Making the most of one 13A mains outlet - Page 1
Forum section: electronics / projects

author: C_Norris
author_rank: Newbie
timestamp: July 11, 2016, 08:19:39 pm
content: Hi all,I'm building a driving simulator with many parts (computers, screens, force feedback wheel, amplifier...) and I want to use just one outlet for it because of reasons.Here in the UK our mains (240V) outlets are rated for max 13A though, and obviously I want to be careful not to exceed that because of safety and laws.I added up the maximum input current of all the components' power supplies and it came to 18A. Obviously the devices using those power supplies won't be using that much power all the time though.So the plan in my head is to obtain a current clamp, then measure the current for each device with it under whatever maximum realistic load is for that device (e.g. run a burn-in program on the PCs, set the screens to 100% brightness etc.). I'm expecting that the results of those tests will be much lower than the maximum input current, and that may result in a realistic maximum current draw for the whole system of comfortably less than 13A.Is that a sensible, safe approach or have I made a daft mistake?Thanks for your help!

author: grumpydoc
author_rank: Super Contributor
timestamp: July 11, 2016, 08:44:30 pm
content: 18A is quite a lot, well over 4kWA breakdown of each device and power ratings would be a good start.Oh, and if you want to draw 13A from a single outlet be warned that you need a good quality plug and distribution board - cheap ones tend to burn out if you actually pull 13A through them (BTDT).

author: Gyro
author_rank: Super Contributor
timestamp: July 11, 2016, 08:47:47 pm
content: Hi,Looking at your list, I suspect that you're not going to be pulling anywhere near 13A (~3kW) or your room is going to get pretty hot!I think if anything you're more likely to suffer from things like noise pickup through the amplifier. Make sure you use a decent quality mains strip with a short mains lead.If you do get a current clamp, you'll need some way of (safely) splitting out the three cores of the mains cable (make a test lead), so that you can put the current clamp just around the brown 'live' wire (or neutral, but not both) you can't just put the clamp around the whole cable.Edit: Snap!

author: mariush
author_rank: Super Contributor
timestamp: July 11, 2016, 08:52:05 pm
content: You need to buy one of these:https://www.amazon.co.uk/s/ref=nb_sb_noss_2?url=search-alias%3Daps&field-keywords=power+meterThey tell you the voltage, instantaneous current , average , min current, max current over some period of time... You can plug one device at a time and leave it running for 30m - 1 h and see how the device behaves.

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: July 12, 2016, 10:48:18 am
content: I'd be really surprised if you actually use that much current. Definitely get a clamp meter and measure it. I'd second what grumpydoc said as well, our 13A sockets aren't really suitable for pulling over 10 ish A for long periods of time, they tend to get hot and burn out.

author: Towger
author_rank: Super Contributor
timestamp: July 12, 2016, 11:05:26 am
content: Mariush's suggestion of a plug/socket power meter is the simplest solution.

author: ConKbot
author_rank: Super Contributor
timestamp: July 12, 2016, 11:41:38 am
content: How many items are 120/240V universal input? The maximum current on the data plate is going to be with either a 100 or a 90VAC input. It will obviously be lower on 220/240V.

author: Fungus
author_rank: Super Contributor
timestamp: July 12, 2016, 11:48:53 am
content: Simple test: Does the plug get hot?

author: StillTrying
author_rank: Super Contributor
timestamp: July 12, 2016, 11:53:23 am
content: I've got one of these plug in power meter things. An average PC might have a 450 Watt power supply, but in practice it runs at about 125 W including a 19" monitor.

author: Ian.M
author_rank: Super Contributor
timestamp: July 12, 2016, 11:57:01 am
content: The big issue is going to be the inrush current surge. It may be necessary to sequence applying power to individual devices or groups of devices to avoid tripping breakers if the socket is fed as a radial or if its on a heavily loaded ring (e.g if portable heating appliances are in use).

author: Kjelt
author_rank: Super Contributor
timestamp: July 12, 2016, 11:57:48 am
content: Chuck Norris? He blows up everything, don't be like him ! If it was april 1 I would not have answered this postFor now, indeed measure the power consumption of each device but also peak power.The devices with the highest peak power might be buffered using a UPS with large battery, but this works only if it is now and then a peak not continuously.Also check that there are no other devices on the same group in your home, eg your mother wants to vacuum while your driving it will blow the fuse.

author: Towger
author_rank: Super Contributor
timestamp: July 12, 2016, 12:06:25 pm
content: Standard UPSs are generally not used for devices with high peak power requirements, they don't handle them well. A decent size laser printer will happily trip a large rack mounted UPS. Of course you can always get larger UPSs, but that defeats the purpose. Chances are it will run from one socket, just a matter of not turning it all on at once. A cheap Socket power meter with min/max function will help calculate the power requirements. Just remember that it may not be fast enough to accurately record the pulse at switch on.

author: Kjelt
author_rank: Super Contributor
timestamp: July 12, 2016, 12:09:46 pm
content: Ok do not use a standard UPS then , use an inverter or whatever but the idea is to convert AC power to DC power and store the energy in DC batteries and capacitors and re-generate mains, as to overcome peak surges in the mains.

author: Berni
author_rank: Super Contributor
timestamp: July 12, 2016, 12:10:03 pm
content: You are not going to draw 13A with that.Getting a gaming PC with all peripherals to even draw 1kW is tough to do. So 6A is plenty of power for all of it.Where the power written on the back is going to be the biggest lie is your amplifier since yes it might be 500W of its a big one but audio is never at 100% loudness all of the time. I had a good example of that when testing a large audio amp in to a resistive dummy load and with actual music the resistors barely got warm, but then i put a max amplitude sine wave trough it and after some time the chain of power resistors was smoking.

