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Two related questions have been combined here as the answers and concepts overlap:

(Q1) We are building a robot that will be controlled by mini-ITX PC. The power source for robot will be detached car battery. Question is how to power mini-ITX mother board (and HDD) using this battery? What devices are needed?

Edit: I think I need DC-DC converter that converts from battery voltage and converts it to 12V and stabilizes it. Right?

(Q2) Originally from here

I have a linux box powered by a "deep cycle" battery, and I"m wondering, would it be more efficient / possible for me to convert (or replace) the AC power supply in the unit with a DC one so that I don't lose energy in the conversion from AC power to DC, optimizing the use of power from my battery.

DIY link: http://www.instructables.com/id/Convert-an-ATX-Power-Supply-Into-a-Regular-DC-Powe/

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  • \$\begingroup\$ You need to specify if you need the 12V, 5V, 3.3V and -5V/-12V rails, and also how much power (on each rail) it will consume in the worst case. \$\endgroup\$ – Thomas O Mar 17 '11 at 15:03
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    \$\begingroup\$ It looks like your link does something quite different from what you seem to be asking; The linked guide explains turning an ATX computer powersupply into a bench powersupply; but you seem to be asking for an ATX power supply that can run directly off of 12 volts! \$\endgroup\$ – SingleNegationElimination Sep 21 '11 at 23:25
  • \$\begingroup\$ mini-itx.com/store/psu first link in google lists multiple DC power supplies \$\endgroup\$ – Earlz Sep 22 '11 at 16:54
  • \$\begingroup\$ @Kortuk - this question had this question (allegedly) merged with it. Some of the the answers do not now make sense wrt the question as now asked. If people feel the need to do this sort of thing they should also merge at least the useful part of the imported question and also, probably, note on the main text that a merge has occurred and what the original other question was. // Failure to do this produces GIGO. \$\endgroup\$ – Russell McMahon Sep 25 '11 at 0:29
  • \$\begingroup\$ electronics.stackexchange.com/questions/19828/… \$\endgroup\$ – Russell McMahon Sep 25 '11 at 0:31
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Mini-ITX does not standardize a power supply. If your board takes 12V, then yes, you need a DC-DC converter that converts the battery voltage to 12V. However, according to Wikipedia, a 20 or 24-pin standard ATX power connector is conventionally used.

This connector has a number of independent supplies for 3.3V, 5V, and 12V. Here's the PDF standard if you want to develop your own - It's not trivial! You'll need to know the power requirements of your mini-ITX board to determine how many amps each supply needs to provide.

However, there are a number of ready-made solutions. If you have an inverter available, a standard ATX power supply will work fine. mini-box.com has been debugged (good or bad, your choice) on this site before; their m-series power adapters are specifically designed for in-car use.

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  • \$\begingroup\$ Thanks! My board takes 12V, but the problem is that car battery is never 12V exactly, even detached and fully charged. \$\endgroup\$ – Andrey Mar 17 '11 at 14:09
  • \$\begingroup\$ They you need to consider that in the range, for example 8-14 V should be easy to \$\endgroup\$ – Brian Carlton Mar 17 '11 at 14:39
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Yes, and you can buy special power supplies for the job. They are sold as "auto" or "car" power supplies, and usually include circuitry to send an ACPI shutdown signal when the ignition is turned off.

You can also get some very nice little tiny power supplies that are not much bigger than the ATX plug that goes into the motherboard - ideal for Mini-ATX and ITX systems that don't need much power.

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For a DC/DC converter that does exactly what you want see: http://dren.dk/carpower.html

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Minibox offers a number of supplies for motherboards, take a look at this and others at the site. http://www.mini-box.com/M1-ATX-90w-Intelligent-Automotive-DC-DC-Power-Supply

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Yes. You would expect to get efficiency gains.

Efficiency-design capabilities of designers of new and old equipment and Cost / efficiency manufacturing tradeoffs which have been made will have significant impact on what you can achieve. (Efficiency of "what the market will accept" and "best we can do" implementations varies substantially..

Whether it's worthwhile depends on cost versus other options.

To go 12VDC - 110 VAC - PSU/+12/+5/...
Requires energy losses in the upconversion to AC - probably in the 10% to 20% losses range depending on how hard you try. Probably not less than 5% no matter how hard you try.

Making 5/12/... from 110 VAC or 12 VDC will incur losses however done.
110 VAC supply should do this with 5% to 20% losses BUT that's an estimate - I've not measured a typical PC supply to see. Easily enough done.

Making 5/12/... also requires a switching power supply.
12 -> 12 is lossless IF battery version of 12V is acceptable. As battery can droop to 10 - 11 V it MAY need boosting and as it cab go over 12 V you may need buck boost. Say 5 - 15% losses range. 5% only with great care.

12 -> 5VDC requires a standard buck converter. Say 10% losses. Other voltages say 3.3V and CPU voltages of 1.XV. Say 10 -15 %. Could be 5% with great care.

So overall estimates:

  • 12VDC - 110VAC - 12VDC etc at (80%-90%) x 90% =~ 70% - 80% overall.

  • 12 VDC -> psu at say 80% - 90% overall

Difference is perhaps break even (80/80) to as good as 90/70 =~ 30% improvement.
Liable to be somewhere in between - say a 15% to 25% gain.
This translates directly either into increased run time or reduced PV panel capacity if solar powered. Or greater safety factor.

If you do this in a solar powered system then also using an MPPT PV panel controller would make great sense.

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