Overloading/Driving a dimmer channel

Wondering if someone could advise what would happen if a dimmer circuit was overloaded.

For example say a client had 200W uplighter running off a 1A dimmer circuit - and then they decided to put in say a 300W light (drawing around 1.5a) for something to do. Does the dimmer itself lock out, fry itself or otherwise indicate it's displeasure? Is there any rule of thumb on how much the circuit can be driven before it complains?

Is there permanent damage done to the dimmer module or is it a resetable condition?

I appreciate of course matching loads to the right dimmer - but the above scenario is possible after commissioning and I'm just curious what happens to the dimmer......

Put simply - I suppose I'm asking how idiot proof/tolerant is the dimmer...<g>

While I'm at it what happens if more than 10A is drawn through a 10A relay circuit?

Thanks....

 

Good question, I'd also like to know that. I know that the Dynalite units, say 8x 1A dimmer will actually let you pull 10A overall or overload 2 channels eg 6x 1A & 2x2A. Not a bad feature...

Cheers

 

It's really a thermal issue. All C-Bus products can maintain their full rated current in all channels when the dimmer is mounted as recommended and the ambient temperature is the maximum stated for the product.

Running ANY electronic dimmer at higher currents will always mean higher temperature in the active switching devices, and higher temperatures ALWAYS means shorter life for solid-state devices, so there is a trade-off.

If you tried to draw more current through a channel, you probably could, but it would be very difficult to define the maximum overload that would be allowed, because you have to take into account ambient temperature, and what current is being drawn through any other channels.


.. But it's more complicated than that.

For the PRO series of dimmers, which all share the same heatsink, you might assume that any one of the channels individually in any of the 5,10 or 20 Ampere products could draw the full 20 Amps at maximum ambient temperature, and possibly even more when run at a lower temperature, and it might not be damaged, but:
- the product probably won't meet the EMC requirements (ElectroMagnetic Compatibility), because the noise suppression circuitry is tuned for a specific rated load level.
- the product probably won't give as long a service life
- the product is more likely to be damaged if subjected to transients in the mains supply than it would be if operated within the specified range.


Don

 

Mmmm so depending on the ambient heat levels it's possible (if a client say uprated lamps above the initial design levels) that it would be very hard to notice this as the dimmer may well continue to function.....

Just at some point it may just die.....

So what if I understand correctly the non pro range will probably tolerate (subject to ambient heat) some level of "overdriving" - amount unknown - but at some level (or 70 degrees) they will shutdown to protect themselves if the become too hot as the current (and therefore heat generated) exceeds the design spec for the heatsink to deal with.

So long term the units potentially get damaged - short term they will probably tolerate a bit of abuse....so hard to deduce (short of surveying all attached channels) if everything is within spec.

Interesting......

 

Hey - I had a domestic project where that exact thing happened. The electrician wired up 2 wall lights to a 1 amp dimmer channel. The wall lights had 200W lamps in each, so the total load was 400W (1.66A).

It was running like that every day for almost a month before I discovered what they'd done when I went back to program the switches in that floor of the house.

Nothing happened to the dimmer, and most of the channels were fairly well loaded (all channels used, and all switched on each day to provide "temporray lighting" on the site).

Perhaps it survived because none of the loads were actually being DIMMED - it was all just On-Off using the over-ride buttons ??

Cheers, John

 

It would be interesting to know (not that I'm keen to pull one apart) whether the controller handling each dimmer circuit is identical between the 1A and 2A jobs - withthe only difference being a beefier heatsink attached to it.

Anyone know the answer to this?

I saw another thread talking about similiar stuff and the consensus seems to be the dimmers are pretty tough and relatively forgiving but "no guarantees"... on long term damage. Would that be fair comment?

JohnC - in regards that 200W uplighter by 2 problem - can you "bond" together two dimmer channels to get extra supply (eg: say you've got to dim 3A and you don't want to put in a PRO series dimmer - could you do bond two 2A dimmer circuits as one - any tricks/comments gotchas on this?


Cheers

 

There is another thread open answering that exact question brj, and to put it simply, if you're talking about "hard-wiring" or bridging two channels together, plain and simple, dont do it!

 

No problem - I had thought I"d heard someone that bonding together channels was possible. Never tried it (luckily!) though. Maybe I just misheard someone that was meaning logically bonding (programming) the channels together but physically separate circuits.

I suppose standard approach would be just to use a dimmer that has native load capability to handle downstream device or when cabling to physically break the load up to two discrete smaller loads, using two channels (or as necessary) and then program them to act as one.


Cheers

 

Yep - no way that I would suggest connecting the outputs of 2 channels together... it goes against everything I have been taught about electronics. The big problem here would be that the 2 outputs (Triacs) would NOT share the load evenly, so one would get a heap more current than the other.

I had a situation recently where there was a large pendant light in a domestic entry foyer... 50 lamps of 15W. That's 750W, which would normally imply buying a 4x5A Pro dimmer but only using 1 channel of it. Luckily, the light fitting was already "bi-wired"... it had 2 actives, each connected to 25 lamps. So we ran an extra switched active back to the C-Bus Devices then used 2 channels of a 5504, and set them to the same GA. It worked perfectly, and there was no way you could tell that it wasn't all on one circuit.

In most domestic situations, I'd suggest (from a lighting viewpoint) that if you need more than 2 Amps on a circuit you SHOULD break that circuit down smaller. The reason I say that is that the whole idea of a Control System is to provide flexibility of control... so if you have lots of lowish-powered circuits you can then combine them in lots of cool ways using scenes, etc.

I absolutely CRINGE when I see those jobs with 6 or 8 downlights in a lounge room, all connected to one switch/dimmer channel. In my installs, I try to use an absolute Maximum of 4 lights per channel, but always try to convince the client to go for 2 lights per channel if they can wear the cost. The more channels, the more flexibility for the client.. and also the more sales volume too - so it's a win-win situation

 

The light at the end of the tunnel is controlled by C-bus

Reminds me of an installation out in the Donga where the home owner would drive into the nearest town every two months or so to get a new 500W 32V500 stand alone dimmer, when the wholesaler asked him what was going on after the 3rd or 4th ist the guy said the Sparky had put in a 500W dimmer but the load was 1000W, the 500W dimmer would last anywhere from 3 weeks to 2 months and he would replace it, when it was suggested he should get the correct 31V1000 fitted he said he couldn't be bothered and would keep changing them as they failed.

Re the question about 1A and 2A dimmers the 1A has eight channels total load 8 A the 2A has 4 channels total load 8A, the heatsink is essentially the same but the fewer (4 rather than 8) triacs in the 2A can be spaced to efficiently dissipate the extra heat that they each have to handle.

As ususal the Clipsal dimming products are rated to cope with worse case as far as Line Voltage, ambient temperature, load, brightness level etc is concerned but the specs are the specs once you go outside them you are on your own.