Battery Lesson please

[evaderdjo]

I would really appreciate it if someone could help me understand the differences in batteries.

1) the mAh abbreviation stands for milli amp hours, and I believe a bigger number is better than a smaller number. Does a bigger mAh number mean a battery is more powerful, or runs for a longer period?

2) Voltage - each robot appears to operate at a different voltage, and if you use a battery with the wrong voltage, very bad things happen. What determines the voltage required? Is it the RCB, or the servos themselves?

3) I imagine that each type of battery has its own strengths and weaknesses. Could someone check the following brief description of each, to see if I have it right?

NiCd = Nickel Cadmium which is cheap, heavy, weak on power, quick to discharge and slow to recharge, but can be used hundreds of times.

NiMH = Nickel Metal Hydride which is more expensive, heavy, slightly more powerful, slightly slower to discharge and slightly faster to recharge, and can be used hundreds of times

LiMN = Lithium Maganese (or Lithium Polymer) which is very expensive, light, very powerful, slow to discharge, fast to recharge, but can be dangerous if handled improperly.

Thanks for your help.

[NovaOne]

1) the mAh abbreviation stands for milli amp hours, and I believe a bigger number is better than a smaller number. Does a bigger mAh number mean a battery is more powerful, or runs for a longer period?

You are correct mAh, stands for milliamp hours, this tells you the capacity of the battery, and hence how long it will last.
For example a 600mAH battery potentially can supply 600mA for one hour, 1200mA (1.2A) for half an hour, 300mA for two hours.....etc

2) Voltage - each robot appears to operate at a different voltage, and if you use a battery with the wrong voltage, very bad things happen. What determines the voltage required? Is it the RCB, or the servos themselves?

The specific maximum voltages depend on the specs of the modules connected directly to the unregulated battery voltage. Most sensor modules and the main microcontroller inself, operate of 5v or 3.3v and will be run off a voltage regulator on the control board. However since power is a product of voltage and current (Power = Voltage x Current) the higher the voltage you supply to your servo the more powerful it will be BUT the servo specs will have a maximum operating voltage determined mainly by the resistance of the windings on the small DC motor inside the servo. YOU MUST NOT EXCEED THIS VOLTAGE.
Control boards/controllers can be more forgiving because voltage regulators are designed to cope (within reason. see specific datasheets) with quite a wide input supply voltage range

3) I imagine that each type of battery has its own strengths and weaknesses. Could someone check the following brief description of each, to see if I have it right?

NiCd = Nickel Cadmium which is cheap, heavy, weak on power, quick to discharge and slow to recharge, but can be used hundreds of times.

NiMH = Nickel Metal Hydride which is more expensive, heavy, slightly more powerful, slightly slower to discharge and slightly faster to recharge, and can be used hundreds of times

LiMN = Lithium Maganese (or Lithium Polymer) which is very expensive, light, very powerful, slow to discharge, fast to recharge, but can be dangerous if handled improperly.

I think you got most of it right, just change the words "power or powerful" for "capacity or higher capacity" in each case

You could also add that:
NiCd should be discharged before being recharged, otherwise they lose capacity or just generally play up.
NiMh will self discharge quicker than NiCd when left unused.

L ion/poly should not ne charged or discharged to rapidly as heat can build up inside the air tight cell and...... BANG

I'm sure theres lots more but that all I know
Chris