OpenEVSE - Open Source Charging Station

[GerryAZ]

Dear GaryGID. Thanks for the product recommandation and it saves me a lot of reading time. This is really good information. The photo has a pair of what it looks like a low voltage power wires. The installation instruction does not say it needs to be connected. Do you know by any chance whether the $140 EKM-25IDS-N unit needs to be connected to a low voltage power source? Is there a power pin inside the OpenEVSE I can tab the $140 meter. My electrician is coming tomorrow so it's a good time to add if the lower voltage is needed.

Gary started another thread for EKM metring, but I will answer your question here in case you don't see the new thread. The meter needs voltage inputs and current inputs that can be obtained directly from the line side of the EVSE (at the EVSE or junction box). Small donut-shaped current transformers around the supply conductors provide the current inputs. Voltage inputs come from connections to the line side conductors also. The voltage inputs should be fused with 1 ampere inline fuses to protect the meter and the small wires going to it. The meter is powered from the voltage inputs so it does not need a separate low-voltage power supply but it will need the neutral conductor in addition to ground and line conductors. I have been using a couple of EKM meters to monitor my Leaf power consumption and the power usage at my workshop garage for several months, but have not yet tried data logging. I will be looking at the thread Gary started for tips on the software and RS-485 connections.

Gerry

 

[GlennD]

I do not log power but I have a cheap voltage and current display. I purchased it on Ebay and it was shipped from China.

 

[goldserve]

Nice! Got a link to the eBay? I see my firmware in use!

 

[z0ner]

Looks like this one:

http://www.ebay.com/itm/Digital-AC100-300V-0-100A-LCD-Double-DISPLAY-PANEL-VOLT-AMP-Meter-100A-CT-/121058889948?_trksid=p2047675.m2109&_trkparms=aid%3D555003%26algo%3DPW.CAT%26ao%3D1%26asc%3D14641%26meid%3D5990091627552569409%26pid%3D100010%26prg%3D1076%26rk%3D5%26sd%3D370770495540%26" onclick="window.open(this.href);return false;

 

[GlennD]

Thats the one Z0ner but from a different seller and even cheaper.

I had to calibrate mine since it said 14.7A while my Sperry analog meter said 16A. There are 2 holes in the circuit board for voltage and current. The one under the voltage display is for current.

Goldserve, your firmware is working out fine with no problems.

 

[chris1howell]

Hopefully, we will not have to worry about external meters too much longer. An OpenEVSE builder is working on a meter that is based on an ATtiny and will send info to OpenEVSE over i2c... I know he hangs around here so maybe he will post more details...

 

[waidy]

Hopefully, we will not have to worry about external meters too much longer. An OpenEVSE builder is working on a meter that is based on an ATtiny and will send info to OpenEVSE over i2c... I know he hangs around here so maybe he will post more details...

Brilliant!

 

[borland]

That’s the plan. I’m working on an I2C sensor to measure amps and calculate kWh consumption for display on OpenEVSE’s LCD display. I’ve also been thinking about a RFID card reader add-on too, but I think that may require its own separate power supply.

I’m only working on the sensor part time; it’s not a big priority for me. I’m still waiting for parts to build my OpenEVSE.

I’ll send Chris a prototype for his evaluation when it’s close to being finished. He might want to make some boards available at some later date.

Some details of the sensor I'm working on .…

The sensor hardware is very trivial and compact….. Consisting of an inexpensive 0-100 amp non-invasive current transformer, three resistors, couple capacitors, and low power 8-pin ATtiny85 microprocessor. The PC board shouldn’t be larger than 1-1/2” square. This current tap clamps over one of the L1/L2 wires and plugs into the PC board…

I’m currently making good progress writing the sensor software library. The library is to provide sensor functionality…. and also to provide a command set to be used by the OpenEVSE controller to retrieve amp and kWh measurement data over the two wire I2C bus for LCD display. Calibration refinement for specific applications will also be provided for with a sensor calibration command set.

The sensor will draw power from and reside on OpenEVSE’s I2C bus. Sensor functions will be to measure L1/L2 current load over the range 0-100A and estimate both session and cumulative kWh consumption.

This sensor will only measure current…. Charging current is a great way to monitor the charging profile and estimate the ‘state of charge’ without knowing the car’s pack voltage. I know most will want to know the charging kWh consumption, so I’ll add that functionality too.

Most power meters need to measure wave forms of both Voltage and Current. This is so they provide accurate power in kWh of energy with a variety of different load types. Since EVSE is only connected to one type of load, an estimate of kWh consumption based on current measurement alone becomes more trivial. By monitoring only current, it greatly simplifies the sensor hardware construction too.

