Decent amperage 1ph pressure switch?

[julianf]

One of my compressors has just failed. It's the evil direct drive one that eats fuses, won't start when cold, etc etc.

I think this burn out has just been caused by poor terminal conduction. It's lasted like that for years but I've been using it at higher duty recently (to run an air fed mask) and I think it's just melted things where the terminals create higher resistance.

It's wired on 2.5mm.


Anyway, I could get a switch off eBay that will be marked as "ultra heavy duty" 1 million (Chinese) amps etc, but, if I actually want one to work for a while, what should I get?

...and where can I mail order it from?

I mean machine mart has 20 or 25a ones, and I'd trust them slightly more than eBay sellers, so maybe just get one of them?

 

[Gareth J]

Use a cheap one to fire a contactor?

 

[Hopefuldave]

Mine's been running happily for a few years on one of the chinese pressure switch / unloaders, DID have to buy a few 1/4 blanking plugs for the unused ports. £6 with free shipping on EvilBay.

Worth having is a hexagon ferrule crimper and ferrules, makes for much easier . more reliable connections - also not a lot of Local Currency Units on the Bay of Evil.

 

[brightspark]

as in post 2 buy cheap cutout switch and a cheap[ contactor and put in an enclosure job done

 

[knighty]

get a 3 phase one and wire the phase in parallel so you have whatever amps it says x 3 ?

 

[mtt.tr]

i might have a danfoss switch on a shelf will check

 

[timgunn1962]

Condor mdr1 tends to be pretty good IME, but switching a contactor is far and away the better way to do it.

 

[brightspark]

Condor mdr1 tends to be pretty good IME, but switching a contactor is far and away the better way to do it.

there ok using a contactor ive seen 3 give up using there contacts for the full load even looping a 3 phase one to run on single

 

[julianf]

So, to get this clear in my head -

I buy a contactor (i dont know what, or where from!) and wire this from my 2.5mm mains feed.

I take a link off from the unswitched side of this to a cheap pressure switch with the unloader etc, take the live from the pressure switch to the "switch" terminal that, i assume, the contactor must have.

And then wire the contactor output to the motor, right?


Can someone let me know what contactor i should buy? I know so little about this kind of stuff...

Thank you.

 

[Anguz]

Remind me tuesday and i will have a rootle in the cupboard

 

[timgunn1962]

A contactor is really just a big relay. The "switch terminal" you mention is actually one side of the contactor coil. The other side of the coil will have a link to the to the Neutral on the unswitched side of the contactor so that the pressure switch and coil are in series in a circuit. When the pressure switch closes, the coil is fed, pulls in the contactor and closes the contacts. You seem to have the general idea pretty much nailed. The coil Voltage will need to be 230V if you want to keep it simple, and the AC3 Amp rating of the contactor needs to be more than your motor current (Amp) rating.

There are loads of suppliers and any decent electrical wholesaler should be able to sort you out. I think last time I put a contactor on a compressor (3 HP, 3-phase, though I'd just use 2 sets of contacts, switching Live and Neutral if it was single-phase), I used one of these: https://chaloncomponents.co.uk/product/chint-nc1-0910-contactor-5/

 

[knighty]

https://www.ebay.co.uk/itm/304614934424 this is a decent one

they're just like a 12v relay in your car... but 240v :-)

 

[Red'n'Black]

My 1980s compressor came with a Danfoss pressure switch, when the contacts finally wore out I replaced it with the equivalent new Danfoss one, cost about £90 which was more than I paid for the whole machine but I figured it should last another 40 years.

If you go with a cheapy pressure switch I would run it through a contactor.

 

[brightspark]

My 1980s compressor came with a Danfoss pressure switch, when the contacts finally wore out I replaced it with the equivalent new Danfoss one, cost about £90 which was more than I paid for the whole machine but I figured it should last another 40 years.

If you go with a cheapy pressure switch I would run it through a contactor.

i had to use a cheapo pressure switch on my comp the ol;d 3hp motor could pull the pump over starting at 90psi without an unloader had to fit a 2hp one when it burnt out and wouldnt pull it over so cheapo switch and contactor it is and have no bother since

 

[Ruffian]

Contactor is the way forwards for starting and stopping loads especially if your burning a pressure set out (wired in 2.5mm like that)

What size motor is on it and is the capacitor still good as seems could be drawing heavy amperage.

City electric in tiverton will do everything you want/need or screwfix.

Wire the motor through the contactor then loop from L1 to the pressure set, then from the pressure set to a1 then a2 to neutral.

Easy, job jobbed!

 

[julianf]

What size motor is on it and is the capacitor still good as seems could be drawing heavy amperage.

Its one of those compressors thats sold as 13a 1ph, but isnt really. I forget what fuse is in the (13a) plug, but its not 13a. Ill probably just put it on a 16a breaker by itself after this repair.

Its a "michigan" by fiac, not that i can find the specs on the web.

Ive had it over a decade, bought 2nd hand. Ive had to replace the re-settable thermal fuse a couple of years ago, but thats all. Its been wired with the 2.5 by me, years ago, as i needed it some way from the socket and wanted less volt drop.

I think this issue is going to be from running, rather than starting. All im using it for at the moment is running an air fed mask, and it doesnt cycle on that - much to my irritation, it just runs constantly. So, yeah, i suspect standard current draw heating up the poor connection to the terminal, rather than starting peaks.

 

[julianf]

https://www.ebay.co.uk/itm/304614934424 this is a decent one

they're just like a 12v relay in your car... but 240v :-)

The listing says -

The contacts are 2No normally closed rated at 25A


Dont i want "normally open" ? Ie only closed when the coil is energized?



Again, i dont understand this stuff that well, hence checking....

 

[Anguz]

hang on till i have been to work

 

[8ob]

Looks like a fair bit of crud has got under the cover of that pressure switch, no contacts cheap or expensive can cope with that. Just saying.

Bob

 

[julianf]

Looks like a fair bit of crud has got under the cover of that pressure switch, no contacts cheap or expensive can cope with that. Just saying.

Bob

I wont dispute any of that, but the contacts were not the failure point.

The live wire heated up, and the insulation melted on it. The final failure was, i think, the live melting the neutral insulation and blowing the fuse in the correct fashion.

The output terminal was unaffected, so, my suspicion is that the point of resistance / heating was the live wire to terminal.

In this, i think my original post was maybe slightly misleading - i dont think this one was damaged by the contacts, but i think that, if i bought a cheap from china one, it could well be a failure for the future.

Output terminals below -

I think that, if the heat had have come from the contactor, it would likely have been conducted to the output side in a similar way (?) but all the damage is on the inlet side only.

I think the unit would probably actually still work if you could make the connections to it.