L.P. Alpha DC power experiments and observations

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Posts: 374
Joined: Sat Oct 13, 2018 9:16 pm

Sun Oct 14, 2018 3:13 am

I tried powering LP Alpha 864 using type-C port, thru
1) included 45W type-C PD 3.0 power supply, or
2) Apple 60W type-C power supply (also USB PD 3.0)
Both works fine. What I've found using a type-C USB power meter is:
it's not using QC2, QC3, BC 1.2, Android DCP, etc. and definitely not using the classic D+ D- signaling. Also, tried these type of power supplies as well as battery charging packs (e.g., QC3 type), they won't work.
It is using PD and negotiated to 15V output profile (using type-C's CC1 and CC2 pins' communication protocol.)

In the stock, unactivated Win10 Pro environment, power consumption seldom went higher than 16W. (Also as low as 6W.)
Note the system is not under load, except one USB keyboard and one USB mouse connected.


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Sun Oct 14, 2018 3:45 am

Next, I tried to use the DC Power port. (I need to free up the type-C for display port monitor testing. <-- BTW works well)

I made my own 4-pin 2mm pitch DC power plug to LP Alpha's DC in port. Verified that, unless the DC voltage is higher than 10V (actually I have to push a bit higher to 10.5V for stability), the RED-colored LED won't lit. I.e., I won't be able to power the board up. (Actually kind of curious, since in KS forum, LP said 2s LiPo will work. Fully charged that will only be 8.4V, that's well below 10V. Perhaps L.P. can answer that.)

How I created the DC power cable:
1) 4-pin 2mm pitch plug, then
2) used a 2-pin 20AWG cable (about 1 ft long) to connect to a
3) USB-A male (only Vpower and Gnd are connected)
4) I also connected a 2200uF 16V electrolytic capacitor on the USB end to take care of instantaneous power bursty needs
<-- here I am pretty experienced on that trick. A few of my SBCs (Intel ATOM and CORE x86s) will work better that way. Actually I can see less peak voltage readout on my USB power meter, once I have that capacitor there. (Yes, I know, better on the LP Alpha side, but I'd like to make the SBC side cleaner.)

I can use lab bench power supply for this experiment.
I also tried some of my AC-based USB QC3.0 QC 2.0 power supply adapters (**1).
Also tried few Battery charger packs (**2).

Note that I am not running LP Alpha under load thus a 18W device barely meet the minimum power requirement. (18W in this case is 12V 1.5A. No long term overheating condition is ever tested. Suspect it will overheat overtime. Some AC power supply can do 24W, i.e., 12V 2A. It's a bit better.)

I have to find few beefy battery packs that can do 12V 1.5A under QC2 or QC3.) Works okay, especially if I have that 2200uF 16V capacitor to assist.

How I get these QC device to output the right voltage? I used a QuickCharge Tester/Trigger device, setting it as demanding QC2 12V (I can do that under QC3 for 12V, but it's more tedious, QC2 is fine.) This device 's USB-A male plugs into the USB cahrger, and its USB-A female is where my DIY DC power plugs into.

(**1) I would go for a QC2 12V 3A AC-powered device,, if possible. remember 45W power supply is what L.P. had chosen. It's a good engineering practice.

(**2) Battery QC2 12V 1.5A would be my minimal suggestion, since this type tend to overstate its true capability. Just a brief moment when it cannot supply enough juice to the SBC, its operating system will hang. Anyway, I strongly doubt it's the most optimal solution due to battery sizing, heat from the battery, heat from its internal 1s or 2s LiPo to 12V boost converter, and possibly poor construction.
Also, when battery pack shut down, the PC will hang. That's not a great strategy.

I have other ideas such as using 3s LiPo to direct-power the LP Alpha (though 3.2V cutoff voltage per cell 3.2x3 = 9.6V which is lower than the 10V I mentioned earlier.) That'[s going to be another experiment in another day.


