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Old 09-12-2010, 16:46   #1
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DC-to-DC Converter for Laptop

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
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Old 10-12-2010, 11:39   #2
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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.
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Old 11-12-2010, 15:02   #3
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Pete,

I've been using a store-bought DC-DC converter to run my laptop for several years. I use it to power laptop when doing SSB email via WINLINK and haven't had any interference problem. I also use it to power laptop for running electronic charting and no problems there either.

I bought it from www.lindelectronics.com but it wasn't cheap... I think about $100. It uses less power than a 1K inverter to power the laptop. As I recall, they had lots of varieties to power various laptops.
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Old 11-12-2010, 16:46   #4
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We use a radio shack invertor(plugs into a cigarette lighter type socket). Very inexpensive, under $50.00 no noise issues.
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Old 11-12-2010, 18:16   #5
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Quote:
Originally Posted by prroots View Post
Years ago I knew of a ham that had developed a semi-custom DC-DC converter to power laptops aboard sailboats in such a way that they would not interfere with the very sensitive SSB front-end. Can anyone refer me to a source of suitable DC-DC converters?... Thanks, Pete
I think the guy you're remembering is Sam Ulbing, N4UAU. We used his converters for years, but those units (c. 2002) only put out 60W (although it would run laptops that used more power). I don't think Sam is still selling kits, but according to eHam.net, the voltage converters are still in production.

Ham (SSB) receivers are very sensitive now & boats can be pretty electrically noisy environments. At first, I went through my switch-panel turning off circuit breakers 1 by 1, trying to find the source of noise. Then I realized that there were several noise sources, so I turned off everything (except the SSB) & started turning switches ON, noting any received noise. From that I learned that our 12v Danfoss fridge, most small inverters (but not the big Heart), the MPPT solar controller (which uses a DC-DC switching circuit), & the Autopilot drive motor (in fact, most motors) were potential sources of RF noise.
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Old 11-12-2010, 18:47   #6
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Quote:
Originally Posted by Mark Zarley View Post
We use a radio shack invertor(plugs into a cigarette lighter type socket). Very inexpensive, under $50.00 no noise issues.
We use the same converter and it sits right next to the Icom and we have never had noise on the radio from the converter. Chuck
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Old 11-12-2010, 19:31   #7
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I'm a little confused as to why you would want to use a DC to DC converter. It would be much better to use a "True Sine Wave" DC to AC inverter, then use your normal charger for your laptop. You could also use it for other items where a dc to dc would only be good for your output voltage of the converter. The cheaper inverters that are not true sign wave will throw off lots of RF noise, So get a True Sign inverter.
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Old 11-12-2010, 20:35   #8
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Quote:
Originally Posted by Music View Post
I'm a little confused as to why you would want to use a DC to DC converter. It would be much better to use a "True Sine Wave" DC to AC inverter, then use your normal charger for your laptop.

well, power consumption being an issue?!
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Old 11-12-2010, 20:57   #9
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I am still running 2 of Sams converters with no noise issues. If you are still looking for a source since Sam stopped making his units let me know. I upgraded to another laptop and purchased a quality unit that is a similar block to what comes with a laptop ac but forDC. It ran close to 100$ and again is quiet and single power output....no noise.
A
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Old 12-12-2010, 00:12   #10
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well, power consumption being an issue?!
Device efficiency for a DC to DC converter is about 96%. This would equate to a 93.6W at a full draw for a standard 90W computer.
A DC to AC inverter has an efficiency of 95% for a 94.5W draw at full load. The conversion efficiency for a computer supply is about 90% which would equate to a 99W draw at full load. This being stated:
1.) DC to DC Converter = 3.6W in waste Heat
2.) DC to AC inverter = 4.5W in waste heat
3.) A DC to AC inverter and a Laptop power supply = 14.5W in waste heat
These are all averages and accepted ratings for these types of devices.
Yes a DC to DC would be more efficient, but as I said it can only be used for the intended computer. An AC inverter could be used for multiple devices on the boat and is far more cost effective. You would be using and additional 10.9W with the AC Inverter configuration.
I guess it would be up to you if 10.9W is too much.
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Old 12-12-2010, 01:52   #11
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Quote:
Originally Posted by Music View Post
I'm a little confused as to why you would want to use a DC to DC converter. It would be much better to use a "True Sine Wave" DC to AC inverter, then use your normal charger for your laptop. You could also use it for other items where a dc to dc would only be good for your output voltage of the converter. The cheaper inverters that are not true sign wave will throw off lots of RF noise, So get a True Sign inverter.
laptop mains chargers are increadably noisy, all the ones i've tried anyway. I only have ssb reciever but it's impossable to use it with the laptop charging using the mains charger. The cheap inverter is a little noisy but it's the chrger that is the worst.
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Old 12-12-2010, 02:08   #12
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DC-AC-DC or DC-DC?

Quote:
Originally Posted by Music View Post
I'm a little confused as to why you would want to use a DC to DC converter. It would be much better to use a "True Sine Wave" DC to AC inverter, then use your normal charger for your laptop...
Yes, you certainly want a DC-AC inverter on board, especially for running tools (& the blender ). BUT those big inverters (1,500+W) often eat a couple of amps just to turn on (& the small ones are noisy). Those 90+% efficiencies usually only start at 20+% utilization. Yes, ours has a sensing circuit & only turns on if there's a load, but using only 100W for a long time is pretty inefficient, as rodeorm pointed out (lots of folks don't seem to realize this). Also, a friend in the business told me that DC-AC inverters actually have a difficult time with laptop power-supplies.

DC-DC converters are pretty efficient, & are probably what you want for extended computing (writiing emails, running nav programs, contributing to forums etc). These days many of them will auto-adjust to any laptop voltage (typically between 15 & 20v). Some of them may put out some RF on some frequencies (ours don't), but you could just run on batteries for those few minutes you're connected to Winlink or SailMail.
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Old 12-12-2010, 08:55   #13
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@ Music

That's right, thumbs up for the nice write-up you provided.

Those 14, x Watts makes a bit more than an Amp which does make a diffence with a few hours use. Depending of the size of a vessel, battery banks, and charging it might be of more or less significanse to the cruiser. My point is that transforming from DC to Ac and then back to DC is ALWAYS a waste - to some extent-. to each his own - as usual. It's helpful to know the details though
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Old 12-12-2010, 09:09   #14
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I think you're looking for a PC power supply, but if anyone has a Mac, there are various DC-DC power supplies here.
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Old 12-12-2010, 09:34   #15
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Quote:
Originally Posted by Jon Hacking View Post
I think the guy you're remembering is Sam Ulbing, N4UAU. We used his converters for years, but those units (c. 2002) only put out 60W (although it would run laptops that used more power). I don't think Sam is still selling kits, but according to eHam.net, the voltage converters are still in production ...
Sam Ulbing, N4UAU, has lots of ham radio projects.
N4UAU web page

He no longer supplies kits, but you can read about them here and get your own parts.
Kits from N4UAU

Sam Ulbing’s “All-Purpose Switching Regulator” (Voltage Booster)
http://members.cox.net/n4uau/kits/Booster%20QST.pdf
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