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Thread: 12V Inverter or PSU

  1. #1
    Newbie Pegasus50's Avatar
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    12V Inverter or PSU

    Apologies in advance for the title. I'm having a difficult time sorting through some of the things I'm trying to accomplish. My system is restricted to a power inverter in the form of a AC/DC brick (12V@5A). Which is fine for initial setup and development task on the bench.

    My concern is that when it's time to install the system in the car; I want all of the features available. My Car PC is based on Epia P820 and it only has a 2 pin DC-in connector. I'm fairly convinced that I can modify a M1 to power this Pico ITX board and the 7" screen. I just can't find sufficient info from others who have done it. Unlike many of you I dislike being on the cutting edge. Total power required for this system shouldn't be more than 30W, most of which I'm reserving for USB devices. Can someone please help me get on track with this?

  2. #2
    Raw Wave
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    Not that I have fully digested your intent & system...

    But 30W is a relatively small power requirement - ie, well under normal >90W DC-AC inverters and DC-DC PC supplies.

    For powering in a car etc, a DC-DC converter is probably best, especially when designed with low standby currents (as in uA = micro-Amps).
    The exception might be when using more common AC devices - like PCs, phone chargers etc - without the need to get DC equivalents.


    Since your system has a DC input, there is no point going DC-AC (inverter) and then AC-DC. Better going DC-DC.

    A 30W output is 6A at 5V for USB which should a similar 6A input for a "linear" voltage regulator converter, or maybe 3A for a 12V-5V "inverting" converter. (12V@3A = 36W; ie, 30W out & 6W = 20% inefficiency.
    BTW - "inverter" sometimes means DC-AC converter, but since DC-AC-DC converters use "inverters", are they also inverters despite their DC output? The true jargon is probably SMPS = Switched-Mode Power Supply which is the "DC switching" used for DC-DC via an intermediate AC transform(no pun)ation.

    Confused?
    Good!

    I'm saying DC-DC, not a DC-AC "inverter".
    If you load is happy with a normal battery and car "+12V DC" supply - which means typically 11.5V to 14.5V at the battery excluding occasional dips down to perhaps 10V or 8V due to cranking, or headlight switching etc, the you can just connect it to the battery (via a fuse etc).
    Though usually isolation, transient protection etc are required.....

  3. #3
    Newbie Pegasus50's Avatar
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    Thanks for your reply OldSpark. A big part of my misunderstanding with this board is the lack of data from Via. the DC-in would usually denote that the device attached to it has some power circuitry on-board. Via's User Guide and OP's Manual don't explicitly state or even allude to it.

    My estimation of the wattage requirements is ultra-conservative; the number was garnered from one of the many sources I have been studying. For the sake of discussion though --let's say that the board already has on-board power. What can I do to verify my assumption?

  4. #4
    Raw Wave
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    Damn bluddy rastin' frastin' friggin' fracken questions involving research....

    I read the Epia P820 has "onboard PSU", but haven't yet found where the "12V DC input voltage" is properly described - eg, 11.99V to 12.01V or 8V-16V etc.
    I HATE that! And it is totally unacceptable for suppliers etc NOT to state the range.
    (When anyone tells me it's 12V, I reply "it's no good for my car then - that's normally 13.6-14.4 when charging so will blow the crap out of it..."... "And it's no good for anyone else - unless they add a 12V-12V converter... and brand-X product doesn't need that!...") (Whose the smartarse now M[r:s] SalesFolk?)

    But is is a matter of finding the specs.
    Else getting the specs.
    Else harassing some supplier/manufacturer etc.
    Strictly speaking, their warranty info should cover that because stating "12V" is insufficient and would/should be rejected by courts etc. No such thing as "exactly 12V" in practice, and do they mean 12V as in a 12V battery (say 11.3-12.8V), or 12V auto system (typically specified as 8V to 16V)??

    But I can't do more for another 12 hours or more.....
    Till then....

    Cheers.

  5. #5
    Neither darque nor pervert DarquePervert's Avatar
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    OldSpark, I'll help you out here....

    GENERALLY, a PC motherboard that has onboard power requires regulated power of the appropriate voltage. I haven't seen a motherboard that doesn't.


    Pegasus50, you could jury-rig an M1, but why? That's a kluuge job, not to mention you'll have additional, unnecessary voltages trying to be generated by the M1.
    A Carnetix regulator is going to provide only the voltage you need (12vDC) to power that board.

    If you already own the M1, then great. Go for it. If you're buying new parts, be smart about it and bu the appropriate pieces for your setup.
    Have you looked in the FAQ yet?
    How about the Wiki?



    Under normal circumstances, a signature would go here.

  6. #6
    Newbie Pegasus50's Avatar
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    Quote Originally Posted by OldSpark View Post
    Damn bluddy rastin' frastin' friggin' fracken questions involving research....

