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Author Topic: brain storm an optimal human safety system for back line  (Read 97390 times)

John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #330 on: August 25, 2015, 03:16:01 pm »

Good news bad news.

Bad news first... The clear plug housing is not opaque enough when plug is oriented upside down and I have to look at the bottom LEDs through the thick housing. To hard to see in bright daylight (at a different neighbors house).  :'( So back to the drawing board for a prototype package.

Good news. I have just determined that I can reliably solder to the too-tight MOSFET footprint by not soldering the middle pin that is also connected to the tab, by soldering just the tab and two outside pins, no solder bridges.  ;D These proto boards are all usable... while hand popping tiny SMD parts may not be the best use of my time, but I'm too cheap to pay somebody for onsey-twosey builds.

I may put out a few units for more beta testing... I can just solder these to a short line cord for that. I may make beta testers sign a statement that they will hold me harmless if they use these in their bathtub.

JR   

PS: While we're talking any suggestions for who i could partner with to merchandise these? I don't think GE who sells the cheap hardwares store version would be interested.  8) I figure a couple $10k for UL listing, another $10-20k for tooling slick packaging. Should be relatively cheap to build in production quantity. Should be a large niche market for informed customers.
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Jonathan Johnson

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Re: brain storm an optimal human safety system for back line
« Reply #331 on: August 25, 2015, 04:10:09 pm »

PS: While we're talking any suggestions for who i could partner with to merchandise these? I don't think GE who sells the cheap hardwares store version would be interested.  8) I figure a couple $10k for UL listing, another $10-20k for tooling slick packaging. Should be relatively cheap to build in production quantity. Should be a large niche market for informed customers.

I can't help you with PCB assembly or merchandising, but for the package tooling, my brother-in-law works for a custom injection mold (mould, if you're from the UK) manufacturer that also does prototype, short- and long-production runs as well as in-house engineering and design services.  http://pilleraimmco.com/
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #332 on: August 25, 2015, 05:15:41 pm »

I can't help you with PCB assembly or merchandising, but for the package tooling, my brother-in-law works for a custom injection mold (mould, if you're from the UK) manufacturer that also does prototype, short- and long-production runs as well as in-house engineering and design services.  http://pilleraimmco.com/
It's not that i can't I just don't want to do it... I have 3-D cad design software on one of my PCs and actually designed the injection molded case for my drum tuner..  A two-part front back clamshell that nests together. I designed it and had the injection molding tool base machined in China  (Your brother in law's company probably farms out their tooling overseas too..) It is a lot cheaper than using machinists in the west.


This outlet tester would be a smaller/simpler package than I already did, but even better is to partner with somebody that already has something similar tooled up. It would be sweet to drop my circuit into that cheap outlet tester package.

But at this point I don't want to spend a few $10k of my own money, and develop another new product. I need a partner who can take this and run with it. I already did the hard part.  8)

While i don't underestimate the value of good execution.

JR 
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Jonathan Johnson

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Re: brain storm an optimal human safety system for back line
« Reply #333 on: August 26, 2015, 02:20:28 am »

It's not that i can't I just don't want to do it... I have 3-D cad design software on one of my PCs and actually designed the injection molded case for my drum tuner..  A two-part front back clamshell that nests together. I designed it and had the injection molding tool base machined in China  (Your brother in law's company probably farms out their tooling overseas too..) It is a lot cheaper than using machinists in the west.

An understandable assumption, but they actually do the tooling in-house in their Woodland, Washington facility, and part production runs in a nearby facility. They have built molds for many well-known companies from athletics to aerospace and many other industries. My BIL says that they've had to repair some Chinese-made molds, and that the molds from China are getting better (but still not up to their standards ;) ). Many of their molds get sent to China by their customers for production. Their business has been growing, so that's a good sign. It's always nice to see an onshore shop doing well.

They may not be able to compete on price, but they are very competitive with tooling quality, customer service, lead time, and turnaround time. If you can ramp up production a month earlier, that can mean a significant revenue boost that easily pays for the higher cost of onshore machining.
« Last Edit: August 26, 2015, 02:25:24 am by Jonathan Johnson »
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #334 on: August 26, 2015, 06:31:40 pm »

An understandable assumption, but they actually do the tooling in-house in their Woodland, Washington facility, and part production runs in a nearby facility. They have built molds for many well-known companies from athletics to aerospace and many other industries. My BIL says that they've had to repair some Chinese-made molds, and that the molds from China are getting better (but still not up to their standards ;) ). Many of their molds get sent to China by their customers for production. Their business has been growing, so that's a good sign. It's always nice to see an onshore shop doing well.
I know just enough about injection molding to know that mold design involves a lot of experience. I worked with a plastic pusher in TX, who took my part design and spec'd out a mold to be made with a different partner in China (i think he quoted with 3 vendors). I worked out all the draft angles so part was actually manufacturable, but the TX guy worked out the runners and gates to make the part not suck.

I had some fun and games with translation errors between my 3D cad format and the 3D cad format the Chinese were using, but we made a couple SLA (?) parts or whatever they used to call the 3D printer prototypes before they were so commonplace, to prove we were on the same page. A test push through the tool in China proved it was really OK..

We then shipped my tool back to TX to push plastic here. 
Quote
They may not be able to compete on price, but they are very competitive with tooling quality, customer service, lead time, and turnaround time. If you can ramp up production a month earlier, that can mean a significant revenue boost that easily pays for the higher cost of onshore machining.

I have no doubt that US tool quality would be excellent. Being able to communicate in English is certainly a plus. It was not an accident that I used a middle man for the nuts and bolts communication with the Chinese vendor. I will need to think about how valuable a US made tool might be. I am not pushing plastic domestically because it is cheap but for the control with my low volume product. The cost nut for my injection molding project was the tool not the parts.

