Tuesday, April 27, 2010

April 23 Friday Show

I've posted the April 23rd Friday Show. We had a lot of wind noise I had to filter out so forgive Brain and I in the opening segments. We hadn't been breathing helium or anything, I just had to lose the low frequencies to make the wind more or less go away. We're still learning this video game, and most of it seems to be audio actually.

We did do a walk around of the newly reassembled Mini Cooper. We talk quite a bit about the Speedster Part Duh heater assembly. This is actually a kit from Canadian EV that we used and Brain and Trace did a marvelous job of installing it. It is just factory in operation and fit.

We ground off the fiberglass around the frame in the engine compartment. And I did a bit more in-depth review of the Xantrex LinkPro/TBS E-Xpert Pro instrumentation. It is cheesy looking. But it actually works quite well. It is quite accurate. And it is much more flexible than I realized when I dismissed it out of hand initially. At $250 it appears to be THE extant solution in EVland for the very necessary counting of AH to determine state of charge.

I've since done a bit of testing on the 2009 Mini Cooper Clubman. Yesterday I drove it to Perryville and back at as constant a 60 mph on the Interstate Highway as I could manage. It was 78 miles roundtrip with a consumption of 75.1 AH. It took 42.9AH to get there and a little over 32 to get back, indicating Perryville is mostly uphill from here.

At 60 mph, in the Getrag's 6th gear, I'm loafing along at about 1400 rpm. We did NOT get the Tach on the Mini working yet, but we did install a Summit Racing tach temporarily and the output of the TIMS600 controller seems to drive it admirably using the TIMS default and the 4 cyclinder setting on the tach.

We average about 60 amps at 60 mph on the straight and level, not even breaking a sweat for the 100AH SE cells. I DID mash the accelerator a couple of times - ZOOMING over 85 almost immediately. This drew a maximum of 372 amperes and dropped the cell voltage to a saggy 2.79volts for a total power of about 116kva (nearly enough kilowatts). I took this as a VERY good sign. It's hard to zoom anywhere with such an overdrive gear. The TIMS 600 is SUPPOSED to have a 300 amp limit.

I stopped in Perryville to do a Marine Corp temperature check of the motor and controller. They were at about skin temperature. In fact, the transmission was hotter than the motor. Our AN-8 sized cooling system, using the MIni radiator and fan, do indeed seem to be doing a superb job of keeping things cool and allowing MAX POWER out of the TIMS600 without stress. Probably a combination of the high flow rate and huge heat sink relative to what is normally used with this.

Finished the drive at ostensibly 75% Depth of DIscharge (DOD). However, the average cell voltage was 3.278. This is a bit of a puzzle. The SE discharge curve is quite flat. But I can't imagine it being THAT flat. We did do one measurement when the cells were first installed at 111 amp hours out of these 100 AH cells. It is quite likely, we have much more capacity than it appears. That would somewhat explain such a high resting voltage after the drive.

In any event, though I'm always looking for a bugger in the potato salad, the EV grin is starting to widen. The weight and coilover springs make the ride almost stately - like an Escalade. The performance is quite beyond the ICE engine which was already perky as you recall. The steering is stiff in local quarters but actually pretty good on the road. And with NO regen really on the highway we seem to be doing about 0,96 amp hours per mile. This indicates a "no regen" range of about 80 miles at 80%DOD.

The drive shaft issue (fingers crossed, eyes skyward) seems to be solved for the moment. I'm growing more confident in shifting and driving without fear of throwing a drive shaft. And the EV grin is starting to come on. This is a marvelous car. We have plenty left to do, but it is shaping up as an all weather all season ride with bluetooth and IPOD. Good performance. Good economy. Good creature comforts. And the Getrag transmission verifies our selection of this car. We take off in 3rd and road cruise in 6th for a good solid 4 speed experience.

Jack RIckard

Wednesday, April 21, 2010

April 16 Friday Show

This week we digress a bit from vehicle issues and take a look at the progression of LiFePo4 cell offerings over the past two years.  We also do some full 1C discharge and charge tests on the cells.

The first cell in this series is a Thundersky TS-LFP160AH cell we purchased about 18 months ago.  This cell is a Lithium Ion Iron Phosphate cathode cell.  The spec sheet for this cell is available here.  Note that the cell measures 182 x 276.4 x 71 mm in volume and weighs 5.6kg.  It would contain 3.4v x 160AH = 544 watt hours of energy.  With shipping, this cell cost almost exactly $244.

Second cell was a Sky Energy SE-180AHA cell. You can download the spec sheet here. It is only slightly taller at 279.5 mm but is also 182x71 mm and 5.6kg, but offers 180 amp hours at the same voltage - essentially 612 watt-hours of energy. It was purchased at $241 with shipping 9 months ago.

The third cell is a brand new Thundersky TS-LFP-200AH cell. Spec sheet here. This cell features the addition of Yttrium to the cathode material and offers longer cell life cycles - 3000 cycles vice 2000 at 80% DOD and 5000 cycles vice 3000 at 70% DOD. This is a pretty significant extension of life cycle claims. It's dimensions are actually 183 x 276 x 101 mm  or 362 x 256 x 55.5 and quite a bit heavier at 7.3kg. It is also about $240 once delivered to Cape Girardeau MO.

The latest Thundersky cells are quite interesting. Most significantly, they manufacture an unadvertised  variant of this cell at the original 183 x 276 x 71 mm size and 5.6kg weight. But they can sell enough of these without advertising it that there is NO MENTION OF IT on the Thundersky web site.

Because of the quantities of these cells they are now selling, EVCOMPONENTS can get these 276x183x71 mm cells. They do test out to 200AH, though not any more than that. That's 680 watt-hours per cell. http://www.evcomponents.com.  You do have to know to ask

This is rather an amazing occurrence.  In the space of 18 months, we've gone from 160AH to 200AH in the same form factor and at the same price.  That's a 25% increase in energy density, and at least a 50% gain in cycle life.

We developed an Arduino based circuit with some LEM-HASS hall effect current sensors to measure current and AH into and out of the cells. We used our GIgavac contactor box, described in last weeks show, to switch the batteries in and out.

We used a pair of ACME 1500 watt constant current loads to load the cells to a 1C rate, 200AH, 180AH, and 160AH respectively for an hour and recorded the voltages and temperatures at each 2.5% increment by counting 5, 4.5 or 4 AH between each notation.

And then we reversed the process and used a Lambda 10v/200A power supply to do the charge curves the same way.

The result is a series of graphs.  Here is the discharge/charge curve for the original TS 160AH cell.  Click on the image for a larger version.

Here is the results of the Sky Energy 180AH cell.

Here is the results of the new Thundersky 200AH cell.

Because we measured these cells at the same percentage of their total AH capacity, we can compare them. Here is the charge curve comparison of the three cells.

We can do the same thing with the discharge curves.

The interesting area of this test is of course the temperature gain during charge and discharge. The discharge process caused the greatest temperature gain.

But there were some additional temperature gain during the recharge process.

Finally, we're making the entire Microsoft XLS spreadsheet file with all the collected data available for download here.