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1 vote

How to drive 12V from a RPi GPIO?

I would consider going to your favorite china supplier or even ebay etc. Use this term: "arduino switch opto" and expect a large choice of devices. The first one I looked at stated: "...
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1 vote

Op-Amp transistor voltage regulator considerations

Much depends on how fast you need the output V8V to change when you switch off the reference. As it stands, Q6 will charge C3 (10 uF) very quickly (and perhaps cause excess current in Q6), but when ...
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1 vote
Accepted

Op-Amp transistor voltage regulator considerations

A simple fix is to add a diode in reverse parallel with the Q6 base-emitter. This will clamp the reverse voltage to 0.7 V. Adding this diode means that the opamp is discharging the load cap through ...
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1 vote

How to drive 12V from a RPi GPIO?

It's always best to search for solutions with progressively narrower searches on keywords. (Socratic method, where you interact with the search engine) Then you might find a way to do it with spares, ...
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2 votes
Accepted

RS-485 possible ground loop

Based on your wiring diagrams and modules you use, this is not a problem of a ground loop, but a problem of completely lacking a common ground reference between RS-485 devices. While it is true that ...
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  • 90k
0 votes

RS-485 possible ground loop

If the nodes are powered over the same CAT5 that carries the data and not grounded in any other way and the RS485 driver/receiver grounds are connected to the DC supply negative it will not be a ...
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1 vote

Powering two 12 V amplifiers wired in series from a single 24 V supply

I agree that you really should not try to connect these amplifiers, or any dynamic and unequal loads, in series on a single supply. However, you might be able to get away with just one 24-12 volt DC ...
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7 votes
Accepted

Powering two 12 V amplifiers wired in series from a single 24 V supply

Applying a supply voltage to two series-connected loads doesn't mean that they'll see equal input voltage, because they are dynamic loads. The input current of a Class-D amp has a pulse waveform, and ...
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3 votes
Accepted

Is there such thing as a tunable DC/DC converter?

You seem to be confusing two things: Voltage regulation, and adjustable output. Any circuit sold as a "voltage regulator" should adjust its behavior to provide the same output voltage when ...
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0 votes

Leakage Current in a AC/DC PSU without earth?

My experience with power adapter SMPS primary AC 240v , Secondary 24v , 4 Amp , DC . If Human body is touched to tip , the leakage is reducing to 12V. Hence I have used 10 nF across -ve to earth , ...
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0 votes

What circuit for the following input and output?

Using reduction methods, and analyzing trace in question, reduction in realization is possible, this is a synchronous divided by 2/3 counter with 75 % duty factor. XOR gates ( and diode bridges) both ...
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0 votes
Accepted

What circuit for the following input and output?

PLL is king and queen of binary gates.
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1 vote

Higher current or higher voltage from a power supply

If the device was a resistor it wouldn't matter (assuming that the power supply maintains both limits) Say you have a 12V 12W resistor, (perhaps it's a an essential oil heater), you could use a 1A ...
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3 votes

Higher current or higher voltage from a power supply

There are two types of ratings: One is what the device does. The other is what the device is the maximum capability or limiting conditions within which the device is able to properly perform its thing....
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-1 votes

Higher current or higher voltage from a power supply

I had originally posted this as a comment, but I think it is really more of an answer. The answer is obvious for a device that is essentially resistive, where there is a linear relationship between ...
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0 votes
Accepted

Is this power supply not properly grounded?

Unfortunately some manufacturers, particularly ones in China, seem to treat grounding as an optional extra. If the importer (into your country) isn't going to test the grounding, then they don't ...
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0 votes

Is this power supply not properly grounded?

