133v out of balanced power transformer?!?

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  • Eric S
    Senior Member
    • Sep 2000
    • 175

    133v out of balanced power transformer?!?

    Hey Guys,

    As my basement theater is coming closer to completion, I need to build a power filter/sequencer for all of my gear. So now I've got a box, a bunch of EMI/RFI filters, a pile of heavy duty relays, and some delay timer circuits from Apogee.

    The sequencer will have a number of outlets and the front end gear (preamp, CD player, DVD player) will be running from balanced power. I picked up an Avel Lindberg 800VA transformer from Parts Express (that link on the HTGuide webpage has been getting a real workout from me as my projects are nearing completion!).

    The wiring schematic for the transformer is here. I wired the primaries in parallel and the secondaries in series as shown in the diagrams.

    The problem is that each secondary is providing just over 66VAC, so when I connect them in series, I'm looking at just over 133VAC for my gear. This seems a bit high to me. Since the draw on the transformer will likely remain below 1.5A, I don't imagine any droop in the output voltage of the transformer.

    What is the best solution here? I was thinking of unwrapping the transformer and just unwinding the secondaries by a few turns to bring them down to 60VAC and then re-taping the core.

    Is there any reason I shouldn't do this or is there a better solution?

    Thanks!
    Eric
    My DIY Theater Projects
  • ThomasW
    Moderator Emeritus
    • Aug 2000
    • 10934

    #2
    You have 133VAC coming out of the wall? If so you need to have a chat with the local power company.

    IB subwoofer FAQ page


    "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

    Comment

    • Eric S
      Senior Member
      • Sep 2000
      • 175

      #3
      Sorry, left this detail out. At the time I measured 133vac out of the balanced power transformer, I measured only 122vac out of the wall socket...

      Essentially, instead of an 800VA 60+60 transformer, I have an 800VA 66+66 transformer.
      My DIY Theater Projects

      Comment

      • ThomasW
        Moderator Emeritus
        • Aug 2000
        • 10934

        #4
        I'd call Avel Lindberg, and see what they have to say.

        IB subwoofer FAQ page


        "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

        Comment

        • Eric S
          Senior Member
          • Sep 2000
          • 175

          #5
          I did call Avel (but no actual techs were available at the time) and the quick response is that this toroid is designed to produce 60V at the secondaries under load, thus they are spec'd a little higher to allow for droop due to the load. Since I'm not planning to put any kind of a "real" load on this transformer, I still want to talk with an actual service tech.

          The reason I was a little surprised is the comparison with my gargantuan 1500VA Equi-Tech "transformer in a box" that consistently provides 60-0-60 regardless of load. Then again, I wouldn't really expect a toroid with a 70+ pound core to sag much...

          Eric
          My DIY Theater Projects

          Comment

          • Eric S
            Senior Member
            • Sep 2000
            • 175

            #6
            I also have one more question about building the power center for my theater system. The only element not contained in my box is something for surge/spike/over voltage protection.

            I've been searching the web trying to learn more and it seems that many designs feature multiple MOVs and Gas Discharge Tubes (a series of 2-4 MOVs followed by a similar number of GDTs) in parallel.

            I have a few questions about these devices and how they are used. If I use multiple MOVs, what rating is appropriate? Are all MOVs rated at the same specs (say 150v or so), or are the ratings staggered as you move through the "chain" so that the first two rated at 300v, the next two are lower (say 220v), and the final two are lower still (say 150v)?

            The same set of questions applies to Gas Discharge Tubes: How many is ideal to use? What ratings are appropriate? Are they all the same or somehow staggered?

            I also came across some discussion of TransZorb Diodes and Crowbar Circuits, but these seem to apply to DC power supplies, though I'm wondering how folks like Furman and Panamax use them to realize 1ns suppression of over voltage. I'm envisioning some sort of DC circuit that when activated by either TransZorb or a Crowbar opens a normally closed relay to kill power to everything at once.

            Can someone help me fill in the gaps here?

            Thanks,
            Eric
            My DIY Theater Projects

            Comment

            • cbark
              Member
              • Jan 2010
              • 97

              #7
              Let me preface the information below by saying that the information presented is very general and I have taken many assumptions and that if the information is misapplied, one can injure themselves and/or cause a fire. That said…on with the fun!

