LiPo Batteries Guide
The little "LiPo ABC" for everyday life
Read everything carefully, please!
Lithium polymer (LiPo) batteries are becoming ever more powerful and at the same time ever lighter. This is clearly demonstrated by the new LiPos coming onto the market. However, it cannot go on indefinitely and as it is in life, the good and the bad always balance each other out and so the new LiPo batteries are becoming much more sensitive again. The correct handling of the batteries will be significantly more important in the future and this has prompted us to compile a small "guide" for handling LiPos.
How to use LiPo batteries correctly?
The use of a LiPo is optimal if it is used as often as possible (cycles). The following applies: Do not save on charging cycles, because fast charging the LiPo several times is considerably more efficient than spreading these cycles over many packs. The LiPo appears significantly fresher over the entire cycle duration of (normal) 150 to max. 200 cycles! Age damages more than constant use. Provided you stay within the specifications of the battery. Advantage: One does not buy more, but earlier a new Packs, which experienced besides a manufacturing / technology push.
Basic control
To basically check a LiPo battery, the so-called cell voltage/difference and the /height can be used. When a battery is delivered, the difference should not be more than 0.05V (50mV) or not less than 3.6V/cell. If these values are above, the battery should be claimed at the dealer as soon as possible! You can check the voltages with the balancer display in the charger or alternatively with a LiPo checker. Only, the LiPo-Checker should be checked for correct function beforehand, so that the measured voltage is as accurate as possible. A deviation of up to 0.03V (30mV) is unfortunately normal with many LiPo checkers. If you have a digital multimeter, you should trust its display values for voltage measurement.
Info about the LiPo Checker
Each LiPo type has its "own" voltage curve ... only... but the LiPo-Checker does not know this. Here "only" 50mV/cell (0,05V/cell) already correspond to a filling difference of over 20%! The Checker is a universal instrument and not a measuring instrument tuned to this one LiPo type. The LiPo-Checker should only provide a first indication with a very rough filling accuracy. Much more important is the voltage display, not the percentage value, which should be ignored because of the considerable inaccuracies. With it, you should generally only check three states at idle: Full: >4.15V/Hz - Idle: <3.6V/Hz - Voltage differences: >50mV/Hz would be critical.
The first charges
Only use chargers with integrated balancer and only use the "CC-CV" charging method for charging. As charging current 1C (corresponds to a charging current of 1x the capacity for a 2200mAh battery, i.e. 2.2A) has proven itself for the beginning, after a few charges (cycles) this can then be increased to the maximum charging rate released by the dealer / manufacturer.
Charging when the LiPo is very cold or warm
Of course, the battery can also be charged quickly at temperatures that are warm to the touch (max. 40°C) or cold (minimum 10°C)! However, the highest charge current should never be set to the maximum possible C-rate. If the battery is released e.g. with a maximum charge rate of 4C, then in this case max. 2-3C should be selected.
If the battery is really hot (clearly over 40°C), it makes sense to let it cool down a bit first (it would be important to analyze the drive additionally or to use a battery with a higher C-rate).
If the battery is cold below 10°C, charging rates below 1C (typical: 0.2C to 0.5C) would be advisable. However, as the temperature drops, it should be noted that the transition from 4C to below 1C is not sudden, but equally smooth. Therefore, we recommend significantly reducing the charge current at cold temperatures as low as 15°C.
Balancing
Balancing means equalizing (balancing) the battery voltage within a battery pack. It also increases the operational reliability of the charging process and at the same time ensures that all batteries have the same state of charge. This is not necessary during use/discharge, i.e. in the model, but is indispensable during charging. Even during a test discharge, balancing is not necessary, rather even counterproductive. Likewise when a LiPo is brought to storage voltage. Good chargers start balancing the individual cells only after a certain voltage threshold (e.g. 3.8V / cell). Charging with a constant current also protects the batteries, so it makes sense for the balancer to start balancing only at the transition from constant current (CC) to constant voltage (CV) charging (phase). Some chargers also allow the user to set this voltage. If this is possible, we recommend setting a value of 4.0V/Hz or 4.1V/Hz.
