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| 01 Mar 2008 03:12:58 |
| double insulated external power supplies - dangerous? |
I hope this is not too off topic here, I tried my best to find a group that would be appropriate to post my question... I'm a guitar player, and I'm using an effects processor which is powered by an external 9v transformer connected to mains. Like most external power supplies I see, this is a "double insulated" transformer, and has no ground. Now, knowing how dangerous it is to connect the guitar to an amplifier which is not grounded, I'm kind of worried whether it's possible that these doubly insulated ungrounded external power supplies may put a dangerous voltage on the guitar strings. Anyone? |
| 01 Mar 2008 09:30:07 |
| Tom Biasi |
| Re: double insulated external power supplies - dangerous? |
<gongorians@gmail.com > wrote in message news:059a037d-42f6-4094-a986-9a89da62e7a2@i29g2000prf.googlegroups.com... >I hope this is not too off topic here, I tried my best to find a group > that would be appropriate to post my question... I'm a guitar player, > and I'm using an effects processor which is powered by an external 9v > transformer connected to mains. Like most external power supplies I > see, this is a "double insulated" transformer, and has no ground. Now, > knowing how dangerous it is to connect the guitar to an amplifier > which is not grounded, I'm kind of worried whether it's possible that > these doubly insulated ungrounded external power supplies may put a > dangerous voltage on the guitar strings. Anyone? The supplies are intended for such use. Relax and play. Tom |
| 01 Mar 2008 14:21:47 |
| Tim Wescott |
| Re: double insulated external power supplies - dangerous? |
On Sat, 01 Mar 2008 03:12:58 -0800, gongorians wrote: > I hope this is not too off topic here, I tried my best to find a group > that would be appropriate to post my question... I'm a guitar player, > and I'm using an effects processor which is powered by an external 9v > transformer connected to mains. Like most external power supplies I see, > this is a "double insulated" transformer, and has no ground. Now, > knowing how dangerous it is to connect the guitar to an amplifier which > is not grounded, I'm kind of worried whether it's possible that these > doubly insulated ungrounded external power supplies may put a dangerous > voltage on the guitar strings. Anyone? Safety design on electrical appliances is done by answering the question "how many faults do there need to be before someone gets zapped?". In the case of your guitar amplifier, there are multiple opportunities for you to come into contact with metal that is connected to the internal circuitry. Without a ground connection, a single power supply fault could put dangerous voltages on your guitar (or at least on the sound leads). With a ground connection, that power supply fault would blow a fuse or maybe start a small fire, but it wouldn't kill you right off. So to have a problem requires two faults: one, the ground connection has to break, and two, your power supply needs to have a problem. In the case of your 9V wall wart, the 9V itself won't kill you -- you're in more danger of someone twirling the thing at 90 miles and hour and whacking you on the head with it than you are of getting a shock from 9V. So the thing is designed to put not one, but two layers of insulation between you and the line voltage (and no, I don't know how it's done in wall warts -- I should find out). Here again, it takes two faults before a dangerous condition exists. Make sense? -- Tim Wescott Control systems and communications consulting http://www.wescottdesign.com Need to learn how to apply control theory in your embedded system? "Applied Control Theory for Embedded Systems" by Tim Wescott Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html |
| 02 Mar 2008 11:45:40 |
| Phil Allison |
| Re: double insulated external power supplies - dangerous? |
