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UPS for Raspberry PI Powerboost or Solar charger?
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UPS for Raspberry PI Powerboost or Solar charger?

by Feral_Nerd on Mon May 29, 2017 6:45 am

Hi,
I'm in a the market for an UPS solution for a little embedded project I'm working on and I came accross this thread on your forum:

viewtopic.php?f=8&t=71377

I have basically the same use case for a small board computer that runs off USB at the same voltage as a Raspberry PI.

My requirements are:

  • (must) Charging of the battery whether the computer is running or not.
  • (must) A GPIO signal output on the charger that indicates when the battery is low so I can boot down the computer safely before the battery actually runs out.
  • (must) The charger must not drain the battery when the board computer has been shut off (or has shut itself off in response to low-batt) and the charger is not connected to an external power supply.
  • (would be nice) A batter level indicator would be nice.

It seems to me the solar charger is the only one has all these things except it seems a battery level indicator.

Questions:
  1. It says in that thread that only the Solar charger has 'true load sharing', what advantage does that give over the PowerBoost boards who do not have this feature?
  2. Does this board drain the battery when the board computer is shut off like the PowerBoost boards do?
  3. The thread also says if you are not using a solar panel, just a regular 5v charger, you can get away with using a smaller capacitor, what is the smallest capacitor recommended for this scenario?
  4. Why Is it necessary to loop the load port on the Solar Charger through a PowerBoost 1000 Charger before connecting it to the board computer as shown in the below photo from the solar charger tutorial? Can't I just connect a Raspberry PI or whatever directly to the LOAD output on the solar charger?
    https://cdn-learn.adafruit.com/assets/a ... 1470259382
  5. Since I need to connect a power boost to the LOAD terminal, do all of them drain the battery when the load is switched off and there is no external power supply or is this only an issue with the PowerBoost 1000?
  6. Is there some way of reading the battery level?

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Re: UPS for Raspberry PI Powerboost or Solar charger?

by adafruit_support_bill on Mon May 29, 2017 8:13 am

It seems to me the solar charger is the only one has all these things except it seems a battery level indicator.

The solar charger does not have 5v regulated output for the Pi. You would need a boost converter for that.
It says in that thread that only the Solar charger has 'true load sharing', what advantage does that give over the PowerBoost boards who do not have this feature?

That is an old thread. Currently, both the solar charger and the PowerBoost 1000C (not the 500C) have load-sharing. This directs input power directly to the load so that it does not take away from the battery charge current.
The thread also says if you are not using a solar panel, just a regular 5v charger, you can get away with using a smaller capacitor, what is the smallest capacitor recommended for this scenario?

You do not need a capacitor if you have a steady input power source.
Why Is it necessary to loop the load port on the Solar Charger through a PowerBoost 1000 Charger before connecting it to the board computer as shown in the below photo from the solar charger tutorial? Can't I just connect a Raspberry PI or whatever directly to the LOAD output on the solar charger?

As noted above, the solar charger does not have a regulated 5v output.
Since I need to connect a power boost to the LOAD terminal, do all of them drain the battery when the load is switched off and there is no external power supply or is this only an issue with the PowerBoost 1000?

The PowerBoosts have both a low-battery indicator pin and an Enable pin to shut them down.
Is there some way of reading the battery level?

There is only the low-battery indicator. If you want a better estimation of the remaining hcarge, you would need to use one of the 'fuel gauge' chips. I believe SparkFun has a breakout for one of them.

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Re: UPS for Raspberry PI Powerboost or Solar charger?

by Feral_Nerd on Mon May 29, 2017 9:03 am

Thanks for that, there's still a few things I'm unclear about.

  1. So basically I can short the capacitor terminals with a wire when the solar charger is connected to an external USB power supply?
  2. Does the solar charger it self drain the battery when the load is powered down and there is no external power supply like the PowerBoost does?
  3. ... and if I connect a PowerBoost to the LOAD port, of the solar charger will the PowerBoost itself not be draining the battery due to that LED light issue? ref: viewtopic.php?f=19&t=102032

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Re: UPS for Raspberry PI Powerboost or Solar charger?

by adafruit_support_bill on Mon May 29, 2017 10:59 am

So basically I can short the capacitor terminals with a wire when the solar charger is connected to an external USB power supply?

No. That would short out your power supply.. Just don't install the capacitor.
Does the solar charger it self drain the battery when the load is powered down and there is no external power supply like the PowerBoost does?

No.
... and if I connect a PowerBoost to the LOAD port, of the solar charger will the PowerBoost itself not be draining the battery due to that LED light issue? ref: viewtopic.php?f=19&t=102032

Yes.

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Re: UPS for Raspberry PI Powerboost or Solar charger?

by Feral_Nerd on Mon May 29, 2017 12:02 pm

Thanks, for clarifying that. What I'm trying to put together is a charger circuit with:

  1. Safe shutdown on case mounted button press, or...
  2. ...safe shutdown on low battery, and that...
  3. ...does not drain the battery when the board-computer is booted down.
I wish you guys would make a circuit like that :-) If you already do I apologise in advance for wasting your time here (but please have mercy and link to the shop page).

You seem to be saying that the solar charger fulfils #3 (no battery drain) if I can somehow cut off power to the PowerBoost circuit.

If I'm reading the Solar Charger documentation correctly I can achieve #2 (safe shutdown on low battery), by connecting the CHRG output on the solar charger to a GPIO on the board computer (It says in the Solar Charger DOCU that CHRG is fixed at 3.1 volt which presumably means I can use it for GPIO without frying anything).

I can also achieve #1 (safe shut down on button press) by connecting:

LOAD on the solar charger -> Smart Switch -> PowerBoost 1000 -> Board computer

If the Smart Switch is something like this thing which powers up the PowerBoost 1000 immediately on button press and cuts off power to it completely on a second button press with a delay after notifying the board computer via GPIO of the impending power loss.

It's a dirty and expensive hack but I think it will do what I want it to.

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Re: UPS for Raspberry PI Powerboost or Solar charger?

by adafruit_support_bill on Mon May 29, 2017 12:41 pm

The charge controller in the Solar charger is the same as the charge controller in the PowerBoost 1000C. If you will have a steady power source, the PowerBoost 1000C is a simpler way to go. If you are concerned with the battery drain via the indicator led, you can remove the indicator led from the board.

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Re: UPS for Raspberry PI Powerboost or Solar charger?

by Feral_Nerd on Mon May 29, 2017 2:10 pm

I haven't really taken a look at the PB1k with that in mind. Is there a breakout point on the PowerBoost 1000 suitable for being connected to GPIO signal input pin? From reading other threads on this forum I got the feeling this was not possible.

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Re: UPS for Raspberry PI Powerboost or Solar charger?

by adafruit_support_bill on Mon May 29, 2017 2:19 pm

There is the low battery indicator pin to detect low battery and the enable pin to shut down the boost converter.

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Re: UPS for Raspberry PI Powerboost or Solar charger?

by Feral_Nerd on Mon May 29, 2017 2:57 pm

adafruit_support_bill wrote:There is the low battery indicator pin to detect low battery and the enable pin to shut down the boost converter.


I trust I can connect the LBO breakout directly to a GPIO?

Also I'd like external LEDs for the charge indicator, the way the PB1k seems to be set up there are only on-board LEDs. I don't suppose there is a version with breakout points/pinouts for all the status LEDs? ... and what about using the charge status LED connectors for GPIO? It would be kind of interesting to be able to indicate charge status in a software user interface.

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Re: UPS for Raspberry PI Powerboost or Solar charger?

by adafruit_support_bill on Mon May 29, 2017 5:16 pm

For the Pi, GPIO are limited to 3.3v inputs. Since the LBO can be as high as VBatt, with a fully charged cell it could reach 4.7v. You could clamp that with a zener.

There are no breakout holes for the other indicators on the PowerBoost. You would have to tack-solder some jumpers to the leds.

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Please be positive and constructive with your questions and comments.