed and the wedding speech could actually happen without anyone needing to scream :-) 1: https://en.wikipedia.org/wiki/Tigre,_Buenos_Aires https://en.wikipedia.org/wiki/Tigre,_Buenos_Aires