However, this has a disadvantage because balancing prolongs the entire charging process. The charger will only report "done" when all cells of the battery pack are charged to 4.2V and if one cell is still lagging behind it will discharge the others until they are equal.
Tip: Therefore, when purchasing a charger, make sure that the highest possible balancer current is possible. An efficient balancer should actually manage 1/20 of the charge current to balance the individual cells and the lowest charge current (CV phase) should be at a 1/10 to max. 1/15 of the charge current (adjustable) until the ready message appears ("1/10" example with 5A charge current: at 0.5A charge current the charger would report "FULL" with balanced cells!).
Internal resistance (DC-Ri) display for chargers.
With this value applies: The lower the more voltage the LiPo delivers under load (in the vernacular: more pressure). Only the measuring methods are so simple and inaccurate (with very few exceptions) that only a relative comparability (tendency) over time (cycles) is given here. Please do not make the mistake and consider these values absolute. Only the values of the same charger type can be compared! You must pay attention to the temperature and the degree of charging, which have a very decisive influence on the DC-Ri values!
Discharging correctly or how to have fun with your battery for a long time
Often one hears and reads that the LiPo should be spared during the first discharges. But it is much more important not to overload the battery - no matter if in the first cycles or later!
But how do you recognize the overload of a LiPo battery?
This is easier than you think. An overload can be easily detected at the following four points:
- Under load, there are voltage drops of less than 3.3V per cell.
- The LiPo battery is extremely hot after discharge. The LiPo must not get warmer than 60°C under any circumstances - this damages the chemistry permanently!
- The capacity of the battery is fully utilized. Use of more than 80% of the nominal capacity is not reasonable.
- The no-load cell voltage (no load on the LiPo or open high current connections), should never be or fall below 3.6V.
In summary:
Never discharge the battery lower than 3.3V per cell under load, even for a short time. In idle state (measured without load), the voltage per cell should not be below 3.70V for a longer time. Deeper discharge will destroy the battery. Do not rely on the safety shutdown of the controller if it switches off later. First feel your way to the maximum flight/drive time with only very short flights/drives and then measure the cell voltage bit by bit and then be sure to set a stopwatch in the transmitter. Leave about 20% remaining capacity in the battery. After use (empty battery), you should be able to charge about 80% of the rated capacity. Your charger will display the recharged capacity at the end of the charging process.
Attention: Due to the high performance of the SLS batteries, the voltage level remains almost stable until the end of the discharge.
And if it gets cold (below 18°C)?
LiPos become "slower" (more highly resistive) in the chemical reaction at cold temperatures and therefore it seems as if they no longer have any power. Basically, as the temperature drops, the performance continuously decreases and the discharge rate must take this into account. If you overlook this, you will very quickly overload the battery (voltage drops too low) and damage its life expectancy.
If a battery is below 18°C, the recommended discharge rate drops significantly to the otherwise possible C-rate. If we approach 10°C, then it is already below 50% of the otherwise possible C-rate! In addition, it must be expected that the full capacity is no longer available and the flight time is noticeably reduced. In the end, at these temperatures, the batteries can really only be used as receiver/transmitter power supply. As a drive for a model, the necessary gentle discharge rates are then too low.
If you still want to work with high current loads (more than 5C), it is essential to preheat the batteries. There are various solutions for this. The most common solution is preheating in a LiPo heater. The ideal preheating temperature has been found to be a good hand-warm, i.e. approx. 35°C to 40°C. The preheating time should be at least 90 minutes so that the heat is evenly distributed inside the pack.
Tickle the maximum power out of the LiPo battery.
High current load is defined as currents of more than 5C in LiPo batteries! Therefore it is important to know a few basic conditions around the high current load of the LiPos. In general - if the battery temperature is below 18°C, preheating is mandatory! If the load is within the continuous load capacity of the battery, a temperature of 30°C to 35°C is optimal. If it is above 18°C (from 20°C, summer temperatures), preheating is not necessary. In principle, however, only about 70% of the capacity should be removed at such loads. If the withdrawal capacity is monitored by telemetry, up to 85% (recommended: 80%) can also be withdrawn. It is important that the cell voltage does not drop below 3.3V during load peaks (see discharge rules from above).
