Arduino Primo And its Battery Charger

Does anybody else have an Arduino Primo?

I got a nice lithium ion battery from Sparkfun Lithium Ion Battery - 1Ah - PRT-13813 - SparkFun Electronics At 3.7V and 1A it should be perfect for the Primo after looking at the schematics for the Primo itself. It falls within the stated input voltage range 2.7~5.5, it’s a 1A battery which should be more than enough.

The weird thing is that when the battery is plugged into the JST connector on the Primo the LEDs come on for just a second before shutting off. If I make a bridge between the battery’s anode and the VIN slot on the Primo it comes on and works fine. So why doesn’t the Primo run when the battery is just connected to the JST plug?

I’ve checked the voltage of the battery and it is higher than the said threshold of 3.4V-ish volts where the Primo will switch to a secondary power source and start charging the battery. Therefore the Primo shouldn’t be rejecting the battery because it doesn’t have enough “juice”.

In addition I’m also curious about the battery charger functionality as well, because I was charging the battery I bought and it actually charged it beyond the battery’s nominal voltage of 3.7V (the battery was around 4V).
Aren’t lithium ion batteries very sensitive to overcharging? It makes me wonder if the Primo charger has been made to shut off when the battery is charged or if it relies on the battery’s internal mechanism that prevents overcharging. I’m a bit afraid of waiting to see if the Primo will actually shut down after fully charging the battery or if the battery will catch fire because of being overcharged...

In short, has anyone got the Arduino Primo to run off a battery that is plugged directly into the JST plug? And, has anybody used the battery charger without a problem with a 3.7V 1A lithium ion battery?

Any help would be appreciated about this subject, I’ve been looking through the schematics to the best of my knowledge about circuits, I’ve done some research on lithium ion batteries, but I’ve found next to no help whatsoever when it comes to the mysterious Arduino Primo board.

I don’t know the Primo but the documentation I looked at said it switched power over at 3.5V.

A fully charged lithium-ion/lipo battery is at 4.2V. 3.7V is just a nominal voltage, roughly when the battery is half empty.

BTW that battery is 1Ah not 1A. 1Ah is total capacity. It is NOT the current it can supply.


Ah is the capacity, good to know. I’m going to let the Primo run with the battery plugged in and let it charge until it turns off or stops.

I’m still baffled why the Primo won’t run directly off the battery when there is no other power source, the battery Voltage is above the switching level of 3.5V at 4V.

I found the same thing happened with mine. :frowning:
This post gave me hope since it happened to someone else. Originally I assumed I had somehow put too much voltage on it or got a defective chip.

After going around in circles for half a day, I thought maybe it comes to life if I execute a task. I ran a BLE sketch to send signals to the Nordic Heart Rate Monitor (nRF Toolbox) and to my surprise it was working. I saw no lights blinking on the board. Sooo, looks like some engineer was clever and disabled the LED lights when it is being run from the battery plugged into the 2 pin JST-PH connector. Wish it had been DOCUMENTED some where, but that's ancient history.

So, good news, the JST-PH connector can be used to power the Arduino Primo, just don't expect the ON, WiFi, and BLE LED lights to blink. (not sure about other LEDs, they may light up under S/W control).