Contact cleaning

[andykent]

The main switch has gone on my electric lawn mower. It was fine a few weeks ago. Pretty sure it's just dirty or corroded contacts. Rather than buy a complete new switch assembly, is there a contact cleaner that's safe/effective for mains contacts?

 

[diyer56]

Hi,

I have used this in the past....

https://www.screwfix.com/p/wd-40-specialist-contact-cleaner-400ml/92716
https://www.halfords.com/motoring/e...-specialist-fast-drying-contact-cleaner-250ml

Allow it to fully evaporate before reconnecting to the mains supply.

 

[bernardgreen]

Most switch contacts have a thin coating of arc resistant material and when that coating has gone the underlying base metal which is not arc resistance rapidly oxidises and thus a poor contact results

If the contact are just dirty then cleaning with a dry cloth may give a new, possibly long, lease of life to the switch.

If the contacts are corroded then cleaning may give a new but short lease of life to the switch as the contact material is like to have been corroded away,

 

[ericmark]

Late 60's early 70's switch cleaner was part of my tool kit, however thermal plastics melted with old switch cleaner and new switch cleaner was rather ineffective so today it's new switch job.

 

[ericmark]

Late 60's early 70's switch cleaner was part of my tool kit, however thermal plastics melted with old switch cleaner and new switch cleaner was rather ineffective so today it's new switch job.

 

[bernardgreen]

however thermal plastics melted with old switch cleaner

Thanks for reviving memories of a horrific experience, the lad meant well but replacing 64 closely packed soggy plastic switches soldered onto PCB was a hell of a task.

 

[ericmark]

I think we have all been there. That was why I stopped using it, not sure if allowed anyway today, at one point it was used in fire extinguishers but coloured red, even came is spray cans to wash brake drums rather than blow off, but not seen carbontec for years?

 

[SUNRAY]

Thanks for reviving memories of a horrific experience, the lad meant well but replacing 64 closely packed soggy plastic switches soldered onto PCB was a hell of a task.

Been there too, the only thing is 2 identical bits of kit (which were supplied at the same time and only a few serial numbers different) were 'serviced' at the same time. One was successfully cleaned with spray, the other resulted in lots of bits of metal laying in a puddle of goo.

And yes I agree with Eric about the effectiveness of the later products.

 

[Jackrae]

I think we have all been there. That was why I stopped using it, not sure if allowed anyway today, at one point it was used in fire extinguishers but coloured red, even came is spray cans to wash brake drums rather than blow off, but not seen carbontec for years?

In the early 60s I regularly popped into my local Boots and bought carbon tet in 2litre bottles. Imagine them selling it to 16 year-olds these days

 

[JohnW2]

In the early 60s I regularly popped into my local Boots and bought carbon tet in 2litre bottles. Imagine them selling it to 16 year-olds these days

Same here. It was also freely available as "Thawpit", a popular and widely-used domestic stain remover. I suppose it is probably still available, in a very restricted fashion, to the likes of chemical laboratories (and maybe for some industrial processes), but it is to-all-intents-and-purposes no longer available. It certainly ceased to be used as a refrigerant, in fire extinguishers and as a cleaning agent/solvent a very long time ago.

Kind Regards, John

 

[Jackrae]

I think one of the problems with it being used in fire extinguishers was that when put onto flames it converted into phosgene. I certainly found the products of combustion very unpleasant when I poured some onto a small fire I started inside my dad's shed !!! - but it snuffed the flames.

 

[JohnW2]

I think one of the problems with it being used in fire extinguishers was that when put onto flames it converted into phosgene. I certainly found the products of combustion very unpleasant when I poured some onto a small fire I started inside my dad's shed !!! - but it snuffed the flames.

That's true, and, more generally, I think that the same is also true of most/all of the halomethanes etc. that used to be used as refrigerants etc. Mind you, carbon tetrachloride is so potentially toxic itself that I'm not sure that its ability to turn into phosgene at high temperatures necessarily makes things much worse!

Kind Regards, John

 

[andykent]

Most switch contacts have a thin coating of arc resistant material and when that coating has gone the underlying base metal which is not arc resistance rapidly oxidises and thus a poor contact results

If the contact are just dirty then cleaning with a dry cloth may give a new, possibly long, lease of life to the switch.

If the contacts are corroded then cleaning may give a new but short lease of life to the switch as the contact material is like to have been corroded away,

Thanks for all the replies.
The problem is the switch is the kind that was never intended to be opened up and would be annihilated in the attempt. So realistically I won't know what's actually happened inside and it's certainly not practical to wipe the contacts.
Maybe I'll try a quick squirt of the specialist WD40 stuff, but more likely I'll just have to treat the whole assembly as a service part. Maybe I won't even bother with the good-money-after-bad thing with the WD40.

 

[Jackrae]

That's true, and, more generally, I think that the same is also true of most/all of the halomethanes etc. that used to be used as refrigerants etc. Mind you, carbon tetrachloride is so potentially toxic itself that I'm not sure that its ability to turn into phosgene at high temperatures necessarily makes things much worse!

Kind Regards, John

Yep, but in the early 60s as an apprentice we not only used carbontet' but also benzene as instrument cleaners and it was sloshed around like there was no tomorrow. And that was at a government 'establishment'

 

[JohnW2]

Yep, but in the early 60s as an apprentice we not only used carbontet' but also benzene as instrument cleaners and it was sloshed around like there was no tomorrow. And that was at a government 'establishment'

Sure, but there are countless examples of situations in which, in the past, we happily exposed ourselves to (often very) hazardous things simply because we were unaware of the hazards.

For example ... throughout my secondary schooling, we 'played with' liquid mercury in physics labs (on things called 'mercury trays'). Also, in my youth, most shoe shops had X-ray machines, and us kids were encouraged to 'play' wiuth them, to see the bones of our feet wiggling around inside shes! ... and there are, as I said, countless other examples.

In more recent times, some would argue that we may have gone too far in the other direction, 'banning' things which represent minute (if any) risk.

Kind Regards, John