all 33 comments

[–]NanpaGrandpa 64 points65 points  (6 children)

Is your neighbor plugging their crypto mining rig into your balcony plug at 3am every day?

[–]KenYN関東・東京都 36 points37 points  (5 children)

Or even if you leave your PC on, a virus is mining as you sleep.

[–]bloggie2 20 points21 points  (4 children)

That's very considerate of them to only mine during the night hours when electricity is cheap, must be a polite Japanese virus.

[–]Modifiedfinal 9 points10 points  (0 children)

Or maybe they only mine when you are least likely to notice your fans going apeshit and your pc slowing down.

[–]hanapyon 0 points1 point  (2 children)

Is there different rates for electricity depending on the time of day?

[–]bloggie2 0 points1 point  (1 child)

Yeah, absolutely - random google search for tepco rates - https://www.tepco.co.jp/ep/private/plan/yorutoku/index-j.html

[–]hanapyon 0 points1 point  (0 children)

Oh I see! I'm not sure if I have such a plan or even use tepco. Thanks for the info

[–]HBJ10 16 points17 points  (2 children)

Water heating could explain it. But I’m not sure why the main heater would show up on your personal electricity usage. I live in a house, and we have our hot water tank programmed to refill early morning as it is indeed the cheapest time.

[–]bertsbrows[S] 3 points4 points  (1 child)

I wonder if I'm being charged 1/10 of the water heating costs for the building as there are 10 units in the building...

[–]HBJ10 1 point2 points  (0 children)

Do you have your own electricity meter?

[–]crowkeep関東・茨城県 11 points12 points  (4 children)

I have an ecoCute water heater attached to the house and a solar storage battery for the roof panels.

It's common practice to heat the water and charge the battery when Tepco rates are at their lowest, which is typically during the early hours of the day.

In my case that's between 1am and 3am for the battery system and 5am and 6am for the water heater.

For instance, you can see the early morning spike here, where the battery is recharging, specifically. The subsequent ecoCute usage spike is a little obscured by the popover:


[–]kanben 2 points3 points  (1 child)

What system is that you have there? The one that output that graph

[–]crowkeep関東・茨城県 3 points4 points  (0 children)

It's a part of the service that's provided with the home solar battery system that I had installed:


Here's a shot of the full UI:


[–]quiquejp関東・埼玉県 0 points1 point  (1 child)

Are you sure you only need 1 hour for your EcoCute unit? What's the capacity of your unit? I think it should be 3 or 4 hours average.

[–]crowkeep関東・茨城県 2 points3 points  (0 children)

Offhand, I believe it's the 470 liter type. I'd have to check.

But no, it's never taken three to four hours to heat...

Certainly not in warmer weather conditions.

Again, I'd have to dig it out. None of the documentation is close to hand.

A manual 湯増し, will take about an hour to fill.

[–]HeartInOsaka 11 points12 points  (3 children)

You could do a test. Flip one breaker off per night and see what area of the house is the one affecting it. That might help narrowing it down, at least.

[–]HP_123 10 points11 points  (2 children)

Just be careful not to leave your kitchen without electricity (because refrigerator)

[–]JanneJM沖縄・沖縄県 4 points5 points  (0 children)

It will probably be fine if turned off for ~3-4 hours (set an alarm to wake you up at 4am to turn it on again). Just make sure it's decently full and both the fridge and freezer should make it through.

With that said, I would perhaps try using a pluggable meter to isolate what is causing this instead.

[–]HeartInOsaka 1 point2 points  (0 children)

Oh right, lol. Good point. Well, if you've tried every other breaker and get the same results, you can see it's the kitchen at least.

[–]Apophis2036nihon 8 points9 points  (2 children)

You can run a test by unplugging or turning off the water heater at night to see if it is the source of the electric surge.

[–]bertsbrows[S] 0 points1 point  (1 child)

Unfortunately, I don't have access to the water heater as it is managed by the building's management.

