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KM4-SR10 Questions


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#1 Nicholas Andrew

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Posted 01 January 2014 - 02:05 PM

Okay, so i just started getting into Airsoft..... Bought all kinds of equipment and i'm ready to get out and play...

My main gun, the KM4-SR10, i reviewed that it was LiPo ready.... Do i have to install a mosfet system/device on this ? or can i just throw in the 11.1 lipo battery and roll with it?

Also, i have  Lancer Tactical M4 Series High Capacity magazines... They fit into the KM4 , not TOO TOOO tight, but it's a tight fit, works perfect....

#2 vanevery

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Posted 01 January 2014 - 02:50 PM

You can use a 11.1v low amp / low C rated battery with no issues.  11.1v/1200mah/15C is a good choice. You can buy them cheap at Hobby King and get a few at one time. You can even go as high as 11.1v / 1600mah / 15-25C but will wear down your internals out much faster. If you want more power than that, I suggest to install a mosfet.

Edited by vanevery, 25 February 2014 - 07:11 PM.


#3 cellistle

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Posted 01 January 2014 - 07:46 PM

What are the differences between a 15c and a 25c? Does using a 1600 mah put more stress than a 1200 mah?

#4 Chuck S

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Posted 02 January 2014 - 04:11 AM

No one has yet explained (to my feeble understanding) why a higher mAh or C-rating is harmful.  The only reason I can guess at involves voltage-drop under load.  A higher C-rating should have less voltage drop under load and voltage drives the motor speed.

The milliamp-hour rating is just the capacity of the battery in thousandths of amp-hours -- the size of the fuel tank; the C-rating is the maximum safe Continuous discharge or charge without damaging the battery (not the gun) -- how fast you can dump that electricity.  The battery does not "stress" the gun at all; the gun pulls power from the battery.

KWA guns are fused for 20 amps.  The common 1400mAh 15C battery can safely continuously discharge discharge at 21 amps (1400/1000 x 15 = 21).  More mAh gets more shooting time.   More C-rating gets less voltage drop which should maintain motor speed.

-- Chuck

#5 niko_gpsy

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Posted 02 January 2014 - 03:36 PM

Well just because a battery is capable of delivering high amps does not necessarily mean that it will.  The motor will only draw as much as it needs but it's better to have a battery that can keep up with the demand of the system than something with a low power output that strains under load.  A battery that is not able to supply the power that the gun needs at it's peak will lead to damage to the battery and possibly other electrical components.
A typical draw of a motor in a system that is operating normally is about 14-16amps.  However, with that said a motor is capable of drawing much more if it running under heavier load (stronger spring) or if the gearbox locks up.  So a 20amp fuse seems to be a good fail safe point if for any reason your motor starts to draw more power than the battery can supply or the motor can handle.

#6 caelanbd

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Posted 25 February 2014 - 07:04 PM

Do you really need to shoot 25 bbs per sec....There is really no need to use a 11.1 v lipo in any gun.....a 7.4 lipo is more then enough power and will out perform any 9.6 nicad Ive ever used and give you great rof in the process. In my opinion using a 7.4 lipo will give you less problems down the road and make your gun last longer.

#7 vanevery

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Posted 25 February 2014 - 07:45 PM

View PostChuck S, on 02 January 2014 - 04:11 AM, said:

No one has yet explained (to my feeble understanding) why a higher mAh or C-rating is harmful.  The only reason I can guess at involves voltage-drop under load.  A higher C-rating should have less voltage drop under load and voltage drives the motor speed.

The milliamp-hour rating is just the capacity of the battery in thousandths of amp-hours -- the size of the fuel tank; the C-rating is the maximum safe Continuous discharge or charge without damaging the battery (not the gun) -- how fast you can dump that electricity.  The battery does not "stress" the gun at all; the gun pulls power from the battery.

KWA guns are fused for 20 amps.  The common 1400mAh 15C battery can safely continuously discharge discharge at 21 amps (1400/1000 x 15 = 21).  More mAh gets more shooting time.   More C-rating gets less voltage drop which should maintain motor speed.

-- Chuck
Different Airsoft Techs have different views when it comes to the electrical system in an AEG.
Most have more experience than I do on the subject.
After having installed several mosfets, rewired several guns, and built a couple Franken-Torque motors, I feel I have a qualified opinion on the subject. I am not intending to debate with any other Tech on this issue. It seems that even the most experienced Techs specific to electricals seem to have polar opposite views on some things.

A lot of Techs, such as our experienced and qualified Tech and Forum Moderator Niko, believe the motor only draws the amps and over-all power output needed. Other Techs believe in power spikes where the motor draws all the amps and over-all power output it is capable of on the initial trigger pull, and then settles into only drawing what it needs, this in the time span of a nano-second.
I am not sure that there is a "one size fits all" answer to which is correct. It is certainly possible that both views are correct and the result one gets is due to the brand and construction of the motor and possibly the power output of a given battery it is paired with.

Thoughts:
If the mah's and C-rating made no difference, then there would be no recommended specs by KWA brand.
If they made no difference and volts were the only factor, then no one would ever need a mosfet, because trigger contacts would never melt.  It seems to me, in my own experience with using mosfets and with also not using mosfets, that the amps and C-rating seem to directly relate to volts and over-all power output specifically regarding Li-po batteries.

I say this because it is the initial trigger pulls where "things happen" in my guns that do not have mosfets.
With Li-pos that have high amps and C-rating, there is considerably more arching on the initial trigger pull vs immediate follow up trigger pulls. "Things" such as Contact Plates sticking, Full-auto fire on Semi Auto, and the rest.
I also do not use fuses in my own guns, so I do not have the protection they offer.

Either way, if the mah's and C-rating did not matter, then everyone would be using 5000mah / 50C rated Li-pos and without mosfets. No one does this because it will fry the electrical system at some point, and probably quickly, without a mosfet. I have never seen any electrical issues regarding trigger contacts with low amp and low C-rated Li-po's.

Edited by vanevery, 25 February 2014 - 07:47 PM.


#8 Pyro_Buster

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Posted 28 February 2014 - 12:09 PM

I'm rolling with a custom 11.1, 2200 mAh battery that was made for me buy a battery technician who specifically makes batteries for airsoft guns. I would trust him way more that anything KWA "recommends." That being said, I have never had any problems, and after a few upgrades to my gun (including an M120 long spring), my ROF is right about 14. Not 25.

#9 Larry

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Posted 01 March 2014 - 01:35 PM

My stock SR10 with 7.4 2200 mah,  and JBU high torque turning 20 rps. I think the stock spring is a 120, shoots 415 with.20s. Something is off is off on your gun.  What kind of motor is in it. How did it shoot before the upgrades.




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