available at: 1.1 – maintain vex rechargeable power pack maintain vex rechargeable power packs

Available at: www.etcurr.com Lesson 1.1 – maintain VEX rechargeable power pack

Maintain VEX Rechargeable Power Packs


Maintain VEX Rechargeable Power Packs

Performance Objective: Given a VEX robotics system, maintain VEX rechargeable power packs so the system functions as required.

Enabling Objectives: define the following terms: ohms, volts, milliamps, amp hours, electricity,

alternating current, direct current identify 7.2V and 9.6V power packs test power pack voltage using a multimeter explain how to charge the 7.2V power pack versus the 9.6V power pack set-up the battery charger identify the charging sequence when charging two power packs describe the relationship between the status lights on the charger and

the condition of the power pack(s) being charged


Battery Packs

7.2 volt robot battery Capacity: 1000-2000 mAh Charging time: 1.4 – 2.8 hrs

9.6 volt transmitter battery Capacity: 700 – 1000 mAh Charging time: 1.4 – 2.0 hrs

NOTE: the batteries used to power VEX systems are also known as power packs


Electricity

Electricity is the movement of electrons; particles with a negative charge.

Electrical systems utilize either alternating current (AC) or direct current (DC).

VEX robotic systems utilize batteries that supply DC.


Electrical units of measurement

There are three units of measure that are important when looking at an electrical circuit: Amps Volts Ohms


Amps (A)

Amps is the measure of electrical current.

Current is the amount of electrons flowing through a conductor in a given period of time.

Amps can be measured using a multimeter.


Volts (V)

Volts is the measure of force or pressure moving electrons.

Volts can also be measured using a multimeter.


Ohms (Ω)

Ohms is the measure of resistance to the flow of electrons.

Multimeter can be used to measure ohms.


Digital Multimeter

A multimeter can be used to measure both AC and DC voltage, amperage, ohms, and continuity.


Digital Multimeter

Ohms

DC Amps

AC Amps

AC Volts

DC Volts

DC millivolts

Continuity


Measuring DC Voltage Step 1: Set

multimeter on DC voltage

Step 2: Plug red probe in volts, ohms, and continuity socket

Step 3: Be sure black probe is in the com socket


Measuring DC Voltage Step 4: Place probes in

socket of battery pack, red to red (+), black to black (-)

Step 5: Note voltage value from the multimeter

If reading is negative, you can either ignore the minus sign or reverse the probes


Normal battery readings

A freshly charged 7.2 V (nominal value) battery will read approximately 8.2 volts

A freshly charged 9.6 V(nominal value) battery will read approximately 10.4 volts

When a battery reaches its nominal value, it will need to be recharged


CAUTION using multimeter

DO NOT test the batteries using any other set-up on the multimeter or you may risk damaging the multimeter.


Milliamp-hours (mAh)

An amp-hour is the amount of amps a battery can deliver for one hour

The prefix milli is used to indicate one thousandth (1/1000) of a unit in the SI measurement system

For example: a millimeter (mm) is one thousandth (1/1000 or 0.001) of a meter; a milliamp-hour (mAh) is 0.001 of an amp-hour.


Milliamp-Hours (mAh)

2000 mAh The battery can produce a

steady charge of 2 amps for one hour

1000 mAh The battery can produce a

steady charge of 1 amp for one hour


Battery Charger

Battery charger and battery packs

Transformer and chord


Setting up the battery charger

Plug transformer ‘s 120VAC cord into wall outlet

Plug transformer’s 16VDC cord into the battery charger


Battery charger default setting

Battery packs properly installed in charger

Default override switches: These switches will be engaged when the 7.2 Volt battery is properly installed


Properly inserting batteries

When charging 7.2 volt batteries it is very important the default override switches are pressed down. If these switches are not pressed down, the 7.2 battery pack will be charged to the higher default setting, ruining it. Switch is pressed


Charging order of batteries

Whichever battery is plugged in first is the first one to charge.

The second battery will be charged when the first is completely charged.


LED Status lights Whichever LED is on indicates which battery is

charging If the LED is flashing it indicates there is a

problem If the LED is off it means the battery is fully

charged or waiting for the other battery to charge


Flashing LED

If LED flashes, try a different battery pack If the LED still flashes, try another

charger


The End

Have fun and be safe

available at: 1.1 – maintain vex rechargeable power pack maintain vex rechargeable power packs

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