Tag Archives: Time

How does the FFE Charge?

This question could be answered in many ways depending on how you interpret the question: There is a technical answer (it uses a 6.6kW charger inside the car), simply (you just plug it in and it charges), how much current is used, how fast does it get to 100%.

In this case I was interested in the last answer above: Does the FFE’s % battery full “meter”/value increase linearly when charging? Li-Ion batteries themselves don’t charge up linearly. As the battery gets closer to full the internal resistance of the battery increases making it harder to force more electrons in and thus the charging rate of the battery slows down the closer to full it gets. If you were to plot this you’d get a curve where charging is quite fast at the beginning then as you approach 100% it flattens out slowly approaching 100%.

Having done a little reverse engineering on the API that the mobile app and the website use I was able to make a program that logs the % battery value and the range over time. Now if I were to log these values during a charge cycle I could produce a graph to see the charge curve. The graph could be a line as the internal software in the FFE could normalize the % value to a line while charging (to simplify it for users). Frankly I don’t think they would go through that much effort–there would be no benefit to anyone (other than geeky people like me who write blog posts about graphing the car charging! LOL). So I give you my FFE’s charging plot from about 35% to full on a freezing Friday evening:
Charge Plot
The blue line is the % battery value and the orange line is the estimated range value (only topping out at 70 miles here due to the cold days we’ve been having and the fact that I’ve been using the heater).
What surprises me the most about this plot is how flat it is. I was expecting it to be much steeper with a pronounced knee near the end as it flattened out. Note that there are a few gaps in the data as the API timed out or otherwise gave an error. There is also an unexpected turn faster around 10:00pm where it charges slightly faster. I wonder if this is where the temperature management system kicked in to cool the battery a bit allowing for a slightly faster charge..

I have another idea for this logging: What if I were to let it log while I was driving the car around? That plot may also prove interesting as the % battery value would decrease in a predictable manner but the estimated range (the guess-O-meter) value would be all over the place depending on if the heat was on or off, if I was on the freeway, etc. Some more experimentation is in order here…

How much electricity does the Go Times use on a mild day?

A couple of weeks ago I had noticed that when I had the Go Times set (even with the climate control set to off) there was a very slight reduction in battery usage for my morning commute (like 1%-2% or so). My thinking at the time was that the Go Time was doing something before unplugging that would be happening while driving if the Go Time wasn’t set. Apparently someone else was thinking similar thoughts in the forums. This morning I setup a test:

  • Car fully charged, parked in the garage
  • Garage ambient temperature 72F as measured by the opener (got me why my opener can read the temperature)
  • Set up a Go Time for 6:15 am with climate off
  • When I walked out to check on the car at 6:10am or so the Juicebox relays had already clicked on but it was showing no power draw from the car
  • At about 6:12am (or ~3 minutes to go) the car’s fan turned on and the Juicebox read 7A draw (1.7kW)
  • At the Go Time of 6:15am the car shut off
  • The ending Juicebox display was showing 0.0 kWh of power consumption

If we do a little math using the 3 minutes of 7A power draw (3 minutes is 0.05 hours, and the car was using 1680 Watts–7A * 240V) we can conclude that the car used roughly 84 Wh during that 3 minutes. 84 Wh is really not that much power–on a really good day it can take 200 Wh just to go a mile but it is non-zero. Over the course of a summer it could add up to a “tank” or two (only summer because as the temperatures get colder using the Go Times gets more important).

Update: I’ve left the Go Times setup for the week configured the same: Climate off. I noticed the cooling fan on high this morning so I glanced over at the Juicebox just before unplugging the car: 24A! for 4 minutes, 0.3kWh consumed (Doing the same math as above: 384 Wh). The only weather differences: Slightly warmer at 77F but the humidity is much higher (very foggy out). Interesting, I’ll have to continue watching it…