I remember when my parents got this light. A powerful searchlight, a blinker, an ambient light, a radio, and an alarm! We were so impressed by it that we used it all the time as there were not that many battery-operated devices back then, especially not rechargeable ones.
Over the years the novelty of it faded away and the battery was holding less and less charge so we slowly started using it less and less until it got put in storage.
Some 20 years later, it brought up some really nice memories when I found it in my parent's house so I decided to give it a rebuild and make it modern so I can use it with my kids on our camping trips.
PCBWay offers services for custom PCBs, PCBA, 3D printing, CNC machining, Injection molding, and more.
Check out their full color PCB print service for an amazing looking and colorful PCB prototype!
Lantern Overview
The lantern is branded as Sunca, model SF-178B. It has an AM/FM radio, a spotlight that can tilt and adjust its position, a blinker, and an ambient light with two fluorescent lamps. It was charged from 220V mains with the built-in cable.
It has a few options to turn on lights with other functions, and on the ambient light, it can have either one or two fluorescent lights on.
On the front, it has a small LCD clock with a separate AA battery, and when turned to the alarm function, the speaker is bypassed from the radio to produce a loud alarm sound.
As it is right now, the light does not work as the battery is not holding any charge, the radio antenna is broken off and the blinker is not working.
Tools and Materials
- P13 LED bulb - https://s.click.aliexpress.com/e/_mrGQC0a
- LED Strip - https://s.click.aliexpress.com/e/_opr5ENe
- 18650 Batteries - https://s.click.aliexpress.com/e/_opLA3xe
- 3S Battery Management System - https://s.click.aliexpress.com/e/_onAymtq
- 12.6V battery charger - https://s.click.aliexpress.com/e/_mrCSojY
- Soldering Rework Station - https://s.click.aliexpress.com/e/_m00zmaw
- Multimeter - https://s.click.aliexpress.com/e/_m0CIYDY
- Precision Screwdriver Set - https://s.click.aliexpress.com/e/_msma6OA
- Wire Snips - https://s.click.aliexpress.com/e/_omwVb18
- ESD Safe Tweezers - https://s.click.aliexpress.com/e/_ol7L3Ma
- Bench Power Supply - https://s.click.aliexpress.com/e/_on2Eiuc
Disassembly
The lantern is held together with screws, so after I removed all of them, I separated the case to reveal the battery and circuitry inside. With some more screws, I removed the battery from the holder and I also removed the two fluorescent lights from the front.
I did not remove any of the wires yet, as I first wanted to make sure that the radio works and that it provides power to the various lights before I started replacing them so that I could at least be sure that the repair would be worthwhile.
Testing and Verification
To test the functionalities, I used my bench power supply, set at 6V, to power the light on the battery connections. To my surprise, the radio and most of the other functions worked, except for the blinker light.
That gave me confidence to continue because I knew that it would be functional in the end.
LED Conversion
The spotlight and the blinker use P13-style lamps and I ordered two replacement ones that can work on multiple voltages. This was just accidental luck as it turned out that I later modified the light to work on 12V instead of the original 6V so this was beneficial. To replace them, the top of the latter unscrews and the lamps are held in place with some clips.
After the replacement, I powered the lantern from the beach power supply and was happy to see that both worked now with some nice and powerful lights.
For the ambient lights, I glued two pieces of LED tape to the reflector of the fluorescent lights and I reverse-engineered how all of the connections were made. It turned out that the switch on the front was used to switch the ground connection so I rewired it to do the same without going to the high-voltage circuit for the CFLs but directly to the LED strip.
My original plan was to have a step-up converter here to convert the 6V, up to 12V required for the LED strips but after testing this, I realized that it would be better if I converted the lantern to 12V entirely, and used a step-down converter for the radio only.
Circuit Modification
The step-down converter will only power the radio now, so I removed all of the LED wires from the PCB to power them separately and I also traced out the PCB to find the point where the embedded switch in the radio volume knob was connected. This switch terminates the negative connection of the circuit so I connected the ground pin of the buck module to it. This ensures that the converter is only powered when the radio is on and will prevent any battery drain while idle.
Now, the positive input connection of the buck converter, the positive of the LED strips, and the positive from the top lights were all joined together to be soldered to the battery-positive terminal.
Battery Upgrade
For the battery pack, I used 6 18650 li-ion cells that I have salvaged from old laptop batteries. These are still wired in pairs from the original packs and I did not separate them so that I can use the nickel strips to solder to them instead of the batteries. Lithium batteries can be damaged by the soldering heat so this was a better option.
The three pairs of batteries were soldered in series so that their combined nominal voltage is 11.1V and a suitable BMS (Battery Management System) board was also added to it. The BMS will make sure to charge each pair to the same voltage and it will also provide protection against over-discharge so the batteries can last.
Once everything was soldered together, I added a DC barrel jack to the input of the batter and I soldered the lantern wires to the output.
In the original battery compartment, there was plenty of space left, so I added some cardboard as a placeholder to keep the pack in place. in the future, this might be a good option to expand the cell if we see the need for it and possibly add some USB outputs to use the new pack for charging other devices.
Antenna Replacement
The new antenna for the radio was easily replaced, but I had to make a small hole in the case so that it could fit in the original holder and screw.
Once it was secured, the lantern was now ready to reassemble following the same steps from before but in reverse order.
Final notes and next steps
With the light now reassembled, I was happy with how it turned out and that it works again to be used in our camping trips. The only thing that I lost in the process is the blinker circuit as I had to rewire the lights on 12V but I can live without it. The light still works but it does not blink anymore. Maybe it will be an interesting video to create a separate blinker circuit and add it in the future.
If you have any ideas for improvements on the lantern, be sure to leave them down in the comments and if you liked this conversion, feel free to check out my YouTube channel and subscribe for more electronic videos in the future.
