Have you built an 120 VAC to 110DC converter?

[David Kilnapp]

Hello Friends. Hope you are all doing well on this Memorial Day when we remember, with gratitude, those who gave a full measure to preserve and protect our freedom. I for one am very grateful for the freedoms we enjoy. As they say, freedom is not free.

Anyway, I have recently acquired a DC fan - the first DC fan in my 65 fan collection. I am familiar with how a full bridge rectifier works. I'd like to build a simple but elegant arrangement that uses wall current as the input (AC voltage) which has an outlet on it for plugging in a DC fan. Ideally, I would love to have different settings to allow for other DC voltages.

Some of you are quite clever, and no doubt have built a rig for accomplishing this. Would you be so kind as to respond with a picture or pictures of what you built so I can see what it looks like? Or perhaps, you can recommend one that is not too expensive to purchase. I would prefer to build one myself if I could find a step by step tutorial. The goal would be to get a DC output that is fairly smooth (minimal spikes) using wall current as the input.

One of my AFCA friends is going to provide me with a bridge rectifier so that's a good start.

Suggestions with pictures, please? I would surely appreciate it.

Edited May 27, 2024 by David Kilnapp

[Michael Rathberger]

I just run my variac. AC in to variac, out to rectifier outlet, to DC fan. 

[David Kilnapp]

I like that idea. I would be interested to know how you make a rectifier outlet? And how do you know what the DC voltage is coming out of the outlet? My understanding is that the rectifier reduces the input voltage somewhat so that the output is less than the numeric input, which wouldn't be a problem as long as I know what the output is.

 

Edited May 27, 2024 by David Kilnapp

[Michael Rathberger]

You would wire it per instruction. Two in from AC, two out to outlet. To be honest I bought the thing from John M. way back when Ackley was still a thing. Maybe 2001. I have since wired others though direct into fans.

As for voltage out, I'm not particularly worried. I don't run them all day, I dial the variac to about, and go from there. You'd have to add a meter between outlet and fan to be exacting. I'm not a scientist about it, just making sure things work.

There are ready made variable DC power supplies. Older ones, not the Chinese stuff. I saved a listing on eBay awhile ago but didn't pull the trigger. They were made in the 60s. I personally wondered if they were true DC.

[David Kilnapp]

Thanks for the response, Mike. Appreciate it.

[Russ Huber]

A variable transformer I built for operating a Tesla fan motor on 100 VAC. All you would have to do is put a full wave bridge rectifier inline to the AC output. You could actually toggle (two position/center off) the output of the variac transformer alternative AC or DC current to the outlet on the box. I bought an exposed 3.5 - 4.5 AMP variac off of Ebay to build it.  I had it fused as well if you look inside. The box came from Hobby Lobby mounted on an old wooden plaque I had. The sheet brass came from a trophy shop, cut by them to size. I used a chemical process for the patina on the brass.

Edited May 27, 2024 by Russ Huber

[David Kilnapp]

Now THAT's elegant, Russ! Beautiful and altogether perfect aside that Tesla. The only question I have is regarding the full wave Bridge rectifier. My understanding of how a rectifier works is that it cuts the sine wave in half. But that leaves you with a modulating half sine wave. From what I've read, one needs a capacitor in line to smooth out the power modulation and give one a nice smooth DC output. Ideally, I'd like to have a way of measuring the DC power that exits the arrangement. Your rig is beautiful to look at, Russ. 

Edited May 27, 2024 by David Kilnapp

[Russ Huber]

20 minutes ago, David Kilnapp said:

My understanding of how a rectifier works is that it cuts the sine wave in half. But that leaves you with a modulating half sine wave. From what I've read, one needs a capacitor in line to smooth out the power modulation and give one a nice smooth DC output.  

David, respectively and sincerely said, the word overkill may very well apply to your above statement.  These are just silly small fractional DC fan motors. They will run fine on a full wave bridge rectifier. Don't believe me? Go ahead and buy a pure DC power source and compare the fan's operation running on that as opposed to a full wave bridge rectifier. 

I have roughly $60 vested into that decorative box above. The Tesla fan is a different story. 🙂

Edited May 27, 2024 by Russ Huber

[David Kilnapp]

That box is a thing of beauty. I do believe you but I love to tinker and building a rig that incorporates a gauge to measure the output with a variac at the front end would be ideal. I have three variacs so I would only have to build a box with a full wave bridge rectifier inside it and a gauge to measure the DC volts exiting the contraption.

[Russ Huber]

4 minutes ago, David Kilnapp said:

That box is a thing of beauty. I do believe you but I love to tinker and building a rig that incorporates a gauge to measure the output with a variac at the front end would be ideal. I have three variacs so I would only have to build a box with a full wave bridge rectifier inside it and a gauge to measure the DC volts exiting the contraption.

You can implement a meter to read voltage. You can even put in a digital readout.

FWIW....another option is once your variac is installed and choice of knob secured to the variac, you can also make various voltage stop markings just outside the dial for commonly used 32, 60, 100, 104, 110, 115, 120 voltages. You just use meter probes in the socket as you dial in your voltages and mark them.  

[David Kilnapp]

Thanks Russ.

[Lane Shirey]

I have an old school power strip that could be disassembled.  I have 4 of the outlets wired as 120V, just like they were, and I clipped the wires to the last 2 and wired a rectifier in line.  So I have 2-120 VDC outlets and 4 120VAC.  Used with a Variac it works great.  I marked the 2 DC outlets with fluorescent paint and clearly labelled them.  

[Michael Rathberger]

David, if you decide to go Russ's route, let me know, I'll drop you a few antique quality pieces like Russ's setup. It's every bit as serviceable as new but looks better... 

[Russ Huber]

42 minutes ago, Michael Rathberger said:

David, if you decide to go Russ's route, let me know, I'll drop you a few antique quality pieces like Russ's setup. It's every bit as serviceable as new but looks better... 

Are you insinuating my $6-$10 wooden Hobby Lobby box and its additions are substandard? 🙂

Edited May 28, 2024 by Russ Huber

[Michael Rathberger]

I more meant the electrical components...

[Russ Huber]

7 minutes ago, Michael Rathberger said:

I more meant the electrical components...

Just jerking your chain. I made that over a decade ago. 🙂