Device for reducing power consumption by reducing grid voltage - Page 1
Forum section: electronics / general

author: sanchaz12
author_rank: Regular Contributor
timestamp: August 07, 2021, 08:02:17 pm
content: Just saw this device appear in a local news item. It claims to reduce power consumption by lowering the grid voltage at the in-home fuse box. The first thing that came to mind was that it was just a large power factor correction capacitor but after reading the product page it looks like it uses a transformer. Would this be a viable solution to reduce power usage?Short summary of principle;- Grid voltage has increased over the years, grid operator has lower transport costs.- Devices can work on these voltages but consume more than needed.- Lowering voltage makes devices use less power and last longer.I can see this have an advantage for resistive loads, but does it really matter?For example;- Electric kettle, uses less power but takes longer to boil.- Electric heater, outputs less heat so has to stay on for longer to reach the desired temperature.I don't have a lot of knowledge about how a SMPS would be affected by lowering the voltage but I would think it has even less impact on these loads.Here is the explanation page (through Google Translate from Dutch to English):https://www-pq--eu-com.translate.goog/bespaar-met-lagere-spanning/?_x_tr_sl=nl&_x_tr_tl=en&_x_tr_hl=nl&_x_tr_pto=ajax,elemAnd this is the product page for a 35A secondary current unit:https://www-pq--eu-com.translate.goog/product/kubie-one-35/?_x_tr_sl=nl&_x_tr_tl=en&_x_tr_hl=nl&_x_tr_pto=ajax,elemSo basically, would it be worth it to invest in such a solution or is the cost not justifiable in comparison to the (possible) savings?

author: Kleinstein
author_rank: Super Contributor
timestamp: August 07, 2021, 08:24:12 pm
content: Most modern gear (e.g past 1990 or so) is designed for 230 V (in europe). So a lower voltage would not really help. Some gear may use a little less power, some may use more and some just have lower power. So there would be little savings. A transformer would have extra losses and would need to run 24/7.So don't expect any savings, more like extra consumption or possibly more like a dummy device that does essentially nothing.So this like belongs more to the dodgy technology section.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 07, 2021, 08:56:05 pm
content: Some loads would indeed use less power, probably not by enough to break even on investment. What does save power is reducing both voltage and frequency to motor loads, but that's a lot more complex to do.

author: Alti
author_rank: Frequent Contributor
timestamp: August 07, 2021, 10:52:35 pm
content: Quote from: sanchaz12 on August 07, 2021, 08:02:17 pmWhat kind of home appliances we are talking about here?So this thing drops the input voltage and some appliance delivers same end result (same laundry, same potatoes, same amount of light, same tea) but using less energy? Ok, then this is wrong part of the forum - this belongs toDodgy Technology.

author: themadhippy
author_rank: Super Contributor
timestamp: August 07, 2021, 11:21:29 pm
content: lets half the power so the kettle takes twice as long,but your still using the same amount of kilowatt hours so your still paying the same

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 07, 2021, 11:28:24 pm
content: A few things will use less power (some motors will spin slower, lights dimmer, some idle loads will take less power); most will simply stay on longer (heaters, AC), or draw more current (including most motors and all regulated SMPS).Tim

author: Whales
author_rank: Super Contributor
timestamp: August 08, 2021, 12:02:56 am
content: Technically kettles will require more energy to boil the same water load; as there is more time during the longer get-to-boil period for heat to be leaking out.I'm lead to believe that many induction motors draw more current at lower voltages? This is why you should unplug fridges during brownouts? ie their efficiency goes down.

author: David Hess
author_rank: Super Contributor
timestamp: August 08, 2021, 01:58:27 am
content: Resistive loads like incandescent lamps and heaters will draw less power so take longer to generate the same heating.Switching input loads like most power supplies now are constant power, and will draw more current likely reducing efficiency slightly.A real danger is induction motors operating at their rated load which can either stall during startup or draw enough extra current to overheat damaging them.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 08, 2021, 04:35:04 am
content: To clarify -- strictly speaking, they'll all run slower or equal of course, but induction and synchronous motors will run at a higher slip / displacement angle, thus drawing more current (and in the case of sync, probably a different current phase as well; especially if field is line derived, where the lower field will cause inductive current draw). Some (crappy) induction motors might not care, like shaded-pole or other high slip types. (Ceiling and box fans probably don't add up to much load, hence merely "some".)Universal motors of course draw proportionally less (assuming a linear load of course). Though whether this reduces average power as the utility sees it, is another matter. A slower vacuum cleaner, probably takes longer to use.Or with power tools, they might simply be ran harder, give or take the patience of the user.Or electric kettles, yes indeed.Quote from: David Hess on August 08, 2021, 01:58:27 amYeah, under full brownout conditions (under, what, 90 or 80V?), there might not be enough torque left and it bogs down; single phase motors have much less torque available at high slip (dropping completely to zero at 0 RPM (100% slip), of course), so may be unstable in this region. Which is where the start winding kicks in, when RPM drops below the centrifugal switch threshold. And the start winding isn't made for continuous operation, it'll overheat quickly under load, and magic smoke follows (or, hopefully, a thermal fuse in the winding, and then you're out just a motor, or the repair thereof).Tim

