How much power should a laptop trolley take?

[mikeprice]

Hi all

 

I have a problem with the power tripping to our laptop trolley. The trolley has a MAX of 14 laptops in it and the chargers are rated as

input 100-240V 1.7 A 50-60 Hz

output 18.5 V 3.5 A 65 W

 

It was connected to a double socket with a 20A breaker - which it tripped a couple of times (over 6 months or so) so we moved it to another - which turns out to be on a 32A circuit - yesterday it tripped that

 

so the question is - how much should it take as a max and should I be looking for a faulty power strip or am I expecting too much from a 32A circuit??

 

TIA

 

Mike

[Blue_Cookeh]

I'd say there's a problem with your trolley somewhere, you shouldn't need a 32A circuit for that. Does your trolley turn on plugs in steps? Our's enables each strip with a 5 second delay between them to stop trips. Edited January 4, 2017 by Blue_Cookeh

[mikeprice]

I'd say there's a problem with your trolley somewhere, you shouldn't need a 32A circuit for that. Does your trolley turn on plugs in steps? Our's enables each strip with a 5 second delay between them to stop trips.

 

No - that is my worry - it seems like a very basic trolley (it was here when I started so I wasn't involved in the purchase) which just has 2 10 way power strips down each side

I can't see anything that suggests there is any intelligence or control mechanisms involved

 

and I do not know what make/model it is to check - there is no label/sticker or clue of any kind!

 

Thanks

 

Mike

[localzuk]

Take a photo and post it on here, we may be able to identify it.

[mikeprice]

Good idea - this is what it looks like

 

[Mistert89]

I'd be inclined to think your circuit breaker is over sensitive. Your trolley probably has a 13A plug as standard, so if its fuse doesn't blow (it won't), then you are drawing less than 13A.

Rule of thumb, assume surge is 2x running power, but at 65W each, that's still minimal.

Is there anything else on the same 32A circuit?

Can you plug this in elsewhere in the building - i.e. Different mains circuit. That will tell you where the problem lies.

[Gurtlush]

It's a loxit lapbank.

[Mistert89]

Just re-read that you have moved it.

Check for any loose connections, or faulty socket strips

[steveg]

They do a soft start option for their trolleys, although i'm not sure if you can get one and retro fit it, or if you have to buy it when you buy the trolley.

 

https://loxit.com/shop/laptop-charging-security/laptop-charging-trolleys-15-6/lapbank-laptop-charging-kit-inc-soft-start-surge-for-16-laptops/

 

Have all the power adaptors been individually PAT tested?

 

Steve

[robyholmes]

Have you tried with 1 charger plugged in? Then 2 and so on. Might be one charger causing a spike. Do your chargers have a figure of 8 or clover leaf mains cable?

[IrritableTech]

What is tripping - presumably an MCB? Or is it an RCD in which case it might be an earth leakage issue. They tend to get more sensitive with age - how old is the breaker?

 

What else is on that ring main? If you're plugging in a trolley of laptops which all have low batteries they will demand the most current before tailing off as the cells reach their maximum charge.

 

According to the info you've posted, you've got potentially 14x1.7 amps (23.8a) on a single 13 amp plug? Or have I missed something?

 

MCBs are designed to protect the wiring in the wall and prevent fire. If 14 power supplies connected to 14 laptops with low batteries all fire up at once you're looking at a high draw as the caps fill up and then a sustained current. Typically the wiring on a ring main is rated for 26 amps (I think that's right - I know it's less than 32), but due to the fact it is a ring each socket is normally fed from two bits of cable so the theory is this is safe - unless the ring breaks. A 13 amp fuse will survive a decent over current for a short time, or a small over current for a long time (I've recently tested this).

 

Personally - I'd test it in another area and take from that what I can - but ultimately a professional should be looking at it.

[jaminben]

Typically the wiring on a ring main is rated for 26 amps (I think that's right - I know it's less than 32), but due to the fact it is a ring each socket is normally fed from two bits of cable so the theory is this is safe - unless the ring breaks. A 13 amp fuse will survive a decent over current for a short time, or a small over current for a long time (I've recently tested this).

