Rosemary Ainslie circuit demonstration on Saturday March 12th 2011

[Sprocket]

@Rosemary - Thanks for the info. Yes, I am definitely thinking of specific applications as well, hence my reason for wanting a 'real-world' heater element.  I presumed that the one you were using was somewhat specialised as it seemed fairly low-power - most of the heater elements I've googled were in the 2-4KW range.  Since any garden-variety should do, I'll probably source one locally.

@neptune - that certainly describes my pulse-generator, simple - just pulses, nothing else, and definitely no offset option.  I've been threatening to get a decent function-generator for years but inconveniences like eating/beer etc. always seem to win out!  And recently one of the channels went in my scope.  I finally managed to trace the fault, but the needed i.c. (UB1202AM) has been relegated to the status of "obsolete stock" so it's gonna take mucho deneros if I opt to fix it - most US firms will only sell wholesale and don't even respond to emails, but I managed to find a Chinese supplier who will sell me a minimum of 5 for $10 each, so we're talking at least 100 bucks. The function-generator will have to wait for another while.  As for the 555 circuit, I'm sure I will be able to scare up something to generate the required waveform without too much difficulty.

[Magluvin]

Hey Woops

I stuck us in the Tesla Igniter thread as it is appropriate and this is Roses deal here and the cap shorting is getting away from mine and her discussions. Shorting the cap is just putting direct source across the inductor, thus more voltage seen, and more current seen. ;]   The idea though is on the same lines with the flywheel effect.

You can check us out over there Rose. =]  Always welcome. And I have another treat for ya. Its a way to use 1 energy 2 times, well almost 2 times. Very simple.  ;]

Mags

[cHeeseburger]

On a different subject, but related, is another observation that I think is worth considering.  Seems we have all in the past (self included) assumed that the current in the shunt represents the current in the battery.  To and from, as it were.  This would certainly be the case under a DC analysis, where the MOSFET gate is correctly considered an open circuit without current flow.

At a frequency of 1.5MHz and each MOSFET having (from the data sheet) 2800pF of capacitance from Gate to Source, with five in parallel that is 14nF or 0.014 microfarads  which is substantial.  We see the 1.5MHz oscillations appear on the gate voltage traces in Rosemary's scope shots. 

Here I forgot to mention that the very large narrow spikes we see in all the shunt current traces all correspond to the switching pulses from the pulse generator charging and discharging the gate capacitance through the shunt.

The shunt inductance enlarges these spikes.  They are confined to the gate-source current loop and thus do not appear in the actual battery current.

To obtain an accurate waveform and measure of the battery current ONLY, I would recommend highly that a Kelvin-sensing shunt of extremely low inductance be used, placed on the battery minus side of the common ground point (rather than on the MOSFET source side).

Such a shunt can be easily fabricated in a few minutes for about $5.00 US.  See the picture below for the details.

Kindest regards,

Bryan

CHeeseburger

[hartiberlin]

Hi  Hartiberlin

in response to your inquiry on youtube

hope i have undesrtood your mind

http://www.youtube.com/watch?v=RQFD1cDlEUU

good luck at all

Laurent

Okay, thanks,
but I meant , what would happen,
if you pulse the power supply
to the circuit, not shorting the capacitor.

Anyway, as you did it looks good and you
could use a incandescent lamp like
a 12 Volts 10 Watts Halogen lamp
in series with your switch when you short out the cap,
then this lamp will light up.

P.S: I will move this Forward EMF discussion postings to a different
thread, as it does not apply to the Rosemary circuit..
Regards, STefan.

[hartiberlin]

Here I forgot to mention that the very large narrow spikes we see in all the shunt current traces all correspond to the switching pulses from the pulse generator charging and discharging the gate capacitance through the shunt.

The shunt inductance enlarges these spikes.  They are confined to the gate-source current loop and thus do not appear in the actual battery current.

CHeeseburger

Yes, through the switching of the function generator
additional energy can be flown into the circuit via the
Gate Source and Gate Drain capacitances.

So it will be wise to just use a negative DC power
supply on the Gates to start and keep the oscillations.