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High voltage with LED indicator.

Discussion in 'LEDs and Optoelectronics' started by Boreddood, Jun 21, 2011.

  1. Boreddood

    Boreddood

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    Jun 21, 2011
    I work on a lot of drip irrigation controllers and have been experiencing a large problem with the controllers frying due to high voltage. In the fields we have 480v 3 phase going to a transformer stepping down to 120v. Well we have high voltage which in turn is making our 120v stay up around 140v. I have "surge protectors" that are good for voltage spikes but cannot protect from the constant 140v input longterm. I am not smart enough to make a regulator that will keep my voltage from exceeding 120v so I want to make a simple indicator that I can mount in the face panel of these timers that will light up when voltage exceeds say 125v or so. It will not stop the problem but will at least let the customer know when his controller is acting funny its not the controllers fault but yet the incoming power that is causing the problems. Keep in mind I don't know it all, I do plenty of wiring and some small sized soldering but I am by far not a professional. Hence why I would like to build an indicator rather then a regulator.
    Any information would be greatly appreciated.
     
    Last edited: Jun 21, 2011
  2. poor mystic

    poor mystic

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    Apr 8, 2011
    Hi Boreddood :)
    Where are the controllers usually situated in the customers premises? Is there any possibility of using a UPS to provide a guaranteed supply voltage?
     
  3. daddles

    daddles

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    Jun 10, 2011
    You could get a ferroresonant transformer -- they can do a reasonable job of regulating the line voltage. I use an old Raytheon one for when I'm making scientific measurements so that line voltage variations don't add to the measurement variance. They might not be cheap, but a controller failure and a service call can probably add up to hundreds of bucks, not to mention losses due to loss of water. Their advantage is that they're dirt-simple to hook up (i.e., just plug things in) and there are no moving parts.

    It sounds like you're in a typical farming environment and there will be lots of irrigation pumps turning on and off. Your high voltages might be due to inductive kicks. You might want to monitor with an oscilloscope or a data logger first to find out exactly what you're up against. I've also read about more modern solid state regulators that might be more appropriate if the ferroresonant transformer approach doesn't work.
     
  4. Boreddood

    Boreddood

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    Jun 21, 2011
    Thanks for the input. Now let me inform you I've worked in the agricultural irrigation areas most of my life and have been wiring things up for a good long while but I have no education on it other then my own hands on experiance. Would a UPS be able to keep the outgoing voltage at 120 if I had a constant incoming voltage of say 140v or so. And if so I could mount something like this in a small enclosure after my power and before my timer and supposedly be ok? http://www.apc.com/resource/include/techspec_index.cfm?base_sku=BE350G

    Now the ferroresonant transformer. This sounds like the way I most likely should go but I have no idea what it is. Sorry for the ignorance. I am quite limited on things such as an oscilloscope or a logger. I've used loggers in the past (borrowed) for pivots that were cooking motors overnight and they were quite effective. A solid state regulator would be great, but where to start looking for one is beyond me. I will be googling it in just a second.
    Thank both of yall for the input, I learn a little everyday.
     
  5. poor mystic

    poor mystic

    1,061
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    Apr 8, 2011
    Hi again Boreddood
    How much power do you need at a stable 120V?
     
  6. Boreddood

    Boreddood

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    Jun 21, 2011
    I just need a stable 120v. Most commonly my readings are around 135v to 145v. The controllers don't pull much at all. I can run one off a 200w inverter with an extension cord out of my pickup just to program one if I don't have power. The controllers are usually under a carport or some kind of overhead tin covering somewhat exposed to the elements. Our voltage goes up and down throughout the day and night because we are out in the middle of farms with multiple wells running all around. I would say from the hundreds of fields I've been to in this area the 480v three phase power ranges from 460 to 520 volts. That variation of voltage makes the 120v vary since its going through a transformer that steps down the 480 to 120. Then inside the controllers theres a small transformer that runs the 120v down to 15 volts 24 volts and 5 volts. When I have say 520 on the 3 phase I usually end up with around 138 to 140 which makes my 24v be around 28 or so and then I'm cooking solenoids that the controller runs. The 5v turns to around 6.5v and kills things like the CPU in the controller. the 15v turns to around 17 - 18 volts and kills out things like my relay boards and so fourth on my controller. Then there is also another controller that runs my wireless valve control and the high voltage makes it just flip out all over until it cooks something. Not sure if this information I'm giving you is very good since I'm not real smart on electricity but thats about as good as I know how to explain it.
     
  7. poor mystic

    poor mystic

    1,061
    30
    Apr 8, 2011
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,219
    2,695
    Jan 21, 2010
    The only thing that you have to be aware of (and this information is from deep in my dark history) is that frequency variations can result in significant voltage swings on the output. Also these things tend to get warm and hum a bit.
     
  9. Boreddood

    Boreddood

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    Jun 21, 2011
    I have a 50 dollar APC brand UPS coming to try on one setup. If this works then everything will be good and I believe that the particular one I ordered might even fit inside the controllers I'm using. I really appreciate the input and the help. I learned a few things too. Thanks again, and I will let you know if this solves the problem. So glad I didn't have to bust out my old soldering iron.
     
  10. daddles

    daddles

    443
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    Jun 10, 2011
    Boreddood, one of the things you should have in your toolkit is a Kill-a-Watt. These can be found on the web for about $20-$30; they will tell you the current, voltage, power factor, VAR, power, and energy consumption of a single phase AC load. I bet you'll find you use it a lot -- mine is sitting about 1 foot away from my elbow and I use it all the time at my bench to see what a load draws power-wise. They'll measure up to 15 A loads. Probably the best $20 I ever spent for a piece of test equipment.

    Steve is quite right about the ferroresonant transformers being noisy and getting warm. They're in the 90% efficient range, so they're going to get warm to the touch. I would imagine your controllers are probably less than a 20 to 50 W load, so you'd only need a small transformer. My Raytheon transformer is rated at 30 W and gets very warm. But when I got it, I characterized it with a Variac and found that it's regulation is just what I needed; I can put up with losing a few W of power for the improved regulation. If you're using the typical US power grid, you won't have to worry about any frequency swings.

    I have no idea if the UPS you've ordered will help deal with your line voltage variations; let us know how things work out. You can connect a Fluke DMM (or similar) DMM to the power line, then capture the max, min, and average to get an idea of whether it's doing any good. Even better, use a second meter to capture the same statistics on the raw power side and compare the numbers.
     
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