Author Topic: 2amp Power for the B+  (Read 4253 times)

natbur

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2amp Power for the B+
« on: July 21, 2014, 08:07:27 PM »
One of the features of the new Raspberry Pi B+ model is that the input can now support 2 amps.  Is the ATXRaspi able to handle that much current?  Additionally, is the power rating per 5v output, or total for the board?

Felix

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Re: 2amp Power for the B+
« Reply #1 on: July 21, 2014, 08:18:02 PM »
I did not try the B+ yet.
2A is a LOT of power and I don't think its a good idea in general to try to suck 2A through USB ports and GPIO etc.
The mosfet on the atxraspi is rated at more than 2A so it should be able to take that load.

I have a new board coming that will be pretty exciting, it will be a combination of ATXRaspi, 5V boost and backup, allowing you to backup power from a Lipo in case of a power failure, and avoid SD damage. It will be controlled by Moteino (no need for radio, or radio can be added to have a compact solution for PSU + Moteino gateway). It should be able to provide up to 1.5-2A of boosted 5V from a Lipo. More on that later ;-)

natbur

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Re: 2amp Power for the B+
« Reply #2 on: July 21, 2014, 09:22:29 PM »
I believe that I'd only be pulling about 1A through the PI for the B+ and GPIO and another 1A to drive a small display off of the secondary 5V pins (If I've done my calculations from the datasheet properly, it should only draw 600mA, but I'm err'ing on the side of caution).

Your new board sounds really interesting, can't wait to see the details!

Felix

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Re: 2amp Power for the B+
« Reply #3 on: July 21, 2014, 09:37:19 PM »
I think you should be fine at up to 2A.
Perhaps I can post some details about the new board...

Felix

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Re: 2amp Power for the B+
« Reply #4 on: July 21, 2014, 11:13:07 PM »
Ok here's the intro to MightyBoost: http://lowpowerlab.com/blog/2014/07/22/mightyboost/

natbur

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Re: 2amp Power for the B+
« Reply #5 on: July 22, 2014, 01:47:58 PM »
I like the look of the board!  Does almost exactly what I need. 
I could probably use it as specd, but I want a bigger battery, and the option of a charging port not tied to the Pi power.  Here's a pic of the component layout for power that I'm considering.  Please excuse the poor VISIO diagram, I'm a programmer, not an EE.  This should allow for full power charging while still providing full power to the MightyBoost (the DFRobot Power Module is capable of a sustained 5A out).
The downside here is that I don't get a power reading from the External battery pack to the MightyBoost.  Not a huge problem as before I didn't have the UPS ability in hardware anyway.  I was planning to handle that in software by tying the power status LEDs from the battery pack into the GPIO pins on the Pi.  Not the most accurate solution, I'll admit. 
What would be nice would be some way to disable the charging circuit on the MightyBoost, then I could tie the battery pack directly into the LiOn-In (bypassing the boost-converter on the pack) letting MightyBoost handle power level monitoring (I'm assuming you're doing a voltage based solution) while letting the circuit that came with the pack handle the charging.  The Anker E5 pack that I'm looking at is 15000mAh, so charging at 200mA or 500mA would be, well, painful. 
Alternatively, you could let me dump 4A into the MightyBoost so I can just hook a huge battery pack up to it directly.  ;D
« Last Edit: July 22, 2014, 01:50:11 PM by natbur »

Felix

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Re: 2amp Power for the B+
« Reply #6 on: July 23, 2014, 08:39:21 AM »
Thanks for the suggestions.
It expects 5V input for the MCP73831 charger chip which can do a max of 500mA.
However as I mentioned in the article, it is not meant as a charger primarily but as a boost/backup board. The charge is low on purpose. It is assumed that most of the time the input power is ON. That will slowly charge the battery. Most people will use their existing supplies which might be something like up to 1A. So I bettet on the fact that they will still have 200mA to spare for charging from their existing supplies.  Even I used a simple phone charger of 700mA and when plugged into MightyBoost it was not able to supply the Pi and charge the battery as well so I had to upgrade to a 1A one.

natbur

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Re: 2amp Power for the B+
« Reply #7 on: July 23, 2014, 08:21:47 PM »
Nor would I realistically expect it to.  Looking at the datasheet for the MCP73831, it looks like cutting the PROG pin would disable the charge controller, which I believe would allow me to safely use an external charging system.  Can you forsee this being an issue for the rest of the circuitry in the MightyBoost?

Felix

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Re: 2amp Power for the B+
« Reply #8 on: July 23, 2014, 10:18:38 PM »
Nor would I realistically expect it to.  Looking at the datasheet for the MCP73831, it looks like cutting the PROG pin would disable the charge controller, which I believe would allow me to safely use an external charging system.  Can you forsee this being an issue for the rest of the circuitry in the MightyBoost?
No, the charger is independent and draws its power from the USB. Taking it out of the circuit just means you will not be charging the battery while uUSB input is getting 5V power.

natbur

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Re: 2amp Power for the B+
« Reply #9 on: July 23, 2014, 10:42:53 PM »
Excellent, that's exactly what I was hoping it would do.  I'll keep an eye out for when you start production!

Felix

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Re: 2amp Power for the B+
« Reply #10 on: July 23, 2014, 11:07:48 PM »
As soon as I get my PCBs made ... its the worst bottleneck ever.
I can't believe we're still making PCBs at fabs.
Someone needs to invent a PCB maker thing.

natbur

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Re: 2amp Power for the B+
« Reply #11 on: July 24, 2014, 01:04:31 AM »
Wouldn't that be nice.  A 3D printer that could do PCBs...one can only dream.

Felix

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Re: 2amp Power for the B+
« Reply #12 on: July 24, 2014, 09:10:12 AM »
For prototyping that wouldn't be bad. For production that would not work since 3d printers are hopelessly slow.
Also it would have to have much better resolution for those 13mil vias.