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Thread: lots and lots (and lots) of power

  1. #1
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    lots and lots (and lots) of power

    My goal is to run a beastly computer inside a car. This is actually a research project (hence, I can't scale down the computer), but I figured this community would be most knowledgeable about what is possible and what is not. I read on the FAQs and other newbie material that DC-DC supplies are relatively under-powered, and that for more power to go with an inverter. However, I'm not even sure that will be enough. The machine uses a 1000W power supply, so I'm trying to figure out if a car's electrical system will produce enough power to run the machine (and if I can *get* that power to the machine). The car model hasn't been decided yet, but the "maximum electrical power output" isn't a big selling point and so isn't advertised on car manufacturers websites. Since I've seen cars with some ridiculous subs I'm guessing it's not impossible to get a lot of power, but I don't know enough to know where to start. So, here are my questions:

    1. does a 1000w dc-dc exist?
    2. if not, does a 1000w inverter exist?
      1. would losses due to DC->AC->DC be a significant concern?
      2. I read on the FAQ not to use the cigarette adapter, so where does the inverter hook up (harness?)?
    3. how can I find out what the maximum current (power) output will be for [X] car?


    Thanks! (and sorry for my nub-ness)

  2. #2
    Constant Bitrate meryan00's Avatar
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    1. I have never seen one
    2. Absolutely, if your car supports it is another issue, but that amount of power will have to hard wired in directly to the battery terminals.
    3. That would be dependent on the alternator output, and the draw of your car. IF yo do some research on highend car audio systems many vehicles will be outfitted with multiple alternators to provide the power needed.

    Sounds like an ambitious project but I do not know why you would need a 1kW PSU, the only systems that need those are usually the SLI multiple 200+ watt video card systems. I first thought maybe you were going with a server type system but most of those would use a dual PSU setup for each physical CPU

    Perhaps a little more info on your research project and we can provide more help for you.

  3. #3
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    Talk to mat at mechman alternators, he's a great guy and will set you up right. One ho alt should support that with a fewdays batts in the back with no problem

  4. #4
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    but that amount of power will have to hard wired in directly to the battery terminals
    Awesome, that is good to know.

    many vehicles will be outfitted with multiple alternators to provide the power needed
    Cool, makes sense. Would you happen to know of any resources where I could look that up (quickly)? I suppose the shop-manual for a particular car would have that info, but, as a driving factor, I'd like to limit our search to only cars which could support the computer.

    the only systems that need those are usually the SLI multiple 200+ watt video card systems
    Thats right. This system has four.

    Perhaps a little more info on your research project and we can provide more help for you
    Self-driving cars . What we're working on will require a lot of computation. Previous incarnations had a dedicated generator in the car for the computer cluster. Consequently, it also had an extra A/C unit. Now we're trying to do more with smaller computers. A machine with four gpu's isn't exactly commodity hardware, but it's a lot closer than a cluster of 10 quad-core PCs. With it's single ATX power supply, I'm hoping we can just put this in the trunk of an SUV or Subaru/crossover/kinda-thing without having to do months worth of design work.

  5. #5
    MySQL Error soundman98's Avatar
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    1000w of proper power is a huge amount of power..

    1. i don't know of any pre-built solutions to this specifically for car-pc's. it is possible that some solutions for it exist in manufacturing circles for parts machining, but i am not a manufacturer, so don't know..

    2. yes. there are many. for something like this, you need to look at name brand, true-sine inverters. and make sure to go by the rms output, not the max output.

    2a. depends on the power of the car.
    2b. math is really required to understand all of this, and i am a horrible mathematician.. a cig lighter puts out a max of 10A, but realistically isn't rated for anymore then 2-3 A continuous. any serious 1000w invertor is going need to be hard-wired to the car-- there will not be any way to connect it to a cig lighter port.

    3. i don't know of any sites that list this info.

    something to know-- all police-edition vehicle include a higher-output alternator(off the top of my head, i think the crown-vic's have a 180A instead of a stock 80a alt) for the extra lights that are required for police cars.

    but i can promise you that none of these will provide 1000w stock. to get 1000w rms, you need to start looking at SPL car audio installs-- many have at least 2 alternators--many with 4, 5-10 batteries, and enough zero gauge wire to carry that power.

    and the other thing to keep in mind-- all alternators do not work at their rated power all the time, they require a minimum RPM to get rated power-- below this threshhold, they do not produce the same amount of power that they are rated for. many high output alternators only work above 2,000-3,000 RPM-- so in order to get the rated power, you need to keep the motor above 2,000-3,000RPM...

  6. #6
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    Quote Originally Posted by soundman98 View Post
    you need to start looking at SPL car audio installs
    Ok cool. I did a quick google search, but just to clairify, what is SPL?

    many have at least 2 alternators--many with 4, 5-10 batteries, and enough zero gauge wire to carry that power...

    many high output alternators only work above 2,000-3,000 RPM--
    So, it sounds like we might need to have a shop do some after-market customization. Is it common for these high-power audio guys to install higher output alternators? Do they tweak the car's idle to run at higher RPM?

    Thanks for the info, so far this has been a lot of help.

