Redsandro
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How to not care about power usage

Mon Nov 16, 2015 12:46 am

So, this Pi, it's pretty sensitive about how much power it uses.

When I attach a camera module and a wifi dongle, it chokes and reboots because there is not enough power. It doesn't matter if the power source has enough amps available, because the Pi seems to limit this to something barely usable.

So hey, we can attach a USB hub and power that one! Although that sucks, because who wants to attach a hub when you only need one USB port.

Anyway, I figured that when a powered hub is attached, you can simply remove the Pi power source and it will still run. Apparently it still takes it's power, doesn't matter from which side (power input or USB port) it comes.

So I thought I'd remove the power, and only power one USB port and use the other for a wifi dongle. Works, but when using the camera module, it will still choke and reboot. It only works smoothly when both power sources are connected.

But come on! I only want to connect one power source! How can I fix this? Is there some kind of component I need to destroy or bypass so this silliness is no longer relevant?

I want to power the USB, or power the Pi. Not both. Silly Pi.

~Pi 1b user

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kusti8
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Re: How to not care about power usage

Mon Nov 16, 2015 1:03 am

Even if you think your power supply is good and says 2A, it may not provide what is needed and/or your cable lead is too long and drops the current.

Try getting the official Pi power supply, that will work well.
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Re: How to not care about power usage

Mon Nov 16, 2015 11:46 am

I have the official one, and it "sucks". It barely takes one amp. It says it can provide one amp, but I've never measured anything above 800mA.

The problem seems to be more technical: Both inputs seem to be limited on the Pi. What hardware component do I need to solder off and bridge in order for this limitation to be gone?

Hold the warnings. A high quality power source (which the official Pi one is not) outputs a steady level of power.

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Re: How to not care about power usage

Mon Nov 16, 2015 12:13 pm

cat /proc/cpuinfo
what model of Rpi ?
a, a+, b, b+ or b2

what is the voltage as measured on the test points ?
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Re: How to not care about power usage

Mon Nov 16, 2015 1:50 pm

Redsandro wrote:I have the official one, and it "sucks". It barely takes one amp. It says it can provide one amp, but I've never measured anything above 800mA.

The problem seems to be more technical: Both inputs seem to be limited on the Pi. What hardware component do I need to solder off and bridge in order for this limitation to be gone?

Hold the warnings. A high quality power source (which the official Pi one is not) outputs a steady level of power.
The only official power supply is 2A https://www.raspberrypi.org/products/un ... er-supply/

Which RPi model do you have and what was attached to the RPi when you got the 800mA measurement?
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

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Re: How to not care about power usage

Mon Nov 16, 2015 2:08 pm

Power problems have been extensively covered, but in short:

Make sure your power supply is good quality
Make sure your USB power cable is also good quality - this can make a big difference
If you have a high powered USB device (ie hard drive), set the usb_max_current variable in config.txt. Search for more details

The camera takes about 250mA when running, so you do need a decent power supply - I was using a desktop PS and using the camera caused ethernet to drop out - it was the cable...

I run a B+ with a wireless USB dongle, keyboard and USB hard disk on a Pi, no problem. Older Pi models may have issues (from 2 or more years ago) - the power circuitry has been redone since then.
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Re: How to not care about power usage

Mon Nov 16, 2015 3:34 pm

klricks wrote:Which RPi model do you have and what was attached to the RPi when you got the 800mA measurement?
It's a long time ago. I think I purchased this in 2012. It was from a company called Farnell Element 14.
I had big plans, but no time. So I am 3 years late to the game. ;)

2x RASPBRRY-MODB-512M SBC, RASPBERRY PI, MODEL B, 512MB 84714900
2x RPI-PSU-EU-MK1 POWER SUPPLY, RASPBERRY 5V, 1A, EURO 85044090

I had connected:

* camera module
* wifi dongle
RaTTuS wrote:what model of Rpi?
I mentioned 1b (or b1) in the TS, but I honestly don't know anything beyond that. Here's the cpuinfo:

Code: Select all

processor	: 0
model name	: ARMv6-compatible processor rev 7 (v6l)
BogoMIPS	: 2.00
Features	: half thumb fastmult vfp edsp java tls 
CPU implementer	: 0x41
CPU architecture: 7
CPU variant	: 0x0
CPU part	: 0xb76
CPU revision	: 7

Hardware	: BCM2708
Revision	: 000d
what is the voltage as measured on the test points ?
Forgot to measure. I was only interested in amps because none of my power supplies could satisfy the Pi from single power source alone, even though they can output 2.1 amps. So I know that the Pi limits this, and was curious to see. I think this Pi is "old" and needs to be "fixed".

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Re: How to not care about power usage

Mon Nov 16, 2015 4:22 pm

Best fix would be to get new one - the latest Pi's are much better in all respects - speed, power etc.

If that is not possible, then a above, ensure you have a good PS, and also a GOOD USB power cable.
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Re: How to not care about power usage

Mon Nov 16, 2015 4:34 pm

Thanks for the tips. I prefer to use my 'old hardware' because, well, I have it. I don't need to buy it.
I also have a proper power supply; a phone charger that goes up to two amps.

