Need help choosing a battery and charging module for my Arduino robot

[Darthmarshie]

I’m wanting to build a robot based on the Arduino platform. The plan is to just use 2 TT Motors with wheels and a few sensors and an Arduino Uno etc. nothing amazing.

 

But what I would like is to be able to keep the battery permanently connected to the robot and include the charging module on the robot too, so that I could hopefully just plug it into a USB cable for charging or in the future have it home to a charging station like a Roomba and have it connect to some contacts to charge. But that’s really a problem for another time.

 

I was looking at getting a couple of 3.7v 18650 batteries and using them in series in a cradle to get the voltage I want, and then using the charging module I already have to charge them. The charging module I have is pretty much this one… 1A, Micro-USB input etc. Can get them anywhere for a few dollars:

 

 

But from what I’ve read that won’t work because the voltage is too low and if I use two batteries then I have to use a balancing circuit.

The other charging module I could get it this: https://www.dfrobot.com/product-1713.html

 

That seems to be for 7.4v LiPos which as I understand are made from two cells, but it doesn’t seem to have anywhere to plug in the JST plug for balancing which the 2 cell LiPos all seem to have. Would it still work? Would I just leave the JST connector unplugged?

This is the 7.4v LiPo which I had my eye on if I can’t get the 18650s to work out: ONBO 1600mah 2S 45C LiPo (I have to order the batteries from in South Africa because there are laws about importing batteries and basically nowhere online will ship batteries here because you need a special license to do it. But if you have a suggestion for a battery from literally anywhere, please share! I'm sure I can find a supplier here!)

 

I would like 7.4v and as many mAh as I can get. But right now I’m feeling totally overwhelmed by all the options for batteries, the S and C ratings (Both charging and discharging) etc. What I know for sure is that I want the batteries to be permanently attached to my robot and have the charging circuitry on the robot too. I don’t want to have to remove and charge the batteries in a separate charger.

 

Can I use the 7.4v charging module from DFRobot with two 18650 cells in series? Can I use the DFRobot module with the ONBO battery? Can I even get a charging module that that will charge a 2 cell LiPo via USB or barrel jack? Heck it doesn't even need a USB or other jack, it just needs to fit on a small robot and have somewhere I can solder onto.

 

Found out about this battery protection board with a balance function. https://www.banggood.com/3S-11_1V-12V-Lipo-Battery-Protection-Board-With-Balance-Function-p-1164376.html?cur_warehouse=CN They seem to be fairly common. Battery protection board with balance function. Would I combine that board with the DFRobot 7.4v charging board? From what I can see it's only meant for using with two 18650 batteries because there isn't a terminal for connecting a 2S LiPo balance lead. But I also saw a YouTube comment saying that these boards are too cheap and don't actually balance the charging at all.

 

Totally overwhelmed by the options and stress headache right now. I’m a programmer, not an electrical engineer. Just need some guidance.

[myselfolli]

Power bank?

[Hackentosher]

That 4056 module is a great little charging module, but you gotta keep an eye on it sometimes. Check in on the final voltage of the cell and if it's charging over 4.2v, throw it out and get another. You can use those for a 2s pack, you just need one 4056 module per cell in series in your pack. Simply set it up so that each module will be connected to the positive and negative of each battery so that they're only charging one cell and not the other. 

[ZicMortal]

You should watch out for one thing actually

If you have 2s battery, you could connect 2 TP4056 modules onto them.

 

And if you take usb cable and connect to first TP4056 and charge it, unplug it and then connect it to second TP4056 and charge it, its all good.

 

But, if you connect inputs of both TP4056 (USB +5V and GND) so you dont have plug-in twice, then you have short circuit because of series connection, in the middle. Minus of one battery is plus of another.

 

I had this problem also, and decided to take batteries out and charge them seperately.

You could also buy 7.4V 2S BMS which offers balanced charging with seperate 8.4-9V adapter that goes into wall.