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OverUnity Research > Benches > Peterae (Moderator: Peterae) > Controller No5 With Protection - Looking for Explosions
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Author Topic: Controller No5 With Protection - Looking for Explosions  (Read 208120 times)
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Re: Controller No5 With Protection - Looking for Explosions « Reply #225 on: 2016-12-02, 16:35:49 »

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I used a dual spark gap into an air-core Brooks-wound coil, with 10kv DC pulses (arbitrary pulse rate, free-running) and instead of crackling, I got very loud sounds like a rifle crack.  There was no flash, just the loud crack sound.

The lack of sync between channels may be why you are getting any crackling at all.  Similar to Peter's use of white noise.
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #226 on: 2016-12-02, 20:08:02 »

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Thanks Grumpy,   sounds impressive.

I at the moment still use a similar setup as Peter with 2 white noise generators.

Itsu
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #227 on: 2016-12-02, 20:10:45 »

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Some further tests, with a starting voltage of 25.19V (2x 12V batteries in series) on the drains.

First the electret mic. test, which only reveals similar crackling sounds as emitting from the coil / magnets, so no howling.
I tried with both coils (so with and without a center loop wire) and with 24V from the  batteries as well as with the 41V from the PS (last one not on video).


Then i tried to measure / show the current through 1 of the MOSFETs.
It shows that the current flows the normal way from drain to source.
Current controller was set to 5A/Div. and the voltage on the MOSFETs was reduced to 12.5V only (single battery), see screenshot 1.
Screenshot 2 is both voltage (yellow) over drain / source and current through (green).


Video here:   https://www.youtube.com/watch?v=yyEAJqV4u7g

Next i will use some different pickup probes to show the different signals.


Itsu
« Last Edit: 2016-12-02, 21:15:45 by Itsu »
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #228 on: 2016-12-02, 21:00:23 »

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I used 3 probes with different sensors to sample the crackling noise.
41V on the drains.

Yellow is a probe with a 120K resistor
Blue is a probe with a shorted loop
purple is a probe with a ferrite bead with 22 turns of thin copper wire

Itsu
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #229 on: 2016-12-02, 21:04:28 »

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Just to clarify Itsu in your last post are you AC or DC coupling on your scope setting.

and maybe a zoom in on the timebase to look at the purple chan oscillations.
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #230 on: 2016-12-02, 21:23:53 »

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Peter,

all are DC coupled.

See screenshot for a zoomed in picture of the purple trace (ferrite bead)

Itsu
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #231 on: 2016-12-02, 22:17:59 »

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Quote from: Itsu on 2016-12-02, 21:23:53
Peter,

all are DC coupled.

See screenshot for a zoomed in picture of the purple trace (ferrite bead)

Itsu
Thanks Itsu  O0
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #232 on: 2016-12-03, 20:11:43 »

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The series batteries measured 25.16V today, so we did loose some charge (0.3V) compared with yesterday. 


Measuring the outputs of the white noise generators (Pics) after the high pass filter going into the dual MOSFET driver (blue and purple), together with the MOSFETs drain signals (yellow and green).

First screenshot is without crackling, second screenshot is with crackling.

Itsu
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #233 on: 2016-12-03, 20:28:03 »

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Same as above, but now measuring the gates (blue and purple) together again with the drains (yellow and green).

first screenshot without crackling, second screenshot with crackling.

To be noticed is that without crackling, all lines are flat (drains on drain voltage), so also the gates.
To me this means that the crackling selection (when the crackling occurres) is being done by the MOSFET driver, not the MOSFETs itself, right?

itsu
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #234 on: 2016-12-04, 21:02:46 »

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I thought that the PICs are generating noise continuously - even when the coil is not crackling, so why is there no sign of that noise on the no-crackling scopeshots ?
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #235 on: 2016-12-04, 21:41:29 »

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Quote
I thought that the PICs are generating noise continuously - even when the coil is not crackling

correct, and as can be seen in upper scopeshot of post #232, we DO have noise coming out of the Pic's continuously, see blue and purple traces.
But this noise coming out of the Pic's (after the high pass filter) and fed into the ixdd604 dual MOSFET driver does NOT come out continuously, from this driver,
see blue and purple traces of upper scopeshot of post #233.

So therfor my question in post #233:
Quote
To me this means that the crackling selection (when the crackling occurres) is being done by the MOSFET driver, not the MOSFETs itself, right?


