mckeevio
Posts: 1
Joined: Fri Nov 02, 2018 8:02 pm

DC-DC 12V-5V Converter power issue

Fri Nov 02, 2018 8:16 pm

Hopefully someone will have some experience with this

I have purchased the following
https://www.amazon.co.uk/gp/product/B00 ... UTF8&psc=1

This is supposed to give me 3A @ 5V
When I hook this up to a 12V 3A PSU and the raspberry pi multimeter it only draws 1.3A on the 5V side
The raspberry pi has the little lightning flash showing that it is underpowered. Everything does work
it is also showing 5.09V on the 5V side which should be fine
Also I am getting an undervoltage warning at startup

I bought another one to see if it was a problem with the unit
https://www.amazon.co.uk/gp/product/B07 ... UTF8&psc=1

Same issue...
I also hooked the little converter up to my bench PSU here and it is giving the same issues

Does anyone have any experience with these...
Is the lightning flash a red herring perhaps?

klricks
Posts: 6609
Joined: Sat Jan 12, 2013 3:01 am
Location: Grants Pass, OR, USA
Contact: Website

Re: DC-DC 12V-5V Converter power issue

Sat Nov 03, 2018 4:08 pm

How are you connecting power from the power supply to the RPi?
What is the voltage at the GPIO pin 2?
Note that many USB cables are too thin or too long or poor quality and will introduce too much voltage drop.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

pfletch101
Posts: 528
Joined: Sat Feb 24, 2018 4:09 am
Location: Illinois, USA

Re: DC-DC 12V-5V Converter power issue

Sat Nov 03, 2018 5:22 pm

klricks wrote:
Sat Nov 03, 2018 4:08 pm
How are you connecting power from the power supply to the RPi?
What is the voltage at the GPIO pin 2?
Note that many USB cables are too thin or too long or poor quality and will introduce too much voltage drop.
And there is the problem that others have emphasized in this context that the Pi sees and doesn't like transient voltage dips related to current draw variations that may be much too short to see without an oscilloscope.

PeersC
Posts: 30
Joined: Fri Apr 01, 2016 6:35 pm

Re: DC-DC 12V-5V Converter power issue

Sat Nov 10, 2018 6:00 am

Hi There,

I have a couple of these running a PI3 and a PI2 - I think the issue is that the problem is the PSU is not truly DC there is still a slight element of a/c in the voltage I have the issue on a benchtop psu and I have checked it with an oscillosope.

Both my units are on mobile platforms one a robot and the other a pi controlled r/c model which are running on 12v batteries once you run on pure DC the issue dissapears try it on a car battery or 12v alarm battery and see what happens

Regards,

PeersC

PeersC
Posts: 30
Joined: Fri Apr 01, 2016 6:35 pm

Re: DC-DC 12V-5V Converter power issue

Sat Nov 10, 2018 6:07 am

Sorry,

As a follow up I can strongly recomend a usb oscilloscope for anyone. They are relatively cheap and you can use the scope to fine tune pwm signals and any issues with GPIO output with endangering your pi. You can access you PI through VNC or other in one window and have another window monitoring scopes output on two channels.

Regards,

PeersC

pfletch101
Posts: 528
Joined: Sat Feb 24, 2018 4:09 am
Location: Illinois, USA

Re: DC-DC 12V-5V Converter power issue

Sat Nov 10, 2018 7:46 pm

PeersC wrote:
Sat Nov 10, 2018 6:07 am
Sorry,

As a follow up I can strongly recomend a usb oscilloscope for anyone. They are relatively cheap and you can use the scope to fine tune pwm signals and any issues with GPIO output with endangering your pi. You can access you PI through VNC or other in one window and have another window monitoring scopes output on two channels.

Regards,

PeersC
Do you have any specific device recommendations?

PeersC
Posts: 30
Joined: Fri Apr 01, 2016 6:35 pm

Re: DC-DC 12V-5V Converter power issue

Sun Nov 11, 2018 5:45 pm

Not sure if it is allowed to reccomend a specific device.

It also depends on the sampling rate - the more you pay the higher the sample rate

So if like me you are looking at PWM signals and stepper motor drivers then only a low sample rate is required on the other hand if you are looking at PC and chip frequencies then you need to pay a lot more.

Also is the accuracy of the sample in general the faster the sample rate the less accurate it gets.

My model samples 48MSa/s, 150MSa/s 250MSa/s and 1GSa/s a/s = a second

simply plug in to two usb ports one for each channel and run the software, the probes need a bit of calibration but it is a doddle the is a ground on the unit and a bar that delivers a 10 MGHZ sinewave to calibrate.

Hope this help, I know we are veering slightly off topic but like I say I have two of these models that given the lightning flash when attached to mains - 12 v psu but on battery all works fine

Hope this helps

Peers

pfletch101
Posts: 528
Joined: Sat Feb 24, 2018 4:09 am
Location: Illinois, USA

Re: DC-DC 12V-5V Converter power issue

Sun Nov 11, 2018 7:40 pm

PeersC wrote:
Sun Nov 11, 2018 5:45 pm
Not sure if it is allowed to reccomend a specific device.
I don't think that anyone would object to something like "I have a [Brand X, Model Y] and have found it to work well in this or that application", particularly in response to a direct question and if you are not in the business of selling the device. Indeed, lots of people (including me) 'advertise' the 'Official' Raspberry Pi power supply in exactly this sort of way.

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