Charging LiPo batteries – How to select the right charger

Dino shares his insights on how to find the right charger for charging LiPo batteries

by Dino of Dino’s drones

Last week we shared with you information on the care and feeding of your LiPo battery and now we continue with insights on finding the right charger for charging your charging LiPo batteries.

When it comes to the right charger for your needs the natural question is, “Which charger will charge my LiPo?” Let’s reverse this thought and start with the battery. Look beyond the now and think of what your future needs may be. One of the best investments you can make is a charger that will take care of all your LiPos. It’s best to make one purchase.

The place to start is with the battery. From my article on LiPo care [here] I talked about the charge settings necessary to charge the LiPo. Let’s take that example:

3S 11.1V, 1000mAh, 20C discharge/50C Burst, 3C max charge

Based on that information we will need the following:

A charger that will charge LiPo batteries
A charger that will handle a 3 cell LiPo or 12.6V
A charger that will provide up to 3 amps (3C Charge Rate)
The charger that came with your drone will certainly handle the job. However, you will find yourself wanting to spend more time flying and less time charging. Most chargers that are included with a ready to fly package charge at a very slow rate and you have already noticed it takes forever to charge your battery. It doesn’t have to be this way!

Look into the future……you now have 3 LiPos of different cell counts and milliamp capacity to charge. The following week you have 2 of each cell count and capacities. You soon find yourself with 4-6 of each cell count and capacity LiPos…..Believe me! It’s not a matter of if this happens, it’s when!

The obvious is that a more powerful charger will definitely charge your lower power LiPos. The most cost effective charging system to have in your shop is one that will take care of all you charging needs. So, you need a charging system with enough power to comfortably charge your largest cell count and capacity LiPos without overloading or running at maximum output. It’s easy to figure out what your needs are by memorizing this simple formula: Volts (V) x Amps (A) = Watts (W).

Let’s look at a larger LiPo. The 6S 22.2V 5000mAh LiPo is a common battery for larger drones and a good place to begin this discussion. When shopping for a charger do not be lured to the charger’s cell count specification and amperage output only. This can be deceiving and lead to unnecessary purchases. The other necessary specification to focus on is how many WATTS does it provide?

My personal charger.
My personal charger.

Example: I have a charger with the following specs:

AC Input: 100-240V
DC Input: 11-18V
Charge Current: 6 Amps
LiPo Cell Count: 1-6 Cells
Wattage: 50W max

These specs look pretty good. I can plug it into a regular wall outlet at home. I can use alligator clips and attach it to my car battery to charge where I’m flying. The Amperage output will charge at 5 amps (5000mAh). It will handle 6 cells BUT the question is what is its power output or watts.

With this charger the limitation is the wattage output of 50W!

Remember the formula: Volts (V) x Amps (A) = Watts (W)

TIP: Always use the fully charged voltage in your calculations. You want to know the maximum you will need. I.e. a 3S LiPo fully charged is 12.6V and a 6S LiPo is 25.2V, this is the voltage you want to use in the formula.

TIP: Your charging system will experience voltage losses and efficiency due to the characteristics of chargers and connections between the LiPo and charger inputs.

Plug in the numbers: 25.2V x 5A = 126W

Whoops…..this charger will not efficiently charge this LiPo! The charge rate will be 1.9A (50W / 25.2V). This charger is no better than the one that came with the drone and would be a waste of money. You need an output of at least 150 Watts to charge at 1C (5A), taking into consideration voltage loss and efficiency of the charger. This charger is; however, great for my smaller LiPos. I use this charger for going out for a quick flight or two with my smaller drones on my way home from work. That way I don’t have to lug the larger system and Honda generator around.

In order to charge the 6S 5000mAh LiPo at a 2C rate here is what your charger needs:

Ability to charge 6 cell LiPos

Output of approx. 12 – 15 Amps

Output Power of approx. 300 Watts

PARALLEL CHARGING

ALERT: Parallel charging is an advanced method of charging and extra care must be taken to ensure the LiPos are connected properly and the charger is set to the proper charge settings. If you are not comfortable with electronic equations; relationships of volts, amps and watts and determining the power output of chargers do not attempt to parallel charge LiPo batteries.

As you grow in this endeavor you will more than likely begin to purchase more LiPos for your drone increasing your charging needs. If your charger can handle the output you can charge more than one LiPo at a time. This is called parallel charging or para-charging. IMPORTANT point: to para-charge multiple LiPos, ALL the LiPos MUST be the EXACT same cell count/voltage. I recommend the capacities of the LiPos be the same; however, opinions vary on whether or not the capacities must match.

Ugh! More math!

When two or more LiPos are connected in parallel the Amps and Watts are doubled. The Volts stay the same. Example: Two 6S 5000mAh (5.0A) LiPos connected in parallel will now be 6S or 25.2V at full charge and 10000mAh capacity. In other words you now have one big 6S 10000mAh (10A) LiPo. To para-charge these two LiPos your charger must be able to output 10 amps (5.0A + 5.0A) and 252 Watts of power in order to para-charge these two LiPos at a 1C rate. Here’s the math: 25.2V x 10A = 252W. To para-charge two 6S 5000mAh at a 2C rate you will need 20A and 504W of output.

