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Thread: Planning my first Carpc - will appreciate any suggestions and help

  1. #51
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    Thanks camo.b, diy'ing the battery setup was sounding complicated anyways.


    There is one more option. We could wire in inductive charging and then you would not need any wires to the tablet, doing everything wirelessly.
    Well that's a novel idea :-) let me see how far can we keep the tablet from the base to charge it.


    Yes, you need a DC-DC converter to get 5v, and those are available at the mp3car.com store. I use one to power my screen.
    Do you mean"Intelligent_DC_DC_Converter", won't this be an over kill.

  2. #52
    Variable Bitrate camo.b's Avatar
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    If its a overkill it means it will not be working so hard..so less heat and longer lifespan.from experience this is a very good thing.i started out with parts that were on paper 'up to the task' in reality there were just getting warm to hot...not a good thing with so many flamables.a dc to dc will produce a nice clean 3.3,5v and 12v (important for electronics) and more than you will ever need.overkill mabee but it will be running nice and cool for a long time

  3. #53
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    One more question:

    The shortlisted speakers are 60W RMS and AMP provides 100W RMS per channel. Now can there be a problem with this setup. I got mixed answers after searching the internet.

    1. A youtube video says - the amp should be at least 150% of speakers. As per which this combination is perfect.

    2. Crutchfield says amp RMS should not be more than 150% of speaker RMS. which could be a problem :-(.

    3. Some forum posts says they should be same.

    What RMS setup is everyone using?

    Also, is gain control on amp used to reduced the RMS output to speakers?

    pkaush

  4. #54
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    Quote Originally Posted by camo.b View Post
    If its a overkill it means it will not be working so hard..so less heat and longer lifespan.from experience this is a very good thing.i started out with parts that were on paper 'up to the task' in reality there were just getting warm to hot...not a good thing with so many flamables.a dc to dc will produce a nice clean 3.3,5v and 12v (important for electronics) and more than you will ever need.overkill mabee but it will be running nice and cool for a long time
    Point taken, thanks for bringing it.

  5. #55
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    For 5V linear converters (as opposed to dc-dc aka SMPS ore switched-mode or switching converters) you can say (with reasonable accuracy) that whatever its output power is, it will waste TWICE as much as in heat. IE, to get 5V at 'a' Amps you have to dissipate from ~7V to ~10V at a Amps - ie, remove 10V @ 2A to get 5V @ 2A => 20W heat for 10W output.
    That 10V removal may seem high - ie, a 15V supply instead of say 14.4V max - but there are other inefficiencies.

    Besides, for small loads (up to a few Amps) dc-dc converters are quite cheap.
    And for large linear converters or voltage regulators, heatsinks or cooling can be costly.

  6. #56
    Variable Bitrate camo.b's Avatar
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    Ive got a excellent picture of a cooked pcb with a 7805 reg that was supplying between 1-2 amps that had a 'reccomended' (not from here) heat sink..7805 reg still works but i swear the pcb almost caught fire as well as is enclosure..
    Live and learn i guess...
    Oldspark is somthing like a M2 psu energy effecient?

  7. #57
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    If it's a T-pack (T0-220?) 7805, they are usually rated for 1A or 1.5A.
    The beauty of the 78xx & 79xx series tho is that they do current limit themselves.
    But yeah, I guess you know how hot a 10W tungsten bulb gets - and that's putting out around the same heat as a 7805 @ 2A on ~14V.


    I don't know about the M2 for efficiency tho as I recall, they have the typical >90% or >95% efficiency when at ~80% of rated load (ie, excluding low output overheads where efficiencies can be very low), but I'd be more wary or concerned about the M-series noise that I occasionally hear about.

    When I mentioned cheap dc-dc converters I was considering equivalents to the 78xx etc, eg:

    (0.8V-24V 5A max; 3 for USD$8 with free shipping)

    or

    (Mini, adjustable 1.3-17V 1.8A; USD$2.30 with free shipping)

    (Sorry about the pic size, but I can't use the usual mp3car site tools (my javascript is OFF).)

  8. #58
    Variable Bitrate camo.b's Avatar
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    The M2 i have seems very quiet..M4 ive heard is very bad with the original caps..So im assuming no heatsink is required for any of those?..must say ive never come across any of those.look very usefull.

  9. #59
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    PSUs like the M series and similar as supplied on mp3car are totally different to the ones I described.
    My 'little' dc-dc cons are mere voltage regulators - ie, switching equivalents to the linear LM317 etc (tho many can be - or include - step-up so their output voltage can be higher than their input voltage).

    dc -dc cons like the M2 are a full-on ATX PC type supply but based on (12V or automotive ) DC input voltages. They include 'dc-dc cons' of different voltages as well as the features required for UPS functionality for automotive stuff. EG - programmable shutdowns & low voltage cutouts and warning alarms; hardened for automotive (say 8-16V) instead of mere 12V dc supplies, etc.

    You should not have to worry about M-series heatsinking; it will have all required unlike mere component-level types where the designer/user has to add whatever circuitry and heatsinking is required. High level PSUs like the M-series might merely define minimum air flow requirements or maximum ambient temperatures for high power outputs.
    Last edited by OldSpark; 02-16-2014 at 06:53 AM.

  10. #60
    Maximum Bitrate rray's Avatar
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    Quote Originally Posted by pkaush View Post
    One more question:

    1. A youtube video says - the amp should be at least 150% of speakers. As per which this combination is perfect.

    2. Crutchfield says amp RMS should not be more than 150% of speaker RMS. which could be a problem :-(.

    3. Some forum posts says they should be same.

    What RMS setup is everyone using?

    Also, is gain control on amp used to reduced the RMS output to speakers?

    pkaush
    As far as RMS ratings go, I rated mine the same, 100W RMS speakers and amp.
    If the speakers are not rated as high as the amp, then full volume might damage the speakers.
    If the speakers are rated higher than the amp, no problem. (The only issue there is often the higher the speaker power rating, the lower it's efficency, so it might not get as loud as would otherwise be possible.)
    As far as the gain goes, I always turn mine all the way down to decrease noise and hiss at low volume play.

    So in case 1 above, 150% amp to speaker power, you can turn the gain all the way down, and still get very loud sound from the speakers. You might also get clipping and speaker damage at extended full volume listening, especially with the tweeters.

    Case 2, yes... blown speakers possible.

    Case 3, no problems, the ratings are matched, so no blown speakers likely.

    RMS required? Most stock stereo's, and after market amplified head units output 14-20 watts RMS. 60 watts will allow a fuller sound setup, and 100 watts will give clean and loud sound with amp gains turned all the way down. Gains down give cleaner sound, up give louder sound, useful for balancing front to rear speakers.


    Summary for charging your tablet...

    Get the Intelligent DC-DC Converter with USB Interface to power your tablet. It has more than enough power, but it's fairly low price is packed with features you will want.
    You can set a jumper to give the output voltage you want, it has an ignition sense line to power it up when the ignition is turned on, and you can set a jumper to delay turnoff from 0 seconds to 2 hours, so it can charge the tablet for a while after you turn off the ignition.
    It also does not get hot if you keep it under 10 amps, so it's perfect for your application.
    I have one in my dash powering my screen, which only uses 2 amps. I have another one in my old carpc that powered the whole thing, but it was low power and used 6-8 amps total at 12V.
    The Intelligent DC-DC Converter a very nice solution, and it's features cannot be found on lesser options. It's got headroom for future expansion, like powering 2 inductive chargers, one to charge your cell phone and one to charge your tablet wirelessly.

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