12v Desk Lamp LED Bulb problem

Thread Starter

spike1947

Joined Feb 4, 2016
288
Have a desk lamp that will not work with a LED cob Bulb which was in it ( The LED bulb just lights and goes straight out ) , but have put a halogen bulb in and it works fine ! .
anything I can do to make it work with a LED cob bulb! .
Spike
 

Yaakov

Joined Jan 27, 2019
2,342
If I had to guess, and with the amount of information I have, I have to...

Assuming the lamp is low voltage (12V), the LED is drawing too much current for the supply.
 

Thread Starter

spike1947

Joined Feb 4, 2016
288
If I had to guess, and with the amount of information I have, I have to...

Assuming the lamp is low voltage (12V), the LED is drawing too much current for the supply.
It does say 12v in the heading !, LED Lights will use a lot less amperage than halogen bulbs !
 

bertus

Joined Apr 5, 2008
21,237
Hello,

There are 12 volts power supplies for halogen lamps that require a minimum load to work properly.
When the load is to low by the led, the powersupply could go blinking or even stop.

bertus
 

Thread Starter

spike1947

Joined Feb 4, 2016
288
Hello,

There are 12 volts power supplies for halogen lamps that require a minimum load to work properly.
When the load is to low by the led, the powersupply could go blinking or even stop.

bertus
Hi
Thanks for that, yes do remember something like from before, so the question would be what would be the best way to apply another load ( Resistor in series ) if so what value would I be looking at to slightly up the load from ( I think 3w max) for the LED, really want to do the min, could start high and go down with he resistor, but what value would I start with ? .

cheers
Spijke
 

Yaakov

Joined Jan 27, 2019
2,342
Hi
Thanks for that, yes do remember something like from before, so the question would be what would be the best way to apply another load ( Resistor in series ) if so what value would I be looking at to slightly up the load from ( I think 3w max) for the LED, really want to do the min, could start high and go down with he resistor, but what value would I start with ? .

cheers
Spijke
You can calculate if this is reasonable. What is the wattage of the working halogen bulb?

You will have to put the additional load in parallel, not series, to decrease the resistance and increase the current.

The downside of this is you will be just heating things up and using more power without getting anything else for it.
 

Thread Starter

spike1947

Joined Feb 4, 2016
288
You can calculate if this is reasonable. What is the wattage of the working halogen bulb?

You will have to put the additional load in parallel, not series, to decrease the resistance and increase the current.

The downside of this is you will be just heating things up and using more power without getting anything else for it.
Hi
Thanks for your reply, yes sorry in parallel, yeh true I won't be benefitting from doing that, just an exercise really .

cheers
Spike
 

Thread Starter

spike1947

Joined Feb 4, 2016
288
Don't have a bulb for it, will tale 12v max 35A Halogen , but hope not go to has high as 35W though, hoping the LED will come on round 10W load including the approx 3W for the LED ! .

cheers
Spike
 

Yaakov

Joined Jan 27, 2019
2,342
Don't have a bulb for it, will tale 12v max 35A Halogen , but hope not go to has high as 35W though, hoping the LED will come on round 10W load including the approx 3W for the LED ! .

cheers
Spike
That would require 7W to be dissipated by the resistor. That is going to get very hot.
 

Thread Starter

spike1947

Joined Feb 4, 2016
288
Each resistor would get less hot but the total heat will be the same. You will be making a little desk heater.
I could just start with a high resistror and see what happens with the LED bulb, bit of a guessing game really, but what would be a high resistor to start off with !
 

DickCappels

Joined Aug 21, 2008
7,147
Two suggestions: don't end every sentence with an exclamation point! That will make your writings easier to read! Also keep in mind that this just a science experiment that should be taken apart when you are done because what you are doing is impractal and can be dangerous! Thank you for taking the time to read this!
 

Yaakov

Joined Jan 27, 2019
2,342
I would get the lowest wattage tungsten lamp that will fit and see if it works. Then measuring the resistance of that lamp will give you any idea of what the total resistance needs to be and you can calculate the resistor value.
 
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