Fried dimmer channel

Hi

Yesterday one of my 50W GU10 lamps blew - and it seems to have fried one of the channels on my 4 x 5A Pro dimmer. The supply to the dimmer is protected with a 16A MCB (B Curve); each output channel is protected by a 4A MCB (C Curve). Both tripped when the lamp failed - but it appears that the 4A MCB on the output didn't provide the protection it was intended to. The channel is stuck on.

I have a few questions:

1) How normal is this? Should I expect to fry dimmer channels whenever a lamp fails? If so, it's going to be a very expensive proposition.

2) When this happens, is it usually just the triac that let's go - or does it take other components with it?

3) Warranty aside (the dimmer is already well outside warranty), is it generally possible to have these units repaired by an eletronics repairer? Are wiring schematics etc. available?

Thankss!

Micky

 

Mains-voltage GU10 halogen lamps can be quite a pain. When they fail they often fail short-circuit and this results in very large currents through both the wiring and any associated controls products. Most incandescent lamps have a fusible section of wire inside them so that, in the event of a short circuit, they fail at a defined upper current however many GU10 240V halogen lamps don't have this, so the current increases until something inside the lamp eventually melts.

Circuit Breakers don't always provide the necessary level of protection because fault currents like these can be very, very high. Hundreds of amps for a fraction of a second is not uncommon. The circuit breaker has a trip curve and this gives you some idea about how quickly it will respond to certain over-current conditions. Nevertheless, they don't react instantly and, until they do, there can be a short period of time (fractions of a second) where extremely large currents flow. This can be enough to damage a dimmer.

Always the triac, occasionally a couple other bits as well.

Clipsal offer a repair service, so you can return it to them for repair (at a fee, of course). The repair isn't difficult so, providing a general electronics repair person can obtain the correct parts, it can be done. I even recall a non-Clipsal company offering C-Bus repair services a number of years ago.

Clipsal do not release schematics for products however it's not really necessary to have the schematic to do the repair.

 

Maybe fuses should be recomended when using GU10's to protect the channel?

Small din rail mount fuse holders are not that expensive and fuses are easy to change and can be sized accordingly.

 

Thanks Guys

Excuse my ignorance - would fuses provide a faster response time and hence more protection than MCBs? If so, perhaps I should put an inline fuse on the supply to each fitting. In total, I have 40 dimmer channels - most feeding several GU10s. I'll need to take-out a second mortgage if dimmer channels frequently get fried!

I'm in the UK, so shipping the dimmer to Australia to be fixed isn't really an option - but I can determine the part number of the triac I can probably obtain one and then try to persuade a local electronics shop to have a go.

Mike