electronic transformers, dimmers and C-bus recomendations

I have read both documents from clipsal re the selection of electronic transformers and some things just dont add up.

Using the atco possum as an example

Step 1 VA/nf ratio

A=60VA/33nf
= 1.8 > 0.85 so it is OK

But if you take another from the current list - anything with 100nF and 60VA

A=60VA/33nf
=0.6 < 0.85 and is deemed not recomended. There are about 8 in the list and some others that are worse (0.4 for one).

What am I missing

Mick

 

Hi Mick - nobody else's answered, so I'll give it a go

I am pretty sure you are referring to the transformers marked "NC" on the list at
http://www3.clipsal.com/cis/pdf_files/Clipsal_170805_Electronic_transformer_compatibility_chart.pdf

C-Bus "Wired" dimmers are only available in Leading Edge design - therefore only Electronic Transformers that are dimmable with Leading Edge dimmers can be used. Some of the small domestic dimmers (and also a couple of C-Bus "Wireless" units) are Trailing Edge design.

There is a (kind-of) misleading statement in the notes at the bottom of the page. The line that reads :
NC - "Not Compatible" - Transformer is listed by the manufacturer as only suitable for Trailing / Lagging Edge dimmer control.
It would be much clearer if it simply read :
NC - "Not Compatible" - Transformer is listed by the manufacturer as only suitable for Trailing Edge dimmer control.

Those "NC" models cannot be used with current Cbus "Wired" dimmers, no matter what the VA or Capacitance values. However, those units are perfect for use with Trailing Edge dimmers.

**************

The others marked "NR" in the 2 separate columns for 32/1000 and 32/2400 are different. For those the Input Capacitance is so high (relative to the VA rating) that only a small quantity of units can be used on each dimmer channel. Therefore they'd be silly to use them (ie: no use paying for a 2400VA dimmer that you can only use 400VA of load on it).

These aspects are explained in the section titled "Note relating to previously mentioned document" on page 2 of the PDF at http://www3.clipsal.com/cis/pdf_files/Clipsal_280504_calc_formulas_for_Cbus.pdf

*******************

The reason for all this stuff is that Electronic Transformers are usually a CAPACITIVE LOAD. Capacitive loads should be dimmed only with Trailing Edge dimmers. The commonly sold Leading Edge dimmers are only really suitable for Resistive or Inductive Loads. Overseas there isn't a problem, because every electrician knows that Electronic Trannies need Trailing, Conventional needs Leading Edge.

Here in Australia, there's little knowledge about this and a lot of transformers and dimmers have been blown up from incorrect usage. So some electronic transformer manufacturers started designing transformers that would work (to a degree) on standard Leading Edge dimmers. The problem is that a capacitor is needed across the mains connections, to supress RFI / EMC and comply with C-tick requirements. And that capacitor makes the load more capacitive, which is what causes the problem for the Leading Edge dimmers.

*******************

If you want to make it really easy for yourself, just use conventional wire-wound transformers. They have slightly higher watts loss (lower efficiency) but they last forever and don't cause the dimmer compatibility issues and derating that ALWAYS applies to Electronic Transformers.

Further, the conventional transformers can be used in HOT places like ceiling voids, while even the best Electronic units can only be installed in a maximum 55?C ambient. Trust me, I'm a lighting guy

Cheers, John

 

Thanks John

Not all are marked NC

As an example look at the first one the Actec mini60. this is an example of one that I was refering to without trying to use any names. It is recomended that only three be used on any one channel (for a 1A din rail dimmer), yet the Va/nF ration is not acceptable - hence my question

I will however take you point re iron core transformers into consideration. 55deg is not hard to reach in a roof space so they may well be a more suitable solution

Mick

 

I didn't write the chart or compile the data (although I was actually indirectly involved in it's creation). But I definitely understand what it means.

For most of the dimmers, the VA/nF ratio is not really a concern. That "ratio" is ONLY really relevant for the 32/1000 and 232/2400 dimmers, as detailed in Formula 1 on page 2 of the PDF. You will note that the Actec is rated "NR" for those dimmers in the cross-reference chart.

