Thursday, December 30, 2010

Lipo and LIFEPO4

I'm doing a interesting mixed chemistry setup that uses the best of LIFEPO4 and Lipo in a diode summed system.
My motivation in doing this stems from the fact that the 40AH Thundersky cells just don't put out enough voltage under load (Sag). For EnerTrac this makes it difficult for my customers to get a true understanding of the power and speed of the 600 series motor, when test riding my bikes. So I need a way to boost voltage under load, without replacing the complete battery pack.
 In the above picture you'll see the CA meter (lower) and a second smaller meter up top. The top meter monitors the Lipo pack current while the CA meter monitors the total system. Up to 1.5C or 60 amps, the LIFEPO4 batteries run the bike, then as current exceeds 60 amps or beyond 2C the LIPO kick in. At 100 amps the LIFEPO4 pack maintain 1.5C and the Lipo pack does the remaining 40 amps. My 40AH LIFEPO4 cells now never see much over 60 amps while my 20C rated Lipo see as much as 200 amps peak.
The Lipo are bulk charged with a separate Meanwell type power supply. Separate balance units are used as needed, they are connected in parallel with the display units.

I accomplished this by exploiting the fact that Thundersky cell have much higher IR than the Lipo cells and setting the Thundersky pack to be at a higher no load voltage. The diodes are 150 volt schocky diodes.
Testing was done on my Dyno. The box under the bike is the Lipo pack 25S 2P

I have only done 4 miles of road testing before the snow hit. I had the Lipo up to 100 amps while the LIFEPO4 stayed under 80 amps during this on road test.
My Dyno Currently can only do 100 amps continuous, measured at controller input. My plan is to do a video record of the display system so I can record in real time the speed, current of both batteries and then put the data in a spreadsheet.
My data so far shows temperature not to be a big problem I've had the batteries on test from 45F to 70F
My big concern is
The 4 to 1 AH ratio - is it correct, only on road testing can determine that.
Battery pack
I think the battery box weights more than the batteries.
The big challenge was getting all the hardware into the bike and still be able to get the skins on.
The bike with the skins back on
I have under belly skins that will mostly hide the Lipo battery box

Conclusion:
More data is needed but my testing to date, shows it's possible to mix two chemistry types and use the best characteristics of each respective battery type.

Mark

3 comments:

  1. Lipo and LIFEPO4 battery use in the bike. Both are very popular in the market but Lifep04 use mainly because it's power strength is good. Lipo also good battery.

    Lipo

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