ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 ... 22 23 [24] 25 26 ... 55   Go Down

Author Topic: brain storm an optimal human safety system for back line  (Read 104269 times)

Tim McCulloch

  • SR Forums
  • Hero Member
  • *
  • Online Online
  • Posts: 20457
  • Wichita, Kansas USA
Re: brain storm an optimal human safety system for back line
« Reply #230 on: May 22, 2015, 04:35:11 pm »

I *have* been following along, John, and your sharing the design evolution is genuinely appreciated.  Even though I'm not playing along at home (like I suspect a couple readers are) I think you're giving a wonderful lesson on what is needed to develop an idea into a concept, and that concept into a prototype.  That's cool.
Logged
"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16397
  • Hickory, Mississippi, USA
    • Resotune
Re: brain storm an optimal human safety system for back line
« Reply #231 on: May 22, 2015, 09:47:31 pm »

Now that I got the ground shunt triac sorted, I went back and revisited my auto-start or auto-restart feature.

I configured the power relay, so that when the relay is powered down, the output side neutral is available to use as an alternate turn-on touch input.

If nothing is plugged into the the GFCI outlet it will not auto start, but with my electric drill plugged in, the capacitance of the line cord and drill is enough to start up and latch the power relay.

In use with a guitar amp plugged in, a momentary power outage should just restart it when power is restored.

I will still provide the touch start terminal. Now with my low capacitance mosfet the input resistor in series is 1M, so 120V is only 120 uA or <1/8th  of a mA. Even I don't feel that.

JR

PS Thanks Tim et al...
 
Logged
Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16397
  • Hickory, Mississippi, USA
    • Resotune
Re: brain storm an optimal human safety system for back line
« Reply #232 on: May 24, 2015, 06:27:14 pm »

here is schematic and a proper description. Note: incorrect symbol for opto-triacs but it didn't feel like creating a new symbol.

The basic premise is to start with a standard GFCI outlet that protects against leakage from it's hot that doesn't find it's way back to it's return. BUT this does not protect musicians from the classic hot mic problem. If the mic is hot because the console ground is hot a standard GFCI will not protect the muso. If the GFCI is plugged into a RPBG outlet the properly grounded mic can still be deadly.  :o

The 3 pole relay not only removes power but also releases the ground. The relay coil is powered from the GFCI output so anytime the GFCI trips, ground is lifted too. An additional circuit senses for current flowing in the ground, and when more than a few mA is detected an opto-triac creates and artificial leakage fault in the GFCI to trip it.

i had some fun figuring out why the shunt opto-triac was tripping the GFCI at start-up. Apparently there is a 1000V/uSec voltage rise time limit, which start-up apparently exceeded, causing the opto-triac to conduct, and trip the GFCI. by adding a C from the shunt R to output side neutral I am able to slow down the edge rate of that voltage, while the RC current in completely in the output side so looks like valid current flow to the GFCI.

In addition to protecting against improper power to the console (mic). Another problem is RPBG outlets. When converting 2-circuit wiring to 3-circuit outlets some people "bootleg" the ground by shorting it to neutral. This is wrong for multiple reasons, but even worse if the line and neutral are reversed, so the bootleg ground instead of grabbing neutral, is now hot. As I have posted before people have been killed by these RPBG (reverse polarity bootleg ground) outlets. My solution to protect against RPBG, is to use a touch switch start up circuit that only works if line and neutral are wired correct polarity.

I accomplish this touch switch start-up using a high impedance MOSFET device with it's source connected to the (hot) line circuit. A small (.1uF) reservoir cap and diode from neutral charges up this floating DC power. Since the MOSFET is swinging at 120VAC, connecting the touch contact to anything near 0V will turn on the MOSFET drawing current through the two opto-triac LEDs, which in turn turns on two 16A triacs to apply power to the GFCI. (two TRIACs are needed to prevent issues from RPBG), Once the GFCI is powered up, the relay coil winding connected to the GFCI output turns on the relay and latches power on.

One downside to requiring a touch switch input to turn on could be momentary power outages causing power to stay off until reset again. This is not cool since power can blink in the middle of a performance and you don't want to have to hunt around to reset power. My design fix for this is to provide an alternate touch input that when the power relay is open, senses the output side neutral. As long as some equipment is plugged into the GFCI outlet, this will probably be enough to automatically reset and latch the relay back on. With my prototype an empty outlet stays off, but plugging as small hand drill into the outlet is enough of an environmental 0V reference to reset power when restored.

