Master Thesis - OUFTI-1

These thermostats were chosen because:
• They have very small dimensions (diameter = 6.68 mm and thickness = 2.04 mm).
• They are lightweight (mass = 0.2 g).
• They are space-qualied (conform to qualication MIL-S-24236/13).
In our case, the selected thermostat is an open-on-rise one. The mechanism of these
thermostats is the following one:
• When the temperature of the batteries passes under 7.2 ◦ C, the thermostats supply
the heaters. This particular value was chosen by the THER subsystem to avoid that
the temperature of the batteries becomes negative. Indeed, the tolerance guaranteed
by the manufacturer is 4.4 ◦ C, and the rst available value above this one is
7.2 ◦ C (4.4 ◦ C is also available but, in this case, the non-negativity of the batteries'
temperature could not be assured at each time).
• They continue until the temperature of the batteries pass above 23.9 ◦ C (± 4.4 ◦ C).
At this moment, the thermostats open the circuit and the heaters are no longer
supplied.
Now, the problem is to determine how many thermostats are necessary to obtain a
reliable control system. Dierent solutions were investigated:
• The rst idea was to use four thermostats per battery. These ones will be connected
2 by 2 in series, and the two parts will be connected in parallel. This solution is
illustrated in Figure 3.12 (where the B stands for Battery, H for Heater and T for
Thermostat).
Figure 3.12: Connection with four thermostats
This solution had to be given up because it is too expensive for this particular application.
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