Hi,
I want to work a DIY network streamer including its power supply. The power supply consists of 2 toroidal transformers (1) 12 V output (2) 6 V output. I'm in US, so the input voltage will be 110-117V. I have been able to understand all the connections from the transformer output to the digital audio output.
One place however I am not getting much headway is how to safely connect the transformers to the AC Mains so that (1) I minimize the chances of any shocks during development phase (2) How to handle grounding from AC Mains (3) What is the right and safe way to measure voltage across the outputs of the transformer when connected to AC mains (4) Where to use a fuse if the AC mains has a surge?
Any help would be really appreciated.
I want to work a DIY network streamer including its power supply. The power supply consists of 2 toroidal transformers (1) 12 V output (2) 6 V output. I'm in US, so the input voltage will be 110-117V. I have been able to understand all the connections from the transformer output to the digital audio output.
One place however I am not getting much headway is how to safely connect the transformers to the AC Mains so that (1) I minimize the chances of any shocks during development phase (2) How to handle grounding from AC Mains (3) What is the right and safe way to measure voltage across the outputs of the transformer when connected to AC mains (4) Where to use a fuse if the AC mains has a surge?
Any help would be really appreciated.
1) Do not touch any of the primary terminals of the transformer.
2) Connect any exposed and electrically unused metallic parts (enclosure etc.) to the utility (mains) ground.
3) Measure directly across the secondary windings using a true RMS multimeter that runs on battery.
4) Any protection fuse must be on the primary side, and appropriately rated to handle the initial inrush currents of the toroid. Surges on the grid occur as inductive loads (motors etc.) turn off and you can't do much about it. However, you may add a small X-capacitor (few nF) across the primary if desired.
2) Connect any exposed and electrically unused metallic parts (enclosure etc.) to the utility (mains) ground.
3) Measure directly across the secondary windings using a true RMS multimeter that runs on battery.
4) Any protection fuse must be on the primary side, and appropriately rated to handle the initial inrush currents of the toroid. Surges on the grid occur as inductive loads (motors etc.) turn off and you can't do much about it. However, you may add a small X-capacitor (few nF) across the primary if desired.
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Use a GFI protected AC outlet to power the transformers, etc. during development.
1. Never work on devices when the mains plug is plugged in. Very effective. In practice this is often "forgotten" but one gets reminded now and then.
2. PE should be connected to the metal casing for safety, always. Whether it should be connected to Audio GND is another matter. I think it should only be referenced to PE.
3. In Vac mode with the red an black cable plugged in the Voltage connectors. Check twice if the DMM is not set to current. Never switch from measuring voltage to current and vice versa in sequence without checking.
4. A fuse is for overcurrent and short circuits. A surge is handled by an MOV. A fuse is mandatory and the most minimal form of protection. It protects the cable and the home installation.
Work tidy, use insulated stuff as much as you can and make stuff electrically safe&sound. Don't fear mains voltage, just respect it.
2. PE should be connected to the metal casing for safety, always. Whether it should be connected to Audio GND is another matter. I think it should only be referenced to PE.
3. In Vac mode with the red an black cable plugged in the Voltage connectors. Check twice if the DMM is not set to current. Never switch from measuring voltage to current and vice versa in sequence without checking.
4. A fuse is for overcurrent and short circuits. A surge is handled by an MOV. A fuse is mandatory and the most minimal form of protection. It protects the cable and the home installation.
Work tidy, use insulated stuff as much as you can and make stuff electrically safe&sound. Don't fear mains voltage, just respect it.
Use a 3 wire AC cord and plug.
Make sure that:
1] the Safety Ground wire (green or g/y) is connected to the metal chassis.
2] the fuse and/or switch are connected to the Hot wire (Black).
While the DMM meter does not need to be a 'true RMS' unit, low budget meters tend to have test leads that are not line voltage safe.
Make sure that:
1] the Safety Ground wire (green or g/y) is connected to the metal chassis.
2] the fuse and/or switch are connected to the Hot wire (Black).
While the DMM meter does not need to be a 'true RMS' unit, low budget meters tend to have test leads that are not line voltage safe.
Unpowered (unplug DUT line cord), connect all test leads, and set up test equipment.
Apply power to make readings.
Remove power (unplug DUT line cord), if any changes are needed.
Never work on a live circuit until you have deep experience and knowledge. This takes years.
Never try to make a floating measurement with a scope. Specialized equipment is needed for this.
Never work when you are tired or distracted. No other persons or animals in the room.
Apply power to make readings.
Remove power (unplug DUT line cord), if any changes are needed.
Never work on a live circuit until you have deep experience and knowledge. This takes years.
Never try to make a floating measurement with a scope. Specialized equipment is needed for this.
Never work when you are tired or distracted. No other persons or animals in the room.
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My suggestion is connect the transformers to AC mains via a IEC socket that comes with fuse and power switch.
It minimize the chances of error, just connect the L and N wire to transformer primary winding, ground wire connected to the metal chassis.
It minimize the chances of error, just connect the L and N wire to transformer primary winding, ground wire connected to the metal chassis.
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^^^^
Use an incandescent bulb wattage rating 1.5 to 2 times higher than the sum of those two transformer's VA rating.
Use an incandescent bulb wattage rating 1.5 to 2 times higher than the sum of those two transformer's VA rating.
Dim bulb is not a safety device in any way, note. In fact most home-made DBT's likely add risk as its another live mains part (often an unprotected bare bulb).
Best practice is always use an isolating transformer when working on mains-powered equipment, so that live and neutral are galvanically isolated from the mains - this eliminates some risks (but not all). If in any doubt don't work on mains powered equipment live.
Ensure that any mains parts are fully insulated so they cannot be accidentally touched by fingers or metal tools, this is very simple and effective mitigation of risk, for instance all computer mains supplies are built like this, and many many lives have been saved as a result I imagine.
Any fuse holders not of the modern safety type should be replaced - older types can allow fingers to make contact with the mains. Replacement is an easy fix.
If you can work on the equipment using a bench power supply rather than its internal mains supply then do so - always safer and you get current limiting and metering, which frankly are invaluable for fault-finding and avoiding cascade failure.
With any high power equipment eye-protection is a great idea - accidental high power short circuits can shoot molten metal and vapour at you.
Just take the time to eliminate unnecessary risks - a Darwin award is not something to aspire to...
Best practice is always use an isolating transformer when working on mains-powered equipment, so that live and neutral are galvanically isolated from the mains - this eliminates some risks (but not all). If in any doubt don't work on mains powered equipment live.
Ensure that any mains parts are fully insulated so they cannot be accidentally touched by fingers or metal tools, this is very simple and effective mitigation of risk, for instance all computer mains supplies are built like this, and many many lives have been saved as a result I imagine.
Any fuse holders not of the modern safety type should be replaced - older types can allow fingers to make contact with the mains. Replacement is an easy fix.
If you can work on the equipment using a bench power supply rather than its internal mains supply then do so - always safer and you get current limiting and metering, which frankly are invaluable for fault-finding and avoiding cascade failure.
With any high power equipment eye-protection is a great idea - accidental high power short circuits can shoot molten metal and vapour at you.
Just take the time to eliminate unnecessary risks - a Darwin award is not something to aspire to...
Dim bulb tester is not a safety device to protect you, it is a current limiting device provide protection to downstream connected components.
The high voltage and current from the isolation transformer secondary winding can be fatal as well. No?
Do you have a suggestion for a good isolation transformer. My research shows that the isolation transformers in US are not really isolation transformers because the input ground is connected to output ground and in the circuit breaker, the ground is connected to the neutral creating a loop.
Should I be using a cheater plug with the isolation transformers instead?
The fear for 115V is making matters more dangerous. Here we have 230V and I can tell one has a hard time to die from 230V AC when one is in good health.
Of course working safe is mandatory but fear really won't help. A safety isolation transformer that decouples N from PE is nice as one can touch L or N (but never both!) without consequences and one gets better filtering. Except a lower power efficiency there are no real drawbacks.
Of course working safe is mandatory but fear really won't help. A safety isolation transformer that decouples N from PE is nice as one can touch L or N (but never both!) without consequences and one gets better filtering. Except a lower power efficiency there are no real drawbacks.
Don't touch anything on the mains side with your left hand!!! Always work with your right hand, as the current won't mainly flow across your heart this way, and of course always use a good gfi protector.
Mains and carelessness dont mix well.
When powered on dont touch anything.
If you have to scope it then attach scope with power off, stand back and power on.
Make sure fuse is in the live phase.
If you do a lot of mains work buy a plug in ELCB "earth leakage circuit breaker" to stop it killing you.
You can buy them for garden equipment.
When powered on dont touch anything.
If you have to scope it then attach scope with power off, stand back and power on.
Make sure fuse is in the live phase.
If you do a lot of mains work buy a plug in ELCB "earth leakage circuit breaker" to stop it killing you.
You can buy them for garden equipment.
a GFCI, RCD or ELCB will only protect a human when touching a Hot lead (or a chassis with a short) and a grounded object.
It will NOT protect when touching the Hot and Neutral leads of the same protected circuit.
It will NOT protect when touching the Hot and Neutral leads of the same protected circuit.
And one other important thing about using a toroidal trans is to not mount it with a bolt that goes through the top and bottom cover of the enclosure you use. Doing so will create a magnetic short circuit and act as a shorted secondary winding. Only mount the transformer through the top OR bottom of the enclosure its going in, not both.