@Mark assures us that "Building a generator can be done at any time:" (just wind copper).
According to an eHow article, after obtaining an engine (we'd use a windmill, waterwheel, bicycle/animal motive power, or some other type of engine; simple exercises left to the reader), you need:
"2: Choose an AC generator head. This head will use an internal magnet to create electricity when the shaft mounted magnet is spun by the external engine."
And on another site, a guy created an wooden (armature) alternator (which contrary to @Youstay-Igo's assertation, does not seem to need that much precision), but the components?:
- "18 surplus NdFeB rare earth magnets"
- (and epoxy, and nice wire)
These magnets are not easy to come by because rare-earths are... well, rare. (and I'm assuming higher-power magnets are what makes this alternator as effective as it is, versus say, lower power magnets).
From the original question, one of the comments is:
@AdamDavis: Building a generator is considerably more difficult than one might assume. Lodestone, naturally occurring magnetic rock, is not only rare, but fairly weak. Generating 5W out of a motor built out of lodestone and crude wire is going to be an exercise in futility. The fabrication of stronger magnets requires electricity, thus a chicken and egg style problem.
I understand that non-mass-produced wire in the past (hand-drawn, ouch!) is a problem. As well as wire coatings, which are at least as problematic (for any type of longer-term use; and/or preventing the melting of your copper wire into a copper lump while under load). But the magnets seem to be the real sticking-point.
Obviously, a time-traveler - like in the existing question - caught in such a situation would begin to assess his problems, and could get magnets and wire and/or a solution anytime before going further back than 1880s. And probably some solutions further back than that (Judean batteries, etc).
But, if a time-traveler jumped back pretty far in his first jump, how would he make magnets/wire to make a generator; or, how would he make a generator (without those)?
Granted, that in the past there's plenty of resources, that you don't have to "mine": native copper, deposits that're still on the Earth's surface, etc. Lodestone is more rare however. Assuming he can prospect or talk to people who know where such resources are, we will assume he can get to it (ie: he doesn't have logistics issues (he's eating Shmoo), and can boop around using his (sealed) antigrav flitter to get to any location).
He's got some limited amount of power in his laptop/cell/etc, so if he's careful, he could set something up (what would he need to get that power out?) to jump-start his chicken-and-egg problem of creating a strong magnet. Maybe. (ie: how much power do you need to make a magnet, for how long?)
But, how would you do that (make a magnet)?
We're leaving the rectification of DC and voltage regulators (capacitors, diodes, etc) and stuff alone. I'm going to assume he has a robust laptop plug that handles a fairly dirty/unregular AC power supply input (ie: about how effective your laptop power cord/block is), as I don't see how he could easily make those, but bonus points if you want to tackle that.
In case it wasn't clear: Previous question assumed (and I am to), that he wasn't well prepared to do this; he just grabbed a few things and jumped in his time machine. Otherwise, obviously, you'd take a solar battery unit/hand-crank generator/@Youstay-Igo recommends a dynamo (and you've got one of those lying next to your briefcase/laptop, don't you? /snark), and a set of tools to make new things and spare parts: rectifier to run off of batteries, magnets, wire, capacitors, diodes, voltage regulators, interfaces, etc. Spare time-machine, etc, etc.
ie: What do you have right next to your laptop/cellphone? Probably not any of those things, nor a large-enough, powerful enough, set of magnets (how large is needed?)
Sounds like we might be using electromagnets (iron with wire wrapt around it) to be our magnets for the first iteration... if there's a way to power it. I'm thinking USB out of the laptop - which avoids the rectification problem. If not, why not power the electromagnets with hand-made chemical batteries; potatoes if nothing else?