| 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.
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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.
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.
Lead-acid
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:
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