Metal Case Safety Advice - help please 
Hello, I am new to amp building and I was looking to some safety advice.
I am putting together a TPA3116 using the blue/back board. I am using a 19V laptop power supply, a chassis jack, and on/off toggle switch for power. I also using a YJ chassis RCA plug with wiring to a potentiometer that has a harness to the board.
I will be using a metal case and I am concerned about electrical shock. Are there any things I need to be aware of when wiring this stuff up to ensure that one is not shocked when touching the case, power switch, volume knob, etc.
Any advice would be greatly appreciated as I would hate to learn the hard way.
Hello, I am new to amp building and I was looking to some safety advice.
I am putting together a TPA3116 using the blue/back board. I am using a 19V laptop power supply, a chassis jack, and on/off toggle switch for power. I also using a YJ chassis RCA plug with wiring to a potentiometer that has a harness to the board.
I will be using a metal case and I am concerned about electrical shock. Are there any things I need to be aware of when wiring this stuff up to ensure that one is not shocked when touching the case, power switch, volume knob, etc.
Any advice would be greatly appreciated as I would hate to learn the hard way.
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Thanks, so it depends on the power supply? I have two laptop psu's. One is two plug and one is three plug. The chassis jack I got from radio shack and it has three prongs. I could always look for one that has two prongs though. Like using the two plug psu is safer?
Yes,
ALL the speaker output connections must be insulated from the chassis.
None of the speaker output connections are at ground potential, therefore, they must all be insulated from the chassis.
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measure the resistance from the output PINS to the Mains Input PINS.
That's 6 measurements in one polarity and 6 more in opposite polarity.
A 3pin mains plug may, or may not, be connected to one of the Output Pins.
It's worth checking the 2pin version as thoroughly !!!!
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This may be a "Belt and Braces" idea coming from a known "overly safe Member", but:
would it make sense to enclose the potentially unreliable SMPS inside a PE protected Chassis?
That way if there was a catastrophic failure in one, or other, of the SMPS the protected Chassis will divert Mains Live back to the Mains Distribution Board and blow the close rated Mains Fuse.
Further doing it this way you can use 3pin or double insulated SMPS and NOT have to alter or modify the SMPS.
The regulations generally do not allow ANY modification of a double insulated product.
would it make sense to enclose the potentially unreliable SMPS inside a PE protected Chassis?
That way if there was a catastrophic failure in one, or other, of the SMPS the protected Chassis will divert Mains Live back to the Mains Distribution Board and blow the close rated Mains Fuse.
Further doing it this way you can use 3pin or double insulated SMPS and NOT have to alter or modify the SMPS.
The regulations generally do not allow ANY modification of a double insulated product.
One of them does. Here's what I have. Also should I use a slow blow fuse between the toggle switch and the power supply? With the double insulated supply no chassis ground is required? But if I use the other one that has three prongs one is? Please let me know, I don't want to hurt myself or someone else.
Attachments
With the SMPS being potentially unreliable on the other side of the Puddle, this might be a necessary design burden. Seems that most SMPS's have adequate Line Side to Load Side isolation as used here in the U.S . Most of Europe seems messed up when it comes to the practice of any real consistent standards.
There has been a lot of bad press on SMPS failures and safety concerns.
Much of this has been blamed on cheap and/or badly manufactured product from the Far East.
The Authorities may decide to step in and "enforce" the CE mark attached to all these goods that should be safety approved before importing into Europe.
I presume the same product is imported into North America.
Don't you have the same failures? Or are the press just not reporting such?
Much of this has been blamed on cheap and/or badly manufactured product from the Far East.
The Authorities may decide to step in and "enforce" the CE mark attached to all these goods that should be safety approved before importing into Europe.
I presume the same product is imported into North America.
Don't you have the same failures? Or are the press just not reporting such?
The Toshiba is double insulated. It should have the 2pin cable.
Both are CE marked. = passed for safety and suitable for import into Europe.
Yeah, it's real. It is from my wife's old Toshiba laptop that we use as a back up. The other PS is from my old Compaq laptop so both are "real." If I use the Toshiba I don't need a chassis ground I suppose. What about the DC chassis mount jack and toggle switch? Do they need to be isolated?
I mean once this stuff is plugged in there will be power coming from the DC jack to the toggle switch with the ground just going to the board. Sorry if these I are dumb questions. I just don't know much. Maybe I should have started with a wood case.
Everyone can attach a CE lable - today it means nothing. But would guess that Toshiba is doing it right.
http://siloscordoba.com/2013/07/09/china-export-is-not-ce-a-symbol-to-cause-confusion/
Even without the modified misuse of China Export, the CE mark is a
declaration of the manufacturer, without control of any independent certification institute.
It is just a legal statement. European regulators force the manufacturers to confirm that their products meet the mandatory standards.
Usually the mandatory standards cover safety, EMI, harmonics, immunity.
Examples for independent certifications: GS or VDE safety sign(s)
https://www.vde.com/en/Institute/Portfolio/Certification/Pages/VDE_Certification_Marks.aspx
Also UL is a certification of an independent institute.
And believe it or not - CCC (China Compulsatory Certification) as well.
..and many others...
Which of these certifications you find worth to trust or not, is another question.
