[MaciekA]

As I'm sure you suspect, most of your questions generate a "it depends" style answer

Originally Posted by Bar1975

So, I keep reading that a 7.4V lipo is basically the same as a 9.6 NiMh battery.

That really depends (1!), but my "lazy" answer is no. They may act similar in the first 50 shots in a workshop environment into a chrono, but the discharge curve of these batteries is really different over time, and their reactions to heavy load as well as temperature changes are different as well. The 9.6 to 7.4 comparison is a really loose rule of thumb that experienced players and techs use to explain the relative strengths and weaknesses of these battery chemistries to people who just want a quick answer. As you will see below, there are some 7.4V batteries that can pull loads that many 9.6V NiMHs can never dream to handle.

Originally Posted by Bar1975

Does the 7.4 lipo offer a better trigger response and snappier actions than the 9.6V though? Otherwise why would you ever use the 7.4 lipo?

It depends (2!) on several factors. I have a 7.4V, 20C, 610mAh Rhino LiPo battery lying around that I like to use for testing:



Hobby King says 30C burst can be sustained for 15 seconds. At 30C then battery is discharging at 18.3A (30C * 0.610A). Is that still more juice than a bigger size 3200mAh 9.6V NiMh stick? Unlikely. I don't see "C" values written on NiMH batteries, but I've heard 12C as an example, that would give you 3.2A * 12 = 38.4A. So it is possible to come up with contrived examples of where a NiMH battery is "better" than a LiPo (when it comes to airsoft that is, charge-discharge considerations are different if you're building an electric vehicle for example).

LiPos are all about how much energy you can pack into a small space. Hobby King claims the nano-tech line "approaches 7.5 kw/kg", which is pretty exceptional. Wikipedia says NiMH batteries contain from 0.5 to 1.0 Mega Joules (MJ) per Litre. Lithium batteries are listed at starting around 1MJ/L and ranging all the way to 4.3MJ/L. Whatever the numbers, a lithium battery occupying the same amount of volume as a NiMH battery is always going to have more juice.

Lithium batteries also discharge differently over the life of a charge. Check out this graph:



As you can see, with a LiPo, you get a more stable, sustained voltage, or shelf, over the course of the charge (i.e. imagine getting a very stable consistent RoF all day long). Towards the end of the usable charge is a sudden falloff, at which point you know it's time to recharge. With a LiPo, your RoF will be consistent most of the day, then at the end of the day it will suddenly drop off. This is a useful signal. You can install mosfets or alarms that detect this slightly quicker than your ears sometimes do. NiMH batteries tend to fade in a more linear fashion from their highest voltage down to their lowest voltage. I'm sure you've been on the field and heard a guy's RoF getting slower and slower and slower... And people around him are saying "dude your battery is dying". That's typical of NiMH.

For trigger response and generating extreme torque in general, you are going to want to choose the LiPo that gives you the highest discharge, or C value. You could have several LiPos that look the same except that they differ only in the C value and they would give you very different characteristics. Some examples:

• 7.4V 2000mAh 15C = 30Amps. Enough for most airsoft rifles pulling M110 springs with 18:1 gears over a few hours of typical airsoft play.
• 7.4V 2000mAh 25C = 50Amps. Enough for almost most harder-firing airsoft rifles (eg: M120 spring with 16:1 gears). Should go for a few hours of typical airsoft play.
• 7.4V 2000mAh 65C = 130Amps. Will give extremely snappy trigger response all day long, and easily handle a M130 spring with 13:1 gears. Should last the day as long as a neo motor is used.

Originally Posted by Bar1975

Is the 7.4 lipo harder on the trigger contacts, wiring, etc? (Is this a general rule of thumb for all lipos or just starting at the 11.1V or higher voltage versions?)

Again, it depends (3!). If you mix the 65C battery mentioned above with the hypothetical gun I've paired it with, you will have tons of arcing at your trigger contacts and your stock wiring will have trouble keeping up.

Originally Posted by Bar1975

In regards to increased wear and tear (when not fully lipo ready) that a higher voltage lipo brings does the 7.4V minimize this?

It depends (4!) hugely on the discharge characteristics of the battery. For example, let's assume you're using a neodymium motor, steel 13:1 gears and a piston with some nylon teeth, like the Lonex blue, and for the purposes of experimentation, you've shoved a small screw driver into your cylinder to cause an artificial jam. The 15C battery is not AS likely to shred a nylon piston tooth as the 65C battery -- both can probably do it, but you're more likely to notice and have time to prevent the shredding in time with the 15C battery. So the voltage of the battery doesn't necessarily "minimize" wear and tear, but it does factor into wear and tear, along with the other characteristics of a LiPo battery.

Originally Posted by Bar1975

I would like to upgrade a couple of stock guns i have with these 7.4V Lipo's if they are easier on the gearbox than higher voltage lipos but offer some of the same benefits of a lipo (a general snappier response all around)

If would say you're safe if you're buying 15 to 20C batteries, but beyond that you are going to eventually find the need to write another post on ASC. I'll see you then