[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: capacitor charge rate/power
Pholp -
Sure, the simulation is attached. It shows how the graphs were computed.
http://1071737050/site/misc/ChrgSim.xls
Remember - charge rate varies with time whether or not the charging source
is a steady DC source or a time varying 60 cycle AC sinusoid because the
capacitor voltage is also changing and it is the voltage difference that
effects the charging rate.
Time and voltage charge are related, so you should be able to lookup the
time to reach a specific charge. The program was written quickly for my
own use so it may not be clear what's going on. It mainly shows when
maximum energy is stored and that, depending on capacitor size, charging
continues past the time of peak voltage (assuming gap is set wide) on the
60 cycle AC source.
Like any simulation, accuracy is dependant upon the no. of iterations.
For most purposes, 100 calculations per 1/4 cycle should be sufficient.
Since Excel was doing all the work, I went for a 1000 calculations and that
gives very very accurate results - more accuracy than is practically needed
for TC purposes.
If you have trouble making a go of it, give me the details of your
proposed system parameters and I'll set up the program for you and send it
back. Right now it is set up for a 15/30 NST.
Good luck with it, Dick
At 05:55 PM 7/30/00 +0000, you wrote:
>That was helpful in that it gives me a basic idea of how it will act, but i
>wanted specific times, or a way i could find out the charge rate for my
>system. Could you send me the simulator you used?
>
>thanks
>
>
>>From: Richard Kircher <richard.kircher-at-worldnet.att-dot-net>
>>To: "Tesla list" <tesla-at-pupman-dot-com,kawanze-at-hotmail-dot-com,twftesla-at-uswest-dot-net
>>Subject: Re: capacitor charge rate/power
>>Date: Sat, 29 Jul 2000 23:48:09 -0400
>>
>>Hi Pholp,
>> This is the same question that I myself about a month ago. When the
>>driving source is anything but a constant voltage, such as a sinusoidal AC
>>waveform, then the simplest way to solve the problem is with a simulation.
>>I did this to determine the optimum capacitor size for a particular size
>>transformer. I have attached a JPG file that shows results and can send
>>you the simulation in Excel if you are interested. It assumes a pure
>>sinusoid driving waveform. I understand that the "real" waveform is
>>distorted due to non-linearities in the NST. The simualion works for any
>>input waveform, so if someone can help with characterizing the
>>non-linearities, then an exact and more useful solution can be computed.
>>Here is text that was sent to another Coiler as we discussed the simulation
>>and resulting graphs that are attached.
>>
>>Look at the jpg graph first. It combines results obtained from the Excel
>>worksheet and shows how I was trying to select the optimum capacitor for my
>>NST.
>>
>>The graph can be verified by simulating the charging of a capacitor as I
>>have done or by direct measurement. It is based on a 60 cycle, 15000 volt
>>rms, 30 ma NST sinusoidal charging source, however the results are
>>scaleable to any size transformer and matching capacitor. The top and
>>bottom graph both use time in milliseconds along the same scale x-axis. A
>>full cycle of 60 Hertz is 16.7 milliseconds while a 1/4 cycle is 4.17
>>milliseconds.
>>
>> The top graph (on jpg file) shows the capacitor voltage without
>>spark gap (no discharges). The C00375 curve is the voltage for a 0.00375
>>uF capacitor, C0053 curve is the voltage for a 0.0053 uF capacitor, C0075
>>curve is the voltage for a 0.0075 uF capacitor. As expected, the smallest
>>capacitor charges to the highest voltage (not energy) and follows the
>>charging waveform most closely, while the larger capacitor lags most behind
>>in voltage. That's because Vcap is the integral of 1/C i dt. Also notice
>>that the cap keeps charging beyond a 1/4 cycle until the driving
>>transformer drops below the cap voltage. Since the larger capacitor has
>>the lowest voltage, it has the longest charge time. You may benefit from
>>this because you have a synchronous spark gap that can be made to fire at
>>any time. Hopefully this could be used to select the optimum firing angle.
>>
>>
>> The bottom graph is the energy stored in the capacitor and is
>>what is really important. The spark gap determines the time and therefore
>>the energy that is released into the primary circuit. This is why one of
>>the final tuning tweaks is to increase the primary spark gap and release as
>>much energy as possible. The J00375 curve is the Energy (in Joules) as a
>>function of time for a 0.00375 uF capacitor, J0053 curve is the Energy for
>>a 0.0053 uF capacitor, J0075 curve is the voltage for a 0.0075 uF
>>capacitor.
>> Several interesting conclusions can be drawn from these curves:
>>
>>1. If the spark gap is set at a low voltage or an async SG is used such
>>that the charging time is short (less than 4 ms in a 60 cycle system), then
>>there is a slight advantage in using a capacitor that is a little smaller
>>than the size that matches the impedance of the transformer.
>>
>>2. All else staying the same (not optimizing design of the cap size),
>>changing to a larger transformer leads to longer sparks because its higher
>>charging current capacity increases the charging rate - same as having a
>>smaller capacitor in voltage, but more energy because the capacitor size
>>stays the same (J = .5 * C * V^2)
>>
>>3. There is a slight advantage in the 6 to 7 ms region in energy stored
>>and spark length if the discharge gap size could be set to fire in this
>>time range. For this 15/30 NST example, the spark setting should be around
>>13,000 volts. Note the same final tuning tweak rule applies. You'll know
>>if the gap firing voltage is too high because it won't fire at all with the
>>larger cap. Yeh, I admit this is tricky tuning but is something to shoot
>>for while squeezing out the longest spark length out.
>>The results shown by the jpg graph were done to try and optimize the
>>capacitor size and determine the best firing voltage or time.
>>
>>Hope this helps, Dick
>>
>>
>>At 06:33 PM 7/29/00 -0600, you wrote:
>> >Original poster: "Pholp Smiff" <kawanze-at-hotmail-dot-com>
>> >
>> >can anyone give me a formula as to how long it takes to charge a
>>capacitor
>> >depending on size and power? i.e.: using a 12kv-at-60mA transformer, how
>>long
>> >would it take to charge a .1mF capacitor? Can someone tell me and show me
>> >the math behind it? And how much power is actually stored and let out in
>>a
>> >discharge. Also i'd like to know how to determing the size of a bleeder
>> >resistor for capacitors.
>> >
>> >thanks
>> >________________________________________________________________________