Charging a car battery at 40 amps shouldn't be done for longer than 2 hours. Fast charging car batteries can be dangerous and should be done in short bursts. Failure to do so could result in explosions.
Amp hours are how many amps an hour a charger can put out. If a battery has 36 amp hours it can output 1 amp for 36 hours, 3 amps for 12 hours, 6 amps for 6 hours, so on and so forth. A 10 amp charger puts out 10 amps an hour to the battery.
Before you start charging make sure you're in a well ventilated area and your battery and charger are compatible. Check your owners manual for more information.
Step 1: Identify the positive and negative terminals. The positive terminal is either red or has a plus sign near it.
Step 2: Disconnect the battery cables and remove the battery. Always disconnect the negative, or ground, first.
Step 3: Clean your battery terminals. Make sure you remove any dirt or corrosion to ensure a proper charge.
Step 4: If required, fill the cells with water. If you have a maintenance free battery you can for go this step.
Step 5: Set the charger to the proper voltage. The proper voltage should be on the battery or in the owners manual.
Step 6: Attach the cables. Attach the positive cable first and then the negative.
Step 7: Plug in the charger. Make sure you're using a grounded outlet without an adapter.
If you know how many amp hours your battery has you can calculate how long it's going to take to charge. To calculate that you can use a simple formula. Time= Amp hour/Battery Amps. For these examples we are using a 48 amp battery.
Using a 2 amp charger on a 48 amp battery takes 24 hours to charge from empty. The charger puts out 2 amps an hour and has to work for 24 hours to reach 48 amps.
Using a 4 amp charger on a 48 amp battery takes 12 hours to charge from empty. The charger puts out 4 amps an hour and has to work for 12 hours to reach 48 amps.
Using a 10 amp charger on a 48 amp battery takes take 4.8 hours to charge from empty. The charger puts out 10 amps an hour and has to work for 4.8 hours to reach 48 amps.
Using a 12 amp charger on a 48 amp battery takes 4 hours to charge from empty. The charger puts out 12 amps an hour and has to work for 4 hours to reach 48 amps.
Using a 40 amp charger on a 48 amp battery takes 1.2 hours to charge from empty. The charger puts out 40 amps an hour and has to work for 1.2 hours to reach 48 amps
Charging a car at above 10 amps is considered fast charging. When fast charging make sure to set a timer for when to stop charging. Otherwise your battery may be overcharged and could explode or develop a fault.
If your battery isn't charging there could be a few things wrong. It could be as complicated as a chemical issue in the battery or as simple as a faulty terminal. Here are some common issues:
When your battery isn't charging it can be demoralizing. However before you dispose of the battery, try and troubleshoot it yourself. Some battery issues can be solved at home. Troubleshooting yourself can save you money and time.
To do some simple troubleshooting on your car battery you need a few tools. A voltmeter, cleaning solution, and a properly sized wrench are the tools you need. The whole troubleshooting process should take about 10 minutes. If troubleshooting doesn't resolve the issue then your battery likely needs to be replaced.
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