A common question I get offten asked is “Is it normal for my charger to get really hot?”. Usually followed by my favourite statement “I recon I could cook an egg on it!”.
The answer is yes, but first, there are some terminology we need to explain.
The charger will give out a constant voltage and will not vary. This is why it is vital to use the correct charger for the battery.
This is the amount of energy that the charger is pushing into the battery. This can be measured in amps or watts.
Bulk Charging Phase
This is a point where the battery charger works at peak power output.
Chargers go through cycles when charging a battery.
From 0% to 50%, the battery charges very quickly and the charger can sometimes warm up. As the battery goes from 50% to 90%, the charger must work harder and as mentioned before, this is the Bulk Charging Phase.
From 90% to 100% the charger starts to step down the amount of current going to the battery. This is to help the battery settle and balance. This is also the longest part of the charge. The last 20% charging will take the same amount of time as the first 80%.
Different Capacity Batteries
Different capacity batteries can also play a role in how hot a charger can get and how long for in Bulk Charging Phase. With bigger capacity batteries, the current needs to be higher to charge the battery in a more reasonable amount of time.
Batteries from 7Ah to 10Ah often get charged at 1.5 Amps, while batteries from 10Ah to 15Ah often get charged at 2 Amps and 16Ah to 21Ah often get charged at 3 Amps.
When the charger is in the Bulk Charging Phase, the charger can get really hot, all the way up to 60 Degrees Celsius.
At first, it feels like the charger is going to melt in your hands but over time, your body acclimatises to the heat where it can become bearable to touch. That is because the charger is converting high-voltage AC into low voltage DC. The voltage is pushed and pulled through coils, rectifiers, and resistors. Not all these systems are 100% efficient and this is why they heat up.
On the inside of almost all chargers, are aluminium plates called heat sinks. The size of the heat sink depends on the efficiency of the charger. The picture below is a charger that has a very large heat sink. This is common in cheap chargers.
Below are pictures of a good-quality charger that has small heat sinks. Even though the heat sinks are small, they will easily warm up to 60 Degrees Celsius.
Buying The Right Charger
Now I know you are thinking, “How do I know if the charger is too hot?”.
If you feel your charger is too hot, it is best to read the back of the charger to ensure that it is the correct charger for the battery.
Another question worth asking is: Is it a brand-specific charger? Some batteries need special chargers, so having a brand-specific charger is highly recommended.
Does the outside of the charger look damaged or are there any rattly bits inside the charger? If the charger is damaged, this could cause a short circuit and damage the battery.
Is the charging port clean? Debris, rust, and water can cause the charger to short-circuit and damage the battery.
The majority of the time, when a charger fails it becomes too hot. The cooling system itself is part of the circuitry. This will fail due to the heat and the charger will become useless for good. This is a failsafe system built into the charger.
You will hear reports about batteries exploding while charging or just after charging. This is most often due to cheap quality chargers that are not suited to the battery. The charger may be the wrong voltage. The charger may be too powerful. Or the charger could even be the wrong type for a chemical battery.
The main thing to do when charging is to remove the battery from the mobility device if you can and charge in a safe open, undercover, dry area, allowing the charger to have space to disperse the heat.
Battery-safe bags are available if space is limited. It is also best to contact your insurance providers as they can often give you great advice on how to store your batteries safely and still be covered under insurance.
Just remember if you have any questions. Please contact the supplier and ask. It doesn’t matter how silly the question may be. Safe battery management is a priority.
Trevor Guest - RE Chief Mechanic