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Action Sport Games - Lithium Polymer Batteries (7.4 and 11.1v 1000mah) Lithium Polymer or LiPO (not to be confused with a popular form of cosmetic surgery) batteries are the next generation of power source for the radio controlled modeller. Offering up to 350% more energy than a conventional NiCAD battery, for up to 30% less density of the same capacity, they are the obvious choice for the electric aeroplane or helicopter enthusiast where high power output with low weight is essential for good flight characteristics. They've been around as early as 1996 (certainly in the Lithium Ion format), so why is it us Airsofters seem to be a little slow on the uptake? Could it be the rumours that these portable power sources are dangerous high explosives if handled incorrectly? Possibly, but then doesn't seem to stop the R/C folk from using them, often with far higher current demands than most of our Airsoft guns will ever need... dEFCONAirsoft were recently provided with two new LiPO packs from ASG (Action Sport Games) to review, and having never used this battery technology before, we felt it was time to put them to the test! (Note: I've tried to keep the preface to this article as short yet detailed as possible - by no means have I covered all aspects of Lithium Polymer batteries, only the information you need to know. Please see the footnotes at the bottom of the text for continued recommended reading).
The two most common voltages, certainly for Airsoft use are the 7.4v and 11.1v packs (2 and 3 cell respectively), well hang on a minute you might think, 7.4v? Surely I'm going to get a slower rate of fire than my current 8.4v pack, right? Wrong... and we'll find out why later. For this review, we will be looking at ASG's 7.4v 1000mah pack, and their 11.1v 1000mah pack, which could be considered direct replacements for 8.4v and 12v set-up's of the NiMH equivalent. In comparison, we will be testing the 7.4v pack against the highest capacity mini battery currently available the 8.4v 1600mah Intellect pack which is used in huge variety of Airsoft models, namely where space is a restriction (usually guns without a solid stock) - in this case the Classic Army MP5-SD3 will be our test piece. Ohms, Amps and Volts... Ok, so I'm going to try and keep this very simple, mainly because up until today I didn't fully understand this myself...! The first thing we needed to do before testing these batteries, was find out how much current does any given AEG draw when fired. You can get theoretical results if you know the resistance of the motor (measured in ohms) in your AEG, but the chances are this information is usually difficult to find from the manufacturer, so you're doing to need to work this out yourself. Also, you need to take into consideration the rest of the electrical circuit, including the wiring, fuse, connectors and switch contacts all have an influence into the 'resistance reading' of our AEG. I'll cover this in another article, because quite frankly it deserves one all to itself! ...Right, so moving on - we've worked out that our electrical circuit in our AEG has a resistance of 0.5 ohms (this is measured at the battery end takes into account wiring, trigger contacts etc). So, to work out the theoretical current drain of your AEG you simply take the voltage of the battery applied, and divide it by the resistance of the electrical circuit, in this case, we'll use a standard 8.4v pack: 8.4v / 0.5ohms = 16.8 amps
Now for most of you these figures will be unimportant and what you're really looking for are statistics on ROF (rate of fire - in rounds per minute) and number of rounds you can get out of a pack, we'll test this later on. But for those of you who've not been paying attention at the back, here is a quick re-cap: Volts - Directly affects the rate of fire, a higher voltage pack will provide a higher rate of fire, however it will run down the pack quicker. Amps - also known as mah (milliamps per hour) or ah (amps per hour) relates to how many shots you will get out of a battery - your 1600mah pack is equal to 1.6ah there for will provide 1.6amps for 1 hour, or 3.2amps for 30 minutes and so on... We've worked out that our test gun draws around 16.8 amps, therefore you could run this gun (in theory) for around 6ish minutes continuous... that would be in an ideal world with no loss due to internal resistance of the cells, wiring, connectors and switch contacts etc and of course the voltage would start to drop off to such a level that it could no longer turn the motor. LiPO battery packs have a maximum continuous and peak rating, which is known as the 'C' figure. To work out how many amps you can safely discharge from the battery continuously, you take the total capacity of the pack and multiply this by the 'C' number. For example, our ASG 7.4v 1000mah LiPO is rated at 15C (or 26C peak), which means it can safely provide 15 amps continuous. Some packs have a far higher C rating, for example a 2200mah pack rated at 20C would be able to provide 44 amps continuously - that is a lot of power! In comparison, the 2/3A cells in a mini pack have a C rating of around 12 - 13 at very best, and for the larger packs (of Sub C size), much higher. Using our formula above, we can see driving our AEG at 7.4v would draw around 14.8 amps - within the recommend limits of our 15C rated battery pack. LiPO vs NiMH - Internal Resistance
