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Author Topic: Buck & Boost Transformers  (Read 2112 times)

Greg Cameron

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Re: Buck & Boost Transformers
« Reply #30 on: June 13, 2014, 04:53:32 pm »

That's a good idea. I'm sending it up the food chain.

I hope Furman has improved the reliability of those smaller ARs. Back in the 90s we would installed those on portable Avid editing systems. I had several burn up in spectacular manner over the course of a few years and they weren't even regulating because the house power was plenty stable. One burned up the rack pretty well and could have burned down the building if someone wasn't present when the flames were present. I believe it was the toroid that cooked in all cases.
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Mike Sokol

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Re: Buck & Boost Transformers
« Reply #31 on: June 14, 2014, 09:08:38 am »

I hope Furman has improved the reliability of those smaller ARs. Back in the 90s we would installed those on portable Avid editing systems. I had several burn up in spectacular manner over the course of a few years and they weren't even regulating because the house power was plenty stable. One burned up the rack pretty well and could have burned down the building if someone wasn't present when the flames were present. I believe it was the toroid that cooked in all cases.
Somewhere in the back of my memory bank I seem to remember hearing something about that type of failure with those Furman units. I'm going to ask them to send me one for review and experimentation. Guess I'll have to keep a fire extinguisher close by the test bench.  ;) 

Mike Sokol

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Re: Buck & Boost Transformers
« Reply #32 on: June 15, 2014, 02:13:15 pm »

Just got a report back from my B&B transformer installation, right during the middle of the Sunday service. The lead tech says the incoming voltage dropped to 110 volts, but the rack never dipped below 117 volts (they have digital meters on everything) and there was no buzzing noise from whatever doesn't like the low voltage. He says the pastor was REALLY HAPPY. He's going to send me a few pictures of the install this week which I'll post here. He knows we want to do additional troubleshooting to find out the exact piece of gear that's unhappy below 110 volts, but at least now he doesn't have to stop the entire service while the monitor system buzzed at 100 dB on the stage. Yikes...

And yes, this is a code compliant fix using UL listed components. Buck & Boost transformers just aren't used very much in Commercial or Residential installations. But we use them all over the place in Industrial wiring. That's where I learned how they work and began installing them 35+ year ago. Good heavens, has it been that long?  :o

As a side note, while I was crawling around in the back of the amp rack in their equipment room I also pulled the drain wire (pin-1 lift) from the Phoenix input connector on one of the amps since all the others had them cut and it looked like a good idea. I also threw in a Whirlwind ISO2 box on another monitor amp that had XLR inputs and a slight hum in the output. Doing those two things corrected a slight ground loop hum I heard on the pastor's monitor speakers. They said the monitors were now "quiet as a mouse and very clean". I really think that any hum in the floor monitors, no matter how little, gets inside your head and messes with your performance. I work hard to get the noise floor of the monitors way down both for my own playing as well as any gigs I'm engineering. I just hate hum...

Mike Sokol

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Re: Buck & Boost Transformers
« Reply #33 on: June 15, 2014, 08:10:54 pm »

So here's a good question on the automatic voltage adjuster alluded to earlier in the thread: http://www.sweetwater.com/store/detail/AR1215/

If you have it inline and very slowly adjust the incoming voltage down so that it begins to add "boost" taps, what exactly happens to the output waveform at the instant of switching....

Have any of you actually looked the output of one of these things with a storage scope while it's switching the voltage?

Found this in the AR1215 Manual. It is indeed a multi-tap buck-boost transformer with Triac switching to provide regulation. Looks good on paper, at least.

DESIGN
The AR-Series uses a design based on an eight-tap
toroidal autoformer. The toroidal design assures
minimal leakage of stray magnetic fi elds, and, be-
cause of its high effi ciency, a very compact size for
its rating. The Voltage Regulator’s circuitry monitors
the incoming line voltage with each cycle, comparing
it to an extremely precise voltage reference, accurate
to ±0.15%. If a voltage fl uctuation requires that a
different tap be selected, the new tap is electronically
switched exactly at the zero-crossing, to avoid dis-
torting the AC waveform. If necessary, it can switch
taps as often as once each cycle. Most commercial
voltage regulators using multiple-tapped trans-
formers switch taps at uncontrolled times, thereby
creating voltage spikes and clicks that can leak into
the audio! Hysteresis in the switching circuits avoids
“chatter” or unnecessary switching back and forth be-
tween adjacent taps.

