Need Help with Transformer. The electrical kind.

[11bravo]

Wasn't sure where this should go.
Its for a DIY curing oven for cooking self-made tubes so, scratch built.

Anyway, I have a 120V AC - 12V DC transformer to run circulating fans (computer chasis fans) in the oven.

It's Radio Shack part number 273-1511.

Well, dummy me didn't pay much attention and now I see that it actually has 2 ~ 6.3V outputs instead of a single 12V out.

See attached.

Should I not be able to attach the two yellows as the pos(+) and get the 12V?
Gets awful hot when I do that and stinks too.

Should I just go find one with a single out?
Could rig up a wall-wart I suppose but something like this is cooler.

Thanks,

Greg

 

[Hospital_Rocket]

Greg

1) That is called a center tapped transformer and if you needed 12VAC you could use the two yellow leads with no problem.

2) The output of your transformer does not have a positive or negative. It is alternating current.


That said...

Is the fan a 12V AC or DC motor? Most of the 12V fans I have dealt with are 12VDC. Unless they are speecifically labeled as such, AS & DC fans are not interchangeable

 

[11bravo]

Well, crap; you're right.
Yeah, the fans are DC and I just plain brainfarted on the transformer just being AC-AC.
I'm gonna end up with some sort of wall-wart, aren't I?

OR
https://cgi.ebay.com/NIB-IGLOO-KOOL-MATE-POWER-SUPPLY-CONVERTER-110V-12V_W0QQitemZ9730567502
Little cut-cut here, and snip-snip there, solder like a mad man AND it'll fit in my enclosure.
Thanks for your help Al.
You're not such a bad guy even if Mr. Flis says you are.
Which he doesn't.
But if he did.....

 

[jflis]

Originally posted by 11Bravo

Thanks for your help Al.
You're not such a bad guy even if Mr. Flis says you are.

Which he doesn't.
But if he did.....

I get pulled into threads in the oddest ways sometime... LOL

 

[TWRackers]

Originally posted by 11Bravo
Should I not be able to attach the two yellows as the pos(+) and get the 12V?
Gets awful hot when I do that and stinks too.

Yup, dead short between the two ends of the secondary winding. The two yellow wires are the opposite ends of the secondary and will have the full 12 VAC across them. The third wire of a different color is a center tap, giving you about 6 VAC between it and either yellow lead. Just ignore it. Your 12 VAC will be fine for heating coils and such, but not good for driving any DC fans. Since fans don't draw nearly as much current as any heating elements would, I'd get a 12 VDC wall wart to drive your 12 VDC fans, and reserve the (higher-current) transformer for your heaters, assuming that's what they need.

Check your local Radio Shack store and see if they still have a book on building power supplies. If you're dealing with 120 VAC, you have a whole 'nother safety code to deal with, such as using a power switch AND an appropriate fuse on the transformer's primary.

 

[11bravo]

Heaters are IR heat lamps. Household current. (110? 115? 120?)
Fans are 12 VDC, there are a total of 4 of them; 3 in the oven and 1 in the control box.
Have a tool box that is being converted for the control box.
Has one of these to control the heat cycles.
It's a whole deal.
Big. 8 feet long, 30 inches wide, and 24 inches tall (outside).
Went overboard.
Now the control box is too.
The two grates at the one end are just open to allow air to be drawn in to cool the controller and the transformer/power adapter. (well, and to keep fingers out of where there is 110V AC)
The single grate at the other end has a fan behind it.
I didn't show pics of the inside because it is outside with paint drying.

 

[TWRackers]

Originally posted by 11Bravo
I didn't show pics of the inside because it is outside with paint drying.

Holy cr@p, the inside is outside? AIEEEE, my universe is turning inside out....



All in all, that's a nice-looking job so far. Now that I've re-read your original post, I see you did say the 12 VDC was for the fans. Yeah, it's a whole lot simpler to get a wall wart for them than having to deal with rectifier bridges and transformers and filter capacitors just to generate 12 VDC. Your time is worth something, after all. Save yourself a few hours and a lot of solder fumes, that's my opinion.

 

[11bravo]

Originally posted by TWRackers
Holy cr@p, the inside is outside? AIEEEE, my universe is turning inside out....

And if I'm not mistaken, it's right-side down.

 

[TWRackers]

(See edited post two floors up.)

 

[11bravo]

Originally posted by jflis
I get pulled into threads in the oddest ways sometime... LOL

Not JIM Flis.

REGINALD Flis.

You live in New Hampshire and sell rocket kits via mail order.

He lives in the CAR (Central African Repubic) and sells rocket kits via mail order.

You sell one made out of styrofoam cups called the "Decaffeinator".

He has gone the other route and sells one made out of old "Jolt" soda cans called, well, the "Caffeinator".

You have a daughter named Jennifer; whereas he has a cross-dressing son named Muhondo that prefers to be called Jennifer.

TOTALLY different!

 

[rharkins]

If you want to run the DC fans with the AC transformer, just put a diode of appropriate capacity (RS 276-1661 - $2.49 for four of them) in series with one of the transformer leads. This will cause the fans to run slower than normal, and possibly hum or buzz (you've created a half-wave rectifier here).

A better solution is a full-wave rectifier module (like RS 276-1146 $1.99). It has four leads; two go to the AC transformer leads (they're marked with a '~'), and the other two are your + and - DC. This should keep the fans spinning at full speed. You won't need any filtering capacitors if all you run are fans, but don't try to use this unfiltered DC to run any electronics.

Make sure you're careful around the 110V AC. I'd go with the wall wart from EBay if you don't have experience wiring house current.

 

[Hospital_Rocket]

edit: This post waited while I was in a meeting and several others chimed in. It should have been betwixt 11B/Flis.

