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Can anyone recommend a good solution for monitoring and charging multiple batteries on a small mobile robotic platform?

I'm trying to build a simple two-wheeled platform, using an arduino for low-level motor and sensor control and a netbook for high-level control. The arduino is powered over USB, so it can use the netbook's built-in battery monitoring and charging. However, the motors require 12V. There are plenty of shields for controlling powerful motors via an arduino, but I've found nothing for monitoring and charging the necessary separate power supply. I want the netbook to be able to read the additional battery's estimated charge and whether or not the battery is currently being charged. The eventual goal would be to plug the robot into a single power supply, and charge both the netbook's battery and the additional 12V battery (likely lipo) simultaneously.

I've found a few boards like this, but it's unclear how well it could function as a UPS to constantly power a device, while automatically handling charging when an external power supply is attached. It has charging status LEDs, but I'm not sure what monitoring options it provides programmatically. Based on the low price, I would assume it has none.

On the other end of the spectrum are programmable UPS boards, but these are much more expensive and need to be calibrated for the specific battery its attached to.

I've seen some hacks for stepping up a USB's 5V supply to 12V, but I'm assuming the netbook wouldn't be able to provide the need amperage, and even if it could, that setup would likely kill the netbook's battery.

Are there any other options?
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Solar panels ?

Your problem is not a particularly simple one.  If I was going to tackle this problem,  I'd first decide
what sort of battery I was going to use.  I'd probably then build a battery charger with another
arduino in it,  to monitor the charging process in terms of voltage and current limits to charge
the battery,  driven from the mains power.  You could use the same device to charge your
12 V power battery  and also what ever lower voltage source you use to drive the electronics.
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Does the laptop not have a built in charger? Thus you will have nothing to do there, other than wait and something like 19.5 V to play with once charged?

The robot will not be moving while tethered, so that is easy. You know how long it takes to charge the laptop or monitor the colour of the charge lamp etc. So do that first.

disconnect the motor power, Then switch the supply to your bat charger. LiPo need special chargers, as have you have found! (and can be dangerous!)

Basically you need to check the battery voltage from time to time until it reaches the required battery voltage or until your specific charger, gives a signal that float mode has been reached (etc). This may be an LED, and then either inform you (break tether), or else switch (bat) power back to motors and trundle off.
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Does the laptop not have a built in charger? Thus you will have nothing to do there, other than wait and something like 19.5 V to play with once charged?

Yes, it does. But that's my point. I'd love to power strong motors directly from the netbook, but I've never seen one that has a general purpose "high voltage" output for motors. It's tightly regulated to power the CPU, HDD, USB, etc, and any attempt to hack that would likely result in making the netbook's power much less reliable if not destroying the netbook outright.
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I think I may have found an interesting option. Although it's not technically a shield, this "Lithium Backpack" mounts over the arduino's holes, and provides a regulated 5V output with monitoring, and recharges via usb. This guy wired two together to get 10V, more than enough to drive a couple good-sized motors.

Does anyone see any potential downsides for this board?
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Nevermind. As the designer mentions here, "it wasn't designed to be charging and powering the circuit in the same switch position." It also requires a manual switch be flipped to initiate charging, which makes it useless for UPS and robotics applications.

*sigh*

So close.
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oh! I thought you were using a seperate supply for the motors
Quote
and charge both the netbook's battery and the additional 12V battery (likely lipo) simultaneously.
I'm making something similar ATM (no laptop), but using a solar panel to charge a 12V gel battery. Power requirements should be within daily charge capability, but I will be adding a sun-bathing routine if the bat gets low. I'll put the panel at optimum angle and allow the unit to rotate toward the sun. Bit dark for testing at the moment smiley-wink So waiting for the spring.  smiley-razz Continuous activity is not necessary as this is an exercise in navigation rather doing any useful work. For that I will probably aim to set up a self serve "fuelling point" as the area available will not allow a high enough current density from a PV panel.

Good luck
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oh! I thought you were using a seperate supply for the motors
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and charge both the netbook's battery and the additional 12V battery (likely lipo) simultaneously.
I'm making something similar ATM (no laptop), but using a solar panel to charge a 12V gel battery. Power requirements should be within daily charge capability, but I will be adding a sun-bathing routine if the bat gets low. I'll put the panel at optimum angle and allow the unit to rotate toward the sun. Bit dark for testing at the moment smiley-wink So waiting for the spring.  smiley-razz Continuous activity is not necessary as this is an exercise in navigation rather doing any useful work. For that I will probably aim to set up a self serve "fuelling point" as the area available will not allow a high enough current density from a PV panel.

