Eliter
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Cheapest power solution

Thu Mar 16, 2017 6:54 pm

What is the cheapest way to get power from the wall to any of the raspberry pi's. They don't have to look nice, or even have to uplug.

I'm trying to figure out how to both use batteries to power the Pi's and the wall outlets, but am wondering if I could possibly get the price of an entire charger down to like $2??? Also, the smallest setup for the batteries.

edo1
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Re: Cheapest power solution

Thu Mar 16, 2017 7:38 pm

You could try the charger from aliexpress, but not sure about the quality.

Beware: a broken power supply can damage Pi!

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TracyLBaker
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Re: Cheapest power solution

Thu Mar 16, 2017 8:51 pm

It has been said time and again, both about the Pi and computers in general: Don't scrimp on the power supply.

Which is a better bargain in the long run, using a $2 cheaply made PSU that has poor output leading to having to replacing the Pi due to bad power (and the PSU), or spending a more on the PSU, ensuring the Pi gets good power?

Just some friendly advice.
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W. H. Heydt
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Re: Cheapest power solution

Thu Mar 16, 2017 9:00 pm

The real risk with an extremely cheaply made PSU is not to the PI, though that can happen. The major risk is that a PSU failue could burn down your house.

stderr
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Re: Cheapest power solution

Thu Mar 16, 2017 9:30 pm

W. H. Heydt wrote:The real risk with an extremely cheaply made PSU is not to the PI, though that can happen. The major risk is that a PSU failue could burn down your house.
How do you know that it's not a cheaply made PSU? Surely there's more to it than just you paying a lot for it.

Heater
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Re: Cheapest power solution

Thu Mar 16, 2017 9:57 pm

stderr,
How do you know that it's not a cheaply made PSU? Surely there's more to it than just you paying a lot for it.
Easy. If your house burns down, and all your worldly possessions are lost to fire, whilst you are out, then you had a cheap power supply.

This may sound flippant but it did happen to one friend of mine.

Of course it's not so simple. An SD card in a Pi can go bad and overheat enough to cause a fire.This has happened to me.

Basically, any kind of electronics is dangerous.

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davidcoton
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Re: Cheapest power solution

Thu Mar 16, 2017 10:02 pm

stderr wrote:
W. H. Heydt wrote:The real risk with an extremely cheaply made PSU is not to the PI, though that can happen. The major risk is that a PSU failue could burn down your house.
How do you know that it's not a cheaply made PSU? Surely there's more to it than just you paying a lot for it.
True, but you can't make a good, safe PSU cheaply. You still need to be able to spot quality among the mid-priced ones.
And if by mistake you buy a PSU without the relevant safety marks, don't use it. The risk is just too great.

Slightly OT. I have seen Chinese imports with "UK" plugs that are unfused. They should be cut off and destroyed on sight. Fortunately destruction (by bending the earth pin by hand) is not difficult. If you try to use them, the earth pin can get left in the first socket it sees.
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fruitoftheloom
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Re: Cheapest power solution

Thu Mar 16, 2017 10:29 pm

Eliter wrote:What is the cheapest way to get power from the wall to any of the raspberry pi's. They don't have to look nice, or even have to uplug.

I'm trying to figure out how to both use batteries to power the Pi's and the wall outlets, but am wondering if I could possibly get the price of an entire charger down to like $2??? Also, the smallest setup for the batteries.
viewtopic.php?f=62&t=176565
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Eliter
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Re: Cheapest power solution

Thu Jan 04, 2018 3:38 am

fruitoftheloom wrote:
Thu Mar 16, 2017 10:29 pm
Eliter wrote:What is the cheapest way to get power from the wall to any of the raspberry pi's. They don't have to look nice, or even have to uplug.

I'm trying to figure out how to both use batteries to power the Pi's and the wall outlets, but am wondering if I could possibly get the price of an entire charger down to like $2??? Also, the smallest setup for the batteries.
viewtopic.php?f=62&t=176565
Thank you for the suggestion. However, I am from the United States and cannot use this.

Now as to the damage towards the Raspberry Pi. The cheapest Raspberry Pi goes for $5, but the cost adds up as you put more stuff to it.

Here are the bare requirements to make the Pi useful at all: the Pi, micro USB (with consistent power coming to it), and an SD card. Already, you're at around $15 if you buy your typical accessories.

That being said, how do you get your Pi setup down to the absolute minimum cost?

I'm thinking a useful scenario in which not actually buying a traditional power supply would be best is if you were trying to cluster multiple computers. You would buy the cheapest Micro USB cable (in which case, any suggestions), and build your own power supply that distributes to all those cables.

