2.4a Output
Micol Cohn
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I was going to order a replacement Micro USB power supply, then I noticed there were several amperages to choose from. So what is the difference? How will this effect my electronics? What should I be concerned of in order to make the right choice?
marine_hm:
I was going to order a replacement Micro USB power supply, then I noticed there were several amperages to choose from. So what is the difference? How will this effect my electronics? What should I be concerned of in order to make the right choice?
Depends what you're going to do with it.
If you are going to power e.g a Nano, then it's pointless to buy a supply over 500mA.
Because the onboard diode between USB and 5volt is limited to 500mA.
Leo..
well budy marine_hm i dont tink wat your circuit be in fire but you have the resistor final of circuit?
is important for the law of ohm
your circuit can be hot for the low resistor and the wats of your circuit
2 different questions in the same thread. Sigh - start new thread for new question.
For the LM7505 question: In this case, never heard of a LM7505 - I assume you mean LM7805 which is a 5v 1A regulator. Your circuit will draw what it needs as long as your regulator/supply can deliver at least that much.
As for the "micro usb supply", same sort of answer - as long as the supply is rated for at least what you need current wise, you should be OK. My preference is to use a somewhat larger supply than needed to allow it to run cooler. You do need to make sure exactly what type of supply it is - some of the 5v supplies are not regulated and will actually have 7 or 8 volts on the output no load, while others are regulated and will be 5v as long as you do not exceed their ratings.
no is for the arduino nano only is for charge my telephone i gona make a charge for telephone whit bateries AA and i need protect my telephone whit 500mA, no 1A but whit 1A is worging Re: 5V 500mA problem
Not nice to hijack someone elses thread.
Quick answer:
The 7805 can deliver up to about 1Amp (if the input voltage is over 7volt and the device is properly heatsinked).
That does not mean you have to draw 1Amp.
The load will draw whatever it needs.
No problem if the load (Arduino, LEDs, etc.) draws only 100mA or 500mA.
Leo..
gpsmikey:
As for the "micro usb supply", same sort of answer - as long as the supply is rated for at least what you need current wise, you should be OK. My preference is to use a somewhat larger supply than needed to allow it to run cooler. You do need to make sure exactly what type of supply it is - some of the 5v supplies are not regulated and will actually have 7 or 8 volts on the output no load, while others are regulated and will be 5v as long as you do not exceed their ratings.
No - a switching type regulator takes a higher voltage and chops it basically so that the output is a constant voltage (not quite that simple but along those lines). A switching regulator is more efficient than a linear regulator because it is switching between on and off instead of in the linear region. Look up "switching regulator" for more details. They can work in both boost or buck mode (boost gives you a higher output than the input and buck gives you a lower output than the input. Either way, they are smaller and more efficient than a linear regulator (like using a LM7805 for example).
You could use a 5V 100A for such devices. The Amp rating only means current available. Devices only draw what they need. As long as you have enough, you're fine. You can't really have 'too much' for amps from a power supply. I think you're missing this point. You need to know it. Remember it.
If you have two such identical devices, they each draw 0.5A, meaning you need at least a 5v 1A (that's 1000mA) power source.
But you can turn one of them off or unplug it, and the other one will still only be drawing its 0.5A. It doesn't suddenly use more power just because more is available.
If it's a device you made yourself, test it with an ammeter before unleashing it on the world. You should understand your project well enough to predict the current draw to a couple tens of milliamps, or a few microamps for a low-power device .
As multiple people here have correctly pointed out, the amp rating is a MAXIMUM rating, just the 5V is a "fixed" property of the supply.
So in theory, you can use a 5V 500mA supply just as well as a 5V 1000A supply to supply your project with 250mA.
If you exceed the rating, in the best case, the supply will shut off, in a slightly worse case, the voltage will drop (resulting in unexpected behavior), in the worst case, it will get hot and catch fire.
In some conditions, it might be interesting to look at the efficiency and the quiescent current. I have seen phone chargers that draw 2W to power an ESP8366 of 0.5W. This might not be important for playing around, but if you have 20 devices lying around always on for home automation, than it gets interesting. A current rating that is closer to the actual demand has the tendency to have better efficiency, but in the phone charger range, there is also a good bunch of quality involved.
I'm trying to decide what is the best option for powering a Pi4. The specs mention for a minimum of 3A. Let's consider we would also like to connect a 2.5" drive to the Pi4. Could someone more experienced with power supplies help me with the following?
How can we tell apart 3rd party chargers that would work with RPi4? Are there any of them? I've seen a couple of models mentioning 5V/4.4A output. But I'm afraid this is only the aggregate amperage (they were multi-port USB chargers).
The best option is a good quality power supply, as cheap brands may say they are rated at 2.4 amps, when they don't actually supply that much. Based on the numerous bad experiences i've had with 3rd party chargers, i'd highly recommend buying the official one from the foundation!
Whether that is adequate for the hard drive is another question. I haven't tried the Pi 4 yet, but my 3B actually worked fine (with no low-voltage warning) with a 1A USB hard drive plugged into it. The adapter powering the Pi was rated at 2.1A.
Third-party USB-C charging devices can be cheaply wired, potentially destroying connected devices as well as starting fires. A safer alternative is to power your Pi using PoE which beyond reducing these risks, offer additional benefits:
Ethernet Cables: Tripp Lite Cat6 Gigabit Snagless Molded Patch Cable. They're quality 24 AWG Ethernet cables at a value price. The link is for a 5 foot length cable which should suit an average use case, but Tripp sell much longer 24 AWG cables if you need more reach. NOTE: the LOWER the AWG cable rating then the BETTER the PoE performance. I use a minimum 24 AWG cable for PoE devices and avoid more common 26 and 28 AWG cables.
Pi 4 Compatibility: Haven't myself yet been able to get a Pi 4 (vendors I tried were out of stock unsurprisingly) but found this link to a Register article about the Pi 4 which notes the PoE Hat IS compatible in their report on the new Pi
Using a 2.4A power supply with the Pi 4 and a 2.5" HDD is going to be borderline assuming a typical power rating of the 2.5" drive of about 1.8W to 2.7W (see here). From the above statement - after all it really says that the Pi will need just 2A - the official supply should however work.
You can either rely on reviews or ask the seller and take their word for it, or you can get the supply, test it, and return it back if it doesn't perform. Obviously, in the latter case you'll want to buy it from a place where you can return it for free.
There is no way to tell from the labels how much current a power supply can really deliver. I've seen 2.5 A chargers which go down to 4V at nominal current. Good enough to charge a phone, not nearly good enough for a voltage-sensitive device such as an RPi.
One place which (surprisingly) sells very decent cheap 5V PSUs is IKEA. They offer a 3-port charger with 3.4A total current, 2.4A per port, which really holds its promises. If you need lots of power, plugging the RPi in one port and a powered hub in another gives you a combined power of 17W.
If you want to (try to) get away with something cheap, check out this charger. It has enough power to get the RPi4 running, so if you deem a non-certified charger safe enough to use (hint: most of the cheap electronics you buy over the Internet isn't properly certified), go ahead.
Fortunately I gathered much experience over the years. The most important with theese is how they are designed. You should never, i mean NEVER buy shady power supply from unknown chinesse sellers / ebay / aliexpress etc.! Majority of them are really badly designed. They might kill not only the device because of poor design, but also YOU because of poor high and low voltage separation. But the shady sellers don't really care, the job is done when the sale is made. Problems they usually have:
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