Transformer with multiple secondaries needed.

[Ice-9]

I'm wanting to build a pedal PSU with a minimum of 6 isolated outputs so the first thing I need to track down is a mains transformer which has 6 secondary windings. I think the best option would be a toroidal but after searching most of the day through parts catalogues and websites I can only find Transformers with dual secondary windings. I'm beginning to think what I am looking for would maybe have to be made to specs for me which then makes this psu project not possible.

I could use 3x smaller transformers with dual secondary windings as long as there not centre tapped windings to get 6 isolated outputs but I really was hoping to get a single transformer for the job.

Has anyone come across one in the past and maybe have a part number or web site link I could check out.

[R.G.]

https://taweber.powweb.com/store/magnetic.htm

WPDLXFMR-2
$24.00 Pedal and effects power supply transformer, Eight 11 volt, 300mA windings and one 9 volt, 2 amp winding. 120-220-240 VAC input. This is a transformer, NOT a power supply. The output is AC, not DC. You must build a power supply that converts AC to DC in order to use this transformer.

Was this what you wanted?

[Tony Forestiere]

WPDLXFMR-2
This is a transformer, NOT a power supply. The output is AC, not DC. You must build a power supply that converts AC to DC in order to use this transformer.

That did make me smile. Also a great price for the iron. Got me to thinking about what one could do with a bunch of 11 VAC outputs.
I found this sheet on rectification, and think the "FULL WAVE BRIDGE Capacitor Input Load" design would give, (properly filtered and regulated), at least 9 VDC 300mA at idle with reserve to spare.


Once again, I must apologize that my post preview is not working. Hope I don't wreck anything.

*edit* link didn't work. http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0CFUQFjAB&url=http%3A%2F%2Fwww.hammondmfg.com%2Fpdf%2F5c007.pdf&ei=f8R_VMH6JNXToATItILYAw&usg=AFQjCNFPNgWFEfkADk5oUMa3KwjgqL3-YA&sig2=YgzpOIzE25DLuYbA_3o29g

*edit 2* I knew I had seen something in the same vein: http://www.geofex.com/article_folders/spyder/spyder.htm 

[R.G.]

It made me smile too.

I included that directly from Weber's web site. I can just see the telephones at Weber melting from the horde of wannabe BUMS builders calling and yelling about this transformer killing my pedals one by one as I plugged them in and they died, then they plugged in another pedal and it died, then ...

[PRR]

> transformer which has 6 secondary windings.

WHO would want such a thing? Most designers aim to -minimize- fancy transformer specs. Leads cost many cents each; why buy sixteen more leads when some circuit-bending could consolidate the system at lower cost?

ONLY pile-of-pedal users would want many windings. And want it bad enough for *some* body to supply the need. Weber works closely with iron-winders, adding this odd-ball to his line was a natural for him.

Yes, the "11VAC" will rectify-out to like 15V DC, which even if it sags will cover the headroom of a 9V regulator.

The other thing you could do is stack it for an 88VAC or 123V DC supply for small tube gear (and particularly making-safe those old hot-chassis radios and amps).

Hmmmmm.... you could stack it as 22V+22V + 53V to make +/-15VDC opamp feed and 48V Phantom feed.
___________________________________________

> link didn't work

And the link you gave goes through Google, and includes Google tracking information.

The link you want is:

http://www.hammondmfg.com/pdf/5c007.pdf   (260KB PDF file)

That IS a very handy file.

[tubegeek]

Hmmmmm.... you could stack it as 22V+22V + 53V to make +/-15VDC opamp feed and 48V Phantom feed.

:O

Holy shit. There's a problem-solver. Thank you.

[Ice-9]

https://taweber.powweb.com/store/magnetic.htm

WPDLXFMR-2
$24.00 Pedal and effects power supply transformer, Eight 11 volt, 300mA windings and one 9 volt, 2 amp winding. 120-220-240 VAC input. This is a transformer, NOT a power supply. The output is AC, not DC. You must build a power supply that converts AC to DC in order to use this transformer.

Was this what you wanted?

That is exactly the type of thing R.G. Cheers,  using this 6 x 9v regulated outputs and 1x 18v would work well.
Just need to get a price for shipping to UK but it does look promising.