Now, four 6S 5000mAh LiPos connected in parallel give you one big 6S 20000mAh LiPo!

(5.0A + 5.0A + 5.0A + 5.0A = 20A = 20000mA)

A special parallel charge cable or parallel charge board is necessary for parallel charging. It is also necessary that you have a parallel balancing cable or board. These can be found at any hobby shop. Pictured are a JST Parallel charge cable and a para-charge board with balance connectors included.

Parallel charging tools.
Parallel charging tools.

ALERT: When connecting a single LiPo to the charger, first, connect the charging system and turn it on. Second, connect the large charging leads of the LiPo to the charge lead from the charger. Third, connect the little white balance plug to the balance board in the correct cell count slot. This will allow the large voltage of the battery to equalize through the charge cable first. If you plug the balance lead in first the LiPo will try to equalize through the small balance wires and potentially overload the wires and cause a fire.

ALERT: When para-charging the order of connection must be considered. It’s like having a super LiPo with lots of power trying to equalize through small balance wires and the potential for fire increases exponentially. Order of connection:

Make sure the all components of the charging system are connected
Plug in the parallel charge cables and/or parallel charging boards
Turn on charging system
Plug the large charge leads of the LiPos in to the charge cables and/or parallel charging board(s)
Plug the balance leads into the balance cables and/or boards.
I para-charge at a 1C rate and do not recommend charging above a 2C rate when para-charging large voltage and capacity LiPos. LiPos are volatile and with the increased amps and watts the potential for something going wrong and causing a fire increases.

ALERT: DO NOT plug multiple balance leads into the balance board connected to the charger. You will short out the board and cause damage and possibly fire. These balance boards are designed for connection of a single LiPo’s balance leads. In order to para-charge you will need a balance cable with multiple connectors wired in parallel. This balance cable is then connected into the appropriate slot on the balance board connected to the charger.

Follow the manufacturer’s recommendations for plugging in the balance boards and leads.

DO NOT USE MULTIPLE LEADS!
DO NOT USE MULTIPLE LEADS!

Safe way to para-charge.
Safe way to para-charge.

POWER SUPPLY

Now, we know what we need to charge the LiPos we have. We have a charger that will produce the power output for our charging needs. What else?

High output charging systems typically are not contained within one unit. You will have a charger and a power supply as stand-alone units. Okay, how do you pick a power supply?

Keep in mind that your charger will only output to the LiPo what your power supply can output to the charger.

Start with your LiPos. How many do you have? What is their cell count and capacities? Do you want to para-charge? We then take a look at your charger. What input power can it handle? What are its output capabilities? You will need a power supply that will handle the power output of the charger.

Let’s now put all of this together in an example:

My charging needs are as follows:

The largest LiPos in my arsenal are 6S 5000mAh LiPos and 6S 3800mAh LiPos

I have 4 of each
I want to be able to para-charge
I want to charge all 8 at the same time
I want to be able to charge two at a time at a 2C rate at the fly field

My home system is as follows:

LiPos:

I need 15.2 Amps @ 384 Watts to charge 4 6S 3800mAh LiPos at 1C

(4 x 3.8A = 15.2A @ 1C); (15.2A x 25.2V = 384W)

I need 20 Amps @ 504 Watts to charge 4 6S 5000mAh LiPos at 1C

(4 x 5.0A = 20A @ 1C); (20A x 25.2V = 504W)

Charger:

Charges LiPo chemistry type batteries
Handles a 6 cell count LiPo
Input Voltage Range: 10 – 30VDC (Volts DC)
2-channel – each channel capable of outputting 30 amps
Charge Power Handling: 1300 Watts

Power Supply (PS):

Input voltage: 100-240VAC (Plugs into wall outlet)
Output Voltage: 12VDC
Maximum Output Current: 47A
Total Output Power: 575W

I have two of these PS wired in series. When wired in series the Volts and Watts are doubled. The result is one power supply that produces an output of:

Output Voltage: 24VDC
Output Current 47A
Output Power: 1150W

Based on my needs this system gives me some head room and neither component is overloaded or working at its maximum. This system gives me the ability to comfortably para-charge 8 6S 5000mAh LiPos at the same time (4 on each channel).

Sample of my para-charging
Sample of my para-charging

ALWAYS FOLLOW THE MANUFACURERS RECOMMENDATIONS WHEN CHARGING LIPO BATTERIES!!!

NEVER CHARGE LIPO BATTERIES UNATTENDED!!!

This is a basic illustration and guide on choosing the correct charging system to fulfill your charging needs. The information provided in the above article is intended as a guide only and not a substitution for seeking the instruction and guidance of the manufacturer nor is it intended to cover every aspect of charging LiPo batteries.

As always, feel free to contact me if you have any additional questions regarding the care and maintenance of your LiPo batteries.

Happy flying and remember to always Fly Safe!

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