Increased mains voltage on sunny days - Page 1
Forum section: electronics / general

author: woodchips
author_rank: Frequent Contributor
timestamp: July 26, 2025, 09:09:16 am
content: I am in the UK and couple of weeks back had a series of very hot and sunny days, outside thermometer just over 100F.I have a boring machine that runs from 3 phase, and when I tried to use it the spindle motor overload kept tripping. This has never happened before. It was taking about 20-30 seconds to trip, so not a serious overload, more the longer term thermal overload. The RCD didn't trip.The borer is French, so has a French motor, 380V. In the UK we normally run at 400V, just measured mains and 244V 422V.Couldn't think why the machine was tripping, worked for 20+ years no problems. Never thought to measure the mains voltage, never been a problem, continue to think it isn't a problem.Then an idea, it was very sunny, was the UK solar panel output enough to raise the mains voltage enough for the voltage to rise and get magnetic saturation in the motor, raise the idle running current enough to trip the overload? It was mid-morning to early afternoon, so peak sunshine. The workshop, with the machines, is nice and cool in that weather!It is now normal, 22C, overcast, no sun, mains 244V 422V, motor runs fine.I can't think of any other answer, any comments?

author: tszaboo
author_rank: Super Contributor
timestamp: July 26, 2025, 09:30:04 am
content: Quote from: woodchips on July 26, 2025, 09:09:16 am"We decided to deviate from the standards used by everyone else, and now stuff doesn't work."

author: nctnico
author_rank: Super Contributor
timestamp: July 26, 2025, 10:13:56 am
content: At a higher voltage, the motor will draw more current. You could set the trip point of the MCB a little bit higher. But the motor will run hotter.

author: shapirus
author_rank: Super Contributor
timestamp: July 26, 2025, 10:18:57 am
content: Quote from: tszaboo on July 26, 2025, 09:30:04 amIsn't the 230V/400V standard a universal European thing now, on which everyone has been settling for the last decade or two?The 220V/380V standard is now in the past as far as I know. But of course the old equipment isn't.

author: jfiresto
author_rank: Frequent Contributor
timestamp: July 26, 2025, 10:26:44 am
content: Next time, can you see any wind turbines and are they feathered?

author: brucehoult
author_rank: Super Contributor
timestamp: July 26, 2025, 10:50:55 am
content: Quote from: woodchips on July 26, 2025, 09:09:16 amI can't imagine that would happen on the high voltage grid, but maybe just in your street/suburb if a lot of your neighbours have large solar installations exporting power at that time?

author: brucehoult
author_rank: Super Contributor
timestamp: July 26, 2025, 10:51:59 am
content: Quote from: nctnico on July 26, 2025, 10:13:56 amYes, everyone understands that. The question is "Why is the voltage higher?"

author: nctnico
author_rank: Super Contributor
timestamp: July 26, 2025, 01:46:33 pm
content: Quote from: brucehoult on July 26, 2025, 10:51:59 amThat was not the question. The question is: why does the motor trip and the answer is simple: due to higher voltage. We don't know how much higher exactly. But say it is 440VAC for argument's sake, that is 15% higher than 380VAC. So not a whole lot but if the MCB is adjusted marginally, it could trip. Hence my suggestion to adjust the MCB a little bit and see if that improves things.

author: themadhippy
author_rank: Super Contributor
timestamp: July 26, 2025, 01:53:01 pm
content: sure yer not chasing a red herring and instead of a voltage increase its the increase in ambient tempreture thats the issue

author: brucehoult
author_rank: Super Contributor
timestamp: July 26, 2025, 02:07:29 pm
content: Quote from: nctnico on July 26, 2025, 01:46:33 pmRead again: "it was very sunny, was the UK solar panel output enough to raise the mains voltage enough for the voltage to rise and get magnetic saturation in the motor, raise the idle running current enough to trip the overload?"The assumption, the understanding, is that IF the voltage rises THEN the overload will trip. That is taken as a given.The QUESTION is "was the UK solar panel output enough to raise the mains voltage?"

author: ahbushnell
author_rank: Frequent Contributor
timestamp: July 26, 2025, 03:38:25 pm
content: Get a buck transformer.

