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FreezeTile
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Should I use this power switch with my Pi 3B?

Fri Apr 13, 2018 12:14 pm

https://www.ebay.co.uk/itm/181775204587

Is it safe to use a switch like this with my Raspberry Pi 3 Model B? Is there a better option? When it comes to powering the Pi, I want to be on the safe side. :D

alphanumeric
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Re: Should I use this with my Pi 3B?

Fri Apr 13, 2018 12:25 pm

Should be fine as long as you do a shutdown first and wait for it to fully shut down. I have a switch on one of my portable Pi setups to turn off my power boost and kill any power to my Pi when not in use. I have a second button wired to a GPIO pin that I press first to do the shut down.

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FreezeTile
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Re: Should I use this with my Pi 3B?

Fri Apr 13, 2018 12:31 pm

Thank you! :mrgreen:

hippy
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Re: Should I use this with my Pi 3B?

Fri Apr 13, 2018 12:58 pm

I would say that switch is probably not advisable for use with a Pi.

It is not clear what gauge wire is used for carrying power or what current carrying capacity that wire has, and there is no current rating given for the switch either.

From the official Raspberry Pi FAQ a 2.4A power supply is recommended for a 3B and any cable used for extending or switching that should be rated the same or higher.

alphanumeric
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Re: Should I use this with my Pi 3B?

Fri Apr 13, 2018 1:25 pm

A picture on the product page shows it plugged into a Pi. Hard to tell if its a 2B or 3B though. Typical bare-board active current consumption for a 3B is 400ma. 350ma for a 2B. https://www.raspberrypi.org/help/faqs/#topPower Only way to know is to try it and se if you get the lightning bolt warning. What you have plugged into your Pi's USB etc will factor in also. 2.5 A is recommended, that doesn't mean your going to draw that much though.

hippy
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Re: Should I use this with my Pi 3B?

Fri Apr 13, 2018 2:00 pm

alphanumeric wrote:
Fri Apr 13, 2018 1:25 pm
A picture on the product page shows it plugged into a Pi.
Fair point. That looks like a 2B to me and the power LED is on.

The trouble is without knowing the rating one cannot tell what it will support, without information from the OP as to what will be plugged in and how hard it may be used, one cannot tell how much it may need. I would always recommend taking the worse case to cover an unknown future.

Being in the UK, rather than waste a fiver on something which might not work, I would stick to turning power to the PSU off at the wall socket.

alphanumeric
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Re: Should I use this with my Pi 3B?

Fri Apr 13, 2018 3:09 pm

I agree you have a point about the lack of info. My original post was more along the lines of, if your going to use it, make sure you do the following. It's not something I would personally use. I should have taken a closer look at the web site etc. The OP will just have to decide to go for it or not I guess.

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HawaiianPi
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Re: Should I use this with my Pi 3B?

Fri Apr 13, 2018 6:59 pm

I tested a similar product and found it had too much internal resistance to work on a Pi3B. There was too much voltage loss under heavy loads, even with an input of 5.3V! I use it on my Pi Zero and it works okay for that.

Again, this is based on a similar product, but not the exact same one. The product I tested was a full micro-USB cable and not just a short extension, but the switch looks identical (and adding additional connector losses will not help).
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alphanumeric
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Re: Should I use this with my Pi 3B?

Fri Apr 13, 2018 7:21 pm

It looks like my "should be fine" comment was a bit premature. :oops: Caution may be advised.

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FreezeTile
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Re: Should I use this with my Pi 3B?

Sat Apr 14, 2018 12:13 am

Sorry I took so long to reply. I'm trying to make my Pi portable, so I need a power switch. Has anyone got any recommendations? My Pi setup uses about 2A of power in total. :D

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HawaiianPi
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Re: Should I use this with my Pi 3B?

Sat Apr 14, 2018 12:39 am

alphanumeric wrote:
Fri Apr 13, 2018 7:21 pm
It looks like my "should be fine" comment was a bit premature. :oops: Caution may be advised.
The thing is, products like this should actually be fine. The idea is good, but (at least in the case of the one I tested) it's the implementation that fails. They could have built it with large gauge wire and a quality switch, but they didn't. The product description in the OP link says 28 AWG wire, which is not suitable to power a Pi3B(+). I have thought about making one myself using something like a Volutz Equilibrium micro-USB cable as the base (someday ... maybe).
FreezeTile wrote:
Sat Apr 14, 2018 12:13 am
Sorry I took so long to reply. I'm trying to make my Pi portable, so I need a power switch. Has anyone got any recommendations? My Pi setup uses about 2A of power in total. :D
Other than making it yourself, I don't have anything to recommend. The one I tested was advertised as having either 22 or 20 AWG wire, but based on the amount of voltage loss I experienced under load I seriously doubt that's true.
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FreezeTile
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Re: Should I use this with my Pi 3B?

Sat Apr 14, 2018 3:23 am

Darn it!

Well, if a cable manufacturer happens to read this, a switched USB cable with a gauge of 24 AWG or less would be a great device for Pi users, especially those who are making their Pis portable.

alphanumeric
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Re: Should I use this with my Pi 3B?

Sat Apr 14, 2018 9:26 am

FreezeTile wrote:
Sat Apr 14, 2018 12:13 am
Sorry I took so long to reply. I'm trying to make my Pi portable, so I need a power switch. Has anyone got any recommendations? My Pi setup uses about 2A of power in total. :D
What is the power source? I have one portable setup that uses an Adafruit PowerBoost 1000c (1A out) and a LIPO battery. The PowerBoost has an Enable pin that you can ground to turn it off. It's what I wired my on off switch too. Your just grounding a pin on a chip so next to no current goes through the switch. If you have a similar setup you may be able to do something along those lines. I'm guessing your maybe using a power bank etc though?

