BRP-Rotax
INSTALLATION MANUAL
Formula 3
The sum of the currents from I_BAT and I_Load results in I_28 V and must not exceed
27.9 A:
I_BAT + I_Lad < 27.9 A
Formula 4
I_BAT + I_Load = I_28 V
If I_28 V is greater than 27.9 A, the 28 V output is switched off, as already mentioned at
the beginning. Therefore, the condition from formula 3 must always be fulfilled. The ex-
pected load current I_BAT and the load current I_Load must be calculated by the installer.
Formula 5
Special attention must be paid to the dimensioning of the resistor with regard to the
power dissipation:
P = I
2
*R
Once the battery is charged, the current flow is reduced to a minimum and thus also the
power loss, which is converted into heat.
Example 2 – Calculate power dissipation:
I = 10 A, R_I = 0.89 Ω
From formula 5, the worst-case power dissipation is 89 Watts.
To supply the aircraft with voltage when the AC-DC converter is not active, the accumula-
tor is used. Therefore, it must also be connected to the loads R_L1 and R_L2. Without the
diode D1, the resistor R_I would be bypassed, and a current limitation would no longer ex-
ist. The choice and dimensioning of the diode must be adapted to the individual require-
ments of the aircraft. Parameters like voltage drop, current and cooling must be
considered.
Summary:
By using a series resistor R_I the charging current to the accumulator can be limited.
Feeding the aircraft via the accumulator gate is made possible by a diode which prevents
bridging of the series resistor R_I.
Special attention must be paid to the component dimensioning in order to achieve the de-
sired reliability at these relatively high currents.
Effectivity: 916 i A / C24
Edition 0/Rev. 1
24–00–00
Page 27
December 01 2023
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