What transformer to use with LED bulbs.

joebre

Have a room with 9 MR16 bulbs, each on their own transformer.
Decided to replace with 3W bulbs. Ran all off one of the existing transformers, 20-60W, running in series to all 9 bulbs. Bulbs will flash if I use 9 LED's. However, if use one halogen with 8 LED's, will work ok.

What can I do to rectify ?

Is the original transformer an AC model?
Any DC version ought to work...the higher end LED's are AC compatible these days in an effort to stop people complaining that they didn't work because they were installed with the wrong polarity.

s8n

Optimus prime

Rectify it with a full wave rectifier. :pac:

LED bulbs ought to be in parallel though.

joebre

Sir Liamalot wrote: »

Is the original transformer an AC model?
Any DC version ought to work...the higher end LED's are AC compatible these days in an effort to stop people complaining that they didn't work because they were installed with the wrong polarity.

Was re-using an existing transformer that I presume is AC.
Will get a DC one instead.

joebre

s8n wrote: »

Optimus prime

Thanks s8n for the really useless reply.

I mean AC in DC out.
Some are AC in & AC out.

joebre

Sir Liamalot wrote: »

I mean AC in DC out.
Some are AC in & AC out.

I think I know what you mean.
Had to get one before where I was running 3 LED's.
Got transformer with range 0.5 to 12W.
Do you think one with an output of 30W would be too low for 9 x 3W bulbs?

27W is fine on a 30Watt.
I'd confirm the transformers you have aren't suitable first before you buy anything though, it'll be written on it (careful of the mains-side wiring).
Sometimes you can get flicker from under-loading large PSUs/dimmers...I don't think this is the case because you are within the output parameters >20W, best know what the solution is before buying kit.
Might also be worth trying another transformer in case that's just faulty...they're not the most reliable of devices.

If you wire the bulbs in series you are making a 108v string...they need to be parallel; 9 x 12v.

joebre

Sir Liamalot wrote: »

27W is fine on a 30Watt.
I'd confirm the transformers you have aren't suitable first before you buy anything though, it'll be written on it (careful of the mains-side wiring).
Sometimes you can get flicker from under-loading large PSUs/dimmers...I don't think this is the case because you are within the output parameters >20W, best know what the solution is before buying kit.
Might also be worth trying another transformer in case that's just faulty...they're not the most reliable of devices.

If you wire the bulbs in series you are making a 108v string...they need to be parallel; 9 x 12v.

I have eight spare transformers that I have taken out so I can use them to test.

I have the transformer at the first light and ran cable from one to the next to the next.
That is wrong.
What is the best way to run cable from the transformer to the nine bulbs?

Thanks for your advice

Parallel = positive to positive and negative to negative.
Series = positive to negative.

You can daisy chain them but you need to be aware of polarity.


Pretending the battery is your transformer
Left diagram is series, right diagram is parallel.

If you are running a long line on thin cable the bulbs at the end of the line may appear dimmer. This is due to voltage drop. You can remedy this with larger gauge cable or splitting the loads on localised shorter runs for two or more transformers. Eg. 3 banks of 3, or a bank of 4 and a bank of 5. Do not link the transformers in this case they ought to be isolated from each other on the DC side of things.
Using 1.5mm CSA cable over < 20m should not present any noticeable issues.
If in doubt call an electrician [waiver].

Bruthal

joebre wrote: »

Have a room with 9 MR16 bulbs, each on their own transformer.
Decided to replace with 3W bulbs. Ran all off one of the existing transformers, 20-60W, running in series to all 9 bulbs. Bulbs will flash if I use 9 LED's. However, if use one halogen with 8 LED's, will work ok.

What can I do to rectify ?

That sounds like the led lights not loading the transformer enough. Adding the halogen is possibly stabilising it by loading the transformer better.

joebre

Bruthal wrote: »

That sounds like the led lights not loading the transformer enough. Adding the halogen is possibly stabilising it by loading the transformer better.

That's what I thought, with my limited knowledge. I want to take the halogen out as it looks different to the other bulbs and uses as much as the other 8 put together.

ted1

can you return lamps? Remove the transformer and use mains gu10

Could be under-loading, AC ripple or EMI. You could use a 20watt halogen as a load lamp somewhere discrete where it won't start a fire, less than ideal solution though. Maybe a smaller traffo is best, perhaps an led specific one would have better filtering. Are your 12volt cables running near to any high current mains cables?
I use two circuits with 6w on 60w traffo's, no issue. They're Robus brand; 20w - 60w.

joebre

ted1 wrote: »

can you return lamps? Remove the transformer and use mains gu10

Could quite easily as wiring as wiring is in place.
Is there an situation to use GU10 over MR16 or vice versa?

GU 10s are 230vAC bulbs no transformer needed. Different bulb holders. You'd just have to put the new holders on the wiring to the old traffo AC in's.

joebre

Sir Liamalot wrote: »

GU 10s are 230vAC bulbs no transformer needed. Different bulb holders. You'd just have to put the new holders on the wiring to the old traffo AC in's.

Just trying to find out when one would a particular bulb type, say in a new build

joebre

joebre wrote: »

Is there an situation to use GU10 over MR16 or vice versa?

