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Summary

  • I have an AllPowers R600 Solar Generator, which can output AC and DC power
  • I want to use it to power my laptop in the next room (approx. 4m away)
  • The 1m charger works fine when I connect it directly but whenever I add an extension cable to the circuit (to make it the required 4m) it no longer works

Further Info

  • As the R600 battery is DC, I thought it made sense to drive my laptop directly rather than use the R600's AC out DC-->AC then plug in my laptop charger AC-->DC
  • I bought a laptop car charger, which let's me charge my laptop from the cigarette lighter port on the R600
  • When I connect the laptop charger directly to the R600 it works fine
  • However the cable is only 1m and so needs to be extended, however when I then connect my laptop with the DC extension lead, it then doesn't power.

History & Technical Info

  • My laptop draws 90w (max) -- 19.5v, upto 4.65A
  • I initially tried connecting the laptop charger to 1x the R600 DC 5.5 x 2.5mm sockets, however this didn't work either (also, the DC 5.5 x 2.5mm extension cables were generally very thin >20 AWG) and I discovered only suitable for 2A or less.
  • I switched to using a car charger/cigarette lighter port as the extension cables were generally better
  • The cable I tried was 16 AWG -- According to what I read online this should have been fine for the 4.65A and 4m distance (giving only 3% voltage drop) but this still didn't work

Stuck

  • At this point I just don't know why it's not working
  • I just want to run a 12v DC cable 4m and don't understand why it seems to be proving so difficult
  • From what I've read, it seems like this should be a valid use-case so would be very grateful for any help trying to figure out why it isn't working / what I need to fix it.
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  • 1
    Have you tested the socket end of your extension to ensure you're getting the volts/amps you're expecting? It could simply be a defective extension.
    – FreeMan
    Commented Nov 21, 2023 at 13:33
  • The USB-C port should work just fine (100W) output.
    – Jon Custer
    Commented Nov 21, 2023 at 14:46
  • 2
    Your laptop might support up to 19.5V, but this circuit is only 12V. So if it draws 90W, that's not 4.65A, it's 7.5A. If that's true, the drop would be more like 7+%, almost a volt, which is probably enough to make the laptop refuse to charge. (If that 4.65A is a maximum current rating, you wouldn't run into this, but instead your maximum charging power would be reduced to <60W by the lower voltage .) Commented Nov 21, 2023 at 21:22
  • In general it's a bad idea to run low voltage high current a long distance, as you are discovering. Even if you can make it work, the losses from going DC-AC-DC might prove to be less. Commented Nov 21, 2023 at 21:23

3 Answers 3

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It's wire losses for sure.

I would plug the car charger into the box directly, and then chop the output lead of the car charger, and extend the port by splicing in 12awg (or 14awg OFC) speaker wire to extend it into the next room as needed. I would use lever wago connectors to make the splices; simple, low-resistance, safe, and re-usable.

This topology keeps the loss behind the charger low, to avoid a low-battery detection disconnect. If the voltage to the laptop sags a little bit, it shouldn't matter as much, and by extending with the thicker/better wire, you don't lose as much as you would going the distance with a cheap 16AWG run as seen in the DC extension cable.

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90 watts at the laptop, with some conversion losses, is more like 108-120W or 9-10 amps.

Now what is the calculated voltage drop for the size of wire in that Chinese thing? I bet at 10 amps, it's taking a big chunk of your 12 volts. That's making your car charger go "nope".

Yeah even if that cheapo is actually 16 AWG, that's still (at 4 ohms per 1000') 0.104 ohms round trip, and at 10 amps that's 1.04 volts. So you're definitely adding at least 1 volt drop out of your 12 volts.

Voltage drop with low voltage is no joke. If this was 120V, then a 1 volt drop would be trivial obviously, just 1/120 of rating, and anyway current would be 1/10 as much at just 1 amp since the voltage is 120V. But with 12 volts, you have to think about voltage drop in every wire run.

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It's possible that the laptop car charger has an automatic low-voltage shutdown, to prevent running a car battery flat. When run directly on 12V, it will think the battery is good and charge normally. When it tries to draw the full current from a cheap extension lead, the voltage drops, and the charger thinks the battery is nearly flat.

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