- #1
lekh2003
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- TL;DR Summary
- I need some help with an LRC circuit I have, and charging/discharging capacitors to function as needed.
I've been working on designing an experiment over the past few weeks as part of a school project, under the supervision of a teacher.
I have designed a small low-power coil-gun. I have a coil of roughly 60m 24 AWG copper wire wrapped around a length of 2.5cm of clear PVC pipe. I tested the resistance to be 5.4 ohms. The projectiles are small 5cm iron bolts. The idea is to have a current flowing through the coil for a short period of time to "shoot" the bolt. The speeds of the bolt are under 3 m/s and inside of a long PVC tube, keeping me well within safety. The idea isn't to create an optimal gun, but rather to test out some concepts in physics.
By using a DC power supply at 20V, I did some trial and error (with video analysis) that the optimal time for a current to be flowing through the coil is between 20-30ms. Obviously, I can't use a DC power supply since the trial and error method is too inaccurate. I would have to use an arduino to control the circuit to release current for a short period of time, but I don't have the access or the capability to use an arduino.
Hence, the solution is to use a capacitor. I calculated that a capacitance of 500##\mu##F would be optimal in the circuit to discharge within 20-30ms. My variable for the experiment is to check the impact of adding a resistor to the LRC circuit (which would increase the discharge time and decrease the current).
My issue is the capacitors themselves (electrolytic ones). I initially purchased a couple of 16 V 100##\mu##F capacitors, but I found that the voltage was too low to power the coil. Hence, I bought a couple of 50 V 100##\mu##F capacitors. So far I've only been working with one of them (for testing purposes), but hopefully I can eventually connect them in parallel to achieve 500##\mu##F as required.
My process has been the following:
1. Set up a circuit with the DC power supply at 20 V, connected with a 3k##\Omega## resistor (I read this was needed to keep the current low so as not to damage the capacitor).
2. Charge up the capacitor using this circuit.
3. Connect the capacitor to the coil.
4. Watch the results.
The problem is in the charging up of the capacitor. Firstly, I can charge it up to roughly 19 V. However, as I am looking at the voltage with my multimeter connected to the capacitor it loses voltage in real time. After a minute or so, it seems like its almost fully discharged. Not to mention, when plugged into my coil, it does absolutely nothing, ever.
Am I doing something wrong with my capacitors? Like some sort of special important rule that I'm missing? Are my capacitors just crap? I know they are the problem since everything else works fine, the coil and everything "fires" fine when connected to the power supply.
I can provide any images if necessary, I would greatly appreciate the help.
I have designed a small low-power coil-gun. I have a coil of roughly 60m 24 AWG copper wire wrapped around a length of 2.5cm of clear PVC pipe. I tested the resistance to be 5.4 ohms. The projectiles are small 5cm iron bolts. The idea is to have a current flowing through the coil for a short period of time to "shoot" the bolt. The speeds of the bolt are under 3 m/s and inside of a long PVC tube, keeping me well within safety. The idea isn't to create an optimal gun, but rather to test out some concepts in physics.
By using a DC power supply at 20V, I did some trial and error (with video analysis) that the optimal time for a current to be flowing through the coil is between 20-30ms. Obviously, I can't use a DC power supply since the trial and error method is too inaccurate. I would have to use an arduino to control the circuit to release current for a short period of time, but I don't have the access or the capability to use an arduino.
Hence, the solution is to use a capacitor. I calculated that a capacitance of 500##\mu##F would be optimal in the circuit to discharge within 20-30ms. My variable for the experiment is to check the impact of adding a resistor to the LRC circuit (which would increase the discharge time and decrease the current).
My issue is the capacitors themselves (electrolytic ones). I initially purchased a couple of 16 V 100##\mu##F capacitors, but I found that the voltage was too low to power the coil. Hence, I bought a couple of 50 V 100##\mu##F capacitors. So far I've only been working with one of them (for testing purposes), but hopefully I can eventually connect them in parallel to achieve 500##\mu##F as required.
My process has been the following:
1. Set up a circuit with the DC power supply at 20 V, connected with a 3k##\Omega## resistor (I read this was needed to keep the current low so as not to damage the capacitor).
2. Charge up the capacitor using this circuit.
3. Connect the capacitor to the coil.
4. Watch the results.
The problem is in the charging up of the capacitor. Firstly, I can charge it up to roughly 19 V. However, as I am looking at the voltage with my multimeter connected to the capacitor it loses voltage in real time. After a minute or so, it seems like its almost fully discharged. Not to mention, when plugged into my coil, it does absolutely nothing, ever.
Am I doing something wrong with my capacitors? Like some sort of special important rule that I'm missing? Are my capacitors just crap? I know they are the problem since everything else works fine, the coil and everything "fires" fine when connected to the power supply.
I can provide any images if necessary, I would greatly appreciate the help.