author: woodchips
author_rank: Frequent Contributor
timestamp: July 26, 2025, 04:28:55 pm
content: Yes, interesting.The EU voltage is 230V or 400V, -6% +10%, so the UK voltage is well within spec.No wind farms, or solar panels anywhere near here, south Lincolnshire.I had some German transformer PSUs that were rated at 220V, quite old, and when I tested them on my variac power source I found that at 240V the magnetising current had risen from near nothing to over 2A. No use for 240V so all got scrapped.

author: madires
author_rank: Super Contributor
timestamp: July 26, 2025, 04:50:16 pm
content: Devices/machines for 220V were usually designed with a tolerance of +/- 10%. Same for 380V. Mains voltages around 240V (or 420V) should be fine. My guess is that the high ambient temperature plus the higher load current (because of the higher voltage) caused the motor overload (typically a bimetal) to trip.

author: tszaboo
author_rank: Super Contributor
timestamp: July 26, 2025, 05:44:40 pm
content: Quote from: madires on July 26, 2025, 04:50:16 pmActually, it was 220V for most countries a while ago. Up until this year, it was 230V +/-6% which was increased to +10/-6 by people who think changing a standard will retroactively change all the connected equipment.

author: brucehoult
author_rank: Super Contributor
timestamp: July 27, 2025, 12:13:13 am
content: Quote from: woodchips on July 26, 2025, 04:28:55 pmObviously I don't know where in south Lincolnshire you are, but I randomly looked at a place in the middle of south Lincolnshire and very quickly found houses with solar panels. It looks from the immediate surrounds like they're still somewhat rare -- much rarer than here in NZ -- but clearly not illegal or anything. I didn't do a full survey, this is just what I found in 10 seconds.https://maps.app.goo.gl/KCXfb36hmmP2k15T7Depending on the exact panels, the house on the left can generate up to about 5.5 kW of electricity in ideal conditions, and the house on the right 6.5 kW.Average consumption in that region is apparently 8-10 kWh per day (that must assume using gas for space and water heating?) or an average demand of 330W-420W.That's a big mismatch, so in good sunny weather in late morning and early afternoon they're likely to be shoving 90% of their generation out on to the wires that lead to their neighbours houses.In small amounts, that just leads to them feeding their neighbours and the local 240V lines drawing less from the local 11kV (?) transformer than otherwise would be with probably no detectable voltage change.I don't know what happens if the local 240V line goes to negative demand as a whole, or how efficiently that gets fed back into the 11kV lines or whether there is a voltage change as a result.If you say that none of your neighbours have solar panels then of course I believe you, but it was worth asking. I'm pretty sure that "anywhere near here" will indeed exist some solar panels if "near" means a km or two. But, sure, perhaps not on your local wires.

author: radiolistener
author_rank: Super Contributor
timestamp: July 27, 2025, 02:33:20 am
content: besides the ambient heat and overvoltage, a likely cause could be phase imbalance in the three-phase supply line, especially if nearby solar panels are connected to one of these phases. This can create asymmetry between phases, increasing current in the motor windings and causing the thermal overload to trip even without a clear overload.I recommend measuring the phase voltages and currents under load to help clarify the issue.

author: Whales
author_rank: Super Contributor
timestamp: July 27, 2025, 02:55:24 am
content: I am under the impression that induction motors running at low slip will pull less current at higher voltages, not more. That should in turn mean the motor runs cooler? Or am I misunderstanding?

author: johansen
author_rank: Super Contributor
timestamp: July 27, 2025, 03:41:48 am
content: Quote from: Whales on July 27, 2025, 02:55:24 amthe voltage gets higher and the core saturates and its all downhill from there.

author: ejeffrey
author_rank: Super Contributor
timestamp: July 27, 2025, 04:58:09 am
content: I would find it rather unlikely that a 380V three phase motor would be designed so close to the limit that a mere 11% over the rated would cause enough core saturation to lead to over current faults when idle.I think it's probably something else. Maybe caused directly by the ambient heat, or a problem with the motor or tool.

author: MF-jockey
author_rank: Regular Contributor
timestamp: July 27, 2025, 09:16:34 am
content: Quote from: woodchips on July 26, 2025, 09:09:16 amThe motor's nameplate would be helpful. Three-phase motors vary greatly in design and response to higher voltages varies.

