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Cyparagon

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Plan is to measure at LD+, LD- and RS+, all referenced to GND.
While the ground plane is low resistance, it is not zero resistance. In fact, it may even be comparable to the shunt you use, which will throw the current reading way off. If you want high accuracy, you want to sense the voltage across the shunt (directly - kelvin sense).

Have considered swapping the transistor(s) out for MOSFETs
I tried that. I couldn't get it to stabilize and actually popped a pricey diode when I THOUGHT I had it figured out :(. It can be done, obviously, as the flexmod is FET based. But it seems a lot harder for some reason.

I have a real beefy TO-3 heatsink, easily big enough to handle the heat
The heat sink isn't always the limitation. It's sometimes the thermal resistance to case, and the case resistance to the heat sink when it comes to high dissipation. It is possible for the heat sink to be barely above room temperature, while the junction is over 100C. Just monitor the case temperature and don't start with full power.

Friend has an O-scope
I hope it has single shot. You'll want to capture power on, power off, quick power cycle, and rms noise at several different input voltages and output currents.
 
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diachi

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While the ground plane is low resistance, it is not zero resistance. In fact, it may even be comparable to the shunt you use, which will throw the current reading way off. If you want high accuracy, you want to sense the voltage across the shunt (directly - kelvin sense).

Good point, I'll look into a few options for that. I'd be happy if I can get it within 0.05V of the true value, not super accurate but good enough.

I tried that. I couldn't get it to stabilize and actually popped a pricey diode when I THOUGHT I had it figured out :(. It can be done, obviously, as the flexmod is FET based. But it seems a lot harder for some reason.


Hmm good to know you encountered issues. I've seen it done too, but perhaps there's something I'm missing. Something else to experiment with anyway. Hopefully I can get it figured out. Open to other ideas, no plans to make this a commercial product or anything, really it's just to give me something to do and to get some practice with designing my own drivers/PCBs. I feel I've learned a bunch already.



The heat sink isn't always the limitation. It's sometimes the thermal resistance to case, and the case resistance to the heat sink when it comes to high dissipation. It is possible for the heat sink to be barely above room temperature, while the junction is over 100C. Just monitor the case temperature and don't start with full power.

Good point, another reason to spread the load across several transistors and be conservative with current ratings. A quick calculation puts Tj at 91°C above Tc for 120W split across two transistors (Rθjc = 1.52°C/W), so that's looking at worst case, even if Tc is 50°C that'd still be 60°C below maximum. Power dissipation at Tc=50°C is still ~100W. Hotter than I'd probably like, but still within spec with some headroom left I should think.

That said, the MOSFET option is looking more appealing as I look at the base current numbers...


I hope it has single shot. You'll want to capture power on, power off, quick power cycle, and rms noise at several different input voltages and output currents.

Nope, it's ancient, it'll catch any major noise or oscillations, may catch any big ON/OFF spikes. A more modern scope is next on my list of tools, just need to save some cash and find a deal.

Thanks again for your input Cyp, I'll work on another revision or two of this over the next couple days, taking note of your suggestions as best I can. :) First for an update is transistor drive... This is getting more complicated than I had originally thought, not complaining, I can learn more this way. :eek:
 

BowtieGuy

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Looks like a big city that's getting bigger yet, and even better, the best Italian breakfast buffet around! :drool:
 

paul1598419

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That photo is much different than the ones we are used to seeing here in the states of Iraq. I wonder how good the Italian food is there. It appears that the Iraqis are trying to appeal to American tastes.
 

Alaskan

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This is in Kurdistan territory, they want to be the next Dubai. Although part of Iraq, most individuals here do not see themselves as part of Iraq and "Kurdistan" instead. They hope to break off from Iraq to be their own country someday. I also hope that happens, they want it and the people are different here than many other parts of this country. Mostly Christian too, instead of Muslim. That alone is a big divide between the rest of Iraq.
 

