Why does my LED lamp have AC voltage from case to ground and is it dangerous?

Here's the deal:  3-section under-counter LED light strip in an aluminum housing, with a 2 wire AC cable and plug for 220v. I found however, that when I set a voltmeter to AC and measure between the case and a ground (water faucet, natural gas line or the ground from an electrical socket) I get 74 volts with one unit and 89 with another. The seller first pointed out that a grounded cable should be used. I replied with pictures showing the unit is built to accept only two wire and comes with a two wire cord. Then they said using a sink as ground didn't truly represent ground and that the measurement was faulty and that the current is not dangerous regardless.  I took additional measurements using an electrical ground and the metal pipe from the natural gas line. Same result. However, I'm having trouble measuring current. I put the probe into the ten amp side, set the meter to the mA/A position and got nothing, although I did hear a buzzing sound emanating from the lamp housing--that can't be good. I then put the probe into the mA socket and tried again.  Same buzzing, no reading.  My questions: 1. What's wrong with my setup that I see no current measurement.  2. Is this a dangerous lamp? I took the one near the sink down. The other one is not within reach of an accidental grounding, so it is up until I'm ready to return both units. -Bob

Topic by bobcov 4 years ago  |  last reply 4 years ago


HV capacitor leakage? Answered

I have just built a high voltage glass capacitor for my Tesla coil at a 0.03uF 50KV rating and I have found that the leakage is quite high, the stored energy is almost completely gone in 15 seconds does anyone know how to resolve this?

Question by The MadScientist 7 years ago  |  last reply 7 years ago



Transistor as switch with low leakage current

I don't really know much about transistors, alas, but I am looking to use a transistor as a switch in a device where it's important to me to that the batteries (3xAAA) last about a year. This means that I want to minimize leakage current. I would like to use about 20 mA at 2.7V to control 0.5-1 A at 3.3V (I have 4.5V at my disposal, so I can handle a 1.2V drop through the transistor). The device is a water leak alarm which I assume uses almost no current except when it's alarming. Any suggestions on what to use?  A lot of people use TIP120s as switches, but I've also seen comments that indicate that they have an unpleasantly large leakage current. And I don't need the high voltage/current/amplification capabilities of the TIP120. Or should I just use a solid state or electromechanical relay?

Topic by arpruss 4 years ago  |  last reply 4 years ago


How to set up a desired threshold voltage? Answered

Hi, What I need-A circuit which allows voltage which is greater than or equal to 3 volts "ONLY" to pass through and power a buzzer i.e,shouldn't allow theuzzer to be powered with a voltage lower than 3 volts. The details-I just finished a project which makes a buzzer sound at its final phase.But,yet another obstacle-A darlington pair first completes a circuit with a relay in it when the base of it receives positive current via a resistor.The relay is activated which in turn powers the buzzer with - ve 12 volts and this makes the buzzer sound as +ve 12 volts is already connected to the buzzer.But somehow the buzzer is making a feeble,rather irritating sound even before the relay is activated..and it is somehow getting powered with a stray 3 volt power due to a leakage,somewhere.I tried to trace the flaw but couldn't find it.What I have in mind is a circuit which will allow voltage greater than 3 volts only to pass through and power the buzzer,somewhat like the function of a zener diode.I kindly request your guidance in designing a circuit which has a threshold voltage of 3 volts and higher.(I'm thinking BC 547s,555 timers etc.).

Question by Adarsh_tronix 5 years ago  |  last reply 4 years ago


transformer design... Answered

Designing a transformer, currently i have a 250mm by 250mm window for wire and interchangeable coils, some only a few turns, but will leakage flux cause large power loss?, or will it just limmit current, i read some stuff and im not really sure, i mean i don't want to start building it if it won't work

Question by pwnag3 7 years ago  |  last reply 7 years ago


Residential 3-way switch problem with leaking voltage?

