Kapanadze Cousin - DALLY FREE ENERGY

[Void]

Hi Itsu. I am not sure why I am getting different results now, but I guess maybe
the addition of the 10 uF cap. I will test more later when I get the chance. I thought
about it further, and another thing that is different now is I have two of these snubbers
connected now, but when I tested previously I only had one connected to one of the MOSFETs. 
Not sure yet if that could be a factor at all or not.

It's certainly possible that Schottky diodes could behave differently in this setup. I used the
UF4007 diodes because I already had some available, and they are fast recovery diodes.
The power supply I have been testing with is a bench power supply, and at 12V my test setup is
drawing less than 1 Amp, which shouldn't be a problem for the bench power supply.

Anyway, just wanted to post those new test results for something to watch out for, in case anyone
else was thinking of trying this type of snubber. I still have some more investigating to do to see
if I can figure out why I am getting different results now. The joys of snubbery.

All the best...

[MenofFather]

Now I don't get the high frequency ringing any more, but just a single pulse that is limited [/size]at a lower peak voltage. This is causing diodes D3 and D4 to get hot with V+ set only to 12V. With V+ at 24V it looks like they could well burn.

Maybe try use shottky diodes 40-100 V?

[Void]

Maybe try use shottky diodes 40-100 V?

Hi Menof. Welcome back! Long time no see.

My concern about using Schottky diodes is they typically don't have a very high
reverse voltage rating, and there are voltage spikes on the MOSFET Drains of
250+ volts peak with a power supply voltage of only 12V. This is why I used the
UF4007 diodes, because they have a reverse voltage rating of 1000V, so there should be
no danger of them blowing due to the voltage spikes. The diodes in these non-dissipative snubbers
may not see voltage peaks that high however, so a Schottky diode with a reverse voltage rating
of 100 volts or even less might possibly be ok. I would have to do some voltage measurements
on the diodes with my scope when the PWM driver is running to see what kind of voltage
swings the diodes get on them. 12R06D fast recovery diodes are another option (600V, 12A), but
Schottky diodes with a lower reverse voltage rating may still be ok, and may possibly work even
better than than regular fast recovery diodes in these snubbers.


I disconnected the 10uF at V+, and the Drain waveforms are more similar to what I saw in
my previous testing with some high frequency ringing, but not as much high frequency
ringing as previously. I don't have the two varistors connected in right now however, so they
may have contributed to the more prominent high frequency ringing previously and the lower
spike voltage peaks. Not sure.

With the 10uF cap disconnected from V+, all the diodes in the non-dissipative snubbers
are staying pretty cool however. They have just a little warming to the touch. The 2W resistors
in my series RC snubbers are only getting a little bit warm as well. The MOSFETs are staying
completely cool with only small heat sinks on them. I let the PWM driver run for about 5 minutes
with the 10uF cap disconnected and the non-dissipative snubber diodes and series RC snubber resistors
were only a little warm to the touch after the 5 mnutes. The MOSFETs were still completely cool.
The limited switching pulses were not balanced between my two FETs with the 10uF disconnected,
so not sure why. See the attached scope shot

Putting an electrolytic cap right at the yoke winding center tap point (V+) gives a cleaner and better
spike reduction, but you will need diodes that can handle a higher current than the UF4007
diodes can handle (1 Amp rating). 12R06D diodes or some type of Schottky diodes are a possible choice.

I still haven't tested at 24 volts yet however, but the non-dissipative snubbers may not keep the
spikes below 200V peak with a V+ of 24V. I need to add a better low pass filter setup for my
power supply before I test with 24 VDC. For now though, I think more experimenting with
different component value choices for the non-dissipative snubber might be a good idea to
to try to get even better results before trying with a  V+ of 24V. Without the 10uF cap connected,
the UF4007 diodes only get a bit warm with a V+ of 12V, but they may get too hot if using a
V+ of 24V.  It looks like I may well need to make some component value changes yet in those
non-dissipative snubbers to try to get better results before moving to testing with 24V.

The Allega RCD snubber configuration using around say a 10 Watt ceramic resistor value of 680 Ohms
or 820 Ohms may be less hassle if you don't want to mess around experimenting with different component
values with the non-dissipative snubber, even though the RCD snubber is less efficient...

P.S. I just looked it up and you can get Schottly diodes with quite high reverse voltage ratings and
high current ratings as well, so that might be the way to go since Schottky diodes have a lower
forward voltage drop, so less power consumption than regular diodes. Maybe I will give it a try,
but I would have to order some Schottky diodes first.

All the best...

[NickZ]

  Perhaps a heavy duty snubber system like the one in this video below, may be what is needed to deal with the heat on the resistors.
  Itsu, notice the 47 and 56 ohm white ceramic resistors in the video, same values as what I had on.
I can't tell what the blue caps are. I'd need Hoppy's magnifier for that, or someone that can understand what he's saying about those blue caps.
  https://www.youtube.com/watch?v=gqurZk12qIk&feature=youtu.be

   I used a similar white 2.2k ceramic resistor on the Oleg snubber, and it still got hot.
   Carbon, ceramic, wirewound, non wirewound, all get hot. The higher the ohm value of the Oleg snubber resistor, the hotter the RC snubber resistors get.
   I can get RM at lower voltages, at times now, like at around 150v and also the effect from hand movements on the antenna, etz... But, the resistors get hot at resonance, still. Too hot at loads over 100w.
The load is also an important consideration, as each bulb added, changes everything.

  Itsu: If I just use the blue 2000v caps on the RC snubber, and just a 1k ohm on the Oleg snubber,  I get real nice signals, almost perfect. But the resistors can't handle it after just a short while. However, the math provided for their values was right, though.

  Any ways, I'll wait a few days for you guys to have a chance to work the non dissapating snubber tests, or I might just jump in, even beforehand.

[Void]

Just measured the voltage on the cathode of diode D3 in the non-dissipative snubber.
With a V+ of 12V it is peaking at around 150V. If you use a V+ of 24V it is probably
going to be a fair bit higher, so Schottky or fast recovery diodes with a reverse breakdown
voltage of at least 250V would seem to be a good idea. A reverse breakdown voltage of 500V
or higher would probably be even safer.

The yellow trace shows the waveform on the cathode of diode D3 with V+ at 12V.

Nick, you could maybe go with a 10 Watt ceramic block resistor and it may well be able to take the
heat even if it gets really hot. You can get ceramic block power resistors that are metal oxide film.