# Questions tagged [watts]

The unit of measurement and SI unit for power, named after James Watt. It is equivalent to energy flow per second or Joules/Second. In electrical terms $W = IR = I^2 * R = V^2/R$

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### Is the watt value on the device, or appliance label in watts per seconds or kWh? [closed]

I know the label says watts on the device, but since units of watts and kWh are used interchangeably to solve for amperage and calculating energy usage, it's not clear to me, and I can't find a ...
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### How long would a 48 volt battery with 40 Ah last with a 2000 watt motor?

If it is not over 3 hours what would be good to make it last longer? I am trying to build a 48 volt dirt bike with 2000 watts.
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### Can I replace a 12 V 40 W heating element with several 12 V 7 W elements?

Here is the environment: An RV fridge has a heat exchanger for cooling, looks like what you would stick on an IC chip, only 12" square. It has heater stuck on the back of it that is activated for ...
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### Calculating Fuse Panel Wattage

I am trying to figure out how many watts my house is drawing. I used a clamp-on meter to measure the current on the hot leg of my fuse panel which showed 128.8A. I am then assuming 120V which gives me ...
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### Convert kWh during a 1 hour period to average 15 min kW output

If I have a photovoltaic system that outputs 100 kWh from 1PM - 2PM on a given day and I am trying to figure out what the average 15 minute kW would be during that time period, would that be equal to ...
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### How to calculate watt hours gained charging battery?

I need an estimate of how many watt hours a battery has gained after charging to a certain number of volts. With a 12 V, 50 Ah lead-acid car battery, charged from 12.5 V to 13.0 V, is it as simple as ...
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### How to calculate the power of an uninterruptible power supply (UPS)

I was looking at the datasheets of some UPSs and I noticed some oddities: https://www.durantesrl.it/assets/files/serie-compact.pdf For example, the COMPACT 1000 model claims to have a capacity of 600W,...
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### I need help with putting together a battery

I want to make a 14V, 5A battery out of DIY crystal cells. Each cell is about 1.5V and 0.3A I know I can connect on series until I get my desired voltage, but I need to increase the amps. Is there a ...
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Hey all I am venturing into making a DIY reflow oven. Been looking at many different types/styles over the last couple of years and feel now is a good time to start one. I originally planned on ...
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### Impact of underpowered speakers [closed]

I have an Onkyo TX-8220 Stereo Receiver and a pair of Polk Audio TSi400s. The receiver specs: With 8 ohm loads, both channels driver, [...] rated 45 watts per channel minimum RMS power. The speaker ...
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### Is my interpretation of voltage, amperes and ohms correct? [closed]

This is probably a very common question, but I feel most metaphors are somewhat simplified and therefore lack accuracy and I think that makes me unable to fully understand them, but I've looked at it ...
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### How many devices consuming 6.5W peak can I connect to a 100VA transformer?

Our customer wants to know the number of devices that they can connect to a transformer rated at 100VA. Our devices consume 6.5W peak when the batteries are charging. Here is my calculation and please ...
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### Why is power specified in watts rather than amperes?

This probably has an obvious answer I'm missing, but searching the web only gave me information on how watts are defined, not why we use them. Many electric appliances (from things used to build ...
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### How important is it for a device (laptop) to identify wattage of a charger? [closed]

I have several "old" Thinkpads. Recently I came across that Type-C PD mod to replace charge port with Type-C one. Description said: Please pay attention what you order because normally your ...
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### How can the efficiency of LED emitters be approximated?

The data sheet usually indicates the power consumed and the luminous flux in lumens. The luminous flux per watt can be calculated from this, but this does not allow any direct statement about the ...
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### Why does the wattage on the back of a tube amplifier not match the rating?

