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I have a setting where there is power armor along with a somewhat compact power source that powers not only the suit, but some basic weapons and additional features on the suit. The problem I am currently having is that such a power source at such a compact level would have unintentional consequences. Namely that the exact same power miniaturization technology could be mass applied to other concepts. A battery or compact reactor would end up solving a lot of power generation problems in nonmilitary uses. For example, the compact fusion reactors in Fallout for the power armor cause unintentional problems in that they are somehow able to harness that much power into such a small unit. Array enough of them together and you probably wouldn't need an internal combustion engine for a tank, you'd probably end up saving overall weight as well.

Why would my power armor source NOT benefit the civilian world or radically change other aspects of military hardware to the point that things like jets or tanks can be greatly reduced in size when it comes to their powerplant size. The power armor in this case isn't much bigger than a standard human. But it ends up powering a lot of sensors, processors, communications devices, particle beam weapons (helps power it), low level offensive laser weaponry, NBC filtration, air conditioning etc. Essentially why a power source be able to deliver a lot of power to a power armored suit, but not be effective when scaled up for armored vehicles, jets, ships or even power grid production.

One angle I've considered is heat dissipation scaling exponentially for such a source, though it's not as ironclad/plausible as I'd like it to be so far.

The setting involves early interstellar travel to other solar systems/planetary networks so exotic materials or different ores w/ non-Earth based properties are well within scope.

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    $\begingroup$ Particle beams are already a no-no when discussing realistic power sources. $\endgroup$
    – Daron
    Commented Jul 11, 2022 at 10:49
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    $\begingroup$ @FIRES_ICE if your scenario supports magic physics, then you already have the answer to your question ;-) $\endgroup$ Commented Jul 11, 2022 at 11:02
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    $\begingroup$ Consider though that it isn't practical to prevent combining of reactors together. You can just scoop out the engine of your tank and just have a bunch of power-armour peeps inside pushing it around like a scifi flintstone's vehicle... $\endgroup$ Commented Jul 11, 2022 at 11:04
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    $\begingroup$ It looks like you're asking to brainstorm and generate ideas for you. Such questions are not a good fit for this site. Can you instead try coming up with your own solution and ask us for help resolving any specific difficulties you run into. $\endgroup$
    – sphennings
    Commented Jul 11, 2022 at 15:39
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    $\begingroup$ From a storytelling perspective, is there any problems with having other things be powered by an efficient power source? having power armor sounds like a bigger change from the real world than tanks are more efficient now. In other words, I think it'd be interesting to write a story where the cells are used for other things as well. $\endgroup$ Commented Jul 12, 2022 at 13:12

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It is powered by a single use battery.

It can't be recharged as the battery destroys itself as it discharges, you just need a new battery. This makes it useless for largescale power production, and a poor choice for the vast majority of civilian equipment. It might sound like a good idea for cars but heavier rechargeable batteries are better for a car that can passively support weigh and see a lot of use. Only the military can afford to buy/build a constant supply of the batteries. The powerplant for a tank or jet are not that big compared to the vehicle itself, and replacing banks of batteries is a bigger hassle for armored tanks or streamlined aircraft.

If the battery needs to stay plugged in or cryogenically cooled when not in use that makes it even better, that is easy for a smaller battery but makes it a major negative for vehicles that may need to operate in a forward position. you can build a truck portable generator powered box that carries enough small batteries for a platoon but carrying enough for a a detachment of tanks requires connection to a grid.

As Vesper thought up making discharge or degradation unstoppable once the battery is plugged in makes it even more unusable for other applications. Maybe that is why it has to be refrigerated/plugged in to prevent it. say if once the battery is plugged in you have 12 or 24 hours before it eats itself. You will still have high end sport vehicles that use it and maybe some emergency equipment but that's about it.

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    $\begingroup$ This makes sense to me. high-performance/high-degredation is fine for things with active combat lifespans of minutes or hours, but for a tank, you need a vehicle capable of going cross-country and operating semi-independently for days. You'd want something more flexible. $\endgroup$
    – Ruadhan
    Commented Jul 12, 2022 at 7:02
  • $\begingroup$ Also, tanks, planes etc. are heavily dependent on functioning support anyway, so adding fuel supply to the long list of already necessary support tasks isn't worth it. [And yes, tanks can go solo, but that's wasting a lot of their value and potential] $\endgroup$
    – Hobbamok
    Commented Jul 12, 2022 at 12:29
  • $\begingroup$ Not enough - after all, there is a megaton of stuff in the real world that's powered by batteries, and rarely a person complains about this (they do about where to put dead batteries but that's all). Having a car powered by a single-use battery is perfectly acceptable, for example. But, having the batter to be unstoppable discharge, like a radioisotope generator of current manufacture, would probably put a more serious damper on employing such batteries in civilian tech. $\endgroup$
    – Vesper
    Commented Jul 14, 2022 at 12:32
  • $\begingroup$ @Vesper Having a car powered by a single use battery is perfectly acceptable assuming the cost of the battery is anywhere near the price of a tank of gas, and not say ten or a hundred times that much. but yes making the discharge unstoppable would make it even better so I will add that. $\endgroup$
    – John
    Commented Jul 14, 2022 at 16:41
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Extreme Inefficiency

Each magic fuel cell is super lightweight but only contains an hour of juice. That means the mech suits must be deployed surgically and turned off and on at the traffic lights.