Another headache is that there is not much control, whether the signs on the label are based on a real certification or had just been printed to trick the customers.
Fortunately well regarded large companies have to much to loose in terms of reputation, so that I tend to trust the signs on both of the shown products (Compaq and Toshiba/Delta).
One thing you have to keep in mind:
Even when you have two PSUs, which both provide double isolation - it does not mean that they remain safe if you connect multiple outputs together.
The safety requirements also include touch currents, means small currents due parasitic couplings between mains and the isolated output.
When you connect multiple outputs together these currents can add up and can exceed the limits which are regarded to be safe.
If you do so, you should double check the touch currents with permutations of main cord orientations.
The more PSUs you connect together the more critical...
declaration of the manufacturer, without control of any independent certification institute.
It is just a legal statement. European regulators force the manufacturers to confirm that their products meet the mandatory standards.
Usually the mandatory standards cover safety, EMI, harmonics, immunity.
Examples for independent certifications: GS or VDE safety sign(s)
https://www.vde.com/en/Institute/Portfolio/Certification/Pages/VDE_Certification_Marks.aspx
Also UL is a certification of an independent institute.
And believe it or not - CCC (China Compulsatory Certification) as well.
..and many others...
Which of these certifications you find worth to trust or not, is another question.
Another headache is that there is not much control, whether the signs on the label are based on a real certification or had just been printed to trick the customers.
Fortunately well regarded large companies have to much to loose in terms of reputation, so that I tend to trust the signs on both of the shown products (Compaq and Toshiba/Delta).
One thing you have to keep in mind:
Even when you have two PSUs, which both provide double isolation - it does not mean that they remain safe if you connect multiple outputs together.
The safety requirements also include touch currents, means small currents due parasitic couplings between mains and the isolated output.
When you connect multiple outputs together these currents can add up and can exceed the limits which are regarded to be safe.
If you do so, you should double check the touch currents with permutations of main cord orientations.
The more PSUs you connect together the more critical...
Then "Everyone" is breaking the law !Everyone can attach a CE lable - today it means nothing. But would guess that Toshiba is doing it right.
China Export is not CE: a symbol to cause confusion | Silos Cordoba
This last bit sounds like confirmation that an external PE protected Chassis around multiple SMPS would be good practice.
Usually it is not an issue to touch the plastic housing. If at all, it is more an issue to touch the output of the PSU - and the output will be connected with all your audio circuits, which you can easily touch at the RCA jackets or speaker wires.
In order to get an safety advantage you would then need to properly connect (as shown earlier in this thread) also your audio GND to the PE like it is common in pro audio units, but makes the audio unit more difficult to handle in terms of earth loops and hum.
The parasitic currents will now add up in the PE wire and there is also max allowed limit of such earth leakage currents... fortunately with just two laptop SMPS it is not likely to exceed this limit...
Also this connection will change the device type from protection class 2 to protection class 1 and formally you would need to remove the double rectangle and redo EMI tests in class 1 config - but, well formally DIYers are always lost.
Already by using a PSU which might have been certified acc. a standard of another branch which is not relevant for your application - you might find an attorney who tells you that you are a bad boy...
Regarding 'McGyvering' a laptop SMPS (often certified acc. the harmonized UL 60950 and/or EN60950) into an Audio application (calling for EN60065) I am not sure if there is a formal agreement, but for my personal use at home I would not bother.
Standards are a devil's hell of complications and safety standards are the worst.
Over the last 15 years I have developed several safety relevant devices and the key learning was that I would not dare to confirm 100% compliance to any of the relevant safety standards without a specialized safety engineer at my side.
But I learned enough to judge a design for using it in my home and came to the conclusion that some small companies are serving the market place more relaxed than I would do for my home.
Best excuse was that the safety issue was only present, because I had ordered the version with the large caps. Very convincing safety philosophy...
Fortunately my complaint lead to an improved redesign.
In order to get an safety advantage you would then need to properly connect (as shown earlier in this thread) also your audio GND to the PE like it is common in pro audio units, but makes the audio unit more difficult to handle in terms of earth loops and hum.
The parasitic currents will now add up in the PE wire and there is also max allowed limit of such earth leakage currents... fortunately with just two laptop SMPS it is not likely to exceed this limit...
Also this connection will change the device type from protection class 2 to protection class 1 and formally you would need to remove the double rectangle and redo EMI tests in class 1 config - but, well formally DIYers are always lost.
Already by using a PSU which might have been certified acc. a standard of another branch which is not relevant for your application - you might find an attorney who tells you that you are a bad boy...
Regarding 'McGyvering' a laptop SMPS (often certified acc. the harmonized UL 60950 and/or EN60950) into an Audio application (calling for EN60065) I am not sure if there is a formal agreement, but for my personal use at home I would not bother.
Standards are a devil's hell of complications and safety standards are the worst.
Over the last 15 years I have developed several safety relevant devices and the key learning was that I would not dare to confirm 100% compliance to any of the relevant safety standards without a specialized safety engineer at my side.
But I learned enough to judge a design for using it in my home and came to the conclusion that some small companies are serving the market place more relaxed than I would do for my home.
Best excuse was that the safety issue was only present, because I had ordered the version with the large caps. Very convincing safety philosophy...
Fortunately my complaint lead to an improved redesign.
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