Itsu
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #236 on: 2016-12-04, 21:53:46 »

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Something strange going on then, there should be whitenoise all the time going into the fet driver and into the fet gate but the crackling is random but constant.
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #237 on: 2016-12-04, 22:06:02 »

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When you look at the upper scopeshot of post #232 to the blue and purple traces (white noise output after the high pass filter) you can see
that the signal levels are mostly below the zero lines.

So could it be that the high pass filter is causing this so that the IXDD604 dual MOSFET driver is getting a to low (normal noise) signal and not amplify it?
Only when a certain combination of noise occurres it gets above this threshold (see lower scopeshot of post #232) and then amplifies the signal to the gates.


Itsu
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #238 on: 2016-12-05, 15:20:21 »

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Here i zoomed in on the signals before the high pass filter and after (high pass filter sits between the white noise Pic's and the IXDD604 dual MOSFET driver).

We can clearly see that the HP filter is leveling the signal so only half of its amplitude is above ground, which probably is too less for the IXDD604.

Blue is BEFORE HP filter, purple AFTER HP filter.


Itsu
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #239 on: 2016-12-05, 15:29:49 »

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These are the same signals (with higher vertical setting) but now when crackling occurres.

This must be some kind of feedback as there is no way these Pic's can generate these kind of signals.
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #240 on: 2016-12-05, 15:42:36 »

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How far are the Pic's from the switching devices?
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #241 on: 2016-12-05, 16:08:38 »

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See this physical layout of the used PCB, red are the Pic's, green the both MOSFETs, so about 2cm apart.

itsu
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #242 on: 2016-12-05, 16:16:29 »

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Concerning the quality of the white noise generated by the Pic's, see the screenshot where blue is the signal coming from one of the Pic's, compared to purple which is
the white noise signal generated by my FG (5Vpp, 2V offset).


The purple looks to me really like a white noise signal, while the blue signal more looks like a FM modulated signal.

Itsu
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #243 on: 2016-12-05, 19:10:49 »

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Scope the power rails across the pic when crackling happens, this looks like power rail noise to me, if so you need a high quality 10nF & 100nF in parallel across the pic rail.
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #244 on: 2016-12-05, 20:42:29 »

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Hi Peter,

yes, i guess you are right, but after adding wima 10nF caps parallel to the existing 100nF caps across the Pic's supply, i still have heavy spikes on that 5V rail, see screenshot.
There is not much room to add additional chokes / caps there, so i might need to rebuild the setup to get it quiet.

Itsu
 
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #245 on: 2016-12-05, 22:13:07 »

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In the below video i removed the MOSFETs drain voltage and just run the Pic's and MOSFET driver.

I monitor with the yellow and green probes the continuous white noise outputs from the Pic's before the high pass filters and with
the blue and purple probes the signals on the gates of the MOSFETs (without any drain voltage on).

We still see the crackling (sort of) occure, but because the MOSFETs are down they cannot push it through to the coils.

To me this means that the decision when the crackling happens is being made by the MOSFET driver when it receives a certain combination of signals from the Pic's.

Video here:  https://www.youtube.com/watch?v=KuFZBqQnHjk

Screenshot shows a possible trigger combination.


Itsu
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #246 on: 2016-12-06, 01:00:11 »

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Is your driver a dual driver on one chip?
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #247 on: 2016-12-06, 09:38:07 »

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correct, i followed Peters original design which uses an IXDD604 dual MOSFET driver chip.
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #248 on: 2016-12-06, 21:46:54 »

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I removed the both Pic's and used my dual channel FG to feed white noise (5Vpp, 1.5V offset) to the both MOSFET driver inputs via a 50 Ohm series resistor.

There seem to be some (thermal?) runaway condition happening as (with no drain voltage on the MOSFETs), gradually the current into the PCB (driver only) increases untill its that hot i can smell it.

Same when also putting on the drain voltage on the MOSFETs, gradually the current through the MOSFETs increase untill i stop it.

I think the circuit is missing some kind of MOSFET driver output / MOSFET gate clamping (10K to ground and / or zeners).

I will add that tomorrow to see if it stabilize it.

Itsu
   
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Re: Controller No5 With Protection - Looking for Explosions « Reply #249 on: 2016-12-07, 01:02:46 »

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Spherics said that output snubber circuits were required for the mosfet drive he proposed.

attached are the docs that reference his snubber
   
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