For some reason I leave up to your imagination, the military figures the advantages (what advantages?) of having a powered exoskeleton rather than a tank or fighter jet, outweigh the disadvantages of the inefficient fuel cell.

You could put the cell inside a tank or fighter jet but those guys can already carry their own engines and fuel. They don't need the upgrade.

The fuel cells cost more energy to create than they can store. So you cannot use one to power a power plant.


Taken to the extreme, the mech suit weighs nothing at all. It appears around the body when turned on and disappears when turned off.

enter image description here

In this case the advantages are clear. They are for sneaky operations where you can store the on/off button in your coat pocket or bumhole.

They are also a panic button for a troop of ordinary soldiers. The suit is only turned on in an emergency. When it is off it does not use up power and costs nothing to maintain. Except the opportunity cost of using it elsewhere.

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    $\begingroup$ Please disclose sources of your images, and why you believe it's fair use (unless license is compatible). Otherwise it's piracy. $\endgroup$
    – Mołot
    Commented Jul 11, 2022 at 20:08
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    $\begingroup$ When you say "what advantages" I look at some things used in Ukraine. Apparently they use electric (mountain)bikes to quickly and quietly cross terrain, attack a target with like a rocket or other suitable weapon and then be gone before even a dispersed artillery barrage can threaten them. Time and again, small mobile forces win from tanks in many situations outside of flat terrain open combat. Power armor correctly designed gives just enough protection against common threats and helps carry the weapons they need to combat high-end stuff or attack something without a big, loud visible vehicle. $\endgroup$
    – Demigan
    Commented Jul 11, 2022 at 20:54
  • $\begingroup$ @Mołot Fair use does not apply to StackExchange, see meta.stackexchange.com/q/327528/184432 . This image must have been created by Daron, as he indicated he has the legal right to publish it under the CC license when he uploaded it. $\endgroup$ Commented Jul 12, 2022 at 10:39
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    $\begingroup$ Bonus: 90% of the functions OP describes cost almost no power, stuff that could be handled by todays (or in 5 years) batteries already. So the suit does provide a lot of that funcionality all the time based off of regular batteries that are charged from regular generators at base camp (or hydrogen gens for deeper missions), and the magic fuel is only used for the superstrength/shields?/nanobots/weapons when the actual fight begins $\endgroup$
    – Hobbamok
    Commented Jul 12, 2022 at 12:26
  • $\begingroup$ @Mołot See edits. $\endgroup$
    – Daron
    Commented Jul 13, 2022 at 11:11
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Extreme Danger:

Your tiny reactors have a distressing tendency to explode. Now, this isn't a BIG chance, but the more reactors you have in close proximity, the higher the chances they blow. In parallel, they may even set up a dangerous resonance that increases the odds of failure.

Or perhaps they emit a subatomic particle that can destabilize other reactors. Now a few troopers in a battlefield feet apart don't emit enough to trigger the reactors (especially if they are moving around and constantly varying the emissions). They would need to wait to activate the reactors until immediately before going into battle so a packed troop transport didn't result in exploding suits.

The risk is too high to tolerate in a civilian use. But war is war, and the chance of your soldier dying from his own reactor blowing is lower than the increased chance of death from NOT having powered armor.

New Tech:

Sure, after the war this tech will transform your world. For right now, however, your armor is brand-spanking new. It took years to get it working, and the engineering is very finicky. Existing tanks and planes are expensive to retrofit, and the engineering to do it safely will take years. In the meanwhile, the value of the armor suits is so high in battle that all the output for these is going just to the mechanized infantry.

Military developers are also notoriously hidebound. Until a new technology is proved beyond a shadow of a doubt, they will spend vast sums on old tech because they know it and understand it. So the Air Force, Navy, and Cavalry (tanks) are in the hands of different branches of the military. But the infantry (widely considered irrelevant to modern war) is desperate enough to be willing to take risks on unproven equipment rather than have their troops be mere cannon fodder.

