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Thread: Anyone savvy on buck and boost transformers?

  1. #1

    Anyone savvy on buck and boost transformers?

    We are in a rural area but are hearing from most all equipment manufacturers we speak with that seeing utilities deliver higher and higher voltages in an attempt to avoid upgrading old, undersized, lines is pretty much the norm now. In our area and in speaking with electrical inspectors it seems to be the case in our entire region, its not uncommon to see 130-134 volts per leg (260-265). Our shop is located right on the main road in town and there are several rural roads running out miles and our shop frequently see's 262-264 volts. We have taken issue with the power company and they have installed recording meters and told us that they are allowed 10% which means on a 240v service they can hit as much as 264 volts and still be in spec..

    Well, our shop was dead at 262 for the longest time (I installed a digital meter beside the panel). We have now installed a CNC which we are told has Mitsubishi controllers that dont want to see anything more than 238. So we have installed a buck an boost (single phase) to buck the voltage down to 238. It has always been my understanding that unbalanced legs on a single phase system are not a problem. The buck and boost drops L2 to 106 and leaves L1 at 132.

    Low and behold today I look at the meter and its reading 263.9 volts. A tenth of a volt below their allowable limit.

    I will be taking this up with the PSC as we go through light bulbs, and fluorescent ballasts like toilet paper but wondering if anyone knows for sure about the unbalanced legs on a single phase system.

    Thanks
    Last edited by Mark Bolton; 07-26-2017 at 6:10 PM.

  2. #2
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    Take it up with your cnc mfg or fix this yourself and get some dc servos that run through a 80v cap. Bs that your mit drives are that picky. I run some nema42 servos and encoders off dc drives from centroid. Zero issues. Your barking up the wrong tree Imo.

  3. #3
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    I know just a little bit about buck/boost transformers. My shop gets 208 3-phase. That is, each phase is 115 volts to ground, and between any two hots is 208 volts. My 230 volt single phase cyclone really doesn't like that, so I used a buck/boost transformer to make 230 volts from the 208. It works just like it is supposed to, and the cyclone is happy.

    When your meter says 263.9 at the transformer output, what does the input say? Perhaps you haven't wired the transformer correctly?

  4. #4
    Jamie, The 263.9 is from the service entrance. That is whats coming into the building. The buck and boost is wired to a fixed percentage. As I mentioned, at 262 incoming its bucking to 238. If the 262 goes up by 2 volts so does the output from the BB (close). The transformer is static. Its only going to buck a given percentage based on its wiring. I have (had) a solid 237.X coming out of the buck and boost with the unbalanced legs, one leg is 106, the other is 132 as in a single phase wiring BB transformers pass one leg straight through and buck the other leg.

  5. #5
    Well, unfortunately we are taking this up with the CNC manufacturer and the BB is the specified solution. Beyond the CNC it is very frustrating that we change flourescent ballasts on a regular basis. Incandescent bulbs for us, and virtually all our local customers simply dont last (even buying 130v filaments). Its simply not realistic to be feeding 264 on a 240v service. No appliance, tool, motor, etc. is going to tolerate that for the long haul.

    I have had this conversation with everyone to appliance dealers to service tech's. A recent one was with a tech that is installing transformers on nearly all of Walmarts critical equipment because they cant rely on the power companies spec's.

    Our power company told us that point blank when we upgraded our service.

    They know whats going on.

  6. #6
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    My mother got a smart meter several years ago and it is much smarter then the one I got several years later. Mine just has numbers that say how much KW it has passed. No indication of current load or any other info.
    My mother's does that and alternates to show supply voltage, current draw and some other stuff I can not remember. She lives one block down from a big substation so power supply has not been a issue for her.
    Bill

  7. #7
    Quote Originally Posted by Bill Dufour View Post
    My mother got a smart meter several years ago and it is much smarter then the one I got several years later. Mine just has numbers that say how much KW it has passed. No indication of current load or any other info.
    My mother's does that and alternates to show supply voltage, current draw and some other stuff I can not remember. She lives one block down from a big substation so power supply has not been a issue for her.
    Bill

    Thanks Bill,
    I dont think smart meters do anything other than record and report. They dont have any control capacity over the quantity, quality, or volume, of current/voltage passed through them.