Gabe

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Hey guys, been reluctant to upload the photos I've taken recently because there's lots and it's tedious uploading them, but I really wanted to share this one because I'm super super proud and stunned. This is my first true attempt at photographing the Milky Way core, less than a year ago I knew nothing about astrophotography and this is where learning on my free time has brought me. Took this in fairly light polluted skies on a beach in Playa Del Carmen, Mexico. This is where I did my first attempt because the Milky Way core is high in the sky at that latitude, as opposed to up here where the core barely peeks above the horizon at best. 16 stacked images to reduce noise, I was battling 90% humidity and constant clouds, and the light pollution made the raw frames almost completely white. I made sure to not completely overexpose the photo, however, so I could keep all the detail. For those who want the deets, sixteen identical 10 sec exposures, ISO 6400 and at f/1.8 with my 35mm portrait lens, 1.5x crop sensor too.



Had to downsize, so think of that as like a thumbnail. The original is like 2100 x 1500. Heres the full res, would recommend/10
 

CurtisOliver

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Wow is the first thing that came to my head when I saw that pic Gabe. Amazing! Just think that our recent discoveries could place planets around nearly every single one of those points of light you see in that image.
Pics like this make me wonder how some people can show no interest in space whatsoever. :thinking:
I've given out too much rep, but I will return to rep you Gabe. ;) :gj:
 

Gabe

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Wow is the first thing that came to my head when I saw that pic Gabe. Amazing! Just think that our recent discoveries could place planets around nearly every single one of those points of light you see in that image.
Pics like this make me wonder how some people can show no interest in space whatsoever. :thinking:
I've given out too much rep, but I will return to rep you Gabe. ;) :gj:
Thanks so much! Same here rep-wise :D
And crazier to think of how small of a part of the universe this snapshot is, when there are to our best guesses roughly 1,000,000,000,000,000,000,000,000 stars in the observable universe, and probably many times more planets.... just incomprehensible!
 

CurtisOliver

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Absolutely. The numbers are stacking up more and more as our technology is getting better at detecting them. To think that a vast majority of those planetary systems also have one of more planets in the so called Goldilocks zone.
It is rather unbelievable. One of the reasons why I am in favour for us not being alone. :)
 

trencheel303

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Hey guys, been reluctant to upload the photos I've taken recently because there's lots and it's tedious uploading them, but I really wanted to share this one because I'm super super proud and stunned. This is my first true attempt at photographing the Milky Way core, less than a year ago I knew nothing about astrophotography and this is where learning on my free time has brought me. Took this in fairly light polluted skies on a beach in Playa Del Carmen, Mexico. This is where I did my first attempt because the Milky Way core is high in the sky at that latitude, as opposed to up here where the core barely peeks above the horizon at best. 16 stacked images to reduce noise, I was battling 90% humidity and constant clouds, and the light pollution made the raw frames almost completely white. I made sure to not completely overexpose the photo, however, so I could keep all the detail. For those who want the deets, sixteen identical 10 sec exposures, ISO 6400 and at f/1.8 with my 35mm portrait lens, 1.5x crop sensor too.



Had to downsize, so think of that as like a thumbnail. The original is like 2100 x 1500. Heres the full res, would recommend/10
so sharp, much pixel, very resolution. Wow!
 

RB astro

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I made sure to not completely overexpose the photo, however, so I could keep all the detail. For those who want the deets, sixteen identical 10 sec exposures, ISO 6400 and at f/1.8 with my 35mm portrait lens, 1.5x crop sensor too.
Nice shot Gabe.
The Milkyway core is amazing to shoot.
It's breathtaking to realise how many stars are in there.

:beer:
 

BowtieGuy

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Extraordinary photo, Gabe, you ought to be proud of that one!
It makes you feel awfully small in the grand scheme of things that's for sure.
:kewlpics: +rep!
 
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CurtisOliver

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Extraordinary photo, Gabe, you ought to be proud of that one!
It makes you feel awfully small in the grand scheme of things that's for sure.
:kewlpics: +rep!

Yep, imagine your kitty in the grand scheme of space. :D

 
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BowtieGuy

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If you could read his mind, he's probably thinking ..."look at all those laser dots to catch". :yh:
 




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