Tag Archives: Juicebox

How efficient is charging?

These days everyone is concerned with how much resources do they use. Tracking things down to the penny/gallon/kWh/etc. When you have an ICE vehicle there are no losses from fueling the tank: The amount of gas that went into your tank is exactly equal to the amount of gas that was extracted from the tank in the ground and is equal to the amount of gas that was in the tanker truck, etc. (within reason). When you plug in your EV its not the same: When you charge what happens? The battery and the electronics heat up. That heat is wasted energy. Not all of the electrons going through the charge cable end up in the battery. But how many? Is there a way to measure this?

Many modern charge stations will report out the kWh value they put into the car (Chargepoint, for one), in addition some home stations (like the Juicebox) also report out the kWh value. This gives us one figure, but to figure out the charge efficiency we also need another number: The kWh the car used from the battery. This value is the amount of kWh the car consumed that the charger replaced. Divide these two values into each other and you’ll get a measure of how efficient the charge process is in the FFE.

For example: This morning my commute in to work consumed 3.5 kWh according to Ford’s online application (one of the few values in the trip history that have been accurately reported here). Once at work I used a local Chargepoint station to top it off. Chargepoint reported that the car consumed 4.14 kWh during charging. This would work out to a 85% efficiency while charging (at least for the top 20% of the battery or so which is what these values amount to).

I’ll have to do the math again with a deeper charge and using the Juiceboxes values for a different comparison (I’m not expecting it to be much different but more datapoints is always better).

Update: The commute home consumed 3.3 kWh according to the trip meter and the Juicebox put in 4.2 kWh to charge it back up (about 79% efficient).

Also note that the amount of energy going in also is used to run the TMS (temperature management system) and thus when its running will lower the efficiency.

Update 2: After a deeper discharge (9.6) charging took 11.7 for an efficiency of 82%

Update 3: A normal commute usage (11.1) and overnight charge (13.0) yields: 85%.

Update 4: Another normal (10.3/12.4): 83%

Update 5: 10.5/12.8: 82%


What is this Juicebox saved value?

When perusing the Juicebox source in a previous post I also noticed how it was calculating the “saved” value. If you are not familiar with the Juicebox saved value: On the premium Juicebox with a display it shows a $ saved value that increases as you use the JB.

What is this value? How is it calculated?

To begin with the Juicebox makes a few assumptions (constants declared in the code):

  • Price of gas $3.50
  • mpg of car to compare to 25
  • Price of electricity per kWh $0.12
  • Efficiency of the EV 300 Wh/mile

It then uses those values to come up with a “savings per kWh” value:

gas cost per mile = price of gas / mpg (3.50/25 or $0.14 /mile)

gas cost per kWh = gas cost per mile * 1000 / wH/mile ($0.14 * 1000 / 300 or 0.466 per kWh)

savings per kWh = gas cost per kWh – price of electricity per kWh ($0.466 – $0.12 = $0.346)

The total savings then is this savings per kWh value multiplied by the total kWh the JB has put into the car.

The total kWh is calculated by multiplying the input voltage, output current, and time interval (Watts = Volts * Amps, kWh = Watts over standard time interval–hours).

Much like my previous post this all is pretty straight forward math. The number it reports out may or may not be meaningful to you if your situation closely matches the configuration of the Juicebox (25 mpg prior car, EV burning 300 Wh/mile, etc.).

For those of us with the FFE, the Wh/mile value is more like 240-250 (about 15% more efficient) and, in my case since I drove an ICE Focus before the FFE, the mpg figure would be more like 30 mpg (about 15% more efficient as well). Which, for my case, the two differences pretty much cancel out making the $ saved value fairly accurate–if gas prices remain near $3.50.


Digging into the Juicebox

Since the Juicebox is open source we can pull back details about the design and poke around. In this post I’m going to give a look-see through the source code running on the Arduino board that runs the Juicebox.

The Juicebox code is a very simple loop running on the Arduino (an ATmega328P microcontroller equivalent). There is no RTOS running on the Arduino–just the Juicebox code. There really isn’t enough room on the chip to have a full RTOS; there is barely enough room there for the code that is running on it.

During setup/startup the code configures the Juicebox:

  • Configure I/O
  • Setup timers
  • Check for and Initialize display
  • Read the last clock value out of EEPROM (there is no real-time clock on the board so it remembers the last time it was powered up)
  • If the “A” button on the remote is pressed all the configuration parameters are reset to default
  • Checks for the presence of the remote (not sure why this is after the above check)
  • Calibrate the pilot signal: It will adjust the pilot signal based on temperature and voltage output
  • Determine the input voltage (120V or 240V)
  • Perform some diagnostics on the GFI circuitry

Now its finally ready to go. You can pretty much see/hear this sequence being performed when the Juicebox is first plugged in as it takes about 10 seconds or so to get through it all.

