Laptop/Chromebook Trollies: Power Safety and Electricity Costs

[LeMarchand]

I was always told that trollies should be on a timer so that they charge overnight and are "off" when people are taking machines out/returning them. Is this correct?

 

Also, is it more economical to do the above or will the machines only draw power while the battery is charging?

 

Finally, plugging 2 trollies (4 plugs) into a four gang socket: Safe or not?

[DavR]

1 hour ago, LeMarchand said:

I was always told that trollies should be on a timer so that they charge overnight and are "off" when people are taking machines out/returning them. Is this correct?

 

My understanding is that this is recommendation for older technologies, which would continue to draw power even what batteries were full. It was to prevent overcharging, as well as present some economies. With more intelligent charging these days, devices should stop drawing power when the battery is full. Should, being the operative word. Either way, I leave ours available all day and night, charge on demand, because then things can charge between lessons. No point having the things if a device dies at lunchtime and you can't recharge it.

 

1 hour ago, LeMarchand said:

Finally, plugging 2 trollies (4 plugs) into a four gang socket: Safe or not?

 

EDIT - misread your question, sorry. I was replying about putting two trolleys on one 4-way extension (now deleted). Two trolleys of four plugs total, into one four gang wall socket? That would depend on what else is on that mains circuit, and what the breaker is rated to. Theoretical maximum of the trolleys is 13A x 4 = 52A, but even with trolleys, it's rare they'll be drawing the full 13A. I'd take my chances and plug in all four using the sockets available. If it's too much, the breaker will trip, and you'll know why.

 

Another consideration could be power-on surge, depending on how well designed the trolleys are. When powering on that circuit from the breaker, four high-draw devices could cause a power-on surge and trip the breaker again. To prevent this, a lot of trolleys are designed to power up in stages.

 

[Andrew_C]

DavR has got his current and power mixed up a bit.  1 amp at 12 volts is 12W.  Insignificant at 230V.

 

However, I'd be uncomfortable about the potential for earth leakage (intentional) on one circuit from 4 trollies with chargers in.  Also consider mechanical safety unless the 4 way is fixed to a wall.

[DavR]

19 minutes ago, Andrew_C said:

DavR has got his current and power mixed up a bit.  1 amp at 12 volts is 12W.  Insignificant at 230V.

 

It wouldn't be the first time 😂

 

Looking at the adapters we have for our Chromebooks, they're rated 45W. Even assuming they're running at full power, 45W on 230V should only be 0.2A per charger, so 6A total for a trolley of 30. If you were using 65W chargers, almost 0.3A each, so closer to 9A per trolley.

 

Not a huge amount, but more than I'd trust multiples of on a 13 amp four way extension lead. Hypothetically not a big problem for a fixed mains circuit at 30A or similar. But I defer to @Andrew_C's point on earth leakage, though.

[DrBeaker]

3 hours ago, LeMarchand said:

I was always told that trollies should be on a timer so that they charge overnight and are "off" when people are taking machines out/returning them. Is this correct?

 

We tried all variations of timers on the trolleys. ABSOLUTELY POINTLESS trying to use cheaper overnight electric (at the time) if the little darlings (staff and students) couldn't be bothered to plug them in to charge them, despite all best efforts to try to get them to do so.

 

So in the end we just put it on charge 24/7. So when they DID bother to plug the jack in, it charged it.

 

 

 

Edited November 11, 2025 by DrBeaker

[flipthebit]

If in doubt get a main socket power meter off amazon and test. They're cheap. It'll indicate how much power is being drawn in their charging and charged states.

[Andrew_C]

That won't show what the total earth leakage is through the filters.  Much more likely to be an issue than current.  You could connect a PAT box to the 4 trollies (or individually and add up) to get this value.

[dhicks]

17 hours ago, Andrew_C said:

However, I'd be uncomfortable about the potential for earth leakage (intentional) on one circuit from 4 trollies with chargers in.

