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Safe LiPo / PB 500 discharge point
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Please be positive and constructive with your questions and comments.

Safe LiPo / PB 500 discharge point

by pdh on Fri Nov 17, 2017 7:00 pm

I have a PowerBoost 500 shield and a 2500 mAH battery from Adafruit, attached to an Arduino Uno WiFi, and it periodically sends data to an MQTT broker. All well and good, it can run unattended and it works beautifully. My question is, is it safe to let it run until the power runs out, or do I need to be more careful about monitoring the battery level?

The way I use it today, it's almost inevitable that I'm going to run the battery all the way down once in a while. If I see the red low-power LED on the PB 500 then I'll stop it and recharge, but I can't check as often as I'd like so as things currently stand, it will occasionally run itself into the ground. Is that bad?

I know that the Adafruit batteries have protection circuits to shut them down at 3 volts or so, which is a good start. But I'm wondering if it will damage the battery (or even the PB 500 or the Uno) if the battery drops down to that level a few times each week. And even if that doesn't do serious damage, would it shorten the life of the battery or the other components?

I realize that I could monitor the battery voltage via the jumper pads on the PB 500, and I'm trying to figure out if it's worthwhile to do that. My application will be OK if the gadget drops out for a few hours every now and then, but I don't want to destroy the electronics if I can avoid it. Any advice would be appreciated... thanks!
pdh
 
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Re: Safe LiPo / PB 500 discharge point

by pdh on Wed Nov 22, 2017 9:42 am

Any thoughts on this?

[Typo in the original: the LiPo battery is 2000 mAH, not 2500.]

Yesterday the gadget ran all the way until the battery ran down. I measured 2.82 V on the battery after it stopped; I'm wondering whether the battery is damaged (i.e. is its life shortened or capacity reduced) when that happens.

For the record, the 2000 mAH battery + PowerBoost 500 shield was powering an Arduino Uno Wifi. I measured the Uno's current draw to be about 103 mAH. It ran for just over 11 hours on a freshly charged battery.

I estimate that 105 mAH for the Uno requires roughly 160 mAH from the battery (accounting for the voltage boost plus some inefficiency) so I would have expected about 2000 / 160 = 12.5 hours. I got 11.2 hours, which is about 90% of what I expected -- seems reasonable for a battery that's 18 months old. So I think the battery is fine at the moment, but will it suffer if I run it down like this once or twice a week?
pdh
 
Posts: 148
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Location: Northwest Pennsylvania

Re: Safe LiPo / PB 500 discharge point

by adafruit_support_bill on Wed Nov 22, 2017 9:55 am

The exact cutoff voltage for the protection circuit is set by the factory and should be appropriate for the characteristics of the particular LiPo cell. There are many factors that will affect battery lifetime. Over-discharge and high charge & discharge rates are the major ones. The protection circuit guards against over-discharge and high discharge rates. The charge controller in the PowerBoost 500 is set to well under the maximum charge rate recommended for that cell.

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Please be positive and constructive with your questions and comments.