Fast Charger

User Manual

Circuit diagram
If Struck by lightning
How It Works

Intended use:

This model is designed to be used to charge 6V or 7.2V 1400mAh Nicad batteries used with remote controlled model racing cars. Attempting to use this model to charge lower voltage batteries or low mAh batteries (e.g. 7.2V 75mAh transistor battery) will result in permanent damage to that battery. Make sure you have the correct model charger for the type of battery you wish to charge (table 1).


TABLE 1

 Battery

 Model to use
 2 size AAA, AA, C, or D  FC12
 1 Transistor Battery  FC7200
 1 Racing Pack  FC7214


Simple Limited Warranty:

  • Your Fast Charger will work when you get it and continue to do so for at least a year:
    • as long as you treat it right
    • or unless one of it's electronic components dies
  • We are not responsible for:
    • Any injury through the misuse of this gadget
    • Acts of God
    • Murphy's Law
  • Your Fast Charger does not like:
    • Water
    • Being dropped
    • Being opened up
  • In the unlikely event that something does go wrong with your Fast Charger, feel free to contact our nearest office.
    We will immediately:
    • Tell you with a straight face that you are the first person who ever had a problem with one of our chargers.
    • Send you a replacement unit ,or
    • Send you your money back, or
    • Ask you to return the defective unit prepaid, or
    • Recommend you to a competitor

NOTE: No panics accepted during morning coffee break.


How to use it:

You can use one of two power sources:
A car battery
A mains plug pack (13.8V, 1.5Amp)

To use a car battery

Plug the alligator clips into your charger (they will only go in one plug - unless you really really force it in really really well), and connect the red lead to your car battery's positive terminal and the black lead to the negative terminal.
If you connect the leads to the wrong terminals, your charger will not work (it won't be damaged as we have designed it to handle such mistakes).
Don't turn your car's engine on. This will upset and confuse your charger.
Plug your NiCad battery into the other plug. If the little green light comes on, just press the RESET button.

Your Fast Charger will begin to charge your battery. Your battery will be fully charged in about 30 minutes (depending on how good your car battery is). The charger will automatically stop charging your NiCad battery when it detects the voltage across the NiCad battery has peaked. It will light the little green light to indicate that the battery is charged.

To use a mains plug pack

Plug it into your charger using the same plug as for the alligator clips.
Plug your NiCad battery into the other plug. If the little green light comes on, just press the RESET button.

Your Fast Charger will begin to charge your battery. Your battery will be fully charged in about 1 hour. The charger will automatically stop charging your NiCad battery when it detects the voltage across the NiCad battery has peaked. It will light the little green light to indicate that the battery is charged.

 

The alligator clip leads and mains plug pack are available from most hobby stores or Dick Smith Electronics.

 

CIRCUIT DIAGRAM:

IF STRUCK BY LIGHTNING:

If struck by lightning, replace U1 to U5, and anything else that has turned black.

 

HOW IT WORKS:

Our engineer insisted on this part being included. It's really just an excuse to blow his own trumpet, and if he had been really clever, you wouldn't need to know anything about the circuitry and this whole section would be superfluous.

We have actually compressed the "How it Works" section down into the following sentence:

"It's really very clever".

But, read on if you want to know how it all works, and see how clever our engineer is...

 

When a NiCad battery is charging it's characteristic is such that once the battery is fully charged, the voltage will start to drop if it is continually charged. This circuit uses a "Sample and Hold" method to look for the peak in the NiCad's voltage.

U1, U2, Switch 1 of U5, R9, and C3 form the Sample and Hold circuit. U4 provides a pulse once every minute which turns on switch 1 for 10 seconds. Once the switch is off, the charge is held in C3. This capacitor is a very low leakage type, and the CA3140 Op Amp is a very high input impedance (10Meg), therefore the charge will take a very long time to dissipate (very much longer than the sample period). The output from the Sample and Hold circuit goes into U3, an LM393 comparator, which compares the sampled voltage with the present voltage. As soon as the present voltage falls below the last sampled voltage, the Comparator goes low, disabling the relay and stopping the charging current to the NiCad battery, and turning on the LED to indicate charging has finished.