Here is the problem: It seems like this particular model of Raspberry Pi takes a maximum of 800 mA from the front. So when using a 2100 mA charger, it will still take 800 mA max, even if that's not enough.

When I power the Pi from the 'back' (only powered USB hub), the Pi also takes 800mA maximum. Apparently, this is not enough to feed the Pi and the camera module.

When I put power in the front AND the back, it seems that it drains 800mA max from both sides, totalling enough to feed the camera. The Pi doesn't crash anymore.

So - I want to remove that component that limits the power. Or I want to bypass that component. I would like to remove both limiters on the Pi itself and on the power it gives out to the USB ports. I think it can handle this.

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Re: How to not care about power usage

Mon Nov 16, 2015 4:51 pm

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Re: How to not care about power usage

Mon Nov 16, 2015 6:18 pm

On the RPi B Rev 1 there are polyfuses on the USB ports F1 and F2 near the USB ports. These were removed in later versions. I think they are rated at 180mA and would not allow higher power devices such a WIFI to work. They also block 'backfeeding' from the USB ports. You can remove F1 and F2 and short the pads with a wire or just leave them in and solder a wire jumper across them. This will make a B Rev 1 like the B Rev 2.

The main fuse F3 is rated at 750mA. The RPi will be unstable if you attempt to draw more than that. Your RPi will probably work after fixing F1 and F2. If not, you can decide what to do with F3, or you can power from the GPIO pins which bypasses F3.
Last edited by klricks on Mon Nov 16, 2015 6:21 pm, edited 1 time in total.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

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Re: How to not care about power usage

Mon Nov 16, 2015 6:21 pm

You seem pretty sure your Pi is taking 800mA; how are you measuring this? Putting anything in series with the power supply is going to reduce the 5v

Have a look at the board: between the USB sockets and the LEDs there may be two green poly-fuses. If so, you could short them out (each feeds 5v to one of the sockets)
On the back of the board, next to the u-USB power input socket, there's a poly-fuse. If you short that out, you won't be limited as regards current. Even in a fault condition, so be warned.

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Re: How to not care about power usage

Mon Nov 16, 2015 8:23 pm

klricks wrote:On the RPi B Rev 1 there are polyfuses on the USB ports F1 and F2 near the USB ports. These were removed in later versions. I think they are rated at 180mA and would not allow higher power devices such a WIFI to work. They also block 'backfeeding' from the USB ports. You can remove F1 and F2 and short the pads with a wire or just leave them in and solder a wire jumper across them. This will make a B Rev 1 like the B Rev 2.

The main fuse F3 is rated at 750mA. The RPi will be unstable if you attempt to draw more than that. Your RPi will probably work after fixing F1 and F2. If not, you can decide what to do with F3, or you can power from the GPIO pins which bypasses F3.
Thank you, this is very valuable information.

So shorting them is not necessarily advised against; in fact it is what they updated for the Rev 2.
Burngate wrote:You seem pretty sure your Pi is taking 800mA; how are you measuring this? Putting anything in series with the power supply is going to reduce the 5v
I cannot reproduce this right now because I don't have the right cables to backfeed from USB alone so the Pi plus the dongle are fed through this one power supply. But I'm using a Charger Doctor:

Image

Image

The dongle adds about 300 mA.
So I guess I worded things wrong: I would like the 800mA to pass through, but not enough passes through, even if I have a power supply that can provide.

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Re: How to not care about power usage

Mon Nov 16, 2015 8:41 pm

It looks like your PS is not adequate, or more likely the conductors in the cable from the PS to the RPi are too small so you're dropping a lot of voltage between the PS and the RPi.

It appears you're down to 4.68V with only a .5A load, and that's too low. Increase that load to .8A like you want and you'll probably be down to ~4.5V.

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Re: How to not care about power usage

Tue Nov 17, 2015 12:02 am

If it's a bad power source and/or bad cable, I am in the clear. I can replace both. I have better power sources. This is just a (cheap) power source + separate cheap cable I could hook up to demonstrate the Charger Doctor. The other adapters connect straight to micro-usb so I cannot put the CD monitor in between, but the cables are better.

I need to use my best power source and bypass one of those regulators so more amps are being fed into the usb thingie without needing a separate power supply. We're only talking about ~300 mA extra.

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Re: How to not care about power usage

Tue Nov 17, 2015 6:37 am

If you need to supply your Pi with more power (the 700mA/1A fuse on the early model was a bit of a limitation, you could power via a 5V and GND pin on the GPIO. That will bypass the input fuse (but you'll have no protection).

If you have a Rev1 pi with the USB fuses F1 and F2 (140mA each), you can also short those out with a short length of wire each. In the later revision of that Pi they were replaced with 0 Ohm resistors (basically just links), so it is perfectly safe.

