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I'm looking for a way to supply 19V at 6.32A, with an input voltage of 11.5-15V.

I'm currently using a pure-sine 1000w inverter + OEM 120w power supply. It draws about 3.33 A at 11.96V (40w). The laptop self-reports to using approx 25w, giving an efficiency of ~60-70%.

I've looked at a previous previous answer, which suggested:

  • building one from scratch (I don't know how to do it)
  • buying an OEM "car" power supply (I haven't found any that support 120w, only 90w)
  • using a boost converter from eBay/Aliexpress

Non-OEM "car" power supplies exist which support 120w. Most seem to be cheap crap. I bought a branded one ("Lavolta") which had good reviews on Amazon, but first it refused to charge the battery until I turned off/on the computer. Then it fried my battery. Maybe it produced voltage spikes higher than 19V.

I already have a 6A DC-DC boost converter that I bought from AliExpress. But when adjusting the potentiometer, the voltage can jump quite a bit +/- 1v.

My conclusion is that the cheapest and simplest solution is to use the DC-DC boost converter, but add some over-voltage protection, perhaps with a crowbar circuit.

Is there a better way? Any suggestions for the components I should use in the crowbar circuit?

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  • \$\begingroup\$ Crowbar circuit? \$\endgroup\$ – VBwhatnow Dec 9 '16 at 17:31
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    \$\begingroup\$ en.wikipedia.org/wiki/Crowbar_%28circuit%29 \$\endgroup\$ – user95482301 Dec 9 '16 at 17:31
  • \$\begingroup\$ Why not use a car charger? I'm not too familiar with them, but cars fundamentally use 12V so it should be good. Probably you could even find and OEM car charger. Although 15V seems a little high for this kind of things. \$\endgroup\$ – Jan Dorniak Dec 9 '16 at 17:38
  • \$\begingroup\$ As I mentioned, the OEM chargers are typically only available at 90w, which is meant for use with smaller laptops. The non-OEM chargers are also mostly 90w, although a few exist at 120w. Unfortunately, they all seem to be of horrific quality, as is evidenced by mostly bad reviews on almost all such chargers found on Amazon. As I mentioned, I even tried to buy one such charger, and it fried my battery. Maybe I wasn't clear enough in what I wrote? \$\endgroup\$ – user95482301 Dec 9 '16 at 18:00
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    \$\begingroup\$ Replace the pot on your DC to DC converter with fixed resistor values. You shouldn't need a crowbar either. \$\endgroup\$ – Andy aka Dec 9 '16 at 18:49
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The DC-DC converter route is, by far, the simplest and most efficient solution.

That being said, with DC-DC's you do tend to get what you pay for. A nice CUI or MuRata (name brand) DC-DC likely will keep your laptop safe. As you noted, off-brand products, may need some sort of filter on their output to avoid voltage spikes.

The issue you are seeing with the potentiometer is likely because they used a dirt-cheap and low-grade pot, with poor linearity or a dirty wiper. Once you adjust it to the right voltage, you can use some stiff epoxy/glue to lock it into place, and it should be fine.

For the crowbar circuit, a 20V Zener diode and 6A fuse are what you'd want. That's the simplest, albeit not great; it'll still allow voltage spikes, but at least keep them contained to about 24V. A large capacitor (the DC-DC converter should list the maximum capacitance it can tolerate in its datasheet) would help, too.

One final consideration: the high-power laptop chargers often have some level of intelligence to them. My HP laptop, for example, knows when I plug in a non-OEM charger, and complains about that; it will still charge, but at a reduced rate.

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