I am working on robot, and I want it completely automated. Everything I can tackle, except for when it comes with power. (Pretty big problem, I know.) I want to know how I can make a charger circuit that can charge (a) battery(s), have a light or something when it's done charging (all I need is a way to check with my microcontroller, Arduino, of coarse!), and then also be able to supply power to my device while charging so it can still perform tasks like organizing data, etc, or waiting to get a signal to "dispatch" itself. I know a fair amount of electronics, but I'm no expert or anything like that.

Basic Power Requirements (Voltage, etc.):

I need around 8-12 V output from the battery, lets say up to 750 mA to 1 A at a time, and have about 2-3 hours without a charge.

How should I get started: (I know this is a broad question but it still can be answered with recommendations and previous experience.)

  • Should I do lots of low-voltage batteries or fewer higher voltage batteries? I would think that lots of low-voltage ones would provide more instantaneous current, but how would you put them in series with charging?
  • How should I handle safely charging? Should I have power bypass the batteries while plugged in to prevent tons of current being drawn through them?
  • Is there an affordable (I'm on a tight budget) breakout board or similar that would satisfy my needs? I cannot find anything on Google.
  • How would I go about efficiently handling step up/down voltages without loosing lots of power but still using the most out of the battery as possible?

What's the best approach for my needs and can be very cheap? What types of chips are there for my needs? I have seen a few ICs that manage voltage and current, but how would I match that up with a battery?

  • \$\begingroup\$ This is rather broad. Perhaps you can further define one of the options that you favor? \$\endgroup\$
    – Samuel
    Oct 17, 2013 at 23:05
  • \$\begingroup\$ try and focus on the battery technology first. Choose what suits your expected requirements. Then decide on charging regimes and then on producing higher or lower voltages to suit different circuits. But to do this you need to know what the hungry elements are such as motors and actuators. \$\endgroup\$
    – Andy aka
    Oct 17, 2013 at 23:17
  • \$\begingroup\$ Supercaps leak charge badly. Personally I'd start with a commercially available battery for RC toy use (e.g. dx.com/p/… ) and its matching charger. \$\endgroup\$
    – pjc50
    Oct 18, 2013 at 9:35

3 Answers 3

  1. Use 3 Li-Ion cells connected in series - like in the notebooks.

  2. Create the charger, based on one of the specialized charger ICs - for example this, but there are thousands of them, so search the best for yourself.

2.1 If this design is too complex for you, buy some cheap Li-Ion battery charger and use its electronics - for example this one.

  1. Design the charger as a dock station with some very-easy-to-plug-connector and put some fast blinking IR LED on it.

  2. Using the IR LED light as a navigation signal, program your robot to go to the charger by itself, when the battery is critically discharged and to touch the connector.

Charging time for the Li-Ion batteries can be as small as 1h, but if it is too big for you, you can use another trick - instead of waiting for battery to charge, use two replaceable batteries mounted externally to the robot and design the charger to have two connect places. Then learn your robot to leave the discharged battery in the charger and to get the charged one from the second docking place.

  • \$\begingroup\$ This is really cool. You can connect the Li-Ion voltage through an op-amp to generate a pulse wave, which can be picked up by your MPU to tell your bot to go charge \$\endgroup\$
    – Raaj
    Oct 18, 2013 at 18:44
  • \$\begingroup\$ @user1436508 How would I do this? Where would I connect to my charger or similar? \$\endgroup\$ Oct 18, 2013 at 22:08
  • \$\begingroup\$ @user1436508 - Ah, ask this somehow with more details... \$\endgroup\$
    – johnfound
    Oct 19, 2013 at 5:13

I would recommend using a combination of the

  1. MCP7383 Safely charges your LiPo or whatever battery at whatever voltage you like 3.3V/5V etc.
  2. TPS61200 Booster- Boosts up your Lipo to whatever voltage you like.

Google those two data sheets, they have sample circuits in them.

  • \$\begingroup\$ Seems like the TPS61200 only has a max of 5.5 Vout. Looking for a similar one will post if I find one. \$\endgroup\$ Oct 18, 2013 at 17:54

If it were me I would try to get a circuit already built for the task like an old alarm panel, or any device that uses a battery for backup. Most devices are 12 volts, and you can step that down to whatever voltage, or voltages you need, plus those types of power supplies do double duty as they provide power, as well as charge the battery. Once the batter is charged they trickle charge the battery. Alarm panels or UPS unit usually have a high amp per hour battery.

I always see UPS units at Goodwill for a few dollars, usually the problem with those units is the battery goes bad, but the charging circuit is good, and should be easy to remove, and reuse.

  • \$\begingroup\$ UPS units where would I get replacement batteries and how expensive are they usually? Seems like a good idea, but I feel like that energy is going to be wasted storing that much voltage OR transforming it up than down and through DC to AC THEN AC to DC it doesn't seem that efficient though. \$\endgroup\$ Oct 18, 2013 at 17:41

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