When a power transformer is used with low voltage high current, a ground wire may not be necessary. The usual requirement for 2 pronged plugs or without the PE ground connection is "double ...
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2 votes

Wide range power supply accepting both AC and DC from 12 to 240V

With a peak voltage range >30:1 input might be possible for low power and low DC output in buck, hysteretic or forward converters such as to drive a relay coil in your examples. The best design ...
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1 vote

Photovoltaic solar cell attached to load device

"I want to run a load off solar, but I don't want to involve a battery" gets asked a lot. It is a grail, but not a very workable idea IMO. You are dealing with hypothetical MPPT controllers ...
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1 vote

Photovoltaic solar cell attached to load device

If you try to withdraw too much current from the system, reality hits you hard in your face. The voltage at the load will drop, it can't stay at the set level. There's no energy to maintain the ...
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6 votes
Accepted

Sizing the DC/DC inductor for only momentary high currents

The inductor should be sized to handle the peak current loads without saturating. Most parts will spec both saturation (usually at 20-30% drop in inductance) and DC/thermal limits (typ. 30 C rise). ...
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1 vote

Dynamic Power Path Management (DPPM): Why does the output voltage drops when the current exceeds the adapter's limit?

Your diagram shows that USB is a possible power source for the DPPM circuit. For something like USB, the host/charger is obligated to follow whichever parts of the USB specification it claims to ...
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0 votes

Dynamic Power Path Management (DPPM): Why does the output voltage drops when the current exceeds the adapter's limit?

If the battery charger cannot meet load demand, then the battery supplies the extra current as the voltage decays. I do not know why they don't sense battery current separate from charge current where ...
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5 votes

Sizing the DC/DC inductor for only momentary high currents

The inductor current limit is thermal only. RMS current is what matters, and averaged over the thermal time constant, so, some seconds. The regulator however needs nominal inductance, so saturation ...
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  • 3,052
0 votes

Can I add a second solar panel to a battery powered gate opener, to get more charging?

Your problem isn't that the batteries are not getting charged, because your issue is only on cloudy days, after you added a continuous load. The led light is discharging one battery, and that's ...
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1 vote

Can I add a second solar panel to a battery powered gate opener, to get more charging?

Step 1: Clean the solar panels Simple, easy, you've probably already tried it. Wiping off the panel, even if it doesn't look dirty, can make a big difference. Step 2: Get a new set of batteries You ...
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1 vote

Resonant frequency of power supply (audio amplifiers)

Your setup has a regulated supply of unknown impedance, followed by inductive wiring and then the onboard caps. A typical audio amp will either use: Transformer, rectifier, and smoothing caps. These ...
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1 vote
Accepted

Do I need an isolation transformer?

The entire question is under the scope of IEC 62368-1. To the 1st question: It's indicated in the datasheet that the device is an IEC Class II device which means a device having a "double" ...
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1 vote

Windmills generate electricity by the spinning blades. Why can't EV vehicles recharge their batteries from their spinning wheels? Is that too hard?

The motion of a car is a form of energy, and to get the car moving in the first place that energy had to come from somewhere, either fuel or batteries. If your car is electric, energy stored in the ...
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14 votes
Accepted

Windmills generate electricity by the spinning blades. Why can't EV vehicles recharge their batteries from their spinning wheels? Is that too hard?

They do. It's called regenerative braking. The only time you can practically recover energy from the wheels is during braking. Taking energy from them slows them down. If you do it while they are ...
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  • 4,595
0 votes

Amp and voltage effect on solenoid coil

The term used for determining the magnetomotive force of a solenoid is "ampere-turns" which alone should answer your question. Think of it another way: your solenoid has a given resistance, ...
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0 votes

Amp and voltage effect on solenoid coil

The solenoid coil has a certain DC resistance, R, that depends on its construction (mainly the gauge and length of the coil wire). Ohm's law then determines the relationship between voltage across the ...
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  • 15k
0 votes

Amp and voltage effect on solenoid coil

Solenoids have very low DCR. The battery is expected to have much lower ESR so the voltage does not drop significantly and this resistance decreases as the Ah rating increases. Without any details I ...
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0 votes

What circuit for the following input and output?

The logic derived from the drawing is that from every third transition, output a negative pulse approximately 50% of the clock rising edge interval. This could be made more precise if there were ...
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0 votes

Power-Supply "Combination": Solar for voltage + Battery for current

Ok, having played with the rpi for nearly 9 years I can honestly say the only thing powered directly by the 5v rail is the usb devices (only models 1-3) the cpu is 1.8v and the cpu io is 3.3v both ...
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0 votes

Sepic converter

It is not a trivial matter to make such a conversion. You can learn how to analyze such questions about various power-conversion topologies from this well written textbook, available online. Erickson,...
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0 votes

Is 7.4 V safe to power servo motors?

A Lithium-ion or Li-PO battery cell averages 3.7V during a discharge. It is 4.2V when fully charged. It should be disconnected at about 3.0V. A Ni-MH battery cell averages 1.25V during a discharge. It ...
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3 votes

Is 7.4 V safe to power servo motors?

it will be safe for servos? The specs say that the maximum allowed voltage is 6V. So no, it will not. The motor itself may survive but the servo section (i.e. controller board/sub-circuit) may not.
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5 votes

Why don't we make negative output voltage like this?

Your idea is correct, in that the polarity of the output of a single supply just depends on which one you "call positive". You could connect any component or circuit to the output to get one ...
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  • 8,348
9 votes

Why don't we make negative output voltage like this?

You're on the right track for one fairly common method of generating a negative output voltage. Take a look at the circuit below: simulate this circuit – Schematic created using CircuitLab The ...
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1 vote
Accepted

Select PSU for 12V DC water pump

What about "headroom"? Let's assume something blocks the motor. Centrifugal pumps often experience reduced torque when the inlet or output is blocked. so electrically that may not be a ...
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  • 26.9k
1 vote

Select PSU for 12V DC water pump

If you use a power supply to it's maximum rating, it will always reach it's maximum rated temperature. Pumps demand at least 5x the rated power on startup, often 10x so lower voltage is expected ...
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-2 votes

USB-C cable layout

Try connecting the control wire to one of the red wires and then test the wire again. You should get between 5 and 3 V.
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5 votes

Running 15 amps through a 10 amp switch to power a 13 amp circuit?

Is the switch I was given able to handle the current? It will work well for a while, then the contacts will die or weld themselves shorted. Do I have to find a way to reduce the current, so the ...
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  • 60.1k
2 votes

Running 15 amps through a 10 amp switch to power a 13 amp circuit?

A DC power supply often see a capacitive 0 charge on switching. Thus the ESR of the load cap and supply can be much less than <<0.1 Ohm and the switch must handle this contact turn on current ...
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13 votes

Running 15 amps through a 10 amp switch to power a 13 amp circuit?

You need a better switch to handle the 13A. That doesn't mean you can't also use the switch you are given. If for example it is the only one that fits on the front panel of your device (and fits ...
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  • 2,572
2 votes

Running 15 amps through a 10 amp switch to power a 13 amp circuit?

No. Switch is rated for 10A, not 13A. The load takes 13A at 24V. It might not work properly if you limit current to 10A. Depending on what the load is, it may not be possible to reduce current. If ...
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  • 90k
9 votes

Running 15 amps through a 10 amp switch to power a 13 amp circuit?

1: No. The switch says 10 amps; 10 amps is less than 13 amps. 2: It's hard to "reduce the current" going through the switch. It's not so much putting a flow restrictor washer in your ...
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  • 7,220
0 votes

Power supply switching off and on again after load drop

OFTEN issues like this are caused by inductive spikes which occur when coils are powered off. These produce spikes on the power wiring and cause processor maloperation. If not already installed, add a ...
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  • 143k
2 votes
Accepted

Capacitor keeps exploding on nixie HV power supply

From MC34063 datasheet the 680pF cap on pin CT sets the frequency to something like 45kHz. It's not very accurate but let's go with that. A 45kHz period lasts ~22µs. With 12V input and 160V output, ...
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