              MOV’s are clamping devices; GDT’s are crowbar devices.

              In the general consumer electronics application, some MOVs will provide more than enough protection for the occasional line occurrence. For an application of protecting a whole facility or severe electrical event, a “system” is usually developed. A system could contain a combination of MOVs, GDT, TVS, inductors, filters, resistance, and active circuits. All of this depends on how much protection is needed and what the cost limitations are.

              Using MOVs with GDTs can help create a more robust set-up. The MOVs are much faster than the GDTs, but the GDTs can withstand a much larger event. So in essence, the MOV acts first, with the GDT finishing out the event, if severe enough. Problem is that you really need to know the AC characteristics of the device that you will use. GDTs may or may not switch off after the event causing thermal runaway.

              When using MOVs, they should all be the same rating. Multiple MOVs offer the greatest protection due to a better clamping voltage and built in redundancy. When using multiples, the lowest voltage units (even same rated units will vary voltages), which carry the highest current, are the most likely to be damaged by a significant surge and it is unlikely that all MOVs would fail at the same time. You can add fusing to the MOVs to add some protection, and also individually fuse them for added redundancy, but even without such protection multiple MOVs have a higher chance of retaining functioning protection after an electrical event.

              I have never used a GDT in an application of mine, so I don’t have much to say there, other than what was mentioned above. It always came down to cost and application.

              TVSs are the fastest protection as far as clamp times, but have to be used in conjunction with other devices if used in a power application.

              As far as manufactures that state 1ns suppression, not sure what the big deal is. Well, except to that marketing guy.

              Good luck.

              Comment

              • ThomasW
                Moderator Emeritus
                • Aug 2000
                • 10934

                #8
                I leave surge suppression to the pros. I have a whole house unit mounted in the main breaker box.

                IB subwoofer FAQ page


                "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

                Comment

                • cbark
                  Member
                  • Jan 2010
                  • 97

                  #9
                  Originally posted by ThomasW
                  I leave surge suppression to the pros. I have a whole house unit mounted in the main breaker box.
                  Sounds like a great idea Thomas. It's not as simple as most people believe it is. :T

                  Comment

                  • Eric S
                    Senior Member
                    • Sep 2000
                    • 175

                    #10
                    I do have a bit of whole house protection, its a $50 device that installed into a knockout in the main breaker box that shorts when activated, thus popping the main breaker for the whole house.

                    My thinking was to add some additional local protection to my box, something like Panamax, Furman, etc. do. After doing some additional research, I'm thinking I will use something from LittleFuse's iTMOV line: http://www.littelfuse.com/data/en/Da...istor_TMOV.pdf

                    These have an integrated thermal fuse and a third leg that can be used as an indicator that the thermal fuse is still intact and functioning. I think I'll just install 3 of them: L-N, L-G, and N-G. They have one (p/n TMOV20R130M) that has a working voltage of 130v and a clamping voltage of 300v. The power entry to my box will be fused on both hot and neutral, have the 3 MOVs, and then go to individual EMI/RFI power filters for each outlet as well as balanced power plus additional filtration for the front end gear.
                    My DIY Theater Projects

                    Comment

                    • Eric S
                      Senior Member
                      • Sep 2000
                      • 175

                      #11
                      Returning to my original topic of "over voltage" for the transformer, I did speak with someone else at Avel and they confirmed that the 60+60 transformer is spec'd to provide 60vac at full load (6.6A draw), thus the voltage is a bit higher when there is no load. Since I'm only planning to pull ~2 amps from it (preamp, dvd player, cd player), their first suggestion was to exchange the transformer for a somewhat smaller one (300-500VA 55+55). I'm not really interested in mailing this heaving thing around, though...

                      After some further discussion, I learned that the only difference in their 800VA transformers that are rated at 60+60 vs. the one rated at 55+55 is the number of turns of the secondary (exactly what I suspected). The person I spoke with further confirmed that both secondaries are wound together and at the same time in order to keep them balanced and that the secondaries are wound last in the process of making the transformer.

                      So, I figure my best course of action is to unwrap the toroid, remove a turn or two from the secondaries, put a 2A load on it with a few light bulbs, and measure the resulting voltage, and keep going until it hits the target of 120. I'll then put a fuse in series with the primaries to keep the total current draw from the transformer below 3-4A.
                      My DIY Theater Projects

                      Comment

                      • cbark
                        Member
                        • Jan 2010
                        • 97

                        #12
                        Unwinding the transformer sounds fine; I’m surprised that it is not varnished.

                        For the MOVs, that voltage is too low. For a 120Vac line, you should be closer to 200V for the working voltage. Clamp will be higher, but they start to clamp lower than the published Maximum. The Max is a good reference to insure that components downstream of the protection are accounted for.

                        Comment

                        • Eric S
                          Senior Member
                          • Sep 2000
                          • 175

                          #13
                          Cbark: Thanks for the insights on power management! I found some IEEE papers and a number of other sources that cite 330v as a minimum recommended clamping voltage. I've also just stumbled across a number of patents that provide circuit diagrams, so I am getting a better feel for the do's and don'ts of suppressors and arrestors. It seems that most use multiple stages that are separated by EMI/RFI type elements to provide either isolation or delay (in the case of using GDTs) between stages. This approach will work well as each outlet has its own dedicated EMI/RFI filter.
                          My DIY Theater Projects

                          Comment

                          • cbark
                            Member
                            • Jan 2010
                            • 97

                            #14
                            Originally posted by Eric S
                            Cbark: Thanks for the insights on power management! I found some IEEE papers and a number of other sources that cite 330v as a minimum recommended clamping voltage. I've also just stumbled across a number of patents that provide circuit diagrams, so I am getting a better feel for the do's and don'ts of suppressors and arrestors. It seems that most use multiple stages that are separated by EMI/RFI type elements to provide either isolation or delay (in the case of using GDTs) between stages. This approach will work well as each outlet has its own dedicated EMI/RFI filter.
                            Yes you are correct about the multistage stuff, the inductors in the EMI filter will build additional voltage which will help to "trigger" certain devices within the chain. It just has to do with the building blocks. The higher voltage MOVs will clamp at a fairly low voltage, but the 130s that you mentioned are too low for your application. The may not give you issues, but more than likely will start to conduct when you don't want them to. If you look closer at the specs, the minumum conduction voltage is just barely more than a "nominal" line voltage. The problem lies in that the power company works off a + or - X number of % (can't remember off hand). They may conduct and take themselves out of the circuit during normal operating conditions. Rule of thumb is average working voltage x 1.5 plus a little extra.

                            Buy using additional components within the circuit the overall voltage can be lowered and the time very quick. One of the main things you are trying to do is reduce the overall impact on the components downstream. Sometimes higher voltage and slower is better, sounds odd but true sometimes.

                            Comment

                            • cbark
                              Member
                              • Jan 2010
                              • 97

                              #15
                              Ohh, one other thing, go ahead with your plan. I am not trying to discourage you, its just that it can be counterproductive or dangerous more so than helpful if done wrong.

                              As mentioned above, throw some MOVs on the input, you have enough added items in the power path that overvoltage shouldn't be much an issue, unless your power comes from a small child riding a bamboo unicycle tied to a generator.

                              Comment

                              • Eric S
                                Senior Member
                                • Sep 2000
                                • 175

                                #16
                                Originally posted by cbark
                                Ohh, one other thing, go ahead with your plan. I am not trying to discourage you, its just that it can be counterproductive or dangerous more so than helpful if done wrong.
                                I completely agree with you - I realize that you're not trying to be discouraging. Playing around with power management is something to be done thoughtfully and carefully! Hence all of the reading I have been doing lately.

                                I'll post a few images of my work shortly, things are moving along well (but slowly). I started by investigating how the toroid behaved under various load conditions. I measured its output with no load, 1A, 2A, 3A, 4A, and 5A (using paralleled light bulbs). At no load, I was seeing 133vac and the voltage dropped by 1v for each additional amp of draw placed on it. So I unwrapped it and pulled about 8-9 turns off of the secondaries and then spread the wire out so all of the leads were grouped back together again. While I had it open, I wrapped an additional 18ga solid core wire so I get about 9vac out from the new secondary winding. Then I re-wrapped the toroid and secured it to the chassis.