When I look at the back plate of a 15 watt Fender blues junior amp (which is a tube amplifier, meaning it uses vacuum tubes) it says 150W. However, the amp is sold as a "15 watt" amp. Why is ...
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### Could I use a resistor rated for 1000w in a 1w circuit? [duplicate]

I am learning about resistors and may not understand something fundamental, but are there any reasons to prefer a low wattage resistor over a high wattage one? Other than space & cost, are there ...
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### Audio amplifier: output power higher than input?

I'm checking the audio amplifier Behringer NX6000D. In the doc it says The NX6000D power amplifier packs 6000 Watts (2 x 3000 Watts @ 4 Ohms; 2 x 1600 Watts @ 8 Ohms)...` In the quick start guide / ...
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### what is the difference between 100 W and 1000 W step down transformer?

I need a transformer of 1350 W and just realize that it is very expensive compared with one of 30 W. What is the physical difference of transformers from 220 to 110 V of 100 W and other of 1000 W? Or ...
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### Formula to calculate wattage required to heat stainless steel?

Original Scope: I am trying to make a heating element using a 304 stainless steel flat bar for simplicity. I'm choosing stainless steel instead of nichrome since it will be more durable. If I know its ...
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### How to calculate wattage for gate/base protection resistor for a TRIAC

I am working on a project using the following circuit, which uses an Arduino type microcontroller to do pulse width dimming of AC circuitry using a TRIAC: I am wondering what wattage I should choose ...
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### Battery - high capacity but low power

I recently saw an advertisement for a battery with 50,000mAh storage capacity, with an output of 5V and 10W power. Is this even possible? Shouldn't it be 250W power, or did I misunderstand things? I ...
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### Calculate battery requirement

I am really new into this. I hope I phrased my question appropiately Assuming I have 200 Ah / 6 volt battery rating, that would mean it could cover 1.2 kWh load. And if I need to run my 400 kWh / 220 ...
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### Computing power of 3 phase system without knowing the load configuration

I am trying to find out the power consumption for a 3 phase balanced system below: I only have access to the L1, L2, L3 and N connection points at the main connection box and I only know that it is ...
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### Energy consumption Calculation

I work for a food processing plant and working on a project that calculates energy consumption. Am having a hard time converting information given by the manufacture to calculate the average kWh. ...
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### My soldering station's iron is rated for 70W, can I modify a 75W one to work with it?

I have an Aoyue 936A soldering iron rated at 24V/70 watts. I came across a cheapo soldering iron rated at 24V/75W and rewired it according to the pinouts of the original one. The thermocouple readings ...
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### Why are high power LEDs categorized by wattage, not voltage & amperage?

In searching for the correct replacement LED for a project, I've noticed that, more often than not, high power LEDs seem to be primarily categorized by their wattage. Why is this the standard? It ...
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### DC motor with battery [closed]

I am new with electrical and want to install motor on my bike. I want to know how volt and watt are related in DC motor and how can they help me choose the right battery pack. If I have 1kW motor but ...
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### MWh for one day expressed in MW

I have read the other question on this topic, but having gone through the answer I'm still unsure about the answer to my own, so I hope this is helpful. If a generator generated 20MWh of electricity ...
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### How to measure power consumption of pulsed DC motor correctly?

I built a permanent magnet pulsed DC motor, and am trying to accurately measure power input, which proves to be harder than expected. The motor is pulsed with a 25% duty cycle square wave and powered ...
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### Precisely determine the actual consumed watt of the device [closed]

What is the actual consumed watt of the device stated a value of input watt and a value of output watt which we often see it?
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### Find an amplifier voltage output to match my subwoofer rating [closed]

I have two amplifiers with a subwoofer connected to each one and I was wondering how to check what the output wattage to make sure I don't blow my subs. Since they are two exact same pairs, I'll just ...
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### Can I power a 100w amplifier with a 33w PSU?

I purchased a small 2 channel amplifier for a DIY audio project (Amazon link). I'm hoping I can connect it to a power supply I already have to drive a pair of small speakers. PSU: 19V 1.75A DC (33w?) ...
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### When using a Primera-Line Wattage and Current Meter, is it showing AC or DC measurements?

