Burning Amplifier BA-2

[highfieldrebel]

I’ve found four transformers specified to 115 or 230 V primary and 2*35 V secondary, 2-300 VA (aprox). I´m pretty novice when it comes to electronics and therefore I might ask very naive questions.

Could I make these transformers work in the PSU for the BA2 by connecting the secondaries in series? Would that give me a secondary AC voltage of 35/2=17.5 V?

Kind regards
/Forsman

I'll assume your mains is 230 VAC Forsman.

I think not the secondaries, I wonder if you connected the primaries of two transformers together, would you have 4 AC secondaries of 17.5 VAC.

 

[tinitus]

I’ve found four transformers specified to 115 or 230

if those trafos are for free, I dont know, or else, well

but you hope to wire them to give half the voltage

Im not sure if this will be safe, or whatever happens

edit
ah, I see now thats what is "suggested" in above post

 

[pchw]

Not sure it can be treated as one 600VA in this configuration. The limit is the current that can be drawn through the secondary winding.

300VA, 35VAC x 2 => 300/35/2 (4.2857142857)A secondary winding limit.

300VA 18VAC x 2 => 300/18/2 (8.3333333333)A.

It is like overclocking a CPU, it is hard to tell how much current it can safely pass beyond what it is designed for. I wouldn't push a toroid beyond it's specs for long term safety and reliability reason.

 

[Zen Mod]

if those trafos are for free, I dont know, or else, well

but you hope to wire them to give half the voltage

Im not sure if this will be safe, or whatever happens

edit
ah, I see now thats what is "suggested" in above post

to be sure that you always have identical loads for both xformers - primary wise - combine (parallel) their secondaries - secondary 1 from xformer A with secondary 1 from xformer B ;

same for secondaries 2 - s. 2 from x. 1 with s.2 from x.2

but - parallel them after diode bridges , to prevent any current hogging in case of slightest difference in secondaries voltages ;

so - one bridge per secondary

 

[Forsman]

Thanks for all the answers and suggestions. Very helpful!

As a matter of fact I can get hold on four of these transformers at a really affordable price so I think I´m going to give it a try.

Kind regards
/Forsman

 

[Zen Mod]

if you need sketch , just buzz

 

[Forsman]

if you need sketch , just buzz

A sketch is always welcome especially for me who are an armature in this domain.

The make is Dantrafo and they have been mounted in some model from Primare originally.

Kind regads
/Fredrik

 

[Zen Mod]

what's your intention - to use 2 xformers per channel ?

give us lam dimensions , so we can calculate what's resulting VA of each

 

[Forsman]

The seller tells me that they probably are rated 200-300 VA each. I’m not sure about the lam-size but a not so qualified guess would be lam-248. That figure is a gestimation from the picture. I haven’t got hold on them yet so I can’t measure them.

Because I’m not sure of their VA specifications I’m thinking if I use two of them per channel I probably have enough VA even if they should turn out to be rated 200 VA.

Later the coming week, I will pick them up and then I probably can get you a better answer on their lam-dimensions.

I really appreciate that all of you are taking you time to help me out with this!


Kind regards
/Forsman

 

[Zen Mod]

point is that you'll have just half VA of each of them

that's always the case when you are feeding xformer with just halv prymary voltage

so - be sure what you have , before paying them

BA amps are VA- hungry

 

[Forsman]

Aha, in that case they need to be at least 300 VA or I will not get enough VA in the end. I’ll look in to the transformers specs better before I purchase them.

Thanks
/Forsman

 

[Zen Mod]

exactly

 

[tinitus]

but with paralel secondary, wouldnt Ampere double, and VA remain the same ?

 

[tinitus]

ach, not only voltage but also current will half

 

[h_a]

Hi Frederik,

you may want to make the mounting of this brick flexible in the sense that you can adjust its orientation. These EI-types have quite some stray fields that could make problems (that are often solved by rotating them by 90 degrees or so).

 

[Backbones]

If you connect two transformers in parallel or series you may have problems if there are differences in their impedences. This could result in overloading of one of the pair.
If you connect secondaries in parallel you double the current whilst the voltage remains the same.
I don't feel confident enough to play around with mains voltages when it comes to transformers. I can recommend Canterbury Windings in the UK to hand build something to your specs. You can email your requirements and Terry will email you back the price. I'd rather pay the extra on the transformers than medical bills if things go wrong. Medical bills, that is, if you are lucky!
Regards,
Chris

 

[Backbones]

On another note now that the new pcb boards have arrived, what do I need to order if I'm building two monoblock BA-2s?
Regards,
Chris

 

[h_a]

You might want to search for the BOM (bill of materials), I'm sure there's one somewhere in this thread.

Of course, you need quite some stuff in addition that is usually not included in the BOM, like toroid, heatsinks, power supply caps, rectifiers, connectors, cabling

Enjoy, Hannes

 

[Forsman]

Hi again

Now the transformers are tested to see how they perform in reality.

With 2 transformers with the mains (230 VAC) in series and the secedaries in parallel with pure resistance as a load (not sure on how much) we get the following figures:

• 20.4 A - 15.7 VAC
• 15.6 A – 16.4 VAC
• 11.1 A – 17.1 VAC

The temperature of the transformers became approximately 40-45 C.

The numbers above are measured on 2 transformers and I have 4 available.

What is your take on this?


Kind regards
/Forsman

 

[AndrewT]

The temperature of the transformers became approximately 40-45 C.

Hi,
what is the temperature inside the transformer?
Do you think the internal temperature rise has any relevance to reliability?