Capacitor to feeda servo while using a lr2032 battery

Hi,
I haven't used a lot of capacitors for high energy bursts in the past, but I have started to get more comfortable with battery protection/overcharge/discharge circuits and wanted to try something. I'd use a LR2032 rechargeable battery with a servo on a 5v boosted circuit, but this cell battery only has 50-60 mA peak currents, while the servo can use over 80 mA (its a cheap china microservo, so it doesnt use a lot). is a capacitor enough to feed that servo if I want to use it for 10 seconds in a row on a daily basis? How can I tell what capacitance to get?

If It's not doable, I'll switch for a circuit with 2 aa batteries, boosted to 5v this time. However, I should add a protection circuit if one day someone decides to put NiMH batteries in right? I normally use DW01 IC for Lipo cell circuits, but I don't think this IC works for NiMH. How could I build that protection circuit so that NiMH and normal alkaline batteries are still usable? That made me wonder if commercial devices which require 2 aa batteries normally have a protection circuit in case the user puts rechargeable batteries?

As always, thanks for your great help!

You could do it with a beefy capacitor, but it would need to be a pretty beefy one to provide 80mA for 10 seconds without the voltage dropping much (80mA also sounds really low for even a small servo - like, order of magnitude low; quick bit of googling suggests an SG90 microservo can pull over 500mA). Also if you're using a 3v coin cell, and boosting it to 5v, the current requirement is almost doubled (5/3rds, plus inefficiency in the boost converter). I don't think you're going to be happy with the battery life you could get out of a coin cell with that sort of configuration - those coin cells have absolutely miserable capaity.

Why do you think you need some sort of protection for using NiMH in place of alkaline batteries? NiMH is 1.2v, vs 1.5v for alkaline (1.8v for the fancy advanced lithium AA batteries). If you're boosting it to 5v, the only thing you need to worry about is whether your boost converter will work when supplies with ~2v (partly-discharged NiMH).

What about using a 18650 LiPo battery on one of those cheap "18650 battery shields" (that's the ebay search term) that has a micro USB port to charge it from and integrated 5v boost converter and 3.3v regulated output? This is 2019 - micro USB for charging is ubiquitous and most people prefer it over having to swap out batteries.

DrAzzy:
What about using a 18650 LiPo battery on one of those cheap "18650 battery shields" (that's the ebay search term) that has a micro USB port to charge it from and integrated 5v boost converter and 3.3v regulated output? This is 2019 - micro USB for charging is ubiquitous and most people prefer it over having to swap out batteries.

I just thought 18650 was a little overkill for that project, since it will be in sleep mode most of the time. A rechargeable project that needs to be recharged every 2 months loses a bit its sense doesn't it? But I might as well do that! I'd be building my own protection circuit instead of a shield though. For the regulator, can a 34063 regulate to 3.3v? Since a lipo battery starts out at 4.2v and Lions 4.1v and ends up at 3v, the regulator needs to buck at first and then boost once it's below 3.3v. Is 34063 ok or I'll need to buy a low dropout like this one https://uk.farnell.com/texas-instruments/tlv70033ddct/ic-ldo-200ma-3-3v-5sot23/dp/1778230
Ho, and I have the ams1117 3.3 too, but I'm not sure it can go below 3.3V am I right?

Why do you think you need some sort of protection for using NiMH in place of alkaline batteries?

I think NiMH batteries can be damaged when overdischarged. I just wanted to make sure this doesnt happen because some regulators can operate at 1V, no? is this type of precaution something people often do with aa batteries?

Thanks for your great reply!

Yes, you don't want to over-discharge any type of secondary (rechargable) cell.

JCSB:
I just thought 18650 was a little overkill for that project, since it will be in sleep mode most of the time. A rechargeable project that needs to be recharged every 2 months loses a bit its sense doesn’t it?

Still better than having to replace the battery every few days… Though a 3-4 set of alkalines may work really long, provided you keep your Arduino in deep sleep most of the time. That may power your project for 1-2 years. That one 18650 should also last for much longer than 2 months, provided you have a good quality battery with low self-discharge.

500 mA x 10 seconds = 1.4 mAh. That’s some 1,500 such servo movements on alkaline batteries (about 2,200 mAh capacity for AA size), though at this high current overall capacity drops.

Ho, and I have the ams1117 3.3 too, but I’m not sure it can go below 3.3V am I right?

If your input voltage drops below about 4.5V, it may actually produce an output of <3.3V simply because of it’s minimum drop-out.

wvmarle:
If your input voltage drops below about 4.5V, it may actually produce an output of <3.3V simply because of it’s minimum drop-out.

I kind of screwed up my question… I meant I dont think the ams1117 3.3 can take an input voltage below 3.3v, right? So you cannot really use this voltage regulator for a lipo battery?

Is the 34063 a good option for every battery? like you can regulate 3.3 or 5v throughout all the voltage spans ov a lipo/Lion and could boost 2 AAs from 3 to 1.8 input volts? Im just looking for the right regulators for my projects that I can buy in bulks for cheap on ebay.

That one 18650 should also last for much longer than 2 months, provided you have a good quality battery with low self-discharge.

So do you think I should opt for a secondary battery? It would just sound weird for a company to offer a product with recharging features when you don’t really have to recharge it. looks like its lifespan will get reduced from not being discharged fast enough??

MarkT:
Yes, you don’t want to over-discharge any type of secondary (rechargable) cell.

Great, but I still have that same question about which protection IC should I use for such a task and then which regulator (is 34063 suited?). DW01 probably isn’t suited for 2 rechargeable AAs since it’s built for LiPo cells.

JCSB:
I kind of screwed up my question.. I meant I dont think the ams1117 3.3 can take an input voltage below 3.3v, right? So you cannot really use this voltage regulator for a lipo battery?

There are regulators with a minimum dropout of as little as 200-300 mV. Those are more suited for such an application. But why use a regulator in the first place? An Arduino is perfectly happy at the full range of voltages a LiPo produces.

Same for a set of 3xAA batteries. No regulator needed. Much cheaper than LiPo batteries, in this case even in the long run.

wvmarle:
There are regulators with a minimum dropout of as little as 200-300 mV. Those are more suited for such an application. But why use a regulator in the first place? An Arduino is perfectly happy at the full range of voltages a LiPo produces.

Same for a set of 3xAA batteries. No regulator needed. Much cheaper than LiPo batteries, in this case even in the long run.

Because I did not want the internal clock or voltage dividers to be influenced by the varying voltage of the battery. And what about the 34063? is it a good regulator choice? might not be the best, but its cheaper, right?