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Re: How to not care about power usage

Tue Nov 17, 2015 8:10 am

Redsandro wrote:..
Hardware : BCM2708
Revision : 000d[/code]...
suggest that is is a later version with 0 ohm resisters

a good 2A PSU [and I mean good]
powering a 5 port USB hub - then use that to both power the RPi and run as a HUB for the RPI

and get a test meter and measure the voltage on the test points
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Re: How to not care about power usage

Tue Nov 17, 2015 11:48 am

Is there a way to see what version Pi something is just looking at the board?
This one says "2011.12" but it seems I can still 'backfeed' it with power from USB.

Someone also gave me a red Pi. <3 Works just the same, but it is red. Is it a replica?
rpdom wrote:you could power via a 5V and GND pin on the GPIO. That will bypass the input fuse (but you'll have no protection).
You hero! That works? I had never thought of that. I was cutting precious USB cables to connect to other power (like PC PSU).
RaTTuS wrote:measure the voltage on the test points
I suddenly started using the Pi's that I have for 2 - 3 years now, so I am pretty new with it. What are considered "the" test points?
This thing is pretty small and my fingers are pretty fat, that's why I love my Charger Doctor. :lol:

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Re: How to not care about power usage

Tue Nov 17, 2015 12:08 pm

Redsandro wrote:
RaTTuS wrote:measure the voltage on the test points
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Re: How to not care about power usage

Tue Nov 17, 2015 12:18 pm

Redsandro wrote:Is there a way to see what version Pi something is just looking at the board?
It's much easier to see if you can boot an operating system.

cat /proc/cmdline
cat /proc/cpuinfo

both of those give you the hardware revision details.

[email protected] /tmp # cat /proc/cmdline
dma.dmachans=0x7f35 bcm2708_fb.fbwidth=656 bcm2708_fb.fbheight=416 bcm2709.boardrev=0xa01041 bcm2709.serial=0x5a67d427 smsc95xx.macaddr=B8:27:EB:67:D4:27 bcm2708_fb.fbswap=1 bcm2709.disk_led_gpio=47 bcm2709.disk_led_active_low=0 sdhci-bcm2708.emmc_clock_freq=250000000 vc_mem.mem_base=0x3dc00000 vc_mem.mem_size=0x3f000000 dwc_otg.lpm_enable=0 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait quiet
[email protected] /tmp # cat /proc/cpuinfo
processor : 0
model name : ARMv7 Processor rev 5 (v7l)
BogoMIPS : 38.40
Features : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x0
CPU part : 0xc07
CPU revision : 5

processor : 1
model name : ARMv7 Processor rev 5 (v7l)
BogoMIPS : 38.40
Features : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x0
CPU part : 0xc07
CPU revision : 5

processor : 2
model name : ARMv7 Processor rev 5 (v7l)
BogoMIPS : 38.40
Features : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x0
CPU part : 0xc07
CPU revision : 5

processor : 3
model name : ARMv7 Processor rev 5 (v7l)
BogoMIPS : 38.40
Features : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x0
CPU part : 0xc07
CPU revision : 5

Hardware : BCM2709
Revision : a01041
Serial : 000000005a67d427
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Re: How to not care about power usage

Tue Nov 17, 2015 12:40 pm

If you have a kernel with devicetree enabled (like all the recent ones), you can use:

Code: Select all

[email protected] ~ $ cat /sys/firmware/devicetree/base/model;echo
Raspberry Pi 2 Model B Rev 1.1

Code: Select all

[email protected]:~$ cat /sys/firmware/devicetree/base/model;echo
Raspberry Pi Model B Rev 1
The echo command on the end is to give a newline, as the entry is terminated with a Null instead.

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Re: How to not care about power usage

Tue Nov 17, 2015 4:41 pm

I thought I understood the problem. Not enough power is allowed through the Pi, To the USB Wifi Dongle.
I understood I could bypass F1 and F2 in order to fix that. However, now I understand that I have the Rev 2 (0x000d), which doesn't have F1 and F2. So why doesn't it drain more amps from my 2.1 amp power charger?

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Re: How to not care about power usage

Tue Nov 17, 2015 5:08 pm

You can't force current into a device, it will draw what it needs. I think you need to be more concerned with voltage input than amp draw.
While it's running with camera, wireless, etc, plugged in measure the voltage across the 5V and GND pins, what do you have?

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Re: How to not care about power usage

Tue Nov 17, 2015 7:02 pm

Redsandro wrote: ...
But I'm using a Charger Doctor:
Image
Image
The dongle adds about 300 mA.
...
I'm fairly certain that you're incorrect w.r.t. "The dongle adds about 300 mA". This is based upon extensive tests I performed upon three such devices when they first became available:
http://www.cpmspectrepi.webspace.virgin ... octor.html
(Unless you have a faulty device, of course)
FWIW, I've also tested quite a few power supplies and, more recently, power-banks:
http://www.cpmspectrepi.webspace.virgin ... plies.html
http://www.cpmspectrepi.webspace.virgin ... pecific.22
Trev.
Still running Raspbian Jessie or Stretch on some older Pi's (an A, B1, B2, B+, P2B, 3xP0, P0W, 2xP3A+, P3B+, P3B, B+, A+ and a B2) but Buster on the P4B's. See: https://www.cpmspectrepi.uk/raspberry_pi/raspiidx.htm

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