working on a project but not sure on what type of battery to use

Battery charger: more power or more current? helps to understand the principles.

Clem

Hi Reuben,

Of the batteries listed the Lithium ion and polymer would have the most energy density. ( More energy capacity for a unit of weight). That being said they also have greater danger of failing catastrophically and are more problematic to charge. Your idea certainly has merit and any technical advances in this area would be of great benefit. I do not know how familiar you are with the physics of solar power or generating electricity from body movement so I will give you a couple insights. The first rule is that there is no free energy. In the case of solar the cost is in terms of getting a surface area of cells exposed to sunlight for a period of time. The smaller the surface area and the shorter the time exposed the less energy is collected. For the case of getting energy from muscle movement the cost is the extra energy that must be used to overcome the obstruction caused by the electric generator. It is a fallacy that there is a lot of extra wasted energy generated by the human body in motion. Evolution has sculpted us to be very energy efficient. If we go for an hour walk and we want to generate the energy needed to recharge a 7.2 Volt 1200 mA hour battery in that time period we must do the equivalent of lifting a 1 kg weight (2.2 pounds) the distance of one meter every second of the walk. These are rough calculations and assume that we can be 100 percent efficient in our conversion of mechanical energy to electrical energy. (Not possible in reality) As you can see from this it is much more practical to ask the person to carry an extra charged battery that weighs grams instead of expecting him to generate the additional energy to recharge an existing battery. Your idea to standardize batteries for military applications is a great idea and worthy of pursuing. I suspect that the demands of size and location of the different pieces of equipment will limit the ability to standardize but it is still worth making the effort. Perhaps just standardizing the connections and voltages would at least give the ability to cobble temporary patches of batteries from one piece of equipment to another in situations of emergency. Keep thinking and good luck with your project.

John

so far on the project I've completed the wiring harness and the magnetic electrical coupling that connects up to 2 plates which are form moulded to the grip of the weapon system. the wiring harness took the longest as it has to manage a few different voltages and also be completely sealed. the main concept is to make a system to reduce weight also the allow free movement and ease of use and to work with standardized equipment with little to no modification

Well articulated John,

A couple of additional notes:

Lithium Polymer is generally available in safer batteries than Lithium Ion.

Solar provides by far the most scavenge-able power although only during daylight hours. You can get flexible or fabric solar cells that can double as exterior fabric, so the extra weight might not be as significant as carrying a big solar panel. As John points out, cost of fabricating everything with exterior solar cells can be high, and even with every exposed surface covered with a solar cell, the efficiency is not that high. At least half of your surface will be in the shade. Given the angles and materials available, efficiency may be much less than 10%. However, if you have the money for complete coverage with the best materials, there is significant power available - about a kilowatt per square meter. Also as John points out you will need to calculate if the effort to carry the solar cells exceeds the effort to carry extra batteries.

This is a universal question, everyone wants 'battery to be as small as possible' while 'it can be charged with a small power source' and 'it should deliver for long time with enough voltage & current'. Guess we need to wait more. Who knows we might even develop True Free Energy Sources.

But till then, If you want to work with low power delivering source i.e. solar panel go with low current battery.

Good Luck !

mudz

I think expecting 1KW/Sq Meter is also very optimistic with today's panels, unless you on the equator in the midday sun it will be way less. I would imaging you would need the very latest technologies still in the LAB or with NASA to get close to that otherwise. Also do the math on how much power is consumed vs pit back in. If the Kit is being used during the day (Radios, Drones and the like) then without additional cells or batteries, you won't keep up typically. Now if you have plenty of vehicles around you could cover them with solar cells and use them as "Charging stations"

One concern I would have is the "Painting of a Target" on the wearer of the panels, they will warm up and have quite a heat or other reflection on them ?

Just to clarify a couple of points:

1 kW/sq meter is the energy available from the sun - a solar panel can only convert a small percentage of this into electricity (that is why I indicated less than 10% effective efficiency)

Batteries can deliver far more energy per kilogram than any commercial solar panel, so trying to make solar cells outperform batteries in high current applications wouldn't be very feasible right now, but there are all sorts of applications where solar energy is sufficient to run the electronics without any help from batteries, and for power intensive applications, solar power helps batteries last longer.

The energy that solar panels convert to electricity will mostly end up as heat when the electricity is used, but so will any electricity from a battery. The energy that is not converted to electricity will partly be absorbed and converted to heat and partly be reflected, just like any other material, so it is not particularly worse than most other materials in terms of becoming a thermal target.