Psychic Handwavium:

I think the best answer to this is that your suits are powered by psychic ability. Each person's mind is able to tap into a deeper level of reality, and the energy differential is such that it powers the suit. You might have a few genuine psychics around who could power a vehicle (and read minds or bend spoons), but for the most part, the psychic potential of an ordinary person only allows them to access a small amount of power.

This also helps with the physics of your particle beam. The weapon generates a psychically-charged plasma that is actually a primitive form of life. It acts like a predator and is imbued with the intentions of the user. This is why it behaves outside of standard physics - because it has intent.

MUFON and other alien-experiencer organizations have suggested such plasma actually exists as an explanation for various phenomenon. They also suggest aliens have various psychic abilities, although the aliens would likely not need such "primitive" sources of power to run their equipment.

Your users might need to get semi-dangerous implants or drugs to access this energy. Thus, they are considered unsafe for use by civilians. But the military has shown a wide willingness to use tools dangerous to the users to make more effective weapons. After all, soldiers are already risking their lives to fight. So what if 10% of your army will go insane or die of strokes over the course of the war?

Black Box:

Your people don't really understand exactly how this tech works. Perhaps it is captured alien tech, or the work of a brilliant but erratic (and now dead) scientist. It works, and amazingly, but any attempts to use the tech for anything else fails - catastrophically. Folks are spending billions trying to figure it out, and they can COPY the tech perfectly, but in the meanwhile, all it is good for is to power exoskeletons.

Low Transmission:

Your suits utilize a new way of using energy. The real trick is HOW the suit receives power. They create a field a bit like a Tesla coil that transmits power. Only the range of this field is VERY small - a few feet, at most. The fields can interfere with each other if in too close of a proximity.

So while the devices can power things very close to it, they can't funnel into a power grid or network. They might be able to generate very brief fields to contain particle beams, but this effect is only stable for a fraction of a second (long enough to fire a weapon...)

enter image description here

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    $\begingroup$ I like "extreme danger" as a reason. I think we put nuclear fission reactors on Navy ships but not on cargo ships for this reason -- not so much that it's a danger to the user, but it's a danger to society if misused or poorly maintained. $\endgroup$
    – JamieB
    Commented Jul 11, 2022 at 19:50
  • $\begingroup$ We put nuclear fission reactors on Navy ships and submarines because they are needed there. For a carrier, it is needed for the power - the planes don't take off, they are thrown off the ship. For the submarine it is needed for the silence. If they were put on cargo ships, then other countries could capture or buy the cargo ship and enrich uranium with those same reactors. The only limit to nuclear weapons is uranium and therefore enriched uranium. $\endgroup$ Commented Jul 11, 2022 at 20:11
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    $\begingroup$ Not only that but nuclear reactors are safe only if properly operated and maintained. I have heard enough stories from the merchant Navy to know that they would not be properly looked after on civilian vessels. $\endgroup$
    – Turksarama
    Commented Jul 12, 2022 at 3:45
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    $\begingroup$ @J.ChrisCompton Worse--shipboard reactors have to be small. They're fueled with weapons grade uranium. Obtaining uranium isn't that hard, it's enrichment that's the real bottleneck to a bomb--and if they can dismantle shipboard reactors it's already done. $\endgroup$ Commented Jul 12, 2022 at 4:57
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    $\begingroup$ @LorenPechtel I thought that shipbaord reactors were fueled with 90% enriched, and that weapons grade is above 98. In the grand scheme of things getting from 90 to 98+ would be difficult, but yes far less of a haul than getting from the 2-8% in a civilian reactor to 98+. If my numbers are off let me know, it has been a while since I was close enough to the industry, so I may not know what the current numbers are. $\endgroup$ Commented Jul 12, 2022 at 9:23
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one way would be scarcity - the source is theoretically usable for other applications, but there's not enough to go around, and military has precedence.

another idea would be that it somehow needs to be integrated with an organism to work, for example via a neural interface to control it. it could still be used for civilian "suit-based" applications, but it's limited to one unit per person, and you've put a stop to scalability.

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  • $\begingroup$ My concern with scarcity is that it would have to be scarce enough to not use in the civilian world but not scarce enough that the military would deem it strategically unviable to deploy down to the squad level. Even if not all soldiers are outfitted with power armor, there's enough of it where it occupies its own column/tab in the logistics report. But organism integration is an interesting thought, especially if only one person can control one power source at a time. $\endgroup$
    – FIRES_ICE
    Commented Jul 11, 2022 at 10:59
  • $\begingroup$ Scarcity would mean priority, and then it would be fitted to jets first because these can't have too much energy on-board to power their systems. $\endgroup$
    – toolforger
    Commented Jul 12, 2022 at 9:39
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Numerous reasons.

