Why is this Toroid BUZZing and getting hot?

[Ethan]

I gave them a ring. He basically said: "dunno, maybe a manufacturing defect... maybe the they mixed up the insulation color on the secondaries... Try it in parallel."

Well here's what I did. I pulled apart the center tap so that I once again had dual secondaries. ohm'ed out the secondary windings and I get continuity between green-red, and brown-blue. Which would lead me to believe that I at least indeed have dual secondaries (and the secondaries are not shorted). If the polarities are twisted, could I check this out by trying Green+Blue as my center tap (and ground it) then connect to red and brown? Or would that even matter?

 

[SSLtech]

If you had secondaries with one set of colours reversed, you'd get no load and no output. -Like connecting two 9V batteries in series to get 18V, but accidentally connecting one the wrong way round... instead of a center tap and 18V between the outside terminals, across the load, you'd get nothing between the outside terminals, you'd be measuring between +9V and +9V, so... -nothing.

The primaries are a totally different thing. Parallel them the wrong way round and you'd have plenty-o-heat! -however, you say that if the secondary is completely open, you don't get any heat, which discounts that scenario.

I think that if you had a short in one of the diodes in the bridge -or one the wrong way round- you could expect similar heating problems. -Check again with a DMM? -I've actually seen wrongly-marked diodes before now... make sure that they all read the same, would you?

Keith

 

[Ethan]

I think that if you had a short in one of the diodes in the bridge -or one the wrong way round- you could expect similar heating problems. -Check again with a DMM? -I've actually seen wrongly-marked diodes before now... make sure that they all read the same, would you?

Well I'm using a honky bridge rectifier. I have a few more so I'll try replacing it and report back. But could it really be the bridge, because with one side of the secondary lifted and the center tap grounded I get the buzz and heat. With the secondaries connected to the bridge and the center tap grounded I get no buzz but heat (and the doubler doesn't double). If I float the center tap, NO HEAT and NO BUZZ, but also NO DOUBLER.

Thanks for all the continued help guys!!!

 

[Ethan]

OK. So I got another transformer, replaced the rectifier and after hours of headaches later, I finally got everything to work. I thought this doubler would only work with the CT grounded, but apparently, it only seems to work when I have it floating. If I ground it the transformer gets hot.

I left it on for a minute and checked voltages, and everything looked as it should. Then I hear POP.....POP....POP.... So I shut it down, and took a look but I couldn't smell smoke or notice any scorched components. So I turned it on again, after a few seconds, i hear POP POP again. I'm getting good voltages... Any idea what this could be?
The curious side of me wants to leave it on and find out...but the part of me that respects electricity is telling me not to.

 

[Ethan]

OK disregard that last post. The doubler isn't working when the CT is floating. My tired mind just thought it was, when actually it was just higher voltage of having the secondaries in series.

My next question is.....why isn't this doubler working? When I have the CT grounded all I get is a HOT transformer without double the voltage at the output. In fact, I actually get LESS. Can anyone shed some light on this ferrrr me ?

 

[SSLtech]

Ethan,

The schemo which you posted:

Is essentially the same as the 48V circuit in my own design PSU:

in mine, BR2 is the same as your 4 diodes. C3 and C4 are the "shifting" caps which move the charge up to double the single winding peak voltage. C5 is the final charge capacitor.

It works fine in my implementation, as used here, so I guess that either there's something else not shown in your drawing, or a faulty component.

With no power connected, make sure that there's no path to ground from either side of the caps or any part of the transformer secondary, when the ground link is lifted, but the center tap is still connected to the low leg of the third (Final charge) capacitor.

Just to make sure: Without making ANY connections to ground, make sure that the low leg of the third capacitor is connected back to the center tap, and see if there's a voltage across it. This is basically just two Cockroft-Walton multipliers in parallel, so two diodes, one winding and two caps are al it takes to get the voltage that you are looking for; the enhancement that I used in using 4 diodes in a standard bridge and 3 caps is just a compact and convenient solution. Any one bad diode in the bridge will make life miserable though...

Keith

 

[bcarso]

I'm thinking, let's get even more basic: disconnect the transformer from the bridge and caps. Measure the a.c. voltages on the secondaries. Then tie the ends that supposedly form the center tap and measure again, from end to end. Never mind the diodes and capacitors for now.

