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Charge 7 AA batteries in series

tim687

Hello element14 users!

 

I'm completely new to powerdesigns and all that stuff, so execuse me if I may ask stupid things :-P

 

I got an Arduino powered by 7 AA 1,2 Ni-HM batteries (why not use 1 single 9V bat? -> it's draining to fast with 2 motors).

The 7 batteries are housed in a custom batterypack (with ofcourse a + and - terminal).

The project is a car that drives itself around to clean things, the car needs to go back to the "mainstation" when it needs charging.

 

However, charging batteries in serial seems to be very complicated, and I couldn't find anything usefull.

So I'd like to ask for advice/explainations.

The battery pack must stay in the car when it's being charged (I'll fit 2 terminals on the bottom of the car once it's the time to do so).

 

The capacity per battery is 2100mAh @ 1,2V.

 

I can read schematics (not too diffucult ones)

 

How would you design such a charging circuit?

Can somebody give some advice about onboard (on the car itself) battery capacity readings? I've found this, but I'm not sure if it will work out well.

 

Thank you in advance!

 

 

Tim

  • 0

    Hi Tim,

    From your voltage specifications I am assuming that you are probably using NiMH batteries which are giving you a nominal 8.4 volts to power your arduino and car. The series configuration itself should not pose a problem but to be done correctly the temperature of the batteries while charging must be considered and a special controlled charging cycle should be followed. The seven cell 8.4 volt NiMH power pack is fairly common. Here is one charger that I found on the internet that should work for your application.

     

    http://www.amazon.com/Tenergy-Charger-8-4V-9-6V-Connector-Standard/dp/B004W8H5CM

     

    There are likely many others and perhaps even some recommended circuits out there, however in circumstances that are important like charging batteries it is sometimes best not to try to reinvent the wheel.

     

    John

  • 0

    Hi,

     

    You could use a LT1505 or similar to build your own charger, but you should get the datasheet of your batteries to know the maximum charging current, the voltage value when charged, decide if you want fast charging or not, make some calculations,... and start building it.

    In fact it won't be so diffcut, It would be the option if your real intention is learning how this kind of chargers work, but if you don't realy care about it I completly agree with , do not reinvent the wheel, using a oem solutions will make you save time, avoid headaches, and probably also save money.

     

    Miguel