Electron Power Managment on Four AA Batteries

Hardware
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I would like to power the Electron on four AA batteries because sometimes out in the field it would easier to replace four AA batteries than swap out a LiPo battery. Below are the features just documented on power management for the Electron. Which of the features would still work with four AA batteries plugged into VIN and GND?

Power Management

Cellular communication requires a different current consumption profile than Wi-Fi communication, so we’ve included an attachable Li-Po battery (2,000mAH) and battery management system to make product creation easier.

JST connector. Each Electron includes a JST connector to make attaching an external battery quick and simple. All batteries we sell come with compatible connectors.
Charge Management. The Electron includes a very powerful charge management IC that handles all of the charge/discharge responsibilities of the device.
Battery Indicator LED. An additional red LED lets you know when your device is accumulating charge and when it’s all filled up.
Fuel Gauge. The Electron’s fuel gauge makes it very easy to monitor power levels in software so your device can save power when it needs it most.

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Hey there, I would probably keep the Li-Po battery connected all the time and use this to plug into the micro-USB connector: http://www.bgmicro.com/BH341USB.aspx

This way you can use the AA batteries to recharge the LiPo battery and not have to worry about having to modify the Electron firmware to avoid the blinking red LED. I would also keep the Li-Po battery to handle the high current spikes when the cell radio kicks in.

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Thanks @squeakywheel for getting back with me.

How long do you think the AA batteries might last in recharging the LiPo? Here is my current model with a Photon:

I have a Photon connected to four AA batteries reading sensors for seven different times during the day for about a minute at a time. In between the seven period times the Photon is sleeping and power is turned off to the sensors. Other than the seven period times the Photon is sleeping the rest of the day and night. I have few models running this way for a couple of months now.

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tl;dr it's a range when LiPo battery and AA batteries are fully charged.

13.33 < total hours of operation < 18,461

Detailed explanation:
Well, it depends on how often you turn on the GSM (cell) module to send data.

We know the following:

AA batteries have around 400–900 milliamp-hours capacity, with measured capacity highly dependent on test conditions. Wikipedia article

and we also know that:

[Particle Electron's] typical current consumption is around 180mA and upto 1.8A transients at 5VDC. In deep sleep mode, the quiescent current is 130uA (powered from the battery alone). See Particle Electron Docs

I assume that the AA battery holder will connect the AA cells in series to generate 6V at 400-900 mAh. If it is going to be outside, let's assume that the total capacity for the AA cell holder is 400 mAh for worst case scenario. The LiPo capacity is 2000 mAh.

With a fully charged LiPo at 2000 mAh and AA holder at 400 mAh, the total deep sleep time is

Battery Capacity (mAh) / Current Draw (mA) = 2400 / 0.13  = 18,461.54 hours

And if you leave the Electron powered up, and turn off cell phone connection, the total run time is

2400 mAh / 2 mA  = 1200 hours

If you send data continuously using the GSM chip, you will be consuming potentially a whopping 180 mA with peaks at 1800 mA reducing your total run time to:

2400 mAh / 180 mA  = 13.33 hours

So the answer to your question, is it depends on how often you send data via the cell phone connection. Also, there is a special mode called Operating Current (Cellular ON, w/powersave) that only consumes 50 mA as opposed to 180 mA as in the standard Cellular ON mode.

by the way here is a picture from Sparkfun showing how to power projects with AA batteries:

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@squeakywheel thank you so much for your detailed response.
I will only send data the seven times a day when the sensors are read for about a minute, figuring powering up and down. Hopefully I can try and shoot for around the 1000 hours mark with the Operating Current (Cellular ON, w/powersave) mode on since it is not critical that the data be immediately uploaded.

Are the LiPo batteries always being tricked charged from the AA batteries or does it recharge them at a certain threshold benchmarks?

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from the Electron docs:

The Electron will intelligently source power from the USB most of the time and keep the battery charged. During peak current requirements, the additional power will be sourced from the battery. This reduces the charge-discharge cycle load on the battery, thus improving its longevity.

In your case, read USB as the AA cell holder. It will probably use up the AA batteries first and then consume the LiPo battery. Which begs the question, do you really need the extra AA battery holder? 400 mAh is nice to have, but maybe it's ok to try with standard LiPo battery first?

