Friday, July 20, 2012

Why I wasn't posting...

I didn't want to jinks anything.  However my car has reached that stage where I had to pick my batteries.

  • Lead acid would be cheap, and workable.  
  • AGM has come down in price, and they have 'good' performance.  

But that I wanted was...

  • Lithium.  

But could I; a humble shady-tree mechanic possible afford (and get) what I knew I wanted.

Some background.  AC motors and converters COULD be run as a 'low' 114 volts DC.   And the lead acid folks run at that voltage.  It doesn't leave much head-room; but it works.

AC motors scale directly to voltage.  The more volts, the more efficient the motor works.  This is why Tesla runs their Roadster with an insane number of batteries.  They want the voltage as high as possible, while keeping the Ah around 60 (I don't know the actual layout math for Tesla, but if I was a betting man).

So I knew I didn't want to run at just 114V (36 cells).  Also the folks over at Azure (the makers of my inverter) had already said that between 114V ~ 205V they have a kind of dead zone for how well the 440 works.  Mine was already programmed and rated at 364V max, 312V normal.  So it was on the other side of that dead-mans valley.

However anyone with a calculator out there is saying, wait a minute... that's 98 cells!  You can't fit that many batteries into that car.

Enter Sinopoly.  They bought Thundersky; and earlier this year announced the SP-LFP60AHA(B).  A 60 amp hour cell half the size (36mm thick instead of 61mm).  And; they said, at the same cost. Cost at the time for a TS60Ah was running about $1 an amp hour.  Could Sinopoly be serious?

I called for a local distributor; and was told they wanted to sell directly to the end user (from China).  They would drop ship to a local port (I'm on the west coast); but they also had a courier service that would deliver (for an additional fee) right to your door.

E-mails and money wires followed...
I now have 109 60Ah batteries to test, balance and install!  That's 348V for those playing along at home.