How far can a time traveller go into the past before his electrical equipment becomes unchargeable?
My time traveller has a maybe 20-minutes-into-the-future smartphone and laptop. They can store large amounts of data, on the Petabytes level or higher. The time traveller can effectively store the entirety of the current day's internet and library of congress or other information on his laptop.
The problem is, they have a limited battery life. On very conservative use, it would be around 2-3 weeks before it runs out. Any DC current can charge the time traveller's equipment, though it supply a minimum of 5W of power on average to charge.
The so long as the time traveller's equipment is working, he can consult his database to help him construct devices necessary to charge his equipment. eg. Give him a motor and he would be able to rig it so that he can charge his equipment.
However, once the battery dies, he would no longer be able to do anything except the anything say, a college graduate would be able to do.
How far can this time traveller go back in time before his electrical equipment becomes unchargeable?
EDIT: I did not expect a solar powered solution, though it seems like a pretty good idea. However, some of the answers gave rise to some clarification I should make about the time traveller's equipment.
His laptop and smartphone require a DC current to charge, simply because a AC current would discharge when the polarity gets reversed on the other side of the waveform. (average current is 0) Essentially, this would mean that a rectifier would be neccessary if a AC current is used.
The idea is that the laptop and smartphone are off-the-shelf from the time traveller's time, so such external power methods would not be incorporated by default. The batteries are high-capacity such that although the laptop and smartphone consume significant amount of power, they can last for a relatively long period of time. Their actual specs are that on general continuous use, they last about 24 hours. But if you turn them off and on just for minor uses (such as just referencing some data), they can be expected to last 2-3 weeks.
In a sense, this question could be converted to: when is the earliest time that a DC power source with at least 5 watts of power (or more likely, enough a rectifier) can be obtained within 2-3 weeks?
This post was sourced from https://worldbuilding.stackexchange.com/q/6827. It is licensed under CC BY-SA 3.0.
1 answer
I'm going to take a shot at near-term technology forecasting, and say that your time traveller's near future smartphone and laptop are probably charged over some version of USB (unless they're Apple devices, in which case they'll probably use some more-or-less equivalent proprietary system).
The common everyday USB port hides quite a bit of complexity, with the same wires carrying both power and data, and with a complex hardware/software protocol for negotiating communication and power delivery parameters. This makes "hotwiring" a primitive power source into a USB connector pretty difficult, and likely to risk damaging the electronics if you do it wrong.
Fortunately, however, our intrepid time traveller probably won't have to do that, not unless they also forgot to bring a charger for their devices. There are several types of such chargers, each of them good for different situations:
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Standard AC "wall wart" chargers: Good anywhere you can get AC.
Modern switched-mode AC chargers tend to be designed for international use, and are thus rated to accept anything from 100 to 250 volts AC at anywhere from 50 to 60 Hz (and may work with sources somewhat past those official limits, too). That means they'll be compatible with most AC systems used since the late 1800s.
In a pinch, if you happen to know the general theory (or carry a copy of Wikipedia on your laptop), you could even try to build your own AC generator (or maybe team up with a local down-time inventor to do so). As long as you can find enough copper wire for the coils somewhere, and have a general idea of what you're doing, it should not be too difficult to build something that produces a voltage and frequency roughly in the needed range.
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Automobile chargers: Good anywhere you can get DC.
The DC voltage provided by a typical car "cigarette lighter" socket is nominally 12 volts DC, but in practice can fluctuate anywhere from 5 to 15 volts. Thus, USB (and other) chargers designed to be plugged into such a socket feature a switched-mode DC-to-DC converter that takes the "dirty" power from the car socket and converts it into a nice, clean, regulated supply. As with wall chargers, car USB chargers also contain circuitry to regulate and negotiate the current, and to take care of all the other fiddly little details of the USB protocol.
All this makes such a charger the perfect tool for powering modern electronics from a primitive DC supply. Just hook up some down-time batteries in series to get a voltage somewhere near 12 VCD, plug the charger in and go. Mind you, it helps if you know how to build an efficient battery — some of the earliest batteries, while technically capable of generating electricity, had really lousy power densities.
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Solar chargers: Good anywhere there's sunlight.
For powering your electronics "off the grid", it's hard to beat a solar charger. These are sold for travel use, for places where no other source of electricity is easily available. Internally, they generally feature a modern solar panel and a DC-to-DC converter, just like in the car chargers, for regulating the output voltage. You're not going to be able to build one using primitive technology (building an efficient solar panel is still a cutting-edge research topic today), but if you happened to pack one with you, you're pretty much set.
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Hand-crank chargers: The last resort.
If you need to charge your phone off the grid, and don't fancy carrying a solar panel with out, you could always go for one of these. They basically contain a small generator and a power regulator, and are mostly meant for emergency use (and/or as gimmicks).
If you don't fancy developing your muscles (and/or a repetitive stress injury) by winding a tiny crank for hours and hours, you could always hook the crank up to something like a water wheel, and let it grind away while you do something more useful. The main risk with these things is that they may not have been designed for long-term continuous use, and the moving parts might wear and break down after a while. If you were good with your hands, though (or had someone who was to help you), you might be able to rebuild a working generator from the parts.
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