navitron
 
Renewable Energy and Sustainability Forum
Welcome, Guest. Please login or register.

Login with username, password and session length
News: Anyone wishing to register as a new member on the forum is strongly recommended to use a "proper" email address. Following continuous spam/hack attempts on the forum, "disposable" email addresses like Gmail, Yahoo and Hotmail tend to be viewed with suspicion, and the application rejected if there is any doubt whatsoever
 
Recent Articles: Navitron Partners With Solax to Help Create A More Sustainable Future | Navitron Calls for Increased Carbon Footprint Reduction In Light of Earth Overshoot Day | A plea from The David School - Issue 18
   Home   Help Search Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: Building my own electric car charger to use surplus PV  (Read 992 times)
andrewellis
Full Member
***
Offline Offline

Posts: 134


« on: March 01, 2019, 02:46:40 PM »

Hi, I am looking at building my own type 1 car charger which will modify the demand from the car based on the surplus power from the PV array.  I am looking at using the mainline EPC with an ESP8266(Arduino) modifiying the control signal as per the setup on EVBitz.  I have access to the Modbus signal from the inverter already which includes current export/import.

I have a question that I hope someone with more detailed knowledge of electrical rules might be able to answer.  Currently I have a pod point which comes from a CU in the garage set up as follows by the installers.

 CU (with RCD and fuse) -> Dedicated RCD (installed for pod point) -> approx 10m of wire -> Podpoint

I am planning to have a changeover switch so I have either the pod point or homemade charger active at once but not both.  The reference design seems to have an  RCD, Contactor and Mainpine EPC all housed within a dedicated box.  Can I dispense with the RCD within the box as I already have the RCD for the pod point?  

Thanks
Andy
« Last Edit: March 01, 2019, 02:53:45 PM by andrewellis » Logged

6.48kw Solar PV JA (300W)Panels, SolarEdge inverter
Borehole -> Nibe F1255 12kw GSHP -> Radiators
Nissan Leaf
sunandwindy
Sr. Member
****
Offline Offline

Posts: 415



WWW
« Reply #1 on: March 01, 2019, 03:03:48 PM »

I think there's already an off-the-shelf product that does this, similar to immersun. I think its the zappi.
Logged

andrewellis
Full Member
***
Offline Offline

Posts: 134


« Reply #2 on: March 01, 2019, 03:10:09 PM »

Hi sunandwindy thanks.  I had already seen that and although its nice to have a ready to go product, its £500 which I don't really have.  That home built is looking circa £150 which has also obviously has a much better payback.  I also don't have an easy way to get another CT cable wired in so I'm using my wifi network with a raspberry pi as the control centre.  Its all part of a bigger plan to control various things in the house depending on the PV production to maximise self use.  e.g bathroom towel radiator/GSHP/dump load etc.  The dump load is a bit unfortunate but it is the only way to get over the 3.68kw export limit during periods of low use in order to get the full 5kw going through the inverter for the purposes of metering. I'm trying to work out what I can do as a useful dump load. DHW is out as I have stacks of that.
« Last Edit: March 01, 2019, 03:15:49 PM by andrewellis » Logged

6.48kw Solar PV JA (300W)Panels, SolarEdge inverter
Borehole -> Nibe F1255 12kw GSHP -> Radiators
Nissan Leaf
jonesy
Hero Member
*****
Offline Offline

Posts: 846



« Reply #3 on: March 07, 2019, 11:11:54 PM »

