HOME Schematics Discover Forum Hobby Corner Dave's Circuits Electronic Resources Book Corner Contact Info


 Good Ideas done Badly

  Previous Issues

Bad Fluorescent Night Light      March 30, 2010

The wife knows that Im constantly searching for that perfect night light design.  When she saw this blister pack with two compact fluorescent night lights, she knew they had my name on them.  I really liked the style and size.  The package said that they consumed only 1.6 watts, which was 40% of the typical 4 watt incandescent night light style lamp.  Being fluorescent, they should also produce more light and last longer than the typical 6 months I usually got from the standard incandescent 4 watt lamps. 

I marked the installed date on the side of the lamps with a pen and then plugged one into the laundry room, where it would run 24/7.  I plugged another lamp in the dark upstairs hallway, where it would also run day and night.  In only two months both units died within days of each other with the telltale smell of burned electronics.  I cracked open the assembly to have a look. Sure enough, there was a burned resistor.  Clearly, its power dissipation value had been exceeded, which eventually caused the failure. 

I traced out the circuit.  The schematic is shown below.  Note that the resistor R6 is 100 ohms.  It appeared to be only a watt size.  To dissipate 250mw of power the average current would only have to be 50ma.  There are two 0.68uF capacitors in the circuit, which are supposed to limit the average current.  The capacitance reactance of a 0.68uf cap is 3.9K at 60Hz.  In theory, with a 120vac line, the average current should only be about 30ma max.  But, the voltage rating of the part is only 160v.  The peak of a 120vac line is closer to 170v.  So, I suspect that the capacitor was breaking down, causing current spikes to flow through the poor 100 ohm resistor, which over time, finally killed the part.  I think the 100 ohm resistor should be increased in size to at least a watt and those two capacitors should have had a 250v rating.  After those change, perhaps the lamp would last longer than just 2 months.  Yet another bad Chinese product.

1.6W Fluorescent Night Light Circuit Board Burned watt 100 Ohm Resistor

bad chinese product - flourscent night light


April 2010     Issue 8

Page 1 Back
Envelope
Circuit
Diagnosis
Experimenter's
Corner
Good Idea
gone Badly
New Products Rants &
Raves
What the World
needs Now
Wily Widget


HOME Schematics Index Hobby Corner Dave's Circuits Electronic Resources Contact Info
Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches


 About Us   |  Advertise on DiscoverCircuits.com   |   Report Broken Links  |    Link to DiscoverCircuits.com  |    Privacy Policy

Copyright  2002 - 2015 David A. Johnson & Associates.  All Rights reserved. 
 Linking is ALLOWED but COPYING any content or graphics to your web site is EXPRESSLY PROHIBITED.