  8. #8
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    Quote Originally Posted by Mark Bolton View Post
    Jamie, The 263.9 is from the service entrance. That is whats coming into the building. The buck and boost is wired to a fixed percentage. As I mentioned, at 262 incoming its bucking to 238. If the 262 goes up by 2 volts so does the output from the BB (close). The transformer is static. Its only going to buck a given percentage based on its wiring. I have (had) a solid 237.X coming out of the buck and boost with the unbalanced legs, one leg is 106, the other is 132 as in a single phase wiring BB transformers pass one leg straight through and buck the other leg.
    The buck/boost transformer I bought had many taps. Depending on how I connected it, it could produce quite a few different output voltages. Can you review the wiring of your unit to see if you can get it to make something lower than 238 from the 262? Or get a different transformer?

  9. #9
    Quote Originally Posted by Jamie Buxton View Post
    The buck/boost transformer I bought had many taps. Depending on how I connected it, it could produce quite a few different output voltages. Can you review the wiring of your unit to see if you can get it to make something lower than 238 from the 262? Or get a different transformer?
    We are fine with the 238. And yes, 8 taps for standard BB. 2 high side coils and 2 low. There are no wiring options i have seen that buck both legs but that doesnt mean it isnt possible.

  10. #10
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    Quote Originally Posted by Mark Bolton View Post
    We are fine with the 238. And yes, 8 taps for standard BB. 2 high side coils and 2 low. There are no wiring options i have seen that buck both legs but that doesnt mean it isnt possible.
    I'm confused. You say in your first post that you are getting 238 when you include the buck/boost transformer. You say here you're fine with the 238. So what's your problem?

  11. #11
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    Buck-Boost transformers will work very well to lower or raise voltages, but be careful not to lower it too far. Power companies sometimes have brown outs where they lower line voltages 15 or more % in times of very high power demand. Lower your voltages with buck-boost transformers on voltage critical equipment, but not to the point where the voltages to that equipment would be too low if the power company decided to do a brown out. Every location is different, so there isn't a single fix that applies to all.

    I used to install and service large printing presses that were made in Europe where real 220 volt (not 208 or 240 volt) 50 cycle 3 phase Delta power was the norm. When installing these presses in the US, all of the locations had power that was 60 cycle and not 50 cycle. This made induction motors run faster, but otherwise they operated acceptably, but the 3 phase voltages here varied significantly from location to location. In the US we have nominal voltages of 208 volt Wye connected three phase (with a neutral) in some locations and also several variations of 240 volt Delta connections in others. It was quite a challenge to get The right combination of Buck-Boost transformers installed to meet the needs of these presses, as most electricians here have never worked with buck-boost transformers.

    In your situation, I would want to know not only the day to day average peak voltage from the power company at your location, but also the lowest voltage that it ever runs. I would also want to know not only the highest voltage that your single phase equipment could run on, but also the lowest voltage that would be acceptable for it. You should also ask the equipment company if the equipment uses any 120 volt power within it (does it require Neutral). I would then choose a buck-boost transformer or transformers that would lower the voltage supply to the equipment based on all of this. Only one buck-boost transformer would be needed if there is no neutral connected to the equipment, but two would be needed if neutral was required by the equipment (lower the line voltage based on each hot to neutral voltage reading). I would seek a voltage that is in the high, but acceptable range for your equipment so that a power company brown out wouldn't drop the voltage to the equipment lower than the equipment's acceptable low limit.

    Since your location seems to always have too much voltage, relocating the circuit breakers that power your lighting to a new electric panel with it powered from a buck-boost transformer or group of them to lower the voltages so that your lights are not burning out constantly, might also be a solution for them.

    Buck-Boost transformers are not very expensive for what they can do for you, and I have no idea how large your shop is or how great your total power requirements are, but large transformers are available with taps to raise or lower voltages and one of these might be a better "whole shop solution" to allow you to drop the voltage supply to everything in your shop. You need a good industrial electrician (not a residential house wiring electrician) or industrial power engineer to help you make the correct decisions on this and then have it installed.

    In your situation, it would be good to permanently mount some volt meters somewhere in your shop to keep track of what you are getting from the power company by just checking it from time to time, as you would do with a wall clock to see what time it is several times a day. With these, switches could be added so that you could check not only the incoming voltage, but the voltage actually going to your equipment by just throwing a switch to change the voltmeters from one measuring source to another. Get big voltmeters so they can be read from across the room.

