Current switch? Answered

I have some solar panels that produce 3v at 175ma. I was wondering if i could somehow make a switch to have it turn on when the panels are producing at least 100ma. Maybe also a switch for 150ma too :) Any ideas?? If additional voltage is needed it shouldn't be a problem :) Thanks!

Question by astroboy907   |  last reply


free current

I have a current source of 50 v from a phone line can i reduce it into 12 volt to make a 12 v bulb glow?

Question by faintedbrain_007   |  last reply


how to decrease current??

I have 12volt 8.5amps battery with me i want the output of 12v & 4amp  i dont knw how plz anyone suggest me

Question by SrinidhiS5   |  last reply


What is an Alternating current? Answered

It is always easy to understand the working of Direct current, but I need to know about Alternating current right from the basics till advance. I would be grateful if you could help me understand about Alternating current better.

Question by DeeptiR3   |  last reply


how to reduce current ?

We designed a circuit . But it is drawing 70mA of current. I want tot reduce it for atleast 30-40mA.

Question by SunnyJ1   |  last reply


Current in IC chip

Hello, It's a bit stupid to ask (I think), but essential to me. From all schematic I readed over intructables I never saw anything or anybody that cared for that. If a IC have a maximum and minimum current to respect ie: 6mA to 10mA, do we even care? Do I need to limit the current somehow? As I said, every schematic I readed never added any resistor or talked about anything relate to limiting the current on the VCC for the integrated circuit. I'm currently building a device that use one 555 timer IC in astable and a few others IC and they are all connected in parralel to the power suply. Thanks

Topic by sxdemon   |  last reply


High Current measurement

I need to measure Current from a welding machine to make a alarm if it goes down below some level for ensuring better quality of welding. The current normally set is of the order of 200A max with around 100V DC.Not sure if i could use some clamp-on meters and pass those values out to Arduino for switching circuit. Shunt resistors may be a better option. But to make a signal conditioner to convert the ma output will be a problem i guess..is there something i can do with Arduino.. any ideas guys....? Thanks in advance Chuppandi

Topic by chuppandi 


Transformer current restriction? Answered

I am aware mostly how transformers (AC - AC) work, but I am lest informed on a few key parts.  I know there is a direct relationship between windings and voltage as well as an inverse relationship between voltage and amperage. The thing I don't understand is what limits the current produced by the transformer.  I know you can keep droping the secondary windings to increase amperage, but eventually you get to a point you can no longer do that.  To overcome this one can use three sets of windings wired in parallel which will retain voltage but increase amperage.  The amount of amperage is still limited to the maximum throughput of the primary, but how do you actually find this out.  If one wanted to make a variable current AC welder, it would be relatively easy to predict the voltage, but establishing a potential amperage is more difficult.  What actually establishes the maximum output of a transformer because in some cases the max current is reached long before the actual failure, and is there a way to predict the end product.  P.S. I am not looking for the answer they use voltage/current limiting circuts ect...  I am looking at something like a pole pig which maxes out output before internal failure and contains no additional circutry, not a wall wart

Question by jj.inc   |  last reply


Current Problems with speakers...

Hey guys, I've uploaded some pictures of my problem. What I have here is an attempt to add bass to my speakers - I'm a newb, so this isn't going so well. The music is comeing from an iDock, and is being routed in parallel to a set of computer speakers. The right speaker has volume & tone knob, the left is simply plugged into the right. I unplugged the left speaker, took the circuitry out, and connected its input & output to a larger bass speaker - quickly was I suprised with a smoking capacitor (lol how healthy!) so... what should I do, simply add a resistor? Edit: Note the resistor (brown red red = 12k? or 1.2k?) is only in series with the LED and is not affecting the bass speaker. I am just wondering how a bass speaker could draw MORE amperage than the small speaker without any circuitry?

Topic by GreenD   |  last reply


Specific output of current? Answered

I'm getting a little more knowledge about current measured in mA, but it's still all confusing. From my understanding, your project draws the current needed out of your battery. If my LED uses 25 mA, then the LED will be sucking 25 mA from the battery. If I have two LEDs, then it would be sucking 50mA from the battery, thus reducing its life. So, based on that, how can wall warts have a specific output of amps? How can a wall wart put out 1000 mA? If you use a project that only takes 700mA what happens to the other 300 mA? What if your project use 1,500 mA? And. . . How do you measure the current being pulled through a basic circuit and your average 555 circuit? Thanks,  

Question by HavocRC   |  last reply


Diode current ratings Answered

How can I determine the current rating of a diode  A forward current of 2 amps is needed and the reverse voltage is 12v                                                                hopefully   Gordon                                                                                                   Thank you

Question by GordonT3   |  last reply


Varialbe current regulator?

Have you ever seen a variable current regulator? i googled it but i keep getting standard voltage regulators Any help would be appreciated!

Topic by Sandisk1duo   |  last reply


How much will be the current?

If i use a transformer of 2A to make a 12v dc power supply, what will be the output current? Will it be same or some variance will come?

Question by Naveedm15   |  last reply


Current measurement with arduino

Hey I try to measure current with hall-sensor amploc 25A, it sense magnetic-fields, offset voltage is 2.5V and I use arduino uno. I get 519 value from analog pin and 37mV/A is hall sensor sensitivity. My formula is outputValue = ((((sensorValue*5000.0)/1023.0)-2500)/37 multimeter shows 0.112amps when I put load but I dont gett correct value on LCD Is my formula OK?

Topic by mattilaniko   |  last reply


Is it a current limiter or what???

when rebuilding a battery pack for a Sears cordless drill,I encountered a tiny diode or fuse or thermistor of sorts,in the wire coming from the negative pole.It appears this is only active during charging. At any rate,what is it and where do you find a new one??

Question by    |  last reply


Conventional current. A question about DC current flow. Answered

I just started reading electronics for dummies and it tells me that DC current flows from negative to positive.  It later states that in the early days of electronics it was assumed that current flowed from positive to negative.  Later they discovered that it flows from negative to positive.  Some schematics will have an arrow for current flow going from positive to negative (conventional flow).   Why do they still do this if they know the current flows from negative to positive?  This is confusing.  Thanks.

Question by pennsteve   |  last reply


how to make a dc current from ac current?

I m making a power supply project which works on dc. but i don't wan't a battery, so i wanna connect it direct to ac to dc convertor i don't know how to make it :[...... Anyone who answer plzz give detail summary with a perfect diagram of the circuit

Question by arihant   |  last reply


what makes collector current to be beeta(current amplification factor) times base current?

What makes collector current to be beeta(current amplification factor) times base current? Is it because of shape of the transistor or doping? or Why it is acting as constant current source? or Why the collector current is independent on collector resistor and Vcc(voltage across collector and emitter)?

Question by deepakmurali   |  last reply


Ac current limiting per light bulb? Answered

Dear all.. Please help me to know: how wattage of light bulb(please see photo) is needed for limiting my circuit 120ac 60 watt maximum Thank you so much.

Question by lam   |  last reply


How to increase AC current without using amplifiers and external power source? Answered

Iam having 12V AC and the current 100mA.When i apply the 12V AC to secondary winding of 5V transformer.The voltage gets boosted up to 64V.I don't want voltage to be boosted,instead i want to increase the AC current without using transistors,external power sources,etc.Like the transformer which is boosting voltage when applying AC voltage at secondary.I need to increase AC current only and not the voltage.I want these to be done without using amplifiers.Because amplifiers uses external power source.Any one tell me how to increase current.Otherwise is there any way to increase AC current by reducing the voltage?

Question by Rajkumar2506   |  last reply


Electronics help

I need an easy way to distribute power 2 way and when the on button is switched the correct goes one way and when off then on again it goes another? Thanks

Question by Camyo   |  last reply



can I turn 2A into 5A? Answered

I am makinga hot wire foam cutter and using the hot wire foam calculator from Shawn James and it says that I need a supply of 7.5V 5A, but my transformer only gives 2 A. I've seen voltage multipliers and I don't know if there's a current multiplier. If so, please give me the instructions to make one.

