Newbie transformer question

[Wingfeather]

I have a question, and I think it's something of a silly one - but I've searched around and I can't find the answer elsewhere.

Looking for power transformers, www.rswww.com (UK) seems to have some good deals:
500VA is the highest they go in "encapsulated" form. This costs £36.90
They go as high as 1000VA in open-form, which sounds a little better for high-power projects. This costs £56.06.

Now, 1000VA of open-form is cheaper than 1000VA of encapsulated, plus the fact that it's in a single package, whereas the latter would require 2 separate units.

The secondary voltages each is available in appear to be the same, and they all have two separate secondary coils.

Is there any reason I would need to go for an encapsulated supply? What are the real differences between the two?

Thanks,

 

[pinkmouse]

AFAIK the encapsulated designs from RS are just epoxy potted, no extra screening or anything, so they will just act to reduce mechanical noise from the traffo.

If you are building a stereo amp, two separate traffos are a good idea anyway to increase channel isolation, and prevent peaks in one channel pulling down the supply to the other.

You may want to look at Farnells, the website is much more difficult to navigate, but they can be a little cheaper

 

[Wingfeather]

Thanks for the link to Farnell. I already knew about them as it happens, reasoning that if their website is that blo*dy dificult to navigate (and their searches are just THAT buggy), they don't deserve my money!

Considering the differences in cost between the open-form and encapsulated designs, I thought there might be extra shielding involved in the encapsulated type. Does it depend on the manufacturer in particular or are all encapsulated designs the same?

Also, from the pictures, the encapsulated designs look somewhat easier to mount onto a chassis (bolt straight through the middle?). As I have precisely no experience with transformers, is this true? How exactly are these things mounted?

Thanks

 

[pinkmouse]

I have done some reading on the Nuvotem/Talema website and the spces seem to indicate no screening. Some manufacturers may have screening, but I suspect it is a custom option, not available on standard production models.

As for mounting, open style traffos come with a mounting dish and bolt to secure them to a chassis, whereas with a encapsulated, you have to buy your own bolt!

If you want, I will post a pic later, ( batteries are flat in my camera at the moment!), but if you search through pics of projects on the site I'm sure you will find loads of references