41
votes
Accepted
I ripped the lead off this film capacitor by mistake - is it beyond repair?
Do not try to repair the capacitor. You're more likely to create a short and possibly damage something else in the circuit. Just buy a suitable replacement.
The leads are connected with the edge of ...
24
votes
Accepted
Why does this isolation transformer have another transformer in it?
That "transformer" is a common mode choke.
It's used to suppress EMI (either being induced onto the line and affecting the circuit or being transmitted from the circuit out over the line).
It's ...
- 16.4k
21
votes
Accepted
What is this white trace on this PCB?
It's a visual indication of where the separation is. It makes it easy to visually inspect that there's 8 mm creepage distance with no components or tracks in the 'keep out' zone.
That's the charitable ...
- 171k
20
votes
Accepted
Safest way to ground a metal enclosure
Option 4: bond the enclosure to earth, and connect it to the clock ground with a high impedance, maybe 1 megohm.
This prevents large voltages building up between the internal circuit and the enclosure,...
- 132k
16
votes
I ripped the lead off this film capacitor by mistake - is it beyond repair?
It really is not worth trying to attach the leg back to capacitor. The layers may have suffered mechanical damage. Buy a new one.
- 164k
15
votes
Accepted
Protecting two layers of PCB with electric tape?
Kapton tape is a widely available industry standard product for this scenario. You can view the specs here - from table 3 you can see that it has a dielectric strength of over 100kV/mm, plenty strong ...
- 608
15
votes
Accepted
Why are there so few oscilloscopes with dedicated isolated channels?
Why are there so few bench osilloscopes with dedicated isolated channels?
Is it a design issue, a cost issue, a business issue or is it just better with differential probes?
It is a cost (price) ...
- 81.1k
14
votes
Puzzle how isolated RS-485 (ADM2582) sends signal without signal ground
The RS485 standard says transceiver and receiver grounds should be connected. This gives much better noise immunity and is how it should be done, but... some equipment doesn't have the ground ...
- 80.3k
13
votes
Accepted
Relevance of Galvanic Isolation of Boost Converters
Galvanic isolation means that no (significant) current can flow between two parts of the circuit (here, the input side and the output side). It doesn't mean the output voltage of a circuit has to be ...
- 2,606
13
votes
Preventing oscilloscope magic smoke by inverter vs isolation transformer? Good idea or not?
The problem is you touch your oscilloscope a lot when you're working with it. Things like buttons and knobs with metal and circuitry right behind them and are not designed to isolate high voltages; ...
- 57k
13
votes
Why is the telecom input power supply range 36 to 72 V (polarity ignored)?
It's to allow a telephone exchange to run on batteries during a power cut. Specifically, a 48V stack of lead acid batteries.
While the batteries are charging, the voltage could be around 57V. When ...
- 19.6k
12
votes
Accepted
Puzzle how isolated RS-485 (ADM2582) sends signal without signal ground
It works due to RS-485 receiver having a high but yet finite input impedance which equalizes common mode potential between the two chips even without the common reference wire. And this is also the ...
- 164k
11
votes
Accepted
Does power delivery over ethernet always have to use isolated DC/DC converters?
If you want to call it PoE, you need to stick to IEEE 802.3af-2003 or IEEE 802.3at-2009.
These standards call for isolation. This answer could end here: no, you cannot build a PoE device without ...
- 98.3k
11
votes
Can an op-amp's Vin+ and Vin- be outside the supply voltage as long as their difference is inside it?
Generally speaking, no. The datasheet should clearly tell you what is permissible without damage and what might work and what is guaranteed to work (six different numbers in general).
Both inputs of ...
10
votes
Accepted
Can I use a dual primary transformer to generate isolated 110v output?
You can if you only need functional isolation. If safety isolation is required you need a transformer designed for that.
Since you are only powering half the primary you can only put in half of the ...
- 35.1k
10
votes
Accepted
Why does increasing altitude (low air pressure) results in lower resistivity/ breakdown voltage?
The behaviour is described by Paschen's Law.
Electrons are accelerated in the electric field between two electrodes. If there are gas molecules in the path of the electron it will collide with them ...
- 9,679
10
votes
Is this a safe way to measure mains power on an oscilloscope?
From your description, it sounds like you've made a safe isolated source of 9 VAC.
To verify that the output is isolated from the AC Mains, you could measure (with the thing unplugged!) the resistance ...
- 60.2k
10
votes
What is this white trace on this PCB?
Look to the PCB very carefully. The white area is made with the same silkscreen legend print as used for part numbers and part outlines. It is a paint cured by UV light or heat in order to be ...
- 2,873
10
votes
Accepted
What options exist for isolating a high power DC analog signal?
Analog Devices has a large portfolio of isolated amplifiers and data converters. Many of them include isolated power, so you don't have to come up with a low voltage power source on the field (high ...
- 22k
9
votes
Accepted
Efficient method for isolated detection of AC voltage without a stepdown transformer
Here is how I have dealt with AC line detection in an efficient manner using an isolated opto-coupler. Key attributes of the circuit:
The selected opto-coupler is one with a low forward current ...
- 57.6k
9
votes
Why does this isolation transformer have another transformer in it?
That is what's known as a common-mode choke. It presents a high impedance to any common-mode currents which might flow in the + and - pairs. Any common-mode currents which flow in the attached ...
- 340
9
votes
RS 485 ground signal and chassis
Looks like a common mode voltage problem to me. Although differential signalling, it still needs a common GND.
(source)
Replace your 1nf 500v capacitor with a jumper. Or wire signal ground to all ...
- 23.5k
9
votes
Accepted
Isolated audio without a transformer
Is there any reason this wouldn't work the way I think it would?
You cannot expect that circuit to work because the guitar signal ground connection has to connect into the op-amp circuit ground node ...
- 467k
8
votes
Accepted
How can a higher power circuit share the ground with a lower powered circuit?
Because of a basic rule of electricity, current only flows around circuit loops.
When you have two circuits, with no other connection between them, you can tie them together at ANY point to form a ...
- 46.9k
8
votes
Accepted
How do they get good primary-secondary isolation on concentric windings?
There are two keys to making such a concentrically wound design work safely at mains voltage:
For most insulating materials used for the interwinding film, mylar included, DTI (distance through ...
- 9,008
8
votes
Spikes in raw acceleration data from AC motor
The spikes seem to have a few common heights that are roughly related by factors of 2, which strongly suggests that they are noise-induced single-bit errors in the binary data.
One good way to ...
- 176k
8
votes
Optocoupler with the same power supply
No, there is no good reason to use an expensive and large optocoupler if you're sharing ground. The optocoupler's prime advantage is isolation. The common use of this appears to be cargo cult adoption ...
- 7,969
8
votes
Safest way to ground a metal enclosure
From a safety standpoint the enclosure should be connected to earth, not to the neutral leg of the power supply. You should have a three prong plug with the enclosure connected to the ground pin. ...
- 260
8
votes
What is this white trace on this PCB?
It looks like normal silkscreen print. It is quite typical to have two narrow lines at edges of isolation area for visual marking, but I haven't seen such wide fill before.
This seems like a bad idea ...
- 9,021
Only top scored, non community-wiki answers of a minimum length are eligible