Additional Math Pages & Resources

Friday, September 30, 2011

Battery Math, Part IV

We've been considering the math of batteries this week. Today we're looking at battery chargers. All of them work in a similar way - they push electrical current into your battery until its chemistry is returned to the original state. Beyond that, they vary in almost every way possible.

Here are a few chargers I found around my house and my office at AnsMar Publishers, home of Excel Math curriculum. You may find an assortment around your house too. Why not check? And while you are at it, count your batteries ... you will be amazed!

Assorted regular battery chargers
Apple iPhone
Blackberry phone
Warehouse Pallet Jack Charger
Forklift and Truck starting charger
Car charger in use (my car, sigh)
High-tech new charger
Here's a new charger I bought to refresh my wife's batteries. It can test batteries, deplete them until empty, recharge, cycle down and up multiple times, etc. There's a display for each cell being charged. I hope it's an improvement over the twenty-year-old chargers (first photo) we've been using.

Most newer chargers indicate when a battery is fully charged. There may also be options, as shown on the big Craftsman charger. We can adjust the current, and the voltage, and the charging time. You can also see actual charging current on the ammeter.

Some devices use external power supplies along with internal charging circuits (mobile phones), and others have removable batteries that you put into an external charger (cameras).

Most chargers "pump electricity into a battery" (restore its chemistry) by providing voltage slightly higher than the battery  generates. So if you have a 1.5 volt cell, you can charge with 2 volts, and the battery would "receive" electrical energy. This has to be done carefully, to avoid overheating, damage or fire. So chargers incorporate many safety devices.

Electropaedia, a UK-based website, provided this handy advice on 3 main functions of a charger:
  1. Getting the charge into the battery - Starting the charging process
  2. Optimizing the charging rate - Stabilizing the charge
  3. Knowing when to stop - Terminating the charge
I recommend you visit this page, scroll down, and watch the animated battery charging.

They suggest an analogy for battery charging - filling a glass with beer. If you pour too quickly, the beer foams up and creates a mess, and you can't get much liquid beer into the glass. If you pour slowly, it gives the beer a chance to settle in the glass with a manageable amount of foam. And so it is with electrical charging of a battery - slower is better - unless you are waiting anxiously for the Auto Club to start your car!

The choice of "how to charge" depends on how much time, money, sophisticated circuitry, charging voltage and current available. Since more and more devices are becoming portable, and they all take batteries, recharging is a common household chore today. Knowing how and when to charge each battery properly is asking too much of the average person (us) so the trend is to build the intelligence into the charger.

Here are some charging options your smart charger might employ:
  • constant voltage
  • constant current
  • taper current
  • pulsed charge
  • negative pulse (discharge then charge)
  • IUI charge
  • trickle charge
  • float charge
  • random charge
  • slow charge
  • fast charge
And I think that's just about enough information on batteries and chargers for this week - going farther will take more than elementary math.