[–]SweetBeanBread 1 point2 points  (0 children)

isn’t there a monitor near/inside your bathroom or kitchen that allows you to adjust the water temperature? it’s technically possible to turn heating off with that so you don’t waste money when you go on a vacation.

the problem is, most machines aren’t as simple as switching it on and off. you need to set the the number of date you will be away and stuff. pretty complex doing it the first time…

[–]SweetBeanBread 5 points6 points  (3 children)

is your house all electric (no gas)? something like エコキュート

[–]bertsbrows[S] 2 points3 points  (2 children)

I live in a 10 unit mansion. No gas, all electric. I don't know if エコキュート is used.

[–]SweetBeanBread 3 points4 points  (1 child)

then I think its your water heating system charging the batteries. try checking outside your entrance. probably there’s a metallic door on the wall right next to your entrance and inside it there will be the systems for heating, etc. It should be independent per room.

japan traditionally didn’t have central heating like in the west and things were done separately. rooms were heated with air-con or gas based heater, floor was heated with electric carpet, and water was heated with gas (importantly, on demand basis).

when all-electric started (due to ecology, cheaper running cost, etc) heating water was an issue because electricity can’t heat water as quickly as gas and couldn’t supply hot water on demand. the solution was to keep preheated water in a tank. the makers noticed that if the machines need to keep water heated all day it would be cheaper for the users if they added a battery and charged it during the night when electricity is cheaper.

i think thats what’s happening.

all-electric private houses tend to have larger system that integrates solar charging and night time charging for the whole house (not just heating water) and has a much larger battery (like u/crowkeep ‘s i think), but since you live in an apartment I think that won’t be the case.

[–]quiquejp関東・埼玉県 -1 points0 points  (0 children)

your water heating system charging the batteries


[–]blosphere関東・神奈川県 4 points5 points  (4 children)

TEPCO cheap nighttime rate for all-electric homes is from 1AM to 6AM, mine is currently 13JPY/kWh. 1AM comes and I indeed start the dishwasher (200v) and clothes washing machine (heating type). EcoCute (200v) indeed kicks in around 2-2:30.

That kicks it to about 4kW usage. Once I had oven cleaning at the same time and AC (both 200v) and I was pulling over 8kW from the grid :D

Anyway, not many appliances can suddenly pull multiple kW's from the grid, it's most likely your EcoCute.

[–]kyoka135 1 point2 points  (1 child)

Got me curious, why do you use a 200v dishwasher? Did you bring it from overseas?

[–]blosphere関東・神奈川県 1 point2 points  (0 children)

It's AEG Japan full-size dishwasher and it wants 200v. I built a house so this was the perfect time to get the proper appliances too (and get proper electricity wired up at the same time).

My IH stove and the Oven are also from AEG Japan. Both are 200v, IH is 30A max load though, instead of 20 for the others.

Nevertheless the sparky pulled thick enough wire for 30A to all locations specced for 200v service.

[–]bertsbrows[S] 0 points1 point  (1 child)

Thanks for the detailed info! Just checked, my nighttime rate with TEPCO is 17JPY/kWh. Is it different depending on locatioin?

I live in a mansion with 10 units. I'm guessing I'm being charged 1/10 of the usage for heating water for the entire building. Does that make sense?

[–]blosphere関東・神奈川県 0 points1 point  (0 children)

I live in Kanagawa and actually switched from TEPCO to htb energy recently, so there might be a diff there.

[–]quiquejp関東・埼玉県 0 points1 point  (0 children)

You might have an ecocute unit instead of a gas heater. Electricity is cheaper from 1:00am to 6:00am ... only if you changed your billing plan to the Smartlife plan.

[–]sytyue中部・長野県 0 points1 point  (0 children)

It's probably the buildings ecocute. My house uses the ecocute system as well. I have the water level set pretty low since I only need enough for two people but it takes about 3 hours to heat up. We have it set for the morning hours as well since it's the cheapest. Once winter comes, it will take up even more electricity and maybe for a longer period of time depending on the temp of where you live.