Powering LED screw lights

Dave_H

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What voltage are the lights designed for? We need to know a lot more than just the wattage rating.

Yes, more info on lamps is needed. If they use simple resistive current limiting and (assuming they are white LED) if you use four in series, 12v supply may not be quite enough to light to full brightness, three might work.

In general a voltage-regulated dc wallplug does not provide current regulation required by LEDs; not to say it can't be used under
the right conditions. Adapter itself seems pretty ordinary, except the terminal block. I find 12v/1A regularly in 2nd-hand stores for $2 each over the counter.

Even this is overkill for 1W worth of lamps. There exist very small 12v/0.25A adapters generally to charge batteries in equipment.

I've been using small flange-based LED bulb replacements for years, they can work well. One variant is 1-2 cell which uses step-up
circuit in the base. I would be careful putting these is series. Other 3-4 cell variant seems to only use a dropping resistor but higher
input voltage requirements.


Dave
 
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Dave_H

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Hi thanks for the reply the LED's are rated at 12v.

Now I'm confused...

12v 0.25W bulbs wired in series with a 12v supply is not going to work. Wiring in parallel
should be OK assuming the bulbs have built-in current limiting.

Even wiring four in parallel, the 12v 2A wall adapter is way overkill.

Are these by chance automotive-type bulbs? Those contain series resistors and usually one or more
series diodes for reverse-polarity protection.

(Actually one which is sealed which I can't easily get apart, I can see contains a constant-current regulator
which allows it to operate over 10-30v with constant brightness).

Dave
 

Dave_H

Flashlight Enthusiast
Joined
Nov 3, 2009
Messages
1,345
Location
Ottawa Ont. Canada
Are these by chance automotive-type bulbs? Those contain series resistors and usually one or more
series diodes for reverse-polarity protection.

(Actually one which is sealed which I can't easily get apart, I can see contains a constant-current regulator
which allows it to operate over 10-30v with constant brightness).

Dave

I mention this is due to interest in low-voltage, low-level LED lighting primarily designed for automotive use, which can run from 12v dc adapter or battery.

Over several years I have acquired a variety of LED bulbs including older bayonet-base such as 1156/1157 type; likely similar to what you want to use. Other lamps are meant for hard-wiring into vehicle power. 12v 0.25W is about 20mA, typical for small 3-5mm or SMT LEDs.

Most are not very efficient as they are connected as 3 series LEDs (or parallel groups of 3) run from 12-14v which is right off the bat, 50% or lower efficiency for red/yellow/amber; more so with some with only 1-2 in series such as "penny" style marker lights.

What colour are your bulbs?

Let me know if this is of not too off-topic, or I could make it a new thread.

Dave
 
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