The main section of code is just a large loop. The loop repeatedly cycles through the following tasks:

  • Check for presence of a car and if it is charging
  • Manage a change in state from the previous iteration through the loop (e.g. car plugged in, car charging, charging complete, etc.)
  • Set the configuration to the new state (if changed)
  • Update the display (real-time status on charging)
  • If there is WiFi send some data out to the Web (EMW)
  • Check if a menu button has been pressed
  • Check if the GFI has tripped
  • Repeat

That is about it. Pretty simple operation but then I really wouldn’t expect a lot from an EVSE since it really has only two purposes: Provide power to the car and provide GFI protection.

One feature that I’d like to see in the Juicebox that it currently doesn’t do: Turn off the display after 5-10 minutes when not plugged into the car. There really is no reason to keep the display lit when not plugged in. (I’m not sure if this is even possible simply by looking at the source code–may have to take a peek at some circuit diagrams to figure that one out.)


Juicebox after 5 days…

Its been 5 days since the Juicebox arrived. So far all has performed as well as expected. The Juicebox is reporting 43 kWh charged lifetime.

At this point I haven’t made use of the Juicebox’s charge timer, just using it like I used the other EVSE’s. So far I’ve noticed the following about it:

  • The clock doesn’t seem that accurate: Since this one doesn’t have WiFi it can’t sync to a time server so I wouldn’t expect it to keep perfect time (was off about an hour today when I checked–will have to monitor that more closely)
  • When the FFE is set for Value Charge (timed charge) I’m getting a charge fault right after plugging in. I’ve seen this occasionally with the other EVSE’s. It seems that the Focus gets out of sync with itself (like the charge module thinks its time to charge but the MyFordTouch timer says no it isn’t resulting in a fault). This clears itself up after a few minutes (Pressing “Update” a few times in the mobile app also appears to clear up the condition).

It still feels like a higher quality design/build than the other EVSE’s I have–this is mostly due to the case and the construction of the J1772 plug.


Chargers are us…or rather EVSEs

I seem to be collecting EVSE’s lately! A year ago when I picked up the FFE–my first plugin car of any kind–I didn’t know what EVSE to get and just got the one the power company recommended as part of their installation deal. Now today I have a small collection of them:
EVSE Collection
On the left is my original Bosch/SPX PowerXPress unit which is proving to be a little troublesome. In the middle is a Clipper Creek LCS-25P. The far right is the newest of my four EVSEs (4th is the 120V one included with the car): An EMW Juicebox.

Now I didn’t really pay for all of them:

  • The Ford EVSE comes with the car (so yeah its cost is baked into the car)
  • The Bosch/SPX unit had a tax deal where my power company paid for almost all of it
  • I did purchase the LCS-25P as a Level 2 backup to the Ford EVSE
  • The EWM Juicebox I won right here for this blog!

Yes you read that right: I’m the winner of the myevblog contest from September/October last year. The Juicebox only just arrived today–I had expected it to take some time given that it is a Kickstarter project. So I finally have something to write about other than “I won!”.

(A note about the wiring in the picture above: The Juicebox is rated for 60A and thus its two cables are quite beefy. To get it to plug into my outlet and be “compatible” with some of my options I removed the 14-50P end of the cable and put a L6-30 plug on it. Since the cable was so thick I wasn’t able to put the strain relief on–yet. With the L6-30 plug it uses the same pigtail that the LCS-25 does. I only have it set for 27A.)

Lets take a look at the vehicle connectors for the four EVSEs:
EVSE Plugs
EVSE Plugs

Left to right the connectors are: Bosch/SPX, Clipper Creek LCS-25, Juicebox, and finally the Ford “convenience cable”. A few remarks about each:

  • Bosch/SPX: This one seems to be the cheapest design. A rubber overmold over some plastic with a small hole for drainage.
  • Clipper Creek: This is a very nice connector. In the second picture you can see the green O-ring used to seal the plug against the car. The cable has a Delphi tag and part number on it.
  • Juicebox: This connector seems to be the best of all four, similar sealing to the LCS-25 and a bit more solid feeling. It even includes a rubber dust cap.
  • Ford: The Ford plug is very similar to the LCS-25 plug in design and about the same quality.

On the whole they all get the job done, some quicker than others of course. The Juicebox stands out, though, because it has some extra features:
Juicebox display

The display shows the current power consumption and charge rate (above I’m charging at 240V, 27A and the Juicebox has put in 0.1 kWh into the car for the past minute).

You can set the max current level via a menu item (even adjust it while the car is charging–the “outC+” and “outC-” shown on the display above). If I had the WiFi adapter I could also setup a charge schedule in it similar to the Value Charge schedule in the FFE.

So far after about two hours of using the Juicebox it appears to be a very nice unit–albeit a little large case but does look cool like an AA battery.

More to come after I’ve used it a while…