LED lights transformers

[robgraham]

I recently bought in one of those 5m rolls of LED strip lighting. Great st uff for lighting awkward places - in this case a rather deep larder in whic h we can now find everything due to a run of LEDs for each shelf. I used a metal cased 25W transformer for this.

So that's the solution for the under-cupboard worktop lighting then too. F or this I had a load of 13W, so ordered one of the plastic cased 18W transf ormers. This lasted for an hour before becoming so hot it smelt and was to o hot to touch, and stopped working.

I had another 25W one so did the replacement - I'd opted not do use this on e previously as it required an earth, and the terminals are exposed; both h ad to be addressed.

On looking inside the plastic cased device (I'm an electronics engineer) I was surprised by the lack of any high power devices or heat-sinking as in t he metal cased equivalent. I've not been involved in switching PSU design but for something generating 1.5A everything looked horribly lightweight. The switching transformer appears to be the source of the heat.

OK it may have been a faulty one, but this makes me a bit suspicious of the se plastic cased transformers.

Rob

[charles]

I agree with you. They all seem to run hot - too hot for my liking.

[Dave Plowman (News)]

Can you measure the actual current draw of the LEDs on that PS? I think you may find it's rather more than the wattage stated implies.

[Bob Eager]

Just wondering if it's perhaps 13W per metre, or something.

[Adam Aglionby]

60LEDs/m 5050 is likely around 15+W meter...

[ARW]

I had another 25W one so did the replacement - I'd opted not do use this one previously as it required an earth, and the terminals are exposed; both had to be addressed.

Care to name that one?

I refused to fit something similar a few months ago. It was bought from an electrical wholesalers (that I do not use) by the customer.

[Cursitor Doom]

Ideal transformers as you will know don't generate heat. So the heat must be coming from the resistance of the windings. Be interesting to measure that resistance and calculate the I^2R losses to see if they come in line with reasonable expectations.

[robgraham]

The nasty plastic one, which no doubt, Adam, you would have been comfortable fitting because it's got covered terminals and doesn't require an earth, is of the type Ebay 230843971628. I won't be buying this type again.

The better one, but does have the issue of exposed terminals is Ebay 391165796386. I've now run this one for 24 hours and it barely gets warm. I covered the terminals with a plastic cover.

Rob

[Bob Eager]

Did you check the wattage of the entire string?

[Tim Watts]

And some iron losses due to hysteresis...

[Bob Eager]

True, but presumably not so much in an SMPSU. My money is on the stated wattage of the load being incorrect.

[ARW]

I can find better things do in life other than install eBay Chinese LED drivers with little or no warranty bought by a customer.

[robgraham]

Hey, hey - guys. I bit less of the slagging please. I posted to warn othe rs off these plastic cased transformers.

Adam - I got a full refund from the supplier and have done in cases past wh ere Ebay items have failed; and let's be serious how do you know that the t ransformers you are buying aren't Chinese made too, and then you have the c ost of going back to the shop when they fail.

And Bob - hardly fair to challenge a stated electronics engineer on his abi lity to measure current. In theory the PSU was at 80% of capacity and shoul d have coped, but having looked inside I reckon it would never have done.

[Bob Eager]

Sorry about that! Pretty awful PSUs then.

[ARW]

Hey, hey - guys. I bit less of the slagging please. I posted to warn others off these plastic cased transformers.

Adam - I got a full refund from the supplier and have done in cases past where Ebay items have failed; and let's be serious how do you know that the transformers you are buying aren't Chinese made too, and then you have the cost of going back to the shop when they fail.

No offence meant:-)

It was the customer that bought what I thought were inappropriate drivers from the wholesalers not me:-)

They had exposed L&N terminals and there were not IMHO fit for their proposed use.

Cheers

[Dave Plowman (News)]

You'd be hard pressed to find ones not made in China (or the components used) - regardless of the branding, or where it claims to come from.

[ARW]

My main point (and one that I mad badly) was that my customers want the job doing NOW. I could not do that if I ordered my parts from eBay.

I sometime forget that this is a DIY group as many of the DIYers here put to shame some of the pro work that I see when I am at work, or have the time to wait for an eBay delivery - my stuff is expected to be delivered to me before 7.30am the next morning.

[Dave Plowman (News)]

You could if you were a one man band. Several reputable wholesalers sell on Ebay. And likely deliver just about as quickly as a local wholesaler does. But obviously not to site. But might well be worth it for 'stock' items at a better price. It's common these days to have things delivered to say a local shop where you could collect from on the way home.

Actually electrical stuff is the one thing I don't use Ebay for. Prefer to collect from my local wholesaler. Of which there are still several. But for so much else, Ebay suits me better.