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Registered Member #1107
Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792
I am making a very small coilgun that fits entirely in a disposible camera case. i figured were i will put all the components but i am running into trouble with the capacitor charger. 1st i took the old 80uf cap out and replaced it with a 160uf cap. but i know that the driver circut is charging the capacitor with - voltage and i am not sure if the scr hookup would be the same or do i have to modify the circut so it charges the capacitor with + voltage.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
You cannot charge electrolytic caps with a negative voltage, they will not last long with any appreciable negative voltage across their terminals (might even explode on you if you are lucky).
Just reverse the +/- leads coming from the charger circuit, or reverse the diode that is in series with the capacitor (but not both).
Registered Member #1107
Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792
correct so now i tried to reverse the diode so it supplys +320v and reversed so the negative is negative and positive is positive and now the capacitor will not charge.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
correct so now i tried to reverse the diode so it supplys +320v and reversed so the negative is negative and positive is positive and now the capacitor will not charge.
If you've got a charger that works, don't f* around reversing this or that. It doesn't really matter whether the +ve or -ve end of the storage cap is connected to the terminal called "common" on the charger circuit, it will still have 320v between the terminals when charged.
The charging and firing side can each have their own local common, although then you have to be careful to treat each side independantly, especially when connected grounded equipment like PSUs or 'scopes. Just makw sure the scr in the firing side is the right way round.
If in the original circuit you put your DMM black (common) lead to the common terminal, and put the red lead on the capacitor hot, it will read -320v. The difference between a +320v and a -320v reading is observing the polarity conventions correctly. I suspect you measured the cap by putting red on the cap +ve terminal and black on the cap -ve terminal, and so would read +320v?
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-v capacitor charging?