Jeff Bankston

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Re: Buck & Boost Transformers
« Reply #34 on: June 16, 2014, 06:09:23 am »

i'v never installed a buck-n-boost to correct for the problem you encountered. i have installed quite a few in wired for boost when the service is 120/208V and the machinery/equipment requires 240V. the last one i installed was for a very large 3 phase computerized HASS lathe that required 240V and the service was 120/208. the buck-n-boost trransformers work great. as for thr problem you encountered Mike thats a conditon of either the main service feeders being to small or the feeder wire coming from the weatherhead to the main panel being too small due to the main breakers on the panel being to small. i wpuld need to see the service but imo its too small for what they need. if you need a 225 amp service but only have 200 you will get vd. its also possible the receptical run is too long for the size wires and this is also contributing to the problem. i'v troubleshooted a lot of low voltage problems and its usually the service is too small. people trying to save money. the buck-n-boost will take care of it but if they add more stuff and draw more current the problem will probably return. i would be currious what the voltage is at the lugs/pigtails in the a/c unit is. if its too low those motors and compressors might nit last as long as they should. i'v seen motors and compressors burn up from low voltage. if the service is 277/480 you could also move the stepdown transformer coil taps to boost the voltage. Mike Sokol if you ever want to talk to me on the phone send me a pm and i'll give you my number.
« Last Edit: June 16, 2014, 06:19:56 am by Jeff Harrell »
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Mike Sokol

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Re: Buck & Boost Transformers
« Reply #35 on: June 16, 2014, 06:42:13 am »

Thats a condition of either the main service feeders being to small or the feeder wire coming from the weatherhead to the main panel being too small due to the main breakers on the panel being to small. i

Yeah, you're right. If my B&B correction on the rack continues to work for the next month, we'll have solid proof that the voltage drop during HVAC current draw is causing the sound equipment to malfunction and can justify troubleshooting the entire electrical distribution system. I'm going to suggest a meeting with the plant maintenance guy (who knows where all the panels and breakers are), the lead sound tech (who's been living with this problem), the local electrician (who's been fighting this problem for over a year), the POCO (who can measure voltage and confirm the size of the street transformers), and me (who can make the sound system buzz and misbehave). Maybe we can then get everybody to stop pointing fingers at each other and fix the actual problem.
« Last Edit: June 16, 2014, 08:24:35 am by Mike Sokol »
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Mike Sokol

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Re: Buck & Boost Transformers
« Reply #36 on: June 24, 2014, 12:42:49 pm »

Buck & Boost Transformer Update: Just got an email from the electrician who reports that the sound system at the church worked perfectly again last weekend, even though all the HVAC units were running full-tilt-boogie. So it seems that if we can keep the processing rack above 110 volts then the system is quiet. They're reporting that the voltage on the rack with the transformer in boost mode didn't drop below 115 even with 108-109 volts incoming, and everything is working perfectly. I'm now recommending that we troubleshoot the rack to find exactly which piece of gear is acting sensitive to the low voltage, then backtrack and figure out if there's any taps on the incoming transformer that can be changed to get the nominal voltage up closer to 120 volts. But at least the preacher is happy and we now have intel about the actual failure mechanism. I'll post later once I learn more.

Mike Sokol

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Re: Buck & Boost Transformers
« Reply #37 on: July 01, 2014, 08:12:04 pm »

Buck & Boost fix worked perfectly for another very hot weekend. This is getting boring (not really).

I need to get a 10-amp Variac for this type of testing. No need for an isolated secondary like on my bench units.

Also, I've been reading all sorts of reports of strange buzzes that seem to randomly come and go on various church sound forums. I'm wondering just how often this sort of low-voltage induced buzz happens in other places. Have any of you guys ever seen or diagnosed it? Maybe I'll start a thread on the PSW church forum and pose the question.

frank kayser

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Re: Buck & Boost Transformers
« Reply #38 on: July 02, 2014, 07:58:06 pm »

IIRC, Dick Rees is a big Furman 1215 proponent.  I've used one at FOH where genny voltage hovered around 101.  No problems at FOH, but the Crown XTI 1000 amps were VERY UNHAPPY with the low voltage, running hot and prematurely hard clipping.  Since then, if there is even a hint of doubt about low or high voltage (within the limits of the 1215), it gets plugged in.


As far as the PoCo not wanting to replace the pole transformer... and rather than trying to load it to the point of meltdown...


A totally irresponsible individual (none on this board) might suggest just to place something about .308 diameter and 170 grains very close (maybe even touching) the windings in the can.


Call the PoCo and then them the pole transformer is shot.


frank





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John Roberts {JR}

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Re: Buck & Boost Transformers
« Reply #39 on: July 02, 2014, 08:37:14 pm »

I'd be curious to dig a little deeper and ID the product, or products that are dropping out of regulation. I recall when designing for products to work around the world that low line and high line voltages were more extreme than typical data sheets suggest.

The old CS800 amp was nick named the "Burro" down in SA because it would work to silly low voltages... The Australian outback was notorious for silly high line voltages when they pumped up the distro voltage to send it too many miles down the feed lines.

My guess is some smaller domestic electronic company may have not been conservative enough about PS regulation, but somebody will be the weakest link in any chain and even old companies hire junior engineers.

JR
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