Tuesday, August 5, 2014

1000 Lithium Miles

Yesterday, I passed 1000 miles since I got back on the road with LiFePO4 cells.  I've continued to track my daily drives.  Here is the chart as of this morning:

You can see that it is very linear - not a lot of variation other than two outliers (both of which happened early on, and both of which were unusual circumstances).  From this, some statistics:

Average daily drive: 15.9 miles
Average daily energy used: 7.13 kWh
Average watt-hours/mile: 424.5
Average mpge: 79.4

The energy consumption numbers are from the wall and include any charger inefficiencies, etc.  The electricity for the average daily drive would cost me 57 cents, if it were not for the fact that much of our electricity comes from our rooftop solar array.  Given that the Jeep got 19 mpg in-city on gasoline (on a good day!), I save roughly $950 per year on gasoline at today's price of roughly $3.50 per gallon.

In related news, I've tracked the efficiency versus temperature.  There is not a lot of correlation here:

From what I know of LiFePO4, low temperature will affect capacity, not efficiency.  Basically, when cold, LiFePO4 sags a lot more than when warm.  This translates to fewer watt-hours available, and, since watts required to drive is independent of temperature (if a cabin heater is not included), colder temperature means lower range.

Saturday, June 14, 2014

500 miles on LiFePO4

Yesterday, the ElectroJeep pushed over the 500 mile mark with its new lithium battery.   I've been tracking its performance along the way.  First, as detailed earlier on this blog, it has a "parasitic load" which at this time looks like about 39 milliamps, which translates to about 300 Wh lost per day regardless of whether the ElectroJeep was driven or not.  Second, after correcting for this parasitic load, it is getting about 428 Wh/mi wall-to-wheels.  This translates to 79 mpge (a standard metric used to compare electric vehicles to others).  Compare this to the Jeep's original factory rating of 19 mpg!

Finally, here is a chart plotting miles driven against kWh used:

The red dotted trend line is a least-squares fit to the usage, corrected for the parasitic load.  It's very linear, except for that one drive where the ElectroJeep sat idle for a couple of weeks.

It's exciting how reliable and useful the ElectroJeep is, especially compared to the old lead AGM batteries.  It's my daily driver (especially with the Porsche undergoing a similar upgrade).  For anybody looking to convert a vehicle, I strongly suggest you save your pennies until you can afford LiFePO4 - you will be much happier in the long run.

Sunday, May 18, 2014

"Parasitic" losses

A reality of the instrumentation and configuration of the ElectroJeep is that it requires some power even when not in use.  Its DC-DC converter is always on, float-charging the accessory battery. Additionally, the MiniBMS modules consume some charge at all times.

I had the opportunity to measure this the last couple of weeks.  For a variety of reasons, I did not end up driving the ElectroJeep between May 2 and May 17.  I drove it about 6 miles yesterday, and then charged it.  I've been keeping track of the charging energy, and here is what the chart shows, including yesterday:

Note the little dot way above the trend line on the lower left.  That is yesterday.  By simplistic calculations, yesterday's drive was expensive at 1135 Wh/mi (compared to the average of about 450 Wh/mi).  But a little digging teases out the ongoing parasitic power consumption.

Yesterday's charge consumed 6.47 kWh.  Using the least-squares trend, it should instead have used 3.26 kWh.  The difference of 3.21 kWh, divided by the time (15 days), gives the ongoing parasitic power draw: about 8.9 watts.  At the typical battery voltage of around 317 volts, this is about 28 milliamps.  Looking at it another way, about 0.68 Ah of capacity are used each day, just sitting around. At my "70% DOD" threshold, this means I can leave it idle for about 100 days before needing to charge again.

Another thing of note: that 28 milliamp draw is too low for my EV Dashboard to detect - it thought the batteries were fairly near "full", even though they had lost about 10 Ah (10% of capacity) over the 15 days of idle time.  I may contact the vendor to see if they might consider adding some sort of "correction" factor based on this kind of measurement.

Monday, April 28, 2014

New Vacuum Pump

Nearly 5 years ago, I installed ElectroJeep's power brake vacuum pump.  It was a noisy little beast, and it always irritated me.  Some time in the past 5 years, I got a new, quieter pump to replace it - the MES 70/6E2 - but I never got around to installing it because it was taller than the old pump and would not fit in the same spot.  However, with the new LiFePO4 layout, I had a blank spot where one of the 26 old AGM batteries had gone.  A perfect spot to mount both the new pump as well as the power steering reservoir:

The pump is mounted on little anti-vibration feet, and is much MUCH quieter than the previous pump.  I hooked it in to the original vacuum reservoir, which includes an adjustable vacuum sensor switch:

And now I have power brakes - in style!

Saturday, April 26, 2014

100 Lithium Miles

Today, the ElectroJeep celebrated 100 miles of Lithium!  I've used it as my daily driver all week.  I'm very happy with it.  I've been keeping track of the power required to charge it - here is a chart as of this week:

You can see the spreadsheet data here - I'll update it every day that I drive.  From this data, I can see that my target of "50 miles range" will be met, easily (at least at spring/summer temperatures).  I'm getting about 380 Wh/mi range (I had guessed "400"), with a 1.4 kWh "per-charge" overhead.  Given that this is a 30.7 kWh pack, that translates directly to a 56 mile range at 70% depth-of-discharge. That would be an 80 mile range at 100% DOD, but that runs the significant risk of killing the pack.  Not going to tempt fate.

Sunday, April 20, 2014

EMW EV Dashboard

I had previously installed a sender board for the EMW EV Dashboard Android app:

Today, I hooked up the BlueTooth module and got it calibrated and running to my taste.  Here is a screen shot:

It shows current (both analog and digital), voltage (both analog and digital), charge (both analog and amp-hours remaining), and power being consumed.  I drove about 5 miles around the section block - the app worked really well.  And it looks like my estimate of roughly 50 miles range is going to be accurate - I consumed about 7 Ah for the 5 mile range.  70% DOD from 100 Ah is 70 Ah - and 70 Ah * 5 Mi / 7 Ah = 50 miles.  To one significant digit.

It's a vehicle again!

With everything wired up and functional, it is time for a test drive.  So, without further ado - the ElectroJeep rides again!

It's riding pretty high, so I will probably ratchet back the lift kit to avoid undue stress on the transmission.