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Registered Member #1805
Joined: Sat Nov 08 2008, 06:29AM
Location:
Posts: 67
Hi,
My coil gun is powered by a bank of photo flash capacitors at 330v 1000uf with a bank of camera chargers. I want to know how I could wire a blue LED to switch on at 330v because the camera chargers LED's switch on at only 250v. I'm sure its just a couple of resistors in series or something but the calculators on the net don't go up to 330v so can anyone help? Also is there a simple way of making the chargers stop charging at 330v? because they just keep going and I don't wanna blow my capacitors.
I don't want to move to a boost converter just yet but I will in the future when I learn a bit more about electronics.
EDIT - I found some NIMH batteries in a toy plane I had lying around and they are joined to equal 4.8v is there a way to cut them down to 3v but keep them at 4.8v for charging? sorry if that sounds confusing.
Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
you can put the output of the comparator that Arcstarter mentioned to a relay that will disconnect the cap bank from the positive charger supply... you can also put your blue LED along with a 470R resistor from the output of the comparator to show when charging is complete.
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
Just hook an LED directly to the bank with some high resistance resistors. As charging goes, the LED will get brighter. Make sure your resistors wont blow, or they let too much current through.
Registered Member #1805
Joined: Sat Nov 08 2008, 06:29AM
Location:
Posts: 67
rp181 wrote ...
Just hook an LED directly to the bank with some high resistance resistors. As charging goes, the LED will get brighter. Make sure your resistors wont blow, or they let too much current through.
Do you know where I could find out how to work out what resistors I would need for the blue LED to switch on at 330v? Like would the 1/4 watt ones I have work or would I have to get 1watt ones? I'm not really sure about resistors at high voltages.
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
The LED doesn't switch on, it slowly gets brighter as voltage goes up. I used some 1/4w ones. Im not sure about the resistance, i heat shrinked it all. Just start high, and come down (by high, a couple million ohms). Just to be safe, put the LED and resistors in a container, it can blow pretty catastrophically.
Come to think of it, just use ohms law. current is = voltage/resistance. That would (led power, in Amperes)=330/x. Solve for x.
I reread your original post, you said that the capacitors are 330v. f your in 120v land, just use a voltage doubler (google voltage doubler). I use one, and it charges directly to 330v, peak ive had is around 335v. You wont need an indicator then, it immediatly charges.
Registered Member #1805
Joined: Sat Nov 08 2008, 06:29AM
Location:
Posts: 67
rp181 wrote ...
The LED doesn't switch on, it slowly gets brighter as voltage goes up. I used some 1/4w ones. Im not sure about the resistance, i heat shrinked it all. Just start high, and come down (by high, a couple million ohms). Just to be safe, put the LED and resistors in a container, it can blow pretty catastrophically.
Come to think of it, just use ohms law. current is = voltage/resistance. That would (led power, in Amperes)=330/x. Solve for x.
I reread your original post, you said that the capacitors are 330v. f your in 120v land, just use a voltage doubler (Google voltage doubler). I use one, and it charges directly to 330v, peak I've had is around 335v. You wont need an indicator then, it immediately charges.
Ok thanks, Ill mess around with some resistors and see what I can do. I'm in a 240v land so the voltage doubler wont work and I like my coil guns being portable so I think this will be my last coil gun before I build a boost converter. I did try a resister and LED just before and it burnt out and burnt my finger. Would it be a good idea to try and build a voltage regulator to work with camera chargers so that I can slowly learn how parts of boost converters work?
Registered Member #1694
Joined: Sat Sept 13 2008, 09:13AM
Location: Australia
Posts: 108
I'd say if you are going to put in a voltage comparator, you should just go the whole way and build a boost converter. Basic boost converters are pretty basic, its just an inductor and a switch :)
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
Camel wrote ...
I'd say if you are going to put in a voltage comparator, you should just go the whole way and build a boost converter. Basic boost converters are pretty basic, its just an inductor and a switch :)
I wanted to make a boost converter, and got the stuff for it, but I wanted it to run off a few double A batterys, and things show, camera circuits are best for what I want. So :/ I want small and portability thus is why i wanted to use only a few AA battery, and not some car battery or moto cycle battery.
One question with that boost converter is how do I know what capacitors I need? It says 10nf which I'm sure is 0.01uf but what type of capacitor do I need and what voltage?
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Coilgun Capacitors and Charging
