BU-401a: Fast and Ultra-fast Chargers

Learn about the good and bad on ultra-fast charging

Ultra-fast Chargers

Nowhere is ultra-fast charging in bigger demand than with the electric vehicle. Recharging an EV in minutes replicates the convenience of filling 50 liters (13 gallons) of fuel into a tank that delivers 600kWh of energy. Such large energy storage in an electrochemical device is not practical as a battery with such a capacity would weigh 6 tons. Most Li-ion only produces about 150Wh per kg; the energy from fossil fuel is roughly 100 times higher. (See BU-1007: Net Calorific Value).

Charging an EV will always take longer than filling a tank, and the battery will always deliver less energy per weight than fossil fuel. Breaking the rule of law and forcing ultra-fast charging adds stress, even if the battery is designed for such a purpose. We must keep in mind that a battery is sluggish in nature. Like an aging man, its physical condition becomes less ideal with use and age. So is the ability to fast-charge.

Whether it’s an EV, e-bike, a flying object, a portable device or a hobby gadget, the following conditions must be respected when charging a battery ultra-fast:

  1. The battery must be designed to accept an ultra-fast charge and must be in good condition.
  2. Ultra-fast charging only applies during the first charge phase. The charge current should be lowered after the battery reaches 70 percent state-of-charge (SoC).
  3. All cells in the pack must be balanced and have ultra-low resistance. Aging cells often diverge in capacity and resistance, causing mismatch and undue stress on weaker cells.
  4. Ultra-fast charging can only be done under moderate temperatures, as low temperature slows the chemical reaction. Unused energy turns into gassing, metal-plating and heat.

An ultra-fast charger can be compared to a high-speed train (Figure 1) traveling at 300km per hour (188 mph). Increasing power is relatively simple. It’s the track that governs the permissible speed of a train and not the machinery. In the same manner, the condition of the battery dictates the charging speed.


High Speed Train
Figure 1: Ultra-fast charging can be compared to a high-speed train.
Powerful machinery is easy to build, but it’s the track that limits the speed.
 

A well-designed ultra-fast charger evaluates the condition of the “chemical battery” and makes adjustments according to the ability to receive charge. The charger should also include temperature compensations and other safety features to lower the charge current when certain conditions exist and halt the charge if the battery is under undue stress.

A “smart” battery running on SMBus or other protocols is responsible for the charge current. The system observes the battery condition and lowers or discontinues the charge if an anomaly occurs. Common irregularities are cell imbalance or the need for calibration. Some “smart” batteries stop functioning if the error is not corrected.

The maximum charge current a Li-ion can accept is governed by cell design, and not the cathode material, as is commonly assumed. The goal is to avoid lithium-plating on the anode and to keep the temperature under control. A thin anode with high porosity and small graphite particles enables ultra-fast charging because of the large surface area. Power Cells can be charged and discharged at high currents, but the energy density is low. Energy Cells, in comparison, have a thicker anode and lower porosity and the charge rate should 1C or less. Some hybrid Cells in NCA (nickel-cobalt-aluminum) can be charged above 1C with only moderate stress.

Apply the ultra-fast charge only when necessary. A well-designed ultra-fast charger should have charge-time selection to give the user the option to choose the least stressful charge for the time allotted. Figure 2 compares the cycle life of a typical lithium-ion battery when charged and discharged at 1C, 2C and 3C rates. The longevity can further be prolonged by charging and discharging below 1C; 0.8C is the recommended rate.

Cycle performance of Li-ion with 1C, 2C and 3C charge and discharge

Figure 2: Cycle performance of Li-ion with 1C, 2C and 3C charge and discharge.
Charging and discharging Li-ion above 1C reduces service life. Use a slower charge and discharge if possible. This rule applies to most batteries.

Summary

All batteries perform best at room temperature and with a moderate charge and discharge. Such a sheltered life style does not always reflect real world situations where a compact pack must be charged quickly and deliver high currents. Such typical applications are drones and remote control devices for hobbyist. Expect a short cycle life when a small pack must give all it has.

If fast charging and high load requirements are prerequisites, the rugged Power Cell is ideal; however, this increases battery size and weight. An analogy is choosing a heavy diesel engine to run a large truck instead of a souped-up engine designed for a sports car. The big diesel will outlive the light engine even if both have identical horsepower. Going heavier will be more economical in the long run. Table 3 summarizes the charge characteristics of lead, nickel and lithium-based batteries.
 

Type Chemistry C rate Time Temperatures Charge termination
Slow charger NiCd
Lead acid
0.1C 14h 0ºC to 45ºC
(32ºF to 113ºF)
Continuous low charge or fixed timer. Subject to overcharge. Remove battery when charged.
Rapid charger NiCd, NiMH,
Li-ion
0.3-0.5C 3-6h 10ºC to 45ºC
(50ºF to 113ºF)
Senses battery by voltage, current, temperature and time-out timer.
Fast charger NiCd, NiMH,
Li-ion
1C 1h+ 10ºC to 45ºC
(50ºF to 113ºF)
Same as a rapid charger with faster service.
Ultra-fast charger Li-ion, NiCd, NiMH 1-10C 10-60 minutes 10ºC to 45ºC
(50ºF to 113ºF)
Applies ultra-fast charge to 70% SoC; limited to specialty batteries.