Some other thoughts as to how to get the price down from a power supply is if you're getting the power from DC you can put it through a car USB charger, then through USB to micro USB to the Pi. However, I want to know if the cost can go down even further--since you don't really need it to look all beautiful with the casing of the charger, and you can strip down the cost because you don't need a fancy micro USB cable either--it just need to go from a negative/ground and a positive to a Micro USB.

I'm not even sure you need micro USB, since it's just power. Is there a way to just hookup wires directly to the Pi instead of using a Micro USB cable?

I'm doing a high school level Digital Electronics class, so it's a bit foreign to me (plus my school just got rid of a teacher with another one who knows nothing of electronics, so I can't further my education very much). However, how do I make my own device that converts (possibly unstable) DC input to a stable DC input that a Raspberry Pi can take?


EDIT1: so apparently a Raspberry Pi can accept power directly from GPIO pins, according to this article: https://www.modmypi.com/blog/how-do-i-p ... spberry-pi . However, doing it this way increases the risk of frying the Raspberry Pi, as there are fewer safety measures put in place for this method.
That being said, what is the easiest (more importantly, cheapest) way to make sure DC input voltage/amperage spikes don't get to the Pi?

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Re: Cheapest power solution

Thu Jan 04, 2018 6:48 am

Eliter wrote:
Thu Jan 04, 2018 3:38 am
Now as to the damage towards the Raspberry Pi. The cheapest Raspberry Pi goes for $5, but the cost adds up as you put more stuff to it.

Here are the bare requirements to make the Pi useful at all: the Pi, micro USB (with consistent power coming to it), and an SD card. Already, you're at around $15 if you buy your typical accessories.

That being said, how do you get your Pi setup down to the absolute minimum cost?

I'm thinking a useful scenario in which not actually buying a traditional power supply would be best is if you were trying to cluster multiple computers. You would buy the cheapest Micro USB cable (in which case, any suggestions), and build your own power supply that distributes to all those cables.
Bad approach. least cost uUSB cables have very thin wires, which means excessive voltage drop between PSU and Pi which mean unreliable voltage....
Some other thoughts as to how to get the price down from a power supply is if you're getting the power from DC you can put it through a car USB charger, then through USB to micro USB to the Pi. However, I want to know if the cost can go down even further--since you don't really need it to look all beautiful with the casing of the charger, and you can strip down the cost because you don't need a fancy micro USB cable either--it just need to go from a negative/ground and a positive to a Micro USB.

I'm not even sure you need micro USB, since it's just power. Is there a way to just hookup wires directly to the Pi instead of using a Micro USB cable?
Yes, all you need in the cable is +v and ground. PSUs with built in cables are wired that way. And, yes, you can power a Pi without using a uUSB cable. You can connect a 5v supply to one of the 5v GPIO pins (and, of course, ground to one of the ground pins). But be careful...do that and you're bypassing the power protection circuits, so you are depending on the *quality* and *reliability* of your PSU, plus you should put in current limit protections since you've bypassed the ones the Pi has. Basically, doing this on the cheap is false economy.
I'm doing a high school level Digital Electronics class, so it's a bit foreign to me (plus my school just got rid of a teacher with another one who knows nothing of electronics, so I can't further my education very much). However, how do I make my own device that converts (possibly unstable) DC input to a stable DC input that a Raspberry Pi can take?
There are libraries full of books on electronic circuit design. There are books that have circuits to do just about anything you can imagine...and probably some things you can't imagine. I have a book that contains a circuit for an internal combustion engine electronic ignition...using vacuum tubes.

Just because your teacher doesn't know enough to help you (though I'd bet he could take a decent stab at pointing you towards the right section of the library), shouldn't stop you. If you really want to learn about these subjects, start reading. Then read some more.
EDIT1: so apparently a Raspberry Pi can accept power directly from GPIO pins, according to this article: https://www.modmypi.com/blog/how-do-i-p ... spberry-pi . However, doing it this way increases the risk of frying the Raspberry Pi, as there are fewer safety measures put in place for this method.
That being said, what is the easiest (more importantly, cheapest) way to make sure DC input voltage/amperage spikes don't get to the Pi?
That is correct. The secret to reducing spikes is inductors and capacitors. Last ditch way to stop spikes is usually a varistor, though a zener diode can take out some voltage spikes. Read up on them.

What this really all comes down to is this: It is very unlikely that you can build a working PSU for less than you can buy a reasonably decent one. The companies that make them buy the components by the hundreds of thousands if not millions. That gives them componet prices you can't even approach, let alone beat. If you really want to build your own PSU in spite of these facts, then you will probably want to start with pieces of a PSU, rather than the individual components. I suggest you do a web search for a device called a "UBEC" and go from there.