I noticed a slight glow in the light when it was switched off. LED bulbs in a ceiling fan/light fixture. House built in 1905, wired whenever? using all-fabric insulation type wiring but not knob and tube .  Removed the load from sw 2 and tested travel wire voltages and got 95 v on one and 25 v on the other. Flip sw 1 and the voltages trade wires along with the switch position change.  The switches tested OK but replaced both anyway and got duplicate readings when repeating tests. Isolated the travel wires and got no continuity  (infinite resistance) using all scales of an analog meter as well as a Fluke digital multi-meter.. We checked for voltage feedback from another circuit and even used an extension cord to a different circuit in order to use a different ground wire. With the load connected, the travel wire being used shows 120 v but we still get 25 v on the other wire. I discovered this because when I bought the house only sw 2 worked the light, and one travel wire was disconnected at sw 1 and taped  off.. I have not opened the ceiling box at the fixture because the problem exists when the wire to it is disconnected.The previous owner said he didn't remember what sw 1 went to because it hadn't worked for many years.   So we eliminated worn insulation or nail into the cable because either one  would cause a resistance reading below infinity. All we can think of is a legacy doorbell. Neither of us remembers working one, but I know some used 120 volts and a relay.  People have told me that relay contacts can cause this problem when they get worn. Does anyone have any ideas? I'm retired on a fixed income and tearing walls open is an absolute last resort.  Thank you in advance for any advice I can get!

Question by gerryk8 3 years ago  |  last reply 3 years ago


lead acid Q's? Answered

So me and papa have been working on farm equipment and an electric golf cart (and I had issues with my jeep cranking over, with a presumably bad battery), but my lack of knowledge of these batteries used in the machines is starting to get to me. Differentiating normal behavior from behavior indicating a bad battery or other problems is not really something I can do right now. What I know: Topped off voltage: 15 (ish) volts ( details?) Dead flat voltage: 10 volts Cold cranking amps: indication of maximum current a battery can deliver in the cold (details ?) Reserve minutes: equivalent to "AH" rating times conversion factor lead acids can take a beating and survive without a, less say, "exciting" failure mode What I don't know: How am I supposed to know what I don't know???? ;) What is a typical topped off voltage for a battery? Does the voltage sag from say 16V when charger is removed? What characteristics change as they age? I would guess increased leakage current/resistance, reduced current capability and reduced capacity (?) would you lose a bit of capacity real quick after cycling a deep cycle marine battery a few times? I know lithium ions do, every new phone I ever had has lost at least 10% of it's capacity in a few short months as it got "broken in." What about maximum charging current? Does ripple current matter?

