A few different times I’ve been at the field flying with a few other like-minded FPVers to find out that really we weren’t all that like-minded. Apparently there are two definitive groups of people in this hobby; those who parallel charge and those who don’t (or should I say won’t?). Since I got involved with drones in 2012 I have heard both sides of the argument and with this article want to outline why I am in the parallel camp and how to parallel charge safely.
This article was submitted through the GetFPV Community Program by Duane Bradley. You can check out more of his content at his Facebook, Instagram, and YouTube.
Disclaimer: This article was written solely by a member of the FPV Community. Views and advice in this article are that of the author and does not necessarily reflect the opinion or views of GetFPV.
Those that aren’t comfortable parallel charging usually state the risk to the battery and/or fire as their reason. I agree that it can be risky however, with the proper precautions I don’t think it is dangerous. With that said, if I can charge in series I will. I do believe by series charging you get a more accurate charge and it will help the life of the battery last longer. For me personally, I series charge at home and only parallel charge when in the field trying to keep batteries charged for constant fly time.
The advantage of parallel charging is that you can charge multiple batteries in the same amount of time that you can charge a single battery and that you can charge up to 6 batteries per charger channel instead of one. This becomes extremely handy when field charging with only one charger.
How Does Parallel Charging Work?
First thing to understand is how a LiPo is ‘seen’ by a charger when it gets connected and how it charges the battery. When you plug in the main connector (XT60, XT30, etc) the charger will see the total voltage of the LiPo. When you plug in the balance connector the charger can now see and monitor the voltage of each individual cell. The charger can now send voltage into the battery (at the predetermined rate) to get the battery to the “full charge” voltage or 4.2 volts per cell (4s = 16.8 total and 6s = 25.2 total). At the same time cells that are higher than others are balanced to make them match the lowest cell ensuring that when the battery is fully charged all the cells are balanced and matched. The charger will send current into the battery until the difference between the charger voltage and the battery voltage is zero. It will then lower the amperage and maintain the battery at that set voltage of 16.8 or 25.2 while it continues to balance the cells and ensure that the resting voltage of the pack will stay at the set voltage once the charger is turned off.
Knowing this, let’s assume I am going to charge one of my 1050mah 6s LiPo. I would plug in the XT60 and plug in the balance lead. Most chargers will now give me a read out of the overall Voltage (as you can see in the photo this pack is at 22.58) and you can see the individual voltage of each cell* (4 cells at 3.77, 1 cell at 3.75 and 1 at 3.76). I would set the charger to charge at 1 C which I figure out by dividing the capacity of the Lipo by 1000 (1050/1000=1.05 amps) and then start the charger.
*Depending on your charger you will either find the individual cell voltage on the main screen or on a secondary screen.
Now that it is clear how the charger is going to send voltage to the pack we must also understand how connecting multiple batteries will affect how they charge. There are two ways of connecting multiple batteries together; series and parallel. Using the same 1050mAh 6s battery as an example, if we connect two of them in series we would have a 1050mAh 12s battery and if connected parallel it would be a 2100 mAh 6s battery. By connecting them in parallel the charger still sees a 6s battery and the charging characteristics don’t change, just the overall capacity changes.
By using a paracharge board we can combine up to 6 batteries together and have the charger charge them as 1 larger battery. To do this we simply adjust the charger to maintain 1C charging by calculating the new capacity of the parallel batteries. For example below see how the amperage increases as the number of batteries increase always using the formula we discussed earlier (Capacity/1000 = Amps from charger)
Capacity of 1 |
Number in Para | New Capacity | Formula | Amps from Charger |
1050 |
1 | 1050 | 1050/1000 | 1.05 |
1050 |
2 |
2100 |
2100/1000 |
2.1 |
1050 |
3 |
3150 |
3150/1000 |
3.15 |
1050 | 4 | 4200 | 4200/1000 |
4.2 |
*My charger doesn’t have 1/10th value so I round up to the next tenth
Seems simple but there are some very important precautions to keep in mind.
IMPORTANT PRECAUTIONS!!!
First, use a good quality paracharge board like the Lumenier Paracharge board that has breakers. This will protect you from the inevitable accident of plugging the wrong cell count battery in parallel with others or break the circuit to prevent further damage or fire when a surge is detected.
Second, only batteries of the same size and cell count can be charged together! Failure to do this could result in damaged batteries at best and increases the risk of an unwanted fire.
Third, the voltages of the batteries need to be similar. For example I fly three packs at the field. I run two of them down to 22.2V and crash early on one pack so it’s at 23.4V. You DO NOT want to put these on parallel charge together. The largest variance in voltage that should be parallel charged together is .1V-.2V.
Fourth, the battery cells should also be checked to ensure the health of the battery is good and that one cell out of the 6 isn’t way out of balance. I always use a battery checker or the charger to read the overall voltage and cell voltage to ensure they are all close before charging. If one cell is not balanced it could lead to the other parallel cells draining too quickly to try and balance the lower cell and damage and battery, all the batteries on the paraboard or cause a fire. Though it might be considered being too safe, I would even suggest comparing internal resistance of the batteries and trying to only parallel charge them if the resistance levels are close in value as well.
Fith, a personal precaution that I have always done with charging is charging in a safe location. I never charge in the house. I typically use my carport or in my shop. If in my shop, I charge in the center of the room on the concrete floor in case of fire and always have a fire extinguisher close at hand. I also never leave them unattended.
Sixth, I only parallel charge when I’m in the field so that I can keep flying throughout the day. When I’m at home and not in a rush, I charge each battery individually. This ensures that each cell gets a proper balance because each cell is being balanced individually instead of the number of cells connected being balanced by average.
Lastly, after flying a pack I let it rest for 15-20 minutes to cool down and come to its resting voltage before trying to recharge. This ensures an accurate voltage and cell reading so you can group it together with batteries of similar voltage.
In conclusion, parallel charging can be done safely if the proper precautions are followed! It will allow you to charge batteries faster and with less time spent connecting to and monitoring a charger. Be smart and cautious and you’ll be able to keep yourself in the air for a full day of flying with a limited number of batteries.
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Fear4fun_fpv (Duane Bradley) has been working with drones since building his first Freefly Cinestar Octocopter in 2012. Since then he has been working full time in film with the company Revered Cinema (www.rvrd.com) using drones and other stabilization equipment (Russian Arms, Remote Heads, Gimbals) on movies, TV shows and commercials like ‘Ghostbusters: Afterlife’, ‘Jurassic World 3’, ‘Lost in Space’, ‘Batwoman’, ‘Flash’ and many more.
Why exactly must the battery capacities be the same?