 

This is the problem we found in our (older) building - half-a-dozen charging cabinets, in different classrooms but on the same standard 32A ring main, the total power draw should have been fine but the circuit breakers kept tripping. We replaced some individual chargers with multi-port USB chargers (proper 20-port chargers) and that seems to have solved the problem. It does cut down on the amount of cabling needing to be crammed into a charging cabinet, too.

 

In theory, we would like to have timer-controlled plugs so that cabinets are only charging during woring hours when someone is available to keep an eye on them. In practice, we haven't yet found a basic timer plug that is reliable enough. We might have a look at Matter-compatible devices (as now sold by Ikea, but other vendors are available).

[mikes]

On 12/11/2025 at 09:55, dhicks said:

 

This is the problem we found in our (older) building - half-a-dozen charging cabinets, in different classrooms but on the same standard 32A ring main, the total power draw should have been fine but the circuit breakers kept tripping.

 

We have a hybrid school  one half from the 90's  the other half is from 2018. The circuit breakers in our new building keep tripping with the chromebook trolleys, this is on a ring with only a projector and a laptop charger plugged in - it is when they turn on that it trips. I wonder if they leave the trolleys turned on, plug them in, and that is doing it?  Our ones have built in timers but I don't use them - sometimes the chromebooks aren't actually plugged back in so they may need to charge some in the morning for a lesson.  Our site has solar panels as well (only generating a measly 2KW at the moment!) so daytime charging hopefully might be a little offset by that

[DavR]

3 hours ago, mikes said:

 

We have a hybrid school  one half from the 90's  the other half is from 2018. The circuit breakers in our new building keep tripping with the chromebook trolleys, this is on a ring with only a projector and a laptop charger plugged in - it is when they turn on that it trips. I wonder if they leave the trolleys turned on, plug them in, and that is doing it?  Our ones have built in timers but I don't use them - sometimes the chromebooks aren't actually plugged back in so they may need to charge some in the morning for a lesson.  Our site has solar panels as well (only generating a measly 2KW at the moment!) so daytime charging hopefully might be a little offset by that

 

Take advice from your electrician and/or site manager, but, you may be able to resolve this by switching the breaker for that circuit from a Type B to a Type C. The Type C allows for a far greater inrush current, taking account of that initial power-on surge, whilst also still allowing a decent protection for the circuit from shorts etc.

 

I had to get this done when commissioning a new IT suite once. There were isolators for the suite, but, every time you switched those isolators on, the surge of 30 PCs taking initial power tripped the breaker. 

[Andrew_C]

You need to identify WHAT is tripping.  Is it the surge, or a large (but normal) earth leakage as filter capacitors charge up.  You can only fix it when you know what is wroong.

[Chris_Cook]

Personally, I think extension leads in schools should be the last solution, unless its temporary. Unless you have something like a lapsafe where it has fewer bigger power supplies, then you will have some sort of extension inside the trolley.

 

You shouldn't have extension leads daisy chained as you increase the chance the the earth wire isn't connected. They are also more likely to get damaged if they are trailing on the floor or hanging from the socket. They look messy too, and make it harder for cleaners to do their job.

 

Breakers can trip for different reasons, depending what it is. Circuit breakers work on current, RCDs on earth leakage (technically the difference in current on the live and neutral wires). RCBOs can trip for both. All can trip if they are old, or faulty.

 

As Andrew says, you need to identify what causes the trip as repeated tripping can damage the protective device over time. An electrician will also be able to test the breaker to ensure it is tripping at the correct point. An RCD or RCBO could trip as low as 20mA of current, even if it is rated as 30mA. A circuit breaker might trip if it is slightly over current for a long time. They often aren't that accurate, and there is a de-rating curve for current. Same goes for fuses.

 

As for the timer, until last week I wouldn't have been too bothered, but after having a device with a swollen battery, I'm thinking maybe they should only be on charge when the school is occupied. At least then someone can raise the alarm early. I'd also argue for fire doors and storing these trolleys where the damage from a fire is limited - not in a corridor/escape route, and not in a room with critical infrastructure/important paperwork. Schools burn well, and quickly.