The intent of the kWh consumption readings is only to present readings which are representative of what he utility meter captures. Since the best place to monitor kWh consumption is at the utility meter, any supply losses up to the EVSE could be included by sensor kWh calibration. The sensor will assume line voltage to be relatively stable or average out over the cumulating period.

 

[QueenBee]

Since EVSE is only connected to one type of load, an estimate of kWh consumption based on current measurement alone becomes more trivial. By monitoring only current, it greatly simplifies the sensor hardware construction too.

I understand this simplifies things but unfortunately that doesn't support 120/240 volt operation such as in a portable EVSE. Even in a fixed install I'm not sure how much variation there is in the voltage but there would certainly be some.

 

[GlennD]

According to my TED my voltage varies from 241 to 251V. Most of the time my display reads 248-249V.

 

[waidy]

Hi hi, have we decided which OpenEVSE silkscreen to use? Please let me know where I can purchase one. One of our OpenEVSE is in (not wired yet). I looks kind of boring.

 

[borland]

Nice install! I like the J1772 holster and hanger. Where did you find or buy those?

Adafruit http://www.adafruit.com/products/693 sells a decal for $1, but it would likely cost $5 with S&H.

You could easily make a stencil from a computer printout on clear transparency film or cardboard and a knife or scissors. The open source hardware logo can be found here. http://oshwlogo.com/

I've recently bought some basic silkscreen supplies, so I might be able to print one for you on your flat panel, but first I need to do some expermenting with the photo masking to find the right exposures for sunlight.... also see if the ink I purchased is suitable.

 

[waidy]

Nice install! I like the J1772 holster and hanger. Where did you find or buy those?

I rescued them from a junk yard at a EVSE startup I invested.

Adafruit http://www.adafruit.com/products/693 sells a decal for $1, but it would likely cost $5 with S&H.

You could easily make a stencil from a computer printout on clear transparency film or cardboard and a knife or scissors. The open source hardware logo can be found here. http://oshwlogo.com/

I've recently bought some basic silkscreen supplies, so I might be able to print one for you on your flat panel, but first I need to do some expermenting with the photo masking to find the right exposures for sunlight.... also see if the ink I purchased is suitable.

Wow, you are professional!! I'd like to buy one from you after you are done. Thanks in advance!

 

[waidy]

Amazing... Thank you thank you!

 

[waidy]

What does 00:00 (under L2:75A) means? The value doesn't seem moving.

 

[mitch672]

What does 00:00 (under L2:75A) means? The value doesn't seem moving.

That's the time of day clock, if you've added the I2C RTC chip.. You can set a start/stop timer for charging, so it doesn't start as soon as you plug it in. If you have "time of day" rates, you could for example, start charging after midnight, if you have a lower rate then. It's also useful to be able to start charging much later, like 4-5AM, so your charging will just finish as you need to go to work.
Your Model S will spend less time at %90 SOC (which is a "standard charge"), by charging closer to when you'll be using it...
I think the less time your pack spends at a high SOC, the better for its long term health.

 

[coolfilmaker]

It would be really cool if Chris went on Jay Leno's Garage and assembled an Open EVSE with him.

 

[waidy]

That's the time of day clock, if you've added the I2C RTC chip.. You can set a start/stop timer for charging, so it doesn't start as soon as you plug it in. If you have "time of day" rates, you could for example, start charging after midnight, if you have a lower rate then. It's also useful to be able to start charging much later, like 4-5AM, so your charging will just finish as you need to go to work.
Your Model S will spend less time at %90 SOC (which is a "standard charge"), by charging closer to when you'll be using it...
I think the less time your pack spends at a high SOC, the better for its long term health.

I see. I don't think we have I2C RTC chip. Both the "EVSE time charge" function or "time of day to change" function is not as important to me as I am positive (net energy producer) of 14MWh/year (it may be less now that I have 2 Rav4EV and a S). I am more interested in getting a power monitor for it. Thank you so much for the information.

 

[chris1howell]

It would be really cool if Chris went on Jay Leno's Garage and assembled an Open EVSE with him.

I am in... Just waiting for the invite.

 

[coolfilmaker]

It would be really cool if Chris went on Jay Leno's Garage and assembled an Open EVSE with him.

I am in... Just waiting for the invite.

I bet all you would have to do is send them a facebook message to set it up.
https://www.facebook.com/jaylenosgarage" onclick="window.open(this.href);return false;

It seems like they put on pretty much everyone who asks. A lot of the products aren't even American made despite that supposedly being the main requirement for products to be on it.

You could probably even replace Jay's EVSE since I'm sure the one he has is only 30 amps.