Classified

The go to excuse for a military organization. Some part of the power source is bleeding edge tech that provides the suit its power would give the adversary an edge that you do not want them to have (maybe the tech is the only way you can fight them on even grounds... if they get it, they would decimate your forces.). It could be that the fuel and the type of reaction are known, but only one guy has cracked how to cool it in a compact way and all his work was classified. Discussing it unless you have a need to know can jeopardize your edge. This happens in real life. The United States makes a lot of money from exporting weapons... but it still keeps the good stuff for itself. The current top line jet the U.S. is producing is the F-35... despite it being an inferior plane to the F-22. The reason for this is simple: The F-22 contains a bevy of tech that is classified and cannot be sold to even our closest allies lest it get into the hands of people we don't want knowing how it works. Removing those stuff would take away any edge the F-22 has over other jet fighters world wide... So the F-35 was creates so countries looking for next gen aircraft could still buy something from the U.S. Otherwise they might take their business elsewhere.

Lack of Infrastructure/Efficiency Gap

This is the biggest thing holding back vehicles that don't rely on fossil fuels or use alternative cleaner sources. Currently electric cars are hampered by the lack of infrastructure to charge the batteries of the car, which makes them much more expensive as you need to have a reliable facilities. It's even worse for the hydrogen fuel cell, which requires an entirely new fuel station to run, despite the fact that the only "waste product" of hydrogen fueled vehicles is pure water. There's also the tendency for hydrogen to be a very volatile when exposed to oxygen and a tiny spark. And despite getting around all those problems the actual range of either car is less than a gas powered vehicle of the same size because the former has had 100+ years to develop more efficiency into their engines.

Military standardization

This might not be a universal problem but if your fuel source is different enough, it might not work for the military because the military has a standard fuel for all it's vehicles. Did you know in the U.S. Military, that you can take fuel intended for jet planes, put it in a tank, and the tank will run just fine? The reason for this is very much intentional. The reason why the United States military is such a powerhouse is because it invested very heavily in logistics... to the point that they can get just about anything to anywhere almost overnight (the special ops teams are prepared to get boots on the ground anywhere in the world in under 48 hours notice.). Armies march on their stomachs after all. Disrupt the supply lines and the army rapidly loses. Invading forces need to secure a victory. The longer an invading force takes to do this, the more likely they are to lose, even if they are superior (see the results of the Revolutionary war or the Vietnam war. Wars tend to favor the home team in the long run). With that in mind, the U.S. military has made as much of their vehicles run on the same type of fuel as everything else because shipping different types of fuels for ground combat vehicles, air vehicles, and sea vessels is asking for a logistics nightmare if there is a supply line disruption and fueling the fleet/motor pool/wing is the difference between victory and defeat. Introducing new tech that requires an entirely new fuel source in the supply line could be undesirable in the short term... they may wait until the engine can be adapted to other vehicles... which leads to the final point...

Steer into the skid

You can't put the genie back into the bottle in weapons tech. And weapons tech tends to advance similar to evolution... the next big thing is a defense to the last big thing... and the thing that follows that will be the ability to overcome the next big thing. You have a sword? They will make armor... You get a bigger sword that can break armor? War... war never changes... just the toys we play the game with.

This means that research into the latest and greatest tends to get prioritization in militaries. And that cool tech tends to see other uses in non-military markets. After all, one of the edges the U.S. had in WWII was an all terrain vehicle that could bring troops to the front lines miles away quickly while the axis powers still had their infantry march... which would make them more tired when the fighting started. This marvelous military machine is now sold at your local Jeep dealer... while still being used by the U.S. Military as light transport. GPS was developed to keep the U.S. military fighter keenly aware of their locations on the battle field. The Internet gained life as a system to ensure command and control of the U.S. military was kept intact in a nuclear war by decentralizing communications and information storage. The came to the civilian market and now I don't need to write down step by step directions to get to a new destination or better yet... I can know exactly what route to take to get to where I need to be, and catch Japanese monsters along the way there! Battlefield medicine translates very well to civilian medicine, and the Army Marching on its Stomach comes back to the home front in better packaging and storage of perishable foods. If it's good enough for our boys on the frontline, it's good enough for our growing children too! Maybe the story of this power armor isn't how to keep it out of the hands of others... perhaps it's "what happens when it does fall into the wrong hands."

There is a reason why so many of Iron Man's foes also have suits of armor. Tony Stark being a weapons maker who gave the world a superweapon it might not be ready for is kind of the critical point of his entire character.

