ToddFun.com: Convert 120v AC to 12v DC using just a light bulb, diode and a capacitor.

[fairyheli2]

what about 240v mains?

[toddrharrison]

@fairyheli2 Just the same, just do the math with 240v instead of 120v

[mikem1959]

Thank you for this video. This brings back memories. I was a electronics geek as a kid. I used to build kits and used the Radio Shack 150 in 1 to build many circuits.

[DOWNERK1226]

best video on youtube

[nixxonnor]

Nice walkthrough. I have just got an oscilloscope and I'm worried about connecting it to any device that is connected to mains. Why is it ok to connect the scope to the circuit in this case. (Why doesn't probe ground short out when connected to the 16VDC?)

[toddrharrison]

@nixxonnor I cover that issue quite completely with my Isolation Transformer post. See my Youtube channel: "toddrharrison" or my blog: "toddfun dot com".

[nixxonnor]

@toddrharrison I see. This video about converting 120VAC to 12VDV was the first of your videos I saw. Nice videos, blog and links. Anyways - I assume you used the isolation transformer on the DUT.

[toddrharrison]

@nixxonnor When testing, I sure did! I love that thing. But when finished and using the DC converter I don't. But then everything dangerous is buttoned up inside a metal box and my power cord has a ground wire strapped to the box for ground safety.

[nixxonnor]

@toddrharrison Does that mean that both the outputs of the DC converter is electrically isolated from the mains? Is there a way to be absolutely certain (ie using a multimeter) that any AC-DC converter is acting as an galvanic isolator? (Do I have an isolation transformer for sure if resistance between in and out connectors are infinite)

[toddrharrison]

@nixxonnor I’m not sure what you’re getting at here. If you want to know if it is safe to connect your ground clip of your scope to a point on your DUT or power system just meter the voltage between the point and your ground clip. If it is not zero or very much close to zero then DON’T connect the ground clip.

[toddrharrison]

@nixxonnor NOTE: check both AC and DC voltage. Try to use a meter with Auto-V LoZ voltage setting like the Fluke 117. This way it will auto show high voltage either AC or DC and with low impedance so you will not see ghost voltages and think it is unsafe to connect the scope ground.

[toddrharrison]

@nixxonnor NOTE: If you use a meter without LoZ voltage setting and you see voltage and think it is just ghost voltage you can get a 20watt to 40watt incandescent light bulb and connect it between the two points and if it glows a bit then you know it is not safe for the scope ground.

[ntydk]

Thanks for the video. Very informative to newbie like me.

Hope to see more projects like this with using oscilloscope and DVM for analysing the results.

[khoham]

you could also run the capacitor before the lightbulb and the capacitor will discharge through the resistor before going to the fan... allowing you to change the fan speed according to the bulb used..

[khoham]

you should run the diode after the lightbulb it would last longer because of the voltage breakdown of the bulb..

[khoham]

you gotta keep it simple.. I'd say you should use a small motor and the bike wheel will act like a flywheel and you can use another dc motor as a generator when you contact it against the wheel..

[frillip]

120V/~18V transformer + diode bridge + 1000uF capacitor + LM7812 + 330uF capacitor = Better solution.

If you're still focusing on a 'hack' method using components you have lying around, you can probably find most of the above in an old AC/DC wall plug

The voice of reason has never been a good look for me but having what is essentially an uncontrollable potential divider circuit connected to a MAINS supply is NEVER a good idea. Change in load = change in voltage = expensive paperweight.

[xeroxcape]

Isn't it also possible to use a smaller diode if you swap it's position with the bulb? To use what you had on hand if you lack a spare microwave.

[SkeluhtoR]

Only 5 minutes so maybe you cover this but... I have used old computer powersupplies tons of times to power 12v car audio equipment. Theres plenty of write ups on how to use them and even make bench power supplies out of them. But they are a little bigger then the transformers.

[SkeluhtoR]

@SkeluhtoR NVM I think you cover this in your power supply repair videos. FYI love your vids originally subscribed for your welding table video. Gonna do some more welding videos? I have built a microwave transformer stick welder. Also interested in building a alternator gas powered welder.

[laharl2k]

you could have also made a step down converter from a burned out low comsumption lamp.

The ones i have teared down so far were all converting 240AC to 311DC and then a simple step up to energize the tube.

maybe modifying that to may it a step down instead with an inductance from an atx suply could also work.