    I read the Epia P820 has "onboard PSU", but haven't yet found where the "12V DC input voltage" is properly described - eg, 11.99V to 12.01V or 8V-16V etc.
    I HATE that! And it is totally unacceptable for suppliers etc NOT to state the range.
    (When anyone tells me it's 12V, I reply "it's no good for my car then - that's normally 13.6-14.4 when charging so will blow the crap out of it..."... "And it's no good for anyone else - unless they add a 12V-12V converter... and brand-X product doesn't need that!...") (Whose the smartarse now M[r:s] SalesFolk?)
    Well at least you found a reference to onboard PSU. I've poured over the P820's datasheet, OP's manual and Users Guide with no mention of it (including there Web hyped press releases). I can see why many people are reluctant to use Via's Products. Thanks none the less; you're reply has helped me focus on the priorities of this project.

    Quote Originally Posted by DarquePervert View Post
    [...]Pegasus50, you could jury-rig an M1, but why? That's a kluuge job, not to mention you'll have additional, unnecessary voltages trying to be generated by the M1. A Carnetix regulator is going to provide only the voltage you need (12vDC) to power that board.[...]
    Opus replied to my inquiry and recommended the DCA5-080-12 for this board. They suggested that I splice the power leads into the 2-pin DC-IN. Can you see any reason I can't do this this with a barrel plug into the DC-IN jack?

  7. #7
    Raw Wave
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    THANKS DarquePervert for the help-out.
    I would have thought as much, and I well understand your "GENERALLY". (Which brings me back to .... lol)

    Hence if it wasn't for the dips that can be experienced by automotive systems, motherboards could be connected to the battery via a simple zenor regulator.
    Maybe that why so many like the dual battery set up (eg - Why did I wait so long).

    So hence WE have to supply a switcher (SMPS) that can regulate (say) 8V to 16V to a constant 12V.

    The bummer is that since the onboard PSU is probably a switcher itself, why does it not do it? Or maybe the only switcher is the 5V supply.

    If they were a 5V input instead, then we could use cheap linear 5V from 8V-16V regulator etc etc.
    So we supply an (8-16V DC) via AC to 12V DC PSU to feed their 12V DC board probably with 12V via AC to 5V DC, else an inefficient 12V-5V linear regulator....
    I see now why most motherboards have its users supply the +5 & +12V power!

    As to that DCA5-080-12 - isn't that and expensive overkill? That's for boards without PSUs needing 12V & 5V.
    In my case, I'd consider a second battery, and/or something like the 50W/100W AUD$23 Oatley DC TO DC CONVERTER - kit #K168.

    BTW - the "onboard PSU" info was merely from the data/specs given by various reviewers or sellers (the first links from a Google search).
    But I wish their "12V in" would have a MAXIMUM allowable - eg, if say 14.4V or 15V etc, then a second battery with a low-voltage cutout set to 12V would be fine (eg, the typical $5 relay controlled by the car's charge light, and a $20 MW728 with series diodes etc (to raise 11.2V trip to 12V) and hence maybe another relay in latching configuration with additional manual on & off controls.... about $30 total excluding the (optional?) 2nd battery, fusing and cabling.

  8. #8
    Newbie Pegasus50's Avatar
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    Quote Originally Posted by OldSpark View Post
    [...]As to that DCA5-080-12 - isn't that and expensive overkill? That's for boards without PSUs needing 12V & 5V.
    Dual batteries? I really don't want to go there for this project. I could just as easily spend the bucks on a Pioneer unit. With respect to the DCA5 I'm almost certain that this is Opus's attempt of a suggestive sales technique. It's nice to know that I'll have options though. The oatley converter looks promising for some other things that I have in mind. Bottom line for me is the need to protect the board and screen as much as possible. If these forums have taught me anything at this point it's that assembling the PC is only half the fun; perfecting it is the real trick.

    Anyhoo--I sent a direct inquiry to Via asking for details of the onboard PSU and I've placed my order with Logicsupply. Since only a few people even have this board I'm sure there will be a lot more reviews and revisions of its strengths and weaknesses. Take a look at this guys rig I'm fairly certain I can do as well.... if not better.

  9. #9
    Raw Wave
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    Quote Originally Posted by Pegasus50 View Post
    Dual batteries? I really don't want to go there for this project. I could just as easily spend the bucks...
    I will merely point to Why did I wait so long...
    ... and merely add a $5 relay, $15 pf circuit breakers, and (say) a $35 7AH AGM battery for faster booting and no flattening of your main battery. Add $20 for a low voltage cut-out. And they are Australian dollar$ - things are often cheaper stateside (but will send you broke in the yUK).

    And I just got word from somebody that implemented the same charge-Lamp controlled circuit - though they used a MOSFET due to low "L" circuit output. (I'm not sure if the MOSFET was instead of the relay,or to dive the relay.)


    Not that that overcomes or solves the "12V" supply regulation issue...
    I'm trying to say that is isn't all that complex, and it usually does NOT need expensive isolators. (Hear me - the charge light is the simplest & most reliable.)

  10. #10
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    Know little about power inverters. But here is a 12V DC/AC Car Power Inverter, is it useful for "Pegasus50"?

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