I fixed something

All you need now is another nine dead Lidl/Aldi battery chargers.

I just used a "car-type" toggle switch, the sort of thing that we used to use for spotlights in the good old days, that I must have had in my spares box for 40 years. It was the one with the highest rating and I used it to bypass the failed glow plug timer relay on my little all terrain vehicle. 16 amps rating, 24 amp load but I am expecting it to out-last me.

Result. ;-) I had spare switches in stock, and the faulty one didn't look any different to those. So dunno why it is a common failure.

Cheap s*it?

They're what's known as a tactile switch. Bit like a tiny bell push. My spares came from CPC, so I assume decent quality. No idea how many operating cycles they're meant to survive. They come in several different sizes of what appears to be the same design.

The much more expensive CTEK charger which is very similar in concept suffers the same problem. Recently fixed one. But don't know of enough of them to have any data on how long they last there.

It's odd, as the first fault you'd normally see on a low cost SMPS would be a much more expensive low ESR capacitor.

Is the circuit missing an inrush limiter ?

NTCR1 is the inrush limiter on this SMPS (upper left corner). Although this schematic shows no switch for mains.

You would need to understand what was inside the Lidl/Aldi unit, to say whether that's a root cause (inrush). Ordinary dumb chargers shouldn't really punish a mains switch, if a mains switch was even present.

While regular laminated transformers are generally pretty safe, the newer toroidal transformers aren't. They have a kind of inrush issue as well. The company making those, warns of the phenomenon, but didn't even provide an application note explaining how they tamed it in practice.

And while the NTCR1 in the above schematic is generally a good thing, if you don't design it right, NTCR1 will burn out on you. That's what some of the early designs did.

To improve supply efficiency, some designs now even short out NTCR1 with a relay, so it does not consume power while the product is running.

Modern ATX supplies (the 80+ kind, with active PFC), those make the active PFC block do double duty, and the active PFC acts as an RC charging circuit for the first few cycles until the caps are charged.

I've seen that kind of switch damage at work. An SMPS with 10 amp mains switch fitted, the switch disintegrated in my fingers one morning, when pressing the switch to turn on the circuit, and this was with about a year of service on the equipment. So 200 cycles of the switch, the excess current absolutely destroyed the switch. I would have expected just the contacts to burn off, but for some reason, even the plastics holding the switch together decided to let go too. (The management team in my project, designed the equipment chassis and infrastructure, so they owned this incident...)

There are also failure mechanisms at low current. The only place I might have seen this, is on the hook switch of an old POTS telephone here (wouldn't switch cleanly).

Wetting current/Sealing current

It's not a mains switch. A led comes on whenever mains is present. This switch is a mode switch. Toggles (effectively) between low, high and maintenance charge. But you'd normally just switch to high, and it will change automatically to maintenance when the battery is full. So I'd say it is simply switching at logic level.

but me that found the fault

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Out of interest/boredom I opened up the old switch. It?s hard to see why it doesn?t work. It?s a simple springy metal diaphragm the should make contact between two outer terminals and one central one.

Tim

The plated-up finish on the metal could be the mistake.

Paul

Yup.

Yup again. They are sort of sealed. Could be a squirt of contact cleaner might fix them, if it could get to the contacts.

It's such a simple device I've never worked out why this switch fails in this application. It would hardly be worth setting up a special production run to make rubbish versions. The actual charger is very well made indeed. No difference in apparent quality between it and a CTEK selling for 3 times the price.

Thanks for the heads up all those years ago. ;-)

I have a CTEK - I needed a charger at one of the points Aldi/Lidl didn't have a clone. I bought it in Jan 2013.

I think the CTEK has a 5 year warranty, and the switch lasted a bit longer than that :-( , I repaired the charger in late 2018 IIRC.

I think people have taken the original switches apart and found tarnishing on the metal disc contact.

Considering that it only has to make a momentary connection it?s odd that just pressing it more firmly doesn?t overcome the tarnishing (or whatever is increasing the resistance).

Oddly, despite very good weatherproofing, there was some crud on the pcb around the switch on mine, almost as if water had got in at some time. I wonder if it happened during manufacture before the unit was fully sealed?

Tim

The Lidl one appears to be very well sealed. Nice rubber gasket between the the case parts. To IP whatever, I'd guess.

Be interesting to know if ones kept in a house have the switch last longer than one kept in an unheated etc garage.

The one I have built into the Rover - one of the first models - has only had the switch changed recently. Quite a few years old and well past any warranty. And the car lives outdoors. This early one has fixing brackets built in - later ones don't.