Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Toroidal power transformer

Status
Not open for further replies.

szzuk

Member
I've been running my circuit off a 2x18V and 0.8A toroidal power (mains) transformer. I've been pulling around 50V and at different times up to 3A. It is a case of I threw a power board together and then used it for various circuits without remember its limitations.

So what exactly has this been doing to my circuits? How much can these be pushed? My circuits worked but it wasn't till just today when I realised I'd reached the limit and rechecked the power board.

Regards,

Szzuk.
 
So what exactly has this been doing to my circuits?
You tell us! Presumably nothing destructive, or it would have been obvious from the smoke, flame and popping noises.
How much can these be pushed?
As far as the maximum values specified in their datasheets. Beyond that, smoke, flame ......
 
I've probably been running under powered, so I will get a better mains transformer to feed the power board. The one I have now is 15VA and I can't get enough power out of it for my use. I guess in a vague way I was hoping someone would say you can get for example upto 30VA at a push - so double. Because if I have to buy a mains transformer that is on spec so to speak, it is very hefty in weight and I'd prefer something less like a toroidal brick :)
 
Have you considered an SMPS? Less brick-like !
 
If you have a 2x18V 0.8 A transformer, it would have two 18 V, 0.8 A windings, so it would be rated to about 30 VA.

Transformer rating is based on heating, and they are heavy, so they take ages to overheat. I would guess that a 30 VA transformer would survive a 50 VA load for half an hour or so.
 
I wondered if something like that might be occuring. I need the power for just a few seconds at a time so the transformer would never overheat. I'm just going to buy a toroidal brick that is 2x25V with 3A windings, it'll solve the problem and I can use it for weight lifting too...
 
Momentarily overloading the transformer is not a problem but just be aware that the internal transformer resistance will reduce the output voltage.
 
Well I bought a new toroidal transformer and it came this morning. It is 2 x 25V with 3A. The problem is that i'm using it with a bridge to create a dual supply, but it is rectifying the DC voltage to +/-37V. Now the chip this board/transformer supplies needs a dual supply of +/-30V at most. I should have thought about this!

Should I see if the chip will tolerate 70V? (It's an OPA548)
Bleed off 10V (how?)
Send it back and get 2x20V transformer? (Not sure if they'll take it)

Regards,

Szzuk.
 
If its a toroidal type transformer you may have a fair chance that the secondaries are wound on the outside and you can simply unwind enough turns from them to drop your output voltage far enough.

In odd cases where I had too high of open circuit voltage or needed a specific voltage I have cheated transformer output voltages down that way. I often buy or recycle the cheap class 2 (side by side winding) 24 VAC furnace transformers and unwind the secondaries a bit to make 24 VDC power packs out of them.
 
regulated rails for the op amps, keep the unregulated rails for output stages (at least it sounds like you are building some kind of amplifier if you are needing short term "raw" power).
 
regulated rails for the op amps, keep the unregulated rails for output stages (at least it sounds like you are building some kind of amplifier if you are needing short term "raw" power).

Yes. That is bang on. I will regulate the supply to the opamp and i'm going to look for some right now.

Regards,

Szzuk.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top