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Thread: Help with what inverter I need!??!

  1. #1
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    Help with what inverter I need!??!

    Hey Guys,

    So Im planning my first in car project at the moment, been reading around a lot but need help on powering it all..

    Now for numerous reasons, Im going to have abit of equipment in the car.. Ill be having, 7/8inch liliput hd touchscreen, acer netbook, appletv3, wireless router and a NAS drive.

    Im in IT so all of that I can work out fine and have my reasons for wanting it all..

    But how will I power it??

    After research I assume it will need to be an inverter??

    Any in particular you would recommend for all of this?

    And I've a few silly questions about them aswell..

    1. Do these have a battery in them?
    2. Lots of them only have 1 plug socket.. can I extend that for numerous plugs?
    3. How do I wire it up to turn on with the ignition? (Just the inverter, the rest I can figure out)

    Any help will be appreciated please guys, Thanks.

  2. #2
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    Welcome. I would check the FAQ's section and wiki as there is a ton of information for newbies like yourself that will answer many of your questions.

    I as well as many will strongly suggest you avoid DC/AC inverters. The reasons can be seen in the FAQ's section but basically they are very inefficient and usually don't survive crank. Not to mention all of the stuff you are trying to run is DC to begin with so you are converting from DC to AC to DC.

    no, they don't have batteries (I won't say all but certainly most)
    You can split it as many times as you like so long as you have enough wattage
    Use a relay. Take a high power fused line off of your battery to a standard auto relay and trigger the relay with the ignition wire at your ignition harness.

  3. #3
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    Agreed!
    dc-dc is the way to go. And ones designed for automotive use which IMO means handling dips to or below 8V (else 9V alt least), and up to 16V (or 15V at least), though dual-battery setups may alleviate that stringency.

    Ditto for relays. Take power from the battery (via a fuse or circuit-breaker), that's generally the cleanest dc source.
    The "12V DC" or voltage that energises the relay coil can fluctuate and be as noisy as a kookaburra's orgasm without effecting the main power through the relay.




    FYI - an inverter with a battery is a UPS, though commonly a UPS is thought of as AC in & out, ie, ac-dc-ac (or rectifier/charger to battery and inverted back to AC; in "off-line" systems, the inverter and rectifier are the same and can only be used "one-way", but that's another story). A UPS can also be dc-dc or ac-dc, but the key ingredient is some form of energy storage, whether a battery, a spinning mass or engine to a motor/generator, etc.

  4. #4
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    yes. I would like a gyro ups please!

    Your mention of spinning mass reminded me of some video documentary I watched on gyro used for storing electricity. I envision a dump truck with one of those things in the bed to power the pc haha.

  5. #5
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    LOL!
    I just think of the guy in the room where an old motor-flyweight-alternator UPS was installed. The flyweight weighed 2 tons - a somewhat heavy fly! Unfortunately the ancient thing happened to fall apart when he was there. There wasn't much left of him - nor anything else for that matter - a 2-ton wheel that launches at several hundred RPM has a hell of a lot of momentum and energy!. I suspect they used a hose to recover whatever they could of him.
    I recently thought if that as a read about the new Porche with its passenger-substituting rotating energy storage system...


    Modern rotary UPS are vastly different and IMO ideal for new buildings. And they are an efficient "on-line" system.

