Anyone have experience installing diodes in 12Vdc systems?

[Kenneth K]

I need to add two diodes each to two simple 12vdc circuits for a bilge pump warning panel but don't know how to spec the diodes.

For the first circuit, a sender wire is connected to the positive (activation) side of each bilge pump. Each sender wire is connected to the same LED, which should illuminate when either pump comes on. Without diodes, the sender wires will cause the second pump to be activated (through the sender wire) when the first pump illuminates the LED. This would cause a ~3amp draw through the sender wires and LED (yeah, but only once, right?).


For the second circuit, each bilge pump switch is factory wired with an "alarm" wire that energizes if the pump runs longer than 2 minutes. I want to connect each alarm wire to a single piezo buzzer. Without diodes, an alarm signal from one switch would backfeed voltage to the alarm circuit of the second switch. The mfg says this is to be avoided.


Both the buzzer and the LED have small draws, likely <10mA each, but both will have long 16-18ga wire runs to power them.

Does anyone know the proper diode specs for such an application? Do I need different specs for each case?

Thanks.

 

[shard7]

You're on the right track here.

Rectifier diodes behave very similarly, with the only difference being how much current they can handle, and their breakdown voltage (usually hundreds of volts, so not a concern). They have a forward drop of around 0.7v.

10mA is not much, and even the smaller ones such as 1N4001 are usually rated for 1A. However, those typically have very thin leads that might be a problem if not secured to a circuit board, so something with a 3A rating (e.g. 1N5400) might be advisable just because it's thicker leads will be better suited for use in a wiring harness.

In your diagrams the outputs of both diodes should be connected together, and then fed to the single positive connection on the LED or buzzer (negative connection to ground/battery-).

 

[Kenneth K]

something with a 3A rating (e.g. 1N5400) might be advisable just because it's thicker leads will be better suited for use in a wiring harness.

Great. Thank you.