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KWA G36C accuracy issues


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#21 Spiggy

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Posted 01 June 2010 - 04:18 PM

yikes, what's the discharge rate on that battery?

#22 PhaseBlue

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Posted 01 June 2010 - 05:55 PM

4000 mAh, 40 Amps continuous output.  The gun has a 20 amp fuse in it though so it's drawing < 20 amps.

View PostSpiggy, on 01 June 2010 - 04:18 PM, said:

yikes, what's the discharge rate on that battery?


#23 Spiggy

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Posted 08 June 2010 - 03:47 PM

So! I found your problem.  You're gonna like this.

Battery

your fuse doesn't do anything to dampen the output of the battery.  A fuse is not a resistor.

Your battery is far too strong for the recommended rating.

#24 Vamp2269

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Posted 10 June 2010 - 12:12 PM

Then what does a fuse do? you should explain this on the lipo battery warning thread.

So the battery is always pushing out forty amps instead of the gearbox only pulling out what it needs.

Edited by Vamp2269, 10 June 2010 - 12:14 PM.


#25 Guest_allizard_*

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Posted 10 June 2010 - 10:51 PM

Fuse is to prevent too much current and fry the contacts.  The gun some with a 20A fuse. If might can tolerate 25a or even 30a.  At 40amp continuous discharge is too much for the fuse to hold.

We give you the spec of a battery to follow.  If you decided to go outside of the recommending spec.  You are on your own.

#26 Spiggy

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Posted 11 June 2010 - 06:20 PM

View PostVamp2269, on 10 June 2010 - 12:12 PM, said:

Then what does a fuse do? you should explain this on the lipo battery warning thread.

So the battery is always pushing out forty amps instead of the gearbox only pulling out what it needs.
The fuse is a check and balance on heat imparted by the battery discharging.  As the amperage goes up, the higher the amount of heat is being discharged through the wiring. That's why fuses pop.  That's why incandescent lightbulbs pop.  That's why surge protectors pop.  That's why switch boxes in a house pop.

A motor doesn't draw "What it needs"

case point, a 1s1p 7.4v lithium 600mah ROF vs a 1s2p 7.4v lithium 4800mah 80c (which I have for R/C) have much different rates of fire.

#27 Vamp2269

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Posted 16 June 2010 - 09:46 AM

View PostSpiggy, on 11 June 2010 - 06:20 PM, said:

The fuse is a check and balance on heat imparted by the battery discharging.  As the amperage goes up, the higher the amount of heat is being discharged through the wiring. That's why fuses pop.  That's why incandescent lightbulbs pop.  That's why surge protectors pop.  That's why switch boxes in a house pop.

A motor doesn't draw "What it needs"

case point, a 1s1p 7.4v lithium 600mah ROF vs a 1s2p 7.4v lithium 4800mah 80c (which I have for R/C) have much different rates of fire.
You make a good point and this question was designed to draw out that answer I have been making that arguement with my friends for a long time. My friend uses a RC helicoter Lip batterry and it has too high of a discharge rate and He won't belive me because he is told by the teachers at his school and on his robotics team that the circutry will draw only what it need. which is false. Maybe in a Rc helicopter with an onboard CPU that controls the flow of electricity but on an airsoft gearbox their is no such inteligent device.

You should put this on the lipo battery warning thread and put the retarded controversy to rest.

Edited by Vamp2269, 16 June 2010 - 09:53 AM.


#28 Paisley Pirate

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Posted 08 August 2010 - 12:37 AM

Ummmm... guys, I hate to disagree here, and I can show you some real world examples to tell you differently.

VOLTAGE of a battery will cause an issue on a motor...  having a higher capacity AMPERAGE available will NOT.

How can I simply prove this?  If a system is designed for a specific voltage (or range) it will draw what it takes at that voltage.

Otherwise, every time you open your car door, your dome light would fry (as an extreme example of why what you are saying is not correct). That would be a single 12v bulb that is only supposed to draw 1 amp, connected to a battery that can supply at least 300 amps... and it is the only thing on the circuit, and there are no limiters (on 99% of cars, anyway...) Trust me, I grew up in an auto mechanics shop, and have gone so far as to build a custom wiring harness for a street car.

