So changing from 12v Halogen to 12v LED (bollox ?)

[Vipersan]

So ..this has me confused atm ...
I have a 12v system in my workroom at home ..
4 banks of 3 lamps ...each bank of 3 in parallel ...and 12volt rated ..
Originally I used 12v 20W halogen bulbs ..MR11+C
So I thought I'd splash out and replace them with LED equivalents ..
So ordered 12 x MR11 GU4 12v 2.5W SMD LED Energy Saving Efficient Spot Light Lamp Bulb LOW VOLT
I replaced three that were out all three being supplied from the same transformer ...and switched on ..
There was an initial brightness ..followed by the entire bank of 3 illuminated ..but dull ..
See the photo..
I then tried replacing 3 more on a different transformer bank ...and got exactly the same..
Confused I put back the 3 halogens ..which illuminated normally ??
Thinking I might be asking too much of the 12v transformer ...I refit 2 of the 3 LED lamps and left one halogen ..
Result ..
All lit OK ..
So the transformer can only handle a maximum of 2 LED bulbs ???
I'm totally confused now as these LED lamps are supposed to be more energy efficient ????
Does this not imply they require less energy from the transformer ?????
Totally stumped now .
rgds
VS

 

[Vipersan]

So ..I think I have my answer ..
Apparently a common problem ..
LED units require a smooth DC supply and constant minimum load ...which the transformers cannot provide ..
So I have options ..
Tear down the ceiling and re-wire to supply mains to each bulb ..
Yeah right ...
Or ..The option I'm going for ..
2 LED lamps and one Halogen per bank ..
The halogen in each bank will provide a suitable load ...I think ..
Basically 3 led lamps cannot draw enough current ..
doh!!

 

[Lazarus]

I'm more interested by the image conjured up by the last two words of the Thread title

 

[TJExcalibur]

I replaced 8- 12v halogen bulbs in my bathroom supplied by a big wound transformer. Worked a treat for 4 years now.
In my den I did the same with 4 on a wound transformer and all still OK. One nightlight half way up the stairs on halogen would not work until I got a 240v/12v dc converter.
AC-DC 12V 18/12/6W Switching Power Supply Lighting LED Driver Transformer

 

[timo_w2s]

I'm facing a similar dilemma. Our new house was wired up for 12V 35W and 50W MR11 type bulbs in almost every room by the previous owners. The lounge has 9 x 50W bulbs at the moment, and the kitchen about double that. That's a few kW of lighting there! Changing them to LEDs is going to be a pain as most are running on individual transformers which will all need taking out. We've already replaced the spots in the bathroom with standard 240V GU10 type fittings with suitable LED bulbs for those. Some rooms where the ceiling lights aren't used much can stay as they are.

 

[Vipersan]

Now ..
you might one day hear about this on watchdog ...so take note.
I relaced 2 halogens in each bank of 3 with the LED lamps I received today ..
granted they are sold unbranded on ebay ...and the vendor is UK based ..
I purchased 12 of these a few days ago at a cost of £36..so not cheap by any means.
They arrived this morning ..and were fitted this evening ...
I left the lights on and went to put the kettle on and make a brew..
I returned some 15 minutes later to find ALL but 3 LED lamps and all 4 Halogens were out..
I removed all the LED lamps and tested them on a 12vDC psu ..
at least 6 of them did not light up ..
Curiosity being something I have to persue ...I bit the bullet and smashed the glass envelope open on one of these dead bulbs ...being careful only to break the glass an leave the internals intact..
Imagine my surprise to find one of the white wires that connect the rear two pins to the led matrix pcb ...floating in mid air thus isolating the pcb from the 12v supply ..
I resoldered this to the board ..and once again powered it ..
It lit no problem ..
So ...it would appear the heatr generated by the LEDs which conducts through the PCB is sufficient to melt and desolder at least one of the connections ...thus the bulb effectively fails as this soldered conection is within the enclosed glass envelope and not repairable..
It could well be that they use low melting point solder in the construction ...thus engineering a potential future fail ...or simply dont solder well enough during manufacture...
either way ..it's bad form ...
..and I may well report my findings to Watchdog ..and send them a failed sample to investigate...
Here is a photo ..
Keep in mind I have soldered this to test the leds ...but unsoldered it again for the photo..
rgds
VS

