L5508D1A Atco Possum Vs Atco Iron Core

I am interested in people comments (scientific and on the job expererience) on the following.

Assuming a L5508SD1A is driving

a) 1 x 50W 12v with Atco Iron Core Transformer
b) 1 x 50W 12v with Atco Electronic Possum Switch mode PS

Both will work Fine..

I am interested in peoples opinions with regard to Pro and Cons of both in terms of the following

1) Cost.
2) Environment (both installed in +50 Degree Roof)
3) Environment (both installed in 10-30 Degree Ceiling Space)
4) Installation Considerations (Vent space/heat generated)
5) Long term Reliability (ie not much can go wrong with an iron core transformer)
6) Heat generated by L5508SD1A channel
7) Noise (ie Swithing noise and hum)
8) Quality of Dimming and Light Color
9) Installation issues (which are quicker to install)
10) Electrical Efficiency (Full on)
11) Electrical Efficiency (Dimmed)
12) EMF or electical noise to audio equipment (Radius of this noise)
13) Vibration and how it how to install to minimise transfer to buinding to keep vibration noise low
14) Buzz in lamp Filiment ? or fitting ?
15) Does the L5508SD1A prefer one over the other. (Even though they both work)

 

JohnC has covered a lot of this in one of his many very informative posts. His comments were not specifically directed to the Atco brand, but more general.

Other than that, I can t offer anything as I am no expert and dont want to say anything that is wrong, and have only use the possums.

Mick

 

Charlie,

I have only use the possum type, but can offer the following comments:

1. cost - there was not much in it when i last checked, the possums were a little more expensive.

2. (is this also the same as 3.) have not ever measured the temp in my ceiling, but on a 35 degree day (yes, we do get them on occasion in melbourne ), you do not tend to use many lights, but i would expect the roofspace to be 50 deg+, and have had no trouble.

3. (see 2.)

4.Check the revised AS3000, now have specified clearances around fittings & transformers.

5. been running 2+ years so far, the onl;y issue i had was over-tightening of the terminals breaking the solder joint to the circuit board.

6. minimal heat, but the max i have on any 1 channel is 4.

7. slight noise at module, you can notice a hum from the tranny if you are in the roof next to it, but inside the house... nothing.

8. colour tends to yellow when dimmes ( same as most others)

9. the little electronic ones are beautiful to install

10-14. No idea, sorry. (look up items posted by JohnC...)

15. From memory, you could put more possums per channel than the iron core equivalent ( but i don't have the compatability chart handy to be sure)

HTH

Cheers

Grant

 

1) Cost.

Electronic transformers are much cheaper for the wholesaler to BUY. Last time I checked (few years ago), a possum was like $6 vs $10 for a TM50. A cheap chinese trannie will be about $1.50, something like a Osram Redback will be about $2-3.

If you are asking for a certain specific transformer, the reseller will "pad the margin" accordingly.

2) Environment (both installed in +50 Degree Roof)

I am pretty sure that a Possum is only rated for Ta 50C (Ta=ambient) - you can confirm by reading the printing on the unit. Life is halved for each 5-10C above that rated Ta.

3) Environment (both installed in 10-30 Degree Ceiling Space)

There is no such thing as a 10C ceiling space that I am aware of.

4) Installation Considerations (Vent space/heat generated)

Iron core thermally cycles at about 110-120C INTERNAL temperature. The electronic ones just overheat (heat kills the capacitors). Remember that a 50W halogen lamp generates much more heat than either type of trannie (watts are watts)... so if the downlights are dichroics and reflect heat back into the ceiling void then the lamps are the main factor, not the transformers.

That said, I usually say that the electronic transformers are great because they fit into small confined spaces. But they are completely unsuitable for use in small confined spaces.

5) Long term Reliability (ie not much can go wrong with an iron core transformer)

Electronics will last maybe 20-30,000 hours on a good day with all the planets aligned, when operated under their rated Ta. In real life they last considerably less than that. An Iron-core will basically last forever under the same circumstances.