 

Ring Final Circuits = 32Amps 2.5mm2 copper conductor phase and neutral with 1.5mm2 earth (in general)... you can have as many socket outlets within 100m2 as you like (diversity) but in reality you wouldn't do that.

Edited January 4, 2017 by jaminben

[IrritableTech]

Ring Final Circuits = 32Amps 2.5mm2 copper conductor phase and neutral with 1.5mm2 earth (in general)... you can have as many socket outlets within 100m2 as you like (diversity) but in reality you wouldn't do that.

 

Thanks. According to the quick Google I've just done 2.5mm2 is rated for 27 amps.

[mikeprice]

eerrrr

 

Ok - lots of stuff I don't know

 

however - up to now it has only tripped every few months so trying one charger at a time might take a few years to work it's way through!

 

plan at the moment is to rejig the balance of the chargers so we have 1/2 on each power strip - if it still trips that I will eliminate one strip for a day or two (thus causing chaos working out how to charge the things)

 

and then switching to the other and seeing what that shows

 

I have also manually checked all the cables for splits etc - as the kids keep trapping them in doors and just closing it harder - but no obvious problems

 

Oh - and talking to the caretaker - the chargers etc were NOT PAT tested - which is annoying

 

could really do with a simple power thingy with a circuit breaker too put between a wall socket and a power strip or charger to see what is happening

dunno if I could get one somewhere (for very few £££)

 

anyway - thanks for all the info and advise

the saga will continue tomorrow - will probably involve hoovering out the cabinet as it is mingin

[jaminben]

Thanks. According to the quick Google I've just done 2.5mm2 is rated for 27 amps.

Yep, that's exactly correct (depending on reference method used) which is why it's a 'Ring' and the overcurrent protection will be rated @ 32amps.... they don't make 26amp MCBs. If it was a radial circuit it would have an overcurrent protection device rated @ 20amps for 2.5mm2.

 

Also note that HSE advice for trolleys in schools should be fitted with a 16amp commando socket if used by pupils and not a 3pin 13amp socket.

 

Guidance - Laptop computer charging trolleys safety alert

Edited January 4, 2017 by jaminben

[steveg]

could really do with a simple power thingy with a circuit breaker too put between a wall socket and a power strip or charger to see what is happening

dunno if I could get one somewhere (for very few £££)

 

It wont detect faults or work as a circuit breaker, but this might be useful to at least see how much current it is using? Energenie ENER007 Energy Saving Power Meter Socket | Plugs | Screwfix.com

 

Steve

[Andrew_C]

Much more likely to be the time characteristic of the breaker giving you problems. If you look at the thing, it will say something like B20A. The B indicates how long it waits before tripping. Try to get it downrated (only allowed if you have a good earth) to a C type.

 

The other thing to be sure of; is it an RCBO? (Over current AND earth leakage) If it is, it will have a "Test" button as well as the switch. The leakage currents in those PSUs could easily add up to close to 30mA and that is the current where the breaker must open. Many will open at 20mA. Again, you could downrate this, if everything else is good.

 

I'd guess that if you put a earth leakage breaker in line, they'd both trip simultaneously, and you'd learn nothing.

Edited January 5, 2017 by Andrew_C

[3s-gtech]

According to the info you've posted, you've got potentially 14x1.7 amps (23.8a) on a single 13 amp plug? Or have I missed something?

 

It may be rated at 1.7A, but there's no way each charger can push 400W+. It's more like 0.32A each (taking typical efficiency of each adaptor into account, at max draw from the laptop) so a total of 4.5A on a 13A socket. The issue here will be earth leakage I suspect.

[jaminben]

Unless you are a competent person you shouldn't really be taking any advice from a forum such as this with regards to electrical safety.... call a qualified electrician and ask them to test the circuit and the appliances to diagnose the problem.

 

As others have said it is most likely an earth leakage issue but you don't know what else that circuit supplies do you (is it really only supplying one double socket outlet)?... so it may not even be the laptop trolley that is causing the issue.

