I have a few of these in the shack for 19/20 V monitors and they seem okay QRM-wise:
https://www.ebay.com/itm/Lind-AC-Adapter-12V-Car-Power-Supply-Dell-90W-Laptop-HP-100-Mobile-Printer-/292957179784?hash=item44359bcf88 I have a Thinkpad W540 and tried using one of the mobile 19V supplies - the same voltage as the Lenovo factory power supply. When I booted I got a new screen I'd never seen before. Lenovo was telling me to go out and buy a genuine Lenovo power supply. I haven't looked further but I guess they are using some signal riding on the 19 V to do this. 73 Martin W6MRR On Sat, Mar 16, 2019 at 3:39 PM Jim Brown <k...@audiosystemsgroup.com> wrote: > On 3/16/2019 12:23 PM, Gary Hinson wrote: > > You could check laptops and their power supplies in a friendly laptop > shop > > (when they are not too busy!), using a portable AM radio. > > Naw -- virtually place that sells or repairs stuff, or where humans > live, is almost certain to be so full of noise that noise from one > device is unlikely stand out. > > > > Alternatively, you could simply banish switchmode supplies of all types > ... > > so either get/build a conventional PSU or find a laptop that will work > from > > the shack 13.8V supply. Many seem to be rated for 18V or more > > Yes, that's been true for nearly a decade. > but I suspect > > they might work at 13.8V although their batteries may not charge (don't > > quote me on that: you'd need to check for yourself). > > The last ones I owned that fall into this category were from the > Thinkpad T41-T42-T43-T44 series. And they do work that way. Beginning > with the T60 models, introduced at least 10 years ago, they went to 20V > power supplies and don't run on 13.8V. > > > > > Hinson tip: look out for cardboard boxes of PSUs in charity shops. > Either > > pick out the bulky/heavy ones, or make an offer for the whole box. Check > > them for safety before use. Supplies rated for wide-range inputs (e.g. > > 110-250V without a selector switch) are generally switchmodes. The > flying > > leads and special connectors might be worth keeping, even if the PSUs > > themselves are junk. Unregulated supplies typically produce several > volts > > above their rating off-load and only vaguely approximate the rated > voltage > > at the rated current ... so avoid powering valuable electronics directly > > from them. Any PSUs that get hot are clearly suspect. > > This is good advice, which I've freely given for years. :) Another > detail about voltage regulation -- the vast majority of linear wall > warts and line lumps are transformer-rectifier-capacitor filter > supplies, so open circuit voltage will rise to nearly the peak value of > the transformer secondary with no load, and drop close to the label > voltage at the label current. > > I break all the DC cables for these things and add PowerPole connectors, > and use an inline meter with Power Poles to monitor voltage and current > when matching a wart to a load. In my experience, you're pretty safe > matching voltage and current ratings of the supply to the voltage and > current spec of the device (usually marked on the SMPS that comes with it). > > 73, Jim K9YC > > > _______________________________________________ > wsjt-devel mailing list > wsjt-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/wsjt-devel >
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