Table 3: Charger characteristics. Each chemistry uses a unique charge termination.
 

Simple Guidelines Regarding Chargers


Last Updated 2016-05-04
 

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Comments

On June 13, 2012 at 7:19am
pakopako wrote:

The URL tab title reads: “Fats and Ultra-fast”

On June 13, 2012 at 9:47am
Cadex Electronics Inc. wrote:

Thanks pakopako, just corrected that.

On July 11, 2012 at 1:38pm
ramon leigh wrote:

I have always found comparisons between fuel weight (like gasoline) and battery weight to be fraudulent. A gallon of gasoline contains around 33kWhrs of energy, but most of that is released in the form of heat (and light). The kinetic energy released is what powers the car and accounts for around 25% of the gasoline’s total energy (8 kWhrs). Range extending gas powered engines (as in the Chevy Volt) produce roughly this amount of juice per gallon (good for around 35 miles of driving). Gas may weigh less than a battery (which actually is not a fuel, but an energy storage container) but one cannot power a car from the fuel itself- to do that requires a very heavy gasoline engine, fuel tank, cooling and exhaust system, etc, etc. which can easily weigh over
1000 pounds.  If one is worried about weight, then one needs to compare the weights of the entire propulsive systems required by the fuel being considered. Actually, weight is not as important as people think when regen is available, which all electric cars have.

On September 1, 2012 at 3:18pm
Jullian wrote:

Thanks, I enjoy BU articles to learn how things ACTUALLY work.  But there’s a couple of errors here ... the graph is the wrong one, and “A 1C charge and discharge cycle causes the capacity drop from 650mAh to 550mAh after 500 cycles, reflecting an 84 percent decrease. ” should read “A 1C charge and discharge cycle causes the capacity drop from 650mAh to 550mAh after 500 cycles, reflecting a decrease to 84 percent. ”  (It’s not an 84% decrease, it’s a 16% decrease).

On September 7, 2012 at 11:25pm
Jignesh Patel wrote:

U mean to say that battery life will increase if we use the slower charger than its capacity. I have 1200 mA battery and i am using 800 mA charger so can i use 350 mA charger for my battery ?

On October 4, 2012 at 3:33am
Andrew Ashton wrote:

Unless I am totally off the mark, the description:

quote
Figure 1 compares the cycle life of a lithium-ion battery when charged and discharged at 1C, 2C and 3C. A 1C charge and discharge cycle causes the capacity drop from 650mAh to 550mAh after 500 cycles, reflecting a decrease to 84 percent. A 2C accelerates capacity fade to 310mAh, representing a decrease to 47 percent, and with 3C the battery fails after only 360 cycles with 26 percent remaining capacity.
endquote

does not match the figure.

The figure shows 4 plots (with no key!) and the cpacities start at around 1000mAh, not 650mAh

On October 5, 2012 at 9:19am
Cadex Electronics Inc. wrote:

Andrew, thanks for pointing out the error. We had the wrong chart displayed and I have added the correct one.

On December 26, 2012 at 7:33am
ANYONE wrote:

Can i charge a 150mAh battery with a 420mA/4,2V charger?

On February 6, 2013 at 3:18pm
Walker wrote:

@ANYONE:  A charger that large for a battery that size would be considered an “ultra-Fast Charger.”  Depending on the age of the cell and the particular chemistry, you may be able to get away with this a number of times.  Eventually, your internal impedance of the cell will increase and could cause an excessive heat buildup within the cell (P=I ^2 * R) which, if not dissipated properly, could cause a breakdown of materials within the cell and a thermal event. 

Also, rapid charge/discharge of standard lithium cells generates significant damage to the SEI layer within the cell (Wikipedia “SEI Layer”) which, when reforming, is an exothermic chemical process…not good.  This could also create an unsafe thermal event condition.

In short:  Don’t do it.  If you have to, be VERY careful and put the cells in a fireproof/nomex bag designed to contain batteries if/when they catch fire…they eventually will.

On August 27, 2013 at 8:32am
Pooran Chand wrote:

I want to design ultra fast charger for my minor project…Which battery can I use for ultra charging?
Can you provide some other relevant information about it….

