Electron Power Managment on Four AA Batteries

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.

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

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

@ScruffR thanks.

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.

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?

1 Like

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?

Where are you plugging in the 6v battery pack? The battery connector or USB port or Vin terminals?

If the battery JST connector then you could damage the fuel gauge chip based on the data sheets 4.5v max rating but ya never know till you test it :smile:

The battery connector, JST connector.

Yea the battery is feeding the cell input on the fuel gauge which has a rated max input of 4.5v so you could kill it or not. If you do then you know why. If your not planning on using the fuel gauge then it may not matter if it failing does not cause any abnormal power loss or heating from failure.

So connecting from the JST connector I should use a 3 AA battery pack. On the Electron there is no voltage protection from the JST connection?

Yea 3 x 1.5v should keep you under the 4.5v max rating.

You can do 2 x 3 series cells to double the mAh storage capacity.

This way the Voltage readings should still workfine and you can then scale them to the proper 0-100% readings.

Parallel AA cells/packs would need to be protected against “cross charging”.
If one pack is drained and the other is fresh, the fresh one might try to recharge the other with the risk of overheating.

@RWB , @ScruffR Good news!
I connected the Electron via the JST connector to a 3 AA battery pack and the unit works well. I then disconnected the battery pack and connected the LiPo battery and the USB cable to my computer and the Electron.
Added the following to lines to see if the Fuel Gauge was harmed by the 6 volts from the 4 AA battery pack yesterday:

FuelGauge fuel;
Serial.println( fuel.getVCell() );
Serial.println( fuel.getSoC() );

Result:
voltage: 3.94
soc: 67.16

Bottom line the Fuel Gage on my Electron is ok!

Like I said earlier in this post I have been running a Photon for three months on 4 AA batteries. Should I pair down the power on the Photon to 3 AA batteries too? I am connected via VIN and GND. It was my understanding from the documentation that the VIN on the Photon could handle 6 volts from the 4 AA batteries but why use the extra battery if not needed. What are your thoughts?

4x1.5V via Vin is no problem and I never intended to suggest so.
My word of caution was solely aimed at the fuel gauge and JST connector.

Going via the JST and the fuel gauge instead of Vin might be safer as there have been reports of Photons getting in a problematic state when under-powered, which might well happen with unmonitored batteries - the Photon has no built-in fuel gauge but since the Electron has, I’d say: “Use the extra safety net”

2 Likes

@ScruffR Thanks.

So I have an electron with the LiPo plugged in and powered via external 12v battery connected to Vin. It wakes, takes a ds18b20 temp reading, shoots it to the web and goes in the SLEEP_MODE_DEEP.

During powerup and cell activity I can see it drawing ~2200mA and once in deep sleep drops off slowly to 640mA but never goes below that.

The idea was to run off external battery using the FuelGauge to monitor the LiPo and when it dropped to 50% or so alert.

The is a production Electron that we just received. Is there something I am missing with Power Saving mode and deep sleep to get down the uA?

thanks,
bill

@luminous Deep Sleep does not turn off the cellular module. To turn off the cellular module you will need to call Cellular.off();

@luminous and @autolib how did you end up going with this? did you get any data on how long it would last for (eg your project was doing 7 calls a day autolib - how many days would the unit last for without needed to be recharged?)

@pjc the LiPo battery lasted 24 days before it died. Four AA alkaline batteries lasted 21 days before dying. Currently using Energizer Ultimate Lithium batteries which seem to be lasting longer.

hey thanks for replying - that is handy info. about on par for what i was hoping - will report back when i get mine up and running