J. Mike Rollins (Sparky) [rollins@wfu.edu]
Hyperbola New
My Cats New
Kitty New
Mike is on
Green Cycle Design Group
  My Stuff  
  My Truck  
   AC Inverter
   Taz (My EV)
   PIC Switch
   LM3524 Motor Control
   SMP with 317
   Power Supply
   Function Gen
   Simulator: Zener
   Charge Controller
      Simple Controller
      Charger 14.4
   IR Audio
   PWM with 555
   Entertainment Center
   GPS & WD-C2401P
Jacob's Ladder
My House
My Cars
My Cats New
My Jokes
Pi Poetry
Toro Mower
Speed of a Piston
Not a Pipe

Disclaimer:The following are my notes. As I am learning electronics, I am making my notes available. I hope they will be of benefit. However, I do not guarantee the accuracy of my work. I recommend the reader exercise critical thinking.
Charge Controller

Charge Controllers

I found a few rechargable batteries in my dresser drawer. I'm not sure if I bought them or if somebody gave them to me. But, I don't have a charger. So, I decided to try and build one for them.

I knew a little about charge controllers from my work with Solar Pannels. The lead-acid 12 volt charge controller from SunForce provides pwer when when the voltage is below a 13 volts and stops charging when above 14.2 volts. I decided to follow the same concept. I found this was not a good idea. The differnt battery composition make them condusive to different discharge rates and require different charging schemes.

Simple Controller
Charger 14.4

Nickle Cadmium

Nickle Cadmium (NiCD) batteries produce a fairly consistent voltage over it's life. These can withstand deep discharge and withstand high discharge rates. They also support different charging rates. At the end of a charge cycle, they will produce heat. Some charging methods provide consistent current over a preset time interval. Other charging methods look for this increase in temperature. Additional information: wikipedia and www.powerstream.com.

Nickel-metal hydride

Nickel-metal hydride (NiMH) batteries cannot withstand deep discharge. There seem to be two methods for recharging NiMH batteries. When supplied a steady current, the voltage increases until fully charged. Then the voltage will decrease a small amount. Smart battery charges will look for this drop in voltage at the end of the cycle. The second charging method checks for an increase in temperature to indicate the end of the charge cycle. Additional information: wikipedia and www.powerstream.com.

Amp Hour

I have some NiMH AAA batteries and some NiCD C batteries. The rate of charge for batteries is dependet on the battery's Amp Hour rating. This value is often denoted by the letter C. "The Amp Hour rating tells you how much amperage is available when discharged evenly over a 20 hour period" 1st-optima-batteries. My NiMH batteries have C=700mAh. My NiCD batteries have C=2000mAh.

A common and safe charge rate for rechargable batteries is C/10 Amp. At the rate of C/10, my NiMH would charge at 70 mAmps and my NiCD could charge at 200 mAmps. However, both of these batteries can support a fast charge rate of C/1 if properly monitored.


Automobiles typically use Lead Acid batteries to run run the starter. Thes can deliver high surge currents, but do not tolerate being fully discharged. The class of deep cycle battery supports being fully discharged, but don't deliver as much peak current.

There are many ways to charge these batteries. Automobiles use the alternator to recharge the battery. Some smart system use three stage systems to deliver C/20 for the first 20% of the charge cycle, C/10 for the middle 70% and C/20 for the last 10%. Some system even use pulse-width modulation to send pulses of power to the battery. I use a simple SunForce charge controller on my truck. This simply allows charging when the voltage is below a 13 volts and stops charging when above 14.2 volts.

Here are some additional references on Lead Acid batteries and battery charging: