IB Rx coil at Tx off

[Altra]

Nice job on your coil windings. A snubber could be used to absorb the flyback energy. See attached schematic of one I have been using. It will help keep the mosfet and damping resistor from running hot.

[green]

Thanks for the snubber suggestion. I would like snub the volts closer to 400V. Not sure what to look for when selecting capacitor and Zener.

Including a simulation of DD coil with 3.6A at Tx off, snubbing at 100, 200 and 400V. Higher Rx signal with faster decay if simulation is correct. Increasing Tx on time would increase peak current to 4A or greater.

[ZED]

Hello Altra

May i ask as to why you are using a 330uf electro as apposed to a smaller size.

[Altra]

Hello Altra

May i ask as to why you are using a 330uf electro as apposed to a smaller size.

Hi Zed, the 330uf was something I had that was rated at 200v. I later ordered in some 100uf, 68uf and 47uf. Test showed below 100uf and the regulation began to change. I would be interested in your thoughts, also I have seen motor driver circuits using series RC snubbers with small value high voltage capacitors.

[Altra]

Thanks for the snubber suggestion. I would like snub the volts closer to 400V. Not sure what to look for when selecting capacitor and Zener.

One thing you can do in your snubber experiments is put the zeners in series. There is a US ebay seller, I believe has some 5w 190v zener diodes. 400v electrolytic capacitors are common, but large. As far as network power dissipation not sure what wattage ratings your components would require.


Ebay zeners
https://www.ebay.com/itm/2-pcs-1N53x...0AAOSwzhxa7h7O

[green]

Trying to understand the snubber reply #61 https://www.geotech1.com/forums/atta...4&d=1592848256. My DD Tx coil, 665uH 4A peak at turnoff. Use (4)1N5378B in series for 400V clamp. 470R resistor in series prevents Zener's from clamping at 400V at 4A. Spec sheet lists impedance, 90 ohms @ 12ma so probably wouldn't clamp at 400V if series resistor is zero ohms. Capacitor is the clamp. If I did the math correct for an ideal capacitor, voltage across a 100uF capacitor would increase 10.3V each time Tx turns off. Would work if capacitor was ideal, don't know about electrolytic capacitors. Anyone know what would happen using electrolytic capacitors?

[Altra]

You do not want to use your electrolytic at it's max rated voltage. No room for error. If you need exactly a 400v snubber look for a 600v capacitor. I was thinking 2 series 190V zener gives you a close 380v shunt regulator, with a 20v buffer for the capacitor. I can't debate your calculations, the circuit I posted works fine at 180 volts. By the way be careful there is a real shock hazard. I can verify.

[Altra]

Green have a look at this useful video. Using series RC in parallel with the switch. I going to play around with the calculations see if it can be used. The demo video uses a large inductance of 500mH. If we rework it for a sub 1mH inductance the capacitors values should also be reduced. Plus add isolation diodes.

https://www.youtube.com/watch?v=wgNMepGIrTk

[green]

Green have a look at this useful video. Using series RC in parallel with the switch. I going to play around with the calculations see if it can be used. The demo video uses a large inductance of 500mH. If we rework it for a sub 1mH inductance the capacitors values should also be reduced. Plus add isolation diodes.

https://www.youtube.com/watch?v=wgNMepGIrTk

Thanks, tried his circuit in spice with 63V aluminum capacitor. Aluminum capacitor seemed alright. If I allowed 20V rise, capacitance would be 27uF instead of 100uF for a 10V rise.

[ZED]

Hi Zed, the 330uf was something I had that was rated at 200v. I later ordered in some 100uf, 68uf and 47uf. Test showed below 100uf and the regulation began to change. I would be interested in your thoughts, also I have seen motor driver circuits using series RC snubbers with small value high voltage capacitors.

Altra i use the same circuit except different values,i use a 1.8uf 250v PP cap and 2r series resistor with the 180v zener,when i run higher TX currents it all gets very hot when the ambient temperature is around 35 C or 100 F.
Larger caps slow the startup times of the detector so i always went for small caps,i was curious as to whether a larger cap would keep things a little cooler.

[Altra]

Altra i use the same circuit except different values,i use a 1.8uf 250v PP cap and 2r series resistor with the 180v zener,when i run higher TX currents it all gets very hot when the ambient temperature is around 35 C or 100 F.
Larger caps slow the startup times of the detector so i always went for small caps,i was curious as to whether a larger cap would keep things a little cooler.

With a 180uS pulse at 7v into a commander mono, it runs warm to the touch(zener,R). But you opened my eyes to using a lower R value. When I tried different value caps, I left the 470 ohm in place. There is a time delay on power up. It's not that long, plus it builds from 0v to 180v and not going to fry your preamp gates. When I get some time, I'm going to look for a combination values that lower the foot print and not get hot. Thanks for your input.

[green]

Coil power(watts)at Tx off=peak current*peak current*coil inductance*Tx pps/2. Damping R, input R if mono coil and snubber dissipate the power. If no snubber, MOSFET avalanche, damping R and input R if mono coil dissipate the power.

[green]

Taped the 30inch DD together and connected Rx to amplifier in. Tx 1A peak. Not shielded yet but looks like it might work. CH2 should be hot lead insulation.

[green]

Tried a snubber in spice. The storage capacitor can be alot less than I was thinking. Not sure why yet. Maybe thinking wrong or something wrong with the simulation.

Was thinking wrong.

[Carl-NC]

Tried a snubber in spice. The storage capacitor can be alot less than I was thinking. Not sure why yet. Maybe thinking wrong or something wrong with the simulation.

Was thinking wrong.

The peak energy in the inductor is . That same energy dumped onto the cap is . Use the expected flyback voltage for V and solve for C. Typically it will be in the 10nF range.