Minipulse Plus Rev My time has come!

[godigit1]

Im still learning so im not a expert with the scope yet. But y our wave form in Post #29 doe not look correct Its like your coil is staying charged at shut off. Top of the wave form should be sharp voltage drop.
Also you are looking at the coil flyback. to damp you need to look at the op amp out TP3.
Put both channels up and that way you can see both as you adjust. But tp3 is what you adjust the ringing away from.
1610 ohms seem way high at least for all m y coils it would be. Im damping from 375 to 800 or so depending on the coil.
Try damping to both signals and play with a desired target while you do it that way you can see the effects of over and under damping.

[godigit1]

Ok look at Post # 36 in the thread right below MPP Op amp is vastly improvable.
Thats 3 different op amps Look at the before shots as that is stock MPP. All of these shots are just slightly underdamped as my coil was stable there and got better sensativity.

[green]

Well here are mine readings (this time dumping resistor 1610Ohms)

[ATTACH]45929[/ATTACH]
[ATTACH]45930[/ATTACH]

How do they look??Comparing to the photo you've sent me mine has a steep rising edge with something weird on the top left edge..

Look good. The pictures in reply#22 showed damping adjustment but the Tx current was a lot lower than it should be. Fixed the problem and recorded again, scope probes connected to Tx hot lead and hot lead insulation. Amplifier out is most important. I like looking at coil decay and amplifier out when adjusting damping. Is underdamped, overdamped or critical damped best? Scope probe connected to Tx hot lead can have a small effect on damping so I usually connect the probe to the wire insulation. Also don't have to remember to switch probe to X10.

[mushaba]

... scope probes connected to Tx hot lead and hot lead insulation. Amplifier out is most important. I like looking at coil decay and amplifier out when adjusting damping. Is underdamped, overdamped or critical damped best? Scope probe connected to Tx hot lead can have a small effect on damping so I usually connect the probe to the wire insulation..

What do you mean by hot wire insulation?I measure with score ground to TP5 and probe to R4 (near trimmer side),im confused...

Here is a video as godigit1 said ch1 yellow (probe to R4 trimmer side and ground TP5) and ch2 (probe to TP3 ground TP5)...With 2,2 kohms pot

Also notice on R4 hot side voltages goes up to 600V...I thing im violating irf840 characteristics?

[green]

What do you mean by hot wire insulation?I measure with score ground to TP5 and probe to R4 (near trimmer side),im confused...

Here is a video as godigit1 said ch1 yellow (probe to R4 trimmer side and ground TP5) and ch2 (probe to TP3 ground TP5)...With 2,2 kohms pot

Also notice on R4 hot side voltages goes up to 600V...I thing im violating irf840 characteristics?

Hot wire is the coil wire connected to MUR460 diode. I use twisted pair so it is easy to clip probe to wire coating(insulation). Coax center wire has a thicker coating, might be harder to clip to. Maybe less signal.

I use a 11N50M2 MOSFET rated minimum break down 500V same as IRF840. I get 550V and you get 600V. Don't know how much higher than minimum to expect.

[mushaba]

Hot wire is the coil wire connected to MUR460 diode. I use twisted pair so it is easy to clip probe to wire coating(insulation). Coax center wire has a thicker coating, might be harder to clip to. Maybe less signal.

I use a 11N50M2 MOSFET rated minimum break down 500V same as IRF840. I get 550V and you get 600V. Don't know how much higher than minimum to expect.

Is it ok to have such voltage?George at step 3 I think says we should measure 350V..

[Qiaozhi]

Is it ok to have such voltage?George at step 3 I think says we should measure 350V..

It depends on the coil inductance and resistance, and the TX pulse width. You should avoid letting the flyback voltage exceed the breakdown voltage of the MOSFET as this will waste energy, make the device get hot, and also slow the decay. The value of 350V is just a guide as what to expect for a typical 300uH coil with a TX pulse rate of 1000pps and a pulse width of 100us.

[green]

It depends on the coil inductance and resistance, and the TX pulse width. You should avoid letting the flyback voltage exceed the breakdown voltage of the MOSFET as this will waste energy, make the device get hot, and also slow the decay. The value of 350V is just a guide as what to expect for a typical 300uH coil with a TX pulse rate of 1000pps and a pulse width of 100us.

