I've been reading here on the fora a lot. Recently the FirstWatt clones really interest me. I was just thinking materials now.
Why are toroid transformers used? Could other types be used? I can get a couple of big transformers with 26V secundaries from some UPS systems. Good starting point for a FirstWatt project? Thanks.
Why are toroid transformers used? Could other types be used? I can get a couple of big transformers with 26V secundaries from some UPS systems. Good starting point for a FirstWatt project? Thanks.
Toroids can be smaller, EI plates are large, No real reason if designing from scratch. Oh yes, toroids have no air gap, so no good for output transformers.
26V. Probably a good starting point for some kind of project. Centre tapped or single secondary? If single-sided, are they identical? When you say big, do you know how much current? If not, what do they weigh?
Toroids can run at higher flux and have lower losses, partly as a result of this. Also they radiate lower stray flux. They do have a downside however - increased inter-winding capacitance.
Single sided, identical, 6.5 kg = 14.3 lbs
Core measures 135 x 162 x 40mm = 5.3 x 6.3 x 1.6 inches. Should be good for some nice amps? True dual mono configuration.
Was thinking along the lines of a balanced F5(t) or F6.
Last edited:
Standard power transformer and cheaper.
(even 30-35 years ago, obtaining an EI/U/C in a >100VA size was difficult here, best chance was buying a core package abroad and WIY)
A potentially better transformer type is much more expensive, and even harder to get (strip wound core transformer, O-core, R-core, etc.)
Well, the ones I can get are salvaged so also cheap (€20/each) and surely big enough for a nice project? Or better to get standard types specified? Thanks.
I'm so cheap I don't even pay for sex.
If they do not hum(p), and you don't mind building larger amp cases, why spend money if you can be a cheapskate.
If they do not hum(p), and you don't mind building larger amp cases, why spend money if you can be a cheapskate.
I read somewhere that UPS transformers don't work so well in reverse. This in part may be due to them having an air gap to prevent saturation from the driving circuitry when being used as intended.
That's could be a slight problem. Can anyone confirm this for the ups transformers?
Lol@jacco like the Belgians make Dutch jokes and the English make Scots jokes. Cheap is good and free is better, but I would pay for a good transformer. They should be as good as, if not better than stock toroid stuff.
Lol@jacco like the Belgians make Dutch jokes and the English make Scots jokes. Cheap is good and free is better, but I would pay for a good transformer. They should be as good as, if not better than stock toroid stuff.
Found this thread: http://www.diyaudio.com/forums/power-supplies/243448-ups-transformers-audio-amp.html
Still not completely sure but might take the plunge.
Still not completely sure but might take the plunge.
no load draw is high because they have to push the power density high enough for a 30 minute full load start at 20C and end at 200 when the battery is dead.
no load temp rise can be 30C or more just from copper and core losses.
reducing the flux 10% is usually enough, 15-20% reduction even better.
many ups transformers have an extra secondary and you can run that in series with the primary. --but that extra secondary sometimes isn't insulated separately, it might be thin gauge wire wound on top of the secondary. so, keep that in mind. but usually there is at least one layer of mylar between it and the secondary, so it should be safe to run it in series with the primary.
I don't recommend taking the core apart, putting it back together always increases the core loss 10-20% and can practically double the no load VA consumption due to the increased air gap caused by scratches in the core insulation and varnish, and if you bake the varnish off then you'll end up increasing eddy current losses.
so if you want to rewind it, i suggest rewinding them without taking the core apart.. yep, its a lot of fun.
no load temp rise can be 30C or more just from copper and core losses.
reducing the flux 10% is usually enough, 15-20% reduction even better.
many ups transformers have an extra secondary and you can run that in series with the primary. --but that extra secondary sometimes isn't insulated separately, it might be thin gauge wire wound on top of the secondary. so, keep that in mind. but usually there is at least one layer of mylar between it and the secondary, so it should be safe to run it in series with the primary.
I don't recommend taking the core apart, putting it back together always increases the core loss 10-20% and can practically double the no load VA consumption due to the increased air gap caused by scratches in the core insulation and varnish, and if you bake the varnish off then you'll end up increasing eddy current losses.
so if you want to rewind it, i suggest rewinding them without taking the core apart.. yep, its a lot of fun.
toroids have large sec to primary capacitances, unless they are with a screen. so be ready for noisy ground currents towards other mains powered circuits. common mode chokes d limit the HF part a bit..
For solid state power amplifiers, even with their inherent downsides, 'stock' toroidals are still way superior to conventional transformers.
Half the weight, much stiffer secondary voltage, with a very friendly magnetic stray field.
Adding a pair of back to back capacitors to block DC, and a mains input filter are a modest surcharge.
(laminated-core transformers for solid state power amps only make sense for ratings over 2kVA, imo. They'd have to have highly oversized cores, and fully bonded laminations, come at a price tag very few can afford)
I consider myself half-Belgian, most jokes I make are also about myself.
- Status
- Not open for further replies.