In case of overload use, i.e. if the continuous load capacity of the battery is significantly exceeded (even for a short time) (sometimes up to three times the max. C-rate!), a few more rules must be observed in order not to unnecessarily shorten the life of the battery.
A LiPo battery develops its highest performance when it is about 40°C warm. Therefore, a preheating of the batteries (even in summer) is mandatory and ensures that the battery starts with maximum performance. A preheating temperature of 38°C - 45°C has proven to be optimal. It is also important that the battery's capacity is not fully used! It is beneficial for the battery life if only about 50% of the nominal capacity is used. Single cell and capacity monitoring via telemetry is especially useful and highly recommended in these load regions.
Store lipos correctly
Storing a LiPo at the correct battery voltage ensures that the battery ages as little as possible. It is important to note that incorrect use (see discharge rules above) will damage the battery much more than correct storage!
Cool and dry is a prerequisite and the LiPos should not be stored fully charged. Not even if it is only over one night. The nights add up gladly and lead in the sum to a damage of the accumulator, thereby one differentiates:
Short term: if you want to be spontaneously "ready for use" with your LiPos, pre-charge the battery to about 4.1V cell voltage (ideal in the LiIon program) and then store it safely and securely. Then, just before use, fully charge in the LiPo program (takes only a few minutes) and off you go. If you can do without about 5% to 8% of the useful capacity, you are welcome to start immediately.
Long-term storage: For longer storage (from two days), a cell voltage of 3.65V to 4.0V is perfectly fine from the LiPo's point of view. This is also the reason why the (average) 3.80V to 3.85V per cell can be read again and again. However, from an energy point of view, these (here it would be 40% to 50%) are not entirely unproblematic. The following applies: the less energy there is in the battery, the less the stored energy has to be dissipated in the event of a supercapacity (short circuit). Unfortunately, the energy content from 3.8V/Z is so high that in the event of a fault (supercurrent) of the battery with a total self-destruction is to be expected. This results in extremely high temperatures which can cause secondary fires (ignition in the battery's surroundings)!
Therefore, a storage voltage of 3.70V - 3.75V (measured in no-load operation, it depends on 0.05V!) would be much more suitable. This corresponds to an energy content of about 10% - 20%. In this case, the storage safety of the LiPos is also increased and in terms of energy it no longer contains the power to cause fire damage in the event of a fault. We recommend a LiPo stored in this way to check its voltage level briefly every month and recharge if necessary, if the voltage approaches 3.65V / Z!
Tip for chargers without adjustable store voltage: Store in the "LiIon-Store" because here mostly 3.75V/Z (or 3.70V/Z) are preset!
Dispose of LiPo batteries correctly
LiPo batteries also do not last forever and show their end with a significant drop in performance. But that doesn't have to mean the end of the battery's life cycle, because if it no longer has enough power for a high-current application, it can still be used in a "secondary application" that is less power hungry. Perfect, then, for youth development. Its entry-level models usually develop much less power hunger than "full-grown" models.
If everything is too late, then the battery must be disposed of correctly and professionally. The first step is to label it so that the battery type is easy to read. Then discharge it well below the storage voltage. Ideally, it should be well below 3.6V per cell in no-load operation (the battery is as good as empty in terms of charging). When discharging with the charger it may also be 3V/Z. If then all cables !individually! directly at the housing are cut and insulated with tape, bring it to the dealer of trust or give it to any battery collection point (e.g. recycling centers).
Gerd Giese
This Lipo Guide was kindly provided to me by Stefan Klee
(SLS - StefansLipoShop GmbH).
Status: 04/2015 © V1.7
© http://stefansliposhop.de
© http://www.elektromodellflug.de
Lipo cutoff voltage
A question that comes up again and again, how do I set the Lipowarner or the cutoff voltage.
I would like to write here now only about crawlerspecific things since it is here also only about these vehicles. Most people here change their controller/BEC to a HW1080 Quicrun or one of the Axe foc series. Here you will find the item "Cut-off voltage" with different values. ""cutoff voltage" with different values. This setting protects our LiPo from undervoltage, which means we are informed that the battery has reached a certain discharge and we should now please change this or please turn off the vehicle.