This is demonstrated when we measured the current being drawn from the pack, whilst firing the gun in fully automatic mode. The 7.4v LiPO pack was able to provide 14.3 amps (bear in mind we calculated the gun would require 14.8 - theoretical), however the mini 8.4v NiMH pack was only able to give 13.2 amps, whereas the gun in theory required 16.8 amps at this voltage to operate at full efficiency. The NiMH pack is simply not capable of discharging high currents on demand, therefore using smaller NiMH cells (2/3A size in a mini pack) your AEG will never operate at it's full capacity. Bear in mind though, that it was designed to use NiMH packs - using high power LiPO packs in your AEG could in fact damage it if the internals are not up to operating with these power levels. In most cases a 7.4v LiPO pack will be fine however, certainly on Classic Army models. LiPO vs NiMH - Discharge Curve The 'discharge curve' is what we used to describe the characteristics of the battery as it's stored energy is depleted, the time it takes for it to be come depleted and it's performance during this period. In scientific terms I could plot you all kinds of wonderful graphs, but in Airsoft terms this will directly affect your AEG's performance, in particular your rate of fire during the battery's usage. With most batteries, be they non-rechargeable alkaline, NiCAD or NiMH cells, even though they have a pre-described voltage (1.5v for non rechargeable, 1.2v for rechargeable), this voltage begins to drop off as the battery is put under load. It is this gradual reduction in voltage under load, which reduces our rate of fire as the battery nears the end of it's charge. For NiMH batteries this discharge curve is quite steep which is why you can audibly hear the reduction in rate of fire as the battery pack is continually used, however for LiPO batteries, this discharge curve is much more shallow, meaning the pack is capable of providing nearly all of it's initial voltage until it becomes unusable. Rather than measuring the voltage at each stage, this can be better observed by monitoring the rate of fire below:
The above figures demonstrate very clearly the steep discharge curve of the NiMH cells over the LiPO pack, although the initial rate of fire was higher for the NiMH it quickly dropped off, then lower than the LiPO, and would continue to do so until the pack becomes flat. However, the LiPO pack, with only a small reduction in performance, would carry on providing that same rate of fire until it too required recharging. Proof therefore, that LiPO cells are more efficient and give better performance than their NiMH counterpart - however, this does come at a slight cost... LiPO Batteries - Limitations And What You Need To Know... LiPO batteries, whilst offering excellent performance and high current discharge rates are not without their limitations. Firstly, they require more care and attention than NiMH batteries, which in comparison are pretty resilient. One of the most important things to bear in mind, is whilst you can run a NiMH battery completely flat, doing the same with a LiPO battery will kill it. LiPO batteries have a peak voltage fully charged of around 4.2v per cell, dropping down to a normal 3.7v per cell when under load - they must NEVER drop below 3v per cell - doing so may render that battery pack useless and it may never recover. Now, this poses a difficult problem, when do you know the pack has reached this point? You can do it by judgement based on decreased performance in rate of fire, however this is not an exact science, and in the heat of the moment temptation to push the battery beyond this point is far too great. There are a number of little gadgets out there for example, low voltage cut-off units or alarms which constantly monitor the voltage of the pack, and when it drops below 3v per cell simply cuts the power or sounds an alarm. There are also LED units which give you a visual reading of the battery's health, although again, this could be missed. Secondly, you must ONLY ever charge a LiPO pack with the recommended charger, NEVER try and charge a LiPO pack using a normal NiMH charger. This is for several important reasons, the first being you should never charge a LiPO at beyond the recommended rate (usually 1C or 1 x total capacity of the pack) and secondly because the cells need to be balanced to ensure they are all charged at the same rate. This is why nearly all LiPO packs have what is called the 'balance and charging plug', an additional charging plug which is different to the normal small Tamiya type connector. Failure to ensure all the cells are balanced correctly could lead to a cell in the pack dropping below the 3v margin, which equals dead battery. Over-charging a LiPO pack, or charging a damaged pack will almost certainly lead to failure of the cells structural integrity, leading to possible fire and or explosion. Not wanting to scare you too much, but have a look at the YouTube video clip to see what I mean. Therefore it is recommended that LiPO batteries are charged in what's called a 'LiPO sack', a flame retardant material which contains and possible fire and smoke vented from a faulty or incorrectly charged pack.
