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Topic: 12VAC G4 led lamp lights up bright on 12VDC. (Read 127 times) previous topic - next topic

GoForSmoke

I'm still seeing spots.

These are what I got. 12VAC 3W led 30W halogen bulb replacements.

I plugged a 12V wall wart in and stuck one pin inside and the other to the outer barrel and it's real bright even through the rectifier. They'd make really good flashlight lamps on 12VDC.
Nick Gammon on multitasking Arduinos:
1) http://gammon.com.au/blink
2) http://gammon.com.au/serial
3) http://gammon.com.au/interrupts

Robin2

#1
Dec 08, 2016, 03:44 pm Last Edit: Dec 08, 2016, 03:45 pm by Robin2
The link says they are 12v DC lamps? Why have you AC in the title?

It is impossible to know if they are identical to similar looking lamps that I have been using for some time.

Recently I got some 12v GU5.3 / MR16 Ac/Dc lamps in Sainsbury's for £4 each. I only noticed now that they are suitable for AC as well as DC.

They have a plastic lens on the front that can easily be sawn off with a small hacksaw. Then they are significantly brighter than any other LED lamps I have tried. They have 4 LEDs and claim to provide 350 lumens. However I don't think I could tell a lumen from a lux even on a dark night.

It is easy to take out the parts and fit them into other lampholders and they also have the big benefit that the lamp is separate from the electronics so the electronics do not get fried - which happened with two other very bright small-format lamps that were much more expensive.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

GoForSmoke

#2
Dec 09, 2016, 01:46 am Last Edit: Dec 09, 2016, 02:07 am by GoForSmoke
There was discussion before but I lost that thread.

These have 12 leds, use 3W and supposed to be 600 lumens used as G4 lamp replacements.
I bought 10, got $1.29 ea. (checked the receipt) Just looked on site, price went up!

Turns out that G4 is supposed to be 12VAC and these disks have rectifiers. Most G4 bulbs are halogen bulbs, car headlight type for spotlights.

There was some concern that 12VAC peaks > 12V and 12VDC might give poor light. It might do better with another volt or 2 but it throws a bright light on 12DC.

It'd make a good flashlight or bike headlight.

For the price, I bought a few.
Nick Gammon on multitasking Arduinos:
1) http://gammon.com.au/blink
2) http://gammon.com.au/serial
3) http://gammon.com.au/interrupts

Robin2

Based on my experience if they are cramming all those watts onto a thin PCB there will be a great risk of premature smoke  :)

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

GoForSmoke

#4
Dec 09, 2016, 06:50 pm Last Edit: Dec 09, 2016, 06:51 pm by GoForSmoke
3 whole Watts at 12V through 12 leds as 4 chains of 3 leds with a resistor, getting about 20mA each all on a 30mm disk didn't get warm in the short periods I lit it up.

In your experience, do 5mm white leds get hot running 20mA? There's 12 on a 30mm disk, they're not in a packed grid though 4 pairs do share 1 side between 2. This is to replace a same-size 30W halogen.

If all 3W went through 1 special big led, I might wonder, but not 12 leds around 20mA.

These can strobe and PWM. They don't have to be spotlights. 
Nick Gammon on multitasking Arduinos:
1) http://gammon.com.au/blink
2) http://gammon.com.au/serial
3) http://gammon.com.au/interrupts

Robin2

3 whole Watts at 12V through 12 leds as 4 chains of 3 leds with a resistor, getting about 20mA each all on a 30mm disk didn't get warm in the short periods I lit it up.
Interesting.

I am typing this in the light from an MR11 led lamp with 12 LEDs and they are hot enough that it would be uncomfortable to leave my finger touching them for any length of time.

The very much brighter Sainsbury lamp (with 4 LEDs) is hotter - but in that case the lamp is seaparate from the electronics.

And now I can't see properly for blue dots in front of my eyes :)

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

GoForSmoke

Looking at Amazon I see a few MR11 12-led bulbs rated at 6W.....

 
Nick Gammon on multitasking Arduinos:
1) http://gammon.com.au/blink
2) http://gammon.com.au/serial
3) http://gammon.com.au/interrupts

GoForSmoke

Running a disk steady on 12V and to a touch it's not burning hot but it gets hot. It gets hotter if I keep my finger pressed on 2 or 3 leds, might get a 1st degree burn if I hold it long.

It sheds enough heat that insulating parts, even the back, quickly raises the temperature. They need to be mounted with good air flow and a heat sink of some kind wouldn't hurt but isn't necessary and could serve as a bracket.
Nick Gammon on multitasking Arduinos:
1) http://gammon.com.au/blink
2) http://gammon.com.au/serial
3) http://gammon.com.au/interrupts

Robin2

It sheds enough heat that insulating parts, even the back, quickly raises the temperature. They need to be mounted with good air flow and a heat sink of some kind wouldn't hurt but isn't necessary and could serve as a bracket.
The ones I had that failed were in lamp units that had been designed for halogen bulbs so there was no airflow. While they lasted quite some time they died long before the energy saving had offset the higher initial cost. I think I paid £6 or £8 each for them a couple of years ago.

The Sainsbury lamps have a big aluminium heat sink / reflector.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

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