Monthly Archives: August 2020

Charger two – updating the hardware

Well, it had to happen. After thirteen-and-a-half years of ownership of a plug-in vehicle we’re about to have two. I have had two briefly before during a vehicle changeover having bought a new one and then sold the old one privately, but now we’re replacing the hybrid that my wife generally drives with a plug-in hybrid. Not only will that give us two plug-in vehicles, but in the six years that I’ve owned the Ampera the standard inlet connector has changed from 5 pins to 7 pins so I can’t charge the new car on my existing smart charger either.

Stepped Mode 3 EVSE in consumer unit case

Most people of course will be content with an off-the-shelf charger, but I had some fairly uniquely requirements. One of the requirements that influenced my original charger was solar self-consumption (the charger automatically turns on when the home is in sufficient solar surplus) but this is now available commercially. My existing charger also adjusts its charge times around the Agile electricity tariff but this too is now available commercially with Ohme. However I still want to be able to coordinate it all centrally via my HEMS so that I can prioritise loads when constrained, or enable interactions like stopping the fixed battery discharging into the car at night and that’s not available commercially.

My solution is similar, but different, to my old charger. Both are modified from existing production chargers as a relatively affordable source of parts, but the new one will retain the production case (because it needs to be waterproof for outdoor use) and be better protected electrically than the old one. It needs to be better protected as electrical standards have moved on and, being outdoors, it needs to be more sophisticated to make up for the UK’s somewhat unusual earthing system (at least by international standards). It will also be smarter, but that will be described in later posts.

The most common earthing system in the UK involves a cable between the home and the substation called a Protective Earth Neutral (PEN) conductor which, as its name implies, provides both the neutral and earth on a single core. Remember PEN as it will come up later..

My new charger will also be higher power than the old one. The old one is designed for 10 Amps continuous grid load (16 Amps peak from solar) based on the limitations of my garage supply, but the new one is designed for 32 Amps continuous load in anticipation of a future fully-electric vehicle. I have owned a fully electric vehicle previously, but for the moment both our vehicles will be plug-in hybrids. Some would argue the case for one being an Extended-Range Electric Vehicle (E-REV) or Range-EXtended Battery Electric Vehicle (REX BEV).

The two internal pictures above show a similar production charger alongside my updated charger. The differences are (from top to bottom):

  • RCBO (combines over-current and residual current detection) – is actually carried over donor, but my charger came with a later model than the similar charger illustrated.
  • Earth terminal – I relocated from centre middle row to right top row to make space.
  • Residual Current Monitor (RCM) – The RCM (a small black box which encircles the live and neutral) sits behind the RCBO and triggers shutdown in the event of a D.C. fault.
  • PEN Loss Current Transformer – between the top and middle rails a small black ring sits around the earth cable. This is similar in principle to the RCM but rather than detect a D.C. fault on the supply, its role is to detect a fault current to earth. That’s not enough alone to provide PEN-loss detection alone but provides additional detection to that in the Protocol Controller (which we’ll get to soon).
  • Power contactor. The second rail starts on the left with a power contactor which disconnects the live and the neutral from the car when not charging. Mine is similar to the Rolec original, but smaller,
  • Switched Protective Earth (SPE) contactor. In the centre of the unit sits a second similar contactor, only this one switches the earth. Switching an earth is unusual but is required to protect against a failure of the PEN conductor between home and substation. The power contactor will not close and the car will not charge if the SPE is open with the result that the car is completely isolated from the mains supply during this failure mode.
  • Protocol controller. To the right of the centre rail is the protocol controller. This replaces the the original protocol controller which was in a similar position. The fundamental need to change was driven by the requirement to vary the charge current dynamically, but the new protocol controller also monitors not only the two current transformers (RCM and PEN-loss) but also the supply voltage in order to decide when to open the SPE contactor.
  • Raspberry Pi. At the bottom is an empty Raspberry Pi case to illustrate the sufficient space is available. The actual Raspberry Pi will be smaller. The role of the Pi is to tell the protocol controller how much current should be drawn. The Pi will tell the protocol controller via an analogue voltage, and the protocol controller will tell the car via a Pulse Width Modulated (PWM) signal – that is the width of a stream of voltage pulse indicates the current that the car should draw. The replaces the Programmable Logic Controller (PLC) and RF Solutions radio link in my older smart charger.
  • LED leads. At the very bottom 4 leads with red connectors leave the picture on the left which go to an external multicolour LED for charger status. I haven’t yet decided how to reproduce this. The donor LED is unsuitable as it only has three colours (Red, Green and Blue) but the protocol controller assumes that two further colours (white and purple) are also available,
ItemMy original smart chargerNew donorMy New smart charger
SwitchDouble pole+ RCBOc/o from donor
PEN-loss CTNoNoNew
Power contactorYesYesYes
SPE contactorNoNoYes
Protocol controllerViridian v1.0
(variable current)
(fixed current)
Viridian v2.0
(variable current with extra safety content)
Smart controllerProgrammable Logic Controller (PLC)NoRaspberry Pi
External communications Radio (RF Solutions)NoWi-Fi (Part of Pi)
Status LEDLED on protocol controller visible through clear cover.External LED.
No LED on protocol controller.
External TBD.
LED on protocol controller (not visible).
Comparison. between my existing smart charger, new donor, and new smart charger.