I use MR16s as dual input relay switched mains or 12 volt battery. I switch between power sources a lot.

Never understood why people use transformers in houses instead of GU10s. Low voltage is a benefit in public spaces and exhibition lighting as an extra safety.

2011

Sir Liamalot wrote: »

Never understood why people use transformers in houses instead of GU10s.

Because in the days of halogen down lighters a 50W 12V MR16 would provide about 50% more light output than a 50W 230V GU10.
So essentially there was a higher light output for the same running cost.

In addition GU10 lamp life and color rendering was generally was never quite as good compared to MR16 (I am still talking about halogen type).

joebre

So now that we are gone to LED, what is the preference?

I still prefer the colour temperature of tungsten.
No standard domestic LED I've seen has ever come close. I use colour filters on mine and still run a select few halogens.
These seem like the way to go but I'm not sure they're worth the asking price.

Sir Arthur Daley

Sir Liamalot wrote: »

Never understood why people use transformers in houses instead of GU10s.

MR16s are in a league of there own compare to GU10s, the average life of a GU10 is hundreds of hours but the the MR16 has thousands, i have fitted MR16s in my sitting room and they are there 7 years and not one bulb or trafo replaced, the light out of an MR16 is away nicer than an GU10.
The only plus i can say for a GU10 fitting is the ease of changing them over to leds, they were fitted in the boom because they were fast and cheap.

2011 wrote: »

Because in the days of halogen down lighters a 50W 12V MR16 would provide about 50% more light output than a 50W 230V GU10.
So essentially there was a higher light output for the same running cost.

I would question that 50% value, a philips GU10 would rattle the light output of an MR16.

In addition GU10 lamp life and color rendering was generally was never quite as good compared to MR16 (I am still talking about halogen type).

+1 on that.

Sir Arthur Daley

Sir Arthur Daley wrote: »

I would question that 50% value

I'm a bit skeptical about that myself, not that I'd call it from my armchair.
I think I'll have to test the theory in my own time.
Considering that the transformer losses depending on the design will be 5% to 30% that makes a 12v 50W MR16 a ~60watt fixture which will throw the numbers out.

In answer to the OP question and thread title:

An led driver would be best if your LEDs are incompatible with your existing transformer.
http://www.amazon.co.uk/30W-Driver-Transformer-Lighting-Converter/dp/B0041B3US8

2011

Sir Liamalot wrote: »

Considering that the transformer losses depending on the design will be 5% to 30% that makes a 12v 50W MR16 a ~60watt fixture which will throw the numbers out.

Why do you think the losses are so high?

Think about it, even if the losses were that high both lamps are 50W.
The current for the MR16 is far higher. It is the larger current that that causes the filiment to glow brighter.

I will look for a link later if I have time.

2011

See efficacy table in link:

http://en.m.wikipedia.org/wiki/Luminous_efficacy


See this link also:
http://www.dusklights.co.uk/technical-advice/fitting-downlights.html#should%20the%20downlights

Although the transformer wastes approximately 10% of the power through stepping down the voltage to 12v this is more than compensated by the improved performance of low voltage downlights.
Due to a thicker filament, the halogen 12v bulbs (size MR16) are more efficient than the halogen 230v (size GU10) equivalent. The thicker filament also means that the bulbs are more robust.

2011

I would expect 5% to 10% myself but I did some looking around and found some much higher figures probably on older technologies like the wire-wound stuff.

Eg. here:
http://www.ledbenchmark.com/faq/Transformers-Output-and-Compatibility.html

2011 wrote: »

Think about it, even if the losses were that high both lamps are 50W.

Bulb for bulb yes, I'd be comparing net consumption vs light, just because you never see (lets say) 5W the MR16 is using doesn't to my mind make it acceptable to sweep it under the carpet. The meter sees a 55W fixture as would I.

cast_iron

Either way, it was never really an efficiency thing with the old MR16s. The light quality from the good dichroic ones was unbeatable and the lamp life of the better ones beat the GU10s hands down.
I remember fitting GE 50w MR16s in a commercial premises that lasted about 3 years running 10 hours a day, 6 days a week. In fact, i think they were still working when the fittings were retired for non-electrical reasons.

2011

Sir Liamalot wrote: »

I would expect 5% to 10% myself but I did some looking around and found some much higher figures probably on older technologies like the wire-wound stuff.

Transformers in general are very efficient.
This was impressed on me when I was involved in a project a few years ago where we installed several large ABB transformers.
To my surprise the efficiency of these units was around 97%.

Bulb for bulb yes, I'd be comparing net consumption vs light, just because you never see (lets say) 5W the MR16 is using doesn't to my mind make it acceptable to sweep it under the carpet.

Fair point.
However even when you take the transformer losses into account the lumens / watt (or luminous efficacy) of the MR16 is vastly superior.

Without doing any maths the difference in light output between a GU10 and an MR16 is very noticeable as is the light quality.
The light from a GU10 is far more yellow resulting in poorer colour rendering.
This is why even now in the age of LED lighting most jewellers still prefer to use 12V halogen down lighters on their displays.