Charging RC LiPo Batteries For Maximum Life Maximum Fun!
Charging RC LiPo Batteries is a topic in itself. LiPo, LiHV, Li-Ion and LiFe batteries obviously have some very different characteristics from conventional RC rechargeable battery types. Therefore, charging them correctly with a charger specifically designed for lithium chemistry batteries is critical to both the lifespan of the battery pack, and your safety.
Before getting into the meat and potato’s of charging lipo RC batteries, here’s a short video I made going over the simple basics of the process on a typical 4 button type charger (the most common type of computerized RC charger).
Maximum Charge Voltage When Charging RC LiPo Batteries: 4.20 Volts Per Cell
As was covered on the RC LiPo ratings page, a 3.70 nominal voltage RC LiPo battery cell is 100% charged when it reaches 4.20 volts. Charging it over that cell voltage will shorten its life.
The cell phone industry did a study looking at the effect of LiPo battery cell fully charged voltages in relation to cycle life. These tests were done under ideal laboratory conditions, naturally at lower phone load discharge rates, and of course the 80% depth of discharge rule was obeyed! Here are the results:
- Charge to 4.10V gave over 2000 cycles.
- Charge to 4.20V gave about 500 cycles.
- Charge to 4.30V gave under 100 cycles.
- Charge to 4.40V gave less than 5 cycles.
Folks in the RC world have reported life cycle increases as well. One ongoing preference seems to indicate if you set your maximum charge voltage to 4.15 volts per cell (if your computerized charge gives you that option), you should be able to get more life out of your packs (if all other LiPo usage rules are religiously obeyed).
and more people are considering this 4.15 termination voltage (95% charge capacity) the sweet spot for both performance and cycle life for RC usage. I usually set my RC chargers to stop charging at 4.18 volts, just for a little reassurance they never top over 4.20 volts and perhaps a tad longer battery life.
Most good RC chargers give you that ability, so provided you have a good charger and you think it’s beneficial to set it lower than 4.20 volts per cell for your LiPo packs, you may want to consider it.
High Voltage LiPo Cells (LiHV): 4.35V Maximum Charge
High voltage LiHV 3S Battery has a nominal voltage of 11.4V and maximum charged voltage of 13.05V.
One caveat to this I should mention are the new generation of high voltage (LiHV) LiPo cells / batteries.
There are several LiPo manufacturers that are producing LiPo cells that can be charged as high as 4.35 volts (3.80V nominal) safely while maintaining a 500 cycle life (in ideal lab conditions).
Just keep that in mind as I’ll be covering conventional LiPo cell voltage charge numbers in this article, but the exact same principles apply to LiHV packs. You’ll just sellect a higher termination voltage if you charger doesn’t have a specific LiHV charge program built in that selects the higher voltage automatically.
Regardless, it is critical that you select the correct voltage or cell count when charging your RC LiPo batteries.
If you have a 2 cell (2S) LiPo pack you must select 7.4 volts or 2 cells on your charger. If you selected 11.1V (a 3S pack) by mistake and tried to charge your 2S pack, the pack will puff up, be destroyed and could even catch fire. Luckily, all the better computerized chargers out there these days will warn you if you selected the wrong cell count. I’ve been saved by that feature countless times when rushing.
All LiPo battery chargers will use the constant current / constant voltage charging method (cc/cv). All this means is that a constant current is applied to the battery during the first part of the charge cycle.
As the battery voltage closes in on the 100% charge voltage, the charger will automatically start reducing the charge current and then apply a constant voltage for the remaining phase of the charge cycle.
The charger will stop charging when the 100% charge voltage of the battery pack equalizes with chargers constant voltage setting (usually 4.2 volts per cell) at this time, the charge cycle is completed. Going past that to 4.3 volts will shorten battery life substantially as we have already seen.
Maximum Safe Charging Current When Charging LiPo RC Batteries: 1C
Selecting The Correct RC LiPo Battery Current. 1C Is ALWAYS Recommended. Here I’m charging 4500mAh pack, so I’m setting my charging current to 4.5 Amps.
