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Artikbot

Tue Sept 28 2010, 09:45AM

Registered Member #3247 Joined: Mon Sept 27 2010, 09:42AM
Location: Spain
Posts: 137

Second schem for the charger circuit:

I want to implement a 555 timer on there, but dunno how to connect it. I imagine it should go somewhere between the power supply and the primary of the transformer, but I'm pretty newb to ICs, have only worked with NAND doors on basic logic circuits. Help there would be appreciated :)

My other doubt goes with the transformer... Don't know where to start to order it O.O maybe I can just recycle some from the photoflash boards?

Oooooooooooooooops! I red thru the whole post again and the word "booster" caught my attention. I thought it was done via a transformer, but Wikipedia said something really interesting!

As far as I see it's way more simple than the design I initially thought of, so I'll investigate on that and might design one :)

So this is the boost converter I got in mind :)

Some points to comment about the booster:

1: How can I connect the timer? It's got 8 tabs as I can see in the datasheets.
2: Where can I buy the inductor? What sixze should I choose for a boost from 6 to 330V?
3: How can I make the voltage output regulable?
4: Is the overall scheme correct? I mean, any component missing/misplaced?

Thanks once more :)

Adam Munich

Tue Sept 28 2010, 10:39AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

This schematic I made a while ago should help. It'll flash from .5hz to about 60hz. Replace the cap with something smaller to get the speed up. A .1 ceramic one will work fine.

Artikbot

Tue Sept 28 2010, 10:44AM

Registered Member #3247 Joined: Mon Sept 27 2010, 09:42AM
Location: Spain
Posts: 137

Ic. Sochanging the capacitance I can adjust the timing?

I guess that end terminals get hooked into 1: the inductance and 2: the Vr to adjust pulse duration? I don't really get the second free tab :P

Thanks a million times and more :)

GhostNull

Tue Sept 28 2010, 12:51PM

Registered Member #2648 Joined: Sun Jan 24 2010, 12:45PM
Location: Australia
Posts: 291

Great work!
It's really good to see that you are putting in the effort to read all this stuff!

You got the concept of the zener diode down =D

With the boost converter your design looks good. Use this: to get the values you need.

For the 555 timer I suggest this article:

In case you don't know what duty cycle is, it is the percentage in the ON state of a single cycle. e.g. if is a single cycle it is on 80% of that cycle, then it has a duty cycle of 80%

To "drive" the MOSFET, you should be able to connect the output pin of the 555 to the gate through a resistor called a gate resistor, 68 ohms should work. A gate resistor is just a normal, low value (resistance) resistor connected to the gate of the MOSFET to reduce parasitic oscillations that cause ringing: there's probably a better article somewhere. It needs to be big enough to stop ringing but not so big as to slow switching. Here is a nice page on gate drive wave forms:

You might want to consider a "closed loop" design as used in this design: It will probably give a more exact output voltage but it will be more complex. I can make a post on how to convert it to output a lower voltage but it will be much more fun if you figure it out yourself.

Also, remember that the solenoid is an inductor and has the *potential* to create HV inductive kick back.

Great work! Keep it up and you should have a sweet coil gun soon =D

Cheers
-Ken

Artikbot

Tue Sept 28 2010, 09:02PM

Registered Member #3247 Joined: Mon Sept 27 2010, 09:42AM
Location: Spain
Posts: 137

Wow it's encouraging to receive good feedback, thank you :)

According tho the Zener diode, would it be necessary if I manually regulate&measure the output voltage with a resistor in the MOSFET and a voltimeter right after the diodes? I'm pretty sure it'll be needed in order to "dissipate" any current going into the capacitors that might ovecharge it, but I got a problem with those values... Or 200 or 390, no values in between...

Doubts concerning the 555 are mostly dissipated. I'll try to make it fit on my circuit right now :)
According to the duty cycle... So, that allows me to regulate the time the inductance stays charged and the time it discharges? I can't read the article, the link seems to be missing

Gate resistor... just as the ones placed on transistors I believe :)

Can you repost the link concerning the closed loop design? I can't see it either :S

So the solenoid is an inductor... Seems I have to add some reverse biased diodes+resistors in parallel with the solenoid to make the back EMF go dissipate on the resistors instead of going BAM on the cap bank. 1000V diode will be enough? I'll be getting a 5W resistor just in case... I'm a bit paranoid with values, I tend to go above the rated specs because I don't like things to burn out :P

So far my only *big* doubt is regarding the inductor on the booster. I don't know where to start searching one, it's hard to in Spain. Maybe I should wind my own because no one seems to sell inductors. I've seen uzzors2k use 130uH inductors, would that be overrated, underrated, situable, unsituable for my booster? If it's not asking too much... Can it be easily wound?

