CYMA M1a1 Thompsons and batteries

Yup. I love my lipos and now use them in every gun I own.

I'll not be buying another NiMH.

We are wandering off topic a bit now but since the original question has been answered, meh.
I must say lipo battery power has been a bit of a revelation to me. I was a tad concerned with the Viva Sten lipo provision but I have to say its been fantastic. How the hell that piddly thing runs an AEG I have no idea.
Small, not expensive, quick to charge, more than enough power for limited ammo WW2 airsoft - ticks all the boxes for me.

http://en.wikipedia.org/wiki/Lithium-io ... er_battery
Li-poly batteries are also gaining ground in PDAs and laptop computers, such as Apple's MacBook, MacBook Pro, and Macbook Air, Amazon's Kindle, Lenovo's Thinkpad X300 and Ultrabay Batteries, the OQO series of palmtops, the HP Mini and Dell products featuring D-bay batteries. They can be found in small digital music devices such as iPods and other MP3 players as well as gaming equipment like Sony's Playstation 3 wireless controllers[2]. They are desirable in applications where small form factors and energy density outweigh cost considerations.

@BedsnHerts

As said before, voltage goes with rof, mah goes with battery duration. Lower voltage=lower rof, therefor using lower voltage will result in lower rof.
Btw spring strenght has a lot of influence on rof & battery duration. Mechanisms with hard springs will have lower rof and will last you less shots.

@101stairborne-506

Since airsofters in UK use 330fps or so, it will probably last 1400-1500 shots. My TM Thompson lasted 2000 shots with 1400mah battery and I didn't even feel that battery is going less powerful. I am saying that with two batteries you are sure that you wont be left with no power if one of them dies. And you can always borrow it to your mate or you can use them in two guns if you have them.

@prophet

I saw what it looks like when LiPo explodes and burns down, and it is not nice. I'd use LiPo only in guns where I am forced to use them (in other words,no space for battery) and I would only buy quality ones. Using chineese LiPo that comes with a gun is probably a free ticket for a hospital trip (if you are unlucky).And it will wreck your gun if it burns inside.

@Everybody
Using LiPo is (in my opinion) not the happiest solution when it comes to Thompson. It has very nice battery compartment where 8.4V and 9.6V batteries sit very good. LiPo will only jump up and down inside the buttstock since it is smaller then NiMh.-- attachment is not available --

OT:

Looking at Lipo under voltage protection I've just purchased one of these.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... K:MEWNX:IT
A little alarm circuit that will tell you (loudly) if your battery is dangerously low voltage.

For £2.50 I thought "what the heck"... And it should fit in my sten along side the lipo.

There are cutoff circuits around, but I couldn't find one suitable for airsoft.... pulsing the throttle isn't going to do much in an AEG. lol

You can also buy fireproof lipo bags to put your battery in when charging should a fire occour. There's vids on youtube.

I also run a VP lipo in my sten and have had no issues with it yet. The china-soft ones (especially the one that comes with it) are useless. Get rid of them in a suitable fashion asap.

I always charge my battery on a balanced auto-cutoff charger and always in my presence (sits next to me when im on the computer). I also always charge it in a ceramic bowl. But like has already been said theres no real point using a lipo in a thompson when you have a perfectly good cutout to enable the use of NIMH batteries. I only use the lipo in my sten becuase im getting a skeleton stock for it.

Yup, I have a fireproof bag as well.

Been a while since I had a Thompson but if the stock and fixings are removed, is there then enough space behind the gearbox, within the main body, to fit a small Li-po ?

Not with a Marui M1A1 receiver, but with my CAW 1928 one there is, just... But I'd have to split the Lipo into two separate cells.

Theres no reason you couldnt wire in a variable resistor to do the same job. You can pick them up from maplins for a couple quid i expect

Excellent. A couple of quid sounds better than $80 plus a C&E reaming

Presumably I just sellotape it to the barrel and I'm away, yes?

Edit: can we rename this thread OHM my God (c'mon, you can't teach stuff like that)

Make sure you fit it somewhere easy to get at to put out the fire, then replace it...