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You could set things up so that each 'power cell' is a sentient life form that has to be grown, raised, and trained. They aren't just power sources, they are an integral part of the control system (the way a hunting dog both powers and guides itself to do what the hunter wants). This solves a number of scaling and distribution issues:

  • As life forms they only grow to a certain size, putting a top limit on their power output.
  • They can only be communicated with through specialized equipment (like implants) and need trained handlers to keep them on task, otherwise they'll take over whatever system they're connected to and go feral. That makes them unsuitable for most civilian uses.
  • They are territorial, and will fight any other of their kind that is connected to the same system, sometimes to the death. Or worse, they'll go into a breeding cycle... That precludes any sort of array or serial system that combines their power.

These factors make them useful for comparatively low-power systems with constant trained human supervision, but not for much else: powered armor suits; small mobile medical bays (where the entity acts as nurse and powers testing and diagnostic equipment); certain construction and engineering jobs where the un-augmented human body is too frail. They might find some use as control systems — e.g., to replace the autopilot of a passenger jet or spaceship with something more intelligent, while the main power source is still 'conventional' — but whether that's feasible depends on the cost and difficulty of breeding the entity and training its handler.

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Only military applications of a certain size

First off, a military development is not always used in civilian applications. It is a miracle we got GPS. though it is locked under a certain height and speed and will stop working above those thresholds. GPS could've been used solely by military for pinpoint accuracy and tracking, never to be released to the public to prevent many other militaries to get insight in the technology.

The power source is great for certain sized machinery. Just like a nuclear reactor of certain types have sizes that are optimal for both price and power generated, so does your power source. The best price to performance is at suit level power sources. Larger will skyrocket the price (aquariums are a good example), or give a certain danger (fatal heat buildup and too little ability to control the cooling). Smaller gives diminishing returns, making them quickly useless.

To make it not power larger stuff you can make it dangerous to implement multiple of such power sources. They can interact in close proximity or the same power grid. This gives a chance on (catastrophic) failure. This way you can't make them power a jet. Bigger ones are just unfeasible in price. Multiple ones can fail or require too much extra calibration and maintenance that it's out of the question.

It will certainly not be used solely for power armour. But you might actually want to implement it in some other machines as well. This is part of world building. You get a new introduction that changes the world in more ways than just power armour. To me that can actually enrich your world. But with price, performance and danger you can still make it unfeasible for many unwanted applications. It can then even be a part of the plot, where unexpected, exotic applications are used for the power source.

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Because the "fuel cells" do not provide electrical power. These fuel cells use ATP or something like it to cause specially engineered artificial muscle fibers to contract. It does not even lend itself very well to rotational power and is thus unsuitable for a tank or wheeled vehicle (and it can't do magical Tony Stark repulsor-style thrust units either). The "relaxation time" of the material is too slow to try to apply it to a piston to cheat this. This probably also rules out using it to cheat flight, you won't get viable ornithopters out of it.

You can definitely get something that's the equivalent of a bulldozer out of it, but it looks more like a loader from Cameron's Aliens than something with treads.

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Your "reactor" is not more fuel or weight efficient than batteries or gasoline, but it is able to output massive surges of electrical output much like a miniaturized capacitor.

Capacitors are similar to batteries except the are able discharge MUCH faster. But they are also much bigger and heavier for how much they hold. So, instead of making a power source that outputs more total power, what you have is a device that can hold just as much electrical charge for its weight as a lithium ion battery, but can discharge it much faster when needed.

Current military prototypes for power armor have most of the bells and whistles you are asking for: heavy body armor, digitally enhanced optics, communications, etc. Because the power requirements of something the size of a person are so small, the average output of such a system during normal operation is only about about 30 watts.

Keep in mind that your power armor does not need a super powerful radar system onboard to see things 100km away, nor does a power suit have a lot of reasons to need to know what is 100km away since their main roles will be urban warfare and infiltration. They only need the ability to communicate with and integrate their tactical information with nearby vehicles or buildings that DO have longer sensory awareness. The power armor's sensory suite will be more interested in features like infrared, range finding, motion detectors, short range sonar, optical zoom, etc. which means your total electronics package's continuous power draw will likely be less than 10 watts.

Even climate control will not consume a lot of power. Since you are only air conditioning the narrow space between you and your suit by a few degrees, a the cooling system will use be orders of magnitude less power than something like a home AC or refrigerator. I would expect this to be about a 7 watt system, similar to the water cooling systems used on high end gaming PCs, but in normal climates, this power draw could be much less.

Walking/running around of course consumes more power, but this is something you will not be doing all day long on a normal mission. A solider spends a lot more time sitting and waiting than he does walking about; so, this could take an average of 10-13 watts even if the power use peaks much higher than this.

The only real power requirement of your suit that you do not already see in current power armor prototypes is the energy weapon(s). If the suit wants a HEL (High Energy Laser) capable of filling antipersonnel roles, it will need to output brief 2000 watt spikes of power. For one capable of taking on armored vehicles, it will need to spike up to 60,000-240,000 watts of power draw. These massive spikes of power discharge is what your system can do that modern batteries can not.

