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  • DC-DC Step Up Converter

    Looking around the forum and trying to decide how to power my laptop. My laptop requires 16v 2.3A in. I have found several inexpensive DC-DC Step Up Converters via eBay. Would a product such as this work for what I need? I realize I will have to have relay set up as well to the actual power on with accessories and off with vehicle RAP (Retained accessory power).

    http://cgi.ebay.com/12V-24V-DC-DC-St...item33643af941


    I appreciate your input!

  • #2
    That will not be sufficient regulation for a laptop. Maybe for a motor or battery or something of similar heft. A laptop does not like huge spikes and large ripple. That thing is a joke.

    Look in the mp3car store, there are ready made products that do exactly what you want with built in auto-on.
    Fusion Brain Version 6 Released!
    1.9in x 2.9in -- 47mm x 73mm
    30 Digital Outputs -- Directly drive a relay
    15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
    Buy now in the MP3Car.com Store

    Comment


    • #3
      Originally posted by 2k1Toaster View Post
      That will not be sufficient regulation for a laptop. Maybe for a motor or battery or something of similar heft. A laptop does not like huge spikes and large ripple. That thing is a joke.

      Look in the mp3car store, there are ready made products that do exactly what you want with built in auto-on.


      I saw those products in the mp3car store. Just a little more than I am willing to spend at the moment. I see that Fujitsu actually makes a product for my model tailored to auto/plane usage. I may opt for one of those.


      Are there any other options out there?

      Comment


      • #4
        Well if you only want voltage conversion and not "smart" features then you are looking at things like the iGo. I don't know what it is called now or what their rebranded chinese clones are called, but basically it is an adapter system where you just put different tips on it to get various voltages and stuff. I have one from 2005-ish and it works great.
        Fusion Brain Version 6 Released!
        1.9in x 2.9in -- 47mm x 73mm
        30 Digital Outputs -- Directly drive a relay
        15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
        Buy now in the MP3Car.com Store

        Comment


        • #5
          That dc-dc converter is probably ok but with sufficient (extra) output capacitors.
          I just picked up the May 2011 copy of Silicon Chip which has an adjustable 12V 1000W inverter (dc-dc converter; 15-35VDC output; based on last month's MPPT solar panel controller) intended for laptops etc.

          It's on the MC34063 chip and has three 1000uF 35V low ESR caps on the output for filtering (up to ~7A output current). Those caps could be reduced - its max input is 10A and it has an efficiency of ~80%. For 2.3A, probably one 1000uF low ESR would suffice.
          The way they have it set up, with the converter off, the output is about 1.2V lower than the input. (In thru a 10A fuse, then thru D1, a 0.025Ω resistor, a 100uH inductor, D2 & out where D1 = D2 = MBR20100CT double diodes.)
          Alas I haven't yet found any mention of the input voltage range, but these guys ain't stupid and they have good expertise wrt automotive 12V systems.


          But the linked converter should be ok if its 3A is sufficient - just add (eg) a 1000uF cap if ripple is too high.

          But yes - they have no features like the mp3car converters. But if it's merely to run or charge a laptop...


          FYI - I bought a 12V 45W laptop converter for AUD$22 a few months back... Settable outputs from ~16V to ~24V and the various dc connectors.

          Comment


          • #6
            I just ended up buying the proper DC-DC Converter for the laptop. Now, to Hardwire it instead of using the cigarette adapter. Should just be able to lop it off and use an in-line fuse rated for the fuse inside the adapter(15A) and setup through a relay with 12v switched.

            Comment


            • #7
              Yep, but you may not need a fuse as big as 15A.

              But match the fuse to the cable and relay etc, or as low as the dc converter takes.

              Comment


              • #8
                The adapter specs are:

                Voltage :
                12V-13.5V (Input), 15V-17V (Output)
                Power :
                90W

                So,

                90W / 12v = 7.5A Fuse needed?


                Correct?

                Comment


                • #9
                  Normally I use a Div10 (divide by 10 rule) so 90/10 = 9A => 10A.

                  But dc-dc converters usually boost from lower than 12V, and you need to factor in the efficiency (usually 80%) and that, as a rule, fuses should be run at (no more than) about 70-80% of rating...

                  Hence the fuse size is 90W/.8/.7 = 160W where you divide that by the minimum voltage - say 10V => 160W/10V = 16A, so 15A was appropriate. (I went from 16A down to 15A because of the /.8/.7 = /.56 "super fat" margin.

                  But of your laptop uses 16v 2.3A = 37W...
                  Then 37W/.56 = 66W.
                  So at 10V that's 66/10 = 6.6A => hence a 10A fuse... or 7.5A if you prefer...


                  I'd probably start with a 10A fuse since that is a common size, otherwise 7.5A is ok.

                  But I'd probably design the circuit (wiring, relay, fuseholder etc) to handle (say) 16A - 20A.
                  Not that it is that critical in this case, but why not design for the converter's max power, and use thicker wires for less voltage drop?

