DRSSTC PRIMARY CAPS
gentoo_daemon, Thu Mar 29 2007, 03:41AMAn update,
So I ordered the famous 942C20P15K(non-stock) MMC caps from rell.com last week. The plan was to have 8 kv at 33 uf. That would be around 9 strings of 4. Running through some threads on this board, I realized that may not get them in time. So that leaves me with the other option of using the GE 42L series capacitors. How do i make the transition since the GE aren't so sturdy? Will I need longer strings?
Re: DRSSTC PRIMARY CAPS
sparky, Thu Mar 29 2007, 05:22AM
run 1/2 power for now... ?
sparky, Thu Mar 29 2007, 05:22AM
run 1/2 power for now... ?
Re: DRSSTC PRIMARY CAPS
Steve Ward, Thu Mar 29 2007, 05:27AM
Well, it really depends on the power level. The GE42L caps are OK for DRSSTC in particular, because its the RMS current rating of the cap that matters much more than the peak rating (which is what the 942C excells with). What 42L cap do you have? And, what is the expected power level you want to run at? Answer that and i can make a suggestion for how many parallel strings are needed.
Steve Ward, Thu Mar 29 2007, 05:27AM
Well, it really depends on the power level. The GE42L caps are OK for DRSSTC in particular, because its the RMS current rating of the cap that matters much more than the peak rating (which is what the 942C excells with). What 42L cap do you have? And, what is the expected power level you want to run at? Answer that and i can make a suggestion for how many parallel strings are needed.
Re: DRSSTC PRIMARY CAPS
gentoo_daemon, Fri Mar 30 2007, 01:16AM
Steve, Here are my numbers.
#primary LC
C = 0.3106 uF
L = 0.0393 mH
z(surge) = sqrt(L/C) = 11.25 ohms
I(pk) = 600 amps #max pulsed current for eupec BSM200GA120
V=I(pk)*Z(surge)=6750 volts
#INT freq = 200 Hz, duty cycle = 8%
ONtime = 0.0004
OFFtime = 0.0046
I(rms) = sqrt((ONtime/OFFtime)*0.7*I(pk)^2) = 148.03 amps
gentoo_daemon, Fri Mar 30 2007, 01:16AM
Steve, Here are my numbers.
#primary LC
C = 0.3106 uF
L = 0.0393 mH
z(surge) = sqrt(L/C) = 11.25 ohms
I(pk) = 600 amps #max pulsed current for eupec BSM200GA120
V=I(pk)*Z(surge)=6750 volts
#INT freq = 200 Hz, duty cycle = 8%
ONtime = 0.0004
OFFtime = 0.0046
I(rms) = sqrt((ONtime/OFFtime)*0.7*I(pk)^2) = 148.03 amps
Re: DRSSTC PRIMARY CAPS
gentoo_daemon, Fri Mar 30 2007, 01:23AM
and I haven't decided on a particular 42L.
gentoo_daemon, Fri Mar 30 2007, 01:23AM
and I haven't decided on a particular 42L.
Re: DRSSTC PRIMARY CAPS
Steve Ward, Fri Mar 30 2007, 03:49PM
That looks familiar... did i post that somewhere or did you happen to come up with the same .7 constant? Anywho, close enough to real life.
Typically, the larger of this 42L series is 9 to 11A RMS rated. So you would need ~13-16 strings and enough in series to handle the 7kV and maybe a bit more for headroom if you want them to last a really long time (ive tested the 1200V 42L caps to 2500V in DRSSTC use... on accident... they start snapping like little fire crackers).
The 942C caps you have are only rated to 13A i think, so you would still want many more parallel strings than you planned on.
My suggestion : lower your duty cycle to reduce the RMS current. 400uS is really too long in my opinion. You will probably find that 200uS is enough if you are supplying ~650VDC. Efficiency really seems to drop off past 250uS (you get longer sparks, but at the expense of much higher input power).
Steve Ward, Fri Mar 30 2007, 03:49PM
I(rms) = sqrt((ONtime/OFFtime)*0.7*I(pk)^2)
That looks familiar... did i post that somewhere or did you happen to come up with the same .7 constant? Anywho, close enough to real life.
Typically, the larger of this 42L series is 9 to 11A RMS rated. So you would need ~13-16 strings and enough in series to handle the 7kV and maybe a bit more for headroom if you want them to last a really long time (ive tested the 1200V 42L caps to 2500V in DRSSTC use... on accident... they start snapping like little fire crackers).
The 942C caps you have are only rated to 13A i think, so you would still want many more parallel strings than you planned on.
My suggestion : lower your duty cycle to reduce the RMS current. 400uS is really too long in my opinion. You will probably find that 200uS is enough if you are supplying ~650VDC. Efficiency really seems to drop off past 250uS (you get longer sparks, but at the expense of much higher input power).
Re: DRSSTC PRIMARY CAPS
gentoo_daemon, Fri Mar 30 2007, 09:59PM
I got that rms formular from the drsstc wiki.
Good news, I spoke with a rep from rell, and ordered the -f roHS compliant 942 capacitors instead, which are in stock. I got 65 of those.
Working out the new numbers, for 148 amps, i'll need 12 strings of 4. For now, I'm only planning to use 440 volts (220 doubler) as in input for my coil. Do you think I'll still be able to pull some decent spark length?
gentoo_daemon, Fri Mar 30 2007, 09:59PM
I got that rms formular from the drsstc wiki.
Good news, I spoke with a rep from rell, and ordered the -f roHS compliant 942 capacitors instead, which are in stock. I got 65 of those.
Working out the new numbers, for 148 amps, i'll need 12 strings of 4. For now, I'm only planning to use 440 volts (220 doubler) as in input for my coil. Do you think I'll still be able to pull some decent spark length?
Re: DRSSTC PRIMARY CAPS
HV Enthusiast, Sat Mar 31 2007, 02:22AM
Who says the GE capacitors aren't so sturdy? We use them exclusively in our solid state coils and have had practically zero failures with these type of capacitors.
HV Enthusiast, Sat Mar 31 2007, 02:22AM
wrote ...
How do i make the transition since the GE aren't so sturdy?
How do i make the transition since the GE aren't so sturdy?
Who says the GE capacitors aren't so sturdy? We use them exclusively in our solid state coils and have had practically zero failures with these type of capacitors.
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