Monthly Archives: July 2018

Ampera – selecting the charge current

My charger control project relies on the electric vehicle tracking the charge current set by the external EVSE / charger to maximise use of the solar panel output.  Most vehicles would readily follow such a signal, but not the Ampera.

The Ampera is designed to default to charging at 6 Amps when using a Mode 2 cable (that is one with a household plug).  Such a cable normally signals 10 Amps to the vehicle (a safety margin inside the UK’s 13 Amp domestic plugs) but the Ampera is designed to draw only 6 Amps by default.

To enable the Ampera to charge at 10 Amps the user has to permit this for every charging event individually.

This screen is reached by selecting Charging | Charge Current. Typically I would push the button in the driver’s door to open the flap over the charge port / vehicle inlet and then select the charge current via the touchscreen before leaving the vehicle.

Current limit from EVSE / AmpsCurrent drawn by vehicle / Amps - 6 Amp settingCurrent drawn by vehicle / Amps - 10 Amp setting

With my Ampera, if the 10 Amp setting is not selected, then the EVSE / charger risks going into an error condition as the Programmable Logic Controller (PLC) expects the control signal from the ImmerSUN to turn off after a few minutes as rising vehicle current should cause the ImmerSUN relay output to cycle on and off around the available current limit. If the 10 Amp setting is effectively disabled then one might not reach the point at which the relay cycles within a reasonable time which the PLC will detect as an error.

4 years with the Ampera

I’ve just had the Ampera serviced and MOT’d at the end of it 4th year, so how has the Ampera been going?

The Ampera is a 4 door, 4 seat, plug-in hybrid car. Unusually for its size it has only four seats as its traction battery is T-shaped occupying the central spine of the vehicle (thus no center rear seat) and then across the Vehicle under the rear seat. By default it runs as an electric vehicle for up to 50 miles or so depending on driving style, heater use etc, and then runs as a petrol-electric hybrid once battery charge reaches a minimum level; although the driver can choose ‘hold’ mode which seeks to save electricity for later (thus using petrol now) so you might drive to the city as a petrol-electric hybrid and then drive within the city as electric.

More recent plug-in hybrid vehicles would include Mitsubishi Outlander PHEV, BMW i3 Rex, and Toyota Prius plug-in hybrid. Compared to Outlander, Ampera is a car (not a SUV) with fewer seats but more range. Compared to BMW i3 Rex, Ampera looks more conventional, has fewer electric miles range, more petrol miles range, and a more complex driveline where petrol engine torque can be transmitted to the wheels (rather than conceptually being more of a generator in an electric car). Compared to Prius, Ampera has more electric range power and performance, and a more sophisticated driveline allowing the petrol engine to be detached from the driveline to allow both electric machines to propel the car, or splitting the driveline to create a BMW-like generator feeding an electric car.

Thus Ampera switches between three Powertrain configurations:

  1. Dual motor mode – divorces petrol engine from the driveline allowing both electric machines to propel the car – more sophisticated that Prius providing improved electric-only capability.
  2. Range-extended mode – splits the powertrain into a BMW-like generator set and a single-motor electric driveline – used at lower speeds.
  3. Mechanically-coupled – a motorway speeds the Ampera links the petrol engine to the driveline allowing engine torque to be transmitted to the wheels in a Prius-like manner for better efficiency.

Anyway, this was supposed to be a 4-year update, not a technology summary.

Electric range is always somewhat seasonal (worse in winter, better in summer), and this summer I’m now seeing 50+ miles reported as the range after a full charge which is effectively 2 days of typical weekday use. No evidence of battery degradation there.

It’s been pretty reliable over the 4 years. It’s been attended to once by the AA when the vehicle wouldn’t start enough to drive but was locked in a sort of limbo between on and off. AA diagnosed a steering lock issue which they managed to reset making the vehicle driveable, but Vauxhall recommended replacement of the steering lock. The sound it now makes suggests that an older solenoid-based steering lock has been replaced by a motor-driven one which makes a distinct buzz rather than a click.

I bought the Ampera principally for local use, cross-shopping against full battery electric vehicles (BEV), correctly anticipating that the Ampera had enough electric range for my daily use at a price considerably cheaper than the full BEVs. However we increasingly use it for longer journeys as it’s big enough for our holiday luggage (2 adults plus 1 child) and, even when the battery is exhausted, is our most economical car.

