six hundred precious joules
Marko, Thu Feb 09 2006, 10:07PMIn my school I just got six 21000 uF 100V electrolytic capacitors, scrapped from some (relatively) old supercomputer power supply, each stores around 100 joules (when almost full)
They seem to be in very good shape, im only wondering could they be of some use for small railgun, coilgun or just exploding (mini).
As mains rectified gives around 300V so I cannot charge them directly.
This could be easily done with few small transformers, but I want ot ask experienced ?!
Is it beter to charge whole bank parallel at ~100 volts or connect them 3 vs 3 in series to get 200V but double less capacitance?
Maybe to go all for voltage and series them all (need multiplier) :D
Most that matters is switch I could use, buyng monstrous SCRs is what I would avoid if possible, and voltage is too low for triggered gaps, some crude mechanical switch will weld every firing but his seems only solution.
Any other suggestions?? !lol
Re: six hundred precious joules
Michael W., Thu Feb 09 2006, 11:04PM
The SCR - Watch ebay, sometimes theres good deals, I think the mechanical switch would be the only way to go.....
Michael W., Thu Feb 09 2006, 11:04PM
The SCR - Watch ebay, sometimes theres good deals, I think the mechanical switch would be the only way to go.....
Re: six hundred precious joules
Simon, Fri Feb 10 2006, 02:28AM
I'd go series - if they work at all. In parallel you've got a lot of capacitance (long pulse) and not much voltage.
Simon, Fri Feb 10 2006, 02:28AM
I'd go series - if they work at all. In parallel you've got a lot of capacitance (long pulse) and not much voltage.
Re: six hundred precious joules
Part Scavenger, Fri Feb 10 2006, 03:07AM
Go for the most voltage and here's why: Wired in parallel, the caps will have the exact same joule capacity as in series. But, the higher the voltage the more amperage flows per fixed resistance. (Ohms law)
Be careful to research seriesing electrolytic capacitors, as I hear this can lead to problems. I have never had trouble, but I have never used 'lytics at that power level before. ;)
BTW, You could use a starter solenoid for the switch.
Part Scavenger, Fri Feb 10 2006, 03:07AM
Go for the most voltage and here's why: Wired in parallel, the caps will have the exact same joule capacity as in series. But, the higher the voltage the more amperage flows per fixed resistance. (Ohms law)
Be careful to research seriesing electrolytic capacitors, as I hear this can lead to problems. I have never had trouble, but I have never used 'lytics at that power level before. ;)
BTW, You could use a starter solenoid for the switch.
Re: six hundred precious joules
Pcnerd, Fri Feb 10 2006, 06:16AM
if you want to go in series or paralels is for yourself, do you want to keep your voltage low, paralel, en do you want high voltage in series. But, the energy stored will rise when put in series, not much, but mostly good for about 10-120&% I think.
be aware of charging, mostly a transformer is not enough, use a ballast, can be anything from a resistor to a lightbulb.
Pcnerd, Fri Feb 10 2006, 06:16AM
if you want to go in series or paralels is for yourself, do you want to keep your voltage low, paralel, en do you want high voltage in series. But, the energy stored will rise when put in series, not much, but mostly good for about 10-120&% I think.
be aware of charging, mostly a transformer is not enough, use a ballast, can be anything from a resistor to a lightbulb.
Re: six hundred precious joules
Steve Conner, Fri Feb 10 2006, 10:17AM
How can the energy stored be more when the caps are in series? Surely it should be no different.
Steve Conner, Fri Feb 10 2006, 10:17AM
How can the energy stored be more when the caps are in series? Surely it should be no different.
Re: six hundred precious joules
Marko, Fri Feb 10 2006, 01:31PM
Stored energy is always the same, seriesing or paralelling cannot give more joules in any way.
capacitance is 21000uF = 0,021F and voltage 100V (round)
series
E = (0.021F/6)*600V^2 = 630 J
paralell
E = (0,21F*6) * 100V^2 = 630 J
(few volts lesser and we can circle 600 joules)
Matches laws of physics excellently.
Also voltage logic is questionable with elecrtolytics, that have relatively high internal resistance (compared to plate caps where 'outside' resistance is more limiting)
If I series them all I have more voltage but max current is exactly samo of max current for 1 capacitor. Voltage is high but limited to this current. (ohms law again)
Probably thats why is spoken that they are not good for seriesing (as plate caps are)
Thats why im asking about series or paralell connection..
In paralell max current is multiplied by 6, but voltage is low.
%-6
100V would be safest,
but to connect 3vs3 for 200V, and I can simply rewire it to 100V if problems occur.
Switch is far bigger problem, I dont like to go arcwelding so mechanical switch cannot be just a solenoid pushing some metal conductor, that will surely weld and dissipate far more power than intended target.
Solenoid is simple and good idea for triggered gaps, but not for direct contact switching.
conclusion: I must buy SCR.
If I dont find something in junk again !dodge
Marko, Fri Feb 10 2006, 01:31PM
you want high voltage in series. But, the energy stored will rise when put in series, not much, but mostly good for about 10-120&% I think.
Stored energy is always the same, seriesing or paralelling cannot give more joules in any way.
capacitance is 21000uF = 0,021F and voltage 100V (round)
series
E = (0.021F/6)*600V^2 = 630 J
paralell
E = (0,21F*6) * 100V^2 = 630 J
(few volts lesser and we can circle 600 joules)
Matches laws of physics excellently.
Also voltage logic is questionable with elecrtolytics, that have relatively high internal resistance (compared to plate caps where 'outside' resistance is more limiting)
If I series them all I have more voltage but max current is exactly samo of max current for 1 capacitor. Voltage is high but limited to this current. (ohms law again)
Probably thats why is spoken that they are not good for seriesing (as plate caps are)
Thats why im asking about series or paralell connection..
In paralell max current is multiplied by 6, but voltage is low.
%-6
100V would be safest,
but to connect 3vs3 for 200V, and I can simply rewire it to 100V if problems occur.
Switch is far bigger problem, I dont like to go arcwelding so mechanical switch cannot be just a solenoid pushing some metal conductor, that will surely weld and dissipate far more power than intended target.
Solenoid is simple and good idea for triggered gaps, but not for direct contact switching.
conclusion: I must buy SCR.
If I dont find something in junk again !dodge
Re: six hundred precious joules
Pcnerd, Fri Feb 10 2006, 02:15PM
whoop's, I miscalculated, thought that 2 cap's in series was just the same, forgotten that that was half of the capacitance, stupid me, i'm sorry :s.
Pcnerd, Fri Feb 10 2006, 02:15PM
whoop's, I miscalculated, thought that 2 cap's in series was just the same, forgotten that that was half of the capacitance, stupid me, i'm sorry :s.
Re: six hundred precious joules
Self Defenestrate, Fri Feb 10 2006, 02:16PM
Definetly go for SCR switching. I'd build a bank with three paralled sets of two caps in series. Whats your line voltage?
Self Defenestrate, Fri Feb 10 2006, 02:16PM
Definetly go for SCR switching. I'd build a bank with three paralled sets of two caps in series. Whats your line voltage?
Re: six hundred precious joules
Part Scavenger, Fri Feb 10 2006, 03:18PM
I don't really know what you mean by this. The higher voltage will allow the capacitors to discharge more quickly.
To demonstrate:
126000uF, 100V(the caps connected in parallel) shorted through 1ohms will discharge in .5-.63sec at peak amperage of 100A. Joule rating is .5C(V)(V) = 630J.
3500uF, 600V(the caps connected in series) shorted through 1ohms will discharge in .014-.018sec at a peak amperage of 600A. Joule rating is still .5C(V)(V) = 630J
Thus, you can see that in the first selection, 630J is discharged in .5-.63sec, but in the second selection it is discharged more than 30x faster! Plus, you have a higher peak current rating.
Here a good link to read:
I'd wire them up in parallel and see what happens, then if you're feeling lucky, wire them in series. Note series will pose a higher stress on your caps because of discharge time. And I have to agree with getting an SCR. I would not be very hard to find a SCR with a pulse rating of 600A, the ones ForceLabs bought handle 1600A. You can fry your SCR by exceeding the pulse current for longer than the rated pulse time. You can figure out how long the capacitor takes to discharge by 4RC, where R is the resistance you are dicharging the capacitance through. It actually takes longer than this, 98% actually discharges in 4RC, but by that time the current will be minimal.
Part Scavenger, Fri Feb 10 2006, 03:18PM
If I series them all I have more voltage but max current is exactly samo of max current for 1 capacitor. Voltage is high but limited to this current. (ohms law again)
Probably thats why is spoken that they are not good for seriesing (as plate caps are)
Thats why im asking about series or paralell connection..
I don't really know what you mean by this. The higher voltage will allow the capacitors to discharge more quickly.
To demonstrate:
126000uF, 100V(the caps connected in parallel) shorted through 1ohms will discharge in .5-.63sec at peak amperage of 100A. Joule rating is .5C(V)(V) = 630J.
3500uF, 600V(the caps connected in series) shorted through 1ohms will discharge in .014-.018sec at a peak amperage of 600A. Joule rating is still .5C(V)(V) = 630J
Thus, you can see that in the first selection, 630J is discharged in .5-.63sec, but in the second selection it is discharged more than 30x faster! Plus, you have a higher peak current rating.
Here a good link to read:
I'd wire them up in parallel and see what happens, then if you're feeling lucky, wire them in series. Note series will pose a higher stress on your caps because of discharge time. And I have to agree with getting an SCR. I would not be very hard to find a SCR with a pulse rating of 600A, the ones ForceLabs bought handle 1600A. You can fry your SCR by exceeding the pulse current for longer than the rated pulse time. You can figure out how long the capacitor takes to discharge by 4RC, where R is the resistance you are dicharging the capacitance through. It actually takes longer than this, 98% actually discharges in 4RC, but by that time the current will be minimal.
Re: six hundred precious joules
Marko, Fri Feb 10 2006, 03:25PM
You dont need to calculate to see obivous, energy is always same otherwise you could rewire charged caps and make prepetuum mobile :D
Line voltage is 220V, vhen rectified hangs around 300 but still too high to charge 3 in series.
Il use transformers for low voltage supply and AC supply for charging transformer.
Or maybe even boost converter/SMPS may be good for voltage regulation.. ?!
200V seems best as in any case transformers must be used.
Also I have original rails that connected capacitors in 3vs 3, just practical !dodge
Marko, Fri Feb 10 2006, 03:25PM
You dont need to calculate to see obivous, energy is always same otherwise you could rewire charged caps and make prepetuum mobile :D
Line voltage is 220V, vhen rectified hangs around 300 but still too high to charge 3 in series.
Il use transformers for low voltage supply and AC supply for charging transformer.
Or maybe even boost converter/SMPS may be good for voltage regulation.. ?!
200V seems best as in any case transformers must be used.
Also I have original rails that connected capacitors in 3vs 3, just practical !dodge
Re: six hundred precious joules
Michael W., Fri Feb 10 2006, 03:48PM
SO I have 2 1000uF 300V Electrolytic Caps for a coil gun. Is it better to hook them in series for 600V 500uF?
Michael W., Fri Feb 10 2006, 03:48PM
SO I have 2 1000uF 300V Electrolytic Caps for a coil gun. Is it better to hook them in series for 600V 500uF?
Re: six hundred precious joules
Marko, Fri Feb 10 2006, 04:10PM
Its true for external load of 1 ohm, but here we just say external load is 0 (imposibble in reality)
and consider only internal resistances of caps, thats what im talking about.
In series they cannot give more current than 1 cap would give, because their resistance is 'stacking' with voltage, we get only max voltage but not in (maximum) current.
This really may be better for SCR-s as the would need to switch lesser current...
Parallel capacitors can give six times more current than one but voltage is lower so external load limits current more...
I think it doesn't really matter so much after all, now i decided 3 vs 3 in series :)
This are rather smll caps but some mini coilgun could be made.
paralell is better as your switching device doesn't need to handle large currents for long, actually again i think its not real problem...
Marko, Fri Feb 10 2006, 04:10PM
126000uF, 100V(the caps connected in parallel) shorted through 1ohms will discharge in .5-.63sec at peak amperage of 100A. Joule rating is .5C(V)(V) = 630J.