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 08, 2021, 04:59:36 am
content: I read somewhere about adding a large diode in series with the heating element of a clothes dryer to cut power usage in half and while that did slow down drying, it was by nowhere as twice as long so less energy used overall. Although that's not the best example since using a clothesline or drying rack saves even more.

author: Gyro
author_rank: Super Contributor
timestamp: August 08, 2021, 10:40:05 am
content: Quote from: NiHaoMike on August 08, 2021, 04:59:36 amAdding a series diode would cause a large DC current inbalance, which would probably disable the supply RCD (GFCI). Significant DC current offset causes their current transformers saturate, making them 'deaf'.

author: woodchips
author_rank: Frequent Contributor
timestamp: August 08, 2021, 02:41:42 pm
content: The torque of an induction motor is proportional to voltage squared, doesn't sound very sensible.We use a cheap rate electric storage boiler, and it is noticeable that when the volts drop to 220 it fails to fully heat up in the allowed 7 hours. Sounds a silly idea, we pay for 7 hours of 240V AC, not 84% of that.

author: mc172
author_rank: Frequent Contributor
timestamp: August 08, 2021, 03:19:13 pm
content: These kinds of bullshit devices actually exist in the wild and an alarming number of companies that sell high tech products and employ very clever people to design them have (according to the website of the companies that make and promote these dodgy things) got them installed in their premises.

author: sanchaz12
author_rank: Regular Contributor
timestamp: August 09, 2021, 10:02:36 am
content: Thank you to everyone who posted their thoughts, that confirms the suspicion!

author: ejeffrey
author_rank: Super Contributor
timestamp: August 09, 2021, 05:50:28 pm
content: Quote from: NiHaoMike on August 08, 2021, 04:59:36 amYes, reducing heater power in a dryer will actually reduce its energy usage since the tumble motor and fan can dry by themselves and use much less power than a heater. The one caveat to that is that it will exhaust more air. If your dryer is in a conditioned space rather than outdoors or in a detached garage then your AC or furnace may have to work harder to compensate. I'd guess it still won't make up the difference except in extreme circumstances. But if you want to do this you should just set your dryer to a lower heat setting (delicates or air dry only) rather than add a diode that will create a huge DC current draw and also cause problems for the motors.

author: twospoons
author_rank: Frequent Contributor
timestamp: August 10, 2021, 05:38:39 am
content: in some cases lowering the supply voltage will actuallyincreasepower use. Any device that pulls fixed power levels (typically SMPS loads) will pull more current to compensate for the reduced supply voltage. That will result in higher I2R losses in the house wiring, and overall higher power draw than running at higher voltage.

author: Alti
author_rank: Frequent Contributor
timestamp: August 10, 2021, 02:28:44 pm
content: I can see one field of application for this deviceIf you have a registered PV that feeds energy into grid for a subsidized price, you could justify an install of this "device for reducing power consumption" (which is a step down transformer I suspect). Then you connect a regular supply (230/400) from your neighbour and this way, with minimal investment for phase shifter, you could sell arbitrary amounts of "clean, carbon free and subsidized, not very PV kilowatthours" by pushing energy around through neighbour's yard and back through your power meter into the grid. This is going to work by itself without any active components or serious investments because transformers are reversible.Still dodgy.

author: DannyG
author_rank: Newbie
timestamp: August 12, 2021, 01:39:40 pm
content: Any appliances with induction motors (refrigerators, dryers, sump pumps...etc) that are operated at a voltage less than there rated value will draw more current. You will easily burn these motors out and risk a potential fire.

author: Gyro
author_rank: Super Contributor
timestamp: August 12, 2021, 07:11:43 pm
content: Aren't we forgetting about our treasured vintage test gear, with their transformers and linear regulators. They run hotter, marginally rated electrolytics and Tantalum caps get closer to voltage rating etc.We regularly reach 249V here and I've had to rig up a toroidal autotransformer for my audio gear as the heater voltages on my valve amp were getting silly. The transformer supplier wound the mains transformer with a European harmonised 230V primary and then added a few percent on the secondary for heater circuit wiring losses!

author: james_s
author_rank: Super Contributor
timestamp: August 12, 2021, 08:09:24 pm
content: Quote from: Gyro on August 08, 2021, 10:40:05 amIn North America a clothes dryer would never be on a GFCI protected circuit, but I still don't think adding a diode is a good way to save energy. If you want to run the dryer cooler almost all of them have multiple heat settings.Incidentally in the ones I've worked on, this works by controlling power to a resistor or heating element within the cycling thermostat, adding heat inside the thermostat shifts the set point.

author: Gyro
author_rank: Super Contributor
timestamp: August 12, 2021, 08:19:35 pm
content: Quote from: james_s on August 12, 2021, 08:09:24 pmThat's interesting, in Europeeverything(without a site specific justification) has to be RCD protected under current regs.

