Most boats or caravans are equipped with two or more battery banks (starter, consumer or thruster batteries, etc.). How can these batteries be charged with the alternator, without being connected in parallel and without the risk of influencing each other or being discharged at the same time? The solution is to use diodes, which electrically isolate one battery from the other. These devices are suitable for 12 and 24 volt systems, they have 3 outputs and 1 or 2 inputs (for 2 motor systems). The connection is made via 8 mm bolts (including nuts and washers). Due to the isolating diodes, a voltage drop of <0.7 volts is reached. To compensate for this loss of voltage, some alternators or charge controllers have a measuring input. This can be connected to the separating diode terminal "S" (6.3 mm plug).
- version with 1 input, dimensions (WxHxD): 175 x 68 x 135 mm, weight: 1.1 kg
- version with 2 inputs, dimensions (WxHxD): 320 x 68 x 135 mm Weight: 2 kg
Due to the semiconducting properties, a voltage loss of up to 0.7 volts occurs in a current-carrying silicon diode. In practice, this also applies to disconnection diodes.
For example, 14 volts for charging the batteries or for supplying the electrical system, then only 14V - 0,7V = 13,3V is present at the isolating diode output. This is not enough for optimaly charging a battery!
Terminal "S" is the connection of an integrated "compensation diode", which is connected in the forward direction to the connection "S" from the isolating diode input.
The term "compensating diode" is misleading because the actual voltage loss compensation does not take place in the separating diode but in the control circuit of the alternator. But why?
The equalizing diode causes a voltage drop corresponding to that of the high-power diodes (about 0.7 volts). The alternator or the controller is then connected to terminal "S" in such a way that the voltage loss is detected and adjusted by the controller. The Lima output voltage is thus raised by the value of the voltage loss and is then available in its entirety behind the separating diode.
One more note on isolating diodes:
Even if you can compensate for the voltage loss of a cut-off diode, you still have a loss of energy in the form of heat!
Example: Assuming that the isolating diode has a voltage drop of 0.7 volts and the alternator delivers 50 amperes, then a power loss of 0.7V x 50A = 35 watts is produced by the isolating diode.
The separating diode will get hot and heat your boat!
If you want to avoid this, you should think about a low-loss charging current distributor, e.g. Art. 48400 or 48401.
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