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MrKevinWeiss / riot-10-promo-board

A promotional board for RIOT's 10 year anniversary
GNU Lesser General Public License v2.1
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Battery management #10

Open chrysn opened 2 years ago

chrysn commented 2 years ago

Does it make sense to have the device field rechargable?

I don't know our power budget yet, but if it's really just using a teeny tiny LiPo, then there could be an "If you care, bring a power bank and donate 5 minutes" aspect to it. (By claiming the NFC code for that duration, you might listed in the hall of fame of People In Charge).

MrKevinWeiss commented 2 years ago

Yup, I like this idea. So we can have a slot to USB charge a small lipo or so. We should choose a very common battery type so we don't have to ship them, it would be up to the device owner to add it. One of these charing IC could probably pass EMC easily and provide some battery life detection (maybe?).

I guess solar would require access to the sun, limiting the hiding places.

chrysn commented 2 years ago

Solar requires different charging circuits. From a power bank we can just (well ... practically) draw 500mA for as long as there is voltage. From solar we'd need an MPP tracker to draw the right amount of current so that the voltage stays at the right one depending on the panel.

If we use an off-the-shelf battery control chip for charging, solar is probably not an option.

If we do charging on our own (probably feasible with some real-time control, PWM and ADC), we should make sure to have the (or an, as it'd be a solder-on connector) input voltage divided down to an ADC so that later firmware updates can do MPP in software.

MrKevinWeiss commented 2 years ago

I am suggesting no solar, just a battery pack that can plug in to top it off.

luisan00 commented 2 years ago

How about a 18650 battery? is easy to get, has good current capacity and can be replaced without tools, also can be charged with a 1 cell IC (not expensive)

chrysn commented 2 years ago

18650 is a form factor (possibly a viable one); for purposes of charging and use an 18650 or different single-cell lipo is all the same.

(what some 18650 and some others have is builtin battery protection, that's probably good to have no matter the shape.)

luisan00 commented 2 years ago

18650 is the size, yes, 18mm x 65mm (diameter x length). Anyway, i named this size earlier at the request of @MrKevinWeiss, "We have to pick a very common battery type so we don't have to ship them."

About the battery management IC, something like the TI BQ24298 can be a solid solution, include smart power path, useful for example if we need to turn on the device while the battery is charging. or programable current charge and dis-charge

mcr commented 2 years ago

Solar requires different charging circuits. From a power bank we can just (well ... practically) draw 500mA for as long as there is voltage. From solar we'd need an MPP tracker to draw the right amount of current so that the voltage stays at the right one depending on the panel.

If we use an off-the-shelf battery control chip for charging, solar is probably not an option.

I'm sad, but okay. can we think about what would be needed for solar, and not preclude it?

MrKevinWeiss commented 2 years ago

How about a 18650 battery?

From the form factor of the 18650 point, I would question if using something that requires clips is the best compared to one of the molex type 2 pin connectors. I have had some pretty bad experience getting the clip size and spacing just right (though it was for a battery powered impact sensor, requiring some bouncing around).

Are there benefits to a cylindrical cell battery with clips vs something like this (but not this)?

MrKevinWeiss commented 2 years ago

can we think about what would be needed for solar, and not preclude it?

For sure, we can always do more iterations. We should plan power control module footprint to have what we may need. For the first board I want to get something simple that works, we can always pimp it later.

luisan00 commented 2 years ago

How about a 18650 battery?

From the form factor of the 18650 point, I would question if using something that requires clips is the best compared to one of the molex type 2 pin connectors. I have had some pretty bad experience getting the clip size and spacing just right (though it was for a battery powered impact sensor, requiring some bouncing around).

Are there benefits to a cylindrical cell battery with clips vs something like this (but not this)?

Resistance, a cylindrical battery has a metallic shield, a flat Lipo not, anyway i was thinking in a socket with a good gripping for the battery and the socket wired with some molex, 2 or 3 wires, depending if we need a thermal sensor for the battery

MrKevinWeiss commented 2 years ago

TI BQ24298

Looks nice, it has quite a lot of features and generally available. Is the leakage going to be a problem? We should find out what our power bottleneck will be.

I think we will require an always on feature, I don't want the RTC to loose time everytime we repower.

MrKevinWeiss commented 2 years ago

depending if we need a thermal sensor for the battery

I really don't think we will be drawing that much current. The peak will probably only due to the LoRa message being transmitted. Maybe @jia200x can give some insight on how much we should expect.

socket with a good gripping for the battery and the socket wired with some molex, 2 or 3 wires

I have no problem with that if the electrical connection is done with the molex!

luisan00 commented 2 years ago

I have no problem with that if the electrical connection is done with the molex!

yes, (this type) is a headache, i was thinking in some of (this other one solution)

I really don't think we will be drawing that much current. The peak will probably only due to the LoRa message being transmitted. Maybe @jia200x can give some insight on how much we should expect.

No problem, then we need to put a 10k resistor tbetween TS and GND

I think we will require an always on feature, I don't want the RTC to loose time everytime we repower.

Also when the r10t-gc is low on battery, the device can notify it to the owner , right?

MrKevinWeiss commented 2 years ago

i was thinking in some of (this other one solution)

Ahh, suppose if that would hold, we could just do direct solder then. I was thinking that the holder would just be a place to secure the battery and we would have something like this, it would make changing the battery types a lot easier...

Also when the r10t-gc is low on battery, the device can notify it to the owner , right?

Yup, that I think is a must.

MrKevinWeiss commented 2 years ago

I am thinking that for rechargeable batteries the self discharge will probably be the bottleneck of the powerbudget. After some quick googling I guess the rule of thumb is that the lipo battery self discharge is around 3% per month though after some cycles it would probably be around 10% per month.

We can assume that everything but the battery would draw less than 20uA. We will probably be sleeping the vast majority of the time and I can't image that our sleep current for the MCU, RTC, and leakage of components would be over that. Thus, we would want to target the self-discharge to be 20uA at 2% (to be conservative), meaning we would need (0.020mA 720hours/month / 0.02discharge = 720mAh) ~800mAh battery, maybe the 18650 is too big then as it around 3000mAh?

I guess the peak current will also only be transmitting a LoRa signal with PA_BOOST is 95mA or so, so we can just say that our regulator should be able to dish out 150mA to be safe.