I am new to the electrical engineering stuff and am looking for some guidance. I'm going to be designing a off-grid power system for some devices. So I will need to get the power measurements from ...
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### Questions about COBs and power supplies from a beginner

I'm planning to use Citizen 1212 COBs, but I don't know how they can be used on 70 watt for each one of them, knowing that each unit will have 5 COBs. So my question is: what is the right power supply ...
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### Powering a 1 watt LED using a 3 V coin cell

I was hoping to power a 1 watt LED (would be great if this is capable of powering 2 or 3 watt LEDs) with a 3 volt coin cell. Will the coin cell be able to output voltages and amperages that are ...
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### Understanding the actual wattage of LED (LM301H)

LED under consideration is LM301H from samsung: Product page link - https://www.samsung.com/led/lighting/mid-power-leds/3030-leds/lm301h/ Datasheet link - https://cdn.samsung.com/led/file/resource/...
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### Does different bulbs in one circuit lead to shorter lifespan? [closed]

I had a conversation with my family regarding lifespans of bulbs. They claimed that they had observed that when different wattage bulbs are plugged in the same hanging light, the bulbs would die ...
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### How can it be 12VDC and 1.2A 30W?

I came across a device at home which has the specs bellow written on it: Rated Power: 30 W Rated Voltage: DC 12 V Current: 1200 mA Since P = V × I, P = 12 × 1.2 = 14.4 W Why on the specs it says 30 ...
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### What do these forward currents at specified wattages mean?

An LED I'm looking at has various specs listed that I can't make heads nor tails of. It is listed as a "3W LED" supporting a 2.5V minimum and 3.6V voltage. However, "Forward voltage&...
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### Is it wattage that kills you and not specifically amps

First of all the actual amounts needed to kill and the body resistance is not important for this scenario. Let's say we are working with dc. Let's say that 100ma is enough to kill across the chest ...
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### Battery Wattage hour requirement for 12v, 3.75 amp device? [closed]

My cpap machine resmed airsense 10 states the following numbers: DC 24v, 3.75 A As per my understanding the wattage required is 24 x 3.75 = 90 I am assuming WattHour is 90x1 = 90. If I need to use it ...
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### How to lower wattage of circuit

I want to power a computer fan from a 12v motorcycle battery. Disregarding the motorcycle battery being 12.6 volts (not charging), lets say that it's a regulated constant voltage source of 12 volts. ...
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### 2 x 90 Ah 12v deep cycle batteries in series runs 77-90w for under 20 minutes. Why?

I am trying to understand the maths here. I have 2x90Ah 12v batteries in series (24v) and they are powering my computer. The peak power is 120w while the computer is shutting down during a power loss. ...
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### Watt output of radio station

I was wondering how many watts an AM radio station outputs, and if I can calculate the watts on a tuned antenna by this equation: Where Win = the watts input for the antenna, Wout = the watts output ...
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### Calculating wattage of electrical appliances

I need some help from you. I don't know how to calculate wattage of my refrigerator. It has a warmer part and cooler part. Below is its configuration. Also, if you guys don't mind, please roughly ...
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### 5V to 12V DC-DC converter to power an 11 watt bulb

I am trying to find a schematic to make a 5V to 12V DC-DC converter to power an 11 watt bulb. I don't know how to tell if a circuit will be able to light up the bulb. I found a schematic that might ...
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### Poor-Man's Power Meter [closed]

I would like to measure the power of a very unusual ac waveform. Please say if this could work... Construct a black pvc tube with a very sensitive light to voltage converter TSL257 in one end, and a ...
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### how to convert/calculate $\text{kJ}/\text{m}^2$ to $\text{W}/\text{m}^2$

I have some solar radiation data that comes in $\text{kJ}/\text{m}^2$. These data were formerly available for download in $\text{W}/\text{m}^2$. I tried to find some ways to do the conversion from ...
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