Question by tgferreira184   |  last reply


Low AC to DC conversion

Hi, I'm looking for simple way to convert a low AC into a usable DC, of say 4 - 5 volts for charging batteries. I recently saw one discussed online, specced at costing about a quarter, but couldn't find a way to do it, or a way to purchase something like that. Thanks!

Topic by fafnir665   |  last reply


how to make current meter with PIC 16f877?

please help, if anyone knows. tell me what components do i need to make current sensor? and the process to be displayed on LCD 16x2

Question by starda   |  last reply


Arduino maximum current draw? Answered

What would the maximum current draw through an Arduino be? (ATMEGA328) - I'm planning on running 16 LEDs from it and I need to know if I should be powering them separately somehow.I have the appropriate resistors (100ohm and 180ohm LED dependent).

Question by jonrb   |  last reply


Charging capacitors with different currents? Answered

How does charging a big capacitor with a high current affect it rather than a low current? Certainly time taken decreased. What are other effects, and is it as safe as using a low current?

Question by ARJOON   |  last reply



current limiting for phone battery? Answered

I have a very old phone and its battery is outdated, I am replacing the battery with a new one but that is rated differently Phone ratings: 3.7V DC ; 350mA New battery rating: 3.7V DC ; 860mAh ; 3.2Wh >what is the difference in "mA" & "mAh"? >My main question is ; do I need to put some resistor in between the battery and phone input to limit the current or the current flow depends upon the load ?, do I need to put resistor in series b/w the phone and battery or in parallel. Try to provide a schematic to make answers more clear NOTE: I dont want to replace the phone and am working on it as a restoration project. Thanks in advance!

Question by MYawar   |  last reply


reducing current on a power supply

So I am trying to reduce the on the current power supply I have from an old router. The out put is 12v DC 800mA (.8A). I want to use it to run a man 12v .3AI just wanted to make sure I did my math right and to make sure I didnt miss anything.Ohms LawI = V/RR= V/I V = 12 I = .812/.8 = 15 ohms resistance in theroy_Current on the fan is .3 A, I am assuming that is the max. So desired current is .25I = .25 V = 12 R is current resistance, X is additional resistance Q=(R+X)I = V/QQ= V/IR+X = V/IX = (V/I) - R V = 12 I = .25 R = 15(12/.25) - 15 = 33 ohm resistance neededSo I would need a minimum of 33 ohm resistor. Am I correct?Sorry for the explicitness of the math, its been drilled into me to show every step.

Topic by dragonkeeper117   |  last reply


Reduce current but maintain voltage?

Do resistors reduce voltage or amprage? It's amprage as far as i know. I've got a power supply thag outputs 9kV at 300mA and I need to get it to 9kV at 0.2mA, someone suggested a 450kOhm resistor. When I phoned go get one they asked if I want a quarter watt resistor, what does that mean (1/4, 1/2 watt). I need to reduce the current comingfrom the power supply because I'm using it to power a fusion reactor and the diodes I have to comvert the AC to DC can only handle 0.02mA

Question by JunaidA44   |  last reply


how is ac current generated? Answered

Ok, so I was under the impression that brushless motors were AC motors (and therefore conducted AC current), until recent internet searches proved me wrong. I am curious how AC current is conducted, is it conducted using brushless motors? Or is it a different type of motor that will generate such electricity?

Question by A-Nony-Mus   |  last reply


Wall outlet current draw

I have built a transformer, that will take 120v, and step it down to 2.5v. I used all the right parts, and the correct rated wire for this. My only issue, is that when i connect the primary coil, to a call outlet, at 120v, it draws more current then my 5A fuse can handle, and the power goes out in my home. I need to get 1.5 amps, @120v going through my primary coil, in order to get the desired output on the secondary. I was wondering, how things "draw" current from the wall, as well as if i where to use a resistor, wouldn't it still draw too much amperage, and just dissipate it in heat, to give the desired output (i cannot use, because it draws more than 5 amps). i could not find a resistor out their, that could handle over 100 watts, so i was also wondering how things like vacuum cleaners only draw a small amount of current. Would i need some sort of current regulator (if that's even a thing)? if you had a light-bulb, and a battery, would the circuit the light-bulb is attached to drain less current, if their was a resistor, and thus having the battery last longer, or would it draw the same amount, and just dissipate energy through the resistor in the form of heat, to give the light-bulb its self less current?

