Pro range weirdness

Has anybody experienced problems with Pro Range dimmers channels in the OFF state emitting voltage only when another channel (on the same dimmer) is on at a medium to low level? When the ON channel is set to 100% or 0% the problem disappears.

We are also noticing that the lights are flickering when set to levels below 75%. The transformers are Atco Speedy's.

Any experiences?

 

Pro series flickering

gday psc,
I have experienced a similar problem of the flickering with a commercial project.The problem is caused from capacitance loading caused by the transformers.i think from memory cap loading of pro series is 1000nf per channel . check the cap loading of the tranis.you may have to tear one apart if you cant find specs.multiply the nano farads by the number of tranis if its over 1000 then thats most likly the problem.unfortunatly you cant load the pro series up to there 5amps with out blowing the cap loading out of the water.we where lucky and only had 10 to 16 tranis on a channel . we changed a few tranis on each channel that was flickering to atco possums which have a loading of 33nf. this brought the overalll cap loading on that channel to around the 1000nf mark .Our channels stabalised.this post will be a bit hard to swallow if you have loaded the channels right up and could potentialy cost someone $$$$$ to fix . Our problem was caused by a builder supplying LV Downlight Kits .He was told to make sure they where CBUS compatable, they where but they had a csp loading of 100nf which put a few of my channels over.As usual the poor old sparkie has to fix the problem .This is a lesson that all CBUSERs should heed.Specify exactly what tranis your prices are based on and explain what can happen if the right tranis are not used. this will at least cover you when the dreaded candle effect crops up.This also can happen with DIN mount product which has a loading of 300nf per channel.I learnt the hard way , Im sure PSC wont forget. So i hope this Info on my experince saves someone else the hollow feeling in your guts when a client says why are the down lights flickering when dimmed or turned off.

 

Great info Nick, it's greatly appreciated.

I'll check out those tranny's tomorrow.

Thanks for taking the time.

 

Nick's post has top info regarding the issues of capacitance and all leading edge dimming technology. This message has been told many many times, however it appears that it does not hurt to keep telling the story. The issues of capacitance and dimming AC is pure electronics. For every half cycle of an AC waveform (50hz = 50 cycles per second, 100 half cycles per second) capacitance presents as an instant short circuit until the cap charges to the polarity applied and then presents a high resistance. The problem is 100th of a second later the polarity starts to swing the other way. The larger the capacitance the longer it takes to charge and therefore the longer it presents that short.

An excess of capacitance on a dimmer channel plays havoc with the triac output stage of the dimmer. The visible / obvious problem is channel flickering as the combined capacitance shorts and charges rapidly. The more sinister and less visible effect is the loading effect and eventual damage of the output circuitry due to the resultant low impedence / high load. The damage to dimmer units due to capacitance loading sticks out like the proverbial.

This issue is not limited to C-Bus equipment. It is electronic theory which applies to all leading edge dimming equipment of all makes and models...

http://www3.clipsal.com/cis/lit_installtraining_dimmer.php3

 

Nick is correct regarding the Possums @ 33nF, but those are only a 60VA trannie and normally are only used 1:1 with 50W LV lamps. The Atco Speedy is rated at 33nF for a 70VA - but the 105VA Speedy is 100nF.

Therefore if they were 105VA's then there's only the possibility of using 10 on a Pro channel, which if using 100W of lamps on each then that's only 1000W worth of load (4.16A). Bit of a waste of capacity, especially when using the 1 and 2 channel Pro Dimmers !

Discussing this with various technical gurus, I've found that it's apparently very hard to make a stable Electronic Trannie without a "high" capacitance on the Input. Too low capacitance (common with Atco Speedy 70VA and Possume 60VA) manifests itself in the trannies "wavering" - being unable to hold a stable dim setting. This is not flickering, but a sliding of the dimming level - I've seen this problem on some sites. From my research, I've been told that 100nF is about the minimum to make a good balance between stability, RFI (EMC) suppression and "Leading Edge Dimmability". And 100nF is not good for C-Bus....

Come on CIS - Bring on some Trailing Edge Dimmers for C-Bus. The problem of capacitance is not going away... in fact it will become more and more common due to the lower relative cost of Electronic Trannies !

John