How to Use a Trickle Charger

Written by thomas west
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Trickle chargers keep lead-acid and nickel-cadmium batteries fully charged to make up for battery self-discharge during storage. Keeping a battery charged at all times extends its life. Trickle chargers are ideal for keeping lawnmower or motorcycle batteries charged when they are stored for the winter. When a trickle charger is connected to your battery, it will automatically shut off when the correct battery voltage is reached, and it will turn back on when it detects battery discharge. Some trickle chargers' settings are preset at the factory and cannot be changed, but others need to be adjusted before use.

Skill level:

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Things you need

  • Trickle charger
  • Voltmeter
  • Ammeter

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  1. 1

    Calibrate the float voltage (if applicable, follow the charger instructions) on the charger to insure its output is sufficient to charge your battery. Plug the electrical power in to the charger. Place the leads of a voltmeter across the red (positive) and black (negative) charger alligator clips. Adjust the float voltage on the charger until it reads 28 volts on the voltmeter. Unplug the power to the charger and disconnect the voltmeter.

  2. 2

    Connect the red (positive) alligator clip on the charger to the positive battery terminal. Squeeze the ends of the clip together to open the jaws. Place the jaws over the positive battery terminal and release the ends of the clip slowly.

  3. 3

    In the same way, connect the black (negative) alligator clip on the charger to the negative battery terminal.

  4. 4

    Calibrate the maximum current on the charger (if applicable, follow the charger instructions) to one volt lower than the voltage of your battery. (Most batteries are 12 volts. Check the label on the top of your battery if you are not sure of its voltage.) Connect an ammeter to either the red (positive) or black (negative) lead on the charger. Switch the ammeter to the 500mA to 1A scale. Adjust the current on your charger to one volt lower than your battery voltage. Remove the ammeter.

  5. 5

    Plug the trickle charger into a wall outlet. Leave the charger plugged in and connected to the battery until the vehicle is taken out of storage. Unplug the charger from the wall, and then from the battery, before using the vehicle.

Tips and warnings

  • A trickle charger merely maintains the battery's charge, so connect one only to a fully charged battery. If the battery is low and needs recharging, use a regular battery charger to bring to battery to its full charge before connecting a trickle charger.
  • Do not plug the trickle charger in before connecting it to the battery terminals. The reverse-polarity protection that's built into the charger can prevent damage to the charger and the battery only if you connect the trickle charger's alligator clips to the battery terminals first.

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