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240 to 12v Question


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Is there such a thing as a 240v to 12v transformer that you can plug a number 12v things into ?   Like a multi plug or a distribution box?

I want to fit a few 12v lights around the bench in the workshop - a 12v bar light in the blast cabinet and a couple of 12v spots over my pillar drill and bench sander etc 

Does such a thing exist ? 
 

eBay searches have shown transformers with more than one terminal - but they are meant for inside of things like strip lights I think and take the 240v to just screw terminals too.

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Yeah, just 12v lighting transformer.

Pretty bog standard stuff for kitchens and bathrooms etc.

Note, they aren't socket, you just push stripped wires into the holes and they grip.

There's lots of types out there, a search will get you there.

 

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Old PC or server PSU's wee all over anything else - I pulled a pile of Dell & HP server ones out of a skip, the smallest one does 12v 750W but 50A or more output isn't uncommon on the server ones.

A big thread on them is here:

https://www.rcgroups.com/forums/showthread.php?1292514-How-to-convert-Server-Power-Supplies/page12

Most of them you just need to join two pins to turn them on.

For standard issue PC power supplies you can get ATX breakout boards:

https://www.ebay.co.uk/itm/293395769738

That give you all the voltages on nice connectors and an on/off switch etc. Again, any old PC pulled from the pile will give you hundreds of watts for no money.

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1 hour ago, Anderzander said:

Wow 😮🤩 brilliant !

I see what you mean about the server psu’s https://www.ebay.co.uk/itm/124069902425

connect that up to the ATX board and I’m in business 👍🏻

You misunderstand - the server ones are 12v only and don't have an ATX connector, the ones in your old desktop PC are a standard thing that has a bundle of wires coming out to the large plastic ATX connector and they give 3.3v, 5v, 12v, -5v at varying currents.

That little one you posted is absolutely fine but you'll have to solder wires on to get the power out, and a little jumper to get it to turn on. I've got a couple like that myself, it's an easy mod.

 

This is a standard PC ATX PSU as found in IT department scrap pile:

atx_psu.thumb.jpg.a7dfc065e328e3725e5c6439e83db7cf.jpg

The big connector is the ATX one, the smaller 4-pin ones have 5v, GND, 12v on them or just 12v & GND

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Ahh - sorry. I was meaning find out what pins from the server pins I could feed into the distribution board. I was googling the pin out diagram for it.
 

I’m learning !  What you’ve shown there though looks much simpler. I’ll do more reading.

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On 5/4/2020 at 1:23 AM, Bowie69 said:

Yeah, just 12v lighting transformer.

Pretty bog standard stuff for kitchens and bathrooms etc.

Note, they aren't socket, you just push stripped wires into the holes and they grip.

There's lots of types out there, a search will get you there.

 

That’s what you want - easy to use and rated for the job, so no building code or insurance issues.  They come in various output wattages, so decide how many light fixtures you want and what power consumption they have and chose the transformers accordingly.  Ceiling halogen spot lights normally run at 25ish or 50w, and usually have independent transformers, but new LED replacement bulbs for those units tend to run at a little over 10% of the current for the same light.  It’s not healthy to run transformers with an output wattage less than their rated output as it generates heat, but a lot of those LED lamps now runs direct 240v AC, so don’t need transformers at all (built into the bulb unit), and just use the old wire harness that ran from the transformer to the halogen bulb.  Have a look for those - easier and probably more efficient and safer.

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1 hour ago, Snagger said:

 It’s not healthy to run transformers with an output wattage less than their rated output as it generates heat

Huh? Sorry but this is wrong.

Also, the GU10 type bulbs that are led, are 12V still, otherwise you could end up plugging a 12V bulb into 240V, that and the fitting is only rated at 12V. Plus, they are 12V for a reason, so you don't end up with having to get an electrician in to fit them near a wet space.

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We have GU10 and the smaller pinned interior bulbs here that run directly off 240v.  I have installed a bunch of them, removing the transformers in the process.  The LEDs inside those bulb units obviously run at much lower voltages, and all the transformer stuff is internal to the unit.

The compound maintenance guys also fitted LED replacements for the halogen units using 6w transformers in place of the original 50w transformers for the the halogen bulbs.

I have read several times that it is bad to have a transformer run for extended periods with an output we’ll below its rating, and that ties up with the lower rated transformers being installed with my new lights.  With an overrated transformer, aren’t you relying on back emf in the primary coil to prevent overloading the secondary which is producing a lot less current than intended?  That energy has to go somewhere...

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46 minutes ago, Snagger said:

With an overrated transformer, aren’t you relying on back emf in the primary coil to prevent overloading the secondary which is producing a lot less current than intended?

No, current only flows if it can, transformers produce voltage, not current.  Input current goes up with output current.

Sure, a transformer running at a much lower intended output will not be *quite* as efficient, but there's no other downsides really. I suspect the 'transformers' you mention are not that at all, but a box of electronics, which are much more efficient, especially at lower power outputs.

.... apologies, I meant GU4 bulbs, GU10s were originally meant for 240V applications. So yes a 240V LED GU10 will have electronics inside to drop the voltage most likely.

 

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Interesting about the transformers.  I have read a that you should try to match the transformer to the bulb wattage - I read that when I first fitted 12v halogen spots nearly 20 years ago, and have come across similar comments about phone and computer chargers getting hotter if left on but disconnected from the device with nowhere for their output to go, generating more back emf and heat.  Comforting if that is not right and there is no safety issue.

I have fitted a load of these smaller pinned bulb units which run without transformers.  Since fitting those in place of some of the 12v halogens, my employer replaced the rest of the halogens with 12v LED units that use the lower rated transformers.  Since they wanted to replace the halogens as part of an efficiency drive to all company accommodation, the transformers may well have been part of that rather than the safety side.  But it’s all Chinese, so safety is a relative term. 😉

86E1798E-0EEC-4BC0-B493-852B6AB80F1F.jpeg

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If it's only for lighting, why not just link several 10w or 20w 240v led lamps together with some cable and junction boxes and put a 3 pin plug on the end?  I've got eight set up in the workshop like that, uses less power than the kettle. 

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Going back to the original question, I think you should find a few cheap and suitable options in ikea.  I bought a cheap set of three led spotlights that are very bright and run off their included 28v transformer.  A little silicone sealant would make them suitable for dirty environments.  They have plenty of other light systems, including strip LEDs.  I also saw ribbons of 12v led strip in local hardware stores alongside spot lights, work lights, outdoor flood lights, ceiling tile panel units, led substitute fluorescent tube units...  the choice is very extensive if you’re not after a decorative look.

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