Hi, Im a total noob to this field and was wondering if anyone could provide input to prevent me from blowing up my ac output. What im doing is charging a home made HV cap with the following. I have a 1 amp 12vdc adapter, which i will be connection to a 12v
1amp neon sign power supply. output is 2kv ac @ 10ma. I will be rectifing & doubling voltage to charge the cap however i was wondering if this AC type conerter could possible draw too much current to burn it out? I have found other similar circuits however only reference to a resistor or charging resistor was after the diode to prevent feedback on discharge of the cap. Im not entirely sure if this was to limit current charging as well as it wasnt clearly explained. I thought this would be the best place to ask before try. I was thinking of adding a
1 or 2amp fuse between the ac adapter and neon supply to prevent killing the adaptor however this wont limit charging current if i need to. For my charging resistors i really dont know what i should put in as i dont want to drop below the 10ma current if possible and also dont want to drop voltage either if i can get away with it. Any recomendations would be greatly appreciated.
for those that are curious this cap is for a pulsed hv lazor experiment
Your point? A gun will kill him too if he points it at his head(first he will need to make sure it is loaded).
Breakdown of air is about 30kV/cm so its not like this thing will jump out at him. Obviously if he's storing charge on the cap then he will need a safe way to discharge it before sticking his hands in there.
In any case 10mA isn't, in general, enough to kill.
You would have been more helpful to try to answer his questions instead of stating the obvious.
Oh!! Great come back. You asked him a question... did he ask for a question to his question or to answer his question? If you know so much about this shit then surely you could supply more information. Your question about how he will convert DC to AC shows just how ignorant you are... Your trying to act like your intelligent by misdirection. The crux of the matter is not that how he will get AC from DC(which I assume he will do by an inverter like everyone else) EXACTLY what he asked.
Unlike you I do not know the true answer so I did not respond. I wouldn't want to give him bad advice. Maybe you should take that advice instead of trying to act like you know something about something you don't.
My answer would be to add about 100kohms in series with the cap to generate a peak instantaneous current of V/R ~= 2k/100k A = 1/50 A. While this is over is rated max of 10mA it is only 10mA above it and will die down to 7% of that within ~5 RC's. For his application this might be to long. He mentions that it is for a pulsed laser but how long between each pulse does he need. How big is the cap? In anycase he could work down from the 100kOhm resistor to increase the charge rate. Although having a resistor of 1ohm produces an instantaneous peak current in the secondary of about 2000 A and that means its over 4M in the primary. I'm sure that he will definitely not get this out. But even if it pulls just 10 amps from the 12VDC supply it could eventually cause problems. (depending on how fast and how many times it is pulsed) Obviously there will be a saturation point that will limit the peak inverse current and most devices can handle a substantially higher peak inverse current but I have no specific answers.
But unlike you have I have no practical experience with the subject so I did not answer... You also obviously have no practical experience but answered with nonsensical questions trying to act like you know something that you don't(which you do a lot of).
I mean, come up... WTF is up with "How will you convert DC to AC?"??? WTF do you think you can ask such stupid questions. You are assuming the guy is a total idiot... and this really means you are the idiot. He did not ask anything about that and you should assume that he as a little bit of a clue what he is doing. Now maybe it is the case he will hook up the 12VDC supply directly to the sign transformer and it won't work... GUESS THE FUCK WHAT??? YOU KNOW THEY MAKE 12VAC POWER SUPPLIES TOO? Your f****ng question is moot and just a waste of time. If he does have that problem he will post back and say it doesn't work and then someone will solve that problem very quickly and he will just have to run to wal-mart and by a 12VAC adapter or tear out the rectification in his 12VDC adaptor.
Now instead of that bs you should have tried to answer his real problem but no, since you have no clue you misdirect like a magician. A magician has no real magical powers so they pretend. You are nothing but an intellectual magician. I see your BS all the time in this NG and you do more harm than good and I think its time someone pointed it out. Surely though there will be those that will jump on me because they too are intellectual magicians and everyone knows you guys stick together.
Also, it is true its a probably a good idea to point out that it could kill him but if he doesn't know this already then maybe natural selection needs to take place. Also, every time someone plugs in a device you need to warn them they might die too. Do you know that only about 200 people a year die from electrocution? Of those how many do you think are not electricians or kids?
"A low-voltage (110 to 220v) 60 Hz AC traveling throughout the chest for a fraction of a second may induce ventricular fibrillation at currents as low as 60 to 100 mA; about 300 to 500 mA of DC are required. If the current has a direct pathway to the heart (e.g., via a cardiac catheter or pacemaker electrodes), much lower currents (>1 mA, AC or DC) can produce fibrillation. Body resistance (measured in ohms/sq. cm)* is concentrated primarily in the skin and varies directly with the skin's condition. Dry, well-keratinized, intact skin has an average resistance of 20,000 to 30,000 ohms/sq. cm, whereas the resistance of moist thin skin is about 500 ohms/sq. cm. "
So assuming the length of is arms to chest is ~30cm gives about
2000/(30*30k) = 2mA. Ofcourse if he's playing with the shit wet or swetting a lot then that goes up to about 133mA.