This is not very cheap... In small quantity the GFCI outlet was $15, the 3-pole relay another $15... the 2x 16A triacs and 3x opto-triacs were maybe $1 each... the small MOSFET was relatively inexpensive.

I will provide an accurate BOM for any who ask.

JR

PS: This touch switch technology is unlike anything that I have seen in my research. Most touch switches use either finger DCR to complete an electrical circuit between two external contacts, Another touch switch uses capacitance to shift the frequency or rise time of some AC signal. A third uses two sandwiched electrical overlays where finger pressure completes an electrical circuit. My approach basically assumes the free standing human body is sitting at a low modest AC voltage, especially relative to the mains 120V. The high impedance MOSFET will turn on from as little as 1V AC so a direct comparison between the human body and either line or neutral would turn on. I had to reduce the sensitivity so that it would ignore a direct comparison to neutral, like for a reversed outlet wiring situation. I pad down the 1M input R into a 240k R so the voltage difference is reduced to 1/5th actual. In a really noisy environment a noisy human might turn on a reverse wired outlet, but the ground sense currect circuit will still protect the talent.

PPS: For another data point when I probe my line voltage using a relatively high impedance VOM, using my body as the low reference, I measure around 50VAC on the 120VAC hot line, but I also measure 10VAC on the cold neutral line. I am not sure how exactly to interpret this. Probing other outlets around my house found neutral readings as low as <1V but I suspect I am really reading my body voltage
Logged
Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Stephen Swaffer

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2245
Re: brain storm an optimal human safety system for back line
« Reply #233 on: May 24, 2015, 10:54:51 pm »

Looks like a job well done-its too bad that getting a UL listing would multiply the development cost many many times.

I understand the situation-as an electrician, I spend a lot of time trying to keep people who don't seem to care from hurting themselves or destroying property.  Without code mandates, it would be really hard to convince a lot of people to install GFCIs-and many other things we do.

Unfortunately, code mandates is likely what it would take to make this product commercially viable.  However,I doubt the statistics would ever flag this as an item worthy of a code mandate-and even if it did happen some would bristle at the mandates.

Hopefully some will see the value and build one for their own protection.
Logged
Steve Swaffer

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16397
  • Hickory, Mississippi, USA
    • Resotune
Re: brain storm an optimal human safety system for back line
« Reply #234 on: May 24, 2015, 11:46:48 pm »

My own judgement is that this is over-designed.. the KISS approach with a stinger cap in series with the ground leg, of a stock GFCI, provides adequate protection against all faults and may not need UL listing at all if properly labelled. (No EGC).

A UL file is probably $10k or more to open, and I doubt there is much market for these. I just wanted to see if I could, and in looks like I could.  8)

JR

Logged
Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Mark Cadwallader

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1281
  • Helena, Montana USA
Re: brain storm an optimal human safety system for back line
« Reply #235 on: May 25, 2015, 12:00:40 am »

JR, I'm trying to picture what the externals of your device looks like, but my imagination is either not good enough, or maybe it is too good. Besides GFCI devices that are box-mounted, I have also seen in-line devices. (I've seen in-line devices with pigtails, and other with molded 5-15 ends.). I'm not sure what the touch switch would look like, however.

Would you give me (us) an idea of what form your device has?  Thanks!
Logged
"Good tools are expensive, but cheap tools are damned expensive."

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16397
  • Hickory, Mississippi, USA
    • Resotune
Re: brain storm an optimal human safety system for back line
« Reply #236 on: May 25, 2015, 12:31:41 am »

http://forums.prosoundweb.com/index.php/topic,152668.msg1406346.html#msg1406346Here's a picture of a prototype I did of the KISS version built into a commercial power drop (ignore the extra switch, that was for testing).

The 16A relay is almost as big as the GFCI outlet but this proto fits inside a standard two outlet box.

The touch switch may not even be necessary, since it will start up as long as a piece of equipment is plugged in.

For the prototype I may connect the touch contact to a face plate screw (it's a plastic box so no grounded to worry about.)

I mainly see this as like an specialized power strip for muso's to use for back line. Especially for singing guitar players.

