Electronics > Projects, Designs, and Technical Stuff
Indicator LED for valve controller
calzap:
Zero999,
Thanks for your reply and the data sheet links. Most of the self-flashers in my collection came from eBay with little or no info on electrical characteristics. I really haven't tried to find data sheets for them, which might have been impossible as no manufacturer or part numbers were given.
The data sheets for the Wenrun and Kingbright LEDs don't specifically address the question of higher voltages and need for current limiting resistors. Reading the Wenrun data sheet, I get the impression that it would be OK to connect it to 3-8 VDC without a current limiting resistor. The Kingbright data sheet is ambiguous. It states operation between 3.5 and 14 VDC. But in a footnote, mentions limiting driving current to avoid killing it.
I have some single-color and alternating-color self-flashers installed for 5-15 years supplied with 9 VDC with a current-limiting resistor. They have had a pretty high percent "on" time. I can recall one failure.
I assume there is a simple timing IC in them. Not sure whether it would be a separate die from the LED die. I've seen a few self-flashers advertised for direct connection to a 12 VDC source w/o a limiting resistor, but they always had pre-attached leads with heat shrink over the solder joints ... could have had a tiny resistor under the heat shrink.
The only self-flashing LED I tested for hours with the 24 VAC circuit in my previous post was a regular red type ... no problems with it. The more exotic ones like fade-in/out, color alternators, etc. were tested for less than a minute ... so I'll try to do some 24-hour tests real soon. Just for fun I may then try a few at 60 or 120 VAC with a correspondingly higher value resistor.
Mike in California
Zero999:
The flasher IC is definitely separate to the LED die. It's the black dot, in a diffused package, when viewed from the side.
If you're going to run the LED off the mains, make sure the resistor can handle the power & voltage. You might also want to try a capacitive dropper.
calzap:
I have no plans to power the LEDs directly from mains. If I do any testing at more than 24 VAC, it will be short term from an isolated supply. I'll use an appropriate resistor, both for resistance and power, for the tests. For an actual application at mains voltages, using a resistor to limit current becomes more than a little wasteful of energy.
Mike in California
wizard69:
There are a number of ways to solve a problem like this. Here is a suggestion that might do it for you, use current sensors to detect power going to any one valve. Something like this guy: http://www.phenixcontrols.com/Download/245/999300D8.pdf There is one big advantage to detecting current instead of voltage, you can have a voltage present with no current flow (an open line). In this particular case you have relay outputs with would allow OR-ing together all of the transducers to drive your one indicator. This particular guy is only one of many types available in the industrial market, some that get very expensive, others on PCBs.
These sorts of transducers are almost zero engineering time compared to many other solutions. Installation is fairly easy, though the one referenced is likely less than ideal for panel mounting, you just turn a screw to fix the set point. The only thing I might consider is having them drive a relay instead of the lamp directly. The reason there is that you may need a relatively bright LED or even a higher wattage "lamp" solution for it to be seen outside.
calzap:
Wizard69,
Good point on sensing current rather than voltage. And it would be hard to beat the isolation.
Most of the valves are pilot-operated solenoid types and have a holding current of 190 mA. So the Phenix sensor should work, although that's near the bottom of its range, which is a concern. A couple of valves are direct-acting solenoid types and draw more current.
A couple are motorized ball valves ... these could be a problem for current sensing because they draw very little except when the motor runs. The type in use now supposedly draws as little as 1 mA when in the closed position (that's from specs; I haven't measured it). These are scheduled to be replaced eventually with ones that supposedly draw 40 mA in the closed position. Simplest solution would be to wire a resistor parallel to the valve terminals to increase current draw to 200 mA total.
Each valve has at its location, a LED indicator assembly wired parallel that draws an additional 12 mA.
I would only need one current sensor per 8 valves. That's because the manual override and enable switches are clustered in modules of 8 with a common wire for all eight valves. Could run the common through the current sensor. A couple of minor problems are where to put the current sensors ... they won't fit inside the switchboard enclosures, which are full already ... and a power source ... they need 5 or 12 VDC, which aren't currently available.
I'll investigate what's available, order one, test it and go from there.
Mike in California
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