VanVince
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Pi 3 b+ power supply issue

Mon Apr 08, 2019 10:37 am

Hi everyone,

I'm developing a project with raspberry pi 3 model B+ with several sensors and external devices. To be more specific these are:
1 waveshare gnss hat (GSM/GPS/GNSS)
1 waveshare 7 inch HDMI touch display
1 bno055 IMU sensor
I suppose I have a power supply issue. Using a standard 5V 2.5A power supply and trying to start the GNSS module, which needs to take the GSM signal at the very beginning, it turns off after 6/7 seconds. It happens also when the module tries to send a SMS, if I'm lucky enough to reach this point. This module is stacked on the pi through the GPIO header and it communicates over usb cable. I presume that is a power supply issue but I cannot find a more powerfull power supply (maybe with 3 or 4 amps maybe even more).
Recently I tried also to use a 12V/10A power supply (input 220AC output 12V/10A) connected to a step down (12V to 5V) but it doesn't work at all (I'm not really sure about the output amperage but it should be 5A).
The 7 inch HDMI display is powered through the usb cable so it is not external powered.
Everytime I turn on the pi on the screen there is a yellow thunderbolt on the upper right corner of the screen. I'm really confused, is there something wrong?

Thank yuo in advance.

Sincerely,
Vincenzo

k-pi
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Re: Pi 3 b+ power supply issue

Mon Apr 08, 2019 1:45 pm

Using a standard 5V 2.5A power supply
That could be your problem, if it's not the recommended RPi power supply, as not all PSU give a constant 5v.

VanVince
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Location: Naples, Italy

Re: Pi 3 b+ power supply issue

Tue Apr 09, 2019 1:12 pm

k-pi wrote:
Mon Apr 08, 2019 1:45 pm
That could be your problem, if it's not the recommended RPi power supply, as not all PSU give a constant 5v.
So Is It not an amperage issue? If I buy a power supply ( real 5V/3A) than the project will work perfectly? :|

fruitoftheloom
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Re: Pi 3 b+ power supply issue

Tue Apr 09, 2019 1:32 pm

VanVince wrote:
Tue Apr 09, 2019 1:12 pm
k-pi wrote:
Mon Apr 08, 2019 1:45 pm
That could be your problem, if it's not the recommended RPi power supply, as not all PSU give a constant 5v.
So Is It not an amperage issue? If I buy a power supply ( real 5V/3A) than the project will work perfectly? :|

Why not use the Official Power Supply:

https://www.raspberrypi.org/products/ra ... er-supply/
adieu

Asus CS10 Chromebit / HP Envy 4500 Wireless Printer / Raspberry Pi Model 2B v1.1 / RealVNC Software...

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Burngate
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Re: Pi 3 b+ power supply issue

Tue Apr 09, 2019 5:14 pm

VanVince wrote:
Tue Apr 09, 2019 1:12 pm
So Is It not an amperage issue? If I buy a power supply ( real 5V/3A) than the project will work perfectly? :|
No, and yes.

I can carry a 140 lb sack, and run at 10 mph,* but not both at the same time.
Lots of "chargers" will give 5v unloaded, and up to 3A if necessary, but not both at the same time.

*Well, I've done so in the past, though not recently

VanVince
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Location: Naples, Italy

Re: Pi 3 b+ power supply issue

Wed Apr 10, 2019 7:53 am

Burngate wrote:
Tue Apr 09, 2019 5:14 pm
VanVince wrote:
Tue Apr 09, 2019 1:12 pm
So Is It not an amperage issue? If I buy a power supply ( real 5V/3A) than the project will work perfectly? :|
No, and yes.

I can carry a 140 lb sack, and run at 10 mph,* but not both at the same time.
Lots of "chargers" will give 5v unloaded, and up to 3A if necessary, but not both at the same time.

*Well, I've done so in the past, though not recently
Ok, I understand.
But how can I understand the power consuption of my project? Because I really don't figure out a reasonable solution. Should I buy an even more powerful power supply? obviously if I detach some sensors the project works good.
The biggest problem is the GNSS/GPS/GSM HAT which need more "energy" when works (send sms or attach to GSM network)

Thank you all for the reply.

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Imperf3kt
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Re: Pi 3 b+ power supply issue

Wed Apr 10, 2019 8:00 am

Lookup the data sheets for the parts you are using, they should list the typical power requirements and other necessary information.
55:55:44:44:4C
52:4C:52:42:41

VanVince
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Re: Pi 3 b+ power supply issue

Wed Apr 10, 2019 12:30 pm

Imperf3kt wrote:
Wed Apr 10, 2019 8:00 am
Lookup the data sheets for the parts you are using, they should list the typical power requirements and other necessary information.
I already check on the data sheets. The GNSS/GPS/GSM HAT requires 5Volt (operating voltage) in addition the 7 inch display is connected directly to raspberry pi's usb port. The last one, IMU sensor, is connected to the GPIO header (3.3V pin and uart pins).

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Imperf3kt
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Re: Pi 3 b+ power supply issue

Wed Apr 10, 2019 12:54 pm

What you're looking for to determine how much power they need, isn't their voltage, but their rated current, usually given in mA.
Add those all up, add about 500mA for your Pi (can use more, but 500 is a fair "average use" value) and then subtract the total from 2500.
If you're in the negative, you need a bigger power supply, if not, then you can use the official power supply or equivalent (beware false claims on 'equivalents')

Its actually somewhat more complicated than that, but this'll give you an idea of whether you're close enough, or way out.
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Paul Hutch
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Re: Pi 3 b+ power supply issue

Wed Apr 10, 2019 1:05 pm

VanVince wrote:
Wed Apr 10, 2019 12:30 pm
I already check on the data sheets. The GNSS/GPS/GSM HAT requires 5Volt (operating voltage) in addition the 7 inch display is connected directly to raspberry pi's usb port. The last one, IMU sensor, is connected to the GPIO header (3.3V pin e uart pins).
You also need to look for the current requirements in Amperes, both are required to determine power requirements.
GNSS/GPS/GSM HAT = 5V @ ??A
USB 7 inch display = 5V @ ??A
IMU sensor = 3.3V @ ??A

With those question marks replaced with actual values the total power requirement can be estimated. Tip: if the data sheet has typical current and maximum current given, use the maximum current for the calculation

Because Raspberry Pi compatible 3.3V powered items draw very little power you can ignore the calculation that accommodates the 5V to 3.3V conversion and simply add all the current values together to calculate the total power requirement.

Example calculation using made up values for the unknowns:

Raspberry Pi 3 Model B+ = 500mA typical, 1.3A maximum (2.5 - 1.2)
Reference: https://www.raspberrypi.org/documentati ... /#pi-power

GNSS/GPS/GSM HAT = 350mA = 0.35A

USB 7 inch display = 0.8A

IMU sensor = 10mA = 0.01A

Total current = 1.3 + 0.65 + 0.8 + 0.01 = 2.76A

VanVince
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Re: Pi 3 b+ power supply issue

Wed Apr 10, 2019 3:22 pm

Thank you Paul Hutch and Imperf3kt !

Surfing internet and looking at data sheets I almost figured out the operating amperage of the IMU sensor and 7 inch display (not really sure about the last one yet). I also sent an email to the product support service and now I'm waiting for a reply.
However, right now I have:
  • pi 1.34A (max)
  • IMU 12.3mA
  • 7" display 750/850mA(not sure yet)
for a total of 2.2023 A so I think it's quite impossible to use the GSM/GPRS/GNSS HAT, isn't it? Considering that I'm not really sure about the power supply output amperage (2.5A declared)

VanVince
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Location: Naples, Italy

Re: Pi 3 b+ power supply issue

Mon Apr 29, 2019 9:05 am

Hello everyone,

I wrote an e-mail to waveshare support asking for the power consumption of their products... They didn't know nothing about the GSM/GPRS/GNSS HAT. So I looked for the user manual of the inner chip (SIM 868), that is mounted onto the hat, trying to understand something. I found that : " IMAX Peak current During Tx burst 2.0 A" It doesn't explain when the tx burst happens but I presume this is one of my power problem.
What do you think? Is It possible?

In that case considering everything I have:
1.34 (pi) + 0.85 (lcd) + 0.0123 (IMU) + 2 A (GSM/GPRS/GNSS) = 4.2023 A
Obviously this is the worse case scenario but is nearly clear that is impossible to work with a 2.5A power supply

Moreover, is possible to erogate 2 A through gpio pin?

Thanks in advance

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mahjongg
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Re: Pi 3 b+ power supply issue

Mon Apr 29, 2019 10:31 am

Make sure your power cables are short and thick, most power problems exist because people don't realize that cables are not ideal conductors, depending on the current flowing through them they can loose a considerable amount of voltage, and if your cables have too much resistance (long and thin, not made of copper) this can cause problems.

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davidcoton
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Re: Pi 3 b+ power supply issue

Mon Apr 29, 2019 11:05 am

If you are drawing all the power through the Pi's microUSB connector, the polyfuse will limit the total to a little over 2A5, in order to protect the Pi's PCB tracks (amongst other things).
Power hungry peripherals need a separate supply route, that bypasses the Pi itself but is protected with a suitable fuse or polyfuse for the rating of the peripheral concerned. It may come from a common 5V supply (of adequate rating) or from a separate PSU with common ground connection.
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