Powering electronics

Hey again,

Sorry to bother you guys but I am rather new to electronics. How do I go about choosing the right battery for a project. I am thinking of making a small scale version of my project using cheaper servos. The problem I am having is the large current draw of the servos 200-500 mA. Can anyone tell me how to choose a battery/ build the right circuit for my projects or point me to a good source to read up on this subject. Thanks!

Just use a standard wall wart type transformer with whatever voltage you need and enough current

wow, I have no idea why this slipped my mind. It is a great solution for the high current draw of the servos I planned on using for my prototype model. Thank you. Also, Can anyone still recommend a process to choosing the right battery for when I go to complete my final robot.

Calculate and/or measure how much total current the project runs. Determine how long you want the project to run between charges. Select a battery rated for that many Amp-Hours.

Thanks James. That was my original assumption but I wasn't sure if it was truely that easy as I am limited in electronics knowledge. By chance do you know the current draw of the uno and mega 2560?

If its not listed on the arduino data sheet just run it with some sample blink code or something running and use a multimeter

Capacity is not the same as current rating.

For high current you need a battery with low internal-resistance, and this varies between chemistries and manufacturers and between different ranges from the same manufacturer - if you can find a datasheet for a battery it will tell you things like this.

Roughly speaking rechargeables do well at high currents, cheap batteries of any sort do not. Lithium batteries are usually pretty powerful but can be more tricky to work with (need specialised charger, need protection circuit (sometimes built-in)).

MarkT: Roughly speaking rechargeables do well at high currents, cheap batteries of any sort do not. Lithium batteries are usually pretty powerful but can be more tricky to work with (need specialised charger, need protection circuit (sometimes built-in)).

There are some newer lithium chemistries which are much safer. Lithium-manganese, for example. LiMn have the further advantage of high current -- 5-6C or more, whereas what I typically see from LiIon is around 1.5C.

Useful site: http://batteryuniversity.com/

for example. LiMn have the further advantage of high current -- 5-6C or more, whereas what I typically see from LiIon is around 1.5C.

But high performance Lipo batteries seen in the R/C hobby world can often supply 20-30C.

Lefty

Just to return for a moment to....

Capacity is not the same as current rating.

When chosing your power supply, you need to look at both current rating and capacity....

Current: How much electricity is flowing... measured in amps. (Hopefully you are dealing with milliamps... but I will leave the "milli" off in what follows. Whether your case is 0.005 amps or 50 amps, the principles here are the same... though at 50 amps MORE things become important!

Current rating: The highest current the device being discussed can operate "normally" at. Exceed the current rating and it will stop "working"... sometimes permanently. Measured in amps

Capacity: Measured in "Amp-Hours". A 10 amp-hour battery MIGHT run a circuit in which 10 amps flows for an hour (if... and it is a big if... the battery's current rating is not exceeded). OR it might drive a 1 amp circuit for 10 hours, or a 0.5 amp circuit for 20 hours, etc. What happens, when one amp is flowing, after 10 hours? The voltage goes below the voltage "they" promised it would deliver. (In the real world, a "10 amp-hour" battery is a BIG beast... but I used the number because it made the discussion transparent.)

Current: How much electricity is flowing... measured in amps. (Hopefully you are dealing with milliamps... but I will leave the "milli" off in what follows. Whether your case is 0.005 amps or 50 amps, the principles here are the same... though at 50 amps MORE things become important!

Are you talking about the board,servo,etc or the battery in this case? I am not sure I understand how this will help me choose a battery as most batteries I have found run higher amps then any of my electronics will need.

Also, can anyone recommend a good place to purchase batteries and chargers?

Check out this fun and interesting video by Afrotechmods:

http://www.youtube.com/watch?v=EoWMF3VkI6U

Bear with him while he talks about ultracapacitors, because about a 1/3 of the way through he explains why ESR (equivalent series resistance) is important (comparing batteries to capacitors).

mblackwolf: Also, can anyone recommend a good place to purchase batteries and chargers?

I like Battery Junction, but it depends on what you're needing. For a LiIon or LiMn battery, AW seems to be the brand with the fewest quality issues. For those, I like the Pila IBC charger, rather than the cheaper Tenergy or Ultrafire. I've read lots of good things about the Sanyo Eneloops.

AW IMR 14560 LiMn cell

IBC Charger

Battery Junction