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Thanks @squeakywheel.

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I will have the Electron in a remote location like I said earlier in the post and USB charging is not an option. It will be easier to replace four AA batteries than bring a charged LiPo battery to replace the dead LiPo battery. My new option is that I want to power the Electron exclusively from VIN and GND on four AA Batteries.

I just received my Electron yesterday and when I powered it from VIN and GND I was confronted with the red blinking battery LED light. The behavior of the simple demo Control LEDs over the net behaved differently than when hooked up to the LiPo, locking up the web page.
How can I turn off the red LiPo blinking LED and any other features attached to the LiPo battery management so the Electron is being exclusively powered from VIN and GND?

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Start looking at the PMIC functions, what your looking for will be in there if the function does exist which I think it does.

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Thanks, found the references but kinda of in the dark how to proceed. Can you give a basic example on what I am trying do?

What would happen if I connected 4AA batteries to the LiPo jack on the Electron and made sure that I would never plug the Electron into a USB port while connected to the AA s? Would this solve my problem? I have a JST connector I could use.

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You wold have to mention the function you were trying to use for us to help with it.

If you connect the AA batteries to the JST jack then it should work but if you connect the USB it will try to recharge the AA batteries which is not good. So yes do not connect the USB while the AA’s are added.

The AA’s will not last very long, maybe 2 days max unless your using deep sleep. System.Sleep is not working right if you want to Particle.publish() data every time you wake up.

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Thanks @RWB. I have a Photon running with the code I want to use in the Electron running on 4 AA batteries now for over three months. The key is the code runs only seven times a day for about a minute and the rest of the time the Photon is in deep sleep. Yes I have been following on the Forum the issue about System.sleep with the Electron so hopefully there will be a firmware update soon for the Electron.

As far as the AA batteries connected to the JST jack the Electron does not know where the power is coming from and so the flashing red battery light should go away and only come on when its time to change batteries right? I assume the fuel gage would not work though.

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Yea if your using Sleep functions on the Photon or Electron when its fixed then you can get by for months on the 4AA’s.

I have a Photon + 2000mAh LiPo + Solar Panel + TI low energy harvesting chip sitting in a window and its been up and running for months now staying fully charged.

The RED LED on the Electron should not light up if no power is supplied to the USB or VIN ports. The LED light flashes if there is no battery connected. It stays lit while charging, and goes out when the battery voltage goes up to 4v.

The PMIC chip does know where its sourcing the power from but you have to use the function that returns that data which is kinda tricky but I managed to get it working for setting the battery charge voltage.

If your just going to run of batteries then there is really no need to try to figure out where the power is coming from since you know its the AA batteries.

The fuel gauge should still return the battery voltage reading, so you could figure out what the AA pack voltage is when full and drained and then scale the readings to show a real 100-0% SOC in your code. Make sense?

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Yes @RWB thanks for your insight!

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While it’s good to plan on not connecting USB while powering via non-rechargables, adding a diode would cater for amnesia too :wink:

And I’m not sure what the fuel gauge would make of seeing 6V when it only expects a max of 4.2V.

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Thanks for the input @ScruffR where would you suggest I place the diode?

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In the wire that comes from the positive contact of your battery pack (red wire).

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@ScruffR thanks.

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Yea probably best not to go over 4.5v on the battery input pin, see the datasheet screenshot below:

I would wire the 4 AA batteries in Series and set the output voltage to 4v. The SOC Voltage readings will always read the same though.

What you could do is setup a resistor divider and read the AA pack voltage on one of the ADC inputs so you can still tell where the battery pack voltage is at.

Here is a Buck+Boost converter that will drain every last bit of power from the battery pack.

Pasted image1053×281 32 KB

If your device is outside then I would consider just charging from solar. Even if it is inside can you get a solar panel to a window that gets light?

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Thanks @RWB I will study your findings later tonight. I currently having it running with a 4 AA battery pack outputting 6V. Everything seems to be working fine. Could I be harming the Electron? It is the same battery pack that I am using with the Photon the last 3 months. Does the Photon have a higher tolerance on voltage input?