Re: [TCML] The Hammertone Predikter

[DC Cox <resonance@xxxxxxxxxxxx>]

Finn:

I ran the numbers on your latest info.  It works out to a 26.3 degree phase
angle.  That's not zero crossing switching.

The phase angle only gives you approx 1/3rd of your current.

If you adjust the turns ratio on your gate drive transformer you get rid of
98% of the overshoot.  At present your are operating slightly above the
"knee" curve for the particular ferrite core you are using, which usually
causes overheating of IGBTs.  If you can borrow an infared thermal camera
you can check the temps while it's running, or just use some thermisters to
check it.

The CM600s are very rugged and will handle it ---- for awhile.  Try either
adding or removing 1-2 turns and this usually gets you right on the knee.

Not complaining on your nice work --- but, just trying to help.  Play with
the gate drive ratios and you will kill the overshoot.

Dr. Resonance










On Mon, Jun 29, 2009 at 7:56 AM, Finn Hammer <f-h@xxxx> wrote:

> piranha skrev:
>
>> Hi,
>>
>> I worked some equations for telling the amplitudes, phase angles and times
>> of the predikters prediktions here:
>>
>> http://team-titanium.com/Predikter-2.jpg
>>
>> Trivial circuit theory, but had to wake up a LOT(!!!) of old brain cells
>> there !*:D
>>
>
> Trivial to you sir, perhaps. But to me out of reach.
>
>
>> You could do a lot of "S" domain stuff, but MicroSim does it easier.  But
>> this allows one to just to punch the stuff into a calculator.
>>
>
> Microsim is my friend, as you saw on the video.
>
>
>> It would be interesting to do ring ups and all to find the phase error.
>>  At least to see which way to select the components to minimize it.  Also to
>> pump in some faults to see how the circuit performs.  But it all looks "just
>> fine" really...
>>
>
> Are you saying that the delay changes with amplitude? Richie said something
> to that effect too.
> Time to review this video which shows delay with current changed from 50A
> to 500A:
> http://www.youtube.com/watch?v=nLcSoo3LcME
> Looks to me like the feedback remains constant.
> What I demonstrated was really like a *condensed* ringup.
>
>
>> May be adding a cap or something could take it to second order to give a
>> more uniform frequency response Prediktion??
>>
>
> A flat response from unloaded coil (start breakout) till final streamer
> loaded frequency would be nice.
> A predikter box that can go from coil to coil? Flat response from 20kHz to
> 300kHz?
>
> Perhaps not high on the wish list. For one reason is that I would like to
> match the output from the current transformers to the input of the front end
> comparator.
> It takes rail to rail, in my case +-15V.
> But if the burden resistor changes then the inductor changes too. There is
> heat in the burden resistor to account for too.
>
> My approach is this:
> Estimate max current. From this calculate sensitivity of current
> transformer.
> Then select burden resistor with regard to Irms heating.
> From this, select transformer turns count.
> select an inductor with 40% reactance of burden resistor.
> This could be smaller with smaller delays, so I am scrapping the opto愀
>
> It is not very scientific, and I still have a problem ending up with a
> combo that exactly matches Vin of comp, but that should be easy, really.
>
>
>>
>> MicroSim, equations, scope pictures, real working coils!!!! - It might
>> actually work!!!  :D  :D  :D
>>
>>
> Might?
> Anyway, If there are tests that I can do to confirm theory, let me know.
>
> Coil is changing fast. Many things to try.
> The fancy current source drivers got the boot today. They had one design
> flaw, and a major one: If I loose power, they turn gate on. Not good.
> So now I am building intermediate H-Bridge with a 4:1 step down ratio for
> the gates.
> This should work well, and at least on Daniels medium sized coil it worked
> well, and it is something I want to try,
> Back to big gate transformers.
>
> Terry
>>
>> Sorry about the too little or too much pic resolutions...  It's late here
>> ;)
>>
>
> No problem. We扉e got 25Mb/25Mb fiber.
>
> Cheers, Finn Hammer
>
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