                  Sorry if that is too complicated, but I'm trying to show some typical rules and considerations.
                  But it isn't worth changing things if you already have the stuff. Your relay is likely to be rated for 30A (assuming it's a common automotive type) but could be 10A or 15A etc.

                  Remember 2 things:
                  The fuse (near the battery) is to protect the wiring and relay (aka distribution) and should be rated equal to or lower than the lowest rated part. (But it is not to protect the dc-converter - that should be a separate fuse for the converter at the converter end, though no reason it cannot be the fuse at the battery - hence only needing one fuse. The cig plug may have contained a fuse for the converter.)
                  And (2), heat will indicate stressed components - eg, a cable that is too warm etc. (But don't burn yourself - especially on fuses that tend to run warm and can be quite hot near their rated current.) It's a check that I sometimes do on occasion - more so at joints and connectors as that can indicate bad contact; cables are usually ok if they were initially ok (unless you add more loads to them).

                  Comment


                  • #10
                    I follow the math and understand your explanation. Well done!


                    Yes, the cigarette adapter itself contained a 15A buss fuse. My thoughts were to only have the one fuse. I had planned on using the existing wiring. The IP2 fuse which powered the factory stereo, disc changer and antenna. (None of which will be used any longer) is rated at 10A.

                    So if GM did their wiring properly and with the calculations above it should be safe to use the existing wiring. As in 12v switched to activate relay and power source being the factory stereo wiring.

                    Comment


                    • #11
                      Based on the cig adapter, then 15A. But you could go 10A as discussed. (And maybe the 15A is to limit for the cig plug/socket which are normally rated at a max of 15A, though few actually handle that!)

                      The GM wiring for 10A should be ok, but many would run separate wiring for stuff like this, though a laptop isn't that critical. IE, it runs off its battery rather than being dependent on a good supply - not that intermittent or bad contacts would be good for it, or the converter. (If it were a cig socket, I'd feel the heat.) Many of us run our own wiring direct from the battery for PCs, audio, etc. (I do, for a normal HU and a spare cranking battery; both have dedicated + & - from the main battery. I have no PC.)


                      One fuse is fine. EG - if it were f.ex 50A wiring from the battery thru a 30A fuse thru a 30A relay to the dc converter with its 10A or 15A fuse, then the converters fuse could be moved to the battery instead. IE - battery with 10A or 15A fuse even though wiring and relay is 50A & 30A etc. The fuse still blows (in theory LOL) before the wire or relay melts, and it still protects the converter. (That protection is against shorts etc - not against failure.)


                      I'm not sure what you mean by the GM circuit supplying to activate & power the relay. In my setup, that circuit might activate the relay which switches the (fused) battery power. But if it both activates & powers, the there is no need for the relay (unless later you wanted to add some sort of off control, but then why not get the heavy power from the battery so you could activate with the GM circuit (= ACC?, hence off when cranking?), or a manual switch or a voltage switch etc?)


                      Glad you understood my crap. It was late last night - not that that necessarily changes anything.
                      But now is early morning, pre-coffee etc. And I'm up early to start a new job. Holy cow - it's still dark outside!

                      Comment


                      • #12
                        What I meant was I'll be taking the 12v switched signal (ACC) to activate relay and use the 10A IP2 (Always Hot) fused circuit which used to be for the factory stereo to power the DC-DC converter. Very much so like this:



                        I however, can easily run a new fused wire from the battery to provide the actual power instead of using the factory IP2 fuse (Battery is under rear seat). I would prefer to not have a bunch of terminals and wires going to the accessory extension on my battery post. I am contemplating getting an auxiliary fuse block. As I have two amplifiers and three separate circuits to my LED tail lights already tied to the battery. Just makes for hassle to remove battery if ever need be. It may also be time for a "tank" circuit with an aux battery.


                        BTW, oldspark, does this project look familiar? I believe we have crossed virtual paths before haha!

                        Comment


                        • #13
                          Good - you did mean the right thing.

                          Stick with your orig idea - change to direct battery connection only if needed etc.
                          (BTW - the LEDs should be low power so off one feed should be ok.)


                          And yes, I remember that blue thing... that was a LED conversion wasn't it? (I'd never recognise a description, but the pic yeah... simple minded me you know lol!)

                          Comment


                          • #14
                            Originally posted by sall View Post
                            Looking around the forum and trying to decide how to power my laptop. My laptop requires 16v 2.3A in. I have found several inexpensive DC-DC Step Up Converters via eBay. Would a product such as this work for what I need? I realize I will have to have relay set up as well to the actual power on with accessories and off with vehicle RAP (Retained accessory power).

                            http://cgi.ebay.com/12V-24V-DC-DC-St...item33643af941


                            I appreciate your input!
                            I use this one (150W DC-DC Boost Converter 10-32V to 12-35V 6A Step Up Voltage Charger Power) that I bought on ebay. The output is adjustable. I run mine at 19vdc and it works fine. If the pc is on, it is not affected at all by cranking.

                            Comment

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