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Electric shutter circuit question - ready for timer?
I have an electric shutter. The circuit works the shutter when testing
with a simple switch, but because I know nothing about electrics, it puzzles me. Here is a drawing of it: http://www.digoliardi.net/electrics2.gif I am dangerously ignorant of electrics so I'm asking: How does it work that one AC pole goes to one pole of the orange thing (capacitor?) and then also go around it? It's there a short there? The electro magnet works just fine. Nothing gets hot even with a long 'on' time (for focusing). Do you think it is safe to hook up to the timer (F-Stop timer by Darkroom Automation)? Thank you, PS: The shutter is on the back of the lens board because if it were on the front it would make changing the F-stop almost impossible. I've also made an extension of the F-stop ring to permit adjustment from below the lens. (Shutter is from a long-rollfilm camera and it fits in a well fitting enclosure around the rear of a Red Dot Artar.) Can provide pictures or a build-article if you like.) |
#2
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Electric shutter circuit question - ready for timer?
ThaNicholas O. Lindan wrote:
[... snip excellent article ...] Thanks for the help, Nicholas. Clearly I'd better leave this to a professional to build. I don't want to make an expensive mistake after wasting my time screwing up the build. I'll stick to analog photography, nuts, bolts, machines. Best, John |
#3
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Electric shutter circuit question - ready for timer?
http://www.digoliardi.net/electrics2.gif I am dangerously ignorant of electrics so I'm asking: How does it work that one AC pole goes to one pole of the orange thing (capacitor?) and then also go around it? It's there a short there? No, the capacitor is charge from the AC line with a resistor and a rectifier diode. You have some problems here that will cause trouble down the line: 1) I am assuming that "TR R210" is a rectifier - the number comes up with zilch when googled. It should be rated 700V (~2x Vp-p) or greater. The standard popcorn part would be a 1N4007. 2) The capacitor needs to be rated for a minimum of 200VDC continuous - it will charge to 170V in this circuit. 3) You should have a fuse in the circuit. It is hard to say what size without knowing the solenoid rating. If the Lectrohm is rated for 5W then a good guess is the circuit needs about a 1/8 amp with the shutter closed. A 1/4 amp slow-blow fuse should be adequate. If you don't have a fuse, and there is a short in the shutter solenoid or capacitor, then there will be 33 watts dissipated in the Lectrohm. This is a very unfortunate number if the Lectrohm is rated for 5W - the Lectrohm will get yellow hot but not fail and you have yourself a fire starter. You should test the fuse, making sure it will blow, by shorting the solenoid and closing the switch: make sure the fuse blows before smoke starts to rise from the Lectrohm. The fuse gets a bit of a workout in this circuit and may fail from fatigue every few years. In lieu of a fuse you can use a 50W Lectrohm. I am assuming the circuit works as follows, though I have no idea of the shutter solenoid's ratings, so some of it is guestimation: The capacitor is normally charged to 170V and it sits there at this voltage until the shutter is switched on. No current is drawn from the 120VAC once the capacitor charges. When the switch closes the capacitor provides a shot of 170V power to close the shutter solenoid. Solenoids need a lower voltage to hold closed than they need to activate. By reducing the holding voltage the solenoid coil can be made smaller - the solenoid doesn't have to be sized to take full voltage all the time. Continuous full voltage will overheat the coil in a solenoid designed to be used in this fashion. When the shutter is closed, and the capacitor has partially discharged, the circuit provides a much lower current to hold the solenoid closed. The 200 ohm resistor drops some of the voltage going to the solenoid and capacitor. When the switch is opened the shutter solenoid opens and the capacitor is charged back to 170V for the next shutter closing. The recharging takes less than half a second. Connecting the circuit to a timer: First, a problem: a timer is wired to supply 120V when exposing. You can't wire the timer's socket across the switch without major pyrotechnics. The "standard" way to connect this circuit to an enlarging timer would be to leave the switch closed and plug the 120V leads into the timer. This may not work very well. If the timer controls the 120V then the capacitor doesn't get fully charged and the shutter solenoid doesn't get a high voltage kick to slam it closed. Without the higher voltage the solenoid may not work or work sluggishly and erratically. You need to wire a relay where the switch is located - the coil of the relay goes to the timer and the relay contacts are wired across the switch. You need a SPST relay with a 120VAC 60Hz coil. You can get one at Radio Shack. -- Nicholas O. Lindan, Cleveland, Ohio Darkroom Automation: F-Stop Timers, Enlarging Meters http://www.darkroomautomation.com/index2.htm n o lindan at ix dot netcom dot com |
#4
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Electric shutter circuit question - ready for timer?