"Tim Wescott" > > In the case of your 9V wall wart, the 9V itself won't kill you -- you're > in more danger of someone twirling the thing at 90 miles and hour and > whacking you on the head with it than you are of getting a shock from > 9V. ** Which is not the issue. The possibility of the un-grounded output wires delivering supply voltage is. > So the thing is designed to put not one, but two layers of > insulation between you and the line voltage (and no, I don't know how > it's done in wall warts -- I should find out). ** Simple having two layers of insulation is no nearly god enough to qualify as "double insulate" or more correctly class 2 insulation. With transformer "wall warts" the construction of the transformer is crucial, so that secondary and primary can never come into contact - even if the windings burn up. Normally, a thermal fuse is fitted inside the windings to eliminate that risk . > Here again, it takes two > faults before a dangerous condition exists. ** Unfortunately not true of many SMPS external supplies that claim to be Class 2. Single component failure or water ingress can render them very dangerous. ...... Phil |
| 02 Mar 2008 01:36:43 |
| Eeyore |
| Re: double insulated external power supplies - dangerous? |
gongorians@gmail.com wrote: > I hope this is not too off topic here, I tried my best to find a group > that would be appropriate to post my question... I'm a guitar player, > and I'm using an effects processor which is powered by an external 9v > transformer connected to mains. Like most external power supplies I > see, this is a "double insulated" transformer, and has no ground. Now, > knowing how dangerous it is to connect the guitar to an amplifier > which is not grounded, I'm kind of worried whether it's possible that > these doubly insulated ungrounded external power supplies may put a > dangerous voltage on the guitar strings. Anyone? Totally safe. That's the whole idea of double insulation. The guitar amplifier however probably SHOULD be grounded. Isn't it ? Graham |
| 02 Mar 2008 02:07:48 |
| Daniel Mandic |
| Re: double insulated external power supplies - dangerous? |
Eeyore wrote: > The guitar amplifier however probably SHOULD be grounded. Isn't it ? > > Graham Hi Graham! Isn't the ground amplified through the guitarist, changing the potential by moving back and forth to the amplifier. ?? ;-) Best regards, Daniel Mandic |
| 01 Mar 2008 21:56:35 |
| Paul E. Schoen |
| Re: double insulated external power supplies - dangerous? |
"Daniel Mandic" <daniel_mandic@aon.at > wrote in message news:47ca0bf2$0$7086$91cee783@newsreader01.highway.telekom.at... > Eeyore wrote: > >> The guitar amplifier however probably SHOULD be grounded. Isn't it ? >> >> Graham > > Hi Graham! > > > Isn't the ground amplified through the guitarist, changing the > potential by moving back and forth to the amplifier. ?? ;-) That's only for feedback, as described by the Beatles in their song "Help". They sang, "Help me get my feedback on the ground!" Paul |
| 01 Mar 2008 21:38:47 |
| Tim Wescott |
| Re: double insulated external power supplies - dangerous? |
On Sun, 02 Mar 2008 11:45:40 +1100, Phil Allison wrote: > "Tim Wescott" > > >> In the case of your 9V wall wart, the 9V itself won't kill you -- >> you're in more danger of someone twirling the thing at 90 miles and >> hour and whacking you on the head with it than you are of getting a >> shock from 9V. > > > ** Which is not the issue. > > The possibility of the un-grounded output wires delivering supply > voltage > is. > > >> So the thing is designed to put not one, but two layers of insulation >> between you and the line voltage (and no, I don't know how it's done in >> wall warts -- I should find out). > > > ** Simple having two layers of insulation is no nearly god enough to > qualify as "double insulate" or more correctly class 2 insulation. > > With transformer "wall warts" the construction of the transformer is > crucial, so that secondary and primary can never come into contact - > even if the windings burn up. Yea, I knew I had no clue of the actual details -- just that there was some magic done to make it happen (or at least claimed magic). Do you know of any web sites that show how this is done? > > Normally, a thermal fuse is fitted inside the windings to eliminate that > risk . > > >> Here again, it takes two >> faults before a dangerous condition exists. > > > ** Unfortunately not true of many SMPS external supplies that claim to > be Class 2. > > Single component failure or water ingress can render them very > dangerous. > > > > ...... Phil -- Tim Wescott Control systems and communications consulting http://www.wescottdesign.com Need to learn how to apply control theory in your embedded system? "Applied Control Theory for Embedded Systems" by Tim Wescott Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html |