Thaumaturgic Automata and Draw Power

[Fred Brackin]

Originally Posted by scc

GURPS has methods for mages to draw FP from electrical sources.

So I opened up both Magic and Spell Charts and found Draw Power (M180), that in turn referred me to pages 178-179, which is where the trouble begins.

GURPS for some reason prefers to define it's energy conversation equation in terms of the killowatt hour,

I knew this wasn't right but I went and looked to see where you could have gotten the idea anyway.

A highly useful table was left out when the Energy spells were brought forward from Grimoire/Technomancer. You probably really want the Technomancer pdf from e23 if you're going to mess around with this sort of thing. It's a great book by any measure.

There was some attempt to embed the critical factoids in the introductory text to the Energy sub-College but this went awry somewhat. It does mention kw/h but this is more of a red herring than a critical factoid. The calculation is needed for the Steal Power Spell but not Draw Power.

Draw Power (and the Conduct Power spell its' mechanics are derived from) runs on straight kw/MW and the critical factoid there is the 360 kw/second equals 1 FP.

You can't actually run a spell/device directly by using Steal Power on a battery directly. A mage can only replenish his own FP with that spell.

Having access to the Technomancer table I can tell you that even then a lap top battery isn't going to help much. Even entirely draining a car battery is only going to net you 5 FP (at best). This sort of spell was really meant to be used with a UT cinematic Power Cell. There were kw/h figures available for those (at least in VE2).

Draw Power is meant to be used with major energy sources. Again the Technomancer table tells you that a household fusebox only gets you 0.1 FP/second. A 945 horsepower automobile engine would only get you 2.

If you want to play around with Draw Power much you need a Technomancer industrial power line at a minimum and a MW-rated power plant if you need more. I had a mage who built a nuclear reactor shielded with permanent Force Walls in his basement to avoid that inconvenience.

[malloyd]

Originally Posted by Fred Brackin

There was some attempt to embed the critical factoids in the introductory text to the Energy sub-College but this went awry somewhat. It does mention kw/h but this is more of a red herring than a critical factoid.

You've got an operation error in there. kW/h or kW/second are meaningless units, you want a multiplication kWh or kWs, not a division. This somehow comes up a *lot* in GURPS energy discussions (though I don't really know why, it's usually right in the actual SJG material), probably more often than the error of reading kWs as a plural of kW.

[Fred Brackin]

Originally Posted by malloyd

You've got an operation error in there. kW/h or kW/second .

I will try and be precise.

The Draw Power spell requires a source of energy rated in kilowatts or more likely megawatts and it needs that energy in a time frame of 1 second (or the standard Gurps Turn to be even more precise).

Steal Power can work on measures of stored energy such as kilowatt-seconds or megajoules but Draw Power needs units in a multiple of watts and it needs it on that 1 second timeframe.

[whswhs]

Originally Posted by Fred Brackin

I will try and be precise.

The Draw Power spell requires a source of energy rated in kilowatts or more likely megawatts and it needs that energy in a time frame of 1 second (or the standard Gurps Turn to be even more precise).

A source of power, not of energy. Energy is rated in joules (watt-seconds), not in watts.

Bill Stoddard

[Anthony]

The whole business with kWh is an attempt to be consistent with ultratech power cells -- in 3rd edition, since 4th edition power cells have no defined energy content. In any case, the actually important conversion is that a power source suitable for spellcasting must be able to provide 360 kW (0.1 kWh/s) per point of fatigue, for at least 1s. This basically means that the vast majority of familiar power sources (e.g. household power) are totally useless for draw power, and even exceptions (such as the drivetrain of a 500 horsepower car) are something like 1 fatigue. Basically, to make draw power useful at TL 8, you'll want something like a flywheel or compulsator, and even then you're talking 100+ pounds of hardware per point of fatigue you can draw from it.

[Fred Brackin]

Originally Posted by whswhs

A source of power, not of energy. Energy is rated in joules (watt-seconds), not in watts.

Bill Stoddard

You're not helping the original poster. I was trying to help him but insisting on technical correctness while not adding anything to the Gurps rules discussion isn't.

[whswhs]

Originally Posted by Fred Brackin

You're not helping the original poster. I was trying to help him but insisting on technical correctness while not adding anything to the Gurps rules discussion isn't.

That would be true if the GURPS rules weren't themselves based on the technical definitions.

Bill Stoddard

[scc]

I've actually got a copy of Technomancer, but I went for the newest rulebook first, but I've got a copy of that table in front of me now.

I actually did some research into this before I posted, so I'm not as confused, however I'd advise against using watt-seconds in official rulings, it's an actual unit of measure, of CHANGE in wattage, so a household outlet, 240V, 10A and 60 hertz can supply .8 FP per second, using the table in Technomancer that a household mains provides 10 times as much that's 8 FP per second

When updating that section I'd suggest switching to the 360 kW/kJ as the baseline, instead of the 1kWh.

Addationally, and I forgot to say this before, I think that M179 has a typo, looking at that Technomacer table only seems to confirm it. M179 reads: "360 kilowatts (kW) is equal to 1 energy/second, and 360 kilowatt-seconds (kWs) or kilojoules (kJ) is equal to 1 energy." I think it should be 360kW/s is one energy per second and 360 kW is 1 energy

[Anthony]

Originally Posted by scc

I actually did some research into this before I posted, so I'm not as confused, however I'd advise against using watt-seconds in official rulings, it's an actual unit of measure, of CHANGE in wattage

That would be W/s, not W·s.

Originally Posted by scc

, so a household outlet, 240V, 10A and 60 hertz can supply .8 FP per second

240V x 10A = 2,400W, or 1/150 FP per second. The AC cyclic rate does not affect power output.

[whswhs]

Originally Posted by scc

Addationally, and I forgot to say this before, I think that M179 has a typo, looking at that Technomacer table only seems to confirm it. M179 reads: "360 kilowatts (kW) is equal to 1 energy/second, and 360 kilowatt-seconds (kWs) or kilojoules (kJ) is equal to 1 energy." I think it should be 360kW/s is one energy per second and 360 kW is 1 energy

No, that's definitely wrong. Energy is measured in joules (I'm going to disregard the metric prefixes, as they don't change the fundamental physics). Power, or flow of energy, is measured in joules/second, also called watts. It's possible to define a unit of watts/second—it would be the rate at which power is increasing or decreasing—but that's not used to any significant extent in engineering or physics, and has no standard unit.

So:

joule = watt x second = energy
watt = joule/second = power
watt/second is undefined

Bill Stoddard