A coat of paint for the “Power Tank”

Fittingly the paint colour is Valspar “Thunderbolt” left over from painting the front door at home. Still waiting on some more industrial looking socket outlets to replace the chrome ones.

I’ve been warned that after going to Powerpole connectors for 12V DC distribution, I’ll never want to touch a cigarette lighter plug again. That sounds about right.

Off-grid power bank

I’ve been renting a 20ft container to use as storage and workshop space, and wanted some electrical power.

The prototype was not very elegant. πŸ˜€ The basic components are a 135W solar panel on the roof, a 12V 100Ah AGM leisure battery, a Victron MPPT charge controller, and a 1kW pure sine wave inverter.

The inverter is a reasonably priced “Mercury” branded unit from TLC Electrical. I believe the Chinese OEM is Ningbo Kosun. I may do a more detailed review in another post.

Lead-acid batteries aren’t great for geek points, but I thought it would be the best technology for the job. I only visit about once or twice per week and rarely drain the battery completely. It can also get very hot in there in summer, so the battery figure of merit I’m interested in is basically calendar life when fully charged at high temperature. Lead-acid offers a lot of that for the money.

The first problem I found is that the Victron’s load output is wimpy. It won’t even run a 12V compressor. However the Victron has a good algorithm for turning off the load when the battery gets low to avoid damaging depth of discharge, and I wanted to make use of that.

So my first addition was a large MOSFET solid-state relay that would allow the Victron load output to control a much heavier load at 12V. I made this myself using 3x IRFP7430 MOSFETs in parallel, driven by a Si8712 isolated driver chip. The MOSFETs are rated at 40V, 195A, 1mOhm Rds(on). Turn-on and off seems to be rather slow. The small package on the right is a flyback diode to avoid a large transient when turning off an inductive load such as a motor. The MOSFETs would probably be ok with this, but it could damage other loads on the 12V bus.

The solid-state relay does not switch the supply to the inverter. This is connected directly to the battery to minimise voltage drop.

I modified the inverter to have a remote on/off switch, which was very easy as the internal on/off switch just connects 12V from the positive input terminal to the control circuitry. I simply hacked it so the control circuitry got its 12V feed from the Victron’s load output via a front panel toggle switch. This allows the Victron’s low battery algorithm to turn off the inverter alongside the other loads, and allows me to bury the inverter inside the enclosure with no access worries…

Note that I couldn’t find the official remote control panel for the “Mercury” inverter. I bought what I thought was the correct one on eBay, and on plugging it in, there was smoke… Luckily it all came from the remote and the inverter still appeared to be in good shape.

I also got this 500 amp battery monitor in Renogy’s Black Friday sale. 500A is overkill but it was cheaper than the lower current versions. The accuracy at low currents turned out to be fine.

I wanted a visual indication that the inverter was on, and also some geeky statistics relating to the AC output. This power meter module from Amazon did the trick with its cheery blue backlight. It is powered from the AC supply, and this increases the 12V power draw of the inverter by about 1 watt.

A British Army F632 ammo box was procured to fit all the parts in and… they didn’t fit. To gain some extra space, I added a wooden frame to the front made from CLS studs. I am quite proud of the Stratocaster jack cups as PV input connectors.

I provided 3 DC outputs: two Powerpole connectors protected by 32A circuit breakers and a cigarette lighter with a 10A breaker. Household AC circuit breakers do seem to work on 12V DC. I’ve seen them used up to 48V DC.

The inverter feeds two British standard socket outlets via RCBOs (earth leakage trips). In order for these to function the inverter’s neutral is connected to earth. Battery negative is also connected to earth and in use the earth stud is connected to the container. I believe this is the best overall solution from an electrical safety point of view.

The RCBOs do consume some AC power to perform their earth leakage monitoring function, but the amount is tiny, and doesn’t increase the inverter standby consumption noticeably. I tried Axiom and British General brands, and the BG ones had the lowest consumption.

These also have a 6A overcurrent trip function (the O in RCBO) but the inverter’s own current limiting would probably always operate before they tripped.

The inverter was mounted on a plywood divider and some holes punched in the sides of the box to promote airflow. I also removed the AC socket outlet from the inverter, leaving a large square hole for extra airflow, cut out the fan grill from the inverter casing, and reversed the fan. Hopefully these changes will make up for jamming it inside a relatively small compartment.