(This of course also assumes you've been able to massively improve laser technology to be able to make a hand held anti-tank laser to begin with.)

If you assume your power system is in every other way similar to the lithium ion batteries in current power armor prototypes, and you were to swap out the typical amount of ammo a solider carries with more batteries, then then your suit would have 72 hours of power set aside for normal field operation, plus an additional 130 hours of power for the extra batteries that are replacing your old ammo load out. With 130 hours of fuel "set aside as ammo" your power armor could in theory operate a 3 day mission, and fire enough shots to take out 65 main battle tanks, 260 light armored vehicles, or 7800 anti-personnel shots with its lasers... or the more likely scenario, allow the solider to operate an entire week between recharging and still be able to fire off the same amount of shots as a solider using bullets.

You could see the same tech used in other places, but it's effect would be far less noticeable.

In contrast, a Main Battle Tank like the M1 Abram consumes ~83 gallons of gasoline per hour. Replacing its engine with batteries would require a ~2,800,000 watt system. So, for a tank to also fire a 240,000 watt blast to kill another tank with a laser would not be nearly as extraordinary of a feat compared to what its existing power and weapon systems could already achieve. Furthermore, tanks do most of their killing with over the horizon weapons; so, replacing a tank's main gun with a direct fire energy weapon that needs line-of-sight would be at a strategical disadvantage against kinetic weapons anyway.

Aircraft consume even far more fuel than tanks. An F-22 for example can consume over 6000 gallons of fuel per hour. Also, aircraft rely a lot more on stealth, and it is a lot easier to fire a stealth missile from a stealth aircraft without being noticed than it is to fire a HEL which would light you up on infrared scanners.

So long story short, tanks and jets would still need their traditional engines and weapons because the power density of a lithium ion battery like system would be WAY to low to replace their primary propulsion systems and still maintain acceptable operational ranges, and the cost/benefit of directed energy weapons is not nearly as enticing for them as they are for infantry.

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    $\begingroup$ Reminds me of the time I asked my Dad why didn't we harness the power of lightning. His response was that it would be a lot of trouble for almost no gain. He (an electrical engineer and a PE) explained that, while a strike of lightning is very powerful and can do a lot of damage... in terms of energy - a single strike of lightning contains less energy than a gallon of gasoline. Gasoline is also both easier and safer to store. $\endgroup$ Commented Jul 11, 2022 at 20:21
  • $\begingroup$ @J.ChrisCompton I get ~5 gal of gasoline, but your Dad's point is still spot on. $\endgroup$
    – Charles
    Commented Jul 13, 2022 at 21:01
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Critical Mass

Radioactive material emits particles as it decays. When those particles strike nearby radioactive material it causes that material to decay, which in turn releases more particles. If too much material is placed close together, you get a runaway reaction and a nuclear explosion.

Let's pretend that the material that powers the reactors is similar to other radioactive material in that it naturally emits some kind of particle, and exposure to that same particle accelerates the release of more energy.

Let's pick the emitted particle to be something harmless to humans and impossible to shield. In that case we can't place more than a tiny quantity of the reactor material in one location. This prevents us from creating large reactors. We could create arrays of small reactors, but they would need to be spaced so far apart physically that they would be too huge to fit in an airplane or tank.

One option for the particle would be something like a neutrino. It's generally harmless, and they can't be shielded against (it is believed after all that neutrinos can pass right through the earth).

Non Use By Civilians

There are many technologies that exist today that aren't used by the civilian world simply because they are classified. Civilians largely don't know they exist, and even if they did, they don't know how to make them.

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Dark magnetism

"Fuel cell" is a bland, declassified, reassuring term meant to help soldiers feel comfortable with the concept of how their power supply works. It is true in a degree. But let's pull aside the curtain.

Researchers hunted for, and apparently found, a dark photon that mediates interactions with dark matter. Where there are photons, there's electromagnetism, so ... dark magnetism! The "fuel cell" projects a wide electromagnetic net that sucks in a certain type of dark matter particle from all around, like a mini Bussard ramjet. The dark matter particles, thanks to some advanced physics, can react with bismuth nuclei, causing them to undergo nuclear fission. This is like a normal nuclear reactor, but on demand at a high rate until the bismuth is used up.

"Used up" is itself a euphemism - there's plenty of bismuth left when the cell reads empty, but reaction products (strangelet isotopes and more unusual things) build up that are unstable in contact with the dark matter. So the "fuel cell" is built with a very strictly hardwired limit on power production, meant not to be defeated even in the heat of battle, lest a conventional war inadvertently turn into a nuclear war. There are treaties about these things.