The values here have a default of 3.0V - 3.2V - 3.4V and off.
Attention never use the value switched off for LiPo's, this setting is only intended for NiMH batteries, and only for them.
For normal crawler operation, the value of 3.2Volt is very safe, it means with these controllers that when our vehicle reaches this value, it massively cuts our performance (the vehicle becomes extremely slow) and so tells us, please take the vehicle to the driver and replace the battery.
It does't mean, drive me further until I stop!
Who can not set a cutoff voltage on his controller should definitely install a Lipowarner. This beeps quite loudly when a preset voltage is reached. Again, when you hear the beep, bring the car back and change the battery.
A Lipowarner does not switch off our controller!
But what about the "bashers" among the crawler drivers?
Who likes to "abuse" his crawler and likes to drive the vehicle with fast engines under maximum load, I recommend 3.4V cutoff voltage. Due to the quite high load of e.g. a 3300KV motor, 160Amps or more will flow if you pull your finger all the way. The motor really sucks the battery at this moment. To protect our battery, the somewhat higher protection is then useful.
Why can't I drive the battery until it runs out?
I see that quite often that people torture their battery until the car turns off completely, so after the motto, oh a little bit still goes there.
Question: Would you do the same with an airplane what circles 100m above you? Or rather watch the battery warning that you land to not see the model crash?
I think that answers the question!
Which Lipos should one buy now where?
LiPo's are now available from every manufacturer and in every store. But the quality differences are not to be despised. On the whole, buy locally, so at the dealer of your confidence. The dealer should always check the LiPo before he hands it over to you, as far as cell drifting is concerned. If he simply hands you a packed and glued battery, you should ask him to check it beforehand. If he does not or refuses to do so, look for another dealer.
GensAce is a well known and good lipo brand that offers very good LiPo's on the market. There are also some other companies.
SLS - StefansLipoShop specializes in batteries and chargers, the advice here is very good. I myself use batteries from GenAce, SLS and Arrowmax and have had no problems with them, but I also treat them with love!
How do I charge safely?
How to do this from the technical side is already explained in detail in the LiPo ABC.
Attention:
LiPo's never and I mean never completely unattended charge.
If the LiPo times, which we do not want to hope, has a defect and burns, which burns down your house!
Always charge the LiPo in a Lipobag/Liposafe or in special Lipo boxes. You can buy these ready-made or build them yourself from sheet steel boxes (instructions are available on the net). When using ammunition boxes, care must be taken that they are airtight and holes must be drilled here so that in case of fire the pressure can escape.
If a LiPo should ignite, it burns only inside the box or the lipo pocket.
Wichtiger Hinweis
The information is only recommendations and no binding security is given. I assume here no liability for damages or even errors on this page!
The right charger
The eternal question, which is the right charger? What must it be able to do, how many watts must such a charger have and how much does it cost.
It makes sense that our charger can charge 1C, the capacity of our Lipo. For this you should look at a small formula.
Our 3S Lipo battery has a capacity of 5500mh. We want to charge the battery with 1C, so with the amperage that corresponds to 1C. That means I set the charger to 5.5A. The formula for this would be:
11,1V x 5,5A = 61,05Watt (3S Lipo with 5500mAh)
If we really want to charge with 5,5A the charger must have at least 61Watt.
In crawling, chargers with 80W per output will always serve their purpose. If you always have 2 or more batteries with you, you should think about a dual charger, i.e. a device with more than one port. If we assume the recommended charge rate of 1C, i.e. the charge current is the capacity of the battery, it takes a little less than an hour to charge a battery.
Since we crawl here and therefore with 3S batteries is actually end I would like to remain with the recommendation of chargers also in the affordable range.
The company RC Plus offers with the Cube 80 Duo an inexpensive dual charger with 2x 80 watts which is more than sufficient in the crawler area. If you are only looking for a simple charger and do not want to spend a lot of money, the Power Plus 80 from RC Plus is also a good choice. For all those who want more and also want to charge 4S - 6S, let you briefly advised, the offer is really quite extensive. In the professional field, the devices with external power supply quickly cost 400 euros.
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