I think you may be getting a bit confused between the different dimmer types, and how they are all referenced on the chart and calculation formulas. Look at it this way :

Each Actec transformer has a capacitance of 100nF. The maximum acceptable for a DINrail dimmers is 300pF. So, no matter whether you use a L5508D1A or a L5504D2A you can only use 3 units. Now, 3x60VA is 180VA (about 0.75A based on unity Power Factor).

Therefore, you can connect 3 of them to a 1A dimmer and not waste too much. You can also only connect 3 of them to a 2A dimmer, and by doing so you waste about 2/3 of it's capacity.

For the C-Bus Pro dimmers, you can have a maxium of 1000pF capacitance. Therefore you can connect 10 x 100pF transformers to those models.

BUT if you use them on the 32/2400 or 32/1000, they are Not Recommended, because their VA/pF ratio is not good. Because of that, you are wasting a heap of money because you can't load the dimmer channel effectively - you'd be better off using a small and cheap switch-mounted mech than the huge and expensive 32/1000 or 32/2400 dimmer assembly !

*******************

So, on the Cross-Reference Chart the "NR" means not recommended because you waste a lot of money on a high powered dimmer where you can only use a small proportion of it's capacity.

The VA/pF ratio as described in section 1 of the Formulas page refers to only TWO dimmer types (31/1000 and 32/2400) which are not C-bus devices, they are old-fashioned conventional wall dimmers (albiet with remote control know).

Don't know how better to describe it - it's actually already clearly explained in the previously mentioned Clipsal PDFs, which is exactly where I am readoing from to write this post.

Cheers, John

 

Wire Wound?

Hi John,
I have looked into this thread because it is an interesting subject at any time, it is also something I spent some time on, and because I have issues here too.

Up to the time when I got involved with C-Bus I was promoting electronic transformers because of their efficiency and because of their safety (the good ones). Then comes along the capacitive problem with the C-Bus product (despite leading / traing edge compatible Transformers) and out go the electronic ones.
However..... I have repeatedly problems with the wire wound ones, particularly with flickering at low (<5%) output. Funny about this is that the dimmers seem to handle the load for about a month, then they start flickering, getting progressively worse. Same with a replacement unit (2A DIN rail dimmer). I could add the ehmmm newest manufacturing location for Clipsal dimmers as a concern, but lets assume that the quality is as good as it was.
Another suggestion was that there are "bad" wire wound Transformers which cause the problem.
Now I am wondering what kind of Transformer is actually usable with the dimmers? If they can't work with the wire wound ones, then the quality of the product needs to be questioned perhaps.
You do get electronic transformers from Atco which are listed a zero capacitance, but of course the price is higher than the conventional product. And who says that the dimmers will actually be happy with these transformers?

I know that this is a tad long-winded, but I am trying to get a bit more depth on what actually works with the Clipsal products? Can you help with this?

Cheers
Thomas

 

I am involved in the Architectural Lighting industry, and as a by product of our extensive commercial work we also get involved in a large number of extremely high-end domestic projects that invariably use a Lighting Control system.

We almost exclusively recommend Atco TM50 wire-wound transformers with C-bus dimmers. There are a few of reasons for this :

a) The heat issue with electronic transformers - they are NOT reliable if you install them in places with higher ambient temps than their Ta Rating. A ceiling cavity with dichroic LV downlights definitely gets hotter than 50?C. See attached screen dump from a training slide I made about the subject.

b) We cannot afford the hassles associated with precisely working out the dimmer loads. With wire-wound trannies we just allow 65w for a 50w lamp... I have a spreadsheet that calculates it automatically (3 on a 1A dimmer, 7 on a 2A). OK, by using a Atco Possum we could get 4 and 8 respectively, but there is always that "doubt" whether it is going to work reliably in the LONG-TERM. There's a danger that the electrician will substitute a different electronic transformer anyway - we've had quite a few cases where the electrician has "kept" the units we supplied, and installed cheap electronics instead!

c) Many electricians think (due to good marketing by Osram) that the Mouse (HTM series) is a better transformer than the Atco Speedy and Possum. So they convince the client to use Mouse instead - but the high capacitance means that we overload the dimmer channels (on 2A dimmers especially). Remember that we quote the C-bus up-front and on a decent sized project the difference could equate to 1 or 2 extra dimmers, and usually also a larger enclosure to accomodate them.

d) There are a heap of low-priced asian transformers flooding the market and many of those are dubious at best, and specifications like input capacitance is hard to obtain. Some smart electrician installs those to save money, then when everything doesn't work it can be very time consuming and expensive sorting out what caused what to blow up (and trust me, it's pretty easy to blow a channel on a 2A dimmer if you put the wrong load on it) !