If I was a high volume cost sensitive manufacturer, I'd probably push plastic and assemble the product completely in China. When I visited contract manufacturers in China for Peavey back last century, one of the facilities I visited was a huge plastic operation. They made plastic parts for all kinds of appliances like computer printers, etc. They had two huge NC milling machines for making molds, and a room full of geeks on PCs tweaking 3D designs.  Of course there is a continuum of high/low quality operation in China so it is hard to make sweeping generalizations. Working with a US vendor should be safer.

JR

PS: I assembled 4 more boards today... this is definitely not fun... :o  It took me an hour and a half just to pop the diodes ( 5 per board) they are tiny and have polarity... I needed three layers of magnifying lenses just to see the cathode marking. These units are definitely not for sale, but I will give away bare PCBs to anybody crazy enough.  ;D ;D
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Steve M Smith

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Re: brain storm an optimal human safety system for back line
« Reply #335 on: August 27, 2015, 05:52:52 am »

It is a TV cliche to restart a stopped heart, kind like the way that every PA system on TV makes feedback.
Yes.  And on The Simpsons it's always the same feedback sound effect every time someone walks up to a microphone!


Steve.
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #336 on: August 27, 2015, 10:36:23 am »

Tweaking and testing my outlet tester I have found a new issue. My ground present LED is too sensitive. Testing around my house I have found a few outlets where stray ground leakage is enough to get a visible ground LED reading. I am confident these outlets are not grounded (none are in my house). When I follow-up test with a neon lamp probe, that indicates a ground present too, so enough leakage for neon lamp (low mA?).

I could apply some circuit design magic and require a higher current threshold before I light the ground present LED, but that could cause a different problem. If I increase the total ground LED current test, this will trip GFCI protected outlets. The ground present LED current is pulled from line or neutral and flowing into ground, so not returning through the GFCI loop.   :'(

In my judgement that would be undesirable since the outlet GFCI turning off the outlet will make it impossible to test for polarity or hazards.  ;D

So options look like:

1- Keep the design as is, that may give some false true ground present readings.

2- Lose the ground present reading- while still testing ground for dangerous voltage. (How important is ground present?)

3- add a ground test switch, running at higher current. This would also double as a GFCI trip test switch, since making the current threshold high enough to ignore possible leakage would also trip GFCI (5mA threshold).

I will keep thinking about a way to finesse this but right now the ground present is not as reliable as I hoped. FWIW testing those same outlets with the cheap hardware store tester gives all kinds of bogus readings. I suspect no ground test might be better than an unreliable reading.

What do you guys think?

JR

PS: that cheap outlet tester is looking worse and worse the more I try it...

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Stephen Swaffer

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Re: brain storm an optimal human safety system for back line
« Reply #337 on: August 27, 2015, 10:03:45 pm »

I like the GFCI test button-I have a standard 3 light tester with a test switch -which doesn't work when there is no ground present.  I would think that would eliminate bogus testing. 

How important is a ground?  If a device needs a ground pin to be UL listed, I would think very-that is the first line of defense safety wise.  Unless the circuit is GFCI protected.  If you run a bunch of LED lights off an edison receptacle without a ground and something shorts to your truss you have just created a major hazard!
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #338 on: August 28, 2015, 02:18:16 pm »

I like the GFCI test button-I have a standard 3 light tester with a test switch -which doesn't work when there is no ground present.  I would think that would eliminate bogus testing. 

I don't like the added complexity but if I make it an optional push button it will allow testing GFCI protected outlets without false readings and unwanted trips.
Quote

How important is a ground?  If a device needs a ground pin to be UL listed, I would think very-that is the first line of defense safety wise.  Unless the circuit is GFCI protected.  If you run a bunch of LED lights off an edison receptacle without a ground and something shorts to your truss you have just created a major hazard!

Grounds are indeed very useful as we cannot ASSume that everything is RCD/GFCI protected. Looking around my house, outlet grounds are pretty scarce. I wouldn't be surprised if there are similar flawed cases of DIY wiring in bars and less professional venues.

For that reason if my tester has a ground test function it needs to be reliable. I figure it will take something like 20 mA to  completely swamp out stray leakage paths.

This adds yet another concern as an outlet with a floating ground, with 20 mA dumped into that ground will energize any chassis plugged into that outlet. That is a motivation to keep that test current < 10 mA.   This may still end up slightly compromised but you should be able to see a strong vs weak ground from the LED intensity.
====
I looked at small power transformers to pull current that wouldn't trip a GFCI and at low secondary voltage would not be a shock risk to humans from energized floating chassis grounds (6.3v is a popular transformer). I found some nice PC mount transformers but none for sale in small quantity.  :'(

A little more exotic option I could whip up a HF switcher so a tiny HF transformer could make a few mA of isolated current. While I need to think about this, I could leave this chopped DC output unfiltered and perhaps impute some information about the inductance of the ground run. Of course this opens up the different can of worms about RF emissions.  :'(

Interesting.. I may do some more testing to see if 10 mA can reliably ignore my leaky outlet grounds. Some are actually appliance related, since my kitchen outlet does not give me the false reading if I unplug the kitchen outlet strip.  IIRC my
kitchenaide mixer is one of the kitchen ground leakage offenders.

But the bathroom outlet has no such appliances and still gives me a false ground present??
 

Interesting, but if this was easy it would already be handled.  8)

JR
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Stephen Swaffer

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Re: brain storm an optimal human safety system for back line
« Reply #339 on: August 29, 2015, 12:15:58 pm »

Maybe a crazy thought-but could you put say a 50V MOV across the ground/neutral to prevent the voltage from going a full 120 volts if the ground was in fact open?  I haven't played with them much so not sure of all the implications.
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