ASG LiPO Batteries - The Stats... Now, having spent some time looking at LiPO batteries in general, let's look at the ones provided to us by Action Sport Games. Currently they have two versions available, the 7.4v and the 11.1v packs both rated at 1000mah 15C, and each of these packs has it's own dedicated charger. Because each LiPO cell has a voltage of 3.7v, you require only 2 to achieve 7.4v and 3 to achieve 11.1v - with this in mind you require a special charger that is capable of charging each cell individually to ensure the voltage is balanced across the whole pack. Each cell which makes up the pack is only 4mm thick, therefore the 7.4v pack measures only 8mm thickness in total. This is compared to 17mm thickness for the 8.4v 1600mah NiMH pack, just goes to show you can squeeze a more power into a smaller package! All the measurements for each pack can be found below:
You might be thinking, well, the difference in size is not that great, but bear in mind the the 11.1v pack offers the same performance of a 12v NiMH, which in comparison would have to be much larger to carry the same voltage. Additionally, with the 7.4v pack, the cells are separated and contained within their shrink-wrap casing, meaning you can stretch the pack out to make one longer but far thinner pack, something which would probably fit under the front RIS rail of an M4 for example, negating the need for an external PEQ battery box. Each battery is supplied with a mini Tamiya connector of good quality, which some people may prefer to swap for alternatives such as Deans connectors for example. The silicone wiring is also of good quality as is the heat-shrink packaging which further protect the cells from any outside damage. Also included on the LiPO cell are the balance and charging plugs which are used to connect each pack to it's relevant solid state electronic charger which in-built balancing.
The charger itself has a 2 pin European plug, so a travel adapter will be required for operation in UK mains sockets. Being electronic, there is no danger of overcharging the battery packs as their condition is constantly monitored. A bi-colour LED displays the condition of the charging cycle, with red showing charging in a progress and green to indicate charging has completed. At this point I must stress again to you ONLY USE THE RECOMMENDED CHARGER FOR YOUR BATTERY. To avoid confusion if you're purchased both packs from ASG, the connectors are slightly different for each pack, making it impossible to plug the 7.4v pack into the 11.v charger, and vice-versa. In Conclusion... Well, that about wraps up this article on LiPO batteries, which turned out to be a lot longer than expected, but with so much information to convey it's difficult to edit it down. What we've learned is that LiPO cells are capable of extraordinary power for their small size, and the fact you can squeeze the equivalent to a 12v NiMH into a pack smaller than an 8.4v mini is incredible. They are not however without their limitations and as with most things in life, a little compromise is needed. LiPO batteries require more care and attention that NiMH packs, not only in a physical sense but in their usage. As mentioned several times, you MUST not run a LiPO pack beyond 3v per cell or you risk permanent damage and that battery may never charge again. You also must never over charge or over-run a LiPO pack beyond it's recommended capacity or you may damage the pack risk fire and/or explosion (worst case). Is it then, that NiMH packs may have seen their day? Well, I don't think so, not for some considerable time. Although LiPO batteries do seem to be making more of an appearance on the Airsoft battlefield, until they can perfect the cell so that it can in effect 'run flat' - the average Airsofter runs the risk of causing damage to the packs. You do need to take extra care with LiPO packs, they're not as 'plug in and go' as NiMH batteries which in comparison are pretty tough.
Oh yes, that reminds me... We said at the beginning of the review that we had two packs, the 7.4 and an 11.1v? Well, we didn't do too much testing on the 11.1v pack, and that was for one very simple reason. We didn't have an AEG man enough to take it, not without breaking one that is... The 11.1v pack offers such high power that you really do need to have an AEG capable of supporting that voltage, which can mean some expensive modifications. For the support gunner for example, where in some models there is only space for a mini pack, this does mean some very good things though - increased rate of fire equals more heads kept down on the playing field! So what did the 11.1v pack put out in terms of ROF on our poor little test subject, the CA MP5-SD3? Well, remember that the 7.4v LiPO was capable of sustaining around 660rpm... the 11.1v topped an awesome 1340!!! We simply could not risk continuing further, as I'm pretty sure 5 magazines later we wouldn't have had much of an AEG left to test it with! As for pricing, currently there are no UK stockists of the ASG Li-PO packs, but you can find European stockists by visiting Action Sport Games website, and clicking on their dealer locator. We will update you as soon as we have UK prices. And Finally... I hope you've found this article useful and informative. By no means is it supposed to be a complete guide to Lithium Polymer batteries, merely a guide to the most important things you need to know. We're always open to feedback or constructive criticism, so if you disagree with any of our statements, please by all means get in touch with us and we'll take your comments onboard. We've also included some links below for some excellent further reading if you wish to find out more : http://infectedairsoft.wordpress.com/tech-info/lithium-polymer-batteries-part-1/ http://infectedairsoft.wordpress.com/tech-info/lithium-polymer-batteries-part-2/ http://infectedairsoft.wordpress.com/tech-info/lithium-polymer-batteries-part-3/ http://infectedairsoft.wordpress.com/tech-info/lithium-polymer-batteries-part-4/
- Special thanks go to Action Sport Games for providing their 7.4v and 11.v packs, plus respective chargers for review purposes. To find out where you can purchase the ASG Li-PO packs, click here to view their retailer locater or click the logo below to be taken direct to their homepage.