So, the easy way (for us) is to say that "Cbus is only suitable for wire-wound transformers". OK, it's not technically correct but it solves ALL the problems in one short, sweet statement.

************

None of these problems occur if the correct type of dimmers are used for Electronic Transformers... and that means Trailing Edge Dimmers. However, for many years CIS have "sidelined" development of C-bus trailing edge dimmers and it is only with the Wireless Range that Trailing Edge has finally appeared.

So, let's all pray that CIS will release a couple of Trailing Edge C-bus dimmers, as that will solve the whole issue completely, once and for all.

************

I have never seen the flickering problem that you describe, but there is no way that it could be related to the transforrmer itself (the device is too simple to create flicker). I cannot comment on the situation that you are experiencing, it sounds very very strange and I can't see what would cause it.

But I definitely have seen that flickering in my own house with Clipsal wall plate dimmers (old non-EMC compliant ones), which are NOWHERE as good at holding a low setting and staying stable compared to HPM dimmers of the same rating. I would hope that the circuitry used in Cbus dimmers is of higher quality to those old things however....

I haven't tested any EMC compliant Clipsal wall dimmers, and we have only just installed some of the "new manufacturing location" c-bus dimmers. I have never heard a complaint of Cbus flickering at low levels, either with wire-wound or electronic trannies. When you say "flicker" do you mean instability of holding a set light level, or do you mean like 50Hz or 100Hz flickering ?

John

 

Just adding - one GOOD solution to fully utilise the dimmer channels is to use multiple lamps per electronic transformer

So, instead of using 1 x 50w dichroic on a 60 or 70VA trans, instead use 2 x 35W IRC (high output) lamps. Apart from saving a HEAP of power, you also halve the number of trannies required, which doubles the quantity per channel.

For example you can run SIX 35w IRC dichroics on a 1A dimmer channel by connecting them to 3 x 30pF 70VA transformers (= 210VA). This definitely works well using Atco Speedy transformers.

And THAT is what Electronic transformers are best for ! But, now a new problem - just you try explaining the concept of doing that (and how to wire it) to an average electrician !

**************

I also re-attached the screen capture re: temperature, as it fell off the previous post

John

 

John

The entire range of wall plate dimmers from Clipsal has been re-designed and re-released over the last 5 years or so. The C-Bus dimmers use their own dedicated design, nothing shared with old wall-plate dimmers.

I would be interested to see if the HPM wall plate dimmers work better when compared to our 32E450LM / TM style of wallplate dimmers. Our testing suggests that the Clipsal ones work better in many regards.

 

try the search function

Try Out the search function . If you type in transformers into it all sorts of info comes up on this topic.that will give you a bit more to chew on

 

I am sure that the new ones are much better (couldn't be much worse )
Note as I said before, I don't have any of the new re-designed Clipsal wall dimmers, nor any new EMC-compliant HPM ones so I cannot comment on the quality of any of the newer models.
And don't get me wrong, I really like the existing Cbus dimmers and how well they work on Inductive & Resistive loads... so I'll just continue to nag and nag about Trailing Edge models until someone gets so tired of me that they build us one

********

For your info, LV is not a huge proportion of our sales but our company sells approx 2000 transformers per month. Over the past 6 months the proportion has changed to around 90% electronic (Possums) vs 10% wire-wound (TM-50). This is almost exclusively for reasons of COST - the electronic ones are so much cheaper to buy.

I would say that the majority of projects now days use Electronic Transformers, and I reckon it's high time that CIS recognised this fact and designed new C-Bus dimmers to suit the market requirements, rather than trying to work against it

JC

 

John,

Trust me.. the Engineering Group is busier than you can possibly imagine

 

John

Thanks for all your comments. There is a lot of goof information there that will have an affect on how the house is wired up.

typically, we have used possums in the past, not only because they allow for 4 on one 1A channel, but they came recomended and have worked (even in a roof space).

