Laptop Trolley Design

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Hello,

We have just taken delivery of some laptop trolleys.

The trolleys house fifteen laptops, a printer and a wireless access point.

The idea is that the trolley can be wheeled into a classroom, connected to the mains and network, instantly turning the classroom into an IT room... great.

However,

The fifteen laptop chargers are simply connected to a large PDU inside the trolley, the PDU then simply has a BS1363 plug on the end of it.

Looking at the specs of the chargers they draw 1.5A at 230V, so a potential current of 22.5A not including the printer and AP.

How can this be right or am I missing something?

What is the breaking time of a 13A BS1362 under a 22.5 amp load?

Cheers.

Matt
 
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I'd suggest that the laptops chargers do not draw 1.5A from the mains in normal opperation... the chargers might be rated at 1.5A, I'd reckon thats the max short duration current it might take.

1.5A @ 230v is 345w now if youimagine the heat from 150w lamps sat on your lap... it starts to seem improbable that the computers will take that much...

Start up current might be another issue, but give it a try, it'l either blow or won't

Another issue, and I'm not too clear on this one, but there is a standard to do with desk basd power distro that means you have to limit the amount of IT load on each plugtop to a certain value.. and its usually done by itting 7A fuse in plug.... if pensdown is around he knows more about that...
 
I did look at a PSU here and it does say 1.7A at 100 - 250volt in and 3.75A at 20 volt out.

So to work backwards to give 3.75A at 20V it will need 1/3A at 230V but 3/4A at 100V so the device seems to be rated well over. I would expect this is to allow for the inrush to charge capacitors.

So I would not think there is any problem and even if there is by switching on the laptops one at a time it will get around any problem.

Next time I use Laptop I'll use the plug in meter I got from Aldi to check. But since you are using 230v not 100v then I would say you can divide 22.5 by 23 and times by 10 giving 10A at 230V so no problem.
 
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From what i've found on the internet, the startup current can be as high as 20a on a laptop charger, even more on lower voltage models isnt this going to trip even a C32?

I agree with you about the chargers probably not drawing 1.5A under normal operation, but there are circumstances where this may happen.

For example if the laptops were left on and allowed to run flat.

Just seems like cack design to me.
 
It will be rated higher than your calculated load becuase the power supply will not be 100% efficient, the BEST units only reach 85-90% and some will be much lower.

There is also the issue of power factor, laptop PSU's are switched mode psu's so will have a power factor anything between 0.7 to 0.95 depending on the design of the PSU. I've no idea if that will directly affect the fuse rating though.

You could try putting a mains ammeter over the psu and see what kinda draw it takes on both power up and on charging.
 
isnt the idea of the trollys as a charging unit? ie the laptops removed, and running from batteries whislt in use.

the max output on a laptop charger is when the battery is flat AND you are running a high power usage program/burning discs etc.

does the AP actually have power, of does it need POE?
 
Yes, the trolley is a charging unit. So the batteries are likely to be run down when reinserted into the trolley.

The AP requires power because its attached to the trolley, we could go POE but there is no poe switch in that cab as yet.

I will measure the input with my clamp meter later, when I get chance to make up a test lead the the conductors seperated.
 
Well, panic over on the BS1363 front, just measured a laptop PSU, with machine connected and running and the nominal current is about 0.25A :LOL:

The startup current, however is a different problem.

We've tested turning the trolley on on a ring protected by a B32, it trips the cb first time every time, the ring however is not dedicated to the laptops, so will already have some loading on it.

Time to get the pro's in I think, could do with a dedicated radial for at least the charging room.
 
As to 3 way adaptor no can't remember where looking for something different and it came up seemed a little daft.

As to Power tried my Lap Top and it peaked at 41 Watt measured at socket I am sure there are things which could cause it to exceed that but needs to be over 4 times that to cause problems.

I used one of these
 
Be cautious with those power measurements, they dont actually mean much unless the laptop was both working flat out AND charging.

Laptops tend to reduce power consumption when they aren't busy by scaling back on processor/graphics clocks etc.

Mine sits at around 85-100W at idle and flat out will break over 200W according to my plug in energy monitor - and thats not while charging. OK its a bit of a beast of a laptop but I'd be surprised if even the weediest couldnt comfortably break 100W.
 
couldn't you just get some of those green wind up laptops that they have in that africa commercial?

100laptop.jpg
 
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