author: nctnico
author_rank: Super Contributor
timestamp: July 12, 2016, 12:22:43 pm
content: Quote from: Kjelt on July 12, 2016, 11:57:48 amThis doesn't work at all. A UPS only kicks in when the input mains shuts down and not when excessive current is being drawn!

author: Berni
author_rank: Super Contributor
timestamp: July 12, 2016, 12:53:18 pm
content: Quote from: nctnico on July 12, 2016, 12:22:43 pmIt does if its one of those weird inefficient UPSes that run the inverter constantly from battery power. But i agree its not really a solution for the problem.Besides exceeding the plug rating for short peaks is pretty common. A lot of large motors draw twice or even more the rated amps of a typical socket when you start them up. Also things that have giant torrid transformers do that since at first the transformer saturates and pulls a massive current it its not turned on at zero crossing and all the giant filtering caps are empty and draw a huge current to fill them. Where this becomes a problem is when multiple such devices are wired to the same power switch, so when they turn on simultaneously the peak is so large it blows fuses. This is why turn on sequencing is sometimes found on giant amplifier racks.

author: johnkenyon
author_rank: Regular Contributor
timestamp: July 12, 2016, 04:43:16 pm
content: Quote from: C_Norris on July 11, 2016, 08:19:39 pmA power supply which can accept 100-240v will draw less than half the maximum current at 240v.A better calculation is to add together the wattages of the devices, and make sure it comes to less than 13*240 = 3120W, and even that will be inaccurate, because (for example) it's unlikely that your 400W PC power supply is actually tugging that amount of power out of the wall.

author: C_Norris
author_rank: Newbie
timestamp: July 13, 2016, 10:52:38 am
content: Thanks very much for your help to everyone who replied. I purchasedhttp://www.maplin.co.uk/p/13a-plug-in-energy-saving-monitor-n67fuin the end.I've checked it with a 300W heat gun and it read 297W so I think it should be good enough for my purposes.Quote from: Kjelt on July 12, 2016, 11:57:48 amNo relation sadly!

author: StillTrying
author_rank: Super Contributor
timestamp: July 13, 2016, 12:30:31 pm
content: Quote from: C_Norris on July 13, 2016, 10:52:38 amMine looks like an older squarer version, with Watt resolution of only 1W, but that's enough to detect if something has a filter before its mains switch - the display flicks between 0 - 1W.That link's "Most Helpful Favourable Review"Having purchased a new type of electric heater that was supposed to be much cheaper to run than other types, we wanted to check the electrical usage....I am that pleased I am going to buy another heater tomorrow...

author: Ice-Tea
author_rank: Super Contributor
timestamp: July 15, 2016, 05:58:34 pm
content: Quote from: Ian.M on July 12, 2016, 11:57:01 amLess of a problem then you might think. Worst case, the circuit breaker trip. Reset it and you're good to go. The breaker will trip immediately when you happen to toggle it near peak voltage but it's only a matter of trying a few times and statistics.

author: Monkeh
author_rank: Super Contributor
timestamp: July 15, 2016, 06:26:32 pm
content: Quote from: Ice-Tea on July 15, 2016, 05:58:34 pmYes, constantly having to reset the breaker is no problem. You just have to cross half the house to get to it, and try repeatedly. No problem at all.

author: Ice-Tea
author_rank: Super Contributor
timestamp: July 15, 2016, 06:34:15 pm
content: Inrush current only happend when you plug in a device, in this case a lot of them. Once the breaker is on and everything is plugged in the breaker will not trip. At least not for inrush.

author: Monkeh
author_rank: Super Contributor
timestamp: July 15, 2016, 06:35:12 pm
content: Quote from: Ice-Tea on July 15, 2016, 06:34:15 pmSo, let's just unplug this for the vacuu- oops.

author: kfitch42
author_rank: Frequent Contributor
timestamp: July 15, 2016, 07:12:38 pm
content: Quote from: Ice-Tea on July 15, 2016, 05:58:34 pmI am not an electrician, but my understanding is that most breakers are only rated for a handful (2-10) of faults/trips (but 1000s of 'mechanical' cycles, i.e. flipping the breaker off/on).

author: Berni
author_rank: Super Contributor
timestamp: July 15, 2016, 07:22:24 pm
content: Yeah they are not designed for thousands of cycles, but if it was tripping that often im sure the user would get annoyed quickly.Thing is that a 13A breaker does not trip at 13.001A. It will usually take a good 50% overload to trip it. For short periods like 100s of miliseconds it might take over 200% of overload to actually trip it since the element inside takes a bit of time to warm up from the current. Circuit breakers are not designed to be accurate or fast, there sole job is to protect the house wiring from overheating and starting a fire because of a short circuit or some idiot that plugged 5 electric room heaters in to one power strip.

author: Wilksey
author_rank: Super Contributor
timestamp: July 18, 2016, 11:16:37 am
content: 18A on the AC side?!What in the world are you powering?!Is it a photonicinduction driving simulator?

author: Berni
author_rank: Super Contributor
timestamp: July 18, 2016, 11:29:42 am
content: Quote from: Wilksey on July 18, 2016, 11:16:37 amIf you are doing a driving simulator might as well do it properly. That 20kW light bulb he got is a perfect artificial sun to simulate the hot sweaty environment in a race car.

author: Wilksey
author_rank: Super Contributor
timestamp: July 18, 2016, 09:39:32 pm
content: You need at least 2 for headlights!