6) Heat generated by L5508SD1A channel

Theoretically this should only be related to the installed (total) load, plus any "back EMF" from capacitive loading. Basically, this relates to the total VA loading - and shouldn't really make much difference either way (the dimmer is rated to handle the 1A either way). I have not heard of issues from either load.

7) Noise (ie Swithing noise and hum)

Not sure - theoretically shouldn't make any difference at the dimmer. At the transformer, poor quality control may cause some wirewounds to get lamination buzz when dimmed. If that happens - just swap them out with quieter ones.

8) Quality of Dimming and Light Color

Should make no difference to dimming "quality" or colour. ALL halogen lamps change colour as dimmed, this is a function of the way that incandescent light sources work. If you are continuously dimming and want a whiter light, use a lower wattage lamp.

9) Installation issues (which are quicker to install)

Irrelevant - both require installation in a safe manner, which includes compliance with regulations relating to surrounding insulation materials.

10) Electrical Efficiency (Full on)

Watts Loss of TM50s depends on the age of the units. The old ones (1990's) were 12W loss, the later models with poorer quality iron in them are up to 16W loss. A Possum will probably lose 4 or 5 watts total.

11) Electrical Efficiency (Dimmed)

Not sure, but theoretically the iron core will become more efficient when dimmed because there is no overhead from the front-end electronics. In other words, when dimmed to 50% RMS output, a TM50 might draw 25 + 8W = 33W whilst the Possum might be 25W + 4W loss = 29W. There is a lot of physics etc involved in this, with copper and iron losses within the wirewound tranny vs the electronics overheads in the Possum.

Irrespective of all that, a couple of watts will not make or break the kyoto agreement

12) EMF or electical noise to audio equipment (Radius of this noise)

Wirewound will almost always be better, as they operate at 50Hz just like the mains supply. Electronic transformers will have significant radiated noise, especially if lamp leads are extended.

That said, all products sold in Australia must meet C-tick for compliance with CISPR15 and if actually tested and approved the device is unlikely to cause any real-world problems. Cheap chinese transformers are a completely different matter (CE stands to "Chinese Export", and C-tick is simply another printing option like your brand logo)

13) Vibration and how it how to install to minimise transfer to buinding to keep vibration noise low

Do not mount onto to ceiling. Mount to ROOF and use a quality lampholder with longer leads. This considerably helps the temperature problem as well.

14) Buzz in lamp Filiment ? or fitting ?

Never heard of such a thing. If there is, it's a function of the lamp. Buy quality lamps.

15) Does the L5508SD1A prefer one over the other. (Even though they both work)

Iron core is ALWAYS going to be a nicer load for a Leading Edge Dimmer than a semi-capacitive load like a electronic transformer.

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The main advantage of electronic transformers is that their output varies far less when exposed to different loads. A 50VA wirewound ONLY gives it's rate output (usually 11.5V or so) when loaded with 50W. Drop to a 35W lamp and the output will rise above 12V, which kills lamp life. Electronic transformers still suffer some voltage rise, but it's far less.

Note also that NEITHER type provides a constant output if input voltage changes. That feature disappeared from electronic transformers many years ago when electricians started demanding that prices be lowered

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This is an informal response done "off the top of my head". There may be some details that I have glossed over and the figures quoted are estimates just to give overall concepts. Hope it helps nevertheless.

 

Thank you John. You have confirmed my thoughts. Both have place. One is not necessarily better than the other.

I hand and interesting experience this week. While in the electrical wholesaler this week. A man came in with a Atco Possum in his hand wanting to know which of the terminals on the 12 V side were positive and negative. He hand been told by his mate (apprentice Electrician) that these were a cheap way to power his car stereo from 240v.

I told him it was a cheap way to toast his car stereo !!!

Charles