Danbury Transformers

[Wendymott]

Hi Peeps.... I needed a 50V/A transformer for my 40M SSB transceiver with 14V and 17V windings. I am fortunate to have some old stock of the R/S 207 554 "make a transformer" kits, but no winding info.
As it was an RS product.... I emailed them last night at 11pm...I had a reply this am, but unfortunately the items were discontinued in 1996.
They do not have much info, but sent me a sheet, which was not much use, but at least they replied.
I googled Danbury Electronics as they were the suppliers to RS, and found a phone number..I rang and a gentleman answered, unfortunately the company has now closed, and he had no information re the transformers.
As I had a pre wound transformer.... the only way was to unwind the secondary's, noting the voltages marked on the label. It turns out that my estimate of 8 turns per volt per sq ins of core material was WAY out. It turns out the windings are 5.25 T per volt.
Obviously the iron core permability has improved since I last wound a transformer.....
The new secondaries were "1" 15.23V unloaded and 14V loaded at 1A
"2" 17V unloaded and 16V loaded at 1.8A
Ed Dinning had kindly helped me, advising the losses due to split core construction,
Testing in the transceiver is next.

[Craig Sawyers]

For what it is worth, I have a later variant of this, which was 182-9910 (50VA), 182-9925 (100VA) and 182-9931 (200VA).

50VA: 3.05 turns/V and 0.71% for every 5VA of load
100VA: 2.17 turns/V and 1.18% for every 20VA of load
200VA: 1.39 turns/V and 1.39% for every 50VA of load

Of course these are also defunct. Were made by Legrand, which also no longer make them.

Someone somewhere has done a risk analysis, methinks.

[KeithsTV]

Here's the data sheet supplied with the RS transformer kit.

Keith

[kalee20]

That looks reasonable - I did a double-take at Craig's figures of 3.05 turns per volt for the 50VA transformer especially! Suspiciously low, unless it was designed for a mains frequency of 100Hz, perhaps, or the core used super-high-saturation cobalt alloy exotica!

[Craig Sawyers]

Here you go

Craig

[Wendymott]

THanks Craig and Kalee and Keith. I do know that my turns are 5.25 / Volt... and as you say... at first look Craigs data seems a bit low, but it all depends upon the core material. I have stored both data sheets for future reference.
Re the "risk analysis" Craig. Possibly will not meet current ISO standards. The other thing is.. that Switch mode power supplies provide a much more efficient power conversion... it just that "us radio people" want SMPS as far away from our front ends as possible.

[kalee20]

Originally Posted by Craig Sawyers

Here you go

Can't argue with the data sheet!

I did some comparisons.

Keith's RS data sheet shows, the 50VA transformer is 79 x 65 x 62mm. And the bobbin is big enough to fit 416 turns of 0.5mm wire.

Craig's RS data sheet shows, the (different) 50VA transformer is 84 x 91 x 86mm. And the bobbin is big enough to fit 256 turns of 0.5mm wire.

Different turns of the same wire indicate different lamination patterns. Though recent 30 years, it has been unusual for small utility transformers to be anything other than 'waste-free' dimensions. That being so, I'd have expected "Keith's" transformer, with the bigger winding area, to also have the bigger centre limb, hence the bigger core area allowing for the lower turns/volt. But it's "Craig's" which has the lower turns per volt! So maybe the transformer in his data sheet has a much deeper lamination stack.

The dimensions aren't over-helpful - without a referenced sketch, it is difficult to be sure like is compared with like.

So - I'll give up! I do take an interest in small transformer design, and how hard the materials are pushed! Thanks to Craig and to Keith for sharing the data sheets, I've found this as interesting as Wendy! Even though mine is academic, and hers has an immediate use!

[Craig Sawyers]

Mine is 100VA. The overall lamination is 84w x 70h (of an E+I). outer limbs are 14mm, centre limb is 28mm. Stack is 86mm deep.

Calculating back from 2.17 T/V indicates that the primary is 230 x 2.17 = 500 turns on the 100VA.

Likewise for the 50VA 700 turns
200VA - 320 turns.

The older transformer works out at

20VA - 1540 turns
50VA - 1175 turns
100VA - 890 turns