TLDR; is a load on/off switch or physical PB disconnection always necessary for the LilLiPo to work?
I’ve had some LilLyPos for a while, but this is my first time trying to get it to work.
I want to make sure I understand what it’s intended behavior is:
When a 1S Lipo is connected and sensed to be > 2.4V, connect it to the output (for me, a Pico and 8x8 2020 matrix set to 5% max brightness)
When it drops below 2.4V, disconnect it from output
When it is below 2.9V, trickle charge. Otherwise charge at 100mA or 212mA (depending on version) until the cell is sensed at 4.2V
No ability to pass through the input voltage to the output if no cell is connected, and (unknown) if the charge current can be activated during load draw.
Is this all correct? While the LVC seems to work, I’m having trouble getting it to charge any cells (I’ve tried three) and I can’t get it to reliably output to the Pico/LEDs given certain connection orders.
My setup:
Input: 5.1V 3A from USB-C PD Decoy (verified at LilLiPo input with voltmeter)
Lipos: 1S, tested with 400, 500, and 850 mAh cells
Output: Pico (not in low power mode) and 5% brightness x qty64 x WS2816-2020 (spec says 20mA max per chip, so this should draw 64mA at full brightness)
I’m wondering if in this configuration (and let’s assume I have the 100mA charge current version), it’s going to be impossible to recharge my wearable project without also installing a power switch or disconnect between the LilLiPo output and the Pico+LEDs.
I’m thinking this because I left it plugged in overnight to charge with the battery at 2.85 V, and in the morning the battery was still at 2.85 V. I’m guessing what happens is:
As soon as it reaches some threshold voltage (which? 2.4V?), it reconnects to the load
…which draws 80-260 mA in my setup depending on WiFi mode and pattern intensity; Even if the PB Pico doesn’t meet a threshold voltage to turn on, it will possibly draw up to 50mA of quiescent current for the 64 WS2818s, which spec “<0.8mA quiescent” (per chip)
… which quickly drains it back below the Pico’s voltage threshold, thus the Pico never turns on or turns on very briefly, because whether the LilLiPo is delivering a trickle charge (what current?) or even a full 100mA, the Pico + quiescent LED draw quickly drains it back below the Pico’s operating threshold voltage.
In addition, when it discharged to about 2.5V during my initial 4 hour test run, it corrupted the Pico’s firmware and was in mandatory recovery mode at the root path (while powered from a benchtop 5V supply).
So, it would seem that it can’t be used for a wearable mode where you’re hoping the user just runs it till empty then plugs it in to charge – You also need an on/off switch, and you need to tell the user to turn it off to charge.
Is this correct? Or perhaps with a 212 mA version, if it’s designed to deliver a full 212mA when above 2.9V on the LiPo, it could putter around with just a Pico connected, but not last long with LEDs drawing over 50mA as well.
Tl;dr: Yes, you will want an on/off switch, unless you are using it for very low power (non-PB) things.
The charge IC has 3 modes, recovery, constant current, and constant voltage. At recovery voltages it uses 10% of the charge current to bring the cell back up to working levels. Then it switches to 100% constant current, then it switches to constant voltage until reaching 4.2V with a low charge current, at which point it will stop charging until voltage drops to 4.1V.
You can draw power during charging, but if you draw more current than its getting, the battery will drain, especially if the voltage is low enough to put it in recovery mode. You are right, it doesn’t pass through power otherwise, and the charge current is often going to be lower than a PB + LEDs would consume in all but the smallest projects.
TBH, this is one of my earlier boards, and not specifically designed for common PB use cases like you mention, I wonder if I should retire it?
Hmm… That shouldn’t happen. Were writes occurring during that time? Were other files lost?
I’m going to put it through more paces and see if I can trigger a recovery mode requiring repair again.
I wouldn’t retire it, especially the 212mA version, because I’m not seeing a better product out there. I see a lot of much bigger boards that are also more expensive that have more functionality, but I like this for the size. I just needed to type out all my observations to make sense of it. One of us might consider mentioning the charge benefit of the on/off switch on the product page.
