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Registered Member #1828
Joined: Sat Nov 29 2008, 03:00PM
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Posts: 55
What is the correct way to set the display?
From the Experience with miniBrute Reference Design? Thread
Yes, something is definitely wrong. The test procedure that is. You simply need to insert a variable DC voltage source across capacitor C31 (i.e. 12V) which is the input to the LM3914 display IC. This will allow you to set the display chip to full scale. When setting the current meter, you need to disconnect one lead of the 1.6 ohm resistor. This is an error in the instructions. The 3W value is sized for low duty cycles during normal operation, not CW as if you were to test the meter with an external source.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068
d20180 wrote ...
What is the correct way to set the display?
From the Experience with miniBrute Reference Design? Thread
Yes, something is definitely wrong. The test procedure that is. You simply need to insert a variable DC voltage source across capacitor C31 (i.e. 12V) which is the input to the LM3914 display IC. This will allow you to set the display chip to full scale. When setting the current meter, you need to disconnect one lead of the 1.6 ohm resistor. This is an error in the instructions. The 3W value is sized for low duty cycles during normal operation, not CW as if you were to test the meter with an external source.
Just as it reads above. Yes, there is a mistake as stated. The 1.6 ohm resistor needs to be disconnected when injecting a DC signal into the input. From there, just follow the instructions as indicated.
Registered Member #1828
Joined: Sat Nov 29 2008, 03:00PM
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Posts: 55
The lowest I can get it adjusted to is where ~11.3V will just light the top. I have tried a different r42. I know I need more resitance, what it the best way to add it, and where? Now I am waiting on digi-key.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
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d20180 wrote ...
The lowest I can get it adjusted to is where ~11.3V will just light the top. I have tried a different r42. I know I need more resitance, what it the best way to add it, and where? Now I am waiting on digi-key.
Read the schematic. It tells you what the setpoints you be set as. 5.24V should illuinate up to the 5th LED while 12V should light the last LED.
Its only a rough indicator of current (+/- 100A), so just roughly tune it.
Registered Member #1828
Joined: Sat Nov 29 2008, 03:00PM
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I understand, I just couldn't get there. With r42 set as high as it would go, the 10th led set would light up @ 11.3. I subbed a r23 10k pot to get it to light up the 10th led @ 12v @ pin 5. I'll have to go back and check what the others light up at.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068
d20180 wrote ...
I understand, I just couldn't get there. With r42 set as high as it would go, the 10th led set would light up @ 11.3. I subbed a r23 10k pot to get it to light up the 10th led @ 12v @ pin 5. I'll have to go back and check what the others light up at.
don't worry. you aren't going to get anywhere near 1000A peak current. my DRSSTCs almost ALWAYS run about 500A maximum. I wouldn't worry about it. the original design went from 0-500A in 50A increments, but i changed the scale to 0-1000A just to give some additional headroom.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
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d20180 wrote ...
can the secondary be grounded to the copper strike rail? (which is grounded to the Bridge power ground pin?)
Everything should be grounded to the same single point. This point is the point where your Earth Ground comes in on the power cord to the system. At this point, you'll connect: 1. Control Board GND, Secondary Ground, Strike Rail Ground, and Safety Ground (panels, etc...) You'll also connect your strike target ground to this point as you want to maintain a short current loop during discharges to the strike target.
Do not allow the miniBrute to strike objects not grounded back to this point. Otherwise you'll get circulating RF currents through your entire house as it tries to make its way back to this single ground point in your miniBrute.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068
d20180 wrote ...
First light!
Got up to about 2' then vaporized F121. 10A doesn't cut it. I went with 10A because that's what the holder called for.
Looking for 20A and 4'.
need to get the display working.
Thanks.
Excellent. Thats great for first light. Yeah, the 10A is too small. A 20A works good.
Also, VERY IMPORTANT and something which isn't listed in the plans. Put a long extension cord between the wall socket and your variac. Very important. Basically, the impedance acts like a nice ballast limiting peak current, especially during discharges, and will GREATLY improve reliability. Sure, and R-L would work here too, but this is very simple to do. It doesn't limit spark length at all either.
Also, don't push it very hard. Be sure to read the section on advanced tuning and then start plotting current vs. discharge length and find the optimum tuning point. Takes a lot of work, but once done, you'll have a coil approaching 4 foot arcs!
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Help needed with MiniBrute
