Calculating peak discharge current, and clamping
Quantum Singularity, Thu Jun 08 2006, 06:48PMI have been running some numbers on the simulator on the Magnetic Gun Clubs site calc and I had a few questions regarding this calculation. For one, I am unsure what the ESR is on my caps. I was wondering if anyone here has a ballpark number? I have shot off an email to CDE asking them, not sure if I will here back. Also, is there ESL in the caps enough to need to include that in the circuits inductance? And also is there any significant resistance in the SCR? The only data on the SCR datasheet that said resistance was 'slope resistance' and I am not familiar with what exactly that means.
On a different note, the circuit representation their shows the clamping diode across the cap. I was under the assumption the best spot for it is directly accross the coil, is that not correct? Or will it work both ways just the same?
Re: Calculating peak discharge current, and clamping
FastMHz, Fri Jun 09 2006, 01:17AM
If the diode were across the cap bank, before the SCRs, I don't think it would protect the SCRs from the back emf...mine is directly across the coil, which to me, makes the most sense. Sorry I can't help with your other Qs...hopefully the company will write back.
FastMHz, Fri Jun 09 2006, 01:17AM
If the diode were across the cap bank, before the SCRs, I don't think it would protect the SCRs from the back emf...mine is directly across the coil, which to me, makes the most sense. Sorry I can't help with your other Qs...hopefully the company will write back.
Re: Calculating peak discharge current, and clamping
Electroholic, Fri Jun 09 2006, 01:34AM
if there is no diode at all, the will be an emf kick.
and the cap will be charged BACKWARD!
if a diode is placed at the caps(the right way), the collapsing mag. field will freewheel thru the diode AND the scr.
if a diode is placed right at the coil(the right way), most if not all of the current will freewheel thru the diode.
I use both in my coil guns, just to play safe,
BTW, my coil guns are reluctant type.
If the diode is placed the wrong way, then something interesting will happen, SCR VS DIODE, see who blow first. I only did it once, 50RIA120 vs 4X1N5408 on ~200J
5408s won.
Electroholic, Fri Jun 09 2006, 01:34AM
if there is no diode at all, the will be an emf kick.
and the cap will be charged BACKWARD!
if a diode is placed at the caps(the right way), the collapsing mag. field will freewheel thru the diode AND the scr.
if a diode is placed right at the coil(the right way), most if not all of the current will freewheel thru the diode.
I use both in my coil guns, just to play safe,
BTW, my coil guns are reluctant type.
If the diode is placed the wrong way, then something interesting will happen, SCR VS DIODE, see who blow first. I only did it once, 50RIA120 vs 4X1N5408 on ~200J
5408s won.
Re: Calculating peak discharge current, and clamping
EDY19, Fri Jun 09 2006, 01:44AM
Haha electroholic- robot wars.....junkyard wars.....semiconductor wars
my diode is located very close to the coil, I think this is the best way.
EDY19, Fri Jun 09 2006, 01:44AM
Haha electroholic- robot wars.....junkyard wars.....semiconductor wars
my diode is located very close to the coil, I think this is the best way.
Re: Calculating peak discharge current, and clamping
Quantum Singularity, Fri Jun 09 2006, 04:21AM
Well, that all reinforces what I thought... just wanted to check. I think I will hook up directly accross the coil then. Like FastMHz says, makes the most sense to me also.
About the ESR/ESL... A rep at CDE did email me back but said he will look into it and hopefully get back to me with some detailed info on monday.
Quantum Singularity, Fri Jun 09 2006, 04:21AM
Well, that all reinforces what I thought... just wanted to check. I think I will hook up directly accross the coil then. Like FastMHz says, makes the most sense to me also.
About the ESR/ESL... A rep at CDE did email me back but said he will look into it and hopefully get back to me with some detailed info on monday.
Re: Calculating peak discharge current, and clamping
Wilson, Fri Jun 09 2006, 04:56AM
The ESR of most large electrolutic caps are quite low, espeically in the inverter grade ones. Its usually between 40-100mohm from memory, so if you're parralling a few caps, the ESR should no longer be the limiting factor on the peak discharge current.
Wilson, Fri Jun 09 2006, 04:56AM
The ESR of most large electrolutic caps are quite low, espeically in the inverter grade ones. Its usually between 40-100mohm from memory, so if you're parralling a few caps, the ESR should no longer be the limiting factor on the peak discharge current.
Re: Calculating peak discharge current, and clamping
Quantum Singularity, Fri Jun 09 2006, 05:26AM
Well, just for comparison I tried 100mohm and 40mohm on the calculator I linked to in the first post. The later increased the current by about 4,000 amps... so you see it makes a kinda big difference
For an induction launcher setup (what I'll be working on first) I'll probably make banks of three caps in parallel, and have 4 of these banks stacked in series so the ESR will be approximately 25% higher than the individual rating of just one cap alone. This is not set in stone and I do plan on testing different arrangments. I would just like to have some kind of calculation that suggests my diodes and scr's will survive.
