Electrical experts on LED's please!
russbost - 22/5/13 at 09:49 AM
Ok, this is a weird one, I thought I understood LED's & electrics fairly well but this one has me stumped.
In my house I have 2 x halogen light fittings, both run from the same transformer & running 50W halogen bulbs with the G4 2 pin base.
Working perfectly but throwing rather more light than we need, so with my "locost" hat on thought why waste 100W of energy when LED's
would do the job for less than 10W?
Bought a couple of led G4 3W LED "bulbs" off Ebay similar to the ones at bottom of pic 3W GU10 Dimmable Warm White/White
LED Light Lamp Spotlight/G4 5 LED Warm White | eBay
When I fitted them they didn't work! However if I take 1 LED bulb out & fit a halogen bulb to the other unit they work fine, doesn't
matter which light & which of the bulbs I use in whichever fitting, 1 halogen & 1 led works but 2 LED's together doesn't! (sometimes
they will flicker as turned on & sometimes glow very dim, but never work properly)
I'm guessing it's something like the transformer not "seeing" sufficient load & cutting off rather than trying to discharge
into "nothing", is there any way I can "trick" the transformer into seeing a higher load - I don't really want to get into
fitting a resistor as that rather defeats the object, or would a relatively low load - high ohm resistor be sufficient?
Any info gratefully received!
loggyboy - 22/5/13 at 10:07 AM
I had a similar problem for our kitchen cabinet lights and our cooker hood g4 bulbs, some google investigating revealed it was likely the transformers
not being specd for the load (or lack of) the LEDs use. I havent resovled yet, as you have found, I just put one normal bulb in to create the load the
transmfomers were expecting.
ReMan - 22/5/13 at 11:25 AM
The led in your advert is a 240v so would not need any transformer.
I presume you halogen were 12v if on a transformer
MakeEverything - 22/5/13 at 11:35 AM
quote:
Originally posted by ReMan
The led in your advert is a 240v so would not need any transformer.
I presume you halogen were 12v if on a transformer
+1.
russbost - 22/5/13 at 12:15 PM
quote:
Originally posted by ReMan
The led in your advert is a 240v so would not need any transformer.
I presume you halogen were 12v if on a transformer
Sorry, probs picked the wrong ad. TTBOMK all G4 are 12v, these most certainly are.
Not Anumber - 22/5/13 at 12:20 PM
The Ebay item includes BOTH GU10 (240volt) and G4 (12 volt) LED bulbs.
I think we can safely assume the OP is not attempting to make a Gu10 240 volt bulb work with a 12 volt transformer.
[Edited on 22/5/2013 by Not Anumber]
v8kid - 22/5/13 at 12:22 PM
Is it a transformer or an electronic box of tricks?
Sounds as if the protectin is cutting in by not seeing the led 'cos its resistance is too high
mcerd1 - 22/5/13 at 12:29 PM
^^^ yes G4 is a 12v bulb and GU10 is a 240/230v bulb....
but that ebay listing is for both a GU10 and a G4 and I would assume he ordered the 12v G4 version shown at the bottom of the pic 
[edit - too slow.....]
[Edited on 22/5/2013 by mcerd1]
ReMan - 22/5/13 at 12:38 PM
In my job I safely assume nothing 
jeffw - 22/5/13 at 12:57 PM
It must be a load issue. Put a 100 Ohm resistor in parallel and it light up...
You will need a LED specific transformer or a load resistor on each LED. Exactly the same as for vehicle LEDs.
loggyboy - 22/5/13 at 01:01 PM
quote:
Originally posted by jeffw
It must be a load issue. Put a 100 Ohm resistor in parallel and it light up...
You will need a LED specific transformer or a load resistor on each LED. Exactly the same as for vehicle LEDs.
Not quite exactly, as with a car it causes flash rate issues, not brightness.
russbost - 22/5/13 at 01:09 PM
quote:
Originally posted by jeffw
It must be a load issue. Put a 100 Ohm resistor in parallel and it light up...
You will need a LED specific transformer or a load resistor on each LED. Exactly the same as for vehicle LEDs.
Is the 100 ohms based on any sort of calculation or is that a random guess? By my reckoning a 100 ohm resistor at 12v is going to draw 0.12A, around
1.5W, surely that's not going to be enough to make any difference is it? That's less than the LED's draw themselves?
Or do I have some fundamental misunderstanding of the issue here?
jeffw - 22/5/13 at 01:22 PM
It appears, from Google, that you'll need specific LED driver for this.
mcerd1 - 22/5/13 at 01:32 PM
other issues aside, but if you end up needing to fit a resistor it can't really be saving you much on the running costs.....
