Graflex.org

robcruickshank · Joined: 25 Feb 2008 Posts: 19 Location: toronto, canada

Does anyone know if the Graflex (or heiland) solenoids will be damaged by applying power for more than the instant that they are normally on? Solenoids in general are rated for continuous or intermittent duty, ie whether they can be held on, or whether they are designed to be simply pulsed, and will overheat if left on. My idea was to make a pinhole shutter that would fit in the lensboard hole, and build a timing circuit to open and close it. It would be cool to use the original solenoid, but I don't want to risk burning it out.

C. Henry · Posted: Tue Feb 26, 2008 8:48 pm Post subject:

A rule of thumb for continuous use of electric devices is that any device will not be damaged as long as the temperature of the device does not get higher than 20 degrees Celsius above the temperature of the surrounding air. (20 C temp. rise). You should be able to check this with a lab thermometer, hold the bulb of the thermometer against the solenoid and energize it. If you see a rise of more than the 20 C turn the solenoid off immediately. The length of time needed to have the 20 C rise is the length of time the solenoid can be continuously energized.
Hope this helps until someone who knows the actual safe energized time of the Graflex solenoids replies.

C. Henry

robcruickshank · Joined: 25 Feb 2008 Posts: 19 Location: toronto, canada

Thanks, that's helpful. I'm a bit concerned about the bodies of the solenoids being so massive as to make it hard to measure the temp. I suppose I could run it longer at less than the rated voltage, and measure the case temp to get some idea of how it behaves.

C. Henry · Posted: Tue Feb 26, 2008 9:54 pm Post subject:

You could also get an idea of the current the solenoid will draw while energized by measuring the resistance with a multimeter. Divide the rated voltage by the ohms shown on the multimeter to get the current drawn by the solenoid. This will give you a ball park estimate of how fast it might heat up.
I do not have a solenoid to check but I would guess that a current draw of less than 0.25 amps (12 ohms + on a #2 solenoid or 18 ohms + on a #3) would indicate that the solenoid could be energized continuously.

C. Henry

BrianShaw · Joined: 24 Dec 2006 Posts: 71 Location: Los Angeles, CA

No "T" on the shutter? I'd be afraid to use the solenoid like you are considering. Why not just remove the lens/shutter, install your pinhole on the board and use a hat as a shutter.

graphicdave · Joined: 29 May 2007 Posts: 67 Location: Maryland

Ok, I tried a little experiment with an HR solenoid. I connected it to 4.5 volts (three cell Graflite) and after two minutes and fourty seconds it was holding steady at 123 F. After a brief cool-down period I connected it to 3 volts (two cell Graflite) and after more than four minutes it was at 103 F. Temperatures were measured with a temp probe on a digital multimeter. I don't know what voltage the solenoid was designed for. There are no markings on it other than "HR" and a patent number. The voltages of the batteries were not measured before or after the experiment but they were not old batteries and had only a dozen flashbulbs use.
Hope this helps.

Dave

C. Henry · Posted: Wed Feb 27, 2008 7:53 pm Post subject:

robcruickshank · Joined: 25 Feb 2008 Posts: 19 Location: toronto, canada

Last night I hooked one up, and measured approx. 700 mA at 4.5 volts, which is 3 watts and change, and it was noticeably warm (although I didn't measure it) running it continuously at 3 v. for a minute or two.
So yes, file under "bad idea".
Normally, when doing pinhole stuff, I use the focal-plane shutter, I just thought it would be a fun project to fabricate something electro-mechanical, that I could interface to some electronics, perhaps design an auto-exposure pinhole shutter that would correct for reciprocity, etc. I'll probably still do that, just not with these solenoids.
Thanks, everyone!

45PSS · Posted: Thu Feb 28, 2008 6:27 am Post subject:

A lot of equipement that uses long time hold on solenoids use a trip voltage then switch to a hold voltage to maintain the solenoid in the energized state. Connect a rheostat in the supply line to your solenoid and once the solenoid is energized decrease the voltage until it releases and measure the voltage at which it let go. Trip at full voltage then switch to the lowest obtainable hold voltage and repeat your temperature test.
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robcruickshank · Joined: 25 Feb 2008 Posts: 19 Location: toronto, canada

jan normandale · Joined: 13 Nov 2007 Posts: 30 Location: Toronto Canada

Rob, let me know when you get this "project" done. I'd like to see the results if you do proceed with it.

robcruickshank · Joined: 25 Feb 2008 Posts: 19 Location: toronto, canada