Introduction: Baofeng USB Mod

This is a relatively simple mod for a Baofeng BF888s model UHF HT radio to allow recharging its battery via USB. The radio is rated at 500ma so any standard USB charger will give it enough current.

Discharging the battery completely by leaving the radio on (with flashlight) and battery saver enabled took three and a half days.

Recharging with a USB hub took two and a half hours. From 0V to 4V

With this mod the radio's utility expands several fold, now instead of being restricted to a 12V car battery eliminator (it will not recharge the battery) you can recharge the battery at the same time you use it in many different situations and not be restricted to the standard 120V AC recharger base.

This mod will not remove the ability to recharge on the standard base.

Nor will it modify the radio itself, everything will fit inside the removable battery and can be swapped out on the fly

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Disclaimer:

Be warned you will be taking a lithium ion battery apart, don't force it, puncture it with a tool or generally abuse it or you may have a very bad time. Treat it like the bomb it is. You may want to make sure the battery is dead before you do this or it might explode badly.

One suggestion is to work on a non-flammable surface and keep a small pail of sand nearby.
If a lithium battery is punctured it can catch fire almost instantly, but can be extinguished by dumping sand on it.

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If anyone reading this finds errors in my work please let me know. Also
I'm willing to assemble a pack for anyone not willing to do it themselves for a reasonable price, just let me know in the comment section and I will try to get in contact with you.

Step 1: Tools&materials

electrical tape

soldering iron

thin solder

small screw driver

some thin wire

a small drill/dremel etc

multimeter, (optional but its best to double check!)

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USB recharger circuit TP4056 (only a dollar or so on amazon/ebay etc)

Baofeng bf888s battery (about 7$)

Step 2: Disasemble the Battery

1: Un-click the bottom latch and slide the battery out

2: Disregard the Caution label at your own risk

3: Carefully (and I mean carefully) pry the bottom tabs off the battery pack with a small flat screwdriver

4: Pry the sticky tape away from the battery casing but make sure you don't bend or deform the battery!

5. Make a note of which wire is + and - the top of the battery and the bottom will tell you, MAKE A NOTE with tape or whatever just don't mix it up whatever you do!

6. Once you are sure of the polarity desolder the battery but leave the wires on the spring terminals at the top alone, give them an inch of wire and just cut it off

7. Rub all the residual double side tape off both sides of the battery and wrap it completely in electrical tape, All the sides including the bottom, you can leave the top exposed for now

Step 3: Prepare the Battery Bay

1. Now that the battery is removed and un-soldered take your usb board and line it up between the grooves at the bottom of the battery case.

2. Now make a mark with a knife or pen and drill out enough of the bottom so the usb plug is as flush as possible to the edge of the case.

3. Make sure you don't remove too much but make sure its flush, we need all the room we can get to put the battery back in straight so it doesn't pop off the back of the radio.

4. In the picture i have removed the wires from the contact pads, you don't have to do this but i found it made it easier when cutting the plastic to get them out of the way.

Step 4: Soldering and Insulating the Board

1. Once you are sure you cut enough plastic away to fit the usb plug solder two wires to the board's terminals keeping note of its polarity, as well as the battery case terminals.

2. Put some tape over the lower terminals to prevent it from scraping the board.

3. Now tape the board in place with a healthy amount of electrical tape so it doesn't move.

Step 5: Refitting the Battery

Okay we are almost there

1. Now that the board is secure and your wires are ready, make sure there is nothing exposed on the cell, the entire thing is positive and it must be completely covered in tape or else it might rub off on the board and short circuit!

2. Play around with fitting it, It should just barely fit behind the usb plug and between the contacts on the top if there is any pressure or it doesn't fit right make sure you adjust the board. DO NOT force anything here or it will not work!

3. Once you are sure everything is set, don't worry about gluing it or taping it, there will be enough pressure between the tape and the board to keep everything together.

4. Use your multimeter to double check the polarity of the usb board while its plugged in, the battery and the contact labels on both the top and the bottom of the battery.

5. Cut the wires even and solder them together, (respecting their polarity) to the top battery contacts and tuck the wires carefully in the small spaces next to the springs, don't tuck it behind the battery.

Step 6: Conclusion

You should be done at this point just double check your solder points that nothing will come loose, especially around the springs, make sure the wires haven't been yanked out and the spring action is smooth.

The back of the battery should click back on nicely if not recheck everything until it does, trust me it will fit don't force it or you could ruin the battery and damage the radio!

Now the only caveat about all this is there is no easy way to expose the leds on the board to the outside so you can see when its charging and full. However you shouldn't have to worry about overcharging or overheating the battery with this circuit in place unlike just running 5V usb straight to the battery it should be safe.

Also this will only work on weaker radio sets with 3.7V battery packs, I haven't tried other packs yet however I'm planning on making one with a DC-DC converter to get it up to 7.4V but that will require a special case/adapter possibly 3D printed in the future.

Stay tuned

Comments

author
KB7UZB made it!(author)2016-04-20

I would love to order one from you maybe a high capacity model?

http://www.amazon.com/ExpertPower%C2%AE-Baofeng-Ex...

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author
RomanS35 made it!(author)2015-12-26

Thanks you for idea, i did similar mod for my BF888 battery

Sorry, no images but its very close to you mod

Only used different TP4056 module with Micro USB connector.

Needed to cut slightly the tabs close to Micro USB so the module can by inserted between two plastic protrusions in the battery case

I placed module with components in the direction to the plastic housing of the battery, in such a way is not only easy to connect the contacts on the battery case to the module ("+" and "-" wires not need to by reversed) but also the opportunity to do a small transparent window made of plexiglass in battery housing to display indication of charge with the leds on the module.

I connected original battery tabs on back of the battery used to charge radio or battery itself in original base to TP4056 tabs that close to Micro USB connector, if battery connected this way to TP4056 module it always charged throught module and newer expose battery voltage on back tabs of the battery so it can`t by accidentally short circuited, and more safe to charge the radio in original Baofeng base.

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author
cyfus made it!(author)2016-01-06

One more thing I forgot to mention. Make sure to check the output from the baofeng base charger, it is rated for 5 volts but because its normally wired directly through the battery it might (should) have some battery regulation built in for 3.7. I'm not sure if wiring the USB regulator input through the base output would upset it (by being under volt) or if the voltage from the base is expected to fluctuate by the return voltage from the discharged cell. It could be set for constant 5V (as printed) at first and reduces its voltage to compensate but i'm not sure at the moment. I know that it does backfeed but I haven't investigated this behavior over time.

When I added a diode to the cell it stopped the backfeeding and didn't upset the base charger's logic so i'm not exactly sure how it senses the change in charge and when to refuse the current when blocked.

I will have to reverse the layout of the charger board and figure out exactly what is going on. I figured it was better to omit the passthrough on the usb input (mine didn't have solder pads) because of this unknown.

And finally the battery itself is lacking a thermal resistor as well as the contact pad to connect it to the charger base which also is lacking the resistor element sensing. The usb charger board however is able to use a thermistor (does yours have it? I can't see the pads in the image) so the last goal of this project will be to acquire the proper component and test it under stressful conditions.

I haven't had the focused time to fully complete this project. If you want to spend time investigating these questions further please let me know.

author
cyfus made it!(author)2016-01-06

I'm glad you found my guide useful! Your idea of using the inputs on the board from the base charger is excellent. I used a diode to save the pins from a short circuit but using the regulator board itself is a more elegant idea. I've been meaning to revise my instrucable for sometime, so I'll include your suggestion!

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