Noob question re wiring 6.3-0-6.3 secondaries for nominal 12.6V output

[Deke609]

All - Just want to double check my thinking here.

In the hopes of bumping up my supply voltage to the BeePre filament heater circuit I am playing around with dedicated filament heater transformers - specifically the Hammond 166L12B - which is spec'd as 25VA and 12.6V (C.T.).  I plan to try one 166L12B for each filament.

Am I right that I should just cap the center tap (leave it disconnected) and wire the remaining two secondary wires into a 4-diode bridge?

Or is another method of wiring recommended - e.g., one that makes use of the center-tap?

many thanks, Derek

[Paul Birkeland]

I'd leave the CT disconnected.  Is your line voltage 115V?

[Deke609]

Thanks PB. Yes, mains power is now 115V but I will be bumping it to 120V +/- 1.5V with the autoformer and buck/boost setup (which I have yet to build - will use the variac in the interim to test).

cheers and thanks, Derek

[Paul Birkeland]

Well, that transformer is for 115V.  I don't recommend giving Hammond transformers more than they say they'll handle.

[Deke609]

OK. I may have to check with Hammond about this - I think they only make 115V and 117V variants - which seems odd for North America where wall voltage can be as much as 125V or more.

I figured than since I'll be drawing a max of 1.35A and the trafo is rated for 2A I'd be ok and not overtax the primary winding. But maybe my thinking about this is wrong?

thanks, Derek

[Paul Birkeland]

https://edcorusa.com/lvp126-3

[Deke609]

Thanks for that, PB. I am going to email Hammond and if they say anything over is 115V is a no go, I will get the Edcors.

Is this is an issue of the dielectric strength of the primary magnet wire coating?

cheers and thanks, Derek

[Paul Birkeland]

No, when you put 120V on the 115V primary, you won't get 12V out.  The transformer may also saturate. 

[Deke609]

Many thanks PB. I was prepared to deal with over voltage output, but hadn't considered saturation. I put in an inquiry with Hammond.

[Deke609]

Hammond reports that 120V mains with 1.35A draw from the secondaries is no problem for the transformer.  It just bumps up raw output from 12.6V to 13.2V - something I've already addressed with a 15W dropping resistor. So all good!

cheers, Derek