MPP revE need help

[waltr]

Hi waltr thank you for the trick do I need 2w resistor or a 1/4w will be sufficient ?

dbanner i bought a 100x probe but with covid-19 i don't know when i will be delivered ....


6666 this is like chinese for me i'm just starting electronic projects

I little bit of math will tell you what Wattage resistor is needed.

Ohm's Law: E = I*R or I = E/R
Power = I*E = E*E/R

Say you expect 300V so 500*500/10100 = 2.47W peak.

But the flyback is low duty cycle. Say 10usec in a 2msec period (500Hz pulse rate). so 0.00001/0.002 = 0.005% duty.
So total Wattage is duty * peak = 2.47W * 0.005 = 0.012 W average.

[6666]

Hi waltr thank you for the trick do I need 2w resistor or a 1/4w will be sufficient ?

dbanner i bought a 100x probe but with covid-19 i don't know when i will be delivered ....


6666 this is like chinese for me i'm just starting electronic projects

its just a voltage divider across the coil, like what waltr was talking about

[dbanner]

Those high voltage probes are about worthless for measuring the flyback Voltage since they will only work for DC (or AC IF low freq (50-60Hz and Sinusoid).

A scope is required to measure the PEAK flyback Voltage since this only lasts for usec and repeats at higher frequency than an AC rms meter can measure. A simple resistor Voltage divider and O'scope works fine.

Yes, I saw that the flyback voltage on the old TV's were rectified, so it's DC. Those probes would indeed be useless.

And since the peak only lasts for a few microseconds, then an O'scope is necessary.

[Albdelafar]

What I do to measure the Flyback voltage is build a 100:1 resistor Voltage divider then use a 10x scope probe.
A 100k:1k resistor divider is close, 101:1, and good enough.
Simply multiply Scope Voltage measurement by 101 to get flyback Voltage.

Hi waltr thank you for the trick do I need 2w resistor or a 1/4w will be sufficient ?

dbanner i bought a 100x probe but with covid-19 i don't know when i will be delivered ....


6666 this is like chinese for me i'm just starting electronic projects

[waltr]

Those high voltage probes are about worthless for measuring the flyback Voltage since they will only work for DC (or AC IF low freq (50-60Hz and Sinusoid).

A scope is required to measure the PEAK flyback Voltage since this only lasts for usec and repeats at higher frequency than an AC rms meter can measure. A simple resistor Voltage divider and O'scope works fine.

[6666]

This works fine

[dbanner]

Now I know the flyback pulses are different in a PI, but perhaps a circuit can be designed that would take care of this. Maybe using software.

[dbanner]

I often wondered if there was a quick and easy way to check the flyback voltage without having to use an oscilloscope with a high voltage probe.

Then I remembered TV repair tech guys using a gizmo to measure the high voltage on a TV bulb (CRT).

Maybe a similar thing could be used without much hassle.

A high voltage probe project would be nice for diy's.

[waltr]

What I do to measure the Flyback voltage is build a 100:1 resistor Voltage divider then use a 10x scope probe.
A 100k:1k resistor divider is close, 101:1, and good enough.
Simply multiply Scope Voltage measurement by 101 to get flyback Voltage.

[Albdelafar]

I see these videos it's a great job!! I did all the steps and my timings was good my periodic pulses width etc... was as described in the instruction manual, but my detector works very poorly. I'm waiting for the resisters to replace my potentiometer used as a damping resistance, I hope this will help me solve my problem.
I bought graphene powder to protect my coil, but for now I just put aluminum foil on it and I don't get any improvement.
I can't read my Flyback voltage spike too. My oscilloscope is rated for 42V max and I use a 10X probe do you think a higher voltage than 420V could be the problem? I'm not used to using an oscilloscope i'm sorry if my questions seem stupid.
Thanks for the help!!
Alban

[surfdetector]

Hello Albdelafar ,

I have posted on my YouTube channel thus far 8 of the steps in the MPP Rev E build that I have done. Tomorrow I will finish up with step #9 and I will post a short video also of that. My channel on YouTube is https://www.youtube.com/channel/UC52...QYGxT8ryMZc1Uw

I hope that the videos will help those who might be like myself .........new to the DIY electronics metal detector kit building.

Cheers

[Albdelafar]

Thank you surfdetector !!
I read many posts on the forum and i found this video

https://www.youtube.com/watch?v=OyS8sfv0XJ0&list=WL&index=18&t=0s

It's for rev-D but i think it could help beginner to understand what they have to expect. Perhaps someone could add it in the MPP rev-E subject ?


So as you can see my signal is not really similar i don't know why ... I finished all the step and my detector work but not really good. I need to shield my coil and adjust my damping resistor.
Please can someone explain me why my signal is different than surfdetector signal ?

[surfdetector]

Hello I did a new test today with my new coil and my 680ohm potentiometer used as damping resistor.I know it is not a good idea but I have nothing else to do it?.
I bought resistors online yesterday with a new o'scope and a 100x probe but I have more than a month to be delivered?.
So I will try like that and if it burns it doesn't matter.
So I read my signal in TP3 with a can of soda and that's what I see at 0.2 V / div (10x probe) and 20us time / div.
Can you please confirm that the signal corresponds to what is expected ?
Thank you !!
Alban
[ATTACH]49777[/ATTACH]
[ATTACH]49778[/ATTACH]

Hello,

I just posted a short video of the oscilloscope image that I get for Step #5 of the project.

https://youtu.be/zQ_1E68n8eo

Cheers

[Albdelafar]

The coil is a mono coil with 25 turn of 1mm coper enameled wire witha a radius of 125mm.
That give me a 413uH with the coil calculator.

[surfdetector]

Hello I did a new test today with my new coil and my 680ohm potentiometer used as damping resistor.I know it is not a good idea but I have nothing else to do it….
I bought resistors online yesterday with a new o'scope and a 100x probe but I have more than a month to be delivered….
So I will try like that and if it burns it doesn't matter.
So I read my signal in TP3 with a can of soda and that's what I see at 0.2 V / div (10x probe) and 20us time / div.
Can you please confirm that the signal corresponds to what is expected ?
Thank you !!
Alban
[ATTACH]49777[/ATTACH]
[ATTACH]49778[/ATTACH]

Hello,

You mention that you have a new coil. What are the specifications of the new coil? Thanks.