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Guide: Upgrading to LiPoly Batteries

Posted: Thu Feb 05, 2009 6:11 pm
by Moondog
Guide: Upgrading to LiPoly Batteries
by Moondog

First let me say, I don't use 11.1v Lipo batteries. I did a lot of research into upgrading my guns to run it and ended up deciding not to. Many players want to run their AEG's with Lipo batteries (Lithium Ion Polymer) to increase their ROF and to pull harder springs.

The first thing you should be aware of, it's the voltage not the battery chemistry which give you the performance. A 12v NiMH battery will give you the same ROF as a 11.1v Lipo. The difference is that a Lipo is smaller in size. You can run a 7.4v Lipo without any risk or modification to your AEG. But for the rest of this article, I'm referring to 11.1v or higher Lipo batteries.

A lot of AEG's now claim to be "Lipo ready". And technically most newer generation AEG's are Lipo ready, because you don't need to change anything internally to run a Lipo battery in them. A stock JG should run a Lipo and without blowing up (unless it's a lemon). But there are things you need to know about what Lipo's do to your AEG.

And a lot of new players want to know how do they make their AEG's "Lipo ready" and what exactly that means. There are two parts to being Lipo Ready: 1) Electrical and 2) Mechanical

ELECTRICAL
Lipo batteries output at much higher voltage (11.1v which is much higher than stock batteries that are 8.4v) and amperage. The wiring and motor of most high quality AEG's are good enough to handle the higher voltage and heat. So there is no need to replace your wiring for all but the cheapest AEG's. Though players who want to pimp their ride may want to buy low resistance wiring which more efficiently conducts current.

DEANS
Because of the higher voltage, your wiring and motor will heat up much faster and so you must be careful that you don't overfire. Melting may occur in the solder around the connections to the motor and with Tamiya type wiring connectors. This is why many switch to DEANS/DIN connectors which are made to handle higher power current.

Image

If you choose DEANs, you will have to convert all of your connectors to DEANS (as any Tamiya connectors will be your weak point) on your AEG and on all of your batteries. The downside is that most players have Tamiya connectors, so if you need to borrow a battery from a friend, you'll probably need to have a DEANs to Tamiya converter.


MOTOR
Because of the higher voltage, your motor will spin faster. Much faster. So your motor will wear out (burn out) sooner than normal. So you may want to buy a high-speed upgrade motor. These motors have reinforced parts for higher RPM's and have internal ball bearings to allow them to spin with less friction.


FUSE
Lipo's output much higher amps than NiCad and NiMH batteries and you need to buy higher amp fuses (or remove your fuse) or you will burn them out quite often. Most stock AEG have 20A-30A fuses. You should upgrade to a 40A or higher fuse with Lipo setups. You can find these in autoparts stores.

http://www.parts-express.com/pe/showdet ... er=070-922
http://www.parts-express.com/pe/showdet ... er=071-390


MOSFET (metal–oxide–semiconductor field-effect transistor)
This is an optional but recommended upgrade. Lipo's higher voltage and amps can cause the metal contacts in your trigger to partially melt due to electrical arc'ing (sparks). MOSFETs are solid state switches that bypass the higher voltage current directly to your motor, shunting lower current to your trigger to prevent melting. JG/Echo-1 have begun producing AEG's with them pre-installed. Some more expensive switches can also function as resettable fuses and programable selective fire controllers (allowing you to fire in 3-shots bursts). http://extreme-fire.com/



MECHANICAL
Because Lipo setups run at much higher RPMs your gearbox will cycle much more often (almost twice the speed that they were originally designed for). So your gearbox parts will wear out twice as fast. Get used to it and be prepared to inspect your gearbox more often.

REINFORCED GEARS
Tokyo Marui, DE, BE and sub $100 AEG's do not have reinforced gearsets and are not 'Lipo Ready'. JG, KWA, CA, G&G, ICS, G&P, STAR, etc. have steel gears which can withstand higher speeds. But nothing lasts forever. All gears eventually wear down and fail. At higher RPMs they will fail that much sooner. So at the first sign of wear, buy a replacement reinforced gear set.