Topic by merlinj   |  last reply


constant current or constant voltage?

Hello, I'm looking into driving about five separate piezo ultrasonic water misters and one of them have the rough requirement of 24 volts. my question is if i wanted to drive all five at the same time I'm thinking I would want a 24 volt constant voltage source, is this accurate? Bonus question: what dictates whether a constant current or a constant voltage source is needed?

Question by waldosan   |  last reply


High Current Power Supply

For a project totally nonrelated to my tesla coil I need a way of regulating a voltage down to 36 Volts at 8 amps. My transformer (or a bunch of transformers hooked together) is suppose to have an output of about 38 volts at 8 amps, yet the voltage (with no load) is actually around 60 volts... Basically I need a way of regulating this voltage. For saftey, lets say the max input is 70 volts and it should be able to handle 10 Amps. The output voltage should be 36.

Topic by guyfrom7up   |  last reply


What is the current on my foam cutter? Should I be worried?

I built the 5 min. foam factory, but instead of a model train transformer ($45 for the cheapest one they had) I used a regular 12 volt transformer and a rectifier bridge (I had to borrow it from my infinite LED tunnel :'( ) Now when I went to buy a variable resistor/potentiometer for the thing my local electronics shop guy said that the 12 volt transformer put out too much current for the ones he had. Now this has me worried. How much current is currently going through this thing? Should I be worried?

Question by shyguy567   |  last reply


How to pulse dc current? Answered

Hi! I was just wondering if people could give me some different ways to pulse dc current. I am trying to power a transformer with dc. Thank you in advanced.

Question by tesla man   |  last reply


VFD voltage and current needed

I've a Futaba 4-LT-16 9L big VFD display. Unfortunately I'm not able to find the datasheet or exact details about it. Maybe I could contact Futaba... The only informations I found are these two schematics https://revspace.nl/old/IMG_2239.JPG (but it doesn't match with the 4-LT-16 display) https://revspace.nl/old/IMG_2240.JPG (not very useful to me) from this page and this video from the same page. Could someone help me? Are there typical voltage and current for the filament (I think it depends from the length and the display dimension)? What about the grid voltage? Thanks!

Question by andrea biffi   |  last reply


Procedure to getting Voltage and current of an LED without knowing ANYTHING else?

Good day good people. I got batches upon batches of various surface mount and dip leds. Not a single god damn seller wrote the specs on neither the website, nor the package and there are so many that I can't tell which one's from who. Regardless, however the ridiculously low price you get these things for, you can't really complain. So I need to know if there is a procedure to finding out the current and voltage of an led and that is without knowing a single rating about it. It it guesswork or is there a proper testing procedure? It can be a 1,5v can be a 2.5 or a 3v led I don't know. What should be tested first, what should be second? All I have is a basic multi-meter and besides checking batteries voltage I have't been using it for anything else. Thank you, folks.

Question by MilesT9   |  last reply



Low Voltage Higher Current?

