help connecting primaries

[Raj1]

Hi,

I have bought a transformer kit to wind a 4v-4v output. The primaries come pre wound, here is the layout starting at the top most tag with the primary side of the transformer on my right hand side and the secondry (no windings yet) on my left hand side,

--------------- 0v (a)


--------------- 120v (b)





--------------- 0v (c)


---------------- 120v (d)


how do I connect this for 230v operation?

Thanks
Raja

[dhaen]

Hi Raj,

Connect B to C.
Connect 230v (240v) between A and D. (Best to connect live to A, and neutral to D).

Although the UK is quoted as being 230v, the allowable voltage tolerance is asymetrical, and the actual average mains voltage is 240v. So I wouldn't worry about the 10v difference.

Cheers,

[Raj1]

Hi,

I've just tried connecting b to c, and supplying ac to points a and d. However the transformer is humming very loudly and begins to heat up rather quickly......
So i disconnect from mains.

Is this happening cause I've not yet wound secondries????

Or am I getting something wrong?

Thanks
Raja

[dhaen]

Raja,

The connection information is correct. With or without secondaries is ok.

One thing comes to mind: Have you fitted the laminations? The E & I sections of coated steel? Without those, the inductance would be low, and too much current taken.

Cheers,

[Raj1]

Cheers,

Your hunch is correct I haven't connected the laminations

In any case, the formula for calculating the secondries is number of volts required X 4.16.

the kit is 100va

Add 1% per 10va.

I need 4v at 1.1 amps.

I am using .9mm enammelled copper wire which gives around 2 amps.

So 4.16 X 4 = 16.64 turns

plus the extra for the va around 17 turns.

So i need to make 2 seperate windings of 17 turns each?

The supply is for a tube rectifier heater.

Once I have made the 2 turns how can I measure with my DMM to see if this is correct?

I assume I set it to 200vac and attach 1 probe to each of the secondries?

Given that the transfo won't be under load, should I expect a higher voltage reading????

Thanks
Raja

[dhaen]

Hi Raja,

Glad that fixed it And that the transformer will be put to a good use

With regard to winding, this is what I'd do:
Use some thin hookup wire and wind a temporary secondary, as per calculations. Connect to one valve and adjust turns if necessary. Remove.
Now wind the secondaries properly. There should be no "fudge factor required for the extra load of a second valve, because the transformer is 100VA.
If the rectifier valves are directly heated, the windings will be at HT (+B) voltage. Ensure sufficient insulation.

Cheers,

Edit: When connecting to the valve, use approximately the same length and gauge of wire you intend to build with. Also, use a valve socket if you have one. Measure the voltage on the actual valve pins.

[Raj1]

Hi,


Finished the heater supply for the 3a5's and it works fine (2.87v at output), a tiny bit higher than the suggd 2.8, but perhaps it will drop just abit on load?

This is the first time I've built without a pcb and I'm quite pleased with my layout, unfortunatley don't have a camera for pictures!


I've just wound the secondries and attached the laminations.

Have put a jumper wire between points b & c, also wired ac hot to a and cold to d.

When I switch on there is still quite a bit of a buzz.

Can I use my Dmm to measure the secondries directly without connecting to the az1 tube, just to make sure it works?

As there is no centre tap, do I just set to 200v ac and apply one probe to each secondry?

Thanks
Raja

[Raj1]

Hi Dhaen,

I measured the output of the secondry, whihc is 3.5 v, a little short....

I'll have to redo using an extra turn or so.....

The annoying thing is the level of buzz I'm getting from this, it really is excessive,
my secondry winding wasn't overly neat, but this is buzz is really loud..

any ideas???

Thanks
raja

[dhaen]

Raja,

I don't understand what this 200v thing is all about. Are we just talking about heaters, or something else as well. A schematic, even hand drawn in M$ Paint would help.

About the buzz: Make sure the laminations are bolted or clamped together tightly, and that you've fitted all of them. If using bolts, check whether they should be using insulated washers. The secondary should also be tight. When you're sure of it, add some laquer to hold the windings completely still.

Cheers,

[Raj1]

hi,


Here's the schematic for the output stage,


http://www.ultranalog.com/cdenhancer...ancer2_3a5.pdf

Thanks
Raja