Heater
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Re: Cheapest power solution

Thu Jan 04, 2018 9:12 am

Eliter,
I'm doing a high school level Digital Electronics class, so it's a bit foreign to me (plus my school just got rid of a teacher with another one who knows nothing of electronics, so I can't further my education very much).
Sure you can. When I was in highschool there were no such things as electronics classes. Although we did learn about charge, current, magnetic fields, resistance, capacitance, inductance etc in "science" class.

I started tinkering with electronics at age 10 when somebody bought me a Philips Electronic Engineer kit. Didn't understand how most of the projects in there worked but it was fun to build them.

I was building receivers and transmitters with vacuum tubes by age 13 and digital logic circuits (with TTL chips) a bit later.

Luckily there were a couple of other kids in school with similar interests in electronics.

You can do the same. The internet is a wash with electronics tutorials, for all levels. There are great learning resources and all the parts you need at https://www.adafruit.com/, https://www.sparkfun.com/ not to mention all the Pi suppliers and many other places.

Al lot of electronic components, kits, boards, gadgets can be found on e-bay amazingly cheaply.

It has never been easier, or cheaper, for youngsters to get into electronics.

Have fun.

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Re: Cheapest power solution

Thu Jan 04, 2018 9:58 am

A pi zero (or original B) isn't too fussy on power - it'll work fine with 4v-5v and 200mA which covers any "bad" Usb cables.
You really can stick it on any USB and expect it to work e.g TV Usb sockets, or a PC hub

A point to make is low voltage won't damage anything but high voltage will...

The pi3 however requires much higher current and stable voltage so really does need a decent dedicated 2-3A PSU to work reliably.
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MaxK1
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Re: Cheapest power solution

Thu Jan 04, 2018 1:43 pm

You could "re-purpose" an ATX power supply from an old (er) desktop PC. You'll get a PSU that can provide 3.3V, 5V and 12V for at least a couple of Pi2/Pi3, external HDD's, Arduino's and breadboards, etc. These are throwaway items so you can't get much cheaper than that. And you'll probably think of other uses.
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Eliter
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Re: Cheapest power solution

Thu Jan 18, 2018 4:10 am

So I bought these four products from the dollar tree. I want to know legitimate answers on how they would work with a Raspberry Pi, WITHOUT looking at the price of these:

https://imgur.com/a/hjbGS

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Imperf3kt
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Re: Cheapest power solution

Thu Jan 18, 2018 7:08 am

Eliter wrote:
Thu Jan 18, 2018 4:10 am
So I bought these four products from the dollar tree. I want to know legitimate answers on how they would work with a Raspberry Pi, WITHOUT looking at the price of these:

https://imgur.com/a/hjbGS
Those (and pretty much every other "lighter socket USB adaptor") are just a 12 supply (car Lead Acid battery - could be up to 14.4v) with a resistor stuck inside plus a fuse. Some (but not the 'dollar' ones) include buck converters.

They'd work okay maybe, but ditch all of them and only use the dual port one, and only one of those ports will be 2.1A, but likely won't stay 5v stable.
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ejolson
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Re: Cheapest power solution

Thu Jan 18, 2018 8:25 am

Eliter wrote:
Thu Jan 18, 2018 4:10 am
So I bought these four products from the dollar tree. I want to know legitimate answers on how they would work with a Raspberry Pi, WITHOUT looking at the price of these:

https://imgur.com/a/hjbGS
Except for the double port car adapter rated at 2.1 amps, the others are 1 amp devices. Chances are none of those power supplies work well with the Pi 3B; however, all may work with a B+ or Zero and possibly even a Zero W.

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Re: Cheapest power solution

Thu Jan 18, 2018 9:04 am

Imperf3kt wrote:
Thu Jan 18, 2018 7:08 am
Eliter wrote:
Thu Jan 18, 2018 4:10 am
So I bought these four products from the dollar tree. I want to know legitimate answers on how they would work with a Raspberry Pi, WITHOUT looking at the price of these:

https://imgur.com/a/hjbGS
Those (and pretty much every other "lighter socket USB adaptor") are just a 12 supply (car Lead Acid battery - could be up to 14.4v) with a resistor stuck inside plus a fuse. Some (but not the 'dollar' ones) include buck converters.

They'd work okay maybe, but ditch all of them and only use the dual port one, and only one of those ports will be 2.1A, but likely won't stay 5v stable.

What do you base that on?

This teardown of a Dollar Tree charger reveals it has a buck converter. Quality is not good and it doesn't meet it's spec, but it's not just a resistor.