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Sun Oct 14, 2018 3:55 am

Example of the 2.0mm pitch PH2.0 connector
https://www.aliexpress.com/item/50pcs-L ... 53465.html
<-- this is just the Nylon body, you also need to buy the pins fitting it, such as
https://www.aliexpress.com/item/Free-sh ... 91516.html

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Location: Germany, NRW

Sun Oct 14, 2018 6:36 am

Thank you very much for your testing. ! :D

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Tue Oct 16, 2018 7:16 pm

This sounds like a cool power supply build, but Idk if I’m able to do this. Is there a 12v power supply that can be purchased from amazon or Ali express that is compatible with the Alpha? Also, are these 4-pin power supplies common? I usually find barrel connectors on SBCs with 12v power.

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Wed Oct 17, 2018 12:56 am

Now that I have some time to start playing with both Linux and Windows, including adding load (benchmarking, playing video, etc.) I don't feel confident to run LPA864 on just 12V 1.5A power supply, unless I know the workload will ALWAYS be low. 12V 2A will be very marginal and IMO minimum requirement.
So I will recommend 12V 3A AC power supply (plenty of them from multiple sources and inexpensive.) 12V 5A is certainly nicer (but bigger/heavier.) 15V 3A (which is at the same spec as what L.P. is supplying, the USB type-C) is also fine.

That DC connector is not a common part, however. Hope someone will make a special power cord, probably put a DC power meter in the middle.

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Wed Oct 17, 2018 3:33 am

Adding meter and DC connector pictures
20181016_2156.jpg (98.83 KiB) Viewed 2541 times
20181016_2158.jpg (230.46 KiB) Viewed 2541 times

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Wed Oct 17, 2018 1:55 pm

Example of Amazon power plug source
https://www.amazon.com/Micro-Connector- ... B01DUC1S7S

Please combine 1-pair thin wires (for V+) close to JST-PH2.0-4 connector to a RED-colored AWG 20 (preferred) or AWG22 wire.
Please combine 1-pair thin wires (for Gnd) close to JST-PH2.0-4 connector to a BLACK-colored AWG 20 (preferred) or AWG 22 wire.

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Wed Oct 24, 2018 3:57 pm

Hello. Thanks for you work!:)
Could you test if Lattepanda Alpha could work directly from half-charged 3 cells of Li-Ion batteries under heavy load?
I mean ~10-10.5 volts. I am trying to understand if I can use this board in my project.
Thank you very much.

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Thu Oct 25, 2018 2:27 am

Setting aside the mysterious "battery connector ("even 2S LiPo can do it")" LP-Alpha folks are talking about (but no real info released yet), here is my response:

1.) I would say supplying a solid 12V 2A to LP Alpha (assuming there is no extreme tweaking on performance or pushing the boundary of design TDP), should be the design target. Do not forget connectors and DC supply wires thickness.

2.) Individual user has to make his/her own judgement on what a battery based supply should work. E.g.,
a. do you want to charge them elsewhere then move them over and use the 3S Li-Ion on LP Alpha in a standalone style,
b. do you want to have an early warning such that LP Alpha will gracefully shutdown before battery protection kicks in (typically 3.4V , some 3.2V per cell, that is 10.2V per battery pack or 9.6V per pack <-- this is so close to that 10V margin), depend on BMS board used <-- I recommend a BMS be used all the time on Li-Ion, if the "battery system" itself does not provide such function;
c. <-- also I recommend using a battery balancer for longevity
d. are you thinking about the laptop type of power system (the battery pack is essentially a UPS and also for occasional portable/no AC near-by usage, if AC power adapter is used as the primary power source as well as charging)

3) In the most basic design: 3S Li-Ion (I suggest using quality name-brand, authentic 18650 Li-Ion cells) with BMS+balacer in the battery pack, I would say it would work fine (I recommend 3s2p arrangement.) <-- Caveat is that battery will go low and LP Alpha will hit its 10V brown-out/shutdown threshold (and stops silently but abruptly.)

4) If you are thinking about the DC UPS type of design, where most of the time AC power adapter is used, I do have a working solution with "few caveats". If that is the path forward, I can describe it more.


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