New to Coilguns - Coilgun Buildlog (Charger apparently fixed) / Electromagnetic Projectile Accelerators / Forums

Forums

4hv.org :: Forums :: Electromagnetic Projectile Accelerators

« Previous topic | Next topic »

New to Coilguns - Coilgun Buildlog (Charger apparently fixed)

first previous 7 8 9 10 next last

Move Thread

LAN_403

Artikbot

Sat Oct 02 2010, 05:23PM

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

Ofc! Parts are arriving by wednesday, but coil is expected to be here on friday/following monday.

Right not I'll be focusing on the design of the enclosure of the whole system itself.

To be honest, when I started and saw ALL that stuff to learn and to develop, I thought I was gonna die in the attempt :P

GhostNull

Sun Oct 03 2010, 08:00AM

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

You should use a voltage regulator. Battery voltage is variable and I think the Op Amp would have needed. The variable voltage from the battery would means that you will have to keep reseting it.

But otherwise, great work! I hope to see this completed soon!

Artikbot

Sun Oct 03 2010, 09:58AM

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

Well, since I'm using lithium cells with capability of delivering 125A sustained without dropping from 7.4V, theorically this circuit is no trouble for it to supply... So I think I'll be fine putting nothing more than a 6.1V Zener in series with the battery and adjusting the resistor dividers for the cap bank.

Thinking it better... I could attach two tiny volt meters to the coilgun with one connected to the battery terminals and the other to the caps... If the voltage falls behind 6.1V at the battery output means it's time to recharge it again, since it isn't any good dropping Lithium cells below 3V.

With a 6.1V 3Amp zener I would be great, considering I'm limiting the output of the battery to 2Amp for obvious speed means. Let too much current flow and you'll have a nice barbecue on the circuit :P

Thankies!

GhostNull

Sun Oct 03 2010, 09:57PM

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

Hm, I think you should still use a regulator regulator. Very simple, just 1 Voltage regulator IC and a Capacitor. It would be much better than a zener. Also always use a proper fuse. It will blow much more reliably and not blow up and start a little fire >.>

Artikbot

Sun Oct 03 2010, 10:15PM

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

Regulator regulator... Okay ima search the nets.

I was considering adding a fuse, don't wanna see everything blow O.o

Btw, fuse in caps or in supply? Supply I guess.

I've searched bout regulator ICs, so far the MC7806CTseems the best alternative. But it just delivers 1Amp, and I need minimum two.

Placing two in parallel will do the trick? I've seen around some ways of putting them in parallel with resistors at each vr output, I guess it can work :)

This datasheet shows how to do so, doesn't seem to be really complicated tbh.

Thanks once more!

GhostNull

Mon Oct 04 2010, 09:21AM

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

With the voltage regulator IC just hook it up to power the 555 and the Op Amp, look in the circuits that I posted before, you'll see what I mean. You don't need the whole circuit to be voltage regulated. Look for Linear voltaqe regulators or LDO (Low Drop Out) voltage regulators. Google should be able to help you with the rest =D

Best of Luck
-Ken

Artikbot

Wed Oct 06 2010, 10:43AM

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

Ohmkay, parts should be here by today evening, I'll see tonight :)

I'm still having trouble with the inductor, CoilCraft refuses to send me a sample (because I am not working for an eningeering company? Maybe I was too honest saying it was for a project), and shippings are expensive, and getting them from digikey is... UBER EXPENSIVE.

I've dismantled every single power supply I had at home (oldies from old computers destinated to the trash), and I've found something interesting.

So far I have three candidates that make me think they're adequate for my purpose.

One matches Digikey's 500uH toroidal 4Amp inductor, the difference between them is that the one in Digikey has 20 turns and mine has 25. It also has 0.9mm wire while Digikey one has 0.3mm It makes me think it matches the high current version, featuring 6.4mm wire, but with 125uH instead. This means I need even faster switching speed in order to not overrun the inductor.

The second one is very much like the first... but with 10 turns and 0.6mm wire. Even less inductance, not situable I guess.

The third candidate has 30 turns, with exactly the same toroidal core as the first one, but this time with way thinner wire. It must be 0.4mm or so, basing to my comparisons with different wire gauges I have lying around. This one seems to be the most situable for my purpose.