Although now an older design, I’m not conscious of a more capable PHEV (apart from the BMW i3 Rex) so little incentive to upgrade.

However the alloy wheels are now peeling quite badly, so I’m likely to get those refurbished soon.

Mid-year thoughts

Summer is definitely upon us now as we enjoy the glorious summer weather.  Disappointing weather earlier in 2018 has given way to two record months in May and June which yielded the highest monthly outputs for their respective months since the system was installed back in 2015.  Some days we buy no measurable electricity or gas  (given that the electricity meter has a resolution of 1 kWh) depending on what the need to charge the car.  If the car is at home then I can fully charge it from the solar panels, whereas if the car is at away from home during the day then I may need to give it some charge overnight.  When charging overnight I have been tending to charge for the minimum number of hours up to 7:30 AM when I typically leave home on a weekday – that pattern provides for mostly Economy 7 Energy from the grid less whatever comes off the solar panels from the rising sun less whatever might be left in the PowerVault from the previous day as illustrated below:
The green ‘hill’ from around 3:30 to 7:30 AM is created by car charging.  Normally this would be seen as a rectangular block as the car charger effectively runs at a constant 10 Amps (2.3 kW) through the operating period.  However in the illustration the charging event (at least in terms of power drawn from the grid) seems rounded at both the beginning and the end.  At the beginning of the car charging period the mustard ‘Device Power Out’ curve shows the last remaining stored energy from yesterday being drawn from the PowerVault, while at the end of the charging period the ramp down is a result of increasing output from the solar panels reducing the need for power from the grid.  Hence at the moment the car charging ends there’s a sudden switch to charging the PowerVault at full power (the blue line) and some surplus power not used by the PowerVault (the purple line) – suggesting that something around 1 kW is suddenly available.  Although the purple line is described as ‘Grid Power Out’ that’s not strictly true here as much of that surplus is being diverted to make hot water (although this is invisible to the PowerVault).

After that digression, my actual purpose in making this post was to reflect upon relative energy costs and the best use of my solar power to reduce energy cost.

Energy usagePetrolDaytime ElectricityNighttime ElectricityGasSolar Electricity
Battery Storagen/an/a - no economic case to charge battery from grid during dayOptional - need to consider value of saved energy versus cost of 1 cycle of battery cycle-lifen/aSelf-use Priority #1 via PowerVault (daytime electricity -> solar)
Car ChargingManual 3rd backup (typically only used for long journeys when charging en-route becomes impractical) Manual 2nd back-upAutomated 1st backupn/aSelf-use Priority #2 via ImmerSUN (nighttime electricity -> solar)
Water Heatingn/aManual 3rd backup (never used in 3 years)Manual 2nd backup (never used in 3 years)Automated 1st backup for dull daysSelf-use Priority #3 via ImmerSUN (gas to solar)
Space Heatingn/aManual backupManual backupDefaultn/a - a summer solar surplus is a poor match to winter heating demand but could be Priority #4

The table above shows columns of energy sources ordered by reverse energy cost versus the major energy consumers in the house: battery storage, car charging, space heating and water heating. Energy consumers are ranked according to the value of displacing the the alternative energy course if not solar:

  1. Battery storage – I currently only charge the battery storage from solar, although there would be a seasonal economic argument to charge from cheap rate electricity if the differential between day and night rates was higher.
  2. Car charging – I generally charge on cheap night-rate electricity when I don’t have enough solar. In summer I program my car charger via the ImmerSUN’s 7-day timer to deliver sufficient charge for the day ahead, but sufficient headroom to make use of any available solar.
  3. Water heating – water heating is my 3rd priority for solar self-use and is automatically based up by the gas boiler which runs for an hour making hot water in the early evening if the tank isn’t already hot from diverted solar power during the day. The gas thermostat is also set slightly colder than the immersion heater – still very usable for a bath or shower from gas but giving some ability to delay water heating from a dull day to a following sunny day.
  4. Space heating – my space heating is generally gas. It would be possible to run a heater (or heaters) such as storage radiators via the ImmerSUN’s third output, but I consider that the cost of the heater(s) and installation is unlikely to be recouped given the major mismatch between surplus solar generally being in summer and heat demand being in winter.