John wrote:
Here is a drawing of it: http://www.digoliardi.net/electrics2.gif I am dangerously ignorant of electrics so I'm asking: How does it work that one AC pole goes to one pole of the orange thing (capacitor?) and then also go around it? It's there a short there? The electro magnet works just fine. Nothing gets hot even with a long 'on' time (for focusing). Do you think it is safe to hook up to the timer (F-Stop timer by Darkroom Automation)? _____ The circuit diagram looks correct. It is a half wave rectifier with an 80 microFarad storage capacitor. The capacitor is always kept charged through the 200 Ohm resistor by the silicon diode (TR210). When the switch to the solenoid is open, the DC voltage across the capacitor will be about 169V (square root of 2 times 120V). When the switch to the solenoid is closed, DC current will flow through the magnetising coil, thereby opening the shutter. The actual voltage seen by the solenoid coil will be lower than 169V because of a small drop across the 200 Ohm resistor. The drop depends on how much current the coil requires. The capacitor could be of a higher voltage rating to be safer. If the solenoid "hums" due to the half wave nature of the circuit, you could increase the size of the capacitor to, say, 150 microFarad, or use a full wave rectifier. You should put a master power switch on the hot side of the the AC line (black wire in USA/Canada). It would be no problem plugging this device into a timer since the current draw will be in the order of 250 mA (my guess). -- Regards / JCH |
#5
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Electric shutter circuit question - ready for timer?
jch wrote:
John wrote: Here is a drawing of it: http://www.digoliardi.net/electrics2.gif I am dangerously ignorant of electrics so I'm asking: How does it work that one AC pole goes to one pole of the orange thing (capacitor?) and then also go around it? It's there a short there? The electro magnet works just fine. Nothing gets hot even with a long 'on' time (for focusing). Do you think it is safe to hook up to the timer (F-Stop timer by Darkroom Automation)? _____ The circuit diagram looks correct. It is a half wave rectifier with an 80 microFarad storage capacitor. The capacitor is always kept charged through the 200 Ohm resistor by the silicon diode (TR210). When the switch to the solenoid is open, the DC voltage across the capacitor will be about 169V (square root of 2 times 120V). When the switch to the solenoid is closed, DC current will flow through the magnetising coil, thereby opening the shutter. The actual voltage seen by the solenoid coil will be lower than 169V because of a small drop across the 200 Ohm resistor. The drop depends on how much current the coil requires. The capacitor could be of a higher voltage rating to be safer. If the solenoid "hums" due to the half wave nature of the circuit, you could increase the size of the capacitor to, say, 150 microFarad, or use a full wave rectifier. You should put a master power switch on the hot side of the the AC line (black wire in USA/Canada). It would be no problem plugging this device into a timer since the current draw will be in the order of 250 mA (my guess). I used to design electronic circuits, much more complicated than this one. N.B.: that was a long time ago. IMO, the AC line slowly charges the capacitor and when the switch is pressed, the energy stored in the capacitor is what fires the shutter (like electronic flash circuits). The current through the resistor does not directly fire the shutter. In fact, with the circuit as shown, the resistor should have high enough resistance so the shutter solenoid will release after tripping the shutter so it can try again. -- .~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 19:00:01 up 4 days, 23:37, 4 users, load average: 4.21, 4.23, 4.18 |
#6
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Electric shutter circuit question - ready for timer?
Nicholas O. Lindan wrote:
The "standard" way to connect this circuit to an enlarging timer would be to leave the switch closed and plug the 120V leads into the timer. This may not work very well. If the timer controls the 120V then the capacitor doesn't get fully charged and the shutter solenoid doesn't get a high voltage kick to slam it closed. Without the higher voltage the solenoid may not work or work sluggishly and erratically. You need to wire a relay where the switch is located - the coil of the relay goes to the timer and the relay contacts are wired across the switch. You need a SPST relay with a 120VAC 60Hz coil. You can get one at Radio Shack. _____ Indeed, you need that initial higher voltage to "kick" the solenoid, then hold it with a lower voltage. The above solution using an interposed relay is the correct way to do the job. Not complex, just a bit more wiring. I also concur about the need for a fuse, and the higher voltage rating of the capacitor. I would use a full wave rectifier. For this service, they are about 3/8 inch in diameter, and 1/4 inch high, having four leads; live, neutral, plus and minus. It would be good to know the DC resistance of the solenoid coil. With that information we can check the sizing of the resistor in terms of Ohms and wattage rating. -- Regards / JCH |
#7
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Electric shutter circuit question - ready for timer?
Quick question: what is the provenance of the circuit?
Is it the one that was in the long-roll camera that supplied the shutter? -- Nicholas O. Lindan, Cleveland, Ohio Darkroom Automation: F-Stop Timers, Enlarging Meters http://www.darkroomautomation.com/index2.htm n o lindan at ix dot netcom dot com |
#8
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Electric shutter circuit question - ready for timer?
Nicholas O. Lindan wrote:
Quick question: what is the provenance of the circuit? Is it the one that was in the long-roll camera that supplied the shutter? Yes. The circuit minus the parts for 'Instant' shutter with flash. |
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