On August 6, 2014 at 2:13pm
teslark wrote:

fast charging radically lowers the lifetime of batteries . this is ultimately a futile exercise in milking out the charge/minute efficiency of a system not yet ready to practically handle high speed charging on a retail industrial basis.

the bottom line is that our battery technology is not ready yet for fast charging.

major strides in battery tech are on the horizon, and when they arrive, they will truly usher in a revolution in electric vehicle production.

the first true revolution will be observed as small 2 stroke 50cc scooters go nearly extinct as that segment gets entirely replaced by electric 2 wheelers. this trend is already happening in china, but it has yet to take in the rest of the world. you will know the battery revolution has arrived when there aren’t any little gas mopeds around anymore at all, because the electric ones provide such superior performance that no factories can profiteably produce the small 2 stroke moped engines anymore.

On September 14, 2014 at 4:21pm
mahmood wrote:

very good

On October 15, 2014 at 3:14pm
akselic wrote:

Does all this information also stand true to the “boom” of superfast charing that we are seeing in several smartphones these days or are they using different technology? I’m interested because considering that before starting to show loss of battery capacity, the lithium-ion batteries used will last a good 2-4 years (unless excessively charged all the time. Will the superfast charing introduced in models such as the One+ One or Nexus 6 mean that batteries will show a significantly shorter lifespan? Will the batteries start to heat up after being fast-charged for 1½ years? Are there safety mechanics that make sure they won’t overheat and cause potentially big issues?

On November 19, 2014 at 12:10pm
Masheen wrote:

How does Qualcomm’s Quick Charge 2.0 affect battery longevity?

Qualcomm’s had UL test and certify this product before being released.  New flagship cell phones with this tech come with only this type of charger in the box.  They assume that everybody will use the charger provided on the corresponding device.  Have they developed a method that doesn’t significantly affect battery life when using it daily?

Does Qualcomm rely on users upgrading to a new device before the batteries get destroyed? Or have they modified the Li-Ion battery and/or charging tech so that the life of the battery is not drastically impacted?

On January 8, 2015 at 4:46am
Bunu Zahra wrote:

What are the effects of fast and slow charging to a battery

On January 21, 2015 at 7:04am
Dave wrote:

I second Masheen’s question. Any insight on how Qualcomm’s Quick Charge 2.0 will effect battery longevity?

On February 3, 2015 at 6:09am
ravishankar b.k. wrote:

I am sure it will be helpful.

On February 3, 2015 at 6:11am
ravishankar b.k. wrote:

I sure it will be a great help.

On February 3, 2015 at 6:18am
Danielus wrote:

http://www.androidauthority.com/quick-charge-explained-563838/

Apparently, basically this “technology” does is provide more amp/power by the charger, so I think the cycles of the battery and capacity is also reduced over time. Too good to be true, it’s just marketing…

On March 1, 2015 at 12:37pm
Masheen wrote:

I think we can deduce that the batteries in our phones only get a numbered amount of cycles in their life, and the rapid charging technology would only impact its life by speeding up these limited cycles.

There is sufficient information supporting the technology behind the quick charge which states that the battery’s temperature is carefully monitored by software and overheating will not be a cause of battery degradation.

A good comparison is: just like 4G allows us to use our data plans faster, Quick-Charge allows us to use our battery’s cycles faster. However, if we stick to one cycle per day, it will be no different than the slower chargers in terms of battery health.

On March 21, 2015 at 8:01am
Troy Giorshev wrote:

Great article, typo on the third last point under simple guidelines.  “Foe nickel” is written instead of “for nickel”

On April 11, 2015 at 9:13am
Nick wrote:

Has anyone heard of the silex chreos? How on earth is that possible? Are they using polymer batteries?

On October 4, 2015 at 5:47pm
Kristian wrote:

My guess is - super capacitor in conjunction with a battery pack. Use the kV charger (say at 11 kV) to dump a huge amount of power into the super capacitor. Advantage is very fast charge and due to low internal resistance - a low heat generation (and higher efficiency). Disadvantage with a super capacitor is that it eventually looses its charge over time - so you cant leave the car standing for a month - where as batteries will hold their charge.

Put both together and you have a solution with a small weight/space penalty.

On October 25, 2015 at 5:00pm
DOROTHEA SCHALL wrote:

Would like to try superb FASTER CHARGER

On November 1, 2015 at 3:35pm
anthony m velleca wrote:

I want to try it

On December 19, 2015 at 10:47am
Bill Moore wrote:

What would be required to build a fast-charge 36 or 48V electric bicycle battery in terms of not only the cells used, presumably li-ion, but also the BMS and the battery charger?

On February 19, 2016 at 1:19pm
Jeff wrote:

More an more phones are coming with Qualcomm Quick Charge 2.0 or 3.0 capability.  All I want to know is, will using Quick Charge 2.0 technology with a compatible device signficanly lower battery life/capacity over time compared to using the standard, slower charges to charge the device?  And is this answer a theoretical answer or an answer based on actual tests?

On March 26, 2016 at 9:17pm
Manaf wrote:

Would you please suggest Fast charger for LTO battery bank ( 580V 150Ah) ?

On May 24, 2016 at 12:12pm
Matteo Croce wrote:

Does this apply to Qualcomm Quick Charge too?