Repair and modify handheld spotlight - Page 1
Forum section: electronics / repair

author: cigmas
author_rank: Regular Contributor
timestamp: October 14, 2019, 09:31:08 pm
content: I have a cheap (< $10) handheld spotlight that no longer works. Maybe the problem is as simple as a dead sealed lead acid battery.Observations:* The battery's voltage measured 0V initially when I first opened it up after having the device non-functional since a few years.* After "charging" for several hours, the battery voltage measured ~2V. The light would not turn on.* The light bulb does turn on (dimly) with a 1.2V AA battery, so the bulb is not dead.* The bulb seems to be a halogen, stamped "H3 4V15W".* The charger says output is 6V 300mA, but a DMM measures ~11.5V at its output terminal (with nothing connected) ??* The voltage at the battery terminals with the charger measures ~10.5V.* There is a sticker on the outside that reads: "Never turn light on while charging as it will damage unit." This may have happened...* Another sticker reads: "Do not recommend to charge the unit for more than three hours using the DC cable to avoid battery overheating. Ideally the battery could be fully charged by household adaptor within 12 hours."So... 3hrs or 12hrs or?? It has previously been left charging overnight. Currently when I try charging, the battery remains cold to the touch.I'm guessing the battery is simply dead, yes? The rest of the circuit is just a switch, a couple of resistors (1 kilo ohm, 3.3 ohm), a diode, and an LED. What could be the cause of death? What do you make of the warnings?Secondly, are there suggestions for a modification to allow the light to function both from battery and/or from the charger?

author: Gyro
author_rank: Super Contributor
timestamp: October 14, 2019, 09:49:23 pm
content: Yep, I've got a couple of similar ones in the garage waiting to be repurposed or thrown away. Trust me, the sealed lead acid battery is completely trashed (in fact if you shake it, you may hear it rattle!).The charger voltage is unregulated (very basic charging), it is supposed to drop to the battery voltage when loaded. The warning about not using while charging was to prevent the possibility of burning out the charger with the additional load and a flat battery.Buying a replacement battery is probably not economical, which is a shame because they have nice reflectors.I did wonder about trying to convert one to LED but it's probably not worth the effort. The other alternative is maybe to find a 12V bulb replacement (if they make one in the same physical size) and fit a 12V plug and lead for use around the car.Basically it has sadly been out-evolved by LED alternatives.

author: TheMG
author_rank: Frequent Contributor
timestamp: October 14, 2019, 10:09:39 pm
content: Once a lead-acid battery has dropped to 0V no-load voltage it's basically dead, it's not ever going to take a charge again. They have a finite life span to begin with, which can be significantly shortened by excessive, or not enough charging (lead-acid batteries that sit for long times with a low state of charge will quickly go bad).The charger is probably fine. It is a very simple charger relying on limited current (the resistors) and basically trickle charges the battery as the voltage output is always higher than the battery's fully charged voltage. No active circuitry to cease charging so the battery can be damaged by leaving the charger plugged in longer than necessary. Since the charger outputs very limited current, it is less current than is necessary to light the bulb, which is why there is a warning not to operate it while charging.You can certainly buy a replacement battery for it, as they are quite common and can be found at many battery stores or online, but I'm not sure I would bother considering these days you can get for the same price as a replacement battery an LED flashlight that will be more powerful and much lighter and smaller. There really is absolutely no advantage whatsoever to these big, heavy, power-hungry, battery-operated halogen spotlights compared to a modern LED flashlight.

author: tautech
author_rank: Super Contributor
timestamp: October 14, 2019, 10:18:11 pm
content: Quote from: cigmas on October 14, 2019, 09:31:08 pmIt's dead Jim !Warnings are good and just user error as you can't neglect any LA battery.QuoteNope, the charger and charge circuitry are insufficient to allow it.

author: cigmas
author_rank: Regular Contributor
timestamp: October 14, 2019, 10:31:24 pm
content: Thanks for the confirmation and info.Most SLA batteries I find are either 12V or 6V. 4V in this size seems harder to find and is mostly on aliexpress or ebay. Economically, yes it doesn't make sense, relative to the original cost and to LED alternatives now.Plus a 15W bulb seems high compared to equivalent LEDs. Still, the light was decently nice and bright when it worked.It's just disappointing that this seems essentially to be a disposable device. It would be nice to find some use for the components or repurpose it in some way.