Measuring or Guessing – Older Inexpensive and useful LED Lantern with Brightness Control Issues

The Lantern: Promier 12 LED Lantern With Compass and Dimmer 

The Repaired Light, Minus the Compass, is shown operating above. Dim on the Left, Bright on the Right, and Daytime is not a good time to Demonstrate Flashlights, and the Batteries have been in the light for over a month, using it several hours each night on Dim. I don’t believe this model is offered anymore, but a similar one is, they now use a COB LED Assembly, Rows of Tiny LEDs I guess resembling Corn Cobs. It’s probably just as reliable. This light is older, it worked fine when new and appears to be working fine again. I still need a knob for the New Dimmer Control, in the photos of the Lanterns on this Blog yellow tape is on the Control Shaft, done to provide grasp to turn the Lamp On/Off, like Turning on a Stereo that used to use knobs. 

Lantern 1

I think this light is, well, delightful (pun intended) and was perplexed by the Brightness Control that, as it aged, had a tendency to suddenly dim the LEDs and leave you in the dark. The Dimming was caused by the same thing that caused Static in Volume Controls. The first thing I did was clean the Brightness Control, and it worked on one or two occasions, but the attached images show that there isn’t much to the Original Control. So I decided to replace the Control.

Across the Brightness Control, there is nearly 1000 Ohms, and it seemed like the minimum resistance is about 25 Ohms. All I found was a Spec for the 1000 Ohms, but no spec for the minimum. So, the one I selected worked fine. 1000 Ohms Max, and almost zero Min. But retesting the original control, this one seems consistent with that.

LED

The New Dimmer Control is Much Bigger, required the plastic posts designed to hold the Original Dimmer Circuit to be cut away, I used a Dremel with Abrasive Wheel, but it could have been cut using a Hacksaw as well. And one hole needed drilled for the tab that prevents the new Dimmer Control (Potentiometer) from rotating. And a Decorative Black Trim around the Dimmer Knob needed a Slight Reduction on the tabs that hold the Trim in place, due to Impinging into the area where the new Dimmer Control is Mounted.

Lantern 3

Those things said and done, and a little solder work, and Voila, a working light. But the new Dimmer had a 500 mw (milliwatts) rating, and I had no idea what the milliwatts spec was for the original Dimmer. So, I measured the current. As a simple schematic shows, all the current flows through the Dimmer Control. So, with the Lantern back together, I partially removed one battery, and put the meter into the circuit, in series with it, and completed the current pathway through the meter (used to measure small currents, milliamps for instance) to measure the following:

On High: .086 Amps

On Low: .0114 Amps

The Voltage, measured, from three Batteries that have seen over a month of use of the Lantern on the Lowest Setting, is 3.75 Volts Total, they each measured 1.25 Volts (new they would be 1.5V or slightly higher).

Power Equals Current x Voltage

Power is .086 x 3.75 = .3225 Watts or 322.5 Milliwatts

Power is .0114 x 3.75 = .0428 Watts or 42.8 Milliwatts

So, even on High, it’s under the 500 mw Design of the New Dimmer Control. Hopefully any heat that builds is better dispersed by the increased mass of the new control.

One last note, the Lantern had a Compass in the Top. I noticed it never worked properly. To disassemble the light, I had to pull the Compass, which I did by using several attempts with Electric Tape pressed onto its top, and pulled up suddenly. There is a long Phillips head Machine Screw that goes through the entire Lantern to hold it together. The Screw is Magnetized, to a degree, not conducive to proper Compass Operations. The Compass works fine out of the Lantern and is going to be repurposed.

 

Author: Dr-Artaud

A Doctor that is not a Doctor, but named after a character in the movie "No Such Thing", as is the Avatar.

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