    (PS: I'm a newbie on this forum so my posts are still moderated... hence the delay).

  7. #7
    Constant Bitrate meryan00's Avatar
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    Perhaps a second battery might be a good thing to have also to help alleviate some strain on the alternator(s). They say you need a minimum of 120% output than your power requirments.

    I was playing with numbers, but forgive me if these are not perfect.

    a 1000 watt computer would run at ~80 Amps under full load, so you would then need to have at least a 100 Watt alternator(continuous output) if that was all you are running, obviously you are going ot be having plenty of other electronics in addition to the standard car load which would be normally 80% of you rated alternator output.

    Depending on your vehicle it might be worthwhile to have a shop install a 250 amp alternator(usually these will output ~150 at idle. Then the issue you will run into is clearance for space for such a large alternator

    it might also help to get a high power voltage regulator that can handle your output

    Search for high output alternators for whatever vehicle you might use and you can see that you can easily rack up a $500 bill jsut for parts

  8. #8
    MySQL Error soundman98's Avatar
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    SPL stands for Sound Pressure Level.

    engine idle: in most SPL contests where the sound systems are used, a individual participant will only run their car for a couple seconds, but no longer then a minute or two.. so some might just stick something on the gas pedal to raise the idle.. i really don't know-- i am more interested in sound quality, so haven't really researched spl contests too much..

    power--take 2:

    after thinking about it, you can expect that most cars will have a 60-100A alternator. though this doesn't really matter. here's why:

    almost all cars use a alternator that fits the cars power requirements only. with the exception of the police-edition vehicles, and specialty-built vehicles, there are not any cars that are built--by normal auto-makers(ford, chrysler, chevy, etc)-- with a alternator that can supply a lot more power then what the car can use. the engineers design the alternator to meet the cars needs only, they don't take consumer-added devices into this formula. it is true that they will add a little to prevent light dimming, and other power loss issues, but there is no way that you will ever be able to power a 1,000w device without extra equipment.

    so, with that in mind:

    a power graph i have--it's specifically for wire gauge, but in this case, we'll be using it for the watts/amps conversion:



    so meryan00 is about right on for the pc's power consumption.

    so with that in mind, you will need a 160A alt just to meet those requirements without taking into consideration any losses...


    time to jump around a little:

    thinking about question 2 in your original post:
    i was wrong about this,

    a 1,000w rms inverter is measured at the output-- not the input, so any loss is not accounted for. the same goes for a ac/dc psu-- the loss is not accounted for because it is the output rating, not the input.. the good thing though is that a 1,000w rms inverter is that it will be able to handle the loss in the ac/dc psu as long as the loss doesn't exceed about 200w(1200w total).

    the bad thing is that the inverter loss is not accounted for.

    so you now need to get into the way that they build the inverters-- while some designs might be 80-90% efficient, other designs are around 50%, or less efficient.. and this would affect the alternator power requirements..



    for average cost, i doubt you will get away for any less then $2,000 all-said-and-done in terms of all the required power equipment(alternator[s], battery[s], wire, and custom fab work). though my gut says a figure closer to $5,000 is more realistic to correctly power a setup like that..

  9. #9
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    Don't forget that power supply are not perfect they are usually rated around 85% of efficiencyso when your power supply pull 1000 watt it actually pull around 1200 watt from the "wall".
    English is not my first language so if I say something weird just say it to me and i try to be clearer :) :)

  10. #10
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    IMO 1kW is not very much - relatively speaking.
    That equates to ~100A. (See below)

    So add 100A or more to your alternator - ie, buy a bigger alternator; 250A is commonly available.
    Do not use parallel alternators unless they handle being paralleled or have been appropriately installed. (Only done for "alternators" larger than the typical 250A...)

    But make sure you have at least the required alternator average output at your average engine RPM to suit your load(s), and suitable battery reserve when the alternator falls short.


    1kW and higher is common for audio buffs, big cooling fans, etc.
    But stick to places like this or the12volt.com rather than trusting info off random audio and 4WD forums....


    [ FYI - that 100A is using a common ROT (Rule Of Thumb) from I = P/V = Amps = Power divided by Voltage where 12V is rounded down to 10V to allow for various inefficiencies. It generally provides an initial conservatively (oversized) figure for use for alternators, batteries, power supplies etc based on output power (eg, audio RMS outputs; ac/dc converter demand for x-Watt loads) assuming ~80% eficiencies, and that system voltages are usually above 12V - eg up to 14.4 or typically perhaps ~14V when charging, or up to 12.6V off a full battery. ]


    PS - spotted some other details...
    Extra batteries are not to take the strain OFF the alternator (most claim they ADD strain LOL!) - they are simply as the alternator's backup...

    dc-dc converters are dc-ac-dc.
    Inverters are often dc converters with ac shaping - ie, dc-ac-dc-ac (especially stepped- or pseudo-sinewave).
    They can have similar efficiencies, though inverters are the followed by the equipment's ac-dc conversion, hence dc-ac-dc-ac-dc instead of dc-ac-dc.
    And they have similar noise sources.
    Last edited by OldSpark; 04-06-2011 at 01:38 AM. Reason: PS...

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