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Imperf3kt
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Re: Cheapest power solution

Thu Jan 18, 2018 11:16 pm

PiGraham wrote:
Thu Jan 18, 2018 9:04 am
Imperf3kt wrote:
Thu Jan 18, 2018 7:08 am
Eliter wrote:
Thu Jan 18, 2018 4:10 am
So I bought these four products from the dollar tree. I want to know legitimate answers on how they would work with a Raspberry Pi, WITHOUT looking at the price of these:

https://imgur.com/a/hjbGS
Those (and pretty much every other "lighter socket USB adaptor") are just a 12 supply (car Lead Acid battery - could be up to 14.4v) with a resistor stuck inside plus a fuse. Some (but not the 'dollar' ones) include buck converters.

They'd work okay maybe, but ditch all of them and only use the dual port one, and only one of those ports will be 2.1A, but likely won't stay 5v stable.

What do you base that on?

This teardown of a Dollar Tree charger reveals it has a buck converter. Quality is not good and it doesn't meet it's spec, but it's not just a resistor.
I based it on personal experience with roughly a dozen different devices I ripped apart myself.

In other words, speculation based on personal experience.
I apologize if I misled anyone.
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Eliter
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Re: Cheapest power solution

Fri Jan 19, 2018 12:45 am

So I got some replies regarding the DC adapter, but what about the AC one (the one that hooks up to the wall)?

Also, the video that talk about the adapter from dollar tree, it looks like there is a minor difference between the red one and the green one, one being sparkled, and the other being just plain. However, on the red one I see a screw, on the green one I don't see a screw, so I figure they may be different than just looks.

PiGraham
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Re: Cheapest power solution

Fri Jan 19, 2018 10:18 am

Imperf3kt wrote:
Thu Jan 18, 2018 11:16 pm

I based it on personal experience with roughly a dozen different devices I ripped apart myself.

In other words, speculation based on personal experience.
I apologize if I misled anyone.
It was a genuine question and if it's based on your direct experience that's as valid as anyone else's

Paul Hutch
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Re: Cheapest power solution

Sat Jan 20, 2018 4:33 pm

Imperf3kt wrote:
Thu Jan 18, 2018 11:16 pm
I based it on personal experience with roughly a dozen different devices I ripped apart myself.

In other words, speculation based on personal experience.
I apologize if I misled anyone.
Any manufacturer/model information so I can all stay away from those prodcuts?

A simple resistor is incredibly dangerous because the voltage will vary with current draw so the voltage supplied could be anywhere from close to 0V on the low end up to 14V on the high end.

e.g. with a 9.1 ohm resistor and 1A draw when charging you'll have 4.9V but when the battery is full if the draw drops to 0.1A you'll have 13V.

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Imperf3kt
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Re: Cheapest power solution

Sun Jan 21, 2018 9:55 pm

Unfortunately not.
The whole reason I disassembled them to begin with was because they broke one way or another.
Since I had no intentions of reusing them, I took screwdrivers and pliers to them during the breakdown.
I never really took notice of the model number or brand, just learnt my lesson and stayed away from anything less than $5
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ejolson
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Re: Cheapest power solution

Sun Jan 21, 2018 10:13 pm

Imperf3kt wrote:
Sun Jan 21, 2018 9:55 pm
Unfortunately not.
I guess it is now up to the person who made the original post to disassemble the USB power adapters from the dollar store to obtain specific information about those individual devices. It would be interesting to see what is inside. Maybe one of them has a linear regulator instead of a buck converter.

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davidcoton
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Re: Cheapest power solution

Sun Jan 21, 2018 10:40 pm

Without letting them anywhere near a Pi, plug them in and measure the output voltage on a known good meter. If it exceeds 5.2V, throw the adaptor away.
Work out your maximum current requirement. (I will assume 2A for now.) Find a resistor that will draw that current at 5v (5V/2A=2R5) an the corresponding power (5Vx2A=10W).
Connect the resistor across the 5V output. Measure the voltage again. If it is under 4.9V, throw the adaptor away (or use for a lower power application).

You do realise that by buying four cheap adaptors, you have probably paid more than the cost of one good one? Maybe good educational value, but a poor choice overall (unless you are trying to identify a good, safe, cheap adaptor to buy in bulk).
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ab1jx
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Re: Cheapest power solution

Sun Jan 21, 2018 10:44 pm

I've had decent luck with a couple variants of these at $5.84, I think I've got 3 of them. https://www.gearbest.com/raspberry-pi/pp_591471.html If you get the version with the switch it's just a push-push switch with no indicator whether it's on or off, in some situations that's a problem. They're rated 2.5 amps, I've run Pis on them and also charged a Kindle Fire which is a power hungry beast. The shape of it is good, being off to one side it's less likely to block an adjacent outlet than most wall warts.

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