author: woofy
author_rank: Frequent Contributor
timestamp: July 27, 2025, 12:40:30 pm
content: Quote from: woodchips on July 26, 2025, 04:28:55 pmHere's a current list:https://data.barbour-abi.com/smart-map/repd/desnz/?type=repd

author: woodchips
author_rank: Frequent Contributor
timestamp: August 05, 2025, 09:56:11 am
content: Not been really sunny for days now, but the machine starts and runs just as it always did, no tripping out after 20-30 seconds.The motor is buried in the headstock, would not like to try and replace it, even reading the nameplate isn't possible, have rating from the manual.We don't have any solar farms anywhere near us, there are many houses with panels, do they all have feed in now? What has changed is that they are doubling the size of the village, building over 300 more houses, each with solar panels so that is the strongest possibility to the theory, need some sun so can measure the voltage. Many houses completed and sold since last summer, if their panels do feed in.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 05, 2025, 10:00:22 am
content: Simply measuring the mains voltage using a cheap multimeter will give you all the answers you are wondering and speculating about in no time.

author: woody
author_rank: Frequent Contributor
timestamp: August 05, 2025, 10:49:46 am
content: Or even better, if you happen to have a 'smart' meter: install Domoticz, home assistant or any of the myriad solutions to monitor the P1 port of your electricity meter. Then you can see voltages over time and season which I found very enlightening.

author: Sorama
author_rank: Frequent Contributor
timestamp: August 05, 2025, 11:14:10 am
content: Quote from: woody on August 05, 2025, 10:49:46 amWe have several P1 meters from Homewizard : 25€ and are pretty perfect.

author: brucehoult
author_rank: Super Contributor
timestamp: August 05, 2025, 11:33:07 am
content: Quote from: woodchips on August 05, 2025, 09:56:11 amCommercial solar farms aren't going to affect anything. They have expensive professional equipment that ties into the high voltage grid. not local lines, feeds all three phases equally, etc etc. You'd never notice a thing.QuoteThere ya go.Octopus, for one in the UK, offer pretty decent export prices -- I see on their web site a fixed 15p/kWh option which is FOUR TIMES what I'd get for export here in NZ. Hell, it's the same as I pay, retail, for off-peak usage.At that price, yes, for sure EVERYONE with any sense will be exporting power in the middle of the day instead of installing a battery to save their generation for later.It's an economically insane export price, to be honest. Makes no sense at all.

author: johansen
author_rank: Super Contributor
timestamp: August 05, 2025, 05:16:01 pm
content: Quote from: brucehoult on August 05, 2025, 11:33:07 amwell, someone made those rules, and it made sense to them.

author: themadhippy
author_rank: Super Contributor
timestamp: August 05, 2025, 05:41:05 pm
content: Quoteyea but there still doubling there money when they flog it on to a consumer,bet they aint getting that sorta profit on the stuff there buying from generation companys

author: brucehoult
author_rank: Super Contributor
timestamp: August 06, 2025, 12:28:32 am
content: Quote from: themadhippy on August 05, 2025, 05:41:05 pmThey're getting FAR more profit on power from the generation companies.Here in NZ they currently pay 8c (GBP 0.035) for domestic exports, but the normal price for wholesale electricity at a local substation is around 3c (GBP 0.013). They sell electricity to us at 32c off peak and 64c peak. plus $1.15/day fixed charge (this just went up from $0.70 this week).The only way they make more money from domestic exports is if another house on your local 11kV to 240V transformer uses your exported power. MAYBE it can feed back into the local 11kV distribution. But if everyone in an area is exporting at a given instant I think it's probably a disaster for them.

author: johansen
author_rank: Super Contributor
timestamp: August 06, 2025, 02:07:49 am
content: Quote from: brucehoult on August 06, 2025, 12:28:32 amnot everyone has solar, so even if all the local demand is offset by those with solar, buying power from you at 8 and selling it to a neighbor at 64 is a pretty solid win.the power back feeds everyone on the same grid network, the only place it can't get through without "being allowed to" is the bidirectional dc-dc links that join two different frequencies together.