To be honest I have no idea if reversing the fan helped the inverter’s own cooling. Stock behaviour is to suck hot air out of the enclosure, and the old rule of thumb is that it’s always better to blow in cooling systems, but the inverter seemed like a quite well balanced and optimised design otherwise, so I can’t believe the designers left much on the table with sub-optimal cooling.

Really it was for my own convenience at a system level, the fan is at the 12V input end of the inverter and I wanted the hot air exhaust at the opposite end to the battery terminals, so I could have shortest possible battery wiring and a neat “signal path” from DC to AC without the inverter’s hot air blowing onto the Victron charge controller.

You might notice the lack of fuses on the battery positive terminal. Every connection to the battery is ultimately protected by a fuse or circuit breaker, but not directly at the terminal.

In use, you can see the inputs from the PV panel and the earth wire leading to an earth clamp on the container. (A steel framed building as far as BS7671 is concerned I guess.) The 12V and 240V wiring are not done yet.

The power bank itself could also do with a coat of paint and some more industrial looking unswitched AC outlets. The chrome ones are a bit flashy. Weighing in at 45kg (perhaps Power Tank would be a more appropriate name?) it also needs some serious handles to assist in moving it around…

I love the way the meter backlights come on when the inverter switch is flipped.

Appliances the inverter has run successfully:

  • Toaster, obviously
  • 1kW electric heater
  • 400W “Eco Henry” vacuum cleaner
  • Clarke CDP102 pillar drill
  • Clarke 6″ bench grinder
  • 1200W travel hair dryer (output sags to 220V, hair dryer only produces 1kW)
  • Ikea TILLREDA induction hotplate (only up to 40% power…)
  • A selection of guitar amps (works surprisingly well with no noise issues)

The Carbon Hat

Recently work has seen me fiddling with JSON APIs and Python’s requests module. I was also intrigued by the talk of decarbonisation and the banning of gas-fired heating systems.

The received wisdom when I studied this stuff was that it was better to burn fossil fuels in your home directly, than have a power station burn them for you and use the resulting electricity for heating, but maybe the increasing amount of wind energy on the grid has changed things?

While researching this I came across this fine effort by National Grid, Oxford University, WWF, and Environmental Defense Fund Europe. They are using machine learning to forecast the carbon intensity of electricity for the UK’s regions up to 48 hours in advance. Interestingly, in spite of the UK having a “national grid”, the carbon intensity can be very different for different regions, as power seems to mostly be consumed in the same region it’s generated. It turns out that living near to one of Europe’s largest wind farms and 2 funky vintage nuclear power stations, the electricity supply to Conner Labs is mostly wind and nuclear and can have a very low carbon footprint indeed.

Since Carbon Intensity didn’t offer a handy regional forecast widget, and JSON APIs are almost fun, the obvious course of action was to grab a Raspberry Pi and make something to inform my electricity consumption decisions.

https://github.com/ConnerLabs/carbonhat The source code is here for your edification and entertainment (?)

Carbon Hat surrounded by other experimental IoT junk

I found a Sense HAT in my drawer of IoT junk (some might say it’s more like an entire building than a drawer) so I used the RGB LED matrix on that to display the result. It fades from green at an intensity of 0, through to red at 215g CO2/kWh, which is approximately the carbon footprint of natural gas burnt for heating. All LEDs are programmed to the same colour, and it is covered with a globe from a broken LED light bulb to make it look like a single light source.

Carbon Intensity’s forecasts are updated every half hour, so I pull the 24 hour regional forecast from their API a few minutes after each half hour, and crunch it down to a single number representing the average carbon intensity for the next 3 hours.

1950s Belling electric fire restoration

This winter I discovered that blocking up the fireplace makes the living room much warmer and cuts down the gas bill substantially. All good for the Conner Labs carbon footprint. πŸ™‚ However I guess an open fire has some sort of primeval appeal. Before I knew it I had bought this “vintage retro” piece of junk on Ebay.

I immediately regretted it in case it turned out to be full of asbestos.

It was :/

As it was also caked full of dust, and to be honest smelt a bit suspect, I decided to take it outdoors and wash it down with soap and water. Everything including the wiring, to get the asbestos wet for safe removal.

It was hardly the most complicated assembly so I stripped it down to the last nut and bolt and cleaned everything. The reflector was polished using T-Cut.

Rewiring with bare copper wire in modern high temperature fibreglass sleeving. The switch marked X had somewhat melted contacts. I couldn’t find a replacement so I retensioned them as best I could and used that switch on the lowest powered heating element.

Modern toggle switch doesn’t have 1/10 of the vintage mojo. Doesn’t fit the panel hole anyway.

Red fireglow lamp is arguably the most important part πŸ™‚ 25W filament ones are still available.

About now I realised the error of using WD40 to free off the nuts holding the heating elements in place, as great clouds of WD40 flavoured smoke belched forth. πŸ™‚

Once the fumes had dissipated it turned out to heat the living room better than the old gas fire and cost less to run.

The Darwin Diet

We’ve had the GI Diet, the Atkins Diet, and a hundred others. But what if Charles Darwin wrote a diet book?

Well, ever since “Man… descended from a hairy, tailed quadruped“, until the discovery of fossil fuels, human populations were limited by competition for resources. What that presumably meant was that, just in order to survive, Man had to eat everything and anything he could lay hands on. So there’s the Darwin diet right there. Eat anything you can lay hands on if you want to live.

Unfortunately, it just doesn’t fit well with a post-industrial society where fossil-fuelled machines do all of our manual labour for us, and the market economy brings us a cornucopia of processed foods designed for profit. Yes, people complain about McDonalds, but it’s exactly the foodstuff you’d expect a free market to produce. Looks nice, tastes nice in an addictive, trashy kind of way, cheap to mass-produce, and who cares what it does to your health. McDonalds don’t, because they don’t have to pay for your healthcare.

The amazing thing isn’t that some people are fat, as the media keep telling us. It’s more remarkable that some people are still thin, while they have the chance to consume everything and do nothing, and the evolutionary mandate for it, too.

“An engine that knows what it’s missing”

So after a couple of weeks of commuting, I finally got my first puncture on the Skyline. I wasn’t looking where I was going, ran over a tiny rock the size of a marble, and got a pinch flat. Even blown up to 100psi, those skinny tyres really are wimpy compared to mountain bike tyres. But I guess that’s the price I pay for getting to work in 20 minutes instead of 40.

Fixing a puncture on a commuter bike is much the same as in a car. You pull over to the side of the road and empty all the stuff out of your “trunk”, a big messenger bag full of junk, in order to access the spare inner tube and tools buried right at the bottom. Then you sit the bike upside down on its handlebars and saddle, unscrew the afflicted wheel and lever the tyre off it. You locate the hole in the inner tube, check the corresponding place on the tyre to make sure the sharp thing isn’t still there, put in a new tube, blah, whatever, done it a million times.

As I was doing this, sitting on a kerb under a tree in the rain, with Asian kids yelling and playing football in the street, I wondered if I hadn’t strayed too far from my roots in mountain biking, by buying into the whole “Quest for freeride” thing. Mountain biking is getting fragmented into more and more different disciplines, driven by bike companies, who want to sell you a different bike for each one. And who could blame them? They need to eat too.

But as some guy on some bike blog once said (I forget which) the cyclist is “An engine that knows what it’s missing”. Riding singletrack on the Frankenstinky feels like shooting squirrels with a cannon. When you hit something it’s spectacular, but I really wish it was lighter and easier to aim… I actually miss my old Inbred πŸ™

Then I found something that made me feel a lot better. According to Colleen Smith’s blog, a cyclist can get 300 miles to the gallon… of ice cream! Or 1000mpg if they ate nothing but peanut butter. Even if the ice cream were entirely made from fossil fuels, which Ben & Jerry’s probably is, that’s pretty damn environmentally sound. I need to test this claim some time. Maybe 100 miles and one-third of a gallon of ice cream to start with.

While I was there, I couldn’t help but notice that Colleen Smith is a 6 foot 6 pro beach volleyball player and really hot. Hey Colleen, if you’re reading this, can I get your number? I’m only 6′ 5″ but I could wear platform shoes.

Oh well, back to reality.