I am having a strange problem on a USB peripheral.... it is a digital radiography sensor that overheats. I believe it may be due to the power supply to the motherboard, but I don't know for sure. I am ASKING FOR YOUR HELP in reasoning out what may be the cause. Anyone with computer/electronics experience, PLEASE HELP!!! I was told that my power supply is too low voltage, and that current is going up in the USB peripheral causing it to heat up. I always thought V=IR means that if voltage drops so does current. But in other places I read that if voltage drops, current goes up so that the wattage/power usage stays the same according to P=VI. So which is it? V=IR or P=VI ? If my power supply has too low voltage, will the current in the device increase to compensate? Or will it just have a lower current? Does it depend on the circuit and the exact electronics in the USB peripheral? Here is my SETUP. It is SIMPLE: Antec AR-350 power supply connected to a motherboard Asus P5N7A-VM in an ATX case. All I have otherwise is a SATA hard drive and a SATA DVD-ROM in there. That's it! Problem started to happen about 1.5 years after I got the computer. That is why I am thinking maybe it is the power supply, or maybe it is the motherboard?  The computer works fine in every other way! It uses Windows XP and has a wireless keyboard/mouse which also works fine. BIOS settings screen Hardware Monitor shows voltage for USB 5v reading about 4.9v, within tolerance. However, one of my USB peripherals is a digital xray sensor. It works ok a few times, then it starts to overheat and fail. This only happens on this computer. When I use another computer (like a laptop) with the same USB hardware it functions ok and never overheats. I don't have any problems on the other computer, even thought I am using the same software/drivers. I bought a different ATX case with a new power supply, and just moved the motherboard, HD and DVD over. Now the motherboard BIOS shows under Hardware Monitor that it is getting 5.2 V instead of 5v, so it is higher! Also the 12 V is higher (around 12.2v) and same for the 3.3V. All the voltages are HIGHER! So I have yet to test this new configuration with the USB peripheral sensor.  Could the motherboard be faulty? I did notice the motherboard looks "curved" with the area under the CPU sort of bulging out. However, with this motherboard you will see there is a huge heat-sink/fan that gets clamped over the CPU and that may be bending the board. Keep in mind the board works perfectly otherwise, so I am wondering WHY it would only affect USB for this one peripheral and not for the keyboard and mouse? Maybe the circuitry on the keyboard/mouse is more tolerant to low voltage? Would appreciate your thoughts please.

Topic by edy   |  last reply


Please help! How do I lower the current strength (Amps) in a parallel circuit so I don't fry my LEDs? Answered

I have a AC/DC adapter that gives out 4.5V and 500mA, how could I lower the strength of the current so that I can connect four LEDs (4.5V, 20mA) in parallel and not fry them? Sorry if I ask the impossible, I'm a total electric beginner. Thank you in advance!

Question by dark_boshkarin   |  last reply


Fan needs 12 volts at .44 amps. How can I limit the current to .44 amps from 2 amps, without losing the 12 volts? Answered

I am trying to power a fan that needs 12 volts at 440 milliamps. I have a wall-wart transformer that is 12 volts, 2.0 amps, and I many components. I have thermal compound,  heat sinks, resistors, 12 volt and lm317 voltage regulators. So, how can I limit the current to 440 milliamps from 2.0 amps, without losing the 12 volts? Also, I tried a resistor at 33 ohms and it burnt out. Thank you, Jeremy (Please note: I am teaching myself electrical engineering, I have not taken physics yet. My knowledge is based on sever books, web resources, and hundreds upon hundreds of youtube videos)

Question by JBronen   |  last reply


Voltage regulator? Answered

Does a voltage regulator IC (e.g 7805, LM317 etc) still draw current when there is no load?

Question by .Unknown.   |  last reply


Measure current and voltage with arduino? Answered

How would I measure the voltage and current of this circuit with an arduino?

Question by flybye22   |  last reply


What is a constant current source?

I had some questions: What is a constant current source? How does a constant current source work? Do i need a cc supply for an led or would a cv supply work? Thanks :)

Question by qwerty156   |  last reply


how to amplify a dc power of 7v and 130mA to maximum?

I know that i could do that using transistors, but how , what type and what rating of components should i use? should i supply transistors a separate current in order to power it? if i have to supply, is it profitable even after giving that current? Becuz we are wasting a power to increase another power!!

Question by SRI HARIH   |  last reply


Building a current booster circuit

Need to understand whats going on in this circuit which is a class project.

Question by ighalo_joshua   |  last reply


Constant voltage AND constant current? Answered

Hi, smart people of the internet :) Is there a power supply or a converter that can be set on a specific voltage and current, and keep both constant at the same time? I looked at ebay converters like B3606, DPS5015, BST400 and the like. They all have constant voltage (CV) and constant current (CC) settings, but they can't do both at the same time. If for example the current being drawn is too high, the unit switches from CV to CC and drops the voltage as much as needed to keep the current constant. Is a simultaneous CC CV power supply even a thing? Thanks!

Question by Morgantao   |  last reply


how to calculate battery current ?

i want to make a ps2 battery, but it is must be up to 5.65 A

Question by Rendydevara   |  last reply