author: kite31
author_rank: Regular Contributor
timestamp: August 06, 2025, 04:35:03 am
content: Regarding the voltage variations, earlier this Winter we noticed on the UPS display, observed also in performance of some appliances, that voltage was varying anywhere from 203 to 257 against the nominal 230V. The energy distributor took out a day to replace the local transformer with "a better one", which took them about 15 hours against a promise of 10, partly because their excavator broke down. Where I live that meant about 14 °C all day and evening. At least our house is well insulated so remained well above ambient.Since the change it has been rock solid. It is not only available solar but how well the microgrid manages it.

author: Sideways
author_rank: Contributor
timestamp: September 09, 2025, 07:37:25 pm
content: Solar PV generation could easily drive the local grid voltage to maximum. In my neighbourhood this effectively stops me exporting power even though I have a G99 license to export 9kW.I log voltages upto and even above 253V regularly. The advice to meter it is sound. But use something decent, not cheap rubbish.

author: johansen
author_rank: Super Contributor
timestamp: September 09, 2025, 07:54:58 pm
content: Quote from: Sideways on September 09, 2025, 07:37:25 pmCan you run a buck boost transformer to fool your inverters into dumping power even when the gris is over 253?

author: Sideways
author_rank: Contributor
timestamp: September 09, 2025, 09:46:04 pm
content: It's not allowed.One cure for high grid voltage is to have an autotransformer fitted directly after the meter to drop your voltage, but if you have solar, the solar must be connected grid side of the autotransformer so you can't boost the voltage and push back into the grid at a higher level than the 230V+10% max.Interestingly one of the substations at the lower end of the HV system must be autotapping at around 1am in the morning to maintain network voltage when people's EV car chargers turn on for their overnight charge.I've noticed a regular spike above 254V at that time of morning which we can't blame on the sunshine :-)

author: Sideways
author_rank: Contributor
timestamp: September 09, 2025, 09:54:16 pm
content: The graphs and stats are from a 6 hour logging session and show a peak voltage of 256 and significant number of excursions above the allowed max.The operator is allowed to go above 253 but only for transients lasting upto, I think, 20mS.This is clearly out of spec.

author: Marco
author_rank: Super Contributor
timestamp: September 09, 2025, 10:12:23 pm
content: Maybe a bunch of friendly neighbours who use transformers on their inverters so they don't cut out on your block? (Why hasn't that been banned that yet???)

author: ejeffrey
author_rank: Super Contributor
timestamp: September 10, 2025, 07:03:55 pm
content: Quote from: Marco on September 09, 2025, 10:12:23 pmThat's literally always been illegal everywhere. I'm not saying people don't do it anyway, but your premise they the practice hasn't been banned is incorrect.

author: Marco
author_rank: Super Contributor
timestamp: September 11, 2025, 11:38:37 am
content: https://www.google.com/search?q=voltage%20optimiser%20site%3AukWink wink, nudge nudge (though on the first page, they are already being advertised for preventing cut off, it's not that subtle).As far as I know, smart meters don't simply recognize feedin during high grid voltages to get you fined, which they easily could do. That's what I would do for a real ban.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 11, 2025, 05:05:25 pm
content: Quote from: Marco on September 11, 2025, 11:38:37 amThese voltage-lowering "energy saving" con devices have existed for a very long time - I remember them from early 1990's. They are not illegal for consumption, but sure enough the installation of solar inverter behind one is illegal exactly because it fakes the voltage sensing of the inverter.I don't think such crap is common at all. Some idiot may have fallen into the "energy saving" scam, and another idiot use one purposely to avoid cutting production during high line voltage - but I'm pretty sure this is 0.001% of households.

author: ejeffrey
author_rank: Super Contributor
timestamp: September 11, 2025, 08:14:58 pm
content: QuoteAnd if it did somehow become common enough to be noticible the utility companies would definitely do something to stop it. That would probably be simply disconnecting customers who used such devices for having unauthorized grid-tie equipment.

author: Marco
author_rank: Super Contributor
timestamp: September 12, 2025, 07:32:16 am
content: Something the algorithm blew my way once, an installer with a youtube sidegig putting the PV behind an optimizer after customer complaint. If this is common knowledge among installers and a quick fix to get rid of complaints, I doubt it's that rare.Then there is this gem from eca.co.ukhttps://www.eca.co.uk/CMSPages/GetFile.aspx?guid=70c8067c-b22d-47ab-b973-550f6191eb51QuoteOptimizers seem to be a large homegrown industry in the UK doing exactly what they are not supposed to do with PV and everyone just looking away, because otherwise it would kill the industry at this point.

author: brucehoult
author_rank: Super Contributor
timestamp: September 12, 2025, 08:15:05 am
content: Quote from: Marco on September 12, 2025, 07:32:16 amNo one installing solar at this point should include exporting power in their calculations. Too many people are doing it already in many countries and everyone has excess at the same time and the price earned is rapidly going to zero or negative. It's not a viable way to "transfer" your production from one time of day to another. For that, get a battery. It's certainly not viable any more to oversize your system compared to your own needs, just because you have a big roof and a persuasive installer with $$$ in their eyes, and think you'll have a nice little earner.Some places are starting to do Time of Day on exports, and paying more at peak morning and evening times. But it's not many yet and, again, you'll need a battery for that.Batteries are getting cheaper, and longer life, but they're still not cheap.I don't know how it's going elsewhere, but here in New Zealand -- where there are no government distortions in the solar or wind markets -- electricity gentailers are now building huge battery farms first and using them for peak-shaving, and only then building a solar farm next to it. One recently went in near me with 200MWh / 100MW of batteries, already commissioned, and in a few months they're starting work on a 130MW solar farm next to it.There are suggestions now to put east- and west-facing panels of the same size, each, as you would have put facing the equator. You'll generate only slightly more electricity over the year, from twice as many panels, but it'll be better-aligned to morning and evening usage. And panels are now the lowest cost part of a system.That's still not going to help in winter if you're having breakfast and dinner in the dark, but it probably does for half the year.In the summer months you can get significant morning and evening power from panels facing towards the pole (i.e. north in the northern hemisphere), the more so the higher your latitude. It would be pretty minimal here at 35.5º S, but if you're at 45º or 50º or more it's worth looking at. i.e. probably anywhere in Canada, the UK, Netherlands, Scandinavia, the Baltics, maybe even Germany and Poland. And in the winter if it's overcast then the more area the better, it doesn't matter so much which direction it's pointing.Gone are the days when it was worth spending money on a tracker to point your expensive panels at the sun throughout the day to get 30% more power from them. Now a tracker costs 5x what the panels do.

author: woodchips
author_rank: Frequent Contributor
timestamp: September 12, 2025, 08:39:19 am
content: Thanks to all for the postings.It seems that the solar panels are useful, if you can afford them. Know someone whi is just installing a ssmall E and W array on a house so trying to be able to tap into the voltage produced. They are not keen at the moment to let me fiddle with it! But, provided there is a diode between panels and controller then what is the harm in monitoring the pre-diode voltage. Have to see.After posting this query, not had any hot and sunny days, just ordinary ones, so when checking the maims voltage it has always been around 247V and the machine has run as normal. Have to wait until next year now.Also did some hunting for solar panels, found ones for £50 each, 400W peak, seemed a good deal but when went back for another look they had disappeared, others were more like £150 each, not so good. I just wanted panels, fit them myself, just feed them into a bank of lead acid batteries I have. Provided maximum charge is less than about 0.05C then the batteries will stand that as an overcharge. In the end it all seems so much expense and hassle for not very much. Annually all our electricity is in cheap rate, 15MW of 17MW, and the rate of £0.065 kWh is cheaper than any means of generating it. The day rate of £0.36 is more than a diesel generator of course. The postings about the idle current taken by the controller/inverter adds more losses to the system, with 18 hour dark days this few % really adds up.

author: tszaboo
author_rank: Super Contributor
timestamp: September 12, 2025, 09:05:28 am
content: Quote from: woodchips on September 12, 2025, 08:39:19 amNot a good argument. You can take out a loan, often times close to 0% interest rate to install panels.Quote from: woodchips on September 12, 2025, 08:39:19 amI really suggest just buying a complete system. Unless you are an expert on solar panels, grid connection, battery charging. You will just make something that's not optimal, or something that sets your house on fire.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 12, 2025, 09:48:49 am
content: Quote from: Marco on September 12, 2025, 07:32:16 amOh,optimizersare very popular and well known. Just that in the context of PV it means a totally different thing. With reusing the same term for a random illegal bullcrap scam, there is a serious risk of miscommunication - and misinterpretation of the commonness, because you can't really google the thing, or even discuss about it without carefully defining whatyoumean with an "optimizer".