    [ I recall my days of professional headbanging. I tried to get our company to install a rotary UPS for a new building, but they thought the $2m price tag was too high - the static (electronic) equivalent only cost $1m.
    I pointed out their economic/fiscal errors etc...
    The rectifiers required diesels with twice the rating of the rectifier (ie, a 100kVA ac-dc-ac UPS required a 200kVA diesel gen-set).
    The $x00,000 batteries would be replaced every 5 years if not earlier.
    The rectifier(charger) - battery - inverter efficiency was 90% if lucky (max 85% was the norm), it needed air-conditioning, and whilst the rectifier/inverter might be of similar size to a generator, it's batteries were not, and they required a separate room plus monitoring and maintenance, various safety measures (>400V DC!) etc - these last things being extremely costly in electricity, floorspace, and maintenance.
    Then there was their behavior...
    Inverters couldn't handle surges or spikes - they could switch over to the mains/AC supply (which of course is not there during a power failure), plus there was the switching risk anyhow. (These were online UPS as used in big or critical installations unlike offline or standby UPS that switch over to the inverter upon power failure as common for domestic PCs etc.)
    And if diesels didn't start, you might only have 8-15 minutes of battery reserve (if they didn't fail!).
    Compare that to a diesel-motor-generator...
    The genny has the same electrical characteristics as power stations - tolerant of surges and shorts etc, and a clean sine-wave output.
    The motor-gen has efficiencies above 97% and needed no air-conditioning.
    The diesel would start within 3 seconds (eg, 1.7 seconds) and then you had as much reserve time or capacity as its fuel tank held, or until topped up by a tanker (can't do that with batteries!).
    And the diesel was half the rating of the ac-dc-ac UPS equivalent.
    Many that needed to upsize static UPS more that doubled their UPS capacity using rotary UPS, and used the old battery rooms as gyms, cafeterias, storage, naughty rooms, whatever.
    But no, "our" wisdom dictated ac-dc-ac UPS, or smaller UPS scattered throughout the building each with there hazards and maintenance, etc.
    Of course many of those people's importance was based on the money they controlled and spent, else maintenance or diesels or electricity etc didn't fall under their budget, so they didn't care . I thinks that's why I was considered such a failure - not only did I work "for the company" rather than my immediate responsibility, but in 3 years I halved my expenditure despite purchasing more equipment and "removing unreliability" and most maintenance. (Hence why I am proud to be a failure.)
    ... ramble ends. ]


    I could go on about the merits of online systems - or rather, the traps with typical domestic offline systems, but I'd hate to hijack and ramble.
    Besides, these days offlines are reliable enough for most situations. In fact many that once INSISTED on online UPS now enjoy the cheaper offline versions (both cheaper in purchase price, and ongoing costs like ~3% versus ~20% inefficiency). Only lightning and interruption prone areas still desire the onlines, as do sensitive installations (hospitals, IT centers, echelon, etc).

  6. #6
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    Ok fair enough..

    But this is now where I start getting confused.

    Can someone post a link to the sort of dc-dc kit I would need?

    The dc-ac ones just make more sense in my head and I can picture it, simply because there's a plug socket on it no doubt.

    But I just cant find the sort of thing I'd need in dc-dc.

  7. #7
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    AWESOME! hijack over.

  8. #8
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    So, after a-lot of reading around..

    Think ive decided that I'm happier going for an ac-dc inverter instead of the dc-dc, which frankly just looks abit too complicated on the electrical side of it for me.

    Looking at the inverter then plugging into a ups and running everything from that.

    http://www.ebay.co.uk/itm/Silverline...ht_2248wt_1392

    http://www.ebay.co.uk/itm/Riello-iPl...ht_1812wt_1393

    These are the two I'm looking at and around the price range I'm looking in.

    Thoughts?

    Also, say hypothetically on that UPS, I were to have just a router and ext hdd running off the battery's after the inverter was turnt off.

    How long would you say they would last work for?

  9. #9
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    Well, my thoughts have been given. I think you are asking for trouble with dc-ac-dc. DC - DC is not complicated. A carnetix would probably be all you need and have the startup shutdown controller built in. Check the items you are powering and compile the list of voltages and post them here. probably 5, 12 and 18 which can be run on that carnetix.

    Those inverters look big and will produce lots of heat.

    I would have to know how much the inverter pulls at idle + how much the HD and router pull. My guess is an hour or so before the car won't start.

  10. #10
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    Yeah thats fair enough and appreciate the info and help!

    Sorry what I mean is.. once the engine switches off.. and I switch the inverter off.. how long would the ups last standalone?

    Router and ext hdd both 12v each.

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