Good luck

Are you using anything like a solar charger shield? Can those use an arbitrary external power source instead of a solar panel to recharge the battery?
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Are you using anything like a solar charger shield? Can those use an arbitrary external power source instead of a solar panel to recharge the battery?

That shield is designed specifically for a single cell lithium battery. Can't change the output voltage.

To charge a lead acid battery a ready made solution would be called an "on board battery charger" (example). In real world use they are designed to stay permanently attached to a car/boat and then plugged in to a wall socket to maintain the battery.

For a non-ready-made solution I'd look at something like a UC3906. Lots of examples from Mr. Google on this.
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No Cerin, not a shield.

I have a microprocessor on board  smiley-cool - ideal for monitoring a battery. But as Chargrin posted, there are many chips to do the job! smiley-wink This allows you to make 'units' that you connect together and the operation of one does not impinge on another.

Do read up on batteries, e.g. if using lead acid, ensure you use it within it's recommended charge/discharge range, otherwise you will shorten the life. Don't forget about weight either! smiley-wink

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Are you using anything like a solar charger shield? Can those use an arbitrary external power source instead of a solar panel to recharge the battery?

That shield is designed specifically for a single cell lithium battery. Can't change the output voltage.

To charge a lead acid battery a ready made solution would be called an "on board battery charger" (example). In real world use they are designed to stay permanently attached to a car/boat and then plugged in to a wall socket to maintain the battery.

For a non-ready-made solution I'd look at something like a UC3906. Lots of examples from Mr. Google on this.

Thanks, but I was referring to the *input* source, not the output. e.g. charging the single lithium from a wall supply instead of a solar panel. If it expects a certain voltage/amperage from the solar panel, what would be the problem in getting that instead from a wall adapter?
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Would it be feasible to hook up the load outputs (not the battery hookups!) of two 3.7 USB Lipo chargers (e.g. this or this) in series to effectively get a 6-7V rechargeable Lipo power supply?
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I'm really not up on LiPo, but then nor is Boeing  smiley-eek

I understand that individual cells within a pack need to be charged individually, and that one should not charge cells that have dropped below a certain voltage, nor mix cells of differing voltages. But I read that a long time ago and it may not apply to current cells. (something else to do!)

Edit
This looks readable http://www.rcgroups.com/forums/showthread.php?t=209187

Edit, Edit
Mmmmm, quite old "Winter 2005"  But worth a read, Check out the lower end of the post if you want to be put off.

I've had a look around for home-brew chargers, but not found any I'd recommend, but there are many low price units out there (if you have a multi pack, get a balance charger). As with NiCd's it's the RC peeps who are pushing with LiPo so go read their forums.

Many years ago I used to make fast NiCd chargers for RC clubs, I always supplied them with metal charging cages due to the possibilities of explosion & fire!

It looks like the first part of your project will be a battery management system... Something for your Masters degree smiley-wink Then you can get a job with Boeing - even the big boys get it wrong.

« Last Edit: January 19, 2013, 04:22:20 am by 0AlphaOmega » Logged

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Quote
Thanks, but I was referring to the *input* source, not the output. e.g. charging the single lithium from a wall supply instead of a solar panel. If it expects a certain voltage/amperage from the solar panel, what would be the problem in getting that instead from a wall adapter?

Ebay, buy a handful of these...

search for "Converter Step Down Module LM2596"  cheaper than chips! No really, you can't buy the parts for the money.

Obviously you will need your wallwart to be able to supply enough current, so you need to know the C rate (current) that you will charge at (always over specify as wallwarts are usually poorly regulated and over optimistic when quoting current, you don't want another source of fire or failure.

AC wallwarts may be better for you, but remember that after rectifying & smoothing, your voltage will increase by root 2 (about 1.4 times) So bare this in mind when specifying your voltage regulator.
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You can use a tl431 and a P-mosfet as lowvoltage detector and shutdown controller, i made a LiIon hack for my bosch powertool: http://techmind.dk/elektronik/under-spaendings-detektor-med-tl431-bruges-til-hack-af-bosch-skruemaskine-med-li-ion-batterier/

I Just connect a standard cheap RC multi charger like this:  http://techmind.dk/tilbeh%C3%B8r/multilader-fundet-pa-ebay-co-uk/

Also, there are IC able to handle multible batterier. A great arduino project could be to make a LiIon/LiPo charger for 20 x cells smiley-wink
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Why not convert the world to run on electricity smiley

http://techmind.dk

Blog is in Danish, use google translate please

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