Question by -max- 2 years ago  |  last reply 2 years ago


PCB Repair Process of 3 different kind of circuits

1 Power Supply Circuit: During the circuit board repair process, power supply part should be inspected at the first hand and then come to the other part. +/-5V, Power supply failure can occur under below several situation: (1) NO power supply voltage or power supply voltage is deficiency, NC system is often used +/-5V, +/-12V, +/-15V and +/-24V, a few of them use +3.3V, and the varied or unstable voltage of power supply will cause the system working impropery; (2) Use voltmeter to test the voltage of power supply, and the result show is normal. Voltage waveform detected by oscillograph has shown the existence of big ripple. This situation maybe caused by open circuit of Filtering capacitance, bad rectifier diode or cold soldering, but sometimes it could be caused by an overloaded component which has been brokendown and damaged by power. (3) System can run properly when it is just being opened, after a while of operating, the voltage begin to drop off. This is usually caused by voltage stabilizing circuit and large power triode. (4) The voltage decrease accompany with temperature increase maybe cause by component cold soldering, it is electrical connection can be affected negatively when the temperature high up. (5) NO power supply voltage or supply voltage decreases significantly will cause the system to interrupt or stop working, this fault can be detected and spotted easier. (6) When the capacity of power supply load drop off or filter circuit become invalid, it will cause the system halt suddenly, this situation which is very difficult to justify can bring damage to the equipment and facility even get personnel wound. 2 Clock Circuit: Clock circuit mainly exist on the systematic motherboard, it is the foundation of large-scale integrated circuit system through which it can work, it can generate the constant square signal in the circuit base upon the crystal oscillator (commonly known as crystal), Once the crystal oscillator stop working, it is same as the heart of human being stop beating, the whole system will fall into the status of paralyzed, only after crystal can work under normal condition, the systematic circuit can operate under the command of CPU according to the frequency of crystal. The number and frequency of the crystal could be different due to the variety of numerical control system, but generally will at least one crystal, different clock frequencies required by the other circuit can be solved by frequency dividing circuit or other crystal. Crystal possess a higher rate of failure or damage, below are some malfuntions of crystal: (1) Leakage: Use multimeter and switch to P*10K level to test it, if the resistance is infinite, then it can be viewed as normal; (2) Internal OPEN CIRCUIT: Value of resistance is infinite tested by Use multimeter, can fail to generate oscillating pulse in the circuit; (3) Alternative crystal: Due to the transformation of crytal will cause its internal parameter change which can only be detected by osillagraph or cymometer. Although the crystal can still has oscillation, but the clock frequency is deviated from its nominal value, and the still existing oscillation pulse can’t make system circuit work properly due to the value of oscillation is wrong. Only cymometer can test its tolerance now. (4) In clock circuit, the both ends of crystal would be connected to ground by one ceramic capacitor value range from several picofarads to tens picofarads, failure of the clock circuit result from this capacitor leakage, deterioration is also more common. The best tool to test whether the crystal is good or bad could be oscillagraph or cymometer, multimeter is very difficult to detect the root cause. 3 Reset Circuit Reset circuit also exist in the circuit system of motherboard, it is unique set of large-scale digital integrated circuit. Microprocessor and interface circuit are all possess reset terminal. Reset pulse generate by reset circuit will clear the progam counter, force CPU recall the orginal files from the memory, execute initiation process on all the controller chips, system will occurs the phenomenon of disorder or crash as a result of faulty reset circuit, the method of using cymometer to illustrate the reset pulse is turn on/off power supply repeatly, observe and record the pulse value at the right moment of power supply on/off since it should be the normal square wave-form. If there is no existence of reset pulse, all the resistor, capacitor and transistor in the reset circuit should be detected. The reset terminal of integrated circuit should be regular low or high electrical level, or else, it is probably the malfunctional reset circuit or damaged integrated circuit.http://www.circuit-engineering.com

Topic by circuiteng 7 years ago  |  last reply 7 years ago


follow-up capacitor Q's ? Answered

I am amazed at all the great responses I got with my last question, thank you all! :D Though now I have a few more: 7) Should I try to learn how to work with complex impedance (capacitors, resistors, and inductors in all sorts of weird configurations) Also, can I treat reactance in general as a resistance when looking at capacitors in series or parallel with resistive loads and stuff? For example, can I simply add up Xc, Xi, and R for a total impedance? Or do I have to worry about phase shifts and stuff?  8) Is it OK to say that "Q" or charge is a more theoretical physics concept and is not too important with practical electronics? (C, V, and I being more of the focus and "ignoring" Q is OK?) 9) I have added a few of the "slides" and sneak-peaks to my upcoming video. If anything is wrong don't hesitate to nitpick and point it out! 10) capacitor fall under 2 major categories, polarized and nonpolarized. 10a) [under the 'polarized' branch] Electrolytic and tantalum capacitors are used for bulk filtering, but are evil and do not tolerate overloads particularly well. Especially tantalums. They tend to be available in huge capacitances, but can be "leaky" and have high ESR and series inductance. 10b) [under nonpolarized branch] Ceramic capacitors are the most common type of capacitors, and come in a few types. Generally used for local decoupling. They are pretty robust and tolerate overloads. Film capacitors find more use in high voltage applications, have lower leakage, better high frequency performance, and certain types have self-healing properties allowing them to tolerate overloads and surges the best. Mica capacitors are generally the most stable, with the lowest leakages, so they find uses for more critical analog applications.

