If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
After abandoning the project due to external factors and frustration of being completely unable to fix the triggering circuit, yesterday I retook it.
The triggers are fixed, they now fiure the SCR banks properly (yay!). I was driving them with pin 7, and that is the collector pin of the LM211. Swapped to pin 1 (open emitter pin) and they now fire successfully. Only tested on LEDs because the converter now has a serious issue I can't sort out sadly, so no 'real world' testing can be done :/
So, going back to the situation:
I made some mods on the converter:
1) Swapped the 1N5408 diode with a Schottky one that runs much faster AND allows for much higher efficiencies to be reached. Kay, that part works. 2) Swapped the 555 timer I burnt, installing a DIP8 socket this time. Fine, it works again. 3) Swapped the UA741CN with a spare LM211 basing upon Uzzors2K's converter design. Why? Because I prefer real comparators to opamps working as comparators. 4) Literally cloned the reset side of Uzzors' boost converter, mainly because the LM211 needs a different layout than the 741. 5) Swapped the resistors in the divider with new ones (not recycled), and added a pot in addition to the fixed resistor to regulate the shutdown voltage.
So here's the problem:
I fire the circuit on, and BAM massive voltage spike that goes out of range in my multimeter (crosses 1200V barrier), followed by a manual circuit insta-shutdown. Multimeter now shows 310V and starts going down slowly. MOSFET is cold, so is the diode, so is the circuitry (IR beam thermometer, I don't wanna touch the live diode lol). The discharge time is the same as when it used to charge capacitors slowly, so I bet they're charged to their limits.
This is happening since I swapped the UA741CN with the LM211. Ah, note that I swapped it because the 741 wasn't triggering the 555 off properly.
So, two issues now:
1) I'm afraid this spike will burn something. Checked MOSFET, ICs, diodes, everything. Found no physical issues. 2) Can't make the LM211 to trigger the 555, and the 741 wasn't able neither. Maybe something's gone bonkers?
The reset pin side is exactly the same as the one used by Uzzors, so this is the circuitry.
If someone would throw a little light on the subject I'd appreciate it forever... Can't wait to start the firing tests!!
Edit: Swapped the LM311 with an UA741CP again, and it does the same.
I'm starting to think that my inductor can have gone bonkers. Which I doubt, because it uses 0.6mm wire and it is pretty much oversized (doesn't even get warm).
I'd like to add that I hear it buzzing with the usual high-pitched sound indicating that the 555 oscillates at a fixed frequency (or that it oscillates at least) and that the inductor is being fed.
Edit2: I've let it on for a while, and seemingly it charges, and then the buzzing sound appears (sounds more like a very fast switching relay, it is a succession of 'clicks'), the LED lits and the DMM reads again, showing a constant voltage of 311V.
Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
Artikbot wrote ...
So here's the problem:
I fire the circuit on, and BAM massive voltage spike that goes out of range in my multimeter (crosses 1200V barrier), followed by a manual circuit insta-shutdown. Multimeter now shows 310V and starts going down slowly. MOSFET is cold, so is the diode, so is the circuitry (IR beam thermometer, I don't wanna touch the live diode lol). The discharge time is the same as when it used to charge capacitors slowly, so I bet they're charged to their limits.
This is happening since I swapped the UA741CN with the LM211. Ah, note that I swapped it because the 741 wasn't triggering the 555 off properly.
So, two issues now:
1) I'm afraid this spike will burn something. Checked MOSFET, ICs, diodes, everything. Found no physical issues. 2) Can't make the LM211 to trigger the 555, and the 741 wasn't able neither. Maybe something's gone bonkers?
I assume you are measuring the voltage across your capacitor bank terminals. I had the same problem when I built Uzzor's converter a couple years ago. The cause was that I had omitted the 68 ohm gate resistor for the mosfet. I'm not sure why that caused it, but it did since adding the resistor fixed the problem.
You are not actually getting a 1200V spike across your capacitors- that's more likely a measurement error with the voltmeter. It's physically impossible- remember capacitors resist voltage change. For it to instantly charge to 1200V you'd have to output kilowatts with your charger.
I'm sure theres nothing wrong with the inductor, its just a coil of wire. Regarding the 555, remember the reset pin has to be grounded (or brought below 0.7V according to the datasheet) to be tirggered. Use your meter to make sure the output of the comperator is going low when your caps are charged to the right level. If not you may need to check your comparaor wiring or swap it out.
Thanks a lot for the feedback! The below 0.7V thing is something I ignored about the 555, did know I had to ground, but not to what level. Now that I remember, I don't have any capacitor preventing ripple on the comparator, that could be the cause of it not switching off.
The resistor to the gate was installed, but possibly it went bonkers? Since I have been doing lots of stuff around the board.
I redid the inductor, single layer this time, as tightly packed as possible, with the core I had resembling more a 200uH capable inductor.
Anyways, I decided to rebuild the whole circuit (and shrink the board space quite a lot) because the board was starting to get messy, molten cables all around due to too much sondering/unsoldering job, and too many failures due to improperly placed components adding noise where I don't want it to be.
