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Tundra10
Joined: 14 Jun 2010
Posts: 102
Location: Scarborough, Ontario
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 Posted: Wed Apr 24, 2013 12:38 pm Post subject: 28V to 15.6V @ 5A |
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A friend of mine has a requirement to power a laptop requiring 15.6V
at 5A from an aircraft with a 28V system.
This unit is almost what is needed, but the spec is only 4A.
http://www.lonestaraviation.com/Step-Down-Converter-24v-to-16v.html
Is anyone aware of a similar product with a little more power capability ?
Thanks,
Jeff Page
Dream Aircraft Tundra #10
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jay(at)horriblehyde.com
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| Posted: Wed Apr 24, 2013 9:58 pm Post subject: 28V to 15.6V @ 5A |
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I would venture that the 4A product would do the trick; laptops do not draw that much current- my laptop power supply is rated at 19V 3.16A.
Johannesburg Jay
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nuckolls.bob(at)aeroelect
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Eric M. Jones
Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts
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| Posted: Thu Apr 25, 2013 5:29 am Post subject: Re: 28V to 15.6V @ 5A |
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I always recommend Astrodyne power supplies for these in experimental aircraft. Their similar supplies are $75.
There are bunches of laptop supplies from 12V (cigar lighter type) but not many from 28V. I have made a couple of these in linear form (no RFI noise), completely adjustable, 10-37V input. See attached.
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| Description: |
| 5A AVR Linear DC-DC Supply |
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Download |
| Filename: |
5A AVR.pdf |
| Filesize: |
125.62 KB |
| Downloaded: |
282 Time(s) |
_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net |
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nuckolls.bob(at)aeroelect
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| Posted: Thu Apr 25, 2013 5:50 am Post subject: 28V to 15.6V @ 5A |
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At 12:56 AM 4/25/2013, you wrote:
| Quote: |
I would venture that the 4A product would do the trick; laptops do
not draw that much current- my laptop power supply is rated at 19V 3.16A.
Johannesburg Jay
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The wattage requirements tend to be constant. If his
battery is nominally lower in voltage than the common
19 volt devices, then the current requirements might
reasonably be expected to go up proportionally. But
even the rated current values are 'max' numbers that
probably assume that the user is charging a depleted
battery while attempting to use the computer. I have
a 14v to 19v boost regulator for use in our cars.
I've measured some sustained 4+ amp draws during
worst case demands . . . but normal computer usage
with a fully charged battery is much less . . . more
like 2.2 amps.
Larger step-down devices are readily available but
may need some attention to noise issues for use on
the airplane . . .
To: aeroelectric-list(at)matronics.com
Subject: Re: 28V to 15.6V (at) 5A
At 03:36 PM 4/24/2013, you wrote:
These show some promise. You might find that they need to be
packaged in a larger enclosure to accommodate some RFI
filtering.
http://tinyurl.com/a9bhfqn
http://tinyurl.com/axlv3ex
http://tinyurl.com/bbylscr
http://tinyurl.com/a5ncthf
http://tinyurl.com/apxepbq
Bob . . .
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Tundra10
Joined: 14 Jun 2010
Posts: 102
Location: Scarborough, Ontario
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| Posted: Thu Apr 25, 2013 7:27 am Post subject: 28V to 15.6V @ 5A |
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Jay,
I agree that most of the time the laptop would draw less than four
amps. However, if the laptop battery is quite low, it will draw more
power trying to charge it and might reach the current draw specified
on the bottom of the laptop.
If there are no alternatives, I will try to get one of their laptops
and measure it. However, if there is a similar product available with
a little more output, that would be the best thing to do.
Jeff
| Quote: | From: "Jay Hyde" <jay(at)horriblehyde.com>
Subject: RE: 28V to 15.6V (at) 5A
I would venture that the 4A product would do the trick; laptops do
not draw that
much current- my laptop power supply is rated at 19V 3.16A.
Johannesburg Jay
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jay(at)horriblehyde.com
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| Posted: Thu Apr 25, 2013 7:59 am Post subject: 28V to 15.6V @ 5A |
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Hey there Jeff,
I agree; my opinion was ventured on the basis that the other product might be difficult to find and/or get your hands on- probably more of an issue here in SA than in the USA. In that case the current draw might be high for a while, if the battery was flat, but lower later. Then one might be able to work within those limits- for example, make sure that your battery is properly charged before flight and the power supply then only supplies top up power.
I also agree with Bob regarding the higher current draw for lower voltage given the same power (W) requirement - basic electrical theory. Looking at my laptop power supply and using transformer theory as a rough calculation estimate my laptop would draw 3.9A at 15.5V.
Not ideal, but if the product you sourced was all that you had to hand, odds are it would be fine. Throw in some usage parameters (take a charged laptop on board) and you'd most likely never have a problem.
But of course, in the land of the big PX  you can just get the right bit... We can get them here too, but it’s a pain in the butt, you will probably have to wait longer and it'll cost more.
Nice almost relevant story: My mate was commissioning plant in Tanzania and needed some resistors which would have been difficult and time consuming to order from there- and then you'd have to wait for delivery (just 10 were required). There is a large bit of plant waiting and your client is hounding you- and your company will be hit with penalties for lateness. Solution- go and buy a couple of cheap battery powered radios that abound in the small general dealers and source your resisters off their boards....
Johannesburg Jay
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Tundra10
Joined: 14 Jun 2010
Posts: 102
Location: Scarborough, Ontario
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| Posted: Fri Apr 26, 2013 10:44 am Post subject: 28V to 15.6V @ 5A |
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Wow - lots of possibilities, far less expensive than the TSO unit I
was looking at.
Astrodyne has some very promising products, that are burnt in and have
noise filtering built-in. I am going to suggest to him that we get
one of these and try it out. Thanks Eric !
Bob - you found some interesting items too. Seller kuuco has some
that I may purchase just to play with.
Jay - I enjoyed your story. Even in Toronto, where everything is
available, sometimes that is the cheapest way to obtain a part 
Thanks everyone.
Jeff Page
Dream Aircraft Tundra #10
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