The bulb is getting less voltage than it needs. Most likely cause is contact resistance. Clean every place contact is made. Battery ends, spring to battery, bulb to battery, switch contacts. A pencil eraser works on most of it. If the switch is sealed you don't need to worry about it. Also check where the reflector rim touches the contact and make sure the bulb is tight. Did I miss anything guys?
Tom
why the hell does my flashlight go dim, but when I knock it hard it gets bright again? What can I do to fix this? I don't understand what's going on here...
Only the possibility that the OP was trolling.
Huh?
The original problem is pretty common, and I sure remember knocking flashlights about in order to get them working again.
Flashlights are simple, and have virtually no soldered parts. So the contact between the bulb and the rest of the circuit is merely pressure contact, the switches are often on a similar level.
Those can suffer, maybe the worse because of the current drain of the bulb.
LED flashlights don't suffer because they aren't put together with pressure, and there's no surge as the bulb first receives current and heats up.
Michael
Spot on, except for the thing about LED flashlights. You're probably sensible enough to buy *good* ones.
The cheap ones I've seen sure do, but not because of high current. Some of them use a solder ball (blob?) to contact the battery + terminal, and a crappy spring at the other end. Dissassembly, cleaning, sometimes stretching the spring, and sometimes adding to the solder ball restores operation. For a while. :-)
Ed
For a long time when I was a kid I thought that's how they're supposed to work.
Tom
If the OP was serious, I apologise. The problem is so common and the cause so obvious (not only to me, but also to all the non-technical people I know who had experienced it) that I doubted that it was a serious question. Those non-technical types may not be able to explain it as clearly as did Mr.Tom Biasi, but I've known them all to immediately diagnose it with terms like "bad contact", "something loose", "corrosion", "bulb loose in the socket", "weak spring", "worn out switch", etc.
I'm more used to hearing "it must be a short" from the non-technical types. MikeK :-)
Oh yeah, that too. But most often in connection with higher power levels than a flashlight. It must stem from the fact that short circuits often produce sparks and burning. So whenever they observe a spark at an electrical joint or contact, they call it a short. And since shorts often result in an open circuit, they sometimes also call that a short.
Most of the LED flashlights I have are subject to dimming out now and then. I have found that it is almost always due to a poor electrical connection between the PC board the LEDs are soldered to and the case of the flashlight. These flashlights have the on/off switch on the end of the cylinder opposite the LEDs. There are solder pads around the perimeter of the LED pc board that on my oldest lights attempted to have the connection by making a solder blob that stuck out beyond the perimeter of the pc board and was held in place by pressure from the cap on the led end of the light. The next attempt was to solder small "whisker wires" to the solder pads, allowing the wires to wedge between the edge of the pc board and case as the lens cap was screwed on. The most recent examples, and by far the most reliable, has a continuous braid of copper soldered to the pads, again friction fit to the case as the end cap is threaded on the LED end of the light. I bought these lights from the same place over about a six month period. I have not had any LEDs go bad individually. Power is via 3 AA cells in a paralell pack in the barrel of the light. regards, Joe. snipped-for-privacy@upwardaccess.com
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.