                                After being rectified and hitting a small set of caps, this provides the 12vdc power supply that I need to power five heavy-duty 40A relays and two delay timer circuits that will be driven by the DC triggers on my preamp. The DC triggers on my preamp are only rated at 44mA, so they directly drive only a small relay. This small relay then controls the new 12vdc power supply that I created, which in turn powers the delay circuits, a number of LED status indicators, and the five heavy-duty relays that are tied to my AC power outlets on the box.

                                The main power flow in the box is fused (both hot and neutral - I'll add Line-Neutral, Line-Ground, and Neutral-Ground MOVs following the fuses shortly as the first stage of over voltage protection) and then splits into two sections: two outlets feature 60-0-60v "balanced power" and the remaining 4 outlets are "normally" configured household power 120-0-0v. Each of the six outlets has its own 10A RFI/EMI filter. I'll add a second level of over-voltage protection (either Gas Discharge Tubes or Transzorb/Transil devices) to the output of the 10A filters. The filters will provide isolation between the second-stage protection devices and the MOVs that are first in the lineup.

                                On the balanced side of things, the power goes into a 20A RFI/EMI filter, a 5A fast acting fuse (so the toroid is not overloaded), a thermistor, then to the 800VA balanced power transformer. Two outlets receive balanced power - the first is for the preamp and is always on. The second is switched with a relay and is controlled by DC Trigger #1 on my preamp. This is for the CD/DVD player and subwoofer eq. After adjusting the toroid and adding the thermistor, the balanced outlets provide 120-122v with a 2-3A load - right on target!

                                The remaining 4 outlets are all switched and run normal 120v power. The first two outlets are controlled by my preamp's DC Trigger #1 (set to always be active when the preamp is on). The first outlet is immediate on (left channel amp) and the second outlet has a 3-5s delay (right channel amp, sub amp). The third and fourth outlets are controlled by preamp DC Trigger #2 which activates only when the preamp is set to DVD input. Outlet #3 is immediate on (projector and a 4 channel Class D surround amp -- my next project) and Outlet #4 also features a 3-4s delay and will power the center channel amp.

                                After all of this, my 17x10x4 inch box is getting a bit full...

                                Pfew - that was more complex to describe than I thought! I'll post some images over the weekend.

                                Eric
                                My DIY Theater Projects

                                Comment

                                • cbark
                                  Member
                                  • Jan 2010
                                  • 97

                                  #17
                                  Jeesh! I had to drink a beer for you after reading that. 8O

                                  Comment

                                  • Eric S
                                    Senior Member
                                    • Sep 2000
                                    • 175

                                    #18
                                    Theater Power Supply/Filter/Delays

                                    Here are two pictures of my power supply with filtration and delay circuits. Its not yet complete, just a few more things to add...

                                    I think the labels in the diagram spell most of it out. Mains come in, will be fused and have MOVs, and an split between the big EMI/RFI filter in the back and four of the relays on the right. The relays as dual pole, and directly feed the individual RFI/EMI filtering for each outlet. The Transient Voltage Suppression Diodes will be connected to the outputs of each of the six smaller RFI/EMI filters.

                                    You can see the additional secondary I wound on the transformer (red wire). This provides 12vDC for the LEDs/relay/delay timer control. I just used a standard 600v 35A bridge rectifier and it feed 4700uF caps.

                                    All wiring inside the chassis is 14ga, mains power entry will be via 10-2 wiring directly to the breaker panel about 35feet away.

                                    Between the 6 individual RFI filters and the outlets (across the bottom) will be 3 circuit boards: One with 12v relays driven directly by the Preamp DC Triggers and next to it will be two delay times circuits stacked one on top of the other. These are Velleman kits that feature variable programmable delays.

                                    In the other image, you can see the outlet panel. The white outlets are balanced power (60-0-60vac) and the tan outlets each feature "normal" 120-0-0vac power.

                                    DC Trigger #1 from the preamp turns on in all cases and will power the preamp, CD, DVD, left channel amp, right channel amp, sub eq, and sub amp.

                                    DC Trigger #2 from the preamp turns on only when the input source is set to DVD and powers the projector, surround amp, and center channel amp.

                                    All of the amps feature their own RFI/EMI EIC power entry, so each device is isolated from the other despite sharing a duplex outlet.

                                    Edit: Ha - I just noticed I misspelled "trigger" as "trigged" in my diagram and then copied/pasted it for each outlet. Oops - you know what I mean...
                                    Attached Files
                                    My DIY Theater Projects

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