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FreezeTile
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Re: Should I use this power switch with my Pi 3B?

Sat Apr 14, 2018 11:43 am

Yes, I'm using a power bank. https://www.anker.com/products/variant/ ... 0/A1263011

I could consider using a PowerBoost... Is there a version with at least 2A out? I'd need that to power the screen, keyboard etc.

alphanumeric
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Re: Should I use this power switch with my Pi 3B?

Sat Apr 14, 2018 12:50 pm

There is this one, https://shop.pimoroni.com/products/mp26 ... er-module I have plans to buy one at some point. I don't know how easy it is to switch on off though. You might have to put a switch on the battery?

cspan
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Re: Should I use this power switch with my Pi 3B?

Sat Apr 14, 2018 11:55 pm

What about a switch like this? (see below)

I have a power strip plugged into a wall, this switch plugged into the power strip (along with other peripherals), and the pi plugged into the switch. Should I be worried about voltage drop? I've not gotten an indication that it's a problem yet, but I wonder if I'd be better off having the switch right into the wall, not the power strip.

I use the switch out of convenience - it's easier than plugging/unplugging the pi every time I want it on/off, and I suspect it's better for wear and tear on the contacts.
switch.jpg
switch.jpg (15.38 KiB) Viewed 1031 times
Thanks!

alphanumeric
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Re: Should I use this power switch with my Pi 3B?

Sun Apr 15, 2018 9:35 am

The OP is powering his PI from a power pack / battery. He wants to disconnect the power pack when the Pi is not in use to save the battery. That's a different situation. He's likely only ever plugged into a wall outlet to recharge the battery.

cspan
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Re: Should I use this power switch with my Pi 3B?

Sun Apr 15, 2018 11:33 am

alphanumeric wrote:
Sun Apr 15, 2018 9:35 am
The OP is powering his PI from a power pack / battery. He wants to disconnect the power pack when the Pi is not in use to save the battery. That's a different situation. He's likely only ever plugged into a wall outlet to recharge the battery.
Sorry, that wasn't evident from the original post. I thought I my question might fit in a thread on on/off switches. Would it be better if I started a new thread?

alphanumeric
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Re: Should I use this power switch with my Pi 3B?

Sun Apr 15, 2018 12:59 pm

cspan wrote:
Sun Apr 15, 2018 11:33 am
alphanumeric wrote:
Sun Apr 15, 2018 9:35 am
The OP is powering his PI from a power pack / battery. He wants to disconnect the power pack when the Pi is not in use to save the battery. That's a different situation. He's likely only ever plugged into a wall outlet to recharge the battery.
Sorry, that wasn't evident from the original post. I thought I my question might fit in a thread on on/off switches. Would it be better if I started a new thread?
In your case, any voltage drop would be on the AC mains side of the power supply. Hardly noticeable to the power supply, and wouldn't affect the +5V out anyway. It would have to be a big drop for it to affect the DC side of the power supply.

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Re: Should I use this power switch with my Pi 3B?

Sun Apr 15, 2018 1:19 pm

Thanks for your quick reply! Although my understanding of electronics/electricity is low, I don't think there's any DC part of the power supply in my case. Isn't a DC source typically a battery? My current setup is:

Wall AC Power ==> multi-outlet power strip ==> On/off switch (pictured above) ==> Canakit 2.5A power supply ==> RPi3B+.

Wondered if those two switches between the wall socket power and the Pi would result in too much voltage drop. My Q was, would I be better off with:

Wall AC Power ==> On/off switch ==> Canakit 2.5A power supply ==> RPi3B+.

Which though still having a switch would obviate the need to regularly unplug/replug the Canakit power supply if I simply had this arrangement:

Wall AC Power ==> Canakit 2.5A power supply ==> RPi3B+.

Thanks

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davidcoton
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Re: Should I use this power switch with my Pi 3B?

Sun Apr 15, 2018 4:35 pm

cspan wrote:
Sun Apr 15, 2018 1:19 pm
Thanks for your quick reply! Although my understanding of electronics/electricity is low, I don't think there's any DC part of the power supply in my case. Isn't a DC source typically a battery? My current setup is:

Wall AC Power ==> multi-outlet power strip ==> On/off switch (pictured above) ==> Canakit 2.5A power supply ==> RPi3B+.

Wondered if those two switches between the wall socket power and the Pi would result in too much voltage drop. My Q was, would I be better off with:

Wall AC Power ==> On/off switch ==> Canakit 2.5A power supply ==> RPi3B+.

Which though still having a switch would obviate the need to regularly unplug/replug the Canakit power supply if I simply had this arrangement:

Wall AC Power ==> Canakit 2.5A power supply ==> RPi3B+.

Thanks
Remember the things like the Canakit supply were originally called "battery eliminators". They convert mains AC to low voltage DC. The wire out of the power supply carries DC at 5V. Everything on the mains side is AC at 120V (at least in USA/Canada).

The voltage drop is proportional to the current. Current (supplying a given load, in this case your Pi) is inversely proportional to voltage. So a voltage drop on the 5V 2A line will be possibly 0.25V, which is significany for a 5V supply. The same switch (if it was safe foer mains voltage) at 120V would have proportionately a much lower current and thererefore voltage drop, around 0.01V. That is totally irrelevant on a 120V supply. (I've kept things simple here, there are other factors, but the conclusion is valid.) So switches on the mains side are fine, switches on the 5V line are a potential problem -- they need to be of very good quality to avoid to much voltage drop.
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cspan
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Re: Should I use this power switch with my Pi 3B?

Sun Apr 15, 2018 6:22 pm

Thank you - that's interesting, I (obviously) knew none of those things. Looks like I'm good on the "mains" side. :)

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