Instead of being a moron about the dangers you should just point out that its not safe and maybe link to a site about the dangers and some saftey precautions. Ofcourse if he's poking around in the circuitry while its life then maybe he deserves to get electrocuted. Its not that bad though, I've messed around inside of life TV's and not be electrocuted. (Maybe it was a stupid thing to do but I'm alive.)
The point is, Homer, is that if your not going to try and answer is questions then why bother to post? I know you need to feel useful but its just a waste. Try volunteering at something your good at like picking up trash.
This was just for a rough approximation. Obviously its an RLC circuit but this should just result in reducing the overall peak instantaneous current which means RC will effectively be larger. I did most of those calculations earlier so they may be wrong. (My memory isn't so good these days). In any case it wasn't suppose to be a detailed analysis but just an overall general idea. The point is that increasing R increases the charge time but decreases the maximum instantaneous current. I would imagine that its not so important because it will be limited by the transformers and as long as the average current isn't to high over the charge time then it shouldn't be a problem but the average will need to include the number of charges per second too.
I would think that if you just use it intermittently then you probably don't need a resistor. If this is pulsed many times a second then you'll need a more detailed analysis. (or just experiment) (also I'm assuming V = 2kVDC but since its suppose to be 2kVAC the above numbers will be off)
In any case I'm not really trying to give any info because I have not done this sorta stuff before and I coudl be wrong. There are many web sites that talk about HV and stuff and you'll find more practical experience there. Also, an important side note, which you probably know, is that the capacitor will probably be the most dangerous thing there. You should make sure you safely discharge the cap if you plan on messing around it. The 2000V could span a mm or so and get you. Probably won't kill you but could hurt.
If your eager to start you might try using a 1M resistor and taking some measurements such as charge time(which you can approximately compute anyways) and run it for a while and see if things get hot(very doubful). Then work your way down from there until you reach your specs. My guess, and its only a guess, that you could probably deal with maybe even just a few hundred ohms or even less and everything will work fine if your not pulsing it hundreds of thousands of times a sec.
You might want to give more information on the specifics so someone that knows about this stuff can give a more informed decision. (although maybe all pulsed lasers follow a specific implementation). I think the two important things are the capacitatance, pulses per second, and operation time.
You're still an idiot. Hooking up a 12 VDC supply to a sign transformer isn't going to do much of anything. Asking questions is the best teaching method.
And your assumptions could kill him. I've been working with electronics and electricity for over 50 years and I don't fool with sign transformers or the like without following a lot of precautions. For someone with as little knowledge as he shows his next few steps could end his world.
ok, I appreciate all your concerns for safety and believe me all precautions will be taken. the cap size will certianly be more than 100 times more powerful enought to kill myself but i will be doing whatever so that wont happen. So lets not worry about that for now . the basic charge curcuit after ac adapter and fuse is as follows the ac current to charge the cap will be 1/2 wave rectified on + and
1/2 wave on - using 4 6kv 200ma diodes. each ac lead will have 2 diodes connected to it ( forward and reverse on each) the the 2 + ends will be positive out and the 2 negative ends will be negative out. this will evenly split the ac into a 1/2 wave rectified positive and 1/2 wave rectified negative. 2kv ac usually means peak + and - is 2kv so by seperating them i will have effective 4kv diference on leads for cap charging without multiplying. now this is where i have questions. 1) imaging this is going straight to a large cap. will discharging the cap cause feedback to the 2kv transformer? I have seen others use a 1k ohm resistor past the diodes for feedback prevention when the cap is discharged? I know that resisters for this could vary and ohms law dictates that if i use large enough Resistors most the current and voltage will go thru however if a return spike came back on discharge it would filter and prevent most or some from hurting my diodes or transformer. Thing is i would like to prevent as much feedback as possible however do not want to drop as much voltage. My experience comes form Whimhurst machines and variants so i dont know alot about HV resistors. Im stepping up from those as my projects need more current that vandegraff. and believe me when it comes to safty, with leyden jars theese can be just as dangerous or more so.
i would also prefer to sync charging ( or at least discharging ) as + and - are perfectly out of phase on diferent leads. can i achieve this by charging first to a 3 way cap ( think of leyden jar setup with ground connection each on like how some whimhurst machines are configured, positive - ground chain - negative ) the discharging from them automatically? this circuit would be the same as a Greinacher voltage doubler
thanks, any thoughts or jokes about the guy that will blow himself up is appreciated ;) lol Thanks,
omg! you must be f****ng l33t all those years of installing ceiling fans and you call yourself an expert. I guess you really think that just because you've been around for 50+ years means your an expert. To bad you don't understand that age != experience. Ofcourse one might think it is correlated but usually arrogance and ego wins out every time.