In principle only 1 rcd is needed to provide protection. In practice you install multiple RCDs,  but like over current protection,  you do not install two RCDs of the same trip current in series,  as you can't predict which will trip first. Sods law would mean the upstream one would go first plunging the house into darkness. To avoid this, you either fit a higher trip current device, or a time delay type upstream.
Having read a tiny amount on the protection in the box, I'd say that a RCBO is not adequately. These are single pole devices, and thus will neither detect an over current in the neutral, nor disconnect it. The devices in the shop are not RCBO, but combined rcd/OC devices. The single phase ones do not detect neutral over current (you can see from the symbol there is no squiggly line on the neutral)
Good luck with your project. I'd personally not rely on wifi, or at least use a robust send/check heart beat type system. My ISP has just upgraded my router in an overnight FW update, with no option to revert it. Now 5G doesnt work, and 3 of my wifi devices no longer connect after a power cut. This resulted in my sending the same temperature to Wunderground for 12 hours.
In terms of a dump load, can you regulate your heat pump. You are only looking to dump say 3kW, which would most likely occur around solar noon for a few hours. Could you run that and marginally over heat/cool the house?
Logged

1.1kWp PV & SB1700. 7kW log burner.
andrewellis
Full Member
***
Offline Offline

Posts: 134


« Reply #4 on: March 08, 2019, 11:46:07 AM »

Hi Jonesy, thanks for the info.  I didn't realise there where such differences in the RCD protection.  I've checked the dedicated RCD on the wall serving the podpoint and it is 2 pole as is the one in the consumer unit in the garage. I have a 20 Amp trip switch from the CU with an anticipated max load from the Nissan leaf of 13Amps.  Having read that having the RCD closer to the point of use is a better way of doing things, do you think I should have one in the box with the charger?  The distance from the RCD at the moment is about 10m of wire.   I'm also thinking of going with a metal box tied to earth as well to just make it a bit safer.

I had thought about the perils of using wifi but since I'd have been paying for the charging, on the rare event of a problem with the house network I decided I was happy with the the risk of paying for a full charge.  I do have a bit of overkill in my house with a 16 port managed switch and a ubiquity edge router to manage the QoS over the small amount of bandwidth we have out in the sticks. I'd certainly recommend them over the ISP routers.  Our network was unusable until I put in the ubiquity edge x router.  I hear you in the requirement to have a heartbeat check. 

I am working towards controlling the heat pump.  There is limited control through programmable switched potential free wires and I was going to try and raise the temperature of the house a few degrees in order to store the extra energy.  Ultimately I'll be able to Modbus in to it but that is going to take a little while.  There is the problem of when making 5kw from the panels, the house temperature naturally climbs quite a few degrees due to the solar insolation and can become unbearable if the heating is on at the same time.  I have 6.4kw of panels so am already maxing at 5kw from  the hours of 1000 to 1400 in early March.  I didn't realise I'd hit these figures so early in the year. Back of the fag packet calculations mean that if I am not dumping the excess 1.3 kw then I lose out to £500+ of metered fit payments over 20 years. I have a few ideas now: radiator in the bathroom though I think that has a thermostat so its not a reliable 600W dump.  I am looking at building a wood kiln in the garage to run a dehumidifier or air heater and fans.  I probably only need a 1kw dump as the house has a base load of about 300 watts.
Logged

6.48kw Solar PV JA (300W)Panels, SolarEdge inverter
Borehole -> Nibe F1255 12kw GSHP -> Radiators
Nissan Leaf
myozone
Sr. Member
****
Offline Offline

Posts: 299


Lizard peninsula - Cornwall


« Reply #5 on: March 08, 2019, 01:40:48 PM »

https://guide.openenergymonitor.org/integrations/ev-charging/
Logged

'Don't live life by the perforations' !
andrewellis
Full Member
***
Offline Offline

Posts: 134


« Reply #6 on: March 08, 2019, 02:04:25 PM »

Thanks for the link myozone.  I had looked at that project but it is considerably more expensive than the using the Mainpine based solution.  With wifi, it is £326.  I think I can get most of the functionality of that project with the ESP8266 and a few bits I have lying around.  I'll need a CT clamp to monitor the electricity going into the car.  One of the problems with the pod point is that I have to rely on the cars timer.  This doesn't allow flexible times to use E10 so another benefit of the home built solution is many timer options.
Logged

6.48kw Solar PV JA (300W)Panels, SolarEdge inverter
Borehole -> Nibe F1255 12kw GSHP -> Radiators
Nissan Leaf
jonesy
Hero Member
*****
Offline Offline

Posts: 846



« Reply #7 on: March 08, 2019, 03:25:36 PM »

Hi Jonesy, thanks for the info.  I didn't realise there where such differences in the RCD protection. 
You and me both. Protection is a serious matter, often overlooked or misunderstood. The internet doesn't help as we tend to copy the mistakes.