For the benefit of others:
Yes, the charge current can be delivered during load draw, offsetting whatever the actual draw is (IE, extending your LiPo’s overall battery capacity when plugged in).
Using an ammeter, with WiFi disabled, lowest CPU speed, and the last pattern being an all-off black output, I’m able to measure a 30mA charge current going IN to the LiPo, so it should recharge my 500mAH in 16 hours, and significantly longer if it’s been drained to 2.4V and is thus to trickle charge at 10mA (10% of my version’s 100mA).
My advice: Unless your using something like a 100mAH cell with max 1C charging spec, definitely use the 212mA version, and plan for an on-off switch to enable faster charging (this would take my setup down to whatever the trickle charge current time comes out to + 2.4 hours).
With wifi off, your PB should be using 30-40mA, plus the idle current of dark addressables can be surprisingly high too, 0.5 mA to 1mA each. So I could see only netting 30mA for charging fairly easily in that setup.
So to capture all this as a feature requirements for an ideal PB lipo companion:
Pass through power, auto-switch between provided power and battery.
On/off switch or power button.
Larger charge currents to match the kind of size you’d typically use with a PB. Small linear charge ICs top out around 500-800mA.
Run and charge at the same time.
5V boost? Maybe optional? While most addressables are happy with lipo voltages, 5V can be nice for longer runs when voltage drop comes in to play. Would probably need at least 2A to pair well with most small LED setups.
USB connector? Or some kind of bidirectional setup you could wire up to PB’s terminal and charge with the existing connector?
Those specs for a next version look good; honestly this is only my second project trying to really minimize the size of a wearable in this way (necklace size). Usually I’m using a 2-3S with bigger regulator and a full size PB for something that will take up more space in a pocket.
So with the understanding that I’d choose other larger components for bigger projects (like a 2-3S LVC and larger balancing charger IC to really use true USB PD), I think your list is spot on with the following opinions attached:
Onboard switch might be of marginal use since for this kind of thing I probably need to locate my on/off switch somewhere else with a small length of wire; perhaps sometimes I could design around the placement of a small slide switch on the board.
5V boost option sounds nice, but I’m loving the tiny size of it now.
USB-C input for sure, but if you were considering a USB output, that’s likely marginal for me. Since I probably wouldn’t want to use up another USB connector’s space even if using a “full size” PB v3 Standard - I’d rather solder when designing something this small.
One interesting option (that might add significantly more components) would be to disconnect the load completely after a full discharge until it reaches a higher voltage that’s assumed to have some significant capacity to it, such as 3.7 V or something. The downside is you can’t just get a quick charge (unless perhaps it’s latched to always reconnect the load between 2.9 and 3.7V if the charging voltage is disconnected?). This would create a hysteresis for projects that draw over the LilLiPo’s inherent charge output capacity.
Picking the charge current as large as possible (like 800mA) is appealing but folks will likely always need to check the C rating on their cells. I’d be ok with tiny solder jumper pads as a selectable current mechanism.
I was thinking just a charge/power input. Are you saying you would not want the USB input on a board like this, but prefer to solder something? Maybe a break-away USB connector end?
…as an idea to have USB in, a connection for the lipo, and a Micro USB or USB-C charge-out for connection to a PB v3 standard.
I think you were instead thinking of something that would let you do the charging power-in via a PB’s main power-in (USB micro for now, USB-C in the future). That’d be slick for sure. I think we’ve discussed this before, but a little larger footprint Standard with 5-24 V in (+integrated buck for PB) and USB PD in might pair well with that and an onboard JST-PH2.0. I think where it gets tricky is choosing the current capacity for that onboard 5V regulator to drive LEDs from USB-PD, and whether to go above 3A (5A seems a practical limit for many single-side injection strips).
Came up with this. Can snap USB off and run wires (or just give 5V). Could connect external switch.
The power switch is rated for up to 2.5A, and with 500mA charge current the total power budget will stay within 3A from USB C. Can even run 1/2 battery voltage to an ADC to keep an eye on battery level. Wasn’t a ton of room for configurable charge currents, but could offer different models.