author: brucehoult
author_rank: Super Contributor
timestamp: September 12, 2025, 10:20:31 am
content: Quote from: woodchips on September 12, 2025, 08:39:19 am10 days ago I bought six JAM54D40 440W panels for £49 (NZ$112) plus tax. The vendor mostly has LONGI panels at £73 plus tax. They say they're going out of the JA Solar because the LONGi panels (Hi-MO LR5-54HTB) are better on rainy and overcast days. I dunno, they'd have to be a lot better (or you don't have much space) for the price difference. The specs don't look much different, plus the JA Solar are bifacial, which apparently can make quite a difference for ground mounted panels, especially at steeper (winter) angles when light is coming from the overcast in all directions.I've had just about all conditions in the last week, except clear blue sky. I'm just using 3 panels at the moment, in series, theoretically 1320W but my MPPT is 1200W. When there's a gap in the clouds in the middle of the day I'm seeing up to 1194W and a lot of 1000+, dropping to 400W-600W when a fluffy cumulous gets in the way for a couple of minutes. Best "sunny spring day" so far with our 60%-70% cloud cover and 11h30m day (35.5º S) is 4kWh with 3 panels propped up to 12º-15º on a chair and a couple of recycling bins. 35º would be more appropriate this early in spring. In complete overcast, including quite heavy rain, but somewhere near the middle of the day, I'm seeing 100W. Once I get all six panels out that will be 200W min, which is more than enough to run my always-on loads (computers, Starlink, fridge). The 6kWh battery can run that stuff for 30-36 hours.This week I've been having 14-15 in the afternoon and as low as 6 at night and need to run heating. From this weekend the forecast is increasingly 18 in the daytime and 12 at night, and more sun less rain, and I'm not going to need heating. At that point, with all six panels out, even if flat on the ground for now, I think I'll be very very close to off-grid other than topping up the battery and doing clothes and dish washing and water heating in the "free hour of power". i.e. basically the £0.44/day (plus tax) daily charge. Maybe I'll need just a little night-rate power before 7 AM. Let's see. That will last until I start to need aircon in mid to late November.QuoteThat's really an incredibly low rate. Not many panels, or a LOT of batteries.If that's your maximum rate -- and you're not limiting it artificially in the middle of the day -- then you can't expect to charge the batteries more the 15% to 25% in a day.How much battery do you have?Batteries are expensive, but if you already have those, then an MPPT controller isn't expensive and will let you use a lot more panels.QuoteThat's really a very cheap night rate, just under half what I'm paying at night.15-17 MWh/year? Low 40s kWh/day? And you have enough battery to charge at night and then last all day? Wow.Maybe think of solar panels as not so much charging the battery, but more as letting the battery discharge at a lower rate, or zero, during the day, thus reducing the amount of charging needed the next night?But yeah solar panels probably aren't going to beat £0.065/kWh. Maybe very slightly. The main advantage would be saving a round-trip through the battery.

author: Someone
author_rank: Super Contributor
timestamp: September 12, 2025, 10:52:17 am
content: Quote from: brucehoult on September 12, 2025, 10:20:31 amThats at the high end of current (todays) LCOE for Australia:https://www.csiro.au/-/media/Energy/GenCost/GenCost-2024-25-Final_20250728.pdfSolar is really cheap, and great value if you already have batteries or dispatchable generation.

author: brucehoult
author_rank: Super Contributor
timestamp: September 12, 2025, 11:34:48 am
content: Quote from: Someone on September 12, 2025, 10:52:17 amThat's industrial scale, not domestic where you don't have access to bulk pricing or large efficient inverters etc, and just generally the one-off overheads of everything is so much larger as a percentage, especially if you pay someone to design or install something for you.

author: Someone
author_rank: Super Contributor
timestamp: September 12, 2025, 11:43:24 am
content: Quote from: brucehoult on September 12, 2025, 11:34:48 amThose costings include domestic rooftop PV as a specific line item. Surprisingly close to grid scale installs in costings (land rent, last mile connection, etc etc).