Beginner - Simple LED Circuit Help

Phil-S

Joined Dec 4, 2015
238
Power banks like Belkin Pocket Power act not quite as expected.
I use one to recharge a secondary Lipo cell.
They turn on automatically in response to a load being plugged in.
After trial and error, I found the the load needed to be 100-mA for 1-second. Once the load falls below 100-mA, the power bank stays on then turns off after 19-minutes.
Other brands like Varta turn off after about 30-seconds.
To keep a power bank running, you need to satisfy the minimum load/time requirements.
 

splud

Joined Jun 30, 2013
38
I don't recall seeing anything which really explained why this was being battery powered. Is that really a hard requirement? Do you not have an outlet at the workbench?

The easy solution would be to get a wallwart with say 3.5V output or so, and set up a suitable current limiting resistor (which you MIGHT get away without if the voltage is low enough). You'd have an easier time sourcing a cheap 5V USB wallwart (or adapting some wallwart from an older cellphone that didn't have a standard USB connector), and power the strip from that with a suitable current limiter - 10 ohms would get you about 180mA, which would be just north of 1/2W on the LED), but you'd be burning 1/3W off on the resistor itself. If you are running the LED off of a USB power bank, either you're over-driving it (= more light but at the expense of service life), or the assembly has a resistor in there already.

A more involved solution would be to construct an adjustable current limiting circuit (wherein you can adjust the amount of current being delivered to the LED, and thus adjust the brightness). A good LED driver doesn't waste a bunch of power in a resistor.

Earlier comments about the rating of the LED elements - they're likely rated at higher than 3V, (3.2 or 3.4), but work fine with the lower voltage of the alkaline cells the switch originally was powered from.

IIRC, those same switches can be found at "Harbor Freight" HF also has "puck" lights, which (at least pre-covid) frequently were available for free with a mailer coupon. Those have one fairly bright element in them. I've modded a couple of those to run from an 18650 LiIon cell, one of those with a reed switch as a cabinet light for under a sink.

I'll readily admit, I have a fair number of battery powered LED lighting spots around my property (generally, with a LiIon or LiFePO4 cell, and a PIR module so it comes on when there's motion - for instance, I don't like turning on a light to pass through part of the workshop - a 20 foot pace, I just need light for a few seconds), but for a workbench, use a wallwart to power the thing rather than burning through batteries.
 

Thread Starter

Pedro243

Joined Oct 18, 2020
6
I don't recall seeing anything which really explained why this was being battery powered. Is that really a hard requirement? Do you not have an outlet at the workbench?
There is no outlet on the work bench and I didn't want to run an extension lead. It is not something that I use all the time. Maybe a few hours in a month so the battery usage isn't that bad. I just wanted to get away from AA batteries and so far the power banks have been better.
 
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