Powering Argon from VUSB, Charge LED Flickers if Under 5V

I am setting up an Argon to be powered by solar and battery. I have an Adafruit Solar charger (Adafruit Universal USB / DC / Solar Lithium Ion/Polymer charger [bq24074] : ID 4755 : $9.95 : Adafruit Industries, Unique & fun DIY electronics and kits) which will handle accepting the power from the solar panel as well as charging a LiPo battery. The output from the Adafruit board is around 4.4V.

It seems to be acceptable to power the Argon from its VUSB pin as long as not providing power via USB, and I am fine with this. I much prefer to power the Argon from the VUSB pin since I can solder directly to it and do not have to mess with a micro USB connector. I also see that when the Argon receives 5V from the USB connector or VUSB, it drops the 5V down to 3.3V. My assumption has been that feeding it anywhere from 3.3V to 5V would be fine, so the 4.4V from the Adafruit board should be no problem.

I have tested this, and the Argon appears to run fine if I give it 4.4V to the VUSB pin, but the strange thing is that the Charge LED on the Argon will flicker on and off, even though I don’t have a LiPo battery connected to the Argon.

My purpose of posting this is to ask if there is a reason why the Charge LED keeps flickering, and if my assumptions above are incorrect, and it is not okay to power the Argon with 4.4V to VUSB.

For what it’s worth, if I use a boost converter to take the 4.4V to 5V, I do not experience the Charge LED flickering. I just don’t want to implement a converter if I can help it since its one more component to fail.

According to the Argon datasheet here, you should not exceed 3.6V supply voltage for long periods of time (refer to the stress-testing section directly above the link). Since the LiPo battery voltage is rated to accept from 3.3V to 4.4V, then perhaps you can power through the LiPo port instead if you have some sort of adapter.

The datasheet also says the max input voltage is 6.2V, and according to the schematic, VUSB is directly connected to the 5V coming in from the USB connector. As far as I am aware, there should not be a difference between powering it with 5V via the USB connector or the VUSB pin.

The Adafruit board has a pin for the LiPo battery, and if I connect that to the LiPo pin on the Argon, it does power up and works fine. My concern there is that the Adafruit board automatically switches its main output between battery and solar. So if the solar panel is supplying power, and the battery is charged, the Adafruit board uses the solar power for the output load and the battery sits there at 100%. But if the Argon is pulling from LiPo, the battery is going to drain, and the Adafruit board will have to switch back to charging the battery more often than it would otherwise. Now I know my power draw on the Argon is very little, so in reality my concerns are likely not much of a problem, but still something I would like to avoid.

Just wanted to say you’re right, the USB is powering at 5V and is shared (directly connected) with the VUSB pin. If you are worried about having the battery too full, or charging/discharging too much, you could manually set/reset the CE pin on the BQ24074.

Sorry I can’t be of more help regarding the LED flickering. I have absolutely no idea why that would be happening.

That’s a really good idea about the CE pin! I would have to play with different values once I actually get this set up outside with the solar panel, but I should have enough battery capacity to run this for days if not weeks on a full charge, so stopping the charging until the battery gets below a certain voltage should not be an issue.

I also have several INA219s in the mix so I can monitor the voltage from the solar panel, to/from the battery, and to/from the Argon. It won’t be an issue at all to figure out when the battery needs charging.

Nice, glad to hear it. I was looking into this recently and decided an operating SoC range between 65% and 80% capacity would be best for prolonging battery life. However, that was Li-ion. LiPo may be different.

Anyway, sounds like you have a good solution! Best wishes :smiley:

My battery pack is actually Li-ion, I was only saying LiPo because that is what the pins are labeled and I wanted to simplify the explanation. So are you saying it would be best to not charge the battery until it gets down to 65%, then stop charging when it hits 80%? I will have to give it a try.

Exactly. Here’s one of the articles I read: Tips for extending the lifetime of lithium-ion batteries | University of Michigan News

I was just doing some searching on this. For a 3.7V Li-Ion battery, I think 80% would be around 3.98V and 65% would be around 3.895V. Does that fit with your findings?

Ahhh, sorry I wasn’t thinking about that. I am using the MAX17048 fuel gauge to estimate state of charge. As far as I know, SoC and voltage are only loosely correlated and differ dramatically with different batteries, so it may be very hard to estimate based on voltage alone. However there may be data on the specific battery you are using, which could give you a better idea of the correlation. Only a hunch. Alternatively you could add a breakout board like this one pretty easily: SparkFun LiPo Fuel Gauge - TOL-10617 - SparkFun Electronics. It is fully supported by the MAX17043 Particle library.

Yeah I knew only using voltage would be a rough estimate, but figure it’s better than nothing. I will keep the fuel gauge in mind, nice to know it exists, but I think I am going to go without for now. I have already spent more on this project than I expected :slight_smile:

Thanks for all the advice, I definitely like this CE pin idea. Like I mentioned before, I should be able to get a ton of battery life on my setup, especially since I will have my Argon sleeping most of the time. Once it gets hot this summer I may even set it to only charge early in the day, before it gets hot out. Not having the equipment in place yet I don’t know how feasible that will be, obviously it depends on how much power my panel can deliver in the morning, but I think I should be okay.

Awesome! Glad I could help. I think that’ll work out just fine :slight_smile: