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Hardware Thread, Building a charging cupboard in Technical; Im testing my chippie skills here but need a bit of help with charging scenario. I have a nice big ...
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    titch's Avatar
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    Building a charging cupboard

    Im testing my chippie skills here but need a bit of help with charging scenario. I have a nice big secure wooden cupboard in the ict suite which is set to be made into somewhere to store and charge 40 netbooks.

    Now I can easily build all the shelves and make cables nice and tidy but I am unsure about safe charging? There are 2 mains sockets situated just outside the cupboard which I have cut holes to but am unsure about rigging up extension leads preoperly. How could I do this safely (if at all). I was thinking of 2 rcds connected to 2 surge protected extension leads then leading to 5 of these:

    Belkin Surge Concealed 8 Way Sure Protector - Misco.co.uk

    Im not sure how the setup works in a proper charging trolley?

    If anyone has any opinion or ideas that would be great. I will take some pictures of my project for those interested.

    Thanks in advance

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    Andrew_C's Avatar
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    Proper trolleys have large 20v power supplies in the back, these then feed several laptops.

    Having just looked at a Dell laptop PSU, it states that it draws 1.5A. If this is anything like true then you won't be able to charge 40 laptops from a double 13A socket (not all makes allow a 26A draw on the pair!) as you would be looking at 60A. There is probably scope to allow some diversity (they probably won't all draw full power at the same time) but how to calculate that, I don't know in this case.

    A while back (spring?) there was a case of shocks from the plug pins reported in CLEAPSS and other places. I think we discussed it here. Would be worth a read before you get to far!

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    titch (17th November 2010)

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    titch's Avatar
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    Can you purchase these sorts of power supply on there own?

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    Yep, available from CPC, RS Components etc. Choosing exactly what you want is down to the voltage you need, and how many laptops you want to run of each one.

    It will be SIMILAR to this.

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    titch (17th November 2010)

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    titch's Avatar
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    If it was my home I would give these a bash at wiring but for obvious reasons dont think I will take that chance. Anyone know of a commercial power supply that might output to figure of eight type leads?

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    plexer's Avatar
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    LapCabby

    Lapcabby utilise a timer and the unit also delays power on of the charging strips so there is no overload.

    Ben

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    titch (17th November 2010)

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    SYSMAN_MK's Avatar
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    Quote Originally Posted by titch View Post
    Im not sure how the setup works in a proper charging trolley?

    If anyone has any opinion or ideas that would be great. I will take some pictures of my project for those interested.

    Thanks in advance
    Here is what the inside of a Lapsafe Unocart looks like.

    unocart-review-15.jpg
    click to enlarge

    Here is what the inside of a Lapsafe Mini Mentor looks like.

    3.jpg
    click to enlarge

    Another important issue to think about is cooling.
    Last edited by SYSMAN_MK; 17th November 2010 at 12:13 PM.

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    titch (17th November 2010)

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    titch's Avatar
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    Starting to think this may be too big a job. I can sort cooling Ok with a few fans but unless I can buy something commercial that I can plug the charger into I think I might be looking at just purchasing a trolley annoyingly. Someone somewhere must have had a go at this? Or does everyone just use trolleys?

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    Butuz's Avatar
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    You need to accurately work out how much power each laptop PSU actually uses. Reading the back of the PSU will not help as most of them do not make sense. E.g the 65w HP one I have here does not make any sense at all when you compare the input and output ratings.

    It states it's input to be 100 - 240v 1.6amp. Firstly that makes no sense as at 240v it will be using less amps than at 100v so how can it have a catch all rating??

    Secondly at UK voltage, 240v*1.6a = 384 watts?? There is no way it uses that - it would actually catch fire if it did. Secondly it states it's output to be 18.5v @ 3.5 amp. This is correct as 18.5v*3.5a = 64.75watt.

    Realistically that laptop PSU should be no less than 60% efficient, so to output 64.75watts it should only be inputting no more than 100watts. 100w @ 240v = 0.4amps. This is the rating I would use whilst you plan how many adaptors you can fit into a 13a plug socket.

    In my case I would be happy to run 30 of these particular laptop adapters from a 13 amp socket. It would also be a good idea to use one of those cheap wattmeters to actually measure the definate input power ratings of your laptop chargers before you commit.

    Butuz
    Last edited by Butuz; 17th November 2010 at 12:49 PM.

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    titch (18th November 2010)

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    titch's Avatar
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    Thanks Butuz. Grabbed my little energy meter from home gonna do some tests. Will work out school ict electricity costs while im in as well. Will let you know how it goes.

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    titch's Avatar
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    Hi Butuz hope you can help with some figures I have put together. I have tested usage when just charging and also powered on. These are my figures.

    25watt(when powered on)/20watt(when charging)
    0.18amp
    49.9hz
    0.63pf
    36va

    Im not sure what all the figures mean but though it best to put them all down. Thanks in advance

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    Butuz's Avatar
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    Hi Titch.

    Ok good work. they are very efficient laptops!!

    If you just look at 0.18 amp rating it means each laptop adaptor is going to use a maximum of 0.18amps. Now a bog standard plug is rated to 13 amps. If you take 13 and divide by 0.18 you get 72.2. This means you could potentially plug in / charge up to 72 laptops from a standard 13 amp plug.

    So basically - this says that for your charging cabinet you won't need to do any advanced / costly electrical work - you can just daisy chain a couple of 8 way adaptors. Be sure to check the rating of the 6/8 way adaptor before you daisy chain though as many are not rated to 13 amps some will be less. Again take the number of amps the extension is rated at e.g 5 amps and divide by 0.18 to get the maximum number of laptops you can plug in.

    I think you'll be fine.

    Butuz

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    dbrown (19th November 2010), titch (19th November 2010)

  19. #13
    titch's Avatar
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    Butuz...Thanks a lot this has been really helpful...Will definitely put rcd on each plug as I have a feeling that the plug sockets are on the same ring as one of our main switch cabs! Will post picks when finished. Tempted to put a switch in the cupboard as well so I can WOL and do remote bits more easily. Again thanks alot really really appreciate the help, that goes to everyone else as well that has commented.

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    Butuz (22nd November 2010)

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    SimpleSi's Avatar
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    The phased switch charging that laptop trolleys employ is needed as you generally replace all the laptops and then plug the unit back into the mains at a socket and the sudden peak rush of current can cause circuits to trip (and even arcing on the mains switches!)

    But if your building yours into a cupboard, then the laptops will normally be plugged in in sequence and the sudden peak demand won't exist.

    As long as the ventilation is OK - you should be alright.

    On Tuesday, I just made up a little rack on a cupboard shelf for 15 netbooks out of some mdf and some 10x50 mm planed timber for a school - total material costs including 2x8way mains extenders = 35 (and even if you include my time at 3 hours at 20/hour the total cost was 95.
    Saved the school quite a few hundred (and since its a school built in 1800 - a trolley would have been no good as its got more stairs than a lighthouse!

    Simon

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    titch's Avatar
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    Any pics Si?

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