I'm building a small robot that will have a battery pack enclosed. The robot is an autonomous self driving vehicle. I'd like to keep the robot closed at most times so the batteries will stay inside.
In short, I'm looking for a permanent wiring solution to be able to charge the 18650s inside the robot without having to remove them.
I am trying to use a standard micro USB plug to charge the batteries inside. It appears that the TP4056 is a common solution, providing a 1A charge rate. I have a few questions regarding how the wiring will be arranged.
The battery pack is a pair of 2,600mAh 18650's ran in series.
The cells will start, stop and always be used equally. Is there any problem with charging in series for just these two? I've seen concerns regarding having a separate wiring set up to charge in parallel.
My second question is how the wiring from the charging board (TP4056) to the batteries would work as the batteries will also supply power when now charging (via an on/off switch)
The battery holder only has a single positive and single negative coming out of it. Can I directly wire in the charging supply to the battery holder leads and also have the leads tee off to the motor power supply board (L298N)?
My concern is when the robot is no longer charging and in use that the leads should flow from the battery to the motor controller but also may positively charge the TP4056. Is this possible?
I have attached a photo for reference to my proposed wiring connection.
Another concern is ; with this wiring set up wouldn't plugging it into the charger essentially power up the motor controller along with charging the battery?
Is it possible to take the micro USB and split it with a y connector to go to two TP4056's so that they both charge equally ?
Yes it is indeed a solved problem, look at our cellphones... but I can't seem to find much info on how it works.
Sure I could just buy an external power pack designed to charge and use that but I'd like to learn the electronics and how it all works and create my own.
Yes it is indeed a solved problem, look at our cellphones... but I can't seem to find much info on how it works.
Most, if not all cell phones have 1S (single cell) lithium batteries.
You need a balanced charger to use lithium based cells in series, and you also need a low voltage cutoff to prevent overdischarge. Cells are completely destroyed if discharged below about 2.6V.
It's a power pack portable charger circuit board
Looks like you can wire it up to the battery and this accepts input to charge the battery and also arranges output to supply power.
Also looks like depending on the complexity of the board but looks like this one comes with:
Overcharge protection
Over discharge protection
Short circuit protection
Over current and even over temp protection
I can just plug a usb cord with open leads on the end to route to the motor power supply unit.
Now back to having multiple cells, would this he appropriate to charge two 18650s properly? These batteries would be ideal.
It's a power pack portable charger circuit board
Looks like you can wire it up to the battery and this accepts input to charge the battery and also arranges output to supply power.
Also looks like depending on the complexity of the board but looks like this one comes with:
Overcharge protection
Over discharge protection
Short circuit protection
Over current and even over temp protection
Be aware that those selling 'cheap' charger circuits probably do not care much about your safety.
Whilst the circuit may have over-discharge protection, the voltage level at which it operates is critical. You really need a cutoff voltage in the 3.3V to 3.0V region.
Lithium cells are all around us and there is often an assumption that using them in projects is easy, but its not, a great deal of care is needed for the project to be safe.
Ask Samsung, they must know a lot about the subject.
The power bank charger circuit board does have a discharge cut off. I will verify the voltage of it prior to purchase/use.
Is it possible to use a power bank circuit board to charge each cell individually per USB output?
Outlet > micro usb cable > power bank circuit board > 1st USB port to One battery > 2nd USB port to 2nd battery
Since the power bank circuit board only has a max voltage of 5V, charging each cell individually will suffice the 3.7V capacity of each.
Now the catch to this, is it still possible to run them in series to create the desired 7.4V while in use?
Or would a DC to DC voltage booster be required to achieve that desired 7.4 and just have them ran in parallel instead.
Samsung did have quite a bad experience with them. Although I do admire their response and investments into a massive testing lab to turn the fiasco into a lesson instead of a loss. This, and the hoverboard incidents are the reasons why I am doing as doing research as possibly before doing so. Definitely don't want to burn anything up!
ericfragola:
Is it possible to use a power bank circuit board to charge each cell individually per USB output?
Outlet > micro usb cable > power bank circuit board > 1st USB port to One battery > 2nd USB port to 2nd battery
Hard to say, the circuits are probably not designed to operate in that way.
Effectivly the ground of each USB charge input is the same connection, so its possible the lower battery could be shorted.
Plenty of circuits out there designed to do the charging properly and safely, for instance;
You can NOT put two separate chargers on two cells in series if they're connected to the same power source. Two USB cables is still only one power source. Do not attempt this!
Two USB power adapters plugged into two wall outlets might work but there's still a high probability of burning something if those adapters aren't properly isolated. Plus, if you have two USB sockets on your robot, someone at some point in the future (probably you) will forget and you'll destroy a laptop.
Look at hobby chargers intended for RC toys. These are mostly going to be 3S devices but I'm sure you can find a 2S one or a higher one that's capable of just charging two cells together. You may pay US$70 for such a device.
In the worst case, can you handle charging the batteries one at a time with a switch to select which battery is being charged?
MorganS:
You can NOT put two separate chargers on two cells in series if they're connected to the same power source. Two USB cables is still only one power source. Do not attempt this!
Thanks MorganS, duly noted!
Alright I have an ever better revised proposal for charging:
5V USB supply > TP4056 > 2x 18650's ran in parallel > vooltage booster > L298N motor controller > motors
The 18650's will have a high discharge amp rating to satisfy the voltage booster, as the booster doesn't magically make higher volts out of nothing
Only concern I have is, will the voltage booster be able to efficiently run the motors? Each motor only draws 380ma under load. Stall is 900ma
Batteries will be able to handle a 2.5A-3A discharge rating to satisfy the voltage booster.
Option 2:
Uses the sane layout but the voltage booster ran before the batteries and ran to a 7.2V holder with two 18650s ran in series. But it sounds like charging in series is a problem. Also using the voltage booster to charge the batteries limits me to the 1A max draw of the charging chip...
The parallel idea sounds workable.You would not normally run motors from a voltage doubler but they are small and you can probably achieve 90percent efficiency.