Some bad information from lighting suppliers has been the casue of us using electronic transformers and not wire wound.

Thanks for you input

Mick

 

Hey Mick, I assume this was a typo

 

god damn! - I reckon I misstype more words than I get right.

At least someone is reading

 

Wire wound

Hi John,
Haven't had a chance to look into this for a bit, but getting back to your earlier post....

The flickering I am referring to is not 50Hz, which would be anyway quite difficult to see with a filament lamp (easy on Fluoros). The best I can tell you is that from what one can see and measure, it would appear that the dimmer is not capable of holding it's output voltage at a low setting. With a DVM you can see the pulsing breakdown of the voltage. What is most notable to me is that the dimmers are fine initially, and this problem starts after some time.

The other problem I have come across is an initial flashing, i.e. if a group is switched on, the lights (incandescent this time) flash once, and then start the normal ramp-up. Same situation in that it is fine at first, then this starts, but only on certain groups.

You also made the point that one could use an electronic trannie of a higher power rating, and attach more than one lamp. Yes, you could, but it sounds to me that the electrician there in Oz are as adventurous as here, so if it is problematic to get the basics right, I would not want to start specifying the cross section for the secondary wiring against cable lengths. Remember that the high frequency output of the electronic trannies also requires a restricted secondary cable length. Also, with concrete ceilings it becomes more difficult to implement this.

Then, I would not worry to much about the max temp rating of the electronic trannies. While you are right that the ceiling cavities get quite warm, consider the fact that an electronic trannie runs cooler and therefore contributes much less to the heating up of the ceilings. Also remember that a wire wound trannie is also restricted in it's maximum operating temp, and if I am not mistaken, you get very few of them which will take more than 130 deg C. At a much greater delta T (I thing as much as 70 deg C) for these, it doesn't take much before they are at their limit either.

Anyway, so much for the theory. John, it seems you guys are selling a fair amount of LV lighting. I would assume that on the commercial side you will not get a lot of similar complaints, but at the upmarket private residences, which applies to the site in question as well, things are different. People really live there and look at the lighting. And you say, you never had something similar?

Thanks for your inputs in the meantime.
Thomas

 

Atco TM50 wire-wound transformers?

Where in Australia is a good supplier of Atco TM50 wire-wound transformers?

Cheers,

Fleetz

 

Hi all

Thomas,

In regars to this problem, if it is only at or below 5% that you are having the flicker, the new C-Bus dimmers let you set a minimum level, which if set just above the level where the flicker occurs may solve your problem. 9While the problem should not exist, but one possible solution)

Regards
Brett

 

To buy them at a really decent price, you need a wholesale account. We are an OEM so buy direct from Atco in Melbourne, but most retailers buy via a different company trading as Atco Distribution (also called Eltad).

The cheapest place I ever saw selling them retail was Bunnings - there was a retail pack Downlight (branded Nelson I think) that included D/L, chinese lamp and TM50 for far far less than $15. Even thowing away the downlight, and using the lamp as a spare gave you a good price for the transformer.

Sometimes you'll see the Discount Lighting Shops selling "downlights packs" too - in these cases the downlights bodies are often useable, but the the lampholders and lamps are rubbish (and the crap lampholder burns off the pins of the original lamp, then all subsequent replacements).

Here's what our company sells the transformers for - first price is excluding Flex&Plug, the 2nd is including F&P - all prices excluding GST. I would consider these a maximum that you should pay :

TM50-2 $11.18 / TM50A-2 $13.80
Possum $10.05 / $11.25
Speedy $14.25 / $15.75

If you need a reasonable quantity, try putting the job out to "tender" with your local Electrical Wholesalers - you'd be surprised the differences in prices that you'll get quoted ! They won't care that you are buying as a cash sale.

Oh, and those TM50's are so heavy that it's not worth freighting them - so buy them "close to home"

Cheers, JC

 

Hey John,

Thanks for the detailed info and excellent clues to the best place to souce them. Many thanks.

Regards,

Fleetz