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All material within is copyright dEFCONAirsoft 2007. dEFCONAirsoft is kindly sponsored by Fire-Support. Some of the views expressed within these pages are not necessarily the views of dEFCONAirsoft or any of the sites affiliated with us. |
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So, what do we know about LiPO
technology and just why can it be so much more useful to us Airsofters than the
NiMH batteries we've been using for years? Well, one of the primary
considerations is size / weight. LiPO packs, just like their NiMH
counterpart come in various different shapes and sizes, and a variety of
different voltages. As mentioned previously, LiPO batteries can offer a
30% reduction in cell density, but a vast increase in power, so their best
application is for where space is an issue. Those of you with rifles
incorporating a large stock probably wouldn't need to consider LiPO battery
packs, as there is plenty of room for the largest Sub-C sized packs, however
there are some occasions where even on larger weapons space can be an issue, for
example, trying to squeeze a 9.6v pack into an M14 stock is pretty tight let
alone a 12v one. This is where LiPO comes into it's own, the 11.1v pack is
smaller than a standard mini battery, but offers far greater power for its size.
Bear in mind at this stage, these
numbers are theoretical, but they do give you a rough guide. Other
considerations to take into account are the gear train, the strength of spring,
poor quality wiring and connectors... these can all have an effect in increasing
these numbers. What is interesting however, using this formula you can see
that by lowering the voltage, the amount of current required also drops off
significantly. For example, if you were to remove a cell from a standard
mini battery, making it 7.2v, the AEG would now require less current to work the
motor, so 16.8 amps becomes 14.4 amps - with this in mind it is obvious that
increasing the voltage certainly increases the rate of fire of any given AEG,
but it also runs the battery down quicker! So, is it possible then, that a
lower voltage and lower capacity (in this case 7.4v 1000mah LiPO) pack can give
better or equal duration performance than a higher voltage higher capacity pack?
We'll find out.
One of the main advantages of LiPO
cells, over the more conventional NiMH cells is the discharge rate, that is the
rate in which the battery can 'dump' all of it's energy on demand. The
problem with the smaller 2/3A size cells which make up a mini pack, is they have
a fairly high internal resistance which limits the maximum continuous discharge,
something which is not found on LiPO cells which are a completely different
chemistry. This is why you may have found that fitting say a large 3300mah
(or indeed larger) 8.4v pack to a gun which normally took a mini pack suddenly
increases the rate of fire, why? Well the voltage has not changed, you are
still applying 8.4v to the motor, but the larger cells having less internal
resistance are capable of releasing their energy quicker and more efficiently,
resulting in no 'bottlenecks' and a far greater rate of fire. LiPO
batteries, having a very low internal resistance and more stable discharge curve
(something we'll look at in a minute) release their energy far more efficiently
offering in most cases a better rate of fire, for a lower voltage than a
standard mini NiMH pack... 
As
you can see, the difference, especially in weight is phenomenal, and going back
to my opening statement at the top of this article, you can see why LiPO
batteries are the power source of choice for the radio controlled modeller,
weighing in 4 times less than the NiMH pack, the 7.4v 1000mah LiPO is a skinny
little powerhouse!
Each
charger is designed differently for the total cell count of each pack. In
the case of the 7.4v pack (2 cells) the charger outputs 8.4v at 1000ma which
states recommend charging time of 90-120 minutes. In reality, my 7.4v pack
charged fully within 43 minutes out of the box - although as LiPO's should never
be stored 'flat' or run down below 3.v per cell, this pack was mostly charged
before shipping. For the 11.v pack (3 cells), it's charger outputs 12.6v
at 1000ma, and a similar total charge time was experienced - and even when
discharged down to the cut-off point, I can see it taking little more than an
hour to charge these packs fully.
One
thing is clear though. The the experienced Airsofter, LiPO battery
technology offers far greater power to weight/size ratio than NiMH will ever be
capable of, meaning AEG upgrades now become easier, and the increased rate of
fire you can gain in such a small package is grin inspiring...