Quantum Singularity, Fri Jun 09 2006, 05:26AM
Well, just for comparison I tried 100mohm and 40mohm on the calculator I linked to in the first post. The later increased the current by about 4,000 amps... so you see it makes a kinda big difference
For an induction launcher setup (what I'll be working on first) I'll probably make banks of three caps in parallel, and have 4 of these banks stacked in series so the ESR will be approximately 25% higher than the individual rating of just one cap alone. This is not set in stone and I do plan on testing different arrangments. I would just like to have some kind of calculation that suggests my diodes and scr's will survive.
Re: Calculating peak discharge current, and clamping
Sulaiman, Fri Jun 09 2006, 08:37AM
Don't know if it helps;
for photoflash electrolytic capacitors,
esr = (80 Ohms)/(uF capacitance)
e.g. C= 1000 uF, R= 0.08 Ohm (80 mOhm)
Sulaiman, Fri Jun 09 2006, 08:37AM
Don't know if it helps;
for photoflash electrolytic capacitors,
esr = (80 Ohms)/(uF capacitance)
e.g. C= 1000 uF, R= 0.08 Ohm (80 mOhm)
Re: Calculating peak discharge current, and clamping
thom, Fri Jul 07 2006, 08:06AM
I'm not sure how accurate this is, or if its correct at all, but if you have access to a LCR meter you could try the resistance mode on it.
I tested a couple caps: a compact size 4700uF that read 75mOhm, and a large industrial 20,000uF that read 17mOhm.
But ESR meters test at around 100kHz+, while this LCR meter is only 1kHz, so impedance would be an issue.
thom, Fri Jul 07 2006, 08:06AM
I'm not sure how accurate this is, or if its correct at all, but if you have access to a LCR meter you could try the resistance mode on it.
I tested a couple caps: a compact size 4700uF that read 75mOhm, and a large industrial 20,000uF that read 17mOhm.
But ESR meters test at around 100kHz+, while this LCR meter is only 1kHz, so impedance would be an issue.
Re: Calculating peak discharge current, and clamping
IamSmooth, Thu Sept 28 2006, 01:04PM
Quantum, what SCR are you using to handle that current surge and where did you buy it? Can you post a picture?
IamSmooth, Thu Sept 28 2006, 01:04PM
Quantum, what SCR are you using to handle that current surge and where did you buy it? Can you post a picture?
Re: Calculating peak discharge current, and clamping
EDY19, Thu Sept 28 2006, 04:44PM
ReddyK is selling some big SCRs if you are looking for one- check out the thread in the sale and trade forum.
EDY19, Thu Sept 28 2006, 04:44PM
ReddyK is selling some big SCRs if you are looking for one- check out the thread in the sale and trade forum.
Re: Calculating peak discharge current, and clamping
Quantum Singularity, Tue Oct 10 2006, 07:55AM
Sorry I havent been on 4hv in a few weeks. The scr's I use are Eupec TT180 series - sorry I dont remember the whole number off hand. They are rated 1200V and a surge (Itsm) of 6700A. Since I cant really calculate the currents involved, or attempted to measure, I just hooked all three that I have in parallel. I purchased them on ebay for about $10 US each. I often see much larger >10ka puck ones for reasonable prices but I like the mounting convinience of the module with bolts. So far I have only tested to about 1.5kJ but with many dozen tests so far no signs of failure. Here is a pic:
Details, pics, and video clips on my website of project EMP3A at http://tristan.homelinux.net/ringlauncher/index.htm
Quantum Singularity, Tue Oct 10 2006, 07:55AM
IamSmooth wrote ...
Quantum, what SCR are you using to handle that current surge and where did you buy it? Can you post a picture?
Quantum, what SCR are you using to handle that current surge and where did you buy it? Can you post a picture?
Sorry I havent been on 4hv in a few weeks. The scr's I use are Eupec TT180 series - sorry I dont remember the whole number off hand. They are rated 1200V and a surge (Itsm) of 6700A. Since I cant really calculate the currents involved, or attempted to measure, I just hooked all three that I have in parallel. I purchased them on ebay for about $10 US each. I often see much larger >10ka puck ones for reasonable prices but I like the mounting convinience of the module with bolts. So far I have only tested to about 1.5kJ but with many dozen tests so far no signs of failure. Here is a pic:
Details, pics, and video clips on my website of project EMP3A at http://tristan.homelinux.net/ringlauncher/index.htm
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