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AMP2 with 3B+, 7" touch display and external SSD drive

Martin

November 20, 2021 23:09

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Hello HifiBerry-Community,

currently, I build up a mobile multimedia player. My hardware setup is AMP2 with Pi 3B+, the official 7" touch display and an external drive. Now I read some posts from 2017,  that the power supply of the AMP2 module will hvbe to less power to drive the 7" display as well as the external SSD drive. Is this still a problem, or is there any modification at the AMP2 that I can use the hardware configuration mentioned above without any changes?

My second question is, if there is any problem, when I use a 24V supply to drive the AMP2 with two 4 Ohm speakers? According to the datasheet this shall work, but I also read some older posts, that 18V will be the best voltage for that combination?

Greetings, Martin

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10 comments

• 0
  
  HiFiBerry team November 22, 2021 06:55

  The Amp2 probably won't be able to power all 3 devices. While you might try, the system might run unstable at higher load.
  
  24V is the absolute maximum limit and not recommended at all for 4 Ohm speakers. Don't do this. 18-20V is the best choice, e.g. this one:
  https://www.hifiberry.com/shop/accessories/power-hifiberry-80/ 

• 0
  
  Martin November 22, 2021 07:35

  Hello HifiBerry-Team,

  thanks for the reply. In that case, I'll disconnect the AMP2 supply of 5V via Pin2 and Pin4 and will supply the Pi3b+, including the display and the SSD drive via external voltage regulator. Regarding the maximum voltage of AMP2 supply I'm a little bit surprised, because 24V are mentioned at the data sheet - even for the 4 Ohm speakers. So I have to redesign the battery supply, because I don't use a power adapter.

  Greetings, Martin

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  HiFiBerry team November 23, 2021 19:17

  For a battery-powered device I would rather recommend 12V. The higher the operating voltage the bigger are the thermal losses. That's not what you want for a battery-powered device.

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  Martin November 23, 2021 21:43

  Thanks for the reply, yes - now, I will reduce the battery voltage: until now the plan was to use an 18650 Li-Ion 6S3P akku pack to get the maximum of power according to your datasheet. But regarding your remarks, I will change the akku setup to a 5S4P akku pack, that the voltage will be beetween 14 - 21 V. A further reduction to a 4S5P setup will have a lower battery voltage of 11,2 V under the minimum of the supply voltage of the AMP2. Attached you can see a table of minimum voltage (if the akku is empty), the typical voltage (nearly at the most of the time, when the akku is used) and the maximum voltage (when the akku is fully loaded).

  

  At the 18650 Li-Ion akku, the voltage will drop after a short period of time to the typical value until he is empty and the battery management system will switch off the akku pack from the electrical circuit.

  So, therefore I think the 5S setup will be the best choice - because I don't want to use a DC/DC converter because of the efficiency and because of the stability of the supply voltage, if a higher current will be needed by the AMP2 in a short period of time. The voltage to charge the akku will be limited to 20 V so that the AMP2 will have enough power with main supply and the akkus won't be charged up to 100% - this will extend the life of the akku cells.

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  HiFiBerry team November 24, 2021 07:13

  Both 4S and 5S will probably work. It's important to have a good battery management. If a Li-Ion battery is fully discharged, it will be damaged. Even the 2.8V minimum in your table seems quite low to me. But I'm not a battery specialist. Make sure to check the recommendation of the battery manufacturer

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  Martin January 03, 2022 10:30

  Thanks, now I reorganized my battery setup and I will use a 5S4P battery pack.

  To supply the display, the raspberry pi3B+ as well as the SDD hard disk drive, I created a supply unit, which provides a stable 5V voltage without ribble at a maximum current of 4A. But I saw at the specifications of the AMP2, that there is also a voltage regulator of 5V onboard to supply the raspberry via GPIO pins. I can cut the two 5V - vcc GPIO pins of the rapsberry, but it's not a very pleasent way. Is there a more friendly possibility to avoid supplying the raspberry via AMP2 - e.g. unsoldering some parts of the AMP2 that no 5V will be supplied via GPIO?

  Unsoldering the coil between at pin 8 (PH) of TPS54232 will be easy, but this will disconnect the sensing at pin 5 (VSNS). Shorten the resistor at pin 3 (EN) to GND will disable the voltage regulator. But which resistor is it: R18? The used size of the resistors is very small to handle it manually by hand - but it can be a possibility. The other way can be, to unsolder the voltage regulator device TPS54232 in complete. What will be your proposal?

  Greetings, Martin

• 0
  
  HiFiBerry team January 03, 2022 11:40

  There is no proposal at all. The Amp2 is designed to power the Pi and we STRONGLY recommend to keep it like this. If you have power-hungry additional devices, power them directly. 

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  Martin January 03, 2022 11:51

  Yes of course: therefore I built-up the supply unit. But the SSD drive only has one USB connector - so the power will be provided directly from the Raspberry. For that reason the idea was to supply the complete Raspberry unit (display, raspberry, SSD drive) with an external supply - like this is done with the wall power supply when using the DAC2pro. But therevore two different 5V supplies will be available which will cause some circulating and equalising current between these two supplies: AMP2 and external 5V supply.

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  Martin January 08, 2022 13:56

  Hello Hifiberry-team, what's the definition of "power hungry"? Which current of 5V supply can be driven by the AMP2? I cannot find any information about that in the data of the AMP2 device. Therefore, I had a look at the specification of the voltage regulator TPS54232 used at AMP2: there are 2 A mentioned...? The problem is, that the SSD drive cannot be supplied external, because it does only have one connector, at which power and data are transmitted and received. The touchdisplay can be supplied externaly without any problems. I already tried this. Greetings, Martin

• 0
  
  HiFiBerry team January 08, 2022 14:43

  As the Pi's load is highly dynamic, there is no simply number. You can try, but we can't guarantee that it will work. There are USB cables with a power splitter, this might be an alternative for you.