Imagine someone from the modern day somehow gets transported back in time around the same time of WW2 without warning ahead of time. He has with him a laptop, graphing calculator (and a hand full of backup batteries), a smart phone, and a digital watch. He wants to show of and use his technology, however, with the exception of possible the watch the all have limited battery life. I want to now how difficult will it be to find ways to charge these devices without damaging them safely?

For the sake of this question presume that the time traveler is not a hardware engineer, EE major, or otherwise has training that would help him to personally know how the electronic devices work or how to jerry rig power supplies himself. However, he has enough smarts and basic understanding of physics/electronics to have a vague idea that there could potentially be an issue with power that needs to be addressed.

He will also be quick to find those who recognize the importance of his hardware and would want to make sure they are safe, thus he will likely have the aid of people from the WW2 era who were trained in electrical engineering, hardware, and the like who would want to try to help him find a safe way to power these devices. These folks only have WW2 level knowledge though, and won't know specifically what type of power (voltage, current, fluctuation tolerance etc) the devices are configured to handle unless it's written on the device or they can reverse engineer it somehow. The only thing the traveler would likely be able to contribute is that wall sockets use AC power and batteries us DC, that's about the limit of his knowledge of specifics of the hardware.

So how hard will it be to jerry rig a safe power supply to charge his devices with the expertise available to him, and how likely is it that a miscalculation could accidentally damage or destroy the device in question?

I listed a bunch of standard electronic devices, but I don't expect any one answer to necessarily touch on all of them. I'm most interested in the laptop, but listed the rest both in case someone can provide feedback about them as well and because it's possible having them may allow more information to be derived before trying to rig the laptop power to ensure that one is safe.

I'm would be most interested in the situation in which the traveler does not have a charger for the laptop or cell phone available. However, if it turns out that having a charger makes it significantly safer (ie less likely to fry the hardware) it's okay to presume one or both exist.

Side question if anyone wants to answer, if the traveler didn't realize the risk how likely is it that he would destroy his hardware by trying to plug it in to outlets of the time?

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    $\begingroup$ It should be pretty easy, as they each input power specifications on the battery / chargers. The risk of frying said tech if you don't know what you're doing and just plug it in? Incredibly high. $\endgroup$
    – AndreiROM
    Dec 3 '15 at 19:05
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    $\begingroup$ Smells to me like you don't know that whole western Europe was fully electrified before ww2 start... $\endgroup$ Dec 3 '15 at 19:11
  • $\begingroup$ @PavelJanicek I know they have electricity. My question is more rather the electricity they have work with the specifications of the machines the traveler has. Not all power is the same, I learned that after frying only one expensive circuit board at work...honest cough. $\endgroup$
    – dsollen
    Dec 3 '15 at 20:09
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    $\begingroup$ No problem. Electronics has not fundamentally changed since then, some of the books still used to teach it predate WWII. The level of integration and size would certainty astound anyone of that time, but the basic design of power circuitry has not changed much. The voltage/current requirements can be whipped up in most any ones garage, anyone that knew how to repair a radio would be able to. The hard part would be the USB connector on the phone if it is fully integrated, would probably need a machinist to cut it out of Bakelite. $\endgroup$ Dec 14 '15 at 20:41
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    $\begingroup$ Most devices have the adapter requirements (voltage, current, pin polarity) marked on them (just as the adapters have markings declaring input requirements and outputs), making it trivial to understand what each device needs from a jerry-rigged substitute. It would be easy for a WWII era electronics lab to cobble together perfectly suitable substitute power sources. $\endgroup$
    – Anthony X
    Jun 23 '18 at 21:09

AndreiROM is correct. It would be very simple for any WWII era electrical engineer to set up a power source based upon the information on the charger cord for the device. They could even use their WWII era tools to test for resistance and voltage properties of the charger cord in the absence of that labeling.

The actual question is what value would these devices provide to a nation during WWII?

Modern computers components are so small that they are beyond WWII level technology to comprehend.

Sure its processing power is great, but unless the person teleported back is a programmer and has the development package installed there would be no tools on the system to be used.

It basically is a fancy paperweight that points out some applicable theory’s that might focus some research and development. However in WWII they were using cathode ray tubes and mechanical computers. Save the lap top until the 1960 -1970s to get its biggest boost.

Unless this computer has some amazing software and or scientific works stored on it there won’t be much to gain.

  • $\begingroup$ My other questions address the implication of the tools, this was just to verify the survival of the hardware. For the record, they do presume a programmer with an IDE, JDK etc :). for the record, without the charger could they still test the battery itself to deduce voltage and other properties? I assume so, but just to make sure :) $\endgroup$
    – dsollen
    Dec 3 '15 at 20:12
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    $\begingroup$ Yes they could. Worse case scenario they might not be able to recharge the battery, but they could build a battery that had similar output. They would have to jury rich a connector, but that's well within their capabilities. $\endgroup$
    – PCSgtL
    Dec 3 '15 at 20:16
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    $\begingroup$ Don't discount the possibilities of Excel - a quite common piece of software. $\endgroup$
    – Monty Wild
    Dec 4 '15 at 2:41
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    $\begingroup$ Modern circuitry is fully comprehensible to a WWII electrician. Amazingly integrated, and fairly mind blowing, but surface components are the same as they always were just smaller, and take a magnifier to an ic and you will see recognizable features. Think about those statues carved from a grain of rice, hella impressive, I wouldn't know how to do it, but fully comprehensible. $\endgroup$ Dec 14 '15 at 20:45
  • $\begingroup$ "Unless this computer has some amazing software and or scientific works stored on it there won’t be much to gain" - if it has compilator/interpretator installed and some docs for that, then if would be extremely powerful cipher breaker by WWII standarts. $\endgroup$
    – Vashu
    Dec 16 '17 at 9:41