Using any resistor to reduce rate of fire is a false economy. It'll use more power for a poorer result.
The high current through the resistor will require a larger-than-normal component (capable of 30Amps - not "a couple of quid" from Maplins), and reduced current flow in the motor, for a longer period will probably damage the motor too.

The microprocessor ROF reduction is either done by semi-auto in rapid succession, or pulse width modulation of the motor power. Either of those provide full power to the motor over short periods - no high power resistors or motor burn-out.

I got the words "fire" and "Maplins".

:blink:

I got the words "fire" and "Maplins".

LOL

OK.
AEG + resistor = VERY hot resistor = BAD!

Missed this earlier:

Been a while since I had a Thompson but if the stock and fixings are removed, is there then enough space behind the gearbox, within the main body, to fit a small Li-po ?

Possibly, but I think all the space back there is needed so that the upper receiver can slide forward for disassembly.

Missed this earlier:

Been a while since I had a Thompson but if the stock and fixings are removed, is there then enough space behind the gearbox, within the main body, to fit a small Li-po ?

Possibly, but I think all the space back there is needed so that the upper receiver can slide forward for disassembly.

Good point... that may stuff it for my 1928 as well... heh.

Hehe, I try to equate tricky stuff like this to real life things I can relate to, for I have little brain (or probably more accurately, can't be bothered to use what little I have).

AEGs are like starting your car engine using a starter motor. A starter motor draws a huge amount of juice from the battery - your lights dim and if the battery is a bit iffy it won't work the starter motor at all. Bloody huge leads are attached to the battery because of this power load. And yet the bulb in the car dashboard draws next to no power yet still draws its energy from the same 12v battery. That is to say, the motor having to turn a gearbox & compress a spring requires a lot of energy all at once.

So, No1, the issue is that you need a beefy resistor to 'resist' the load? If I describe a resistor as 'slowing down the flow' - lets say put a wire gauze membrane in a water pipe then in needs to be very robust - a piece of nylon stocking won't do?

Car.

Nylon stocking.

This is like some awful schoolday deja-vu for me. Any minute now Andrew Palmer will try to flush my head down the toilet.

The problem is that it's to do with voltage drop and power dissipation.

There's an important formula for all this.

V=IxR

V is the voltage dropped across the resistor.
I is the current going through it.
R is the resistance of the resistor.

So as the resistance goes up the current will go down for the same voltage. (It's all complicated for us because the motor does not act like a resistor as well. It's quite a bit more complex than that.)

So you need a high value resistor so enough of the voltage is dropped across it.

However.. the power dissipated in the resistor will be equal to VxI. So your resistor needs to be able to handle that as well.

So you need a resistor with the appropriate resistance which can handle the power being dissipated in it.... otherwise it'll overheat and burn up.

A bit simplified there and no real help, but heck it's 15 years since I did any real electronics and I've always been a digital man really...

:blink:
Car.
Nylon stocking.
This is like some awful schoolday deja-vu for me. Any minute now Andrew Palmer will try to flush my head down the toilet.

My first boss in 1975 was an ex-RAF electrician. I couldn't understand what electricity was (too abstract a concept for me to make sense of - even now I'm not convinced anyone knows what it is) and he taught me how household mains wiring worked using a analogy I could understand which was water pipes. I could understand direction of flow and taps and stuff so once I applied that to ring mains it was easy-peasy.
Heh, who said water and electricity don't mix?

Anyway, wot Yith said. Probably.

Yup... the analogy is sound.

Resistance is the width of the pipe, voltage is height, current is a measure of the amount of water entering at the top.

Current will stay constant along the whole pipe. Voltage is measured as height differences. Resistance can vary over the whole length of the pipe.

I can honestly say I don't remember a blind thing from my Physics lessons. We had a teacher who was an ex RSM and was absolutely terrifying in a way that teachers aren't any more. Great for discipline, not so good for learning stuff.

Ah, feck it - let's go for a smoke behind the bike shed and look at Andrew Palmer's copy of Razzle.

You can if you like, I have an assignment with Caroline Boulter behind the bins outside the kitchen. Who said romance is dead?