 JR
Logged
Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Mark Cadwallader

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1281
  • Helena, Montana USA
Re: brain storm an optimal human safety system for back line
« Reply #237 on: May 25, 2015, 03:46:29 pm »

Thank you. I must have seen that picture, but I didn't recall seeing it.
Logged
"Good tools are expensive, but cheap tools are damned expensive."

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3356
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: brain storm an optimal human safety system for back line
« Reply #238 on: May 25, 2015, 09:23:29 pm »

My own judgement is that this is over-designed.. the KISS approach with a stinger cap in series with the ground leg, of a stock GFCI, provides adequate protection against all faults and may not need UL listing at all if properly labelled. (No EGC).

Yes, I would agree that a stinger cap and a stock GFCI should provide sufficient protection against any failure mechanism I can think of. I know you're interested in disconnecting the EGC and thus stopping the fault current from a hot mic back through the GFIC's ground. But I think that current limiting that to the few mA that the stinger cap will pass is good enough. That should be sufficient to wake up the musician without injuring him/her, and in that scenario won't cause the GFCI to trip. I've never met a musician who appreciated having their backline power go off during a set.

So take your standard GFCI/stinger-cap circuit and just add a neon bulb with current limiting resistor in parallel with the stinger cap. That adds an indicator light that you could put a "Hot Mic" sticker on which would provide some actual troubleshooting intel in addition to saving their life. Let's call this the KISS+ device.

Could this KISS+ device be produced without getting specific UL approval? I don't know myself, but I do know somebody who might, and they're watching this thread. Could it be manufactured cheaply enough that musicians or sound techs would buy it? I think if it doesn't require a huge investment in UL testing and could be built/sold in reasonable quantities, maybe. I'm sure that JR knows a lot more about manufacturing than I do. I'm more of an industrial/calibration guy, but I do know a little about manufacturing scaling and costs.   
Logged
Mike Sokol
mike@noshockzone.org
www.NoShockZone.org

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16397
  • Hickory, Mississippi, USA
    • Resotune
Re: brain storm an optimal human safety system for back line
« Reply #239 on: May 26, 2015, 10:21:00 am »

Yes, I would agree that a stinger cap and a stock GFCI should provide sufficient protection against any failure mechanism I can think of. I know you're interested in disconnecting the EGC and thus stopping the fault current from a hot mic back through the GFIC's ground. But I think that current limiting that to the few mA that the stinger cap will pass is good enough. That should be sufficient to wake up the musician without injuring him/her, and in that scenario won't cause the GFCI to trip. I've never met a musician who appreciated having their backline power go off during a set.
True
Quote
So take your standard GFCI/stinger-cap circuit and just add a neon bulb with current limiting resistor in parallel with the stinger cap. That adds an indicator light that you could put a "Hot Mic" sticker on which would provide some actual troubleshooting intel in addition to saving their life. Let's call this the KISS+ device.
Maybe just label it "Danger".
Quote
Could this KISS+ device be produced without getting specific UL approval? I don't know myself, but I do know somebody who might, and they're watching this thread. Could it be manufactured cheaply enough that musicians or sound techs would buy it? I think if it doesn't require a huge investment in UL testing and could be built/sold in reasonable quantities, maybe. I'm sure that JR knows a lot more about manufacturing than I do. I'm more of an industrial/calibration guy, but I do know a little about manufacturing scaling and costs.
It will be incrementally more expensive than the standard GFCI outlet strip that is already considered pricy by most musicians.  Replacing a pass through ground wire with a suitable "Y" cap (IMO it needs to be large enough to trip the GFCI from a line to ground fault) should cost maybe $1 more in decent volume, but this market will not generate decent volume so a $25 power strop could cost $50+.

I have identified one company that makes GFCI strips but haven't been able to talk with their product guys (yet). 

JR

PS: This +relay design is perhaps more of interest for being able to recognize reverse polarity outlet wiring. Maybe I should think about a dedicated tester. 
Logged
Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

ProSoundWeb Community

Re: brain storm an optimal human safety system for back line
« Reply #239 on: May 26, 2015, 10:21:00 am »


Pages: 1 ... 22 23 [24] 25 26 ... 55   Go Up
 



Page created in 0.027 seconds with 25 queries.