For civilians not enclosed in protective armor, these fuel cells and their radiation are somewhat intimidating. The cost to dispose of used cells is surprisingly high. The military has surveillance requirements because of the risk of someone accidentally modifying one into a nuclear device.

For the tanks and airplanes, the limit pertains to the dark matter. It is hard to pull in that much dark matter to a small region of space using the existing fields, so it is far more expensive to design a giant fuel cell or two that work at high efficiency when adjacent than to just make two.

Note: this answer implies that suits of power armor in close proximity will suffer a reduction in raw power output, though the lifespan of the "fuel cells" is similarly extended.

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Your energy capacity scales with area

For argument, consider some kind of handwavium fabric that generates (small amounts of) energy by exploiting small potential differences in the quantum vacuum across it's face. Therefore your energy storage or power generation capacity scales with the surface area of the fabric.

Now imagine also that two sheets of material placed too close together interfere with each other, so you cannot "artificially" increase the surface area by folding a large amount of fabric into a small volume. Any other possible application that can easily increase it's volume would do better with a regular battery or a fuel tank, but your exo-suit needs to be form-fitting.

Now the applications that make sense for this fabric must fall below the maximum power/unit area produced. A human-sized exoskeleton has relatively low power/area requirements, but an armored vehicle needs much more power, but the surface area is only a few times larger. It scales even worse for aircraft and power plants, especially if the power/area you can get out is less than a good solar panel. Even better if the magic fabric is very lightweight. Pair that with some kind of very lightweight kevlar-carbon fiber-composite armor and you don't need as much power to move the exosuit around. Most other uses aren't as concerned with weight, and those that do, like aircraft, care much more about power/weight ratio where fuel wins.

Such technology might find some niche applications, for example anywhere we might currently use plutonium radio-thermal generator (RTG) such as on spacecraft (assuming your handwavium explanation makes it a power source and not just a battery).

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Limited and Hazardous Production

Perhaps its not the usage that has a limiting factor on this tech, but the production itself: It is very expensive to produce, it causes massive environmental problems... and there is only a limited amount of resources before depletion.

While the above wouldn't stop the tech from being used in a tank, think about it like this: We can already get tanks to work without that technology, but that might not be true for this power-armor. The only reliable way to power it, is either using these fuel cells, or perhaps drag along a mile long power cable.

Since its a limited resource, it won't be wasted on weapons that can run without it - and only on those power-suits. They may also have a tendency to irradiate their surroundings.

And the production itself could be equally problematic or frowned upon; perhaps mining and exposing those resources make an area completely inhabitable, or the waste products are impossible to dispose of safely. Or maybe the magic required to get these batteries to work require a massive sacrifice.

Bonus points if the limited resource is some kind of very rare beneficial creature or asset. Perhaps, each battery requires the sacrifice of a magic user (which could be otherwise valuable), the destruction of an astral leyline (which causes irreparable long-term damage to the magic community) or the killing of beneficial spirits.

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Regulations

The first people to make this tech, sought out to specifically create this power armor. It wasn't that it was the best solution, but the armor is manufactured in pieces across about 15 US states and 3 allied nations, so we can regulate it, but only in favor of the random company to get here first.

Additionally, since the power armor manufacturer has a government contract, traditional manufactures can't openly pursue this technology without beaching contract with their largest client.

Sure, some individuals with too many doctorates in theoretical engineering might be able to jury rig something, and the large traditional manufacturers are looking into it, (possibly with experimental prototypes to be leaked and discovered) but that will forever be 10 years away.

Throw in a bit of propaganda for good measure. Convince education and trade groups to over-emphasize the dangers of the trace amount of handwavium. Maybe some rationing too, since handwavium is always just a bit scarce. But mostly no one does anything else with it because the government says not to, and it's hard to openly oppose governments with powered exosuits.

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Alien tech

Your military figured out how to use it, but they don't know how it works. You were just lucky enough for a small cargo vessel to crash (relatively) gently on your moon with a few dozen. Or...

You haven't invented them yet

You certainly will now that your grandson sent them back to you. It's just a matter of time.

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Copyright laws

The massive multimedia conglomerate that manufactures power armor simply refuses to give the rights to the adapter patents for use elsewhere; uses outdated and overreaching copyright legislation it wrote and lobbied for to sue/takedown/bounty hunt those making technology compatible with their products (which happens to only be their power armor)

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Your fuel cells require a rare blood type for combustion. Preferably fresh.

You could claim that your fuel cell needs a small constant intake of very specific organic fluid (easiest would be an exact blood type) to produce power. Ergo the limiting factor for widespread magical fuel cell use isn't the fuel cells themselves but the far rarer secondary genetic material required to activate the things.