[drolo]

When you get a quote for the shipping, would you mind sharing? (so we don't spam poor Mr Weber with the same questions .. ;-) )
I would be quite interested too ...

[R.G.]

Seriously, you might take a look a what started all the multiple-isolated-outputs fervor - the "Spyder" power supply article at geofex.com : http://geofex.com/Article_Folders/Spyder/spyder.htm  First posted in 2000, the article plumbs most of the options.

It originally showed how to rewind small semi-toroidal transformers to have more secondaries, but then recommended the Weber transformer when years later the Weber became available. It also for safety's sake recommends a plethora of small dual secondary transformers for the purpose.

[Ice-9]

When you get a quote for the shipping, would you mind sharing? (so we don't spam poor Mr Weber with the same questions .. ;-) )
I would be quite interested too ...

I got a quick reply back saying "Thank you for buying these speakers"  seems it was an auto response so I will let you know when the correct email comes through.

Seriously, you might take a look a what started all the multiple-isolated-outputs fervor - the "Spyder" power supply article at geofex.com : http://geofex.com/Article_Folders/Spyder/spyder.htm  First posted in 2000, the article plumbs most of the options.

Yeah, your article on this is what got me interested in building an multi isolated supply and finally rid my pedal board of all the noise it has. That and I built a pedal board for a friend who wanted me to fit a voodoolabs/Trex type psu which surprised me at how much difference it made.

While waiting for a response from weber I have re-read the geofex article and had a look round UK suppliers for some other transformers. I have come up with some options like the ones in the link below which come in many different dual outputs. The 240v primary and dual 12v secondary at 266ma each look good. Two of these for 4x9v regulated outputs and one of the bigger current ones for  2x 400ma 9v or even 12v option outputs.

http://www.rapidonline.com/Electrical-Power/Block-VB-2-0-2-12-PCB-Mount-Transformer-2VA-2x12V-2-x-166mA-51-5453
http://www.block.eu/en_IN/products/electro_transformers/product/393256/

[R.G.]

While waiting for a response from weber I have re-read the geofex article and had a look round UK suppliers for some other transformers. I have come up with some options like the ones in the link below which come in many different dual outputs. The 240v primary and dual 12v secondary at 266ma each look good. Two of these for 4x9v regulated outputs and one of the bigger current ones for  2x 400ma 9v or even 12v option outputs.
http://www.rapidonline.com/Electrical-Power/Block-VB-2-0-2-12-PCB-Mount-Transformer-2VA-2x12V-2-x-166mA-51-5453
http://www.block.eu/en_IN/products/electro_transformers/product/393256/

That will work. It also lets you encapsulate the possible sins of the mains AC power wiring onto a PCB, which is good. I've always intended to use one of those block-style transformers, but never actually got to do it. The specs look good.

Be sure you pick secondary voltages so that with nominal lowest AC line voltage (usually -10%) and highest expected DC loading, the minimum DC voltage going into the regulators is more than 2V higher than the regulators put out. For instance, if you have 7809 regulators for 9Vdc, you need a minimum of 11Vdc going into the regulators in all conditions. Notice on the specifications that the no-load voltage for the 0.35W transformers is approximately 1.8 times the specified fully loaded voltage. This will be important in a minute.

You need at least 11V peak AC from the secondary plus 1.4V for the bridge rectifier diodes, so you need a minimum of 12.4V peak. This converts to 12.4/1.414 = 8.76Vac from the transformer under -10% AC line. So the minimum secondary voltage for properly feeding regulators under -10% line is 8.76/0.9 = 9.74Vac.

That's close enough to 9Vac to decide not to go for the 12Vac secondaries, and simply pick a higher-rated VA transformer, or to assume that each output will not be fully loaded.

This is good because if you have a "9Vac" secondary that's only very lightly loaded, it's 1.8*9 = 16.2V peak, which gets bigger if the AC mains are 10% high, or 16.2*1.1 = 17.8Vdc. This, minus the 1.4V of the bridge diodes says that your regulators are working on 16.4V dc at light loads. This will then sag to 11V under some load near the max for the secondary winding.