 

[Vipersan]

So this may or may not work...
I'm now convinced the issue is the heat generated by the LEDs within the glass envelope of the bulb ..
It simply cannot vent and escape ...coupled with the poor quality lead free solder used ...
So I've ordered some glass cutting discs for my dremel..
I intend to cut and remove the upper portion of the envelope and hopefully expose enough of the pcb to allow me to resolder those connections with lead solder ...and at the same time create better air flow and ventilation whilst retaing a collar of glass just under the pcb to allow correct fitting in the ceiling downlights..
A lot of messing about ..and will void any warranties ..but this should allow cooler running and access to repair the poor build quality issues..
rgds
VS

 

[hairybadger]

You might find the guarantee for the LEDs says something like "you must use a transformer designed for LED lighting" or somesuch. When I replaced all our halogens with the LED equivalent I changed the existing transformers with LED-compatible units as I understood was necessary, or at least a good idea. In 3 years one of the eight bulbs has failed, but that was after only a few weeks so was a faulty unit. They were pretty cheap so I didn't bother sending it back (plus I'd been sent an extra one that I hadn't paid for by mistake so I just swapped in the spare)

 

[PaulR]

I have also been buying el-cheapo LED bulbs from China. I tested them when they arrived and in one batch two out of five were DOA (I think I've already posted this elsewhere) but they were replaced without complaint. Naturally I intend to take the two to pieces at some time but it perhaps augurs badly for the others. Time will tell.

 

[TJExcalibur]

So this may or may not work...
I'm now convinced the issue is the heat generated by the LEDs withing the glass envelope of the bulb ..
It simply cannot vent and escape ...coupled with the poor quality lead free solder used ...
So I've ordered some glass cutting discs for my dremel..
I intend to cut and remove the upper portion of the envelope and hopefully expose enough of the pcb to allow me to resolder those connections with lead solder ...and at the same time create better air flow and ventilation whilst retaing a collar of glass just under the pcb to allow correct fitting in the ceiling downlights..
A lot of messing about ..and will void any warranties ..but this should allow cooler running and access to repair the poor build quality issues..
rgds
VS

I believe you have been conned into buying an inferior product. My bathroom led's have been in for years and only ever had one failure. My bulbs consist of several led's.

 

[pgh13]

Lots of interesting (and some scary) LED bulbs exposed on Youtube

 

[Vipersan]

Well ..
having completely removed a glass envelope from around one of these non fuctional LED lamps last night ..
I then repaired the soldered connections using lead solder ...
The 2 pin push connection having been retained and left intact ..
This free floating pcb now re-connected was fitted into one of the 12v halogen downlight fittings ...and powered up ..
No problems ..it lit up fully ..
The lamp remained on overnight ..and is still fully functional this morning ...
So I'm now convinced of by heat melting solder theory..
The lamp still generates heat ..but this can now escape and vent upwards into the drop ceiling space..
Problem now is that the diameter of the pcb is less than the original 35mm lamps glass enclosure ..
So ..back on ebay ..and much searching later ..
discovered these in china ..
5 Clear Round Glass Dome Seals 35mm
Ordered 3 packs of 5 ....at just over a £1 each pack..
If they fit then I have a way to fit the led pcb securely ...
We shall see..
meanwhile the test will continue and the repaired led lamp will remain on for a few days continuously..
rgds
VS

 

[timo_w2s]

Some transformers designed for halogen bulbs may not be too well regulated and may actually be putting out too high voltage for lower power LEDs, so it may be worth checking what the real voltage is across the LED bulb in case it's substantially more than 12V.

 

[Vipersan]

Some transformers designed for halogen bulbs may not be too well regulated and may actually be putting out too high voltage for lower power LEDs, so it may be worth checking what the real voltage is across the LED bulb in case it's substantially more than 12V.