Here it is the datasheet of the toroidals Digikey has.

I don't have any inductance meter, and I've searched how to build one but... It costs more than getting the coil from Coilcraft!!

So, if you had to choose from those inductors, which one would you choose? I can provide more accurate measures if you need so.

Thanks!

@GhostNull:

Concerning the VRs, I did a bit of research and price/performance the most situable ones are the 7806s, because they output exact and bare 6V at 1Amp, more than enough to feed the OpAmp and because they are very cheap and relatively small, two factors I have to take in account because it will be mounted in a very reduced space, and smaller means more reduced dimensions coilgun, therefore lighter.

About LDOs... I wasn't able to find one fulfilling my requierements that was ready to ship from my local store (I'm using it because I pay no shipping fees and it's relatively cheap), but the 7806 was ready to ship in 3-4 days from their central warehouse at about .70â‚¬.

Oh well, let' see what happens when I mount all this stuff :P

GhostNull

Wed Oct 06 2010, 12:16PM

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

How did you try to order them? Did you say you were a student? I've got samples from them before without any troubles. I've also got some from my local CoilCraft distributer, they told me they have a student program or something of the like.

A bit about the electronics commerce system. In the electronics commerce world you have:

Manufactures, who design and manufacture electronic components e.g. FairChild Semiconductor

Distributors, who hold in stock many different electronic components and sell them off e.g. Farnell

and less commonly, Retailers, who have small local chains or shops and sell a small variety of components e.g. Radio Shack

Normally, manufacturers have many distributors around the world. They sell large quantities from manufacturing runs to their distributors. The distributors hold this stock and sell if off to retailers, companies doing production runs and less commonly hobbyists. This is done because it is uneconomical and less likely to sell if the Manufacturers to hold enormous amounts of their stock.
Samples are provided by companies to encourage engineers and designers to use their products in their prototypes and therefore hopefully, later in their manufacturing runs (when they buy it in the thousands)
Samples are also provided to students and hobbyists because it is good press e.g. a student gets some samples from a company for a small project, a friend/relative/contact (in the industry) hears about their project and goes to the same company and they order for them in the 10000s! (money for the company) or the hobbyist/student later joins the industry and because of their good experience with the company, decides to order from them.
Both manufactures and some manufacturer's direct distributors (the ones listed on the manufacture's website) will give you samples.
Some info on getting samples here:

look around for more info

Voltage regulators:
Not sure that you mean by "bear" but I think it needs to output 5v in order to power the ICs, look at the IC's datasheet Vcc I would have though it would be 5v.
As for the current output capability, it only needs to supply the ICs which consume only a few mA. A 1 amp voltage regulator is more than sufficient.

ScotchTapeLord

Wed Oct 06 2010, 01:39PM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635

When I did this I used the laminated iron core of a disassembled fan motor. I used whatever wire I had lying around, wrapped a couple dozen windings on it and bam, done. Just by turning the knob on my potentiometer I could get from 400-630 volts out of that thing. I think I was using a 12V supply, though. Can't remember any other specs, though, as it was built on a solderless breadboard and the connections weren't terribly reliable. I remember the MOSFET got hot without a heatsink, but that was because it was avalanching heavily, as it was only a 600V device!

Artikbot

Wed Oct 06 2010, 08:51PM

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

@GhostNull: Yes, I did a regular order saying I was a student but they replied saying the order was refused. Well, ima try again.

About VRs: I meant bare, not bear :P "plain and bare" is a literal traduction from a spanish phrase meaning that it just does that and nothing else. In this case it's perfect because it outputs exact 6V, above the 555 and 741 needs, and 1Amp, more than enough to power them. And I can use the full 7.4V to power the rest of the circuitry which doesn't need a specific and precise value to work.

@ScotchTapeLord: I suppose I'll try with the inductor that has more windings, and if it works, I'll leave it. Just in case it doesn't work, I have a spare toroid around here and I'll wind like 40 or 50 windings to it and see what does it do.

The more frequency the less inductance needed, right? I could also rise from my current 6.8kHz to 10kHz or so to make life easier while trying to make a situable coil.

Btw, parts haven't arrived yet, tomorrow morning I'll go to the shop and see what is going on with them.

Thanks!

first previous 7 8 9 10 next last

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob