26
votes
How can a reed switch be used for high current applications?
Don't use the reed switch directly. Use the reed switch to switch the coil of a larger relay. Alternatively, use the reed switch to switch the gate of a FET large enough to handle to load current.
- 57.4k
19
votes
How can a reed switch be used for high current applications?
For long-term reliability, a 60 A load requires relay contacts rated for at least 100 A. The coil current for such a contactor almost certainly is greater than the reed switch rating. There are at ...
- 12.5k
8
votes
dB (decibel) is a relative measure. It's not a physical unit. Decibel relative to what?
dB is a ratio. dBx is with respect to the reference level x.
Originally, it was a power ratio, but it has since become common to also use it for a voltage ratio, and regardless of the impedance levels....
- 140k
7
votes
dB (decibel) is a relative measure. It's not a physical unit. Decibel relative to what?
dB is a ratio of two power levels (at least originally).
Common practise is to give it a suffix indicating what the reference level is, so for example dBm is power relative to 1mW, dBW is power ...
- 16.1k
4
votes
dB (decibel) is a relative measure. It's not a physical unit. Decibel relative to what?
It is relative to any reference value you want to use to know how your value compares to the reference.
- 87k
3
votes
dB (decibel) is a relative measure. It's not a physical unit. Decibel relative to what?
The reference point is arbitrary. Per Wikipedia the reference level most commonly used for sound in air is 20 μPa which roughly corresponds to the sound of a mosquito flying 3 meters away.
- 1,306
3
votes
Battery capacity and parallel vs. series battery connections
Converting 48V to 220V will require a quarter of the current of converting 12V to 220V. That means you can get away with thinner wiring.
The total number of watt-hours in the batteries is the same ...
- 14.6k
3
votes
Powering esp32 via v5 influences ds18b20 working (which is powered with 3.3v)
I've had the same problems with ESP32.
First, read this answer and use the voltage translator circuit to run the sensors on 5V. That will give you much better noise immunity.
Second, the onewire ...
- 57.5k
3
votes
How can I select a suitable cable with these characteristics: 690 V, 550 A, 1 km long, AC three phase underwater cable
For something as out there as this you absolutely need to be talking to the applications engineers at the cable manufacturers, likely one of the specialist sub surface ones.
There should however be ...
- 16.1k
3
votes
What exactly is power? And what limits its generation?
My first question is, why is electric power defined like that?
Because a device that consumes \$I\$ amperes of current at \$V\$ volts can do up to \$V * I\$ joules of useful thermodynamic work every ...
- 13.7k
3
votes
Accepted
Power supply overload protection work around
I need to switch on a contactor that uses around 3.2A inrush current for around 20ms...
...the power supply breaks down the output voltage around 3.1A
... at 3.1A, the output voltage of the power ...
- 12.2k
3
votes
Voltage is below 380
I think what you are looking for is called a Servo Controlled Voltage Stabilizer,
e.g. implemented as variable transformer that automatically adapts its transforming ratio in order to compensate input ...
- 15.7k
3
votes
Accepted
How to regulate 5V 3A to 3.3V for ESP32 and level up 3.3V to 5V on a PCB?
The linear regulator burns the extra voltage as heat. Example:
ESP32 draws maximum 240mA. Let's use 300mA instead, assuming the ESP32 will draw a bit of extra currents to light LEDs, etc.
At this ...
- 57.5k
3
votes
How to reduce power drawn by a resistor heater?
If you need 8067 watts of power to heat whatever it is you're heating, then... you need the watts, can't reduce the power.
If you do not need the watts, but find you need less watts, then you can use ...
- 57.5k
3
votes
How to reduce power drawn by a resistor heater?
220 Volt / 6 Ohms = 36.6 Amps * 220 Volt = 8066 Watts
120 Volt / 6 Ohms = 20 Amps * 120 Volt = 2400 Watts
Reduce the voltage. At these currents you likely want a transformer. Or get a 120V power ...
- 70.7k
3
votes
What is the loading factor of a generator?
What they call "loading factor" seems to be what is usually called "load factor" (in the UK at least). This is measured over long timescales - like years - and includes downtimes ...
- 65.8k
2
votes
Accepted
How to reverse voltage 12-24VDC to use a peltier element for heating and cooling
Build an H-Bridge switching at >20 kHz, ideally >100 kHz. Pass the output through LC lowpass filtering. This will create a smooth DC current through the Peltiert, which can flow in both ...
- 10.2k
2
votes
S = VI*/2 derivation
The way to derive $${S=VI^*}$$ is as follows.
Let there be a voltage $${V\angle\theta_v}$$ and a current $${I\angle\theta_i}$$ in a phasor equivalent circuit in the steady state.
In the time domain, ...
2
votes
What is the real and apparent power of these steel cutters?
Real power is specified in watts. Apparent power is specified in volt-amps (or VA or kVA). So, if the input specification is 120 volts at (presumably) a maximum of 13 amps (both volts and amps in RMS),...
- 378k
2
votes
Measure power with multiple measurements
It is incorrect to multiply the RMS values.
If the V is constant, then there is no need to use its RMS value --and for small amounts of ripple, then a straightforward average is OK.
Given that V is ...
- 12.4k
2
votes
Determining the characteristics of an unidentifiable low-frequency transformer
It sounds like you already have the windings identified. For other readers I'll give a tip. When measuring an unidentified transformer, always apply your excitation to the highest resistance winding. ...
- 140k
2
votes
How can I make this variable power supply go from 1.25V and -1.25V to 0?
How much current do you need? A buffered op-amp could source or sink between +12 and -12.
This answer has some circuit ideas that could do the job: How to increase the output current of a dual supply (...
- 40.2k
2
votes
Voltage is below 380
The problem am facing is voltage supply is variable, that is from
power supplier company. Most of the time I get voltage around 390 but.
sometimes it drops to 375 or below. At that time motors couldn'...
- 9,648
2
votes
How to reduce power drawn by a resistor heater?
Since your application (electric furnace for fused metal) is not going to need
quick reaction times, one flexible way to control the heating power is to use
PWM (Pulse Width Modulation), as mentioned ...
2
votes
How to reduce power drawn by a resistor heater?
In addition to other answers, the simplest approach I can think of is to reduce the diameter of the wire. That will increase the resistance and drop the power. In addition, the smaller-diameter wire ...
- 57.9k
2
votes
I've designed a new style of ac alternator where both the stator and the rotor rotate oppsite directions so that rpms multiply by each other
Unfortunately your conjecture that the rpms will multiply is incorrect. The governing equation behind motors and generators (and alternators) is the faraday induction law:
https://en.m.wikipedia.org/...
- 487
1
vote
How can a reed switch be used for high current applications?
You will want a protection circuit (or BMS, stands for Battery Management System) for the LiPo pack, to implement overtemperature and overcurrent cutoff.
The protection circuit will have a MOSFET that ...
- 4,670
1
vote
Accepted
Relation between line voltage and phase voltage in delta configuration
If I understand that what you are asking is "why are the sums of the other two phases equal to the phase I am looking at".
The other two phases are 120 degrees and 240 degrees shifted in ...
- 7,763
1
vote
What is the real and apparent power of these steel cutters?
I don't see any basis for accurate comparison, there is too little information given. The manuals give even less information than the blurbs.
Given the size of the brushed universal motor appears ...
- 327k
Only top scored, non community-wiki answers of a minimum length are eligible