Having read that having the RCD closer to the point of use is a better way of doing things, do you think I should have one in the box with the charger? 
I'll not type my immediate reaction to this. Where did you read it?

I'm also thinking of going with a metal box tied to earth as well to just make it a bit safer.
The only real advantage with a steel box is that it will sustain a large knock without breaking; I tend to use plastic at home, particularly on large stuff as it gets expensive in steel.
If you have a metal enclosure you then need to include checks that the earth wire is well connected!
 
I am working towards controlling the heat pump.  There is limited control through programmable switched potential free wires and I was going to try and raise the temperature of the house a few degrees in order to store the extra energy. 
I wondered whether that would work; it's surprising how quickly solar insolation warms a place, and makes it too warm. If it's just a 1kW dump load you need to keep within limits, keep it simple and buy the cheapest 2 or 3kW panel heater in B&Q, or freecycle. Connect that to a simple phase angle dimmer and you have a variable dump load. You can use a digital pot run over i2c from the PI, or ESP8266. You can always change your plans as your ideas evolve.

I'm stuck with the ISP router as it also provides VOIP, and they won't release the SIP info, and a lot of us have tried to reverse engineer the box! 
Logged

1.1kWp PV & SB1700. 7kW log burner.
andrewellis
Full Member
***
Offline Offline

Posts: 134


« Reply #8 on: March 08, 2019, 03:48:56 PM »

Hi Jonesy, I can't remember where I read about the RCD. Somewhere to do with portable rcd and horse clipping probably.  I vaguely remember something about ' with a long distance of wire and the reaction time of the RCD' which I was wondering about. It didn't sit right wrt speed of electrons in wire.  Anyhows, thanks for putting me back on the straight and narrow.  Plastic box, and I'll run with the two existing twin pole RCD to save a bit of money.

Logged

6.48kw Solar PV JA (300W)Panels, SolarEdge inverter
Borehole -> Nibe F1255 12kw GSHP -> Radiators
Nissan Leaf
echase
Jr. Member
**
Offline Offline

Posts: 63


« Reply #9 on: April 20, 2020, 11:40:43 AM »

Andy, did you finish your project? I was thinking of doing similar but using the cheaper than Mainpine https://shop.gwl.eu/Connectors-Cabling-1-1/EVSE-Kit-V1-1-for-EV-charging-station-cable-Wallbox-kit-only.html 
Logged
andrewellis
Full Member
***
Offline Offline

Posts: 134


« Reply #10 on: April 20, 2020, 12:22:09 PM »

Hi. It got shelved due to other life commitments. However I restarted it this week.
I have encountered some problems requiring more bits. I was trying to use the DAC from the ESP32. Weirdly when I connect it to the IC pin on the Mainpine the voltage doesnít do as Iíd expect. If I plug in resistors then everything works correctly.

I measured the following from memory

Nothing in IC. IC - GND approx 5v
230 ohm Resistor across IC and gnd.  approx 1.1V. IC to vdd 3.9v
Pin 25 DAC1 esp32 connected to IC always gives about 4V. It doesnít matter what voltage is on the pin when measured disconnected.

Iím not sure if it has something to do with the ESP32 being a 3.3v device. I know enough about electricity to be dangerous Smiley

Anyways, if have ordered a digital potentiometer and a 5v DAC in the hope that one of those solutions will work.