MikeRJ - 22/5/13 at 01:37 PM
Do you have a 24v transformer with the two lamps wired in series?
Chris_Xtreme - 22/5/13 at 01:39 PM
I had exactly the same issue, for some reason the transformers only kick in if there is enough load. In my kitchen i ended up running one halogen bulb
and one led.. Some energy saving at least. The cost of a led transformer seemed to out weigh the whole aim to save a bit and to be greener..
russbost - 22/5/13 at 01:39 PM
quote:
Originally posted by mcerd1
other issues aside, but if you end up needing to fit a resistor it can't really be saving you much on the running costs.....
No, quite, hence why I wanted to avoid fitting resistors, I guess I could go down to a 20W bulb for the halogen, I'd still be using only around
1/5 of the original 100W & would give us the sort of amount of light we need.
If the resistors route draws less than 20W I'm still better off with the leds, but does that mean I simply put something like a 10W 2A resistor
across the 12V supply from the transformer? I don't want to nuke the transformer!
Chris_Xtreme - 22/5/13 at 01:42 PM
In the car it doesnt matter as you are already at 12v, yes the flasher relay wont work without load and nor will the canbus stuff (if i remember that
correctly) which is he dash sensors for a bulb blown. But if you add a resistor in line you end up using the same energy i think.
MikeRJ - 22/5/13 at 01:43 PM
Not overly expensive to get a suitable LED transformer it seems:
LED Driver / Transformer 240V - DC 12V | 6W, 12W, 18W Available | For G4, MR16 | eBay
RedAvon - 22/5/13 at 01:44 PM
Keeping the transformer and potentially a resistor is just wasting power - I would ditch the transformer, hard wire the lamp units to 240V and buy
240v led lamps.
Ian
russbost - 22/5/13 at 01:52 PM
quote:
Originally posted by MikeRJ
Do you have a 24v transformer with the two lamps wired in series?
No, it's 12V transformer, lights in parallel
Looking at the LED driver transformer for £3.50 it seems to be a bit of a no brainer, I guess that's what I'll be getting - anyone want to
buy a slightly used 12V transformer unit, ideal for powering halogen bulbs!
Thnx for all the info guys, hope it helps one or 2 others with similar probs too.
russbost - 22/5/13 at 01:58 PM
Just had a thought about the LED driver/transformer, the existing transformer is AC & the G4 LED's have what looks like a diode/rectifier
across the pins, so are those bulbs going to work with a dc supply? Is it a simple matter that they will work only if connected the correct way
round?
Why is nothing ever dead simple???
mcerd1 - 22/5/13 at 02:29 PM
quote:
Originally posted by Chris_Xtreme
.....the flasher relay wont work without load....
...But if you add a resistor in line you end up using the same energy i think.
yes, but you can sort the flasher by fitting a relay thats designed for LED's instead of adding resistors
Chris_Xtreme - 22/5/13 at 04:26 PM
I should have mentioned the led flasher relay esp as i have one in my car!
Those led transformers seem to have come down in price nicely, i reckon i might get a couple now
Chris_Xtreme - 26/5/13 at 07:01 PM
I bought a couple of the LED drivers mentioned above and they work perfectly !! thank you for pointing me back to them again.
MikeRJ - 31/5/13 at 10:08 AM
quote:
Originally posted by russbost
Just had a thought about the LED driver/transformer, the existing transformer is AC & the G4 LED's have what looks like a diode/rectifier
across the pins, so are those bulbs going to work with a dc supply? Is it a simple matter that they will work only if connected the correct way
round?
Why is nothing ever dead simple???
Sorry for late response, but all the G4 LED lamps I have seen use a bridge rectifier on the input so the polarity of the lamp holder doesn't
matter.
DarrenW - 3/6/13 at 04:34 PM
quote:
Originally posted by RedAvon
Keeping the transformer and potentially a resistor is just wasting power - I would ditch the transformer, hard wire the lamp units to 240V and buy
240v led lamps.
Ian
Depends on where the LEDS are being fitted. Defo not a good idea if the LEDs are in zone 1. Ive got a load of energy wasting 12V downlighters under my
kitchen cupboards. Im pretty sure fitting 240V LED's would contravene 17th edition wiring regs (i did 16th many moons ago so would have to look
it up to be sure, something about how far away the lamps are from a water source - ie sink and tap.).
Safer advice would be that if 12V lamps are used, then continue to use same voltage with correct power source.