Batterytests

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We have build an Open Source battery testing station to Tampere Electric Vehicle Center (TEVC). Station is housed in old half-size sea container, so we can control the ambient temperature if needed. We have currently ability to test batteries ranging roughly from 40-320 volts, with various amounts of charging-power available. We can cool batteries down to -18 Celcius (0 F) with quite large freezer. We can test and measure different BMS-systems and see how they work. We are currently building automated single cell charge and discharge ability, for now just 2 independed cells simultaneously. Hopefully more in the future.

Equipment

  • 1 x 0-320V 10A (3.2 kW) charger, main charger for large batteries
  • 3 x 5V 300A (1.5 kW) chargers, can be used for as single cell chargers
  • 4 x 40-60V 35A (1.5 kW) chargers, can be used for medium-sized batteries
  • 2 x discharge "ladders", with one ladder we can obtain about 80A discharge current
  • 1 x Linux-PC + 32 ch I/O card
  • 5 x isolated RS232 multimeters, used for large battery testing. Voltage, temperature and current is measured and recorder to central database
  • 1 x freezer
  • 1 x 9 kW "construction heater" - used as discharge resistor

Future (in progress)

  • 2 x independed single cell automated cycle stations with 1.5 kW charge capacity and about 80A discharge capacity. We are using these to examine individual cells and possibly to automate internal resistance measurements.

All the measurements are inserted to common database that can handle multiple simultaneous devices sending measurements. Every measurement is accessible with just normal web-browser, including browsers found in popular cell-phones.

Short tour around TEVC battery testing stations (filmed 25th April 2010):

Measurements


Setting up and discharge nro #1: 18.4.2010

graph.png
Celltype ThunderSky LFP40
Cells 72 pcs
Charge current 9.5A
Discharge current 30-35A
Starting temperature (-18 C) -10 C / 14 F
End heat +25 C / 77 F
Mass of the batteries n. 115 kg
BMS "Low Tech BMS"
Notes:
  • This was our first measurement and as such, it contains unnecessary spikes and power applied to the battery due to testing and tuning of charge-control.
  • About 7.3 kWh came out (calculated capacity around 8.9 kWh)
  • Voltage went up when discharged when battery was below 0 C (32 F). In normal situation voltage drops when battery is discharged.
  • When battery was about 0 C (32 F), voltage started to drop.
  • When charge ended, voltage dropped very fast. Voltage drop was about 0.8V / cell.
  • The custom-made BMS we tested, was working fine in low-temperatures.

Low-temperature measurement #2: 25.4.2010

72xLFP30-35A-Discharge-minus17-plus18.png
Celltype ThunderSky LFP40
Cells 72 pcs
Charge 9.5A
Discharge 30-35A
Start temp -17 C (1 F)
End temp +22 C (72 F)
Battery weight n. 115 kg
BMS "Low Tech BMS"
Notes:
  • Battery was charged about two days before discharge so that both voltage and temperature were at constant level before discharge started.
  • Discharge was ended when battery voltage was 180 V.

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