To buck or to boost

Projects General Guidance
1

Hi all, I am trying to figure out the best (simplest) way to power my projects with batteries. I currently have both 3.3v and 5v components and I also occasionally require higher voltage (9-12v) for powering motors.

My solution is to use rechargeable NiMh cells for the motors and use power electronics for the electronics. I created a spread sheet with the number of cells, the usable voltage range, and the type of converter I should use. For example, if I go with two NiMh cells to a 3.3v Arduino I should use a boost converter to boost from 3v to 3.3v when fully charged and 1.8v to 3.3v when dead where as 3 cells would require a buck/boost circuit. It looks like boost and buck/boost circuits are much larger and more expensive than buck converters. I have several projects in the works and it would be nice to have a standard system for powering them (e.g. if it's 3.3v, use a 2 cell pack with a boost circuit or if its a motorized robot use 6 cells and a buck circuit)

From a practical standpoint, what type of regulator is preferred and what is a good "go to" circuit (like the 7805)? It would be real nice to order a box of 2 and 6 cell battery holders and several of the same regulator circuits to have "cookie cutter" power sources.

Note, I am aware of Arduinos including a small regulator but I am currently working with the DIY kind. I am also not interested in using lithium batteries.

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2

Most important is the difference between switching and linear regulators. The linear regulators, like 7805, can only reduce the input voltage, by burning excess voltage. And they literally burn that voltage, and can become very hot. They mostly come with over-temperature and current protection, safe and easy to use. They are fine for small currents, well below 1A, like for powering a controller, but certainly not for motors.

Switching regulators can convert up or down, or both, and are very efficient (>90% typically), well suited for high currents. They are not always safe to use, in detail the cheap ones, and their switching frequency and ripple can affect sensor readings.

3

In my experience the cheap converters you find on eBay from the Far East work better when they are buck converters than boost. Despite what they claim a boost converter current is limited to about half an amp.