Build-in battery charger?

Hi all,

this is isn't exclusively Arduino-related, but I can't find any entry-level info on Google...

I'd like to be able to charge the battery in my Arduino device a) without removing the battery pack and b) while the device is switched on and operating. Same behavior as a cell phone or ipod.

I guess this requires a charging circuit in the device, a circuit decoupling it from the arduino while powering it at the same time, and a regular DC adapter. But don't really know how these would be implemented.

Can somebody point me in the right direction to learn more about this?

Thanks a lot!

What type of battery first? NiMH, NiCad, Li-ion or Lead Acid?

Charging while the circuit is on is simple. You dont have to do anything special, just hook up the charging circuit. The charger will power both the circuit and charge the battery at the same time.

Thanks.

Probably NiMH, maybe Li-Ion. Is there a difference in complexity for the circuit depending on the type used?

Yeah each type of battery needs a different type of charger.

Lead acid is easiest, Li-ion is hardest. There are plenty of tutorials around though.

Maxim has an IC specifically designed to charge a lithium ion battery from USB (+5V). Could be a good fit for a USB Arduino shield.

Is it the MAX1555? can't remember. I think Sparkfun has them, and of course the Maxim web site will find it.

-j

If you want the battery to power the board while on charge, make sure that the voltage of your fully charged battery is less than 6 volts. If you decide to use NiMH cells then don't forget that a full charged fresh four cell battery can exceed this.

In my app i wanted more than 5 volts to drive some servos so used a 5 cell NiMH pack and replaced the 7805 5v regulator with a LF50CV low dropout part (http://www.mouser.com/Search/Refine.aspx?Ntt=511-LF50CV) to ensure the chip was protected.

My charging circuit consists of a 10 ohm resistor that provides trickle charging current from the external power supply to the battery.

I need a simple charging circuit for a 9V NiMh battery. but i cannot find any online anywhere :( its all NiCad and i dont want that..

can anyone help? i need it so i dont have to fork out for non rechargeables

For a simple charging using constant current, you can use the same circuit as for nicads.

However, charging circuits that detect peak voltage do need to be different for NiMH cells.

What type of battery first? NiMH, NiCad, Li-ion or Lead Acid?

Charging while the circuit is on is simple. You dont have to do anything special, just hook up the charging circuit. The charger will power both the circuit and charge the battery at the same time.

Ummmm.... I'd be very careful about that assumption. I have a set of 6v NiCd batteries, and the charger puts out 12 volts. Also, (at least for NiCd) the charger supplies LESS current than the battery, unless you have an "instant" charger. Hooking my NiCd charger to the power supply would a) fry it from over-voltage and b) not have enough current to run everything.

That's not to say that some chargers won't work this way, but you can't assume that they will.

Ni-Cad and Ni-MH chargers are similar. You often get chargers with a switch to change between them. I dont know the differences though.

i just need a really simple digram (and i mean Simple :slight_smile: ) that i can throw together and charge my 9v cells (uniross 160 mAh 8.4v) most i find are for AA cells and the like… :frowning:

If you want the battery to power the board while on charge, make sure that the voltage of your fully charged battery is less than 6 volts.

Could you please explain to me why this is required? Thanks. :)

--Phil.

What I meant was that if you power the board directly (not via the regulator) then the voltage must be less then 6 volts.

If powering through the regulator then that's not an issue, but the battery voltage must be greater then the regulators dropout voltage.

What I meant was that if you power the board directly (not via the regulator) then the voltage must be less then 6 volts.

Ah, I follow you now.

In relation to your original comment, you wouldn't actually want to power the board directly from the battery due to it being an unregulated supply, would you?

--Phil.

What I meant was that if you power the board directly (not via the regulator) then the voltage must be less then 6 volts.

Ah, I follow you now.

In relation to your original comment, you wouldn't actually want to power the board directly from the battery due to it being an unregulated supply, would you?

--Phil.

I have various equipment in my radio control gliders that use embedded mirocontrollers that are connected directly to a battey without a regulator. I would think an arduino would not be a problem on a battery as long as there were no significant power spikes.

I would think an arduino would not be a problem on a battery as long as there were no significant power spikes.

The datasheet says "absolute maximum voltage" is 6V. What happens if you stick 4 brand new, hot AA batteries that are a little over 1.5V each on there? Slip a few AA lithium cells in there - they are 1.7V new. It may not die immediately, but you will stress the ATmega and shorten it's life (again, from the datasheet).

Other microcontrollers (including the lower speed, lower voltage versions of the ATmega8/168, as used on the lillypad) can operate over a wider voltage range. Putting a nominal 3V battery (that you may get 3.2 V out of when it's new) on a part rated for 6V is no big deal.

Low voltages are bad, too. I used a 3 cell 4.5V battery to power my arduino and got very strange results when programming (no program uploaded, program was corrupt, even wiped out the bootloader once).

I think the FTDI rs232/usb chip has tighter tolerances (5.5V absolute max rating, IIRC).

Know the datasheet before you start changing the power supply.

-j

If you're running an Arduino off battery, you really only need to worry about voltage dropping below a level (as other devices, motors for example, make power demands on the battery). Since this will cause a reset, or just loss of controller power, it's pretty easy to tell what's happening. I have my Arduino wired into a bot, with power-thirsty motors. So I wire the battery to the motor controller, which has a 7805 onboard to provide regulated 5V out; I use this power for the Arduino.

I have a similar project (build-in battery charger). It will be for an Arduino BT but I would like that PCB can be used for an Arduino USB. I found the MAX712/MAX713 circuit: http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1666 It can be used to supply the circuit while charging batteries (NiCd or NiMh). You can set the number of cells to charge. But I don't know if it is possible to connect a 9V battery. There's a lot of schematics on the web, and some with the Eagle CAD files.

For Li-ion, thank you kg4wsv! The Max1551/Max1555 seems really good! http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4002 The problem, it seems it can only supply 280mA. I'm not sure, I didn't well-understand the datasheet. Do you think we can use this component and link it directly to the Arduino BT or to the Arduino USB throw the USB connector?

[Sorry for my english, I hope that I didn't write too much mistakes. (I'm french)]

anyone make progress on this? I'm putting together parts for a arduino based weather station, and I would really like to be able to make it rechargable via solar power.

This combined with wireless will make it a standalone device.... but how to detect low power and recharge during the day?

re: battery voltages 4-7v

check out the max710 from maxim. It's a high efficiency boost + LDO regulator. It accepts 1.8 to 11 volts, and gives 5v @ 250mA (vin=1.8v), or 5v@500mA (vin>=3.6v). Can also supply 3.3v if you want.

The booster kicks in if Vin is less than about 6.5v, and the LDO ensures that little to no noise gets into your application, and can be more efficient than a buck in some circumstances.

Would be perfect for powering from a 4 cell nimh or nicad battery, whose voltage ranges from 4v to as much as 8v.

Looks like it would work great in combination with max712 too... sounds like a good project to design properly actually.