Good luck with your project Smiley
Logged

6.48kw Solar PV JA (300W)Panels, SolarEdge inverter
Borehole -> Nibe F1255 12kw GSHP -> Radiators
Nissan Leaf
andrewellis
Full Member
***
Offline Offline

Posts: 134


« Reply #11 on: April 20, 2020, 12:23:50 PM »

Oh and I got a Rolec cheap of eBay and swapped its controller for a mainPine and also added a power meter so I got all the bits required fairly cheap. If you need a 5m cable I no longer require cheap then let me know.
Logged

6.48kw Solar PV JA (300W)Panels, SolarEdge inverter
Borehole -> Nibe F1255 12kw GSHP -> Radiators
Nissan Leaf
echase
Jr. Member
**
Offline Offline

Posts: 63


« Reply #12 on: April 20, 2020, 02:48:48 PM »

What do you find that the minimum that the Leaf can take? I read somewhere that 6A is the standard minimum for all charge points and cars as there is an IEC xxxx document that sets it.

Also how fast can you change the current? I worked out a scheme with PIC processors to change it several times a second to keep export small but I donít think the car will read it and react that often. Maybe once per second. Very hard to find the spec unless buy the IEC docs for £100s.

I have a Leaf too Ė 3kW input. And a 6 year old Polar charge point that I was going to just modify by cutting off its normal PWM and using the new controller to output a new PWM. That keeps the RCD etc protection the same. A bit harder in practice to trick the car and old point  to do the right thing.

The controllerís input does seem to be a problem as they are designed to be fed from changing a resistor, so trying to feed them with a variable voltage may not do the same thing. Should be just a resistor potential divider fed by a reference voltage at the top and the centre tap going to the Mainpine controller. The external resistor is just varying one leg of the divider. To drive it from an analogue voltage though you need a source that can both output and sink current to raise and lower the voltage to the Mainpineís processor, which maybe not all D/As can achieve.
Logged
andrewellis
Full Member
***
Offline Offline

Posts: 134


« Reply #13 on: April 20, 2020, 10:17:45 PM »

What do you find that the minimum that the Leaf can take? I read somewhere that 6A is the standard minimum for all charge points and cars as there is an IEC xxxx document that sets it.

I didn't fit the smallest resistor but from my reading the Leaf should be able to take the 6A.  The bit that concerns me is that on a cloudy day you have to determine how often you are going to stop charging and restart as clouds go in and out.  I have not been able to find anything on how many cycles the relays in the car last.  Some moving averages will have to take care of that with the occasional accidental extra import.

Also how fast can you change the current? I worked out a scheme with PIC processors to change it several times a second to keep export small but I donít think the car will read it and react that often. Maybe once per second. Very hard to find the spec unless buy the IEC docs for £100s.

It seemed to change pretty quickly but I as using my fingers to add/remove without shorting anything out.  It was a quick test.  I think it responded pretty quickly but not on the multiple times a second.  Since relays don't seem to be involved it wouldn't matter if you just keep updating as needed.  I've been logging the electricity stats in my house each second for a while and to be honest it doesn't change that much. The odd second here and there doesn't add up to a great deal financially.  It's not something to be that concerned about.

I have a Leaf too Ė 3kW input. And a 6 year old Polar charge point that I was going to just modify by cutting off its normal PWM and using the new controller to output a new PWM. That keeps the RCD etc protection the same. A bit harder in practice to trick the car and old point  to do the right thing.

There is a lot more going on in negotiating state than just the PWM.  You would need to emulate everything back and forth correctly.  I looked at the EVSE you linked to and the modbus makes things so much easier.  I wish I had that on mine as its a lot easier to deal with using some form of arduino/pi etc.  

Logged

6.48kw Solar PV JA (300W)Panels, SolarEdge inverter
Borehole -> Nibe F1255 12kw GSHP -> Radiators
Nissan Leaf
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.20 | SMF © 2013, Simple Machines
SMFAds for Free Forums
Simple Audio Video Embedder
Valid XHTML 1.0! Valid CSS!