You can't use the fuel cells for non-military use as running them full time would require chaining individuals with the rare bloodtype to powerplant machines to ensure the constant trickle of the required blood. You could claim that even slightly larger machines like tanks can't use the magic fuel cells as mixing batches of the required bloodtype from different donors has wonky effects on the fuel cells - so only machines small enough to be run off a single fuelcell/blood bag combo are viable. Also fuel cells tend to vibrate at the same frequency, so using multiple fuel cells in close proximity tends to damage them.

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There are just batteries

They don't produce power, they just store it. Maybe it contains some anti-matter particles. They take a lot of power to make in the first place and could be used to store energy until its needed. But couldn't be used to get more power than was used to make them.

Also it may not have wide spread use as the general population get a little scared when you tell them its equivalent to a small nuclear bomb strapped to their back. To your soldiers you tell them to follow your orders and be glad that you think you fixed all the issues with anti-matter leaking out of the container.

People get even more worried when you say you want to put kilograms of the stuff in a tank or an airplane. So bowing to public pressure you decide not to equip your tanks or airplanes with the stuff.

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The power source could be something like a zero-point module from Stargate. It creates a ton of energy from basically nowhere. Using your energy device creates a sudden surge of power, but will cause some sort of catastrophe (bend or mess up space/time, cause wide-area sterilization, release radiation, creates a microscopic black hole, etc.) if left on permanently, or if the device is not moved between frequent uses. It cannot be scaled up for the same reason, nor can you use multiples chained together in the same confined area as they could build off each other. The device pulses on and then off for a fraction of a second, dumping the power into energy cells which hold it for use. Normal walking around might use very little energy, resulting in the device flipping on once a day to recharge. During combat, this might get to the point where it is turning on every few minutes. Such a danger would also limit the number of suits a side could field in battle, as eventually their fields might overlap and cause the catastrophe. Perhaps one reason why they are kept so small is to limit such interaction odds.

This technology could still potentially be used in jets, but not near other jets or when parked near each other in a hanger. They would still need to use fuel for taking off and landing. At that point, you are trying to create a jet which can use two different energy sources to accomplish the same thing, a difficult and maybe insurmountable problem. Cars and tanks face the same issue as the jets. Nobody could use the energy device in a parking lot. They might be able to create hybrid cars, but would require some sort of safety feature to avoid turning on while passing another vehicle which is also turned on. Do you really want people driving around with a device which can cause devastation if it fails and stays on too long?

Add to the mix, a lengthy, difficult, and/or expensive manufacturing process, and you limit easy access to such a device. The mere threat such a device could pose would likely prevent civilian usage at all. A terrorist could rig such a device to switch on permanently in the middle of a city and leave behind undefined horror. It could have an almost “nuclear bomb” status. Useful in certain limited applications, but not beyond that.

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Cannot stop the battery from generating energy

Civilian technics is largely not a 24/7 energy consumer, things need to be turned on and off on a regular basis, some stuff is better left off for 99% of the time but require a lot of energy to do its work in the remaining 1%. Making your battery to generate a lot of energy per second but either not last long enough or not be able to stop discharging would be a decent damper for civilian application. Or better, "and". Still, some industry would benefit from such a battery, provided there would be enough of them available, like refining aluminium.

Contamination

Making such a battery could be done off planet, but using it would be close to humans (or who's using energy up there), and no sentient species wants their home becoming extremely dirty from everyday use. Make your battery radiate gamma/alpha/isotopes while discharging, and civilian application would become a lot more complicated. Army doesn't really care about contamination, they've got some deivisions specialized to confront it, and if that power armor of yours would be of enough war impact to turn the tide of battle, the generals would ignore contamination as long as they won't suffer more losses from that than from their enemy.

Insecurity

In fact, any single energy storage is a literal bomb. Should this energy be released at once, things will blow up. Giving such a device to a civilian society is asking for trouble. Thus, if your battery has energy density around 100x gasoline's, short-circuiting a 1kg battery would result in an explosion of about 50kg TNT, resulting in multiple deaths and pretty major destruction. Thus, using an energy source this powerful should be restricted administratively in order to mitigate the threat of it exploding with casualties. This alone puts a great barrier on using such a battery in everyday life.

Internal heat

Oh you've mentioned it already. Okay, add linearly increasing demand for cooling per sq.ft when scaling the battery up.

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It doesn't have to be exclusive to just the power armor.

In the late 60s - early 70s we saw the birth of the Main Battle Tank (MBT) because of advances in combustion engines. This made it possible to make a heavy tank as fast as a medium or maybe a light tank.

A more energy-dense power plant does not mean a smaller power plant. The M1 Abrams is larger than the M60, despite having a far more capable engine. Your tanks can just have more armor, a bigger gun, and maybe be a little faster while remaining the same size.

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