Tech Info : Dealing with Electronic Transformer Capacitance

[JohnC]

As many of you know, transformers and Cbus are a bit of a passion for me :-)

Following questions asked here, I looked further into ways of solving the Capacitive Loading presented by Electronic Transformers to Cbus Leading Edge Dimmers.

Most of the technical info you need to know about is on the 2 x PDFs linked off this page of the new CIS website :
http://www2.clipsal.com/cis/technical/technical_support/newsletters_and_faq/transformers

Which is fine, but those PDFs tend to gloss over "why" there is a problem (which is outside the scope of this post), or to offer a clear and easy to understand solution. But you know what... the answer is actually hidden in there...

What about the (common) situations where the client has already purchased a heap of "high capacitance" transformers? The answer lies with the Clipsal 32EIND Inductor. For every 2A of load, you need one - it is connected in SERIES with the Active between the output of the dimmer and the transformers.

Basically, in a nutshell - the 32EIND blocks all the nasty capacitance from attacking and killing your Cbus Dimmers :eek:

From Clipsal Product FAQ's :
Q: What load can a 32EIND carry?

A: 32EIND can only handle a 2A load because of the limitations of the inductor.

When larger loads are required to be controlled, you need to provide separate 2A feeds, and multiple 32EIND devices.

- The 32/2400 10A leading edge Dimmer can connect 5 x 32EIND (each 32EIND drives up to 2A load)
- The 32/1000 4A leading edge Dimmer can connect 2 x 32EIND (each 32EIND drives up to 2A load)
So, if you want to use a big Pro Dimmer and run lots of trannies off it, you segregate them into "groups" of under 2A, and use one 32EIND for each group.

It's not rocket science to work out how many to use, or to connect them up to your loads. Providing you can split the loads, which might present a problem in some installations...

The other (maybe easier and neater) alternative is to use a 4 channel Pro Dimmer, which allows 1000nF Capacitance on each channel. By setting all 4 channels with the same Group Address, you can dim them in tandem yet spread the capacitance. So, you can connect 4 x 5A (each 1000nF) 4000nF total , instead of only 1000nF for a 20A 1 channel - does that make sense?

I hope that helps - feel free to ask questions etc if required.

And CIS people, please confirm that the information I have stated above is correct.

John

Edited to fix mistakes identified by Wonkey :)

[wanricky]

Just one funny situation: I told my client to change transformers because apparently there are too many (more than 10 electronic transformers) in one channel. Then,to save money, he would like to replace the excess transformers only! For example,if there are 14, he leave 10 electronic and use 4 coil one. Will it work?

[JohnC]

It always amazes me that people try to save money in the most strange situations and ways... a (decent) 60VA or 70VA Electronic transfomer is CHEAPER than a 50VA Wirewound transformer !

If the client is scimping over (say) $10 x 14 = $140 - assuming they replace all the trannies with Atco Possums - then what they going to say about the Cbus pcommissioning and programming costs ?

Anyway, the way I understand it is this :

The remaining 10 Electronic transformers will be a capacitive load. You can calculate what the capacitive and power loading is, and whether it is within the CIS recommendations for the dimmer.

The Wire-wound ones will provide a non-capacitive load. They have higher power loading than the electronics (allow 18W loss on each one to be safe).

Providing the total capacitance (from the Electronic trannies) AND the total power loading (from all trannies) is within the dimmer's specs, it should work OK.

Cheers and good luck, John

[Wonkey]

I would just like to clarify a couple of points in JohnC's post the 32EIND is wired in series with the loads and the max input capacitance allowed on the pro series dimmers is 1000nF (not 1000pF) per channel.

[JohnC]

Thanks Wonkey - I have edited the post above to fix those 2 important issues !