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Power options for RPi + Allo BOSS v1.2
#1
Good Morning,

I've got an RPi 3B+ sitting in front of me, and an Allo BOSS v1.2 arriving tomorrow. I'm trying to determine the prefered way to power the setup, based on the equipment I already own (I may buy a linear power supply in the future, but I don't have one right now):

     Anker PowerCore 10000
     https://www.anker.com/products/variant/P...h/A1263011

     5V 2.4A Switching Power Supply (wall-wart)
     https://www.adafruit.com/product/1995

My options seem to be the following:
     1) Power both from the wall-wart, via the RPi's micro-USB power input.
     2) Power both from the wall-wart, via the DAC's USB-C power input (and a micro-usb-to-usb-c adapter).
     3) Power both from the Anker, via the RPi's micro-USB power input.
     4) Power both from the Anker, via the DAC's USB-C power input.
     5) Power the two separately (with the appropriate jumper removed from the DAC): the RPi via the wall-wart, the DAC via the Anker.

It feels to me as though options 3, 4, and 5 are clearly better, but I'd love some opinions as to which is the best.

Also, if I do choose to power the two separately, it wasn't clear to me what the appropriate power-up and power-down order would be. Ideally it would be essentially simultaneously, but if I'm using a battery for the DAC, there's going to be at least a small delay in time. Am I going to do any damage to the equipment if I power the DAC up first, or vice-versa?

Regards,
William
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#2
Hi William,

I run my Piano 2.1 config with 2 x 5V feeds from an Anker battery similar to #5. The power sequence I use is below.

Powering down

Perform Menu, Restart, Shutdown and wait for the green activityr LED on the Pi to blink 10 times indicating the shutdown sequence is complete and power can safely be disconnected.

1. Disconnect power from the Pi
2. Disconnect power from the DAC

Powering up

1. Connect power to the DAC
2. Connect power to the Pi
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#3
Thanks, Tim. Do you take both feeds from the same battery? If so, do you think this still provides a noise suppression advantage over just providing power to one of the boards?
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#4
Yes, both feeds from same battery. Based on what I've read, start with good quality, stable low noise power and then if the DAC board is engineered and optimized to be powered separately from the Pi then do that.

Below is link to the battery that I use. It can be plugged into mains and continuously maintain a 100% charge while providing battery power. Its very convenient :-) I will say though that I don't have any means to measure the actual quality of the 5V outputs so Im just guessing that battery power will be a notch better than the typical switch-mode power supply for the Pi.

I don't know if its still available.
https://www.anker.com/ca/products/varian...9AN7906-BA

-Tim
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#5
What qualities does the power bank need in order to be a good candidate for powering a Pi and DAC HAT?

mA/hr :
I see that there are power banks ranging from 10,000mA/hr to over 20,000mA/hr with two USB-A outputs, one rated at 1A, the other rated at 2.4A. Since the power bank will be used with the power bank's input always connected to a 5V SMPS, does the mA/hr rating of the battery matter while powering a Pi?

Quick-Charge ports:
All the current Anker 20,000mA/hr power banks have a Quick-Charge port (QC). I assume these have programming to supply a good burst of current to get the smartphone battery to charge as quickly as possible. Would this pose a danger to the Pi or Pi+DAC? There's Quick Charge 2.0, Quick Charge 3.0, Apple 2.4A quick charging... This stuff is confusing.
https://www.powerbankguide.com/anker-pow...s-to-know/

Auto shutoff programming:
I was worried that latest-design power banks would detect that they were fully charged and shut themselves off/power back on depending on current draw, even with the battery input connected to a 5V SMPS. I didn't want the Pi to be shut off prematurely. The current Anker power banks all have verbiage on their packaging touting all sorts of automatic sensing wizardry. Cause for concern?

I decided to test the waters by purchasing a generic 10,400mA/hr power bank with a 1A port and a 2.4A port.
http://www.microcenter.com/product/48535...k---silver

At this point I'm powering my RPi3 with Allo Boss (older version) together from the one 2.4A port. It seems to be working fine. I used my RPi SMPS to charge the power bank up to full, which took all night.
The power bank has a switch on its side, not explained anywhere on the packaging. Seems to be an on/off switch. It doesn't seem to do anything while the power bank input is connected to the SMPS.

A review for this particular power bank mentions that it does not work as a cheap UPS for a RPi3.

"I was looking for a battery usb bank that I could use to power a raspberry pi 3 like an ups. This battery bank fails to perform that task. The battery life is as advertised and it does put out 2.4 and 1 amp on each of its outputs. The problem comes when you plug in the power cord to charge while it is also powering your device. The input charge is only 1 amp or maybe a bit higher but not the 3.4+ amps needed to supply the ports and also charge at same time. So when you plug in a power source even one that is 5+ amps it will still only deliver 1 to 2 amps max regardless of what the battery charge is at and when you remove the power cord it will cycle power on the ports before it starts to deliver its power from the batteries. As a battery bank for out and about to recharge your phones and such it works great but as a back up to power for a usb device that needs full time power it fails."