Yeah, I agree. If your stupid enough not to be careful then your stupid enough to die. (Ofcourse there are always accidents but if one is irrational like homer then they will never get anything done. Sometimes you gotta take a risk to make progress)
Yes, there is things such as inductive kick bad, EMF radiation, etc that can cause problems. I cannot really tell you much because I do not know either. There are several sites I have seen that do discuss this topic though. What you want is some type of path to ground that the feedback can take.
For example, metal oxide varistors are used when a voltage spike on the mains is larger than a certain amount and the mov sorta opens up and proves a least resistive path to ground. This prevents that spike from going through the transformer. You could use somethinglike that but not sure if they make them for that high of a voltage. (although maybe you could use several in series) Theres probably a better method and ofcourse theres a whole industry built around HV stuff and they all have these very special techniques and exotic devices for dealing with these kinds of issues. You might look into how they handle this stuff in power distribution. (usually though its for high currents but maybe something will work).
I would say maybe you could just ignore it for now and see but you might not want to take the chance and ruin your components.
Maybe you can put a relay switch between the cap and diodes to completely remove it from the circuit? The relay can be triggered to open when the cap has reached a certain voltage. Might be a good solution. Ofcourse when it closed there would be an inrush of current and this could effect the contacts.
So you want to charge up one side while discharging the other? (so you would increase the pulse rate by a factor of 2)
No, I have no issues with you doing this. Its better than sitting on your hands or twiddling your thumbs cause your too afraid. There are a lot of weenies out there. If it wasn't for people taking risk we wouldn't be where we are. Ofcourse its not that big a risk and you seem like you know the risks. There are many things you can do such as wearing insulated gloves or even a suit but this isn't really necessary if you just pay attention(which I think you will and its not really my place(or anyones) to tell you what you can and can't do)
i think ill do the throw switch like you suggested to prevent that feed back. Im going to making my own relay switches to insure proper insulated and safely encased . basically all my work will be contained in pexiglass with a few redundant grounding options in case a path burns out.
this is not really necessary for the lazor project. Im looking however for a simple solution to to sync the negative and positive pulse that i split from the same output. the negative ac phase must match the exact positive phase. End result i want for this seperate project is pulsed dc that is equal and opposite + & -. this is for hv tests regarding field polarization effects. Non phase is usless for this test as the oppsite current is gone or stored before the other pulse comes out. That why i was thinking on using the doubler using the ground . just not sure on a circuit that will pulse out from that . that curcuit " i think" just maintains HV voltage if we dont use too much load where i want pulses like discharges instead. I thinking my best option might be to wrap my own transformer with 2 equal output windings. for the sync, any better suggestions? If i wrap one winding in one direction and the next in the opposite direction would each output winding be opposite polarity in sync? im not 100 % sure tho i think thats how it works. of course if this works i woudl run it on a figure 8 laminated core with input on centre and oppsite outs on either end to prevent it from shorting across the increased diference. in voltage. how does that sound? Again thanks for all your input.
here is the transformer i bought and i have 2 of them.
Specifications: Input: 12 Vdc @ 1 Amp (Suggested power source CAT# DCTX-1215). Output: 2,000 Vac @ 10 mA. Open circuit voltage: 3,000 Vac
30Khz. Short circuit current: 15 mA. UL.
I got the recomemded 1.5 amp power supply however other findings show that is a bit much current for this devic and i got another adapter that outputs 1 amp , again i dont want to burn anything out. i got an asortment of resistors and diodes as i was not sure what to get.
6 x 220 ohm 3 wat , 3 x 1k ohm 5 wat.
10 x .2 amp 6k diodes and a wackload lower voltage ones that prob will not ever need now
as for the home made cap i made from 6mil polyethelene which someone else used, surface area for diferent caps for now are ony small for testing now and will get bigger later. ( dangerous either way im sure ) foil surface area is about 30 cm x 5 cm for each pos and negative plate and tightly rolled around a dowel.
other caps are same materials but smaller surface area . later for good discharges i may have to go 10 or 50 times the size as the one i mentioned. i dont expect you to do all the math as im lazy however just want you to have a better idea what i have to start with other then loads of pexiglass
Don't sweat the extra current capacity, the circuit will draw what it requires. If your voltage is regulated to the correct value but your circuit needs more than the available current, expect the voltage to sag. Otherwise, you're good to go.