3500uF, 600V(the caps connected in series) shorted through 1ohms will discharge in .014-.018sec at a peak amperage of 600A. Joule rating is still .5C(V)(V) = 630J
Thus, you can see that in the first selection, 630J is discharged in .5-.63sec, but in the second selection it is discharged more than 30x faster! Plus, you have a higher peak current rating.
Its true for external load of 1 ohm, but here we just say external load is 0 (imposibble in reality)
and consider only internal resistances of caps, thats what im talking about.
In series they cannot give more current than 1 cap would give, because their resistance is 'stacking' with voltage, we get only max voltage but not in (maximum) current.
This really may be better for SCR-s as the would need to switch lesser current...
Parallel capacitors can give six times more current than one but voltage is lower so external load limits current more...
I think it doesn't really matter so much after all, now i decided 3 vs 3 in series :)
SO I have 2 1000uF 300V Electrolytic Caps for a coil gun. Is it better to hook them in series for 600V 500uF?
This are rather smll caps but some mini coilgun could be made.
paralell is better as your switching device doesn't need to handle large currents for long, actually again i think its not real problem...
Re: six hundred precious joules
Tesladownunder, Fri Feb 10 2006, 04:25PM
I have used SCR switching for a 1500 joule cap bank and I have used a mechanical switch comfortably at powers up to 5kJ so far and 80kA plus without welding.
Peter
Tesladownunder, Fri Feb 10 2006, 04:25PM
Firkragg wrote ...
Switch is far bigger problem, I dont like to go arcwelding so mechanical switch cannot be just a solenoid pushing some metal conductor, that will surely weld and dissipate far more power than intended target.
Solenoid is simple and good idea for triggered gaps, but not for direct contact switching.
conclusion: I must buy SCR.
Switch is far bigger problem, I dont like to go arcwelding so mechanical switch cannot be just a solenoid pushing some metal conductor, that will surely weld and dissipate far more power than intended target.
Solenoid is simple and good idea for triggered gaps, but not for direct contact switching.
conclusion: I must buy SCR.
I have used SCR switching for a 1500 joule cap bank and I have used a mechanical switch comfortably at powers up to 5kJ so far and 80kA plus without welding.
Peter
Re: six hundred precious joules
Marko, Fri Feb 10 2006, 04:52PM
I saw your rope-switch !lol maybe that will be in the end only option for me too !shy
PS. really coolest site TDU.. !dodge I saw it year ago and was impressed...
Marko, Fri Feb 10 2006, 04:52PM
I saw your rope-switch !lol maybe that will be in the end only option for me too !shy
PS. really coolest site TDU.. !dodge I saw it year ago and was impressed...
Re: six hundred precious joules
Kolas, Sat Feb 11 2006, 04:32AM
I used very large relays in one of my coil guns, and I had great results. They were 2kj banks
The switch is one of those things that are easy to replace. I'd go with a large relay, and get an scr later.
Kolas
Kolas, Sat Feb 11 2006, 04:32AM
I used very large relays in one of my coil guns, and I had great results. They were 2kj banks
The switch is one of those things that are easy to replace. I'd go with a large relay, and get an scr later.
Kolas
Re: six hundred precious joules
Marko, Sat Feb 11 2006, 05:44PM
I have some contactor switches but im afraid to weld and ruin them...
Also I have acess to big omron relay with visible and easily acessable contact, but it is still too small for that current...
Marko, Sat Feb 11 2006, 05:44PM
I have some contactor switches but im afraid to weld and ruin them...
Also I have acess to big omron relay with visible and easily acessable contact, but it is still too small for that current...
Re: six hundred precious joules
Dr. Shark, Sat Feb 11 2006, 06:21PM
Oh, btw, for charging voltage I don't really see the problem of charging to 200V or 300V from mains. In practice you will need some kind of current limiting which drops voltage anyway, and if you supply voltage is not higher than the cap voltage, charging will take literaly forever.
Dr. Shark, Sat Feb 11 2006, 06:21PM
Oh, btw, for charging voltage I don't really see the problem of charging to 200V or 300V from mains. In practice you will need some kind of current limiting which drops voltage anyway, and if you supply voltage is not higher than the cap voltage, charging will take literaly forever.
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