Not necessarily, although you will have to do a little fabrication to get by...

You would need

(1) a bridge rectifier - El Shacko del Radio Catalog #: 276-1173
(2) a filter capacitor - Same source Catalog #: 272-1020

You will also need a soldering iron, some wire, some 1/8" Heatshrink tubing, and a probably a small box to enclose things in. I have attached a basic circuit diagram.

A

 

[11bravo]

I do have some experience with 110 and should be able to pull this off.
Been working on it for, um, close to three months now.
Don't rush me.
In the pic, the red line would be 13", the blue line 26", the 3 black dots are where I have yet to cut the holes for the fans.
The piece of plywood with the grey "X" is the cover for the hole you see in the bottom.
That hole is where the light bulbs go.
They are to be wired 1 bulb on one circuit and 2 bulbs on the other circuit.
That way I can run 1, 2, or 3 depending on how I plug them into the controller.
Sides, ends, and top have 2 1/2 " rigid styrofoam on them.
Will be able to do 2 12"OD tubes up to about 7 1/2' long at a time.

 

[11bravo]

Originally posted by Hospital_Rocket
edit: This post waited while I was in a meeting and several others chimed in. It should have been betwixt 11B/Flis.

Not necessarily, although you will have to do a little fabrication to get by...

You would need

(1) a bridge rectifier - El Shacko del Radio Catalog #: 276-1173
(2) a filter capacitor - Same source Catalog #: 272-1020

You will also need a soldering iron, some wire, some 1/8" Heatshrink tubing, and a probably a small box to enclose things in. I have attached a basic circuit diagram.

A

Thanks, I might give that a try.
Slapping things together, snorting TWRackers solder fumes.
Smashing way to spend the day.

 

[henry8minus1]

One potential gotcha with rectifing the 12.6 VAC is you will get a little over 16 VDC if you use the schematic Al posted.

The reason being is the 12.6 V is the RMS voltage, and not the zero to peak voltage which is about 17.8 V. Subtracting the drop over the two diodes you will get around 16-16.5 V. This may cause your fans to run a little faster and hotter than normal.

Jeff

 

[Hospital_Rocket]

Rats

I have been out of this too freaking long...

H8-1 is correct the full wave bridge will provide 1.414 times the rated voltage. Ok Henry, how about if he uses a half wave? I think the RMS would still cause an overvoltage situation.

Of course we could complicate the situation as attached....

Build a shunt regulator from a 1N4742 (Rat Shack Catalog #: 276-563) is a 12v 1W Zener, The shunt resistor would (I think) need to restrict current through the regulator to 83mA. I cannot find the appropriate value.

Alternatively 11B could use just one of the two windings and end up with about 9V which may spin the fan OK

 

[henry8minus1]

The half wave would give you about 17 VDC because you will only have one diode instead of two. (.7 V drop instead of 1.4 V)

Your Zener should work, or you could also just use a 7812 regulator (RS# 276-1771). However this is only rated to 1A, so you need to check to see what the current draw of the fans will be. Also if you are using close to an amp I would get a heat sink for it.

However the 16-17 volts may not even be a problem for the fans. It just depends on if they will tolerate the higher voltage.

 

[Speedtek]

Go to Goodwill or Salvation Army (the ones that carry electronic stuff.) There you can buy 12v wall transformers for $1 to 3 dollars!
I think you need about 200ma per fan. Just buy a 12VDC 1A which are very common and you should be good.

 

[m85476585]

I would rectify and filter the output and use a 7812 regulator. 4 fans should run just fine off 1A, but if you need more I'm pretty sure you can stack the regulators (wire 2 or 3 in parallel, preferably with a heat sink for each). If you do use a significant amount of 3A (I don't know how much, I don't really understand what the voltage does and with how much current), you might not need a regulator, but if the load stops the voltage will go up.

 

[SwingWing]

Why don't ya just steal the power supply outta that old PC you got lying around????

 

[BHP]

Quote 11 Bravo:

Heaters are IR heat lamps. Household current. (110? 115? 120?)
Fans are 12 VDC, there are a total of 4 of them; 3 in the oven and 1 in the control box.
Have a tool box that is being converted for the control box.
Has one of these to control the heat cycles.
It's a whole deal.
Big. 8 feet long, 30 inches wide, and 24 inches tall (outside).
Went overboard.
Now the control box is too.
The two grates at the one end are just open to allow air to be drawn in to cool the controller and the transformer/power adapter. (well, and to keep fingers out of where there is 110V AC)
The single grate at the other end has a fan behind it.
I didn't show pics of the inside because it is outside with paint drying.

++++++++++++++++++++++++++++++++

I'd've just stuck a trouble light in there and if it got too hot I'd've open the lid. Maybe even propped it open with and old soup can, screwdriver handle or a tennis shoe. Or even easier is to wait until mid-August when it's really hot in the garage to do my 'glassing.

Oh, yeah, I almost forgot. I've sworn off 'glassing any more airframes and am just sticking to paper and plywood. It works.

 

[11bravo]

Originally posted by BHP
Quote BHP

Oh, yeah, I almost forgot. I've sworn off 'glassing any more airframes and am just sticking to paper and plywood. It works.

Yeah, but you core sample all of yours so it's not worth your time.
Some of us want them back.

Ready for your big trip?

 

[BHP]

Yeah, but you core sample all of yours so it's not worth your time.

I got that one back. It's just that it's now in a 12" x 12" box!

That two good digs in one day, my friend. You're ahead. I owe ya!

Yep, we're ready. Earplugs, rain ponchos and cash will get one through 'most any eventuality at the Indy 500.