Modifying 4builtin TOU timer> from £200 to £70/mo

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Modifying 4builtin TOU timer> from £200 to £70/mo

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EV Charger Hacking Success!
Apr 16 2019  Ryan Walmsley



We’re in the process of switching to our new energy supplier’s (Octopus) EV
Tarrif. Of which the daytime rate of electric is around the same as other
tarrifs at 14p per unit, but for 4 hours a night this reduces down to 5p per
unit. Roughly taking my yearly charging down from £200 to £70.

My car is smart enough to have a timer built in but the issue is, this can
sometimes cost £18 a year to have this feature in my Zoe. But the main issue
is that when charging in public you have to remember to turn it off and then
turn it back on. Compared to some EVs you have to go through a few menus
each time.

Now the charger I brought advertises itself as a “smart” charger with this
being one of the features that smart chargers do. But mine doesn’t yet…

For reference I brought this model of charger as it worked out cheaper with
the extra work I needed than the “dumb” chargers. However I think the dumb
charger would have actually been easier to hack as these use a resistor to
set the maximum charge current and by having a relay connect a lower value
resistor to the module which would effectively disable the controller. Then
connect a different resistor to set the correct amperage.

I did consider a DIY EVSE project however in the UK there’s quite strict
electrical regulations, If I did buy the parts for a DIY unit and the cable
it would have been around £500 in materials. And while I would have been
fine wiring in the cables and routing them to IET standards I would have to
get an electrician to then test and do the final connection to the electric
supply. This would have cost more than the installation as while the
installation was over £1000, the UK Government funded £500 of it of which my
DIY install would not have been allowed the £500 grant.


-High voltage electronics are in play here! This charger specifically should
be treated as if the low voltage circuit is also live!
-Isolate and lock out the RCBO / Isolation switch before touching any

-Throughout testing I did test the +12v Rail in reference to Ground and
Neutral and was showing around 50V difference. So each time I touched the
unit I first isolated it at the RCBO.


As this is the summary I won’t go into much detail of the investigative
work. I was originally hoping a hidden API would be available, or once
opened up I would find some headers that would easily enable what I wanted.

Once I opened it up I just took a lot of high quality photos which can be
seen at . I posted these on
twitter of which I had 2 people message me that the Isolation of the High
and Low Voltage side looked poor and that the low voltage side would
potentially have the ability to shock me.

The UART port of my charger from my initial testing ignored any serial data
and only sent back when charging the real time values of how many KW of
electric was being measured on each phase.

Once I decided the TI MCU inside was a bit more complicated than I wanted to
program I decided to try other leads, I first thought about using the LOCK
header on the unit.

The LOCK header is two pins that can be connected by a key lock as the name
implies. This is so that someone else can’t come along and use your charger
however I was’t worried about this so didn’t get one.

But I thought what if I essentially locked the unit while charging to end
it, and unlock it to start charging.

This worked to end a charge, however when I unlocked the unit the charge did
not resume in my testing so wasn’t suitable.

I then posted on SpeakEV about my postings and within discussion originally
looked at connecting my own MCU between the car and evse’s Control Pilot
Signal. This is a mixture of resistors to tell the charger if the car can
charge or not and a PWM Signal back to tell the car the speed it can charge

But then someone said instead of intercepting the signal as I only wanted to
control the timing to just connect and disconnect the control pilot. Even
easier! Just a simple relay. Throughout discussion someone said the car
might throw errors if the CP is just disconnected mid charging.

The solution to this was to also use the lock feature by locking the charger
first then disconnecting the CP.

It was then time to implement it, I ordered a cheap 5V Dual Relay module off
eBay as this was only low voltage being controlled.

Then the hardest part, what board to use? An arduino was too simple as I
wanted it to have connectivity, after looking through my box of boards
including Raspberry Pi, Onion Omega, Arduinos of lots of varieties and more
I settled on the Particle Photon I have had in its box since backing it on

The great thing is that it can be programmed via a Web IDE but also has
IFTTT integration making it ideal.

Using example code I whipped up a quick piece of code which has a single
function of which if it is sent “on” it’ll turn the charger on and “off”
will turn the charger off. (Code found at

I wired this up to the relay module and then one relay to connect the two
pins of the lock function (In a normally closed configuration as I want the
relay to only be turned on while charging). And the control pilot in a
normally open configuration so when turned on it’ll connect.

I then wired it all up with jumper wires and powered it from the charger’s
12V rail itself. Once again isolating the charger before plugging any
headers in.

And then it was completed! I turned the charger on and tested it without the
cover on to check the LEDs on the relays were acting correct and it seems to
be working fine.

Long term testing is needed but so far it’s working great.

Finally to have it turn on and off with the correct times I use IFTTT with
the day time option.
Time-Of-Use (TOU) Rate Plans

Five Home-Brewed Electric Powertrain Conversions
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