The new hardware will thus shutdown in the event of the following faults:

  • Over-current
  • Residual current (live – neutral)
  • DC current *
  • Earth leakage current *
  • Over-voltage *
  • Under-voltage *
  • Inferred PEN loss *
  • Lack of earth continuity between vehicle and wallbox

* These are additional protections in my new hardware that weren’t present in the old one.

At this point I should have a working dumb charger with 32 Amp capability, albeit that it’s untested as yet through lack of a compatible vehicle with a Type 2 vehicle inlet.

There are two items for which I’m awaiting delivery. Firstly I’ll be using a Raspberry Pi Zero to generate the current demand signal which will replace the empty black case in the picture and secondly I have a small 5V power supply on order to power that Pi.

Future posts will look at adding the smart controls.

Assault and battery

Like many households we actively embrace recycling, sorting our routine household waste into (i) garden and kitchen waste (i.e. uneaten food), (ii) glass (jars, bottles etc), (iii) other recyclables (paper, card, tins, some plastics) and (iv) non-recyclables. Other sorts of waste can be returned to the recycling centre including (I) electrical and electronic (WEEE), (ii) batteries, (iii) used oil and (iv) wood. This post concerns batteries.

The 3Rs: Reuse, Reduce and Recycle

Like many households with small children we have many batteries in use in toys as well as in items like TV remote controls, burglar alarm sensors, and the doorbell. However we also have dozens in smart home devices like radiator valves and sensors including window, movement and environmental. Of the 3Rs of Reuse, Reduce and Recycle we are clearly far from Reduce.

Recycle is clearly possible with many supermarkets adding bins to collect used alkaline batteries which at least prevents that material going to landfill, but does involve energy and other inputs for recycling.

The alternative that I’ve been exploring for some time is Reuse. The closure of the Maplin chain in early 2018 prompted me to acquire some discount Nickel Metal Hydride (NiMH) batteries in both AA and AAA sizes and a suitable charger from my local store’s clearance sale. These batteries are the same size as the mostly commonly used alkaline batteries but have a slightly lower voltage being 1.2 Volts rather than 1.5 Volts.

Different battery sizes compared

I’ve been running these NiMH cells of AA size in Eve smart home devices for two and a half years gradually replacing alkaline batteries as they became exhausted. My only issue has been that the low battery warnings on the Eve devices are almost always set since the batteries have a lower voltage even when full, even though the batteries have plenty of power to run the device. One thus cannot rely on the low battery warning to flag the need to change the batteries, and so I have adopted a pattern of swapping freshly recharged batteries for part-discharged batteries on a quarterly basis. Over the first weekend of the first quarter I work my way around the house room by room swapping and recharging batteries.

After two and a half years I’ve acquired multiple types of rechargeable NiMH batteries from different brands or of different capacities. I make a habit of charging and using only like cells together.

So far I’ve had no failures of rechargeable batteries.

The latest change is that I managed to locate a rechargeable replacement for the 1/2AA non-rechargeable lithium batteries used in the door/window sensors. These 1/2AA batteries are half the length of a regular AA battery, but are 3.7 Volts rather than the 1.5 Volts of an alkaline cell. The voltage of these rechargeable cells is the same as the standard non-rechargeable equivalents so hopefully the near-continuous low voltage warnings can be avoided.

1/2AA batteries with Lithium-based chemistries are commonly described as being of size 14250 – that is a diameter of approximately 14 mm and a height of 250 1/10ths of a millimetre (I.e. 25 mm).

Next time a door or window sensor battery requires changing I’ll be able to put these to the test.