 

MCB Types are not time characteristics but breaking capacity's and are to be used to allow start-up of higher current items such as motors to not trip when the item initially starts (start-up surge).... so for instance a 32A Type B 60898 MCB will be rated at 6000KVA.

 

Type B - trips between 3 and 5 time full load current

Type C - trips between 5 and 10 times full load current

Type D - trips between 10 and 20 times full load current

Edited January 5, 2017 by jaminben

[pcstru]

It may be rated at 1.7A, but there's no way each charger can push 400W+. It's more like 0.32A each (taking typical efficiency of each adaptor into account, at max draw from the laptop) so a total of 4.5A on a 13A socket. The issue here will be earth leakage I suspect.

Startup surge for switched mode power supplies can be 4-5 times the rated draw of the optimal operation (for a very short time as caps charge and coils energise). I'd guess the 1.7A figure relates to the ~110 volt end of the acceptable input rather than 240V but 14 chargers energising at the same instant might just push a breaker beyond it's limit, even though the started power draw should be well within the capability of the circuit.

 

But from what is written it could be an earth leak; I'd agree with getting a qualified electrician to diagnose and remedy the problem.

[jmak]

Unless you are a competent person you shouldn't really be taking any advice from a forum such as this with regards to electrical safety.... call a qualified electrician and ask them to test the circuit and the appliances to diagnose the problem.

 

This would seem to be the most important advice to me - although it's always useful to have some idea of what you think might be causing the problem before you get someone in.

 

To clarify my understanding, I presume the actual current draw will be based on what the output of the charger is when charging the laptops, rather than the rating of the input?

 

E.g (from a charger on my desk), the output is 65 Watts from 20V @ 3.25 amps. 65 Watts @ 230V is only 0.28 amps. Obviously there will be slightly more power drawn due to losses in the charger and there will be a surge on start up, but that's an order of magnitude smaller than working on the input voltage/current.

[pcstru]

To clarify my understanding, I presume the actual current draw will be based on what the output of the charger is when charging the laptops, rather than the rating of the input?

 

E.g (from a charger on my desk), the output is 65 Watts from 20V @ 3.25 amps. 65 Watts @ 230V is only 0.28 amps. Obviously there will be slightly more power drawn due to losses in the charger and there will be a surge on start up, but that's an order of magnitude smaller than working on the input voltage/current.

 

Perhaps I'm not parsing the last sentence as you intended. The surge might be half an order of magnitude bigger than the normal draw, your sentence seems to suggest the surge would be an order of magnitude smaller. So you might have each charger which normally draws ~0.3A, but at start-up that might push up to 1.5A (or more) so 14 energising together might pull 21 Amps or more for a short period. That's on the AC side so we have another difference between the input and output numbers - stated inputs are RMS and the draw is a reactive load which is trying to alter the phase and amplitude of the input. Now, what else is in circuit might contribute to how that happens and what that looks like to a breaker. If we pull an AC circuit waveform so it looks like a DC for a short time the current is no longer RMS and you breaker may see that as even more current being drawn. So that 21A AC might look like 30A+ for a very short time.

 

But that is a lot of maybe ... it all depends on the detail of what is actually happening in the circuit at OP's site. It could be an earth leak for all the info we have and the only way to be sure is to measure what is happening which is probably beyond what most of us are legally allowed to do.

[mikeprice]

Thanks to all for the info

 

Looks to me as if I need to get an electrician in to test the circuit (s) that have tripped and all the chargers. Actually I am annoyed that the chargers and trolley were missed out from the PAT testing - but at least I now know to get them to look at it.

 

The main thing is that it doesn't look like I am doing anything stupid and it looks like there is a fault somewhere - which is progress

 

 

thanks again

 

Mike

[Alis_Klar]

We had three Loxit trolleys and they all tripped the power at certain times. Get the softstart unit from Loxit. I dislike the loxit design and replaced mine with more modern and easily accessible trolleys