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flora v3 power capabilities
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flora v3 power capabilities

by gerry81611 on Sun Jul 01, 2018 5:49 pm

hello,

it looks like my flora v1 may have just died, and if I need to rebuild my hardware I thought about using the new v3 flora. it will be driving 36 30mm ws2810 pixels:

https://www.adafruit.com/product/1547

The current setup is powered off an 11.1V lithium polymer pack. If I recall, the original flora needed to be powered with 5v because I have this traco step down thing in there:

https://www.adafruit.com/product/1065

The output of the battery is split and 12v goes straight through to the pixels and 12v gets converted through the traco to power the flora.

I was looking on the flora product page and it looks like the new floras can take up to 16v? In that case, could I just hook the 11.1V battery straight into the flora and then power the 36 12v pixels straight off the vbatt?

thanks,

gerry

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Re: flora v3 power capabilities

by adafruit_support_bill on Wed Jul 04, 2018 2:55 pm

The Flora can handle up to a 16v input - provided that you do not have a lot of other circuitry powered via the 3.3v pin.

If you are just driving pixels - and powering them direct from VBATT, then it should be fine.

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Re: flora v3 power capabilities

by gerry81611 on Fri Jul 06, 2018 6:07 pm

Thank you! Do you have any concerns about the current draw of those pixels through the flora?

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Re: flora v3 power capabilities

by adafruit_support_bill on Sat Jul 07, 2018 5:42 am

You should not power the pixels through the Flora. Run power and GD directly to the pixels. Then run power and GND from the pixels to the Flora.

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Re: flora v3 power capabilities

by gerry81611 on Sun Jul 08, 2018 4:32 pm

oh! thanks!

the way the hardware is currently, the power is split to the flora (via dc/dc converter) and to the pixels, which are 4 parallel strands of 9 pixels. I'm having trouble picturing what you mean by powering the flora from the pixels. any wiring that I can imagine is powering the flora in parallel with the pixels. In this case where I'm splitting the power to 4 strands of pixels, is powering the flora in parallel like a 5th strand the best way to do this? it sounds like powering the pixels from the batt from the flora is not the way to go.

thanks!

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Re: flora v3 power capabilities

by adafruit_support_bill on Sun Jul 08, 2018 6:24 pm

Essentially, you are powering the Flora in parallel with the pixels - but with a couple of subtle-but-important points.

Your pixels are the primary current consumers. And having power go directly to the pixels rather than via the VBAT pin bypasses the schottky diode on the board which is most likely rated for less than 1A.

You also need to consider that all current consumed by the pixels needs to return to GND. Since the GND is aso your signal reference, you want to avoid any "ground bounce" caused by having large fluctuations in current flowing through the ground wire connecting your Flora to the pixels.

Running power directly to the pixels and then running power from the pixels to the Flora means that the only current flowing on the GND connection between pixels and Flora is the 20mA or so needed to power the Flora.

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Re: flora v3 power capabilities

by gerry81611 on Tue Jul 10, 2018 2:53 pm

Thank you! Forgive me, I'm self taught in all of this and may not know some pretty basic things. I attached an image. I diagrammed the + and - separately to avoid crossing a lot of lines but there is only one battery, one flora, and one matrix of pixels in this project.

The first image is the way that I was picturing setting this up based on the way I had a previous version of the hardware working. Under Option 1 is what I think you are talking about by powering the flora from the pixels. Am I close? Based on my limited EE knowledge these pictures seem functionally identical to me.

thanks,

gerry
Attachments
Flora Wiring.pdf
(40.46 KiB) Downloaded 11 times

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Re: flora v3 power capabilities

by adafruit_support_bill on Tue Jul 10, 2018 3:15 pm

The diagrams are identical if you assume that your wires are perfect superconductors with zero resistance.

But, since we live in the real world where all wires have some resistance and Ohm's Law ( V=IR ) is strictly enforced, there will be a voltage drop that is proportional to the current flow. For many applications you can ignore that reality. But since pixels can draw significant amounts of current, the voltage drop can become large enough to cause problems.

Since the ground wire between the Flora and the pixels is also your signal reference, any voltage drop on the ground wire (a.k.a. "ground bounce") will affect the signals on the signal wire.

So, to avoid ground bounce, we wire the power source directly to the pixels, so any voltage drop will be between the battery and the pixels. The current on your signal reference wire will be only a few mA from the Flora so the voltage drop on that will be negligible.

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Re: flora v3 power capabilities

by gerry81611 on Wed Jul 11, 2018 4:57 pm

Thank you!

I've attached a diagram with what I think is the solution that you are proposing. since I'm running 4 strands of 9 pixels in parallel there is currently a junction point where one wire is split into 4.

If I understand your recommendation, The battery power will go into a junction where it is split into 5: 4 pixel strands and the Flora. In the diagram, I'm still returning the ground of the flora back into the junction. Is that necessary? I'm not sure why I did that in the first place but it seemed like a good idea :)

Out of curiosity, how would the ground bounce issue show up? I've used the first generation of this hardware and software for a few years and I'm wondering if I've observed the problem.

Thanks,

Gerry
Attachments
Flora Wiring 2.pdf
(35.62 KiB) Downloaded 11 times

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Re: flora v3 power capabilities

by adafruit_support_bill on Wed Jul 11, 2018 6:00 pm

That looks like it should work fine.

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Re: flora v3 power capabilities

by gerry81611 on Wed Jul 11, 2018 7:30 pm

thank you!

out of curiosity, can I ground the flora as show in this picture? that way I could get away with one piece of 4 channel wire going to the flora from the junction.

and how would the ground bouncing manifest? I'm wondering what to keep an eye out for or if I've already observed it.

thanks for your continued advice,

gerry
Attachments
Flora Wiring 3.pdf
(35.73 KiB) Downloaded 10 times

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Re: flora v3 power capabilities

by adafruit_support_bill on Thu Jul 12, 2018 6:31 am

All the grounds are connected internally on the Flora board. There is no need for a separate wire.

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Re: flora v3 power capabilities

by gerry81611 on Sun Jul 15, 2018 6:28 pm

oh awesome, thats even easier!

thank you!

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Please be positive and constructive with your questions and comments.