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Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
ben5017 wrote ...
saz, one of my friends tryed hookin it up for me he is an EE and couldnt figure it out i took it apart after it wouldnt work... I tried every way to hook it up and fear i broke it somehow. Why would my multimeter read a resistance when the scr is closed? shouldnt it be infinite? If someone would be so kind as to make me a nice simple drawing.. I have limited EE experience so sometime spec drawings just confuse me even more. this is the last obsticle befor the SCAR1000 is ready to fire so any help is greatly needed
When the SCR is closed it should read in the megaohm range, which for practical purposes is infinite. My best guess is that you're not getting enough current into the gate. Wha voltage are you applying, what value of gate resistor are you using, and how much current is going to your gate?
Registered Member #3315
Joined: Thu Oct 14 2010, 04:23PM
Location:
Posts: 156
got my scr fiugured out. thanks saz. I had the polarity on my gate signel wrong.... last up my back emf protection... I am confused on how exactly to put it in anti parrel and where to put it
Registered Member #3792
Joined: Sun Mar 27 2011, 06:07PM
Location:
Posts: 136
Take a look at this coilgun schematic:
Ignore all the components except the coil (L1) and the quench diode (D2). As you can see, the diode is placed antiparallel with the coil to conduct when back EMF is shown up. In normal operation (when the SCR - in the schematic the push button - conducts) the diode is reverse biased and it cannot conduct (or, when the coilgun fires, you will see a BIG explosion, especially with 1000 J).
By the way, what topology do you use to trigger your SCR (just curious)?
Registered Member #3315
Joined: Thu Oct 14 2010, 04:23PM
Location:
Posts: 156
thx for the chematic. clears things up nicly
new problem. I charged to 100 volts to test the scr. when i actuivated the scr the voltage in the caps dropped but very slowly, approx 5 secs to reach zero. to test the scr I attached a motor and battery to it. i press the trigger and the motors at full power, so i think the gate is wired correctly. another thing I noticed, when i activate the gate the caps went from zero up the the 4 volt gate signal im using. thoughts?
Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
The SCR I used on my coilgun (C185N) is supposed to be triggered with 3V with a max of 150mA. However I found that mine wouldn't trigger fully with any resistor over 1 or 2 ohms. The gate junction itself may have quite a bit of resistance and an external resistor isn't always necessary to limit the current. Use a multimeter to check though, before you go removing or reducing the resistor too much.
Registered Member #3792
Joined: Sun Mar 27 2011, 06:07PM
Location:
Posts: 136
The thyristors that i use for my coilgun project (2 x SK8065K) could not be fully turned on until i dropped the external resistance value to 130 Ohms (12 VDC supply). So, 220 Ohms is not such a low resistor value.....
Registered Member #3315
Joined: Thu Oct 14 2010, 04:23PM
Location:
Posts: 156
alright guys take a look at the schematic i drew up real quick. is is the diode in the correct spot? and which way should it conduct? the gate scr sigmal look alright?
another thing. when measuting the resistance accros the diode one way is over load, the other is 1.2 Mohms? little confused on that one as i thought it would have a very small resistance... I read somewhere that putting them in series will help with suckback, if so i may put them in series and parallel like in the picture,.. thoughts?
PSCG: what do you mean by topology, i am not familiar with that term.
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S.C.A.R. 1000 (single coil assult rifle 1000j)