Selecting the correct charge current is also critical when charging RC LiPo batteries. The golden rule here remains to be never charge a LiPo, LiHV, LiIon, or LiFe pack greater than 1 times its capacity (1C).
Battery voltage / cell count has no impact on charge current.
Regardless if the 4500 mAh example battery in the photo above was a 1S, 2S, or what it actually is, 6S; if charged at a 1C charge rate, all would be set to 4.5 Amps (4500 mA).
Going higher than a 1C charge rate will shorten the life of the pack.
over, if I was to charge this LiPo battery at a significantly higher than the 1C value, say an order of magnitude 10C (45 Amps), the battery would heat up, likely puff up, and may even start on fire.
Charging LiPo Batteries With Balancer
RC LiPo Battery Charging Balancing
I cover LiPo Battery Balancing in detail on my LiPo balancing page, but just wanted to quickly touch on this since it’s such an important topic when it comes to charging RC LiPo Batteries. The two are interconnected!
Again, please reference that LiPo balancing page if you don’t know what balance charging is. Balancing doesn’t change anything covered on this page in regards to charging RC LiPo batteries. The same voltage current settings are used regardless.
The one important point I wanted to mention on this LiPo charging page is you only need to balance charge LiPo’s if they have 2 cells (2S) or more hooked in series. If you are only charging 1 cell (1S) LiPo batteries, balancing is never done for the simple reason there is nothing to balance.
LiPo Battery Voltage State of Charge Capacity
This chart shows the relationship between LiPo battery open circuit (no load) voltage and the state of charge capacity (1S to 6S). Staying within the white region is the safe bet!
Never discharge a LiPo below 20% capacity! This is known as the 80% discharge rule that was covered on the LiPo battery page.
Charging a bunch of my RC LiPo batteries at once with a powerful RC charger. 80 Amps 2000 Watts of Charging Fun!
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Battery Charge Time Calculator
Use our battery charge time calculator to easily estimate how long it’ll take to fully charge your battery.
Tip: If you’re solar charging your battery, you can estimate its charge time much more accurately with our solar battery charge time calculator.
How to Use This Calculator
Enter your battery capacity and select its units from the list. The unit options are milliamp hours (mAh), amp hours (Ah), watt hours (Wh), and kilowatt hours (kWh).
Enter your battery charger’s charge current and select its units from the list. The unit options are milliamps (mA), amps (A), and watts (W).
If the calculator asks for it, enter your battery voltage or charge voltage. Depending on the combination of units you selected for your battery capacity and charge current, the calculator may ask you to input a voltage.
Select your battery type from the list.
Optional: Enter your battery state of charge as a percentage. For instance, if your battery is 20% charged, you’d enter the number 20. If your battery is dead, you’d enter 0.
Click Calculate Charge Time to get your results.
Battery Charging Time Calculation Formulas
For those interested in the underlying math, here are 3 formulas to for calculating battery charging time. I start with the simplest and least accurate formula and end with the most complex but most accurate.
Formula 1
Formula: charge time = battery capacity ÷ charge current
Accuracy: Lowest
Complexity: Lowest
The easiest but least accurate way to estimate charge time is to divide battery capacity by charge current.
Most often, your battery’s capacity will be given in amp hours (Ah), and your charger’s charge current will be given in amps (A). So you’ll often see this formula written with these units:
charge time = battery capacity (Ah) ÷ charge current (A)
However, battery capacity can also be expressed in milliamp hours (mAh), watt hours (Wh) and kilowatt hours (kWh). And your battery charger may tell you its power output in milliamps (mA) or watts (W) rather than amps. So you may also see the formula written with different unit combinations.
charge time = battery capacity (mAh) ÷ charge current (mA) charge time = battery capacity (Wh) ÷ charge rate (W)
And sometimes, your units are mismatched. Your battery capacity may be given in watt hours and your charge rate in amps. Or they may be given in milliamp hours and watts.
In these cases, you need to convert the units until you have a ‘matching’ pair.- such as amp hours and amps, watt hours and watts, or milliamp hours and milliamps.
For reference, here are the formulas you need to convert between the most common units for battery capacity and charge rate. Most of them link to our relevant conversion calculator.
Battery capacity unit conversions:
- watt hours = amp hours × volts
- amp hours = watt hours ÷ volts
- milliamp hours = amp hours × 1000
- amp hours = milliamp hours ÷ 1000
- watt hours = milliamp hours × volts ÷ 1000
- milliamp hours = watt hours ÷ volts × 1000
- kilowatt hours = amp hours × volts ÷ 1000
- amp hours = kilowatt hours ÷ volts × 1000
- watt hours = kilowatt hours × 1000
- kilowatt hours = watt hours ÷ 1000
Charge rate unit conversions:
The formula itself is simple, but taking into account all the possible conversions can get a little overwhelming. So let’s run through a few examples.
Example 1: Battery Capacity in Amp Hours, Charging Current in Amps
Let’s say you have the following setup:
- Battery capacity: 100 amp hours
- Charging current: 10 amps
To calculate charging time using this formula, you simply divide battery capacity by charging current.
In this scenario, your estimated charge time is 10 hours.
Tip: You can estimate how much battery capacity you need by using the inverse of this formula: amps × hours = amp hours.
Example 2: Battery Capacity in Watt Hours, Charging Rate in Watts
Let’s now consider this scenario:
Because your units are again ‘matching’, to calculate charging time you again simply divide battery capacity by charging rate.
In this scenario, your estimated charge time is 8 hours.
Example 3: Battery Capacity in Milliamp Hours, Charging Rate in Watts
Let’s consider the following scenario where the units are mismatched.
First, you need to decide which set of matching units you want to convert to. You consider watt hours for battery capacity and watts for charge rate. But you’re unable to find the battery’s voltage, which you need to convert milliamp hours to watt hours.
You know the charger’s output voltage is 5 volts, so you settle on amp hours for battery capacity and amps for charge rate.
With that decided, you first divide watts by volts to get your charging current in amps.
Next, you convert battery capacity from milliamp hours to amp hours by dividing milliamp hours by 1000.
Now you have your battery capacity and charging current in ‘matching’ units. Finally, you divide battery capacity by charging current to get charge time.
In this example, your estimated battery charging time is 1.5 hours.
Formula 2
Formula: charge time = battery capacity ÷ (charge current × charge efficiency)
Accuracy: Medium
Complexity: Medium
No battery charges and discharges with 100% efficiency. Some of the energy will be lost due to inefficiencies during the charging process.
This formula builds on the previous one by factoring in charge/discharge efficiency, which differs based on battery type.
Ez Peak Plus 8A NiMh/Lipo 4s ID Charger
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4S LiPo Compatibility with up to 8 Amps of Charging Power!
There has never been an easier or safer way to charge your batteries than the Traxxas ID® system. Just plug a Traxxas ID-equipped battery into the EZ-Peak® Plus 4s and press Start. that’s all there is to it! Traxxas pioneered this exclusive ID technology to eliminate complicated charger programming. The ID system detects which Traxxas ID-equipped battery you are using and automatically configures the charger’s settings for the optimal charge. An LED progress bar and audible alerts keep you informed while the advanced high-resolution peak detection delivers a perfect charge every time. One-button Storage Mode protects your LiPo battery investment by safely preparing the batteries for extended storage. With up to 8 amps of charging power, the EZ-Peak Plus 4s is the fastest, easiest, and most convenient way to charge your Traxxas batteries.
Power and Convenience
The faster your batteries charge, the sooner you’re back out having fun. No one understands this better than Traxxas which is why we outfitted the EZ-Peak Plus 4s with 8 full amps (75 watts) of charging power. The charger automatically detects the type of ID-equipped battery you are using and then configures the settings for the fastest charge possible. NiMH batteries charge faster than ever with 4 amps of charging power. LiPo batteries charge even faster with up to 8 full amps. A large 40 mm cooling fan keeps the temperatures down inside the charger for powerful charging sessions. A balance port is built into the charger for older-style LiPo batteries with external balance leads. The EZ-Peak Plus 4s combines EZ-Peak power with the safety of Traxxas’ exclusive ID technology in one convenient and easy-to-use package.
Quick Features on EZ-Peak Plus 4s Charger
- 75-Watt 8-amp max output
- Easy to use interface with charge progress indicator and audible alerts
- Automatically recognizes Traxxas ID® batteries for optimal charger settings
- Optimized for faster LiPo balance charging
- One-button LiPo storage charge protects your battery investment
- Advanced high-resolution peak detection delivers a perfect charge
- Built-in cooling fan
- Advanced Mode for full manual control of charger settings
- Built-in balance port for conventional LiPo batteries
- Charges 5-8-cell NiMH batteries
- Charges 2S, 3S, and 4S LiPo Batteries
EZ-PEAK PLUS 4S (#2981) SPECIFICATIONS
- AC Input: 100-240V, 50-60Hz, 1.2A
- Charge Current Range: Up to 8A
- Discharge Current Range: 500mA
- Current Drain for Balance Ports: 500mA
- NiMH Battery Cell Count: 5-8 Cells
- LiPo Cell Count: 2-4 Cells
- Net Weight: 365g
- Dimensions: 121 x 161 x 54 mm
Step 4: Begin the Charge (LiPo Is
Example: for the LiPo battery shown at the top of this instructable, a 1/20 C charge rate would be 1/20 x 1.3Ah = 0.065A. This is because the battery’s capacity, as stated on the label, is 1300mAh (read as mili-amp-hours), or 1.3Ah (read as amp-hours). So, a 1/20 C charge rate is 1/20 of 1.3, or 0.065A. A 1/10 C charge rate is 1/10 x 1.3 = 0.13A. Note that although some Smart chargers can charge at currents as low as 0.05A, many cannot charge at a rate lower than 0.1A. If you cannot set your charger to charge at a current as low as you’d like, simply choose its lowest setting possible, and carefully monitor the battery during the charge.
Additional Charge Setting Notes: recharging a LiPo below 3.0V/cell may require using a NiMh or NiCad charger setting on the LiPo batteries, as most Smart chargers have safety features which prevent a user from attempting to charge a LiPo which is below 2.5V/cell, as this can be dangerous if a standard charge rate is used. Since all we are after is setting a low (and safe) constant charge current to get the LiPo back up to a safe charge level, using a NiMH/NiCad setting is fine until we get the battery 3.0V/cell. WHEN USING AN NIMH or NiCad SETTING TO GET THE LIPOS ABOVE 3.0V/CELL, NEVER LEAVE THEM UNATTENDED. You should not leave them unattended because the NiMh/NiCad end-of-charge detection method is not compatible with Lithium based batteries, and if left on the charger until full, the end-of-charge state will never be detected and the LiPo battery will be overcharged until it (likely) catches fire and destroys itself.
Step 5: Next Charging Steps
Once above 3.0V/cell, you may optionally increase the charge rate to 1/10~1/5 C rate until the LiPos are ~3.7V/cell or higher.
You may stop holding the battery/constantly feeling it at this time, and place the LiPo in a fireproof container or LiPo-safe charge bag at this point, if desired.
Once above approximately 3.7V/cell, you may optionally increase the charge rate again to 1/2 C rate until they are full (4.20V/cell).
Step 6: Back to Regular Use
Now, use the batteries as normal. The lower the battery was discharged, the more permanent damage it will have. If you use the battery (ex: to fly an RC airplane), and it works ok, then you can safely assume that subsequent charges at 1C are again acceptable. Watch it over the next few cycles, however, and ensure the battery does not puff during discharging or charging. This would be an indication that the internal resistance of the battery is still too high for normal use and standard 1C charge rates.
In any event, due to having over-discharged the LiPos, you may notice a permanent decrease in their capacity (mAh) or maximum discharge rate (ie: they will likely have a reduced discharge C-rating, as noted by lower power output reduced performance), as the battery’s internal resistance will have been increased, and some permanent damage will exist. Additionally, the longevity of the over-discharged LiPo (ie: how many cycles you can get out of it) will have been reduced.
Let me know how this works out for you! Be safe!
Be sure to read my other articles here, especially this one:Parallel Charging Your LiPo Batteries
I also highly recommend this one, called The Power of Arduino.
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