Accumulators: A concept for GURPS Spaceships

[gruundehn]

Originally Posted by Ulzgoroth

Batteries sort of store electrons, but they generate EMF.

(Though at sufficiently high current values it must be more complicated than that.)

Present-day chemical batteries can be thought of as having their own internal circuit - sort of, in a simplistic way. The electrons are stored, but the chemical action of the battery releases them at two levels. The low-level release rate is when there is no external circuit and thus the battery charge can last years, if not decades. If there is an external circuit, the battery releases a steady stream of electrons and the total circuit resistance opposes that release; thus, by Ohm's Law (E=IR or more accurately I=E/R) voltage happens. Any EMF generated is a byproduct of the fact that the battery is releasing electrons.

[Rupert]

Comparing an aircraft engine power/weight ratio with modern battery storage capacities, and considering how Spaceships systems are put together (IC engine systems include some fuel), I get an back-of-the-envelope result of 20-30 minutes of output from modern batteries at one power point (i.e. they can produce the same output as an IC engine+ hours of fuel for 20-30 minutes). If one assumes a heavier IC engine (and given aircraft engines operate in an environment that's easy to dump heat in, this is reasonable) and better batteries, an hour might be reasonable or perhaps two power points for 20 minutes (the longest Spaceships combat turn). Higher TLs would increase duration, not output, to be consistent with the way other power plants work.

Assuming a TL^ 'super battery' with more capacity is the logical way around this fairly small capacity. I expect that to fill the role the OP wants they'd have high output rather than high duration.

[Ulzgoroth]

Originally Posted by gruundehn

Present-day chemical batteries can be thought of as having their own internal circuit - sort of, in a simplistic way. The electrons are stored, but the chemical action of the battery releases them at two levels. The low-level release rate is when there is no external circuit and thus the battery charge can last years, if not decades. If there is an external circuit, the battery releases a steady stream of electrons and the total circuit resistance opposes that release; thus, by Ohm's Law (E=IR or more accurately I=E/R) voltage happens. Any EMF generated is a byproduct of the fact that the battery is releasing electrons.

Are you seriously trying to assert that batteries generate fixed current regardless of the circuit they're in? You have to know that's completely inaccurate. EDIT: That's blatant violation of conservation of energy stuff.

[gruundehn]

Originally Posted by Ulzgoroth

Are you seriously trying to assert that batteries generate fixed current regardless of the circuit they're in? You have to know that's completely inaccurate. EDIT: That's blatant violation of conservation of energy stuff.

No. The chemical composition of chemical batteries will have varying current based upon the resistance of the external circuit. But the chemical action produces electrons not voltage. Granted, by Ohm's Law, the three are highly interconnected but the chemical action produces electrons.

[Ulzgoroth]

Originally Posted by gruundehn

No. The chemical composition of chemical batteries will have varying current based upon the resistance of the external circuit. But the chemical action produces electrons not voltage. Granted, by Ohm's Law, the three are highly interconnected but the chemical action produces electrons.

That's true in a sense, but it's a rather tortured sense. The chemical action 'produces' (at one end, 'consumes' at the other) electrons to (and from) the electrodes. But the reactions also point to a specific electrochemical, and thus electrical, potential.

It should be fairly obvious that the chemistry in a battery doesn't have any direct dependency on the resistance of the external circuit. What the resistance does is determine (in combination with the voltage) a rate limit on the flow of electrons which is (under typical conditions) the rate-limiting step in the battery reactions.

[Kale]

Originally Posted by gruundehn

...thus, by Ohm's Law (E=IR or more accurately I=E/R) voltage happens. Any EMF generated is a byproduct of the fact that the battery is releasing electrons.

It's actually the other way around. The metals/salts in the battery have an inherent voltage (EMF) differential dependent on the chemistry of the combination of salt/ions/metals/acids. The current flow depends on the load attached across the voltage. If you put a wire across the battery then the only 'load' is the internal resistance of the battery, which is quite low. As a result, LOTS of current flows, usually heating up the wire and making it combust, or simply get hot enough to melt the guts of the battery.
In electronics you pretty much always have a voltage differential and the actual current drawn depends on the load. You can create 'current sources' but they are basically self-modulating loads that balance out resistance with the real load so the real load sees a constant current.

[gruundehn]

Originally Posted by Kale

It's actually the other way around. The metals/salts in the battery have an inherent voltage (EMF) differential dependent on the chemistry of the combination of salt/ions/metals/acids. The current flow depends on the load attached across the voltage. If you put a wire across the battery then the only 'load' is the internal resistance of the battery, which is quite low. As a result, LOTS of current flows, usually heating up the wire and making it combust, or simply get hot enough to melt the guts of the battery.
In electronics you pretty much always have a voltage differential and the actual current drawn depends on the load. You can create 'current sources' but they are basically self-modulating loads that balance out resistance with the real load so the real load sees a constant current.

I am an electronics technician, not an engineer. This is what I was taught.

[Kale]

Originally Posted by gruundehn

I am an electronics technician, not an engineer. This is what I was taught.

I'm an engineer, but I hung out with the technicians running the labs a lot when I did my undergrad degree. I learned an awful lot of practical skills from them that weren't taught in the classroom.

[Kale]

Getting back to Accumulators, it seems the only pseudo-realistic tech that makes sense is superconducting loops. Anything else requires a fair bit of handwaving to explain the energy density and discharge rates. I also wonder if star-trek style plasma could do the job? Maybe store the plasma in rings and draw the power down as you need it. Could use superconductors to help with efficient confinement of the plasma to generate containment fields...?

[Johnny1A.2]

Originally Posted by Kale

Getting back to Accumulators, it seems the only pseudo-realistic tech that makes sense is superconducting loops.

There are issues with superconducting loops, too, when we're talking about Smithian energy storage densities. Our current physics might not allow for any means of duplicating those accumulators, at least the ones in use by Kimball Kinnison's time.

Actually, given that the great powers all have access to total-conversion power plants by KK's time, the only real reason for them to use accumulators at all would be speed of delivery, and maybe emergency backup. Otherwise, you could store your energy in a very safe stable high-density form, i.e. matter. If you've got total conversion tech, you can store energy as something like blocks of lead or other compact material, and not have to worry about accidental discharges or anything else until you need it. Furthermore, your storage density is E=mc^2, so a gram of whatever equals 25 gigawatt-hours. That's pretty good.