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Custom Charging Application Issue

Hello all,

May i introduce myself, i am Garrett and am constructing a robot for a class project. I have run into an issue in charging my robot and have not yet been able to locate an answer in this forum and online.

My issue is:

I am going to run two motors with TB6612FNG dual motor controller. To my understanding, i cannot run the power source for these two motors directly off of the EZ-Board... I must supply a seperate power source to the motor connecting it directly to the HBridge and a seperate power source connected to the EZ-Board.

I want to create a docking station that the robot can connect to and charge both the battery for the motors and the EZ-Board without turning the robot off. I cannot seem to find a splitter or the right information to complete this task.

Any ideas?



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only need the 3 diodes and one resistor
Here is a schematic that i put together. My questions are:

1. Does only positive (+) from the charger and battery connect together at C ?

2. Does only positive (+) go from B to A (+) ?

3. Does ground (-) at A tie into the battery ground?

2. What happens at D?

Attached below is the image:

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battery and charger goes to point C and
point B be goes to point A
for point D you need a small back battery like from a cell phone or wireless telephone battery about 6 volts to 7.4 volts ,current of battery can be very small current like 100 ma
so the EZB board will also be on,when you charge main 7.4 volt 3000ma main battery ,also should have a switch to turn it off ,so dont drains both batteries
also i see you have power going straight to motor controller witch is ok,but should have a fuse for rating of the board
@ ROBOTMAKER Okay, sweet thanks for the input. I updated the diagram.


1. location of the switch... should it be located where the switch is current? or at either point A or B?

2. How does the common ground wiring look from the battery/charger to the EZ-Board?


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everything look good,what program did you use to make the drawing also
also you may need a second switch at point B if not using it for a while or dpdt switch
with get 10 ma drain with only switch for EZB and maybe small drain on motor controller
and still need switch going to EZB because of both batteries will drain too

also on instructables website so a very cool wireless battery charger ,what the circuit is using 2 coils one on bottom of robot and one on the floor and a circuit like dc to dc isolation converter ,but instead of using a transformer ,using 2 seperate coils

The program i used was MS Word lol... i just layed down the lines haha... took me like 3 hrs. I agree that point B needs a switch, that way no drawn from the motors can occur. I'll keep the current switch position as well.

Thanks for your help. The next phase is to now buy the components and some how hook everything up. I think i will use a small bread board to make the diod and resistor circuit.


The resistor in this circuit... is it a 1/2 W 680 ohm fuse? or 1 W?

not a fuse 1/2 watt resistor to set the charging current needed for the battery 1/4 watt still ok
Opps, sorry i mean't 1/2 watt 680 ohm resistor.

So which is better i guess? 1 watt, 1/2 watt or 1/4 watt?

here is idea for a backup battery ,close to the kind used in laptops two 3 volt coin cell battery in series like CR2302,i am using that for my robot projects

The battery backup system is great. However my other challenge is how can i charge my 7.2volt battery and continue to have power to the robot for me to take it off teh charging station once it is finished? Below is a picture of an idea that our group had... it does not utilize the battery backup system.

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problem with that is,
charges work like this they charge your battery by current and if you have another load like EZB board hook up to it wont charge correctly
thats why always good to remove or use a disconnect switch or relay to the battery and have a backup battery that keeps the unit on

it may work like that only if EZB and all sensors attached and you measure current to be under 10 ma

wow i just measure the current of EZB without sensors almost 100MA so you really need the backup circuit
Okay, so i definately need to incorperate the battery back up system below

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However, where in this does the relay come into play? In the drawing i show the connection / disconnection point in which the robot will interface with the charger.
Oops, i guess some sort of pressure switch at connection point "S2" would work wouldn't it? Something that the robot could drive up onto the station, then compress the switch to then disconnect the main power source from the robot. Once this happens the robot motors won't be active though... which is a problem to get the robot to move backward uncompressing the switch to allow the main battery to be utilized.

any ideas?

relay instead of switch 2,can use a switch or relay or relay is good becase you can drive it from EZB digital output board ,like a reed relay you do need a transitor to turn on the relay
plus added idea is to monitor the battery when battery fully charged the relay disconnects
then you have a automatic charging station
Ok so a relay at switch two would work. However how can power still get to the motors? The relay would be cutting power to VM positive line which I thought powers the motors?
dont need power at the motors till ready to move after charge,when charge is done battery connects to motors and board

on batteries not all coin cell batteries are rechargeable,found out that cr123 batteries are,and cheap on ebay,need 2 of them,but and small 6 battery will work only need about 300 ma
Okay, i am confused how this relay is going to allow charging and then once the charging is finished it will then somehow allow the batteries to run the robot... Below is another schematic using a relay, does this make any sense how it is hooked up?

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need only normal open contact relay
charger and battery are hook up together and charge the battery ,then when finished charging the battery
battery connect to the circuit
you need reed relay rated at 5 volts coil n.o contact and use a npn to turn the relay on from one of the digital outputs on EZB,can do by time or a battery monitor circuit

here is the circuit to drive a relay from digital pin
driving a relay from digital output