Lipo Question

Irishmaster

I know that when you use these you shouldnt drain them or it could damage them. How do you know when to stop using them before that happens? Does that mean say a 1400mah battery isnt actually that as you cant drain them so is about 1100mah?

Leftyflip

I stop using mine when they start running slow, ie, half the ROF.

It's about voltage though, not amperage with lipos. A 7.4 can be used til it has nothing left, where as an 11.1 can't be used until it has nothing left as the voltage across the 3 cells becomes unstable and it does bad things... so they say.

Dex will ahve a better answer.

Irishmaster

Alri cool! So when rof drops thats when to stop. Thats good to know!

glicster

http://radioactivemodels.ie/store/product_info.php?cPath=28_69&products_id=793

i use this but i dont remember paying that price for it

hobbyking.com have them aswell

BioHazRd

Leftyflip wrote: »

A 7.4 can be used til it has nothing left, where as an 11.1 can't be used until it has nothing left as the voltage across the 3 cells becomes unstable and it does bad things... so they say.

WRONG !!

You over discharge ANY lipo and at best you will wreck it. Invest in a lipo alarm, or get a MOSFET that will monitor your voltage. If you can't do that, just stop using it as soon as it starts to slow down. One of the advantages of lipo is that it will discharge at max voltage For longer throughout it's discharge cycle with a sharp decrease towards the end as opposed to nimh batteries which will gradually drop voltage across the full range of the discharge cycle. The voltage of the battery is what determines your rate of fire. As soon as an aeg powered by lipo starts to slow down, the battery is nearly depleted

Leftyflip

BioHazRd wrote: »

WRONG !!

You over discharge ANY lipo and at best you will wreck it. Invest in a lipo alarm, or get a MOSFET that will monitor your voltage. If you can't do that, just stop using it as soon as it starts to slow down. One of the advantages of lipo is that it will discharge at max voltage For longer throughout it's discharge cycle with a sharp decrease towards the end as opposed to nimh batteries which will gradually drop voltage across the full range of the discharge cycle. The voltage of the battery is what determines your rate of fire. As soon as an aeg powered by lipo starts to slow down, the battery is nearly depleted

*Lefty looks at Lipos* I have mutant lipos so - no matter what abuse I throw at them they keep going...

NakedDex

^^^ what he said.

The discharge curve for a dry-cell pack, like a NiCd or NiMH is a fairly consistent slow drop to "dead" voltage (each cell being nominally 1.2V, charged at 1.5V and discharged or "dead" at .8V).
The curve for a LiPo, and indeed exactly why they're so popular in electronics, R/C and airsoft, is a pretty straight line for it's life and a sudden and sharp drop toward zero.
Zero voltage in cells is never something that happens naturally and, depending upon the speed at which it heads toward zero, can result in a battery with reduced capacity or a puff of dark smoke where your pack used to be. If you keep the trigger pulled while the motor is clearly struggling under low power, you're going to mince the pack. It's unlikely to fail catastrophically, but you'll certainly notice it's performance will be gone to hell. You'll also notice a huge heat build up on the pack if you keep doing this, the heat being an indicator/side effect of the pack struggling with the current demand.

Given the above, and the discharge characteristics, once you notice a difference in rate of fire (and you will), change the pack. Ideally, you'd use a MOSFET with a voltage regulator on board. Cheap and simple to install, and really something I'd consider a necessity for running LiPo. It also improves trigger response, motor speed (fractionally) and reduces trigger contact wear (dramatically), and the more complicated models even offer you a three-round burst option. What's not to love?


Another thing I'd recommend is getting a multimeter. Seriously, every airsofter should own one. You can get a basic one in Maplin or Aldi/Lidl for a tenner, and it's exactly what you need for things like this.

BioHazRd

If you don't have a decent lipo charger with a display, as dex said, get a multimeter. Regarding lipo batteries, you need to know that if a cell gets discharged to below 3.2 volts, you increase the risk of a catastrophic failure the next time you plug it into a charger (fire, toxic smoke) due to a potential higher than normal internal resistance caused by a chemical reaction in the cell due to the over discharge. A cell that is fully charged will sit at approx 4.2 volts. A 7.4v lipo has 2 cells and a 11.1v lipo has 3 cells.
Balance charging ensures that all cells are at the same level and you don't end up with one cell deep discharging prematurely.
The moral of the story is invest in a decent charger and some way of monitoring your battery voltage during use, and you should have no major problems with your batteries.