Best DC-to-DC converter for laptops

[prroots]

Years ago I knew of a ham that had developed a semi-custom DC-to-DC converter to power laptops aboard sailboats in such a way that they would not interfere with the very sensitive front-end of SSBs. Can anyone refer me to a source of suitable DC-to-DC converters. The typical ones operate at a switching frequency that interferes with HF radios whether they be ham or marine. Thanks
Pete

[negrini]

Targus Group | Leading Provider of Laptop Cases, Bags and Accessories .... just turn off your SSB when charging !

[sailingdog]

Or disconnect the power supply if you're using the SSB to check e-mail and such. If the laptop's battery isn't sufficient to last that short amount of time, you've got other issues.

[prroots]

Originally Posted by sailingdog

Or disconnect the power supply if you're using the SSB to check e-mail and such. If the laptop's battery isn't sufficient to last that short amount of time, you've got other issues.

Thanks, that's certainly an alternative. Actually, in years past when I used this semi-custom DC-to-DC converter to power laptop, I also removed the laptop battery. There was no need for it and it kept the battery fresh for those occasional trips ashore with the laptop. It was a very nice solution all things considered. I'll keep searching and if I find the source I'll report back. BTW, the reason I call it semi-custom is that the developer changed a few resistors according to the Voltage required by your laptop. He also sold a kit for those wanting to build their own.
Pete

[SVAuspicious]

DC-to-DC converters come in a wide range of quality. There certainly is a fundamental frequency that can cause interference. That frequency varies from one design to another. There are three issues: 1. the particular conversion frequency and its harmonics, 2. the radiated signals from the converter, and 3. the signals conveyed by the power lines in and out of the converter.

A good design well-executed will radiate less and transmit less over power lines in and out.

Whatever unit you have can be made better by fitting ferrite beads on the power lines, positive and negative, in and out of the unit. Ground the case as well.

I have an IBM/Lenovo laptop and use the 12VDC DC-to-DC converter they sell with no issues. I also have a Mascot ( http://www.mascot.no/?CatID=1168 ) DC-to-DC converter for my sailing instruments. Neither has any impact on my onboard systems.

I haven't had good luck with the aftermarket laptop adapters from Kensington and such. They work fine but the noise output is high.

My suggestion is to shop the big name brands, purchase from a source that will take a return if you have an issue, and test extensively - run through the VHF channels with the convertor on and off (disconnect it completely for 'off') and the principal HF channels (at least one frequency on each marine band, the wefax frequencies, and some ham frequencies like 7268 and 14300). Do all the testing with your refrigeration and inverter turned off - also turn off all fans). Any difference you can hear is too much.

Your laptop battery is likely to help damp out power-line related interference. Don't take it out of the laptop.

[sailingdog]

Generally, removing the laptop battery isn't a good idea. Any voltage fluctuation will cause the laptop to die, where if the battery is in, it acts as an internal UPS effectively, and gives your laptop a much more stable source of power and will power it long enough for you to shut it down safely if the external DC power fails completely.

[asdf38]

The suggestions given so far are best. But, if you want to do some experimentation I'd be curious what the laptop would do with 12V directly. In general it's safe to run something from lower voltages.

Generally laptops run off battery packs that are <12V so it depends on the particular power architecture and the power checks and verification that the laptop implements. I know my laptop will detect and reject a lower power, lower voltage supply on boot-up, but will run from it if you plug it in later (although it won't charge the battery from it). I suspect most laptops would behave that way if given 12V directly.

Beyond that, you could investigate how the laptop ID's particular power supplies to see if you can trick it out (it could be as simple as a sense resistor for example) and try running off other semi-standard voltages such as 15V and 18V. A quick search turned up some quality looking step-up (boost) converters at those voltages.

...but again, best to stick to what was suggested so far.

[prroots]

Thanks for all the feedback. I did learn the answer to my original question from another forum:
DC-to-DC Converter for Laptop - Cruisers & Sailing Forums
The name of the ham was Sam Ulbing, N4UAU. Unfortunately, he is no longer selling the converters.
Pete