Choosing the Right Resistor for Voltage Reduction from 12V to 5V at 0.5A

Question

Hello, I have a problem, maybe someone knows what resistor to use to change the voltage such as in the topic from 12v to 5v with a current of 0.5A in advance, thank you

mr.Sławek · Answer

14 Ohm 5W. But that's not the best idea.

beatom · Answer

I do not have the concept that you want to power it, but whatever it is, the use of a resistor is out of place.

msichal · Answer

The resistor does not reduce the voltage, only the current ...

kogut11 · Answer

Hello. Go to the nearest electronics store and buy a voltage stabilizer from 12v to 5v - cost about PLN 3. Greetings. For example, or here you have a diagram:

Anonymous · Answer

On the Allegro you can get such a cigarette lighter converter which does 12v 5V in the USB output. Very cheap, I recommend taking a look and that would be the best solution .. of course in my opinion. Please look at the 12V USB iPod MP3 MP4 CHARGER type auction, it should look for something for PLN 2 ..

all4you_9 · Answer

Coming back to the resistor: the voltage also depends on the device you want to power with this 5V.
So to know what resistor to plug in, you need to know the resistance of what you connect to the 5V.
As above, I will add that it is better to buy a voltage stabilizer.

kogut11 · Answer

Buddy mhz it is supposed to be a device with a current of about 0.5 amps, and what you proposed - up to 250 mA. Anyway, it is not known where it should be used?

Jacek79 · Answer

It is very surprising. Can you justify it somehow? I am the one who pops up with my resistor theorem - the power to this thing stuck on the other side of the resistor decreases.

Anonymous · Answer

Yes? I have one with a capacity of 1.5A in front of me and I paid PLN 3. Neither does it get hot. But I won't convince anyone about it.

all4you_9 · Answer

Maybe he meant a parallel connection , assuming that there is a limited max current (i.e. power at const. voltage) from the source.

damian3219 · Answer

These are loudspeakers, for example, for mp3 and I want to connect them in the car so that the current is drawn from the battery and not from the battery because they discharge too quickly

all4you_9 · Answer

PLN 10 with shipping on Allegro USB CAR CHARGER for MP3 MP4 IPOD High 5 PLN (number 693053506)

karolglinik · Answer

Hi. and I need a 9V in my car. As you know, the voltage in a car is variable, from 11 to 14V approx. Will I get a voltage of 9V using a 9V voltage stabilizer, or will it change? These stabilizers have 3 feet, how do you connect?
I plan to connect a voltmeter to this 9V source, which will measure the voltage on the battery. not sure if it will work out

etezet · Answer

You're confusing the concept, buddy. As for stabilization - LM7809 - Link In the case of Vin = 11V, stabilization may be difficult because there must be at least a 3V difference between Vin and Vout (in the case of LM78 **). And the idea with a 9V voltmeter is out of the question. Why can't you just plug it directly into 12V? In google under the slogan battery voltage indicator (or similar text) you will find many practical solutions on LEDs. Greetings.

Piotr59mb · Answer

By the way, speaking of the stabilizers ... If we give a voltage, let's say 7V to 7805, what will happen? I always thought that the input voltage just needs to be higher than the output.

kedat4 · Answer

Hello! As my colleagues have already said, changing the voltage with a resistor is not a good idea, sometimes with a constant load it is done, but the ambition would be to know the basic law of the ohm, which is an ordinary electrician, if you want to be an electronics engineer. Thank you!

Ireneo · Answer

11 volts when stationary as a weak battery, so it will always be at least 12.2 volts, usually about 13.8 with efficient charging on a fired car, so 9 volts use this stabilizer

karolglinik · Answer

The point is that I already have a voltmeter, it is only powered by a 9V battery and I was wondering if the power could be taken from the source that will be measured, in this case the car battery.