If you just have a modern lithium ion battery, it could be a bit tricky. Lithium ion batteries can be trickier to recharge than other rechargeable, so you'd need to make sure you brought a charger with you.

However, other devices should have no trouble at all. Nearly all devices actually print enough information on the to do the trick.

Beyond that, you'll find many wall warts are "one size fits all." Its common to see a wall wart labeled "120-240V 50-60Hz" which means it works with anywhere between 120V and 240V, 50Hz to 60Hz. This covers basically all power grids in the world.

  • $\begingroup$ It's true that lithium ion cells are tricky, but the necessary charging "smarts" to deal with the characteristics of these cells is built in to the devices our intrepid traveler has with him (if not the battery packs themselves). The missing A/C adapters are simply providing stable DC at the correct voltage and adequate current to meet the demands of the devices they are intended to power. $\endgroup$
    – Anthony X
    Jun 23 '18 at 21:01

Stories about people somehow landing in WW2 are popular in Russia for reasons. Now, reciting a minor subplot of one of such stories, NKVD (the guys that would be KGB later) obtain a CD/MP3 player from 90s, a bit broken during the erm... acquisition.

Having realised that they deal with some exceptional tech and not some fancy spy radio, as thought earlier, they summon best engineers and sound recording scientists. They manage to save what is saveable and to reproduce the broken parts with local tech. The report and demonstration of the device to the higher-ups looks something like this:

  • The device features sophisticated tech based not possible for us tech level, that, however, bears similarity to the solid state research done in our lab in XY.
  • The device possesses a huge computing power, that appears to be used for a very dumb goal, to play music.
  • The music is recorded on this shiny disc in a way we do not comprehend. It is read with a very bundled light ray, generated in a way we do not comprehend, but done very akin to a gramophone in a very sophisticated and futuristing manner.
  • The device was confiscated from person XY, who was arrested as a spy-suspect. It got damaged a bit during the arrest. The power source and sound amplifier broke and were replaced with our technology.
  • Last, but most importantly, the recordings on this erm... shiny gramophone record, are in legible and understandable Russian, and... Sir, you need to hear this yourself!
  • *60s music about WW2 plays*

(I am abridging and translating the scene as I remember it, as I don't have the book at hand.)

  • $\begingroup$ What is the book called, that sounds super interesting! $\endgroup$ Jan 19 '19 at 23:32

If he has the power bricks for the devices with him then I expect their input requirements could be supplied without too much issue. By world war 2 the mains electricity standards we use today were already in use in some parts of the world.

Plus the input requirements of modern power bricks are very lineant. The things usually have a nominal voltage range of 100V-240V and are designed to accept a tolerance band either side of that. So anywhere from about 90V to about 264V AC would work. Frequency on the label is usually shown as 50-60Hz but again that is a nominal range and there will be wide tolerances either side of it. Many bricks will even run on DC though I would consider it risky to try that on an unknown one.

If he doesn't have the power bricks it would be harder and there would be a greater risk of an accident frying something.


The graphing calculator will be trivially easy to power -- AA batteries already existed at the time; they were invented in 1907. Source: https://en.wikipedia.org/wiki/AA_battery. A coin cell for the watch likely would not have been available, but if you're okay with some wires dangling out then regular battery(s) should be able to power it.

I would say that your premise that "[they] won't know specifically what type of power (voltage, current, fluctuation tolerance etc) the devices are configured to handle unless it's written on the device or they can reverse engineer it somehow" won't be especially relevant, because almost all electronic devices have their power requirements written on them. This is required by various certifications agencies (some details here: https://www.digikey.com/en/articles/techzone/2015/aug/efficiency-standards-for-external-power-supplies)

Assuming that the power supply for the laptop was brought along, it will very likely be one of the universal-input types that are designed to accept mains power input in any country (as Peter Green mentions). Most likely you'll be able to plug into whatever the local power grid is supplying and it will work fine. In any case, the label on the power supply will certainly tell you what it's designed to work with. Most say something along the lines of Input: 100-250VAC, 5A; Output: 19VDC 8A.

Provided you got the laptop charger to function, the USB ports on the laptop can then be used to charge the phone. If not, cell phone chargers are also usually universal-input so you may be able to use that directly as well, though you may need a magnifying glass to read the label.

If none of these methods work out, your best bet is to find an electrical engineer from that era to assist you. They would be able to remove the battery from your laptop, measure its power output, and construct a suitable replacement using the electronic equipment available in that era (which will likely be bigger than the entire laptop, but functional!)


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