Building a charging cupboard

[titch]

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

[Andrew_C]

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!

[titch]

Can you purchase these sorts of power supply on there own?

[Andrew_C]

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.

[titch]

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?

[plexer]

LapCabby

 

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

 

Ben

[titch]

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?

[Butuz]

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

Edited November 17, 2010 by Butuz

[titch]

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.

[titch]

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

[Butuz]

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

[titch]

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.

[SimpleSi]

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

[titch]

Any pics Si?

[SimpleSi]

As long as there not used at any HSE investigation - I'll see what I can do on Tuesday

Si

[maniac]

Loxit sell everything you need.

 

Buy two of these kits:

Laptop Trolleys and Cabinets from Loxit. The Lapbank laptop Charging Kit for 20 Laptops. Also Networking and Secure Docking Options. Lapbank Notebook Trolleys for Best Security, Best Quality, Best Value for Money.

 

And 2 of these (they have 2 outputs on each, so you can run 2 x 10 way leads from the above kit from each one)

Soft Start and Surge Protection for Loxit's Lapbank Range of Laptop Trolleys and laptop safes. For up to 24 Laptops. Electronically Phases the Start Up of Multiple Laptop Charging to Prevent Power Spikes and Conditions the Mains Input Prevents any El

 

That will give you enough for 40.

 

For ventilation, you can easily mount a standard small bathroom extractor inside the unit to extract hot air - the cupboard which contained the server at one of my previous schools had this done and it was surprisingly effective - fan at the top and 2 vents at the bottom meant you got a good flow of air through the cupboard.

 

The big question is, is it worth that much effort when you can quite easily buy ready made cabinets which you just plug in and go.

Edited November 21, 2010 by maniac

[SimpleSi]

As I said before, you don't need soft-start equipment if the mains wall switch is always on and your just plugging and un-pluging laptops one at a time

 

I always buy trolleys for my other schools as they are moved between classrooms and then stored in a corridor overnight.

 

But in this one ancient school, no classroom is on same level as any other and a trolley would just be used as a static cupboard anyway.

 

So I've saved at least £500 by just taking over the top half of an existing cupboard

 

Si

[SimpleSi]

Here is a picture of it in action

At the moment the chargers are just lying around on at the back but I'm planning on mounting them using some velcro to the top - I'll re-upload when done (prob on Thursday)

[flowerpot78]

Hiya... wood, heat from 40 laptops and the shock HSE thing.. I agree with the posts about how you need to be really careful with power supply etc. Not a good idea I think. Copying the photos placed by Sysman could infringe intellectual property theft. Just think the hassle and Health and Safety involved is not worth it. Ta

[titch]

Thanks for all the posts guys. Have finally finished my cupboard now and seems to be working well. Here are some piccies.

 

http://dl.dropbox.com/u/995626/S7306369%20%28Medium%29.JPGhttp://dl.dropbox.com/u/995626/S7306374%20%28Medium%29.JPG http://dl.dropbox.com/u/995626/S7306371%20%28Medium%29.JPGhttp://dl.dropbox.com/u/995626/S7306375%20%28Medium%29.JPG

 

What do you think? Have measured electrics and attached RCD to socket as well. Seems to be going good.

Edited January 24, 2011 by titch

[Andrew_C]

What do you think? Have measured electrics and attached RCD to socket as well. Seems to be going good.

Looks good, but as to the bold bit; why? All the PSUs will be insulated, and the kids only go near low voltage stuff, so you really aren't improving safety. True, it won't be less safe, but just something else to go wrong!

[titch]

reason I did it was because the box that those wall sockets are attached to have a 20a rcd so thought I would just bring it down a little bit to 13a, also if it did trip it wouldnt trip the other stuff in the ict suite (which I have infact unplugged from the relevant sockets for the time being). and on to a few cliches.....you can never be to careful + safety never sleeps. Did that make sense?

[Andrew_C]

20A breaker and 13A fuse are different to the (probably) 30mA/30ms RCDs. You are on the right lines wanting to achieve discrimination, but I'd almost put money on the RCD in the board being faster than the plug-top device.

 

An RCD has two specified parameters. The current which if you exceed it causes tripping, and how long at above that current it needs to be to cause that trip. "Normal" socket circuits are 30mA/30ms, but you can go as fast as 10ms for extra protection, or down to 300ms for fire protection, but not shock. In installations, you can only increase the time parameter if your earth loop resistance is suitably low.

[SimpleSi]

Ncie work

 

Estimated cost?

 

Si

[titch]

Ncie work

 

Estimated cost?

 

Si

 

4 x belkin extension leads with cover thingys £100

1 x surge protected extension lead £5

50 x cable clips £3

10 x studs for extra shelves £3

1 x rcd £10

1 x Padlock + shackle for front £5

 

I got the extra shelves for free in the end so not sure what the timber would have cost. Took about half day of actual work to complete and tidy as well so I reckon £125 + my time all in. Think it suits our need better than a trolley as well. Maxes out at 7 amps when they are all charging.

 

20A breaker and 13A fuse are different to the (probably) 30mA/30ms RCDs. You are on the right lines wanting to achieve discrimination, but I'd almost put money on the RCD in the board being faster than the plug-top device.

 

An RCD has two specified parameters. The current which if you exceed it causes tripping, and how long at above that current it needs to be to cause that trip. "Normal" socket circuits are 30mA/30ms, but you can go as fast as 10ms for extra protection, or down to 300ms for fire protection, but not shock. In installations, you can only increase the time parameter if your earth loop resistance is suitably low.

 

Cheers for the info......not sure if to leave it in the socket or not now? might take another look at the board. Would love to take a basic sparkys course one day.........