I wonder if this means one needs to choose a power bank that is capable of delivering 3.5A or more current to loads on both output ports? Does this mean I'm basically powering my Pi from the SMPS anyway, and merely topping off the charge to the power bank/battery at the same time? That would mean the power bank is doing nothing for the Pi+DAC, and any improvement I think I hear is due purely to placebo effect.

However, the statement, "...when you plug in a power source even one that is 5+ amps it will still only deliver 1 to 2 amps max regardless of what the battery charge is at..." suggests that the battery is actually supplying the power even when the power bank's input is connected to a 5V SMPS. In that case the power bank would be providing DC output from its battery, even if the power bank's stated capacity is only 10,400mA/hr. And, if DC supplied from the battery is cleaner than the DC coming straight from the SMPS, then this would be an improvement for the power to the Pi+DAC, even if the battery pack used is rated at only 10,400mA/hr. 

I may end up with this: 
Quote:5) Power the two separately (with the appropriate jumper removed from the DAC): the RPi via the wall-wart, the DAC via the Anker. 



Thoughts, anyone?
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#6
(06-14-2018, 12:35 AM)Tim Curtis Wrote: Below is link to the battery that I use. It can be plugged into mains and continuously maintain a 100% charge while providing battery power. Its very convenient :-) I will say though that I don't have any means to measure the actual quality of the 5V outputs so Im just guessing that battery power will be a notch better than the typical switch-mode power supply for the Pi.

I don't know if its still available.
https://www.anker.com/ca/products/varian...9AN7906-BA

-Tim

 If you keep the battery continuously connected to the mains, it defeats the main object of using a battery doesn't it? Whereas a battery on its own will give freedom from mains and SMPS noise.
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#7
Possibly. I suppose it would depend on the design of the output circuit in the battery and how well it suppresses noise. I mainly used the battery for convenience because it provided multiple 5V outputs and it could run my Pi/Kali/Piano rig for like 18 hours on a charge so it was great for portability :-) I didn't notice any difference in SQ between Batt only and Batt charging and its an easy A/B test cuz all you do is pull the mains input connector from the Batt.

I'm not really an expert on PSU's and such but there are massive threads on diyAUdio about this subject.

-Tim
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#8
I was doing a little reading on the power supply requirements for the RPi3B+ and the Allo Boss 1.2 DAC.

It seems the RPi3B+ draws quite a bit more current than the older Pi versions.
https://raspi.tv/2018/how-much-power-doe...asurements

From that, it looks like the Pi3B+ by itself draws up to 0.7A under load. Fortunately, audio streaming shouldn't put that much of a strain on the processor, right? 5VDC at 1A should still be plenty to power the Pi3B+. Use a psu rated for 2.5A for some headroom.

It looks like the Allo Boss DAC needs up to 0.6A. In the description of their i2s Isolator, they say:
"Isolator will... provide 5v/0.6A using... LT3042 LDOs."
https://allo.com/sparky/isolator.html

Since the Isolator is designed to be used with their DAC HATs, I figure 0.6A is enough for a Boss DAC. So once again, 1A is plenty.

That bodes well for this battery power bank idea. However, there is a gotcha. Apparently these power banks all use 3.6V batteries internally, with DC-DC boost converters to bring the voltage up to 5VDC.

I'm not sure if this is the exact type of device, but this looks like it might be what's used in these power banks:
https://www.monolithicpower.com/en/mp2637.html

If correct, that means there is switch-mode power supply stuff going on in these power banks too. That does not bode well for them being a significant improvement over a good SMPS.

And around and around we go. I need to take my power bank over to a buddy's place where we can put the output from the power bank and my SMPS on a 'scope and see if one is obviously less noisy than the other, both when it comes to 60Hz or 120Hz ripple and HF switching noise.

I'm thinking it still might be worth it to take a 12V 2A transformer, a worthy diode bridge rectifier, a couple of high-wattage power resistors, a few 4700uF 35V caps, and an LM317 on a heatsink, and just make a brute force 5VDC linear supply to power the DAC separately. If the LM317 is only called on to deliver 0.5A at most, it should work fine. Total power draw should be under 15W for the linear supply feeding the DAC only. The Pi could get the 2.4A power bank battery feed, I suppose.

Great, another project!
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#9
Hi...in my case I am powering my RPi3 with Allo Boss together from the one 2.4A port. It seems to be working fine. I used my RPi SMPS to charge the power bank up to full, which took all night.The power bank has a switch on its side, not explained anywhere on the packaging. Seems to be an on/off switch. It doesn't seem to do anything while the power bank input is connected to the SMPS.
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