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systema m120 vs m120s


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Old April 24th, 2009, 12:50   #16
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Old April 24th, 2009, 13:10   #17
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Here's my take so far on the LiPo-mystery/myth/magic...

With "normal" NiCad, NiMh batteries...most people didn't sweat them much. 8.4v was "regular", 9.6v was "fast" and anything more was insane. Large batteries lasted all day and resulted in a higher rate of fire than a mini battery pack. If the pack was ended up with a gooey mess on the table. Charging/discharging them incorrectly would kill/ruin the pack...but it's simple to plug it in and let the charger finish automatically.

With LiPo batteries there's a lot of stigma around them blowing up, killing your mechbox, gassing you to death, etc...

Here's what I've found so far (NOTE: I am not a be-all-and-end-all fact sheet for batteries...there's lots of other good information out there. But hopefully what I write is comprehensible and correct).

- much of it has to do with the C rating. A 11.1v 1100mAh 15C battery is very different from a 11.1v 2000mAh 20C battery...the first one can provide 16.5Amps and the other 40Amps. There will be a big jump in ROF going from one to the other.
- a 7.4v 2000mAh 20C battery does seem to be about the same as a large 8.4v 3600mAh battery. It does not rip your mechbox apart (unless your mechbox gets destroyed by "normal" batteries ) and of itself. Maybe a little quicker...but nothing like a large 9.6v 2200mAh NiCad
- a 11.1v 1100mAh 15C battery is quick like a small 9.6v 1400mAh mini pack...faster ROF than a 8.4v large. Maybe similar to a 9.6V large.
- Rapid firing with a lipo (i.e. lots of semi or long bursts of full auto) does heat up the battery more noticeably than with NiMh/NiCad batteries. Getting it really, really hot (i.e. too hot to hold in your bare hand) can't be a good thing.
-- I had a "run-away" gun from a pinch probably cut loose a 1000+ shots before I got into the stock and unplugged the battery (11.1v 1100mAh 15C lipo). The battery was EXTREMELY hot...and took a long while to cool down. The voltage of the pack was still above threshold...but the heat generation was a bit unnerving.
- preserving the integrity of the LiPo battery casing (i.e. the plastic wrap it comes in) is important. It's the only thing that prevents it from venting, exploding etc... NiCad/NiMh batteries are in little metal cans...LiPo cells are basically baggies of chemical goo.
- LiPo cells should be charged up to a max of 4.2v per cell and never discharged below 3v per cell. So a 3 cell 11.1v battery has a max of 12.6v and a min of 9v.
- Continuing with the example 11.1v lipo pack example...If a cell in the pack is "dead" and isn't taking a charge...and then you charge up the pack to a total of've overcharged 2 of the cells, driving them up into (and maybe past) the danger zone where the cell packaging bursts and all the firery demons come out and burn down your house. Same thing happens with NiCad/NiMh batteries...but you don't get flames and toxic get a chemical mess of battery acid.
- If a cell in the pack is worse than the may discharge quicker. So when your total Voltage is 9V (for a 11.1v 3S pack)...two of your cells might be higher than 3V and one under (killing it more). Then you go to charge it up and BOOM.
- Balancers and the capability to check the individual cell voltage is important. Balancers monitor the voltage of each pack while it's charging and adds power to individual cells to "balance" them out. It does not guarantee that when discharging one cell is "dying off" faster than the others.

Hope that helps,

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Old April 24th, 2009, 13:11   #18
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Ni-Cd (Ni-Cad) = Nickel Cadmium
Ni-MH = Nickel Metal Hydride
LiPo = Lithium Polymer

LiPo batteries are the same kind used in your cell phones and most modern portable electronics these days, but they require a lot of care, as they are quite volatile and can explode quite violently if mistreated in use or in charging.

If you're pulling an M120 type spring, just make sure the LiPo pack you're getting is rated for at least 20C. 25C recommended. Stick with 7.4v = 11.1v will be too hot for your mechbox.

As for the Systema springs, the standard M120 is an oil quenched steel, whereas the M120S is Stainless steel (hence, the "S"), and the M120S is more suited for a skirmishing gun that goes through full auto cycles. It seems to return springiness faster than an M120 does and is what Systema recommends for the common skirmisher. The Stainless spring also seems to push out a slightly higher velocity than the standard M120.
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Old April 24th, 2009, 17:58   #19
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I'm not so sure that C rating is all that important as long as it's above 15, ideally 20.

THe motor pulls power from the pack and with airsoft motors that maxes around 60amps (or so i'm told). i've seen RC packs up to 68C 3000 mah, If you want insane lipo packs look at the ones for choppers and planes.
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