Question by -max- 3 years ago  |  last reply 3 years ago


LEDs in resistance sensitive circuit

My question is relative to getting a LED to function correctly in a resistance sensitive circuit.  Here is the situation. 1. The Battery Warning Light in an automobile I am restoring currently uses an incandescent bulb.  2. Functionally, the light is on when the ignition is turned on, but goes off when the engine starts.  3. This works fine with the incandescent bulb, but not with a LED, even if I put the same incandescent bulb in the circuit (parallel). 4.With just the LED in the circuit, it never goes off.  This is because the circuit has about .5V leakage voltage through the device (which is a Lucas 3AW Warning Light Unit) when the engine is running (and correctly, 12V when just the ignition is on). 5. With both the LED and the incandescent in the circuit, the incandescent does not come on and the LED does not go off, both with ignition on and engine running. 6. I have also put a potentiometer in the circuit with just the LED and cranked it from 1 Ohm to 100K Ohms, with no effect. 7. Of course, an easy answer is to just use the incandescent, except that the dash is wired and complete and installed, and I prefer to get the LED to work.  Any thoughts or suggestions would be very much appreciated.

Topic by DaleR18 3 years ago  |  last reply 3 years ago


alkaline batteries connected in parallel, quick question

Okay, doing some throwie-inspired LED "artwork" and I'm using alkaline AA batteries instead of the CR2302s or similar smaller cells to get way more mAh and extend the life of my display. I've got all the proper resistors and AAs connected in series to get the right voltage, etc... but I want to rig up a second set of AAs in parallel. I've found a few posts and websites talking mainly about lithium cells and/or specifically rechargeables connected in parallel, but nothing on alkalines. I know to make sure they're of the same make, type, not to mix new and old (aka the same mA)... but will leaving parallel alkaline batteries connected until they are all used up cause any problems, possible fires, leakage, plagues, end of the world? I've found one web page talking about if one of the cells in parallel was lower in mA (or maybe only if it's faulty?) it could drain faster and possibly short, draining the energy from the other cells, possibly causing a fire hazard... Not good for my artwork or the places it will be displayed. Any thoughts would be greatly appreciated. Thanks for the help!

Topic by shanepollard 10 years ago  |  last reply 9 years ago


SMPS H-Bridge trouble

Hi,  I've built a 1kW SMPS designed to take a 350V unsmoothed DC input and convert it to 3kV @ 300mA. The circuit is basically Uzzors2k's design seen here minus the overcurrent protection and smoothing capacitor (for now), however I accidentally wired the GDT outputs backwards so the gate resistors (33ohm 2W) are on the source. I have used alternate MOSFETs the latest attempt with FDPF16N50T's. I've had various problems with the circuit, primarily the MOSFET's exploding seemingly from overvoltage (evidence of flashover in some cases despite no evidence of secondary leakage (i dismantled the transformer to check)). During my last test I had a flashover between the drain and source pins of one of the FET's, in addition all of the gate resistors were smoking hot after, seems the gates had all been shorted (first time this happened, other occurrences were from case to ground). This happened despite the variac only being turned up to 40% which should be well well below the pin spacings maximum voltage tolerance. I have checked the drive signals, they are quite nice square waves at about +-15V with some oscillation on their rise. I have built SMPS's before, one is currently working with similar MOSFETs using a half bridge at 300W. Does anyone have any suggestions as to why these troubles are occurring or have any suggestions to fix it or have any alternative circuits that may be less troublesome (is a h-bridge easier to manage?)? Thanks, Stephen I​ just gave it another test with a H-bridge instead and the source of one of the FET's blew so it appears that there is just FET failure and maybe not arcing between drain and source.

Question by The MadScientist 2 years ago  |  last reply 2 years ago