Choosing the right battery

Introduction:

A robot is only as good as its weakest link. In modern electronics energy storage is one of the weakest modern technologies. This technology has not changed much in the past 200 years.

The definition of any battery is – A device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy.

History:

We have beenIronie_pile_Bagdad using batteries since taround 250 B.C.E. Scientists have uncovered artifacts called” Baghdad Batteries” that were an ancient cell that produced around 1.4volts of electricity. Some scientists believe that there are some cells that are over 2000 years old.

 

Leidse_flessen_Museum_Boerhave_december_2003_2 In 1749 Benjamin Franklin was the first to use the term “battery” to describe a set of linked capacitors he used for his experiments with electricity. By linking these primitive capacitors together in he created a “battery” which produced a stronger discharge.

What does all this mean for a robot? Well, in simple terms, you can only carry what you can. This means that modern rechargeable batteries are still one of the heaviest components of a robot. Think of a robot as an electrical vehicle. The more weight you add the less efficient the overall system is. Finding a battery that does not weigh down the base and supplies enough power for the robot to complete the designed task is paramount.

Fast forward today and we have in my opinion made modest gains in this technology. Some of the common batteries that you made be use to are AA’s CC’s and 9 volts. There are both found as pile alkaline and the more usable rechargeable nickel–metal hydride batteryNiMH” chemistry type. However we are going to focus on larger cell type batteries.

What battery to use:

The battery that I would choose for this size of a base would either be a Li-Ion pack (Pack is another name for a group of cells) or a lithium iron phosphate (LiFePO
4
) battery. Both have are Lithium-Ion battery chemistry’s that have a large power density.  lithium iron phosphate (LiFePO
4
) battery have somewhat lower energy density than the more common LiCoO
2
design found in consumer electronics, but offers longer lifetimes, better power density (the rate that energy can be drawn from them) and are inherently safer. I have listed some packs from StarkPower below and a associated charger. Does this mean you need to use this brand/size, of course not though they are a great capacity with built in protection for a good price. You can also build up a pack with individual cells with protection circuity by soldering it up yourself.  This may save you a bit of cash if you are comfortable in doing this safely.12aH battery

12V 9Ah StarkPower “UltraEnergy” lithium-ion  w/o charger $99.00

If you spring for the 5-6Amp charger it will be significantly faster at charging the battery pack up.

 

Hookup:

The best way to hook this up to your system would be first though a power switch and a fuse. The fuse needs to be slow-blow and rated higher then what the motors will pull if running. The reason a slow blow is used is because when motors first start there is a inrush of current that would trip a fast blow fuse. Around 5-6Amp slow-blow should work. Also make sure the power switch is rated to handle at least 8-10 Amps. The fuse can also be replaced with a 5-6amp resettable circuit breaker. Though be careful before just resetting the fuse and check over all the robots wiring.Power flow

 

The future:

Soon other battery chemistry’s will be released and other technology’s may become more viable for robotics. below is a list of some future methods to supply power to your robot.

Lithium air battery’s – Lithium air batteries are a theoretical battery type that is quickly becoming a reality. These batterys offer a  theoretical energy density 1,000 times greater than the typical lithium ion battery. This will be a quantum leap forward in battery technology. Unstable prototypes are being created now in research labs. However you will most likely not see widespread production until 2020.