What do you mean by waste energy? I have thought signal strength is proportional to peak current. A test with .5A and 1A peak Tx current. Damping was adjusted for peak volts to not reach MOS FET break down with .5A peak current. My tester controls Tx current either .5A constant current or 1A constant rate. Think double the signal with 1A peak is due to double current not constant rate vs constant current. One way to keep peak Tx below break down is to limit current to (break down volts/damping resistor). Any other ways? Someone posted in another thread awhile back, time at breakdown doesn't effect signal strength. My test shows different, am I doing something wrong?

[Qiaozhi]

What do you mean by waste energy? I have thought signal strength is proportional to peak current. A test with .5A and 1A peak Tx current. Damping was adjusted for peak volts to not reach MOS FET break down with .5A peak current. My tester controls Tx current either .5A constant current or 1A constant rate. Think double the signal with 1A peak is due to double current not constant rate vs constant current. One way to keep peak Tx below break down is to limit current to (break down volts/damping resistor). Any other ways? Someone posted in another thread awhile back, time at breakdown doesn't effect signal strength. My test shows different, am I doing something wrong?

When the MOSFET is switched off, you want the all the energy stored in the coil to contribute to the collapsing field and provide maximum energy transfer to the target(s). If you exceed the MOSFET breakdown voltage then some of that stored energy will be dissipated (wasted) within the MOSFET. So, if your MOSFET has a breakdown voltage of 500V, keep the flyback below that figure.

[Qiaozhi]

Here's a document that explains the full story:
https://www.google.co.uk/url?sa=t&rc...5I3XmybeWc9I8Z

[green]

When the MOSFET is switched off, you want the all the energy stored in the coil to contribute to the collapsing field and provide maximum energy transfer to the target(s). If you exceed the MOSFET breakdown voltage then some of that stored energy will be dissipated (wasted) within the MOSFET. So, if your MOSFET has a breakdown voltage of 500V, keep the flyback below that figure.

Still not sure your definition of waste. Did a search and one definition is serves no purpose.

Someone posted in another thread awhile back, time at avalanche doesn't effect signal strength.

I could read your statement that energy dissipated at avalanche is wasted(serves no purpose) and doesn't add to signal strength confirming the posted statement. Is that what you mean? Not suggesting operating at avalanche is ok, just thinking it's not wasted energy.
Avalanche current does go through the battery so it does increase average battery current. If I did the math correct at(1000 pulses/second). Average coil current is 100ma and avalanche current adds less than .5ma to battery current in my example(damping adjust3).

[dbanner]

I think instead of waste, I prefer the phrase "less efficient". I think an examination of the data sheet for particular MOSFET(or some other document) ought to yield some interesting information on operation in avalanche. All those fancy graphs on data sheets, which I never like to read. Too difficult for me. Unnecessary power dissipation by way of heat in MOSFET(wasted energy). Not unlike overdriven transistors, but " overvolting" MOSFETS.
Hey, now that's a sexy term.
The flyback voltage may not only be related to TX current.( Just a hunch) but how quickly is she switched off(zero), making way for the collapsing field.

[mushaba]

Quick question about basket or 3dss coil:the building instructions I found reffers on 0.63mm (awg 22) wire diameter,30 full turns.how can I use 0.4mm(awg26) without messing the coils specs?

[dbanner]

It doesn't matter that much between 0.4 and0.63
Your coil parameters will be OK. I know because I made several basket 3dss using 0.4 and all working very good.
Use same number of turns.
I stopped making them because they are pain to wind.
Pay attention to keeping count as it is easy to forget how many turns you have when focusing on winding in out in out, well you know.

[mushaba]

It doesn't matter that much between 0.4 and0.63
Your coil parameters will be OK. I know because I made several basket 3dss using 0.4 and all working very good.
Use same number of turns.
I stopped making them because they are pain to wind.
Pay attention to keeping count as it is easy to forget how many turns you have when focusing on winding in out in out, well you know.

Well,yes they are a pain to wind them but they are well speced..My first test coil I have in my videos I never successfully shielded it,the shield always dicreased the detecting depth...Also I'm thinking a spiral wind with 0.5mm coil wire,I will engrave the pattern on PE plastic and fit the cable,I will have to adjust the space between the spirals to get as low capacitance as I can..