F2000 - LiPo/NiMh

[Yakito]

Hello again.
I did use the "search" function but it didn't give me the answers I wanted, so ... he's yet another topic about batteries.

I've recently bought a G&G F2000. I love it already, but I haven't had any chance of testing it on the field.

Anyway, the batteries. I measured the battery compartment in the stock and it's something like this:

 

Length - 135 mm
Width - 39 mm
Height - 24 mm

So it's clearly pretty limited.
Now, I've been reading about LiPos the whole day and frankly, I find them cool, but using them is expensive and I already spent a lot of money on my rifle.
What I've been told is that you need a MOSFET and some kind of LiPo guard that will tell you if the batteries are reaching the "critical voltage", otherwise I may not know that I reached it and just break the batteries. As an electronic student I could make a MOSTEF myself, but not the guard, and I can't even see these things anywhere in the shops.

So I thought that as a beginner I should go for 9.6 NiMh. Less hassle, I already have a NiMh charger, I don't need a MOSFET (although I obviously should still have it).

But it still puzzles me how people say 7.4 LiPo still gives more rate of fire than 9.6 NiMh. Is this really true?
It'd be great to put a 9.6 NiMh 5000mAh into my stock, but the battery space is obviously limited.

To all the oldschool airsofters that still prefer NiMh. Do you use a couple of batteries with less amperes, such as 1600 or would you go for something like this -
http://www.component-shop.co.uk/html/8vp2200sc-ll.html

[sp00n]

lipo guard >> http://www.ebay.co.uk/itm/350728100256?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

 

info i have been reading on mosfets >> http://www.airsoftforum.com/board/MOSFETS-t196370.html

 

hope this helps

 

edit:- nice find there ... they seem pretty cheap on the old NiMH's

[Yakito]

Thank you for the links. I did read that MOSFET thread.
And about that lipo guard. Have you got it? Is it something you put into the gun and it stays there all the time or is it only for testing during breaks when you can take the battery out?

[sp00n]

re the lipo guard, I do not have it, it was just something i was adding to a future shopping list, but on that battery site, if you go to lipo chargers and scroll to the bottom they have a similar thing there .

[Yakito]

Have you already got a MOSFET?
If yes: Was it expensive? Or did you make it yourself?

[sp00n]

i have ordered the bits.... they weren't too expensive, but i didn't go down the active braking route

[AK47frizzle]

If you want to be on the safe side, NiMH will do you nicely but if you insist on LiPo, get some sort of auto cut-off charger for it (i dunno how expensive they are).

[ScoobySnacks]

For a LiPO you need to make sure you have a balance charger if you have multiple cells.

 

As an electronics student you'll already know that what most people call a MOSFET is nothing of the sort. It may have a MOSFET acting as a kind of relay, but most of the airsoft "MOSFET"'s are actually IC's of varying complexity which provide certain capabilities (such as programmable burst modes, active braking etc.) A true mosfet, running effectively as an op-amp to limit the current carried by the trigger contacts (and hence reduce damage caused by heating and arcing at the contacts) is one thing. Making the IC with all the programmability and active braking is a different matter entirely.

 

To answer one of your other questions, the LiPO has an internal resistance when new of around 2 milli-ohms. The NiMH will have an IR of around the 25 milli-ohm mark. You can work out the rest of the physics yourself, but it goes a fair way to explaining the increased ROF at a lower voltage, as more of the voltage is "seen" by the motor.

 

Edited to add, I meant 125 milli-ohm for the NiMH, not 25.