 

[Ethan]

I'll have to give that a shot. this thing has been driving me crazy all day.

Here's the full schematic. Can you see anything blatantly wrong?

 

[alk509]

[quote author="Ethan"]

[/quote]

Isn't the second (lower) diode bridge shorting the secondaries? I mean, e.g. when the top wire is negative with respect to the center tap (which is grounded) wouldn't current flow straight through the top-left diode in the bridge and heat things up and make them go *pop* *pop* *pop*?

Peace,
Al.

 

[bcarso]

Yup. That's the problem. Lift the negative end of the lower bridge---let it float. If you were to use it for anything it would go to the neg side of a cap and from there to a negative voltage regulator. See Keith's schemo for an example.

 

[Ethan]

So if I float the currently grounded portion of the bottom rectifier, everythign should be A-OK? PLEASE PLEASE PLEASE say yes :grin:

 

[alk509]

Yeah, it looks that way... Just hook it up to the "ground" of the circuit it's powering and nothng else, and see what happens.

Peace,
Al.

 

[bcarso]

Should be, if everything is wired like the schematic otherwise. Again, compare to Keith's to see the difference.

The bridge won't mind having only half of it used.

 

[Ethan]

But then wouldn't that make the bottom a half-wave rectifier?

 

[bcarso]

No. It makes it a full-wave center-tapped rectifier. Each side of center of the trafo conducts on alternate half cycles.

 

[Ethan]

Why, yes indeed it does... Like many of the tube PS's of yesteryear.

THANK YOU THANK YOU THANK YOU THANK YOU...
and THANK YOU! Now I can sleep with some peace of mind and give it a go tomorrow.

 

[alk509]

Nope. Remember the center tap is grounded, so the two diodes that are still connected are still being alternately forward biased!

Top wire positive with respect to center tap > top diode conducts.
Lower wire positive w.r.t. center tap > bottom diode conducts.

The circuit still gets both halves of the rectified AC.

Peace,
Al.

 

[Ethan]

I love you people :shock:
No. Really... I love you people :razz:

 

[ap123]

I'm having an issue with two toroidal power transformers from avel lindberg (both the y23 range). They have dual primary and dual secondary. I'm experiencing some clearly audible mechanical hum which is resonating with some other equipment nearby in my rack on both of my y23 implementations. One is the JLM 3 rail v2 and the other is the mnats onboard 1176 rev d psu. I'm assuming that I am hooking them up wrong because I just noticed that without any load attached they are silent.

On the JLM pcb, they AC side is labeled 0v, AC, AC. I have black(0v) and orange(0v) in the terminal marked 0v, and red (18v) and yellow (18v) in the terminals marked AC. On the JLM site there are example diagrams of power transformer connections; one of which is the RS 257-4991. According to the datasheet this has the same color coding as the Avel Lindberg y23 range.

What confuses me is that in the JLM diagram the Vsec on one secondary and the 0v of the other are both in the 0v terminal on the psu. Is this diagram correct? I am assuming that I have simply wired my PSUs incorrectly which is causing the mechanical hum in the power transformer. I don't want to blow up my psu, though, so I thought I might get a second opinion.

What is sad is that I emailed Avel Lindberg about it and before asking me anything they sent me a replacement. I expected them to respond with something like "hey dipsh*t you wired your secondary wrong!" I even emailed them back "I will pay for the replacement; I am sure this is my fault" to which they responded "What is more important is that you let us know what the problem was." Their customer service is phenomenal. If they treat an idiot this well imagine how they'd treat someone who knows what they're doing?

 

[dissonantstring]

hi ap123
i think the Avel Lindberg wiring should be like this:
on the primary side connect brown and grey together - goes to Live side.
on the primary side connect blue and violet together - goes to Neutral side.

on the secondary side connect black and yellow and connect both to your 0V center tap of the PSU board.
on the secondary side connect red to one side of AC of PSU board and orange to the other side of the AC of the PSU board.

measure across the 0V and one of the AC connection points on the PSU with your DMM on AC Volts and you should be getting somewhere about 25V or so. If you measure AC Volts across the two AC points you'll get double that.
Remember when measuring straight off a transformer input on the PSU it is unrectified so use AC Volts.

hope this helps.
-grant