Thanks alot! Posting the updated circuit in a minute :)

Adam Munich

Tue Sept 28 2010, 09:18PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Until I see the schematic, all I have to say is get your inductors here.

Artikbot

Tue Sept 28 2010, 09:27PM

Registered Member #3247 Joined: Mon Sept 27 2010, 09:42AM
Location: Spain
Posts: 137

Here we go. A bit messy, but I tried to make wire paths as clear as possible :)

If something isn't really understandable, I'll manage to explain it.

Apart from the inductor values, it misses back EMF protection -basically don't know which components to use-

The variable resistors to variate timings and duration (is duration duty cicle?) I put 10k as shown in Grenadier's scheme. I guess that won't suffice, maybe I'll need higher? (just a supposition, haven't understood the NE555 datasheet part concerning the frequency regulation)

Well, no more delays, here it goes the circuit. With a deep error checking and some specs for the MOSFET and stuff about the inductance, I can start to order the parts and hopefully I'll have it built for the next monday :)

@Grenadier: Yep, I saw that site... but the shipping is kinda high for my country T_T thanks anyway :)

Edit: OMG I didn't see the "Coilcraft Europe" part! They ship from Scotland!! That's rough â‚¬4 shipping, great! (but ima gonna spend more in the inductance than in the rest of the circuit :P)
Edit2: o'wait! They ship FOR FREE?! hey this surely rocks!

Edit3: I've seen they have something as "samples".

What are they? Do they actually send free samples? Or do I have to buy a large quantity after getting a sample? This is pretty new to me :)

Adam Munich

Tue Sept 28 2010, 10:00PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

They do send free samples, which is why I recommended them. You don't have to buy a large quantity, but don't abuse it.

As for the pots, timing is space between the pulses, duration is the length of the pulses. How fast do you want the oscillator to run? With a 10uf capacitor on the 555 timer you'll get a maximum of about 100Hz. You can use a smaller cap to make t run faster. A .1uF cap will allow the timer to run anywhere from a few hundred Hz to a few thousand. I would just try a whole bunch of caps and see what works. They're really cheap, and you can never have enough capacitors.

Also, this is a nice program for designing simple circuits. It's free to use at home.

Artikbot

Tue Sept 28 2010, 10:09PM

Registered Member #3247 Joined: Mon Sept 27 2010, 09:42AM
Location: Spain
Posts: 137

Ahhhmkay. I just want to get a pair of inductors, if I happen to do a larger project I'll buy the products if they satisfy me :)

Do you recommend fast switching speed or slow? What does it change? (voltage output? larger pulses make higher voltages?)
Yea, I can get a huge range of caps at my local store, that aint' a problem :) and I have like... 50 or 60 kinds of capacitors. Not big ones, 350V I just have 10 80, 100 and 120uF. But lower voltages, from 6 to 30V I got lots and lots and lots of salvaged caps :D

I'll try that software, thanks!!

So you have any guidance for the inductor and the mosfet? So I can order them now/tomorrow morning in order to start building this as fast as possible, I'm really really excited about this :D

Thanks a lot! ^^

GhostNull

Tue Sept 28 2010, 10:44PM

Registered Member #2648 Joined: Sun Jan 24 2010, 12:45PM
Location: Australia
Posts: 291

Dam stupid links,

555 timers:

Boost Converter Calculator:

Ringing:

Gate drive wave forms (for GDTs but the resistor concept stilll applies):

A boost Converter with closed loop feedback:

(the Op-amp turns the 555 off when target voltage is reached)

And yep, the back emf diode is called a flyback diode, It goes in anti parallel with the solenoid. It just needs to be at least the capacitor bank voltage, the SCR should be able to block the bulk of the back emf from reaching the cap bank. A flyback diode with a resistor will help to dissipate it faster. I know I found a good page on this this awhile ago some were....

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