Also, a little-known effect also sags the secondary. The high pulse current nature of the charging into the filter caps makes the winding currents look like they're about 1.6 to 1.8 times bigger than the DC output current. So the secondary will sag faster than you might expect. So if you want 100ma DC out, get a 200ma or more rated secondary.

[davent]

Small Bear also has that Weber transfomer. When i built a Spyder type supply it was far less expensive to buy from Digikey enough small dual secondary transformers to cover my needs then the cost of the Weber and shipping would have been to Canada.

[Ice-9]

I had a reply from Weber tonight, Thanks for being so quick with the response.
The postage to the UK was going to be $20 so the total of $44 plus 20% that UK will add to that when it arrives plus the post office duty puts it too much to consider at $65.

Thanks R.G. the maths which does point out that the 12v secondary windings would not cut it. The 15v secondary windings and higher current transformers will be better suited, they also have a better efficiency and a 1.7 x no load voltage.  I am also thinking of using Schottky bridge rectifiers for a lower voltage drop along with using LDO regulators rather than the 790x family of regs.

Thanks davent, I'm definitely now on the side of more, smaller transformers rather than one with many secondary windings. This also has the benefit that if there is any problem all the outputs won't go down.

[drolo]

That's expensive indeed... thanks for sharing.

[davent]

I'll add i had the tranformers sitting on the shelf for a long time, looked like i'd never get to the project so broke down and bought a One Spot.

Did finally get to and finished the Spyder earlier this year, does it's job very well!
dave

[Ice-9]

I have got a couple of those encapsulated transformers to try out over the Christmas holidays, in the meantime I have made up a little schematic which is likely the type of regulator and filtering I am going to try out. Nothing special about the circuit just straight from the datasheet.

The circuit diagram shows 3 blocks which will power 6 outputs at 100ma (depending on transformer selection)


I have also messed around with a 3D pcb view to show the possible layout which has the 3rd transformer driving higher current regs, again the transformer will have to be selected correctly although I have use the same 3d transformer in the picture for all 3 TX's

Once I get somewhere with trying this out I will start a new thread with a better title and I want to be able to get this going with off the shelf parts so anyone can give it a try.

Thanks to everyone for all the info on transformers.

[tubegeek]

A couple of things I learned on the Weber website:

1. Ted's dead. 2009. RIP.
2. The transformer with the multi secondaries, WPDLXFMR-1 costs $25 and has 8 x 11 volt, 300ma windings and one 9 volt, 2 amp winding. 120VAC input.

There is also a version, WPDLXFMR-2 with 120-220-240 VAC input which costs a dollar less for some reason.

Anybody know what the intended use for the 9V @ 2A winding is?

And thanks to PRR for teaching me how to make those links so nice!

[PRR]

R1 R2 are switched.

The resistor from Out to Adj has 1.25V forced across it.

The resistor from Adj to Ground has the same current, so the same voltage multiplied by the ratio of the resistor values.

R1 = Out-Adj = 1.25V = 3K3
R2 = Adj-Gnd = 510 Ohms

The 510 has 510/3300 or 0.15 of the R1 voltage, 1.25V, so drops 0.19V.

Total output is 1.25V+0.19V= 1.44V.

Most "9V" pedals will be useless at 1.44V.

You want the output to be much larger than 1.25V. Therefore the larger resistor goes on the bottom, Adj-Gnd.

R1=510, R2=3K3, gives 9.34V, which is right at the voltage of a fresh 9V battery, and surely what you want.

[Ice-9]

R1 R2 are switched.

The resistor from Out to Adj has 1.25V forced across it.

The resistor from Adj to Ground has the same current, so the same voltage multiplied by the ratio of the resistor values.

R1 = Out-Adj = 1.25V = 3K3
R2 = Adj-Gnd = 510 Ohms

The 510 has 510/3300 or 0.15 of the R1 voltage, 1.25V, so drops 0.19V.

Total output is 1.25V+0.19V= 1.44V.

Most "9V" pedals will be useless at 1.44V.

You want the output to be much larger than 1.25V. Therefore the larger resistor goes on the bottom, Adj-Gnd.

R1=510, R2=3K3, gives 9.34V, which is right at the voltage of a fresh 9V battery, and surely what you want.

Well spotted PRR, I have marked the values in the wrong way around. I will fix that.