Be sure to buy original gear ratio or torque up ratio sets with Lipo. Do not install high-speed gears! Speedup gears were designed to modify the gear ratio in stock motors to increase ROF. A speedup gear set with a Lipo will only cause your gearbox to spin even faster and that may be too fast for your mag and hop-up to feed properly.


HELICAL GEARS
Helical gear sets have more teeth that mesh much tighter and so can handle higher stress by spreading it across those extra teeth. But the tolerances are much tighter. You must have excellent shimming for them to work. And you must change your piston to a half-teeth type.


FULL TEETH PISTON
Most stock pistons come with a single metal gear tooth at the very end of the gear rack. This tooth experiences the most stress because it's the last tooth your gearbox pushes on when your spring is at its most compressed. With Lipo's, when you pull the trigger, your gears start to spin much faster. You get crisper trigger response but you will also experience faster wear on the beginning piston teeth, sometimes stripping them.

Many Lipo users have switched to full teeth pistons where the metal teeth extend across the entire row. The downside is that metal on metal creates more wear and stress to your gears, so your teeth will wear out sooner.


BUSHINGS
Common wisdom is that you should replace your bushings with metal bearing bushings. These will reduce friction and stress on your gears at higher RPMs. I'm a bit of a contrarian about this. I've never seen nylon bushings fail. With springs lower than 350fps, I don't believe you need to change to metal, because nylon is similar to teflon and has very low friction.


Why you may NOT want to switch to Lipo
Lipos are a lot more expense and risk just to increase your ROF to crazy rates. And for CQB games Lipo's ROF is too excessive to be fair. For me a 9.6v battery good enough.

Lipo batteries are also more expensive and more finicky. They are more prone to burning out (technically they can be over drained) and failing. In a worst case situation, they can catch on fire. Not fun.


Glory wrote: From FilForce.org

Good work Moondog.

The only reason why I use a LiPoly (Lithium Polymer) battery is because of its size and weight. Nothing more. And since I don't want any external battery sticking out of my AEG, LiPo is the only battery I use.

Please note that I never go beyond 35amps (constant) in using a LiPo. This means that the max I go for a LiPo is 11.1V (3S) @ 1500mah rated at 20C to save me of headaches of having to replace the internal parts of my AEG. So far this power to gearbox (long life) ratio works for me.

Personal Notes:

AEG: ICS-M4

Using PolyRC 11.1v 1500mah 20C rating
Dimension 100mm x 31mm x 20mm
C Rating: 30A (20C continuous/constant); 45A (30C Burst C rate 1st 30 secs); 25A (17C Nominal)

ICS Turbo 3000 (with no load) draws 11 amps.
ICS Turbo 3000 (stock spring high speed gears) draws 24amps (ROF high 39 rounds/sec low 37 rnds/sec) *
ICS Turbo 3000 (SP120 HS gears) draws 40A instantly ave is 36A (ROF ave 27 rnds/sec) **
ICS Turbo 3000 (SP120 STU gears) draws average of 20amps (ROF ave 15 rnds/sec) ***

* be prepared to replace parts that WILL get damaged. Sector Gear Chip is also a must to prevent double feeding and/or dry firing. With Mid-Cap mags, three short squeeze on the trigger and your empty!
** Low resistance wires is a must preferably 16 gauge. Battery gets very hot. Wires and Motor overworked. Hot too!
*** ideal. Low resistance wire still recommended to get most of the juice out of the battery.


Understanding LiPos

Lipo batteries are very different from previous generation batteries and understanding how they work, and especially how to charge them, is the key to getting the best performance.