author: james_s
author_rank: Super Contributor
timestamp: August 12, 2021, 08:29:43 pm
content: Quote from: Gyro on August 12, 2021, 08:19:35 pmFor many years here only receptacles in bathrooms, garages and outdoors had to be GFCI protected. Then in the 90s they changed the code so that kitchen receptacles also need protection. Now it's a bit more strict and I think most basement receptacles need it and anything that is within a certain distance of outside, such as a receptacle near a door where someone might be tempted to plug something in that is set out on a patio. An electric clothes dryer will be on its own 240V 30A circuit, the only time I've ever seen a 240V GFCI circuit is powering a spa, I'm pretty sure swimming pool pumps and heaters and such need them too but I've never known anyone with a pool. The UK practice of having a big GFCI breaker that protects the entire house has never been a thing here. Unlike there, we also have a range of different receptacle types for high powered appliances since the standard 15A 120V variety used throughout homes is woefully inadequate for something like a dryer or cook stove.

author: Gyro
author_rank: Super Contributor
timestamp: August 12, 2021, 09:04:31 pm
content: Yes, single RCD/GFCI consumer units are becoming far less common here. There are/were a too many problems with them. Firstly you loose the whole house on a leakage trip, which is inconvenient and makes fault tracing too hard. A single 30mA RCD is going to struggle with the accumulated general (cooking and washing heating elements) and Y cap leakage of many electronic appliances too. It's also hard to find RCDs rated higher than 63-80A.The most common installation at the moment is probably a dual RCD consumer unit, where circuits are balanced across the two for load sharing, leakage current sharing, and convenience - for instance you would include upstairs lights and downstairs sockets on one and vice versa on the other, ensuring that you always have some means of lighting if an RCD trips.Most modern installations use an RCBO per circuit, providing RCD and MCB capability in one slim breaker. That cures pretty much everything, with easy fault isolation and minimum disruption while keeping leakage current well below the 30mA level on each. It makes for a very compact consumer unit too...https://www.toolstation.com/electrical-supplies-accessories/consumer-units/c937(18th Edition is current, in fact I'm not sure why there are still some 17th Edition amendment 3 stuff listed). -->https://www.screwfix.com/c/electrical-lighting/domestic-consumer-units/cat7230028(more internal pictures).P.S. The ones with a small number ways are generally for garages and outbuildings, where they are fed from an RCBO (or RCD+MCB) in the main consumer unit, or for expansion where the existing consumer unit isn't being changed.

author: james_s
author_rank: Super Contributor
timestamp: August 13, 2021, 01:45:00 am
content: Quote from: Gyro on August 12, 2021, 09:04:31 pmWhen I visited a friend in England some years back we spent a good bit of time looking over the electrical system in his house, I found that a lot more fascinating than the typical tourist stuff and it was interesting to see up close how it was all done. There are some aspects I liked and considered an improvement over what I'm used to but the whole-house GFCI (RCD) breaker is not an idea that I'm crazy about and I was surprised to see it done that way. In fact we tripped it at one point while doing some wiring out in his shed when a neutral wire happened to brush something grounded, whole house lost power and he had to go inside to the kitchen to reset it. As you say, tracking down a fault can be a real nuisance and there is arguably a significant safety risk in having power to the whole house cut, a person fumbling in the dark trying to make their way to the panel to turn it back on could easily result in a non-electrical injury. When I redid a bathroom in my house I deliberately made sure the lights in there were NOT on the GFCI. I decided that a person getting electrocuted trying to change a lightbulb while in the bath was considerably less likely than finding themselves suddenly in complete darkness in a windowless room due to a GFCI trip, whether from a genuine fault condition or defective GFCI.

author: Gyro
author_rank: Super Contributor
timestamp: August 13, 2021, 11:24:20 am
content: Yes, Neutral - Ground shorts can be a pain in the ass. Our house had one for decades (back when we had original fuses). It turned out to be a Neutral conductor that had its insulation pierced by a screw head in the back-box of a fused spur feeding the gas boiler. Ironically it was installed by British Gas, with all appropriate testing. It took me ages to track it down before the RCBO consumer unit could go in. Ihatetradesmen!

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: August 13, 2021, 06:26:54 pm
content: Quote from: NiHaoMike on August 08, 2021, 04:59:36 am"Power Companies Hate This One Weird Energy Saving Trick"

author: james_s
author_rank: Super Contributor
timestamp: August 13, 2021, 07:44:10 pm
content: I suppose you could energize the neutral and see where the smoke comes from

author: Gyro
author_rank: Super Contributor
timestamp: August 13, 2021, 07:54:50 pm
content: There were moments when I considered it! I ended up dragging a 2kW fan heater around, plugging it in and looking for suspiciously low Neutral-Ground (milli-)voltages!Electricians do it by 'splitting the ring' into smaller segments until they find the culprit, but it's a pain when some of the sockets are fairly inaccessible.