    Charley

  12. #12
    Quote Originally Posted by Jamie Buxton View Post
    I'm confused. You say in your first post that you are getting 238 when you include the buck/boost transformer. You say here you're fine with the 238. So what's your problem?

    My question was about the unbalanced legs. The BB takes it to 238 but leaves L1 at the incoming voltage (132) and bucks L2 to 106.

  13. #13
    I'm a little confused but I'll give it a shot:

    It sounds like you have 240V single-phase service (2 hots and a neutral) supplied by a center-tapped transformer. Your complaint is that the utility is supplying 10% overvoltage. You have equipment that requires 220V (nominally). You have tried to provide this by installing a buck transformer between one hot wire and neutral, reducing ~132V (supplied) down to 108V. You have connected this transformer output and the second (un-bucked) hot wire to your equipment, providing 240V, which is still more than you want.

    Is that all correct?

    If so, why not connect the buck transformer across both hot lines. Sounds like your transformer can do a 20% step-down (108/132=0.8), so if you connected it to 264v, you'd get 211V out and your 220V equipment will be happy.


    To answer your specific question, though: there is nothing wrong with only running one hot leg into the buck transformer and connecting it as you've already done. That works fine (even if it is "unbalanced" relative to ground/neutral), assuming that the CNC doesn't have any 120V loads (which should be obvious based on whether or not it has a neutral connection).

    Many utility service transformers have provisions for tapping the voltage up/down by several percent. I'd ask the utility to install a transformer tap to reduce your voltage. If they won't, I'd buy a center-tapped buck/boost transformer big enough for the entire shop.
    Last edited by Dan Friedrichs; 07-27-2017 at 1:00 PM.

  14. #14
    Quote Originally Posted by Charles Lent View Post
    Buck-Boost transformers will work very well to lower or raise voltages, but be careful not to lower it too far. Charley
    Thanks for the great info Charley. I was very concerned about the very issue you mentioned that if the power company ever gets its act together and reduces the voltage I would be in a low voltage situation behind the buck and boost. The utility came and put a recording meter on the shop for several weeks but I was never supplied a report of the highs, lows, or averages. I mentioned in my post that for the very reasons you mentioned I had put a digital meter on the panels so I can glance at them but that doesnt tell me if there is a drop or surge when Im not looking at the meter. I can say that I have checked the voltage pretty often (as you say like looking at a clock) for nearly a year now and up until a couple days ago it would stay steady at 262. The other day it hit 263.9 Which is a minuscule raise only for the fact that their stated high limit is 264.

    I have it running as is and voltage is holding steady at 238 on the buck'ed circuit. Time will tell.

    Thanks again

  15. #15
    Quote Originally Posted by Dan Friedrichs View Post
    I'm a little confused but I'll give it a shot:

    It sounds like you have 240V single-phase service (2 hots and a neutral) supplied by a center-tapped transformer. Your complaint is that the utility is supplying 10% overvoltage. You have equipment that requires 220V (nominally). You have tried to provide this by installing a buck transformer between one hot wire and neutral, reducing ~132V (supplied) down to 108V. You have connected this transformer output and the second (un-bucked) hot wire to your equipment, providing 240V, which is still more than you want.

    Is that all correct?

    If so, why not connect the buck transformer across both hot lines. Sounds like your transformer can do a 20% step-down (108/132=0.8), so if you connected it to 264v, you'd get 211V out and your 220V equipment will be happy.


    To answer your specific question, though: there is nothing wrong with only running one hot leg into the buck transformer and connecting it as you've already done. That works fine (even if it is "unbalanced" relative to ground/neutral), assuming that the CNC doesn't have any 120V loads (which should be obvious based on whether or not it has a neutral connection).

    Many utility service transformers have provisions for tapping the voltage up/down by several percent. I'd ask the utility to install a transformer tap to reduce your voltage. If they won't, I'd buy a center-tapped buck/boost transformer big enough for the entire shop.
    I have never found or seen a wiring diagram that bucks at the full percentage (which I need) that bucks both hot legs. Diagram here #4
    buck.jpg

    One leg passes straight through.

    Thanks for the confirmation that the unbalanced legs isnt an issue. Was just crossing my T and dotting I.

    I have asked the utility company directly if they have a means to reduce the power coming in from the transformer and they have said no. Perhaps when this goes a little farther they may change their tune.

    I have looked into transformers large enough to cover the entire shop (a 400a and a 200a single phase service) and they look to be cost prohibitive.

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