Battery Management System

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Write a caption30-Mar-2013 19:03, SAMSUNG SCH-I535, 2.6, 3.7mm, 0.05 sec, ISO 125
 
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Write a caption30-Mar-2013 18:51, SAMSUNG SCH-I535, 2.6, 3.7mm, 0.059 sec, ISO 125
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Write a caption30-Mar-2013 18:03, SAMSUNG SCH-I535, 2.6, 3.7mm, 0.017 sec, ISO 100
 

Today, we got the temperature harnesses made and hooked up to the battery management system. The BMS uses the temperature and voltage information about each cell to ensure safety of the battery pack during both charging and discharging. The next step will be to cycle the battery pack a few times from fully charged to fully discharged to balance all the cells.

Batteries are In

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Write a caption26-Mar-2013 00:10, SAMSUNG SCH-I535, 2.6, 3.7mm, 0.059 sec, ISO 125
 

Our batteries are finally in. The fiberglass angle extrusion holds the batteries snugly against the I-beam. A little Hysol 120HP holds the fiberglass extrusion to the chassis members. A piece of dense polyurethane foam keeps the batteries from sliding around horizontally. We carefully connected each series pack of 8 cells to the main contactor and ground blocks.

Tesla Waterblock

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Write a caption23-Mar-2013 21:03, SAMSUNG SCH-I535, 2.6, 3.7mm, 0.033 sec, ISO 80
 

Our Tesla came back from EKWB with a waterblock mounted! This is a custom full size waterblock specifically for the K20. It is milled to ensure that it makes proper contact with every chip that needs cooling. One huge advantage over the air cooler is that it makes the card only 1 slot wide. This frees up a PCI-E slot on our motherboard for the parallel port GPIO card.

Epoxy and Microspheres

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Write a caption20-Mar-2013 21:17, SAMSUNG SCH-I535, 2.6, 3.7mm, 0.067 sec, ISO 800
 
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Write a caption20-Mar-2013 20:51, SAMSUNG SCH-I535, 2.6, 3.7mm, 0.067 sec, ISO 125
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Write a caption20-Mar-2013 20:39, SAMSUNG SCH-I535, 2.6, 3.7mm, 0.025 sec, ISO 100
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Write a caption20-Mar-2013 20:30, SAMSUNG SCH-I535, 2.6, 3.7mm, 0.025 sec, ISO 80
 

Yesterday, we used Hysol 9430 two part epoxy and glass microspheres to structurally bond the fiberglass I-beam in the robot. This provides lateral stiffness for the robot. We used the glass microspheres to provide structure to the epoxy. By adding a small fillet between the fiberglass and the side panels of the robot, we significantly increase the strength of the joint.

Low Voltage Cutoff

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Write a caption20-Mar-2013 11:13, OLYMPUS IMAGING CORP. VR325,VR320,D725, 3.9, 6.61mm, 0.1 sec, ISO 125
 

We assembled our low voltage cutoff circuit. This is a small little circuit that monitors the battery pack voltage. If the voltage falls below 22.5V (or ~2.8V per cell), the cutoff circuit will open the contactor and prevent damage to the batteries. We have cutoff set a little bit higher than recommended by the data sheet, but we decided to have a little more safety margin because the battery cells are expensive.

Hi-Pot Testing the DC ATX Power Supply

Hi-Pot Testing

We wanted to use a 750W DC-input ATX power supply from a previous robot built in the lab. Considering the abuse it had taken over the years and the general lack of quality in the PCB, we decided to Hi-Pot test it to 1kV. Unfortunately, the insulation failed somewhere and the PSU did not pass the Hi-Pot test. Time to find a new power supply!