Charging a Capacitor and Shocking

[YT2095]

yes you`ll need to put more voltage into it, an inductor is a good way to accomplish this.

[5614]

The voltage across a capacitor can never exceed that of the power source.

 

You can see this from that graph, what's it called? This one:

http://hyperphysics.phy-astr.gsu.edu/Hbase/electric/capchg.html

still can't remember the name, maybe it's just a 'time constant graph'.

[zking786]

So I put an induction coil in series with the capacitor and then disconnect the battery, making sure to close the circuit?

 

How big an induction coil do I need to charge it to 100uF?

[YT2095]

that won`t work.

you need the coil and the cap in parallel, with a Diode connecting one lead of the cap to the coil so it`s like one big ring, wire all in series and then connect the remaining 2 ends.

Then apply the power source across the coil only for a fraction of a second.

you`ll find you cap will accumulate quite a bit of charge with repetition of this.

beware though! if the cap is under-rated in voltage or reverse polarised, you`ll not only destroy the cap but they can get quite hot and possibly explode. Secondly, even if done correctly, the charge held in the cap Can Kill!

[zking786]

Wouldn't it have blown the capacitor if the polarities were reversed? Earlier, you mentioned that tantalums are really sensitive when it comes to polarity.

 

Also, I was reading your explanation about how the astable multivibrator works and didn't completely understand it. Firstly, why is it that when one transistor is off the other turns on. Secondly, why aren't both capacitors charged at the same time?

[YT2095]

wrong thread chum, this is about your capacitor charging, not your inverter

[zking786]

The above post is intended to be for another thread. Disregard it.

 

For this thread:

I have the circuit set up as prescribed, but no luck. The inductor does warm up, but the capacitor doesn't charge beyond about 0.8V. Why? I've used two different inductors and two different capacitors--same results. Nothing blows, but no substantial voltage buildup.

[YT2095]

you only need Momentary contact with the power on the inductor, it shouldn`t get HOT.

what inductor are you using????

[zking786]

Once from the camera circuit itself another from a router (about twice the size). I don't know the exact inductance.

[YT2095]

aha, therein lies the problem, I`m thinking single winding inductors (car ignition coils or chokes) those sorts are transformers, and although they CAN be made to work, it`s not as simple as something you can explain in text over here sadly

without seeing them I can`t really help, be sure if I had them here it would be up and running within a minute no problem.

can you actualy See the wires from these where they connect to the Posts?

IF you can, the 2 posts with the thinest tiny wires are the ones to connect to your cap and diode "loop".

the ones with the Thickest wires are then to be where your momentary power is switched on/off (pulsed).

it`ll probably have 3 posts with thick wire, one post will have 2 wires attatched to it (center tap) one coil will be a feedback winding) ignore the center post and attatch the power to the end posts with only one wire each

[zking786]

I've done that, I've connected the two thin wires into the circuit. In fact, the inductors I'm working with only have two leads. They just seem to be coils wrapped around plastic or rubber posts. There isn't a center tap.

[YT2095]

in that case they`re probably only Micro Henries in inductance value then, you`ll get nothing appreciable out of them without oscillating at high frequencies.

the low resistance winding on your inverter transformer should work though, but be carefull as the sparks from back EMF can jump and also make You Jump too!

[zking786]

I see the spark! But it charges really slowly -- I have to tap it about 20 times to get about 5V from a 1.5V battery. I'm afraid I'd blow the 12V lead-acid ups battery I have if I used it.

[YT2095]

well you`de have to be Very fast, I find that if you Brush it across very fast, you`ll not experience any real problems.

it`s alot better than physicaly touching and removing "manualy".

non the less, your 12v SLA will be perfectly fine

[zking786]

I've been brushing the terminals.

 

Also, I'm wondering how small inductors, like those in the camera's circuit, can so quickly charge a capacitor? Are they using some sort of oscilator or transistor switch?

 

Also, what's "back EMF"?

[YT2095]

they use a high frequency oscillator that switches the power on/off several 1000 times per second using a transistor.

your 100 or whatever times a minute will only provide a fraction of that charge.

but you DID get 5v from 1.5v so you now at least you understand the Principal and have demonstrated this and seen it in action

 

as for "back EMF" I suggest you google for it, it`ll explain things a little better than I can at the moment and in greater detail

[zking786]

Maybe if I use a high rpm motor at good gearing I could charge the capacitor quickly and more efficiently by brushing the contacts.

 

Or, I could use the oscillator technique. Would I hook the oscilator to the ground and to the base junction of the proper transistor. The collector I'd connect the voltage source and the emitter the induction coil port.