Redesigned the layout to accomodate the LM211, rewired the LED to indicate when the 555 is in reset state, and built it again. I've also swapped the non inverting input power source, instead of a 7805 I've chosen to use a 6.8V Zener this time, since the voltage on the battery is high enough to drive it (11.1V) and it takes a lot less space and components. Also, the measure is exact enough for it to work.
Here are the results and the size comparison between old charger and current one (I've scavenged loads of components from the old one, but it used to take all the perfboard space available):
Gotta test it though, and the voltage cutoff needs to be calibrated. Will report back soon ;)
----------
Edit: Okay, after some testing, the voltage rises to a point I can't see because my DMM goes mad and shows 'out of range'.
I hear absolutely no whine (I've tuned the frequency down to 4.7kHz), but after like 3-4 secs I hear a sort of tweezing and the LED goes on. But since I can't determine what is the voltage doing, I have absolutely no clue of what's going on until I shut off the thing, and then I see a 317V reading at the cap banks.
What can cause the DMM to not show the actual voltage?
In theory, if the caps are charged to 317V (manually adjusted to approx 315V, so it is accurate enough), it means it works right?
Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
If the capacitors charge to 317V then your boost converter is definitely working. However something is definitely screwy.
I would reccomend running it with all the control circuitry detached. Then you start to zero in on the problem by figguring out if the problem is with the drive and power circuitry (555, inductor, mosftet, output diode) or control components (op amp, zener, etc). The question to ask is "does it work by itself"
If that all works fine, then something is wrong with your control circuitry, which we can attack seperately.
Anyways, tried letting the circuit on for a bit longer, and it worked properly seemingly!
It started, no coil whining at all (lul?), and after 4 secs the crackling noise started (it's similar to a Geiger counter sound), the LED went on and the DMM automatically went in range and shown 311V. Stabilised there until I plugged it out.
What annoys me is that I hear no whine at all even if the circuit is switching. That, and the DMM going out of range when the measures are clearly in range. If it went out of range the LM211 wouldn't have let the 555 oscillate in the first place, right? It has a very fast response time (0.2ms), that's 5kHz capability, and the 555 oscillates at 4.7kHz, so theoretically the 211 should be more than able of stopping it from oscillating.
---------
Edit: Did another test.
Put into the circuit the whole cap bank (4.8mF @330V) and started the charger. Voltage started to rise, and at some point it spiked to 800V (after 3-4 secs). Turned the switch off and the DMM again shown 120V, slowly dropping.
So, with an even bigger capacitance the spike just needs more time to rise, but it still appears.
Can it be a spike? Maybe the DMM is glitchy? Maybe there is a serious fault on the circuit? (Wrong inductance?).
Could it be a faulty DMM? It's an el-cheapo one like those sold in RadioShack for 15 bucks.
Thanks for your help Saz43! Such an honor to have the creator of one of the most awesomesauce coilguns ever here
Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
No prob, I think your circuit is working just fine. Does it stop the charging close to your calculated value? If so, I think you're right to guess that it's a reading error with your DMM. Also, the circuit should be silent for the first few seconds or so, then change the noise it makes as the capacitor fills. Keep in mind capacitor charging is a dynamic process, voltage, current, and power changing with time- so it makes sense that the noise will change.
I'm certain that there isn't a voltage spike occurring, capacitors do not allow this to happen. For it to be an actual surge, (based on your numbers) your charge will have to had passed 384 to 512 watts.
And at a 500W rating my MOSFET would've stuck right on the ceiling LOL.
I'm off to do a full charge and see what does it do. Pray to God that it won't blow :P
The 'sink on the MOSFET is actually pretty beefy, so I think it'll be alright.
Edit: DAMN my mosfet just almost set on fire!! I stopped charging at 290V, it took like 10 seconds, maybe 12 to get to 290V.
4.8mF, will do the calculations.
Maybe the inductor is too small, the inductance is low and it avalanches too much current via the MOSFET?
Edit: I got 18W power output at the cap bank, the inductor is warm, the diode... I won't touch it, it's live 300V. And the MOSFET heatsink is scorching hot. Well, it is so hot that it even smoked up the thermal pad!
I don't have an ammeter, so I can't check the power the circuit is actually eating. I promise the battery can supply as much energy as the cap wants, it's rated at 80A sustained discharge, at 11.1V approx. That is almost 900W power.
Man, my head's literally gonna asplode.
What if I pick a low Rds on MOSFET? Fairchild has similar FETs to the IRFP450 that have .280, and even .150Ohm resistance... And much higher amperage rates, around 20-30A.
For example the IRFP460, it has a Rds on of onlyu 0.27Ohm, half the IRFP450, and it stands up to 20A.
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
I have been having a similar problem with mosfets overheating. I've read that the 555 doesn't properly charge the gate, so the fet doesn't fully switch on or off. the solution is (or atleast should be, haven't tried it yet) to have the output of the 555 fed into a mosfet driver ic such as the ucc37322p. I've tried fets with less than 58mohms rds on and they still overheat with just the 555 driving it. good luck to you, i know how much of a pain these circuits can be to troubleshoot.
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
it's just a little 8 pin chip. same size as the 555. and pins 1,3, and 8 get connected together, pins 4 and 5 connected together, and and 6 and 7 together. so you'll only have 4 leads going to/from it
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
New to Coilguns - Coilgun Buildlog (Charger apparently fixed)