Agreed ..
A voltage in excess of 12 would cause premature led lamp failure ..but this would definately result in one led in each group of 4 in series ..of which there are 3 groups in parallel to fail first ..
This would result in elements of the lamp showing failure first ..
one led in a group of 4 going short circuit placing a higher voltage on each of that group of 4 ...thus these too would eventually fail ...either by going open circuit ...which would leave the other 2 banks of 4 functional for a time ...or by going short circuit resulting in the 43 ohm resistor going open circuit ...or transformer failure ..
This is not what happened ..
Heat generated by the LED s conducted through the pcb and rising upwards ..partially melted the poor soldered joint on the other side of that pcb ...thus the tension of the connecting wire ...pulled and seperated that joint ..totally disconnecting the 12v supply to the LED pcb ..
So regardless of 12vac or 12vdc supplied ...this was always likely to happen ..because the heat cannot escape from within the glass enclosure rapidly enough by conduction or convection ..
It's simply poor build and bad design imo..
rgds
VS

 

[timo_w2s]

I don't doubt your bulbs bad design, just wondering if you where driving them harder than designed they might get even hotter and therefore failing even faster?

 

[Vipersan]

I don't doubt your bulbs bad design, just wondering if you where driving them harder than designed they might get even hotter and therefore failing even faster?

You may well have it spot on buddy ..
but imo ..
nothing should be designed to run _that_ close to breakdown tollerances.
Personally I think the downlight parially enclosed design of the actual fittings also plays a part in upping the working temperature..
Having sort of diagnosed what the problem is ..I now need to find a workable solution that doesn't involve large quantities of money spent ..and the mess it might bring me.
in other words ..a way to make these new led lamps legacy (backwards compatible)
lol

 

[2cvbloke]

There's a reason they sell LED drivers to replace halogen transformers (especially electronic ones)...

 

[Vipersan]

There's a reason they sell LED drivers to replace halogen transformers (especially electronic ones)...

Indeed there is ..and why no one has the gumption to make a thing backwards compatible with an existing system...
Money £££££££$$$$$$$$$$$$
Its not that they can't ...
It's that they want to make you think going green is lifestyle choice ...and you are conned into parting with even more dosh without questioning ...cos you have that feel good factor that comes with nausiating self important belief that you are doing good and sod the cost..
If each lamp included on that small round pcb ..1x12v 1 amp suface mount regulator after the bridge rectifier ..
Cost approx 2p each in bulk ...plus 1x surface mount tantalum electroytic ...another 2p ..
then the lamps would indeed be backwards compatible with ac transformers and existing systems ...
The regulator making sure 12v is never exceeded ..and the caps dealing with the ripple..
But that would be too easy would it not ...and they couldn't offer you new lighting systems costing a small fortune to install ..
sorry I'm grouchy ...but I see this kind of crap every day in the TV tade..
Move the goalposts ..
Re-invent the wheel ..
Charge more money..
It's called churn...and it cause my stomach to do just that..
cest la vie.

 

[2cvbloke]

If each lamp included on that small round pcb ..1x12v 1 amp suface mount regulator after the bridge rectifier ..
Cost approx 2p each in bulk ...plus 1x surface mount tantalum electroytic ...another 2p ..
then the lamps would indeed be backwards compatible with ac transformers and existing systems ...

But the pictured LED bulbs are of very chinese origin (not to mention potentially lethal with exposed connections, if they're used on a capacitive dropper you could become a nice path to ground!!), you can't expect them to pay an extra 2p per unit just to make their product universal...

Buy cheap crap, get cheap crap...

 

[Vipersan]

But the pictured LED bulbs are of very chinese origin (not to mention potentially lethal with exposed connections, if they're used on a capacitive dropper you could become a nice path to ground!!), you can't expect them to pay an extra 2p per unit just to make their product universal...

Buy cheap crap, get cheap crap...

Can't see it being lethal at 12v 1amp..but still..
LOL..
Thanks for making me laugh buddy ...
I needed that..