PDA

View Full Version : Toroidal Transforers vs others



Macrosill
04-24-2008, 02:39 PM
I have been reading alot about the use of toroidal transformers in both Australia and the USA. It is my understanding that their use in Australia is required as their lights run off 24v or so. I have read reference on their use in the USA for isolation and protection.

Now onto the question. What is the benefit of using toroidal transformers vs a standard transformer? Are they used for no other purpose than efficiency?

kmc123
04-24-2008, 02:47 PM
Hey Brian,
Not sure if this will answer it ALL, but out of curiosity I went to wikipedia.org and found the following:
http://en.wikipedia.org/wiki/Transformer_types#Toroidal

Toroidal
http://upload.wikimedia.org/wikipedia/en/thumb/9/92/Toroidal-transformer.jpg/180px-Toroidal-transformer.jpg (http://en.wikipedia.org/wiki/Image:Toroidal-transformer.jpg)



Doughnut shaped toroidal transformers are used to save space compared to EI cores, and sometimes to reduce external magnetic field. These use a ring shaped core, copper windings wrapped round this ring (and thus threaded through the ring during winding), and tape for insulation.
Toroidals compared to EI core transformers:

Lower external magnetic field
Smaller for a given power rating
Higher cost in most cases, as winding requires more complex & slower equipment
Less robust
Central fixing is either
bolt, large metal washers & rubber pads
bolt & potting resin
Overtightening the central fixing bolt may short the windings
greater inrush current at switch-on.Rectangular toroids are also sometimes encountered. These use a rectangular version of a toroidal core, usually wound as a multilayered single flat steel strip. Windings are placed on 2 of the 4 sides of the core.

Macrosill
04-24-2008, 03:16 PM
I had actually read that before posting. Some of the points I read and you posted are the reasoning for my question

* Lower external magnetic field
* Smaller for a given power rating
* Higher cost in most cases, as winding requires more complex & slower equipment
* Less robust
* Central fixing is either
o bolt, large metal washers & rubber pads
o bolt & potting resin
* Overtightening the central fixing bolt may short the windings
* greater inrush current at switch-on.


The only pros I see is the smaller size and greater inrush current, almost everything else seems like a negative to its use.

DennisB
04-25-2008, 02:10 AM
My thoughts are that the Torridal Tx's are great for Electronics etc to the lower magnetic interference that they generate and I believe that they are cheaper then Iron Core Tx's.

A few setup issues with Torridals exist aswell, like tightening the hold down setup to tight, which may compress the windings and short the primary and secondaries together and then wiring them together so that you get the desired voltage out of the Tx.

I prefer Iron core transformer due to the simplicity when it comes to wiring them, usually they have a terminal post or the like on top which allows easy connections of the primary and secondary cabling. Where as the Torridal have to be crimped are soldered on the secondary and primary sides.

Really it is personal choice in our setups we use, Iron core, usually larger and more mounting space required and torridals have a lower profile so less space is required.


Dennis

mrpackethead
04-25-2008, 04:01 AM
Its probably worth thinking about using isolated Switch mode supplies. The $/Watt makes them a very attractive option in many cases. The size of the transformer in a SMPS is small due to the frequency at which they operate. ( typically in the order of 50-200kHz ). You can find a 300W supply for $20 on ebay if you look about.. Try finding a transformer at that price/performance.

Low voltage systems certainly are a good idea, and make all the diy blink blinky bits so much safer.

DennisB
04-25-2008, 04:12 AM
Its probably worth thinking about using isolated Switch mode supplies. The $/Watt makes them a very attractive option in many cases. The size of the transformer in a SMPS is small due to the frequency at which they operate. ( typically in the order of 50-200kHz ). You can find a 300W supply for $20 on ebay if you look about.. Try finding a transformer at that price/performance.

Low voltage systems certainly are a good idea, and make all the diy blink blinky bits so much safer.

Certainly a good idea if you are after AC to DC conversion, however AC to AC conversion via a SMPS would cost a fair bit more then $20.

I use a SMPS to power my controller boards, got it for $1 from the local rubbish dump.

Dennis

aussiephil
04-25-2008, 05:39 AM
I had actually read that before posting. Some of the points I read and you posted are the reasoning for my question

* Lower external magnetic field
* Smaller for a given power rating
* Higher cost in most cases, as winding requires more complex & slower equipment
* Less robust
* Central fixing is either
o bolt, large metal washers & rubber pads
o bolt & potting resin
* Overtightening the central fixing bolt may short the windings
* greater inrush current at switch-on.


The only pros I see is the smaller size and greater inrush current, almost everything else seems like a negative to its use.

Macro -

Simple answer for why Aussies talk about and use Toroids Transformers - The 300VA ones are easy to buy - all the electronics dealers here carry them.
Finding a normal iron core at that VA is near impossible.
A check i did a few months ago on getting prices for 1000VA-1500VA transformers of any type showed next to no price difference as well. The interesting thing was that the over the counter 300VA's Toroids came out cheaper/watt once you bought 4 or more.

The flying leads actually work better from a "make it safe" perspective as it's difficult to insulate the typical iron core's solder tags.

Cheers
Aussiephil

Macrosill
04-25-2008, 11:26 AM
Thanks for the explanations guys. The cheaper cost and readily available supply brings the answer to the mystery.

mrpackethead
04-25-2008, 10:12 PM
just for those interested, you can buy a number of torodals that are encased in plastic, with pins for direct mounting to a pcb.. Particaully in the smaller power ranges.. these tend to be very useful..

prof
04-26-2008, 08:43 AM
The other fun thing to watch out for with toroidal transformers is to make sure that the central steel mounting bolt is not short circuited. As this wil creat a shorted turn, usually with catastrophic results.