Lipo Charging

This is what my battery looks like (sorry if it’s flipped!)

Yes, that circuit board in the battery is for overcharge/overdischarge/overcurrent/overvoltage protection.

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Alright so I keep on forgetting but how do I wire up the micro lipo to my arduino, as well as wiring up a 3 pin slider switch to turn the console on and off?

Assuming you’re powering the Arduino with the raw ~3.7V battery voltage:

Battery+ and Battery- to charger.
Charger GND to Arduino GND.
Charger BAT pin or battery+ to switch.
Other side of switch to Arduino VCC.

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What do you mean by that?

No regulator to boost or drop the voltage (the same way the Arduboy does it). This has already been discussed in the topic you started here:

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I disagree? A battery’s chemistry, construction, and size is what determines, well, everything a battery is capable of. And to say that the mAH has nothing to do with the maximum current a battery can provide is just factually inaccurate. Doing some quick research, every source I find is saying that to find the maximum current you can provide with a lipo you need two pieces of information: the capacity, and the discharge rate. Most lipo batteries discharge at a 1C, meaning a 250mAH battery can provide a maximum current of 250mA.

So I stand by what I originally said. mAH determines the possible amperage, with the other factors being discharge rate and load. That said, I wouldn’t have found that out had you not said anything so thanks :slight_smile: I didn’t know discharge rate would be a key factor but it makes total sense.

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So if I remember correctly, the battery will take longer to charge at 100 mA, and it will charge faster at 500 mA. But it will take longer until the battery is dead, and vice versa for 100 mA. Do you think that 500 mA is better? Or with 500 mA there isn’t much battery life and 100 mA is better?

No. A battery’s discharge current is determined by the voltage at the battery terminals and the resistance of the circuit being powered. Current (I) = Voltage (V) divided by Resistance (R).

The maximum 1C discharge rating is for continuous current and is specified for safely running without overheating. That says nothing about the instantaneous current that a given battery could provide, which could be much higher. This is all determined by the battery’s internal impedance. However, for a given series of batteries of similar construction, those with a higher mAh rating will likely be able to provide a higher peak current due having a lower internal impedance