[Ralph2]

Re: in-line heater test?

This is a great thread and saved me a lot of time looking for the fault in my Zanussi dishwasher. No Leeroypenmut, that relay is not the right pattern, you want something like this: http://cpc.farnell.com/jsp/Components+& … ku=SW02620

But I am here to tell you that the reason these boards are failing is because the relay is underspecified. The unit fitted is rated at 10A 125V. This is derated to 6A at 277V. So at a nominal 240V it will carry about 7A. The 2KW heater will draw about 8A. All these figures are approximate I know, but however you calculate things the relay is running constantly at (or slightly over) it’s max rating.

As a minimum this application requires a relay that will pass a true 10A at 240V. The consequence of long term running at max rating is overheating, and tarnishing/pitting of the contacts when the relay activates. This creates a high resistance across the contacts which itself creates large amounts of heat. So much heat that it melts the solder on the PCB. the way the contacts are designed in a relay means one ‘leg’ of the contacts is almost always shorter than the other. Due to the shorter heat path and less metal to ‘soak’ the heat, this leg will always melt the solder first. This is the situation we have here. As the relay is now effectively ‘shot’, resoldering the joint will only be a temporary fix. I took a photo of my old dissasembled relay to show the contact damage, but can’t figure how to post images on this forum, sorry.

We can only guess this is a result of commercial pressure. No electrical design engineer would deliberately underspecify such a key component. I have not found a relay of this size that will handle the current, so a bigger relay would have meant an offboard component or board redesign, neither of which were deemed acceptable by the beancounters. Pure speculation, but at least the answer is simple. Solder in a new £1 relay and you should get another year to 18 months out of the old girl. I don’t like to think of the number of otherwise servicable machines that have been junked because of this. Not an ecologically friendly descision of the (alleged) beancounter.. 🙁

My thanks again to all who contributed to this thread. Nice work.

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