RCU Chargers



Basics - In order to have a better understanding of chargers, it is important to understand a few basics of electricity and what the individual ratings are.  Once you know this it will be easier to understand how the different ratings of a charger work in concert to provide the juice to your battery pack.  An easy way to visualize what they all mean is to compare the flow of electricity to the flow of water in a pipe.


Amps – Think of amps as the VOLUME of water flowing through a pipe. 


Voltage – Think of Voltage as the PRESSURE of the water in that pipe.


Watts – Think of watts as the POWER that the water in the pipe provides.  Watts are a calculation of amps and voltage (volts x amps = watts). 


AC/DC – One of the main classifications for chargers is whether they are powered by AC current, DC current, or both (AC/DC).  Simply put, AC chargers can be plugged into a wall outlet, while DC chargers require a DC power source such as a car battery or a dedicated power supply.  Batteries used for RC are all DC (direct current), meaning they have one positive, and one negative terminal. AC power (alternating current) is what you have coming out of your wall outlets, where power flows through both terminals in a constantly switching phase. 


AC Chargers - To be plugged into a wall outlet, an AC charger must have the ability to convert that AC power into DC power to charge the battery.  To do this, a transformer inside drops the voltage down to the lower volts of our battery packs, and diodes to convert the AC power to DC power (this is a simplified version of what goes on inside an AC charger).  AC chargers have a power supply built into them to provide the current needed using the AC electricity to charge your battery pack.  Some very basic AC chargers do not have a power supply and only rely on converting the AC power to DC power to charge with.  These are typically the type of chargers that come with some inexpensive RTR type RC’s and these take a long time to charge a battery due to their low power.  Nearly every AC charger is also DC capable, since the charger is just converting AC power to DC power inside of it, it is easy to simply bypass the AC circuitry and use DC power to run the charger.


DC Chargers – DC chargers rely on the power being supplied to them to already be in DC form.  They do not have transformers or power supplies built into them and therefore are not able to run on AC power.


Which is better? – AC chargers have the advantage of being an all-in-one unit, you can simply plug them into a wall outlet and charge your battery with nothing else.  The downside to AC charges is that they are limited on power, an AC charger would have to be very large and much more expensive to contain the power supply needed to charge batteries at high currents.  Additionally, AC chargers are more expensive for the power you get since you need to account for the power supply inside of it, and there is more that can go wrong in an AC charger.  Since a DC charger relies on a dedicated power supply, and those power supplies are generally much more powerful than what you would find inside an AC charger, DC chargers usually have the ability to charge at much higher currents than AC chargers.  DC chargers are also much less expensive for the power they produce since they do not have the added expense of a power supply and they have many less components to potentially fail.


Charge Rates/Charging Time – Charge rates are generally expressed in Amps, but it’s important to factor in the watts of a charger to understand how fast a charger will actually be able to charge a battery.  To understand how current translates into charging times, we will use the example of a 1000mAh battery:


• Charge rates are expressed in Amps, and battery capacity is measured in mAh (milli-amp hours).

• A 1000mAh battery can provide 1 amp of power for one hour, and at a charge rate of 1 amp it would take one hour to charge that battery. At 2 amps, it would take half an hour and so-on.

• The actual power at which a charger can charge is a calculation of how many watts it has and the voltage of the pack it is charging. The charging current is calculated as the charger watts/battery pack voltage.  Let’s look at a charger that has a maximum charge rate of 5.0 Amps and     an 80 Watt power rating:

        • Charging a 2S/7.4V battery you would get the full 5.0 Amps since 80/7.4 = 10.8

        • Charging a 3S/11.1V battery you would get the full 5.0 Amps since 80/11.1 = 7.2

        • Charging a 4S/14.8V battery you would get the full 5.0 Amps since 80/14.8=5.4

       • Charging a 6S/22/2V battery you will see a drop-off in the charging current since 80/22.2=3.6



So now you see how simply looking at the charging Amps of a charger can be misleading as you need to factor in the Watts as well.  Also, while considering that each amp can charge 1000mAH of capacity in one hour it should also be pointed out that chargers do not start and finish a charge cycle at full power, they build up power at the start of the cycle and as pack voltage is topped off they taper down the power towards the end of the cycle.  Additionally, balance charging a pack can add additional time to a charge cycle as the charger is regulating power to individual calls to bring them into balance.




Programs – Nowadays, all but the most basic chargers have options for standard charging, balance charging, storage charging, discharging etc. Most chargers also have the ability to load a “program”, meaning that if you have certain packs that you charge often you can save your charging settings under a program so that you do not need to set the amps, cell-count etc. every time you charge the battery.


Some chargers also have the ability to measure battery pack resistance and individual cell resistance as well.


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