Hi -
I have an issue on a boat I'm working on, where what I assume is a high voltage surge is causing a radar to momentarily lose its picture. It happens when a 12vdc solenoid is switched off. I'm trying to find an appropriate snubber/suppressor to fix this problem, but I don't know what I need.
The solenoid draws about 1.5 amps when energized.
Thanks for any help with this...
Gary

 

Welcome to AAC.

Since it's 12 volts, any solenoid or relay can be snubbed with a diode. Give me five and I'll post a schematic.

 

Didn't draw in a switch. Use your imagination. When +12V is cut off (via switch or any other means) the coil, which is loaded with stored magnetic energy, will flash a much higher voltage than 12V. The diode absorbs that flash. Note that the current can not flow from the battery through the diode. Roughly explained, imagine a spinning wheel (coil and diode). When you shut power off the wheel wants to continue to spin for a few seconds. Without the diode ALL that spinning energy goes back through the electrical system.

 

Thanks for that. In this example, that energy is then shunted to ground? I didn't explain the wiring...the switch is in series with the Positive wire and the negative is not switched. Is the flashed higher voltage sent back on the ground side?
Really appreciate your help

Didn't draw in a switch. Use your imagination. When +12V is cut off (via switch or any other means) the coil, which is loaded with stored magnetic energy, will flash a much higher voltage than 12V. The diode absorbs that flash. Note that the current can not flow from the battery through the diode. Roughly explained, imagine a spinning wheel (coil and diode). When you shut power off the wheel wants to continue to spin for a few seconds. Without the diode ALL that spinning energy goes back through the electrical system.
View attachment 233520

 

The switch off inductive kick (collapsing magnetic field) energy is dumped into the diode. The normal voltage polarity from the DC voltage source (like a battery) makes the diode an open (non-conductor of current) circuit path. The switch off voltage produced from the stored energy in the coil is the opposite voltage polarity causing the diode circuit path to short (conduct current) as a resistive energy dump (energy converted to heat). This stops that energy from being shunted into the wiring.

 

Thanks again. After watching the video it makes sense.

 

One last question ....does it matter where i put the diode as long as its between the solenoid and the switch (in parallel with the solenoid)? It will be far easier to install it in the terminal strip in the wheelhouse, rather than down in the engineroom 50 feet away as the terminals are heatshrunk down in the engineroom.

 

does it matter where i put the diode as long as its between the solenoid and the switch (in parallel with the solenoid)

It can. You don't want a fast rising 300V pulse on a 10V wire, do you? It could radiate and disrupt a microprocessor through radiation. The closer tot he coil, the better.