thanks for the answers

Ireneo · Answer

it can only be below the minimum input voltage threshold, the system will not fire or it will not work while turning the starter, but while driving with efficient charging, you can do so

karolglinik · Answer

when it comes to the LM78L09A stabilizer, I gave 2 capacitors as shown in the catalog, I gave a 1uF and 0.5uF capacitor (in the catalog, tests were done with 0.33 and 0.1uF capacitors) and this system does not work (I also gave a diode to load the circuit). I am not sure if I connected the capacitors correctly. In electrolytic condition, how to recognize which pin is on + and which on GND. It is probably looking at the strip on the capacitor. Or maybe I gave too little legs?

etezet · Answer

In el. Capacitors the - foot is marked on the side of the capacitor with a light strip with minuses. If the system is to be powered by a battery, the set of capacitors you have is enough.

sanmar · Answer

Hello

I have a similar problem in my device, one of the elements is powered with 12 V and consumes about 100 mA of current, other elements are powered at 24 V all direct current, of course, I used the L7812CV stabilizer and two capacitors 0.33 and 0.1 in parallel with and in front of the stabilizer yes as in the technological card. After connecting everything, the whole device works as it should, the only problem is the heating of this stabilizer, which I can do without using any heat sink so that this stabilizer does not heat up. I would like to add that the entire device is powered by 24 V and consumes about 5 A of electricity. A colleague told me that I could use a 240 ohm 5W resistor, it was calculated as follows: 24V / 0.1A = 240 ohm Is this resistor correctly selected and can this problem be solved in this way.

398216 Usunięty · Answer

This is a normal phenomenon in this system, the excess voltage is deposited on the stabilizer itself. Calculate the power based on the data - voltage drop on the stabilizer 24-12 = 12V times the current taken from the stabilizer output (100mA) gives: 12x0.1 = 1.2W. It's not possible. It must be - but for consolation - relatively small - for example: You can also use the housing (as long as it is metal and you will isolate the stabilizer (plate) from it). A patent with a resistor will not give you a stabilized voltage - it will change if the load changes, and it will heat the same way.

Anonymous · Answer

As above - heatsink needed.
If the load current of 0.1A is relatively constant (or at least not higher), you can use a resistor but 100 Ohm with a power of min. 2W (better 3-5W) connected in series before the stabilizer, which will reduce the input voltage seen by the stabilizer and reduce the power of losses (the amount of heat) on it.

398216 Usunięty · Answer

Of course - but the total amount of heat will not decrease by this.

sanmar · Answer

Hello

Thank you very much for your answer. I forgot about the most important thing. The whole device will usually be powered by a battery or power supply and the point is that sometimes you need to connect to a 24 V power supply, more often it will be 12 V, this part of the device consumes exactly 95 mA of current and is never used again I forgot about choosing a resistor and I think you will have to take other data 12 / 0.1 = 120 ohm and also 5 W. The whole device is very small and additionally it is in a plastic housing, so I cannot use any heat sink. It is not so much that it heats up, but that the element does not heat up so much, that is, that it all spreads to both the resistor and the stabilizer, then you will be more sure that the device will work flawlessly.

Anonymous · Answer

Incorrectly counted. It does with 12 / 24V power supply, it cannot be done on a linear stabilizer (even with a series resistor). Inverter only.

sanmar · Answer

Thank you very much for your answer. As for this part of the device for 12 V, the device can work properly from 8 V, in this situation it is also impossible?

Anonymous · Answer

As above - for the given conditions - it is impossible.
You can use a 7809 or 7810 stabilizer (without a series resistor - because it is only possible here for Usas = 24V, with Usas = 12V it would disturb), but then the power lost on the stabilizer will be (29V-9V) x 0.1A = 2W - a it should be without a heat sink (29V - because this voltage can occur in a car installation).
Only the converter 28 / 12V -> approx. 10V.
For example, http://www.tme.eu/pl/katalog/#id_category=100...C36%2C74%2C317%2C364%2C364%2C365%2C365%4307%2 % 2C624% 2C624% 2C632% 2C1776% 2C2390 & used_params = 364% 3A55702% 3B365% 3A41506% 2C24785% 2C26170% 3B624% 3A359897% 2C367338% 3B

[Solved] Choosing the Right Resistor for Voltage Reduction from 12V to 5V at 0.5A

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