help wiring these power tx

[riotubes]

Hi,

I've got 2 transformers and would appreciate input on correct wiring:

Triad n68x - datasheet linked below

http://www.alliedelec.com/Images/Pro...ETIC/N-68X.PDF


If I need just ~120v out does that mean that I just use one secondary pair and ignore the other pair?

What is the "ST. SH." white wire (3rd wire) on the primary side? Does this go to earth/chassis ground?

The other transformer is a 12V, center tap....but I don't plan to wire it as a CT....just need a hot to the PLUS rail and 0V to the neg rail of power supply. What do I do with the center wire? This will power a 5V discrete regulator.

Both power supplies will be SS rectified. thanks for input!

[dave_gerecke]

Hello Mike, Looking at the datasheet:
1)for 120v in and out, wire the two primaries in parallel (i.e. blk connected with red/blk and yel/blk connected with grn/blk.
2) The ST.SH. wire is an electrostatic shield wire. This indeed would connect to ground. This helps keep down radiated noise.
3) In regards to the transformer with the unused C.T., just cover the end of the C.T. with a piece of heatshrink and keep it out of your way. Should work fine otherwise.

Peace,

Dave

P.S. you have your reference to Primary and Secondary on the datasheet reversed.

[riotubes]

Thanks Dave!

Ah, it is a dual primary with one secondary...not the opposite as I had referred to. Got it!

[dave_gerecke]

Hey Mike, easy to mix up the primary and secondary. In all actuality, you could probably use this transformer in the reverse. Then you could use it to step 115v up to 230v, if necessary. You would have to keep in mind that the output current capabilities would reduce commensurately.

Peace,

Dave

[riotubes]

having difficulty finding my wiring mistake. I wired the Triad N68X transformer's primary in parallel (i.e. blk connected with red/blk and yel/blk connected with grn/blk) for 120V use. It feeds a schottky bridge followed by 1uF cap (with 100K bleeder resistor) and this powers a 70V discrete voltage regulator. Turned it on...smell and light smoke within 1 min. I'm sure its lost.

My lingering question is whether I miswired the transformer's static shield (white lead). I connected this to safety ground point (where the safety earth of IEC inlet ties to a brass bolt in a wood chassis. Was this a mistake and caused a dead short?

My only other thought is I somehow I miswired the schottky bridge. I've attached an illustration of how I wired this. I also include a diagram of 2nd bridge that feeds a -5V discrete reg just to make sure I have that one right too.

Please give me your thoughts. Thanks for your help!

[dave_gerecke]

Hello Mike, the first thing I would recommend here is to disconnect the transformer secondary from anything and measure the output. With no load attached, you should see around 115-120v. Make sure you don't touch the wires together, or to you when the transformer is plugged into the power line. Then things get ugly. I would also recommend wiring up a 60 watt light bulb in series with the primary side of the transformer. That way if the transformer is shorted, the light will limit the current, and if the light glows brightly, you know that your tranny is shorted.
The other thing that would help here is to show the full schematic of the power supply, then one could look at it for possible issues.

Peace,

Dave

[riotubes]

Thanks Dave for your continued help with this. I will try your suggestions on testing secondaries of the transformer. I'll look into how to wire the bulb in series...I've seen posts here on this subject.

Here is the psu schematic. Note that none of the reg's outputs are hooked up to the signal circuit. It powers a new analog output stage (John Swenson's CCS stage) for a current output dac. I have deliberately left out the wiring from the IEC-to-fuse-to-DPDT switch-to-Terminal Block because that has NOT changed when the dac was used with the former valve output stage.

The radio shack traffo powers two -5V discrete regs which I have shown (they are just mirror images of each other and the little blue transistors are all BC560Cs). The Triad powers the 70V discrete reg which is not shown cuz its to complicated to show on this page. here is the link to the reg schematic. The reg schematic is on the right...I'm not building the preamp shown on the left. Some parts values were changed to make it 70V. I can repost an accurate schematic if someone thinks that's were the problem lies.

Swenson 70V discrete Reg Schematic

any feedback is greatly appreciated. I'm hoping that something is sticking out like a sore thumb to one of you seasoned DIY'rs

[dave_gerecke]

Hello Again Mike, If you don't find the info for the series wiring of the light bulb, drop me an email. I will draw up a quick schematic and then set it up as a JPG or some other format that you can view.
The purpose of the light bulb in series is just to act as a current limiter if the transformer is shorted. Even if the transformer is shorted, the most current that can be drawn is 0.5A. That is assuming that you use a 60 watt 120V light bulb.
If the transformer checks out ok, the next step will be to hook up the rectifier portion of the PS, without having the 70v reg hooked up. That way you test to see if it's ok. The idea here is to work through the different sections as smaller, simpler blocks until you find the block that causes the problem. When you find that, you can troubleshoot the section that causes the problem. The general layout and schematic that you posted don't seem to indicate any issues. And unless I'm mistaken, your action of hooking the electrostatic shield to the chassis ground is correct.
In the regulator schematic the diode bridge, D3-D6(rectifier) is shown with the regulator. I am assuming that this is the same bridge that you show on the same PCB with the 1uF cap and 100K bleeder.
I'm glad to help where I can. It gets me thinking about electrical theory more regularly, which is good since I'm still a little rusty. Besides, I kind of helped get you into this in the first place!

Peace,

Dave

[riotubes]

Haven't yet had time to do any further tests on the transformer, but after just looking through the schematic and parts values I think I see my mistake. The Triad N68X transformer has 115V on the secondary if I am reading the datasheet correctly (Dave- your feedback on how to hookup the primaries was spot on; I'm 100% responsibility for getting myself in trouble). javascript:smilie('')

So the 1uF filter cap after the Schottky bridge is seeing:

1.414 * 115Vac - 1.4 = ~161 volts DC (if I understand the math)

That 1uF cap is rated at just 50V. This was hard to type...

With a 2X-3X safety margin, that 1uF cap should be rated somewhere between 350V-450VDC

Would this have fried the transformer?
Would this take out the diode bridge as well?
What about the likelihood of downstream parts (only the 70V reg was hooked up to it)?

Thanks for any input

[dave_gerecke]

Hey Mike, Your equation for calculating the rectified peak voltage is correct. The cap connected with the bridge would definitely not like that. It's possible to have done damage to other components in the chain, that's why I recommended the step by step troubleshooting method. Check the transformer unloaded first, check it with the bridge hooked up, remove the resistor and cap you have in parallel with the output of the bridge here. Remember to keep the light bulb in series with the primary of the transformer. Once you have verified whether anything here has been damaged, and fixed that part of the problem, you can replace the cap with a higher voltage one, and work your way forward.
What happened to you with this project is just part of the learning curve. And I can tell you that even the most experienced here can get excited and forget about these steps.

Peace,


Dave