Series
Individual Lithium Polymer cells have a nominal voltage of 3.7 volts (vs. 1.2volts per cell for Ni-Cds or NiMH). Cells are wired in series to give the following pack voltages:

1 cell = 3.7 volts (1S)
2 cells in series = 7.4 volts (2S)
3 cells in series = 11.1 volts (3S or 3 cells connected in series)

C Rating
Where more power is required, cells can be factory assembled to form high energy density light weight battery packs hence the term "C" Rating became an important consideration for me. One can get a smaller LiPo battery pack (if size is an issue) ie 1200mah but having 20 'C' Rating. This means 1200mah x 20C = 24A discharge rate. Moreover, high C capable cells have lower internal resistance. This means that under high load the voltage will stay closer to 3.7v per cell which means more power for your motor.

Charging
Charging LiPo batteries requires a very different charge method than other types of cells. It is CC-CV or constant current constant voltage. It's imperative to use a charger designed specifically for LiPo batteries, and with most LiPo-specific chargers it's necessary to correctly select the cell count (1, 2 or 3 cells) manually. Fortunately, several good chargers are available. I personally use a Duratrax IntelliPeak Ice Charger. This is another consideration that one must undertake if thinking of switching to LiPo battery besides having to rewire everything; buying a motor that is power hungry like the ICS Turbo 3000 and Systema Magnum motor; etc. etc.

Buying at Evike.Com a Firefox LiPoly battery that includes a charger DOES NOT AUTOMATICALLY mean that you can use this charger on any other types of LiPoly battery. Why? one might ask. As I have said earlier most LiPo-specific chargers it's necessary to correctly select the cell count (1, 2 or 3 cells) manually. Not only that. The current that goes into the battery (when charging) should be set at half the battery capacity. Example, if one has an 11.1V (3S) 1200mah LiPo battery, the setting on the charger should be set manually at 600mah (6A) or less and with the correct cell count of 3. If the charger that came with the package is set at this configurations (default factory configuration and no way to alter it), this charger cannot be used on a 7.4V (2S) 600mah LiPo battery.

Lithium Polymer Cells and Battery packs

Fortunately, Lithium Polymer batteries are getting cheaper and is much safer to use than when I started to use it. The LiPo battery packs sold on most RC stores including CheapBatteryPacks.Com have a PCM or Protection Circuit Modules. This provides protection against over voltage, under voltage, and over current/ short circuits. The PCM however increases the dimensions of the bare cell dimensions, as a guide, it will add up to 2 to 3mm to the length of the cell.

The following brands almost certainly will have a PCM chip included in their LiPo battery packs:

- A123 Racing Packs
- Air Thunder
- Elite
- Hyperion
- PolyQuest
- PolyRC
- Thunder Power


Do's and Don'ts

Do: Only use a charger that is specifically designed to charge LiPo batteries. Using other types of chargers can cause an extreme fire hazard!


Do: LiPos don't develop memory or voltage depression characteristics. Do charge them without the worry of cycling or discharging them.


Do: Store LiPos at least partially charged. LiPos will maintain their performance levels over time, even during non-use, much better than Ni-Cds and NiMH and there's no need to cycle them.


Don't: Use any type of charger that is not specifically designed to charge LiPo batteries. Using non-LiPo-specific chargers can cause an extreme fire hazard!


Don't: Fully discharge your LiPo battery pack. Discharging a LiPo beyond it's critical minimum voltage will cause damage to the battery.


Don't: Don't puncture the battery as this can cause a chemical reaction that can cause fire.


Re: Guide: Upgrading to LiPoly Batteries

Posted: Wed Feb 25, 2009 3:34 pm
by whogben
Pistons Note: When you run a lipo in a stock gun with a stock (weak) spring the piston may not travel all the way forward before the gears want to catch it and pull it back again. This results in the gear teeth slamming into the second tooth of the gear with all the power of the spring behind it and tends to blow straight through it and the tooth behind it, making the piston useless. If you add a lipo to a stock gun and aren't afraid of the gearbox, open it up and remove the second tooth that the gears grab with a file. The teeth mesh tightly enough that even with one tooth missing the piston will never slip past the gears - this is necessary for running most guns under 370fps on LiPo, especially ones that come with high quality motors like an ICS gun.