A DC voltage system is a DC voltage system. The electrons go one way only, and will only go as fast and as many as the wiring and specific components will allow. You simply can not burn out a component built for a specific voltage by hooking up a larger capacity (but same VOLTAGE) battery to it. Will not happen.

A larger battery of the correct VOLTAGE is no problem... it will NOT force feed more than the capable amount through.

Of course, the motors that we use in airsoft are really 6v motors to begin with, so I suppose that could be a problem...

Even so, an 11.1v 4k mAh battery will spin one fast enough to cause some problem, but it ought to cycle faster than 20 bps... I'd look at the hop up some more, personally.  I mean, my G36 (when I had the softer spring in it) cycled 20 rps with a 9.6v and never had any issues with it... everything else was bone stock.

And I hooked up a 10.8v NiMH battery to it for a little bit just to see how fast it would go... pretty impressive (24-25) but never caused any issues with shooting it. Still, went back to the 8.4 most of the time.

#29 Spiggy

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Posted 11 August 2010 - 03:15 PM

current, current is the magic thing that kills you in a lightning strike


there's more current in some batteries based on it's build and efficiency.  More current = more flow

watt=voltage*ampere, 7.4v*1600mAh=11,840mW or 11.84 watts.  7.4v*4800mAh=35,520mW or 35.52 watts

Last I checked, commercial lightbulbs are marked in watts, not volts


I'm talking about the power coursing through the battery.  It's flow is higher, the motor is going to spin faster

#30 philstar

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Posted 11 August 2010 - 05:41 PM

View PostSpiggy, on 11 August 2010 - 03:15 PM, said:

there's more current in some batteries based on it's build and efficiency.  More current = more flow

watt=voltage*ampere, 7.4v*1600mAh=11,840mW or 11.84 watts.  7.4v*4800mAh=35,520mW or 35.52 watts

Last I checked, commercial lightbulbs are marked in watts, not volts


I'm talking about the power coursing through the battery.  It's flow is higher, the motor is going to spin faster

Spiggy,

You are incorrect about this.  If you hook an ideal voltage source up to an AEG, the motor and gun setup will dictate how much current is drawn.  An ideal voltage source is one that can provide limitless current without any voltage drop.  You are correct that power (measured in watts) = voltage * current.  The gun itself will dictate how much current is drawn for any given voltage.  More voltage usually causes circuits to draw more current having a 2 fold effect on rpm increase.

Lightbulbs are actually a good example of what I am talking about.  If you hook a lightbulb up to a 120V 20A circuit (typical in households), they don't automatically produce 2,400 watts.  Like the AEG, the bulb limits how much current is drawn for any given supplied voltage.  If you increase the voltage provided to a lightbulb, it will increase the current drawn and power consumed as well.  That's why lightbulbs are marked in Watts for a given voltage.

In addition, you are confusing the battery capacity with its current output.  A 4800mAH battery can provide approximately 4800mA for 1 hour.  It can provide 9600mA for about 1/2 hour.  With Lipo batteries, however, the max rated current is related to the max discharge by the battery's "C" rating.  A 20C lipo can deliver 20 times 1hour current rating continuously without bursting (until the battery runs out of charge).  In other words a 4800mAH 20C lipo can deliver 96 amps without over heating or blowing up.  For a 3S (11.1V) lipo, that is over 1kW.

Paisley,

What you said is largely correct except for one detail.  Batteries are not ideal voltage sources.  They all have internal resistance which causes their output voltage to drop when they are provide current to a load.  That's why your headlights dim when you start your car.  The massive current drawn by the starter causes a voltage drop within the battery itself.

A fully charged 3S lipo will output 4.2V * 3 cells = 12.6V without any load.  If you take that fully charged lipo and draw its maximum rated current, however, the voltage will immediately drop by 1.5-3V depending on the condition of the battery.  If you draw 1/4 that much current, the voltage drop will be approximately 1/4 as much.  In short, I'm saying that the current rating of a battery will have an effect on its voltage output under a load.

A 1300mAH 15C battery can produce 19.5Amps without bursting.
A 3000mAH 20C battery can produce 60Amps without bursting.

The higher cap battery will provide a higher DC voltage when the AEG is firing.  It should be pointed out that the DC voltage difference isn't as large as the difference in voltage when you first pull the trigger.  DC motors in AEGs draw a huge chunk of current when the go from stopped to full speed.  Since the higher cap batteries dip voltage less, they put a harder hit on the gearbox when spinning up.

I must admit, I have a bunch of data on these batteries when used in RC airplanes, but I've never actually measure them in an AEG.  I'm just commenting based off the current ratings of the guns.  If anybody cares, I could take some scope shots post them.  It might be good to know what voltages we actually get with different batteries.

#31 philstar

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Posted 11 August 2010 - 05:44 PM

deleting duplicate post...

Edited by philstar, 11 August 2010 - 05:46 PM.


#32 Scatterplot

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Posted 12 August 2010 - 06:06 AM

Great post philstar. It's always difficult to explain the voltage-current-resistance* phenomenon, and you did it well!

I hope I don't derail too much here, but here's a question for you. Do the C ratings on a battery describe the current draw before physical damage or the current draw before the voltage dips below some percentage of nominal?


*I know it's not all resistance in an AEG, there is gobs of inductance as well, but this ain't the post for that :)

#33 Spiggy

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Posted 12 August 2010 - 11:01 AM

^ i agree, well done.    :turned:

#34 philstar

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Posted 12 August 2010 - 04:18 PM

View PostScatterplot, on 12 August 2010 - 06:06 AM, said:

Great post philstar. It's always difficult to explain the voltage-current-resistance* phenomenon, and you did it well!

I hope I don't derail too much here, but here's a question for you. Do the C ratings on a battery describe the current draw before physical damage or the current draw before the voltage dips below some percentage of nominal?


*I know it's not all resistance in an AEG, there is gobs of inductance as well, but this ain't the post for that :)

I've only ever seen the C rating specified as the max continuous current draw without damage.  Some companies spec it more detailed than others (including temperature constraints, airflow, etc).  I've seen articles calling for a standardized a method of specifying and testing source resistances on Lipos (which would tell you voltage drop for a given load), but the conclusion has always been that it will never happen.  The hard part here is that Lipos (like many rechargeable batteries) change significantly over their lifetime.  As they get used (and abused), their internal resistance goes up.  As a result, their internal heat generation goes up.  This limits their ability to deliver current without damage.  It also increases voltage drop under load.

The lipo burst current is almost more applicable to airsoft than the constant current rating.  A 20C lipo will often have a 30C burst current.  Every manufacturer specifies this a little differently, but the burst spec often says that a battery can provide the burst current for 10seconds without damage.  That's a lot of BBs.  

Your right about saying motors have/are gobs of inductance.  If the DC resistance in the coils was the only thing dictating the current draw, the fuse would blow immediately.  That's why the gears, spring, piston, and drivetrain weight have an effect on current draw.  If you lock up a DC motor, the motor coil resistance is all you have limiting current.  In most applications that will blow a fuse or trip a breaker.  You are even more correct about saying that this isn't the post for that.

#35 Spiggy

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Posted 13 August 2010 - 11:01 AM

If you guys want to start a new thread in the "Mods" section about electronic theory, go ahead.  It's a subject that I think the forum can benefit from.

#36 dsdehan

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Posted 16 September 2010 - 06:06 PM

what part of the battery dictates the rof. ex. mah/voltage/current/amps

what part of the battery dictates the rof. ex. mah/voltage/current/amps

what part of the battery dictates the rof. ex. mah/voltage/current/amps

what part of the battery dictates the rof. ex. mah/voltage/current/amps

#37 xKingSizex

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Posted 17 September 2010 - 10:18 AM

View Postdsdehan, on 16 September 2010 - 06:06 PM, said:

what part of the battery dictates the rof. ex. mah/voltage/current/amps

what part of the battery dictates the rof. ex. mah/voltage/current/amps

what part of the battery dictates the rof. ex. mah/voltage/current/amps

what part of the battery dictates the rof. ex. mah/voltage/current/amps

voltage...

#38 dsdehan

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Posted 17 September 2010 - 01:33 PM

so the discharge rate and amps make no difference?

#39 gcw360

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Posted 17 September 2010 - 03:20 PM

:popcorn:

Oh, what the heck.  Voltage is responsible for ROF.

#40 Guest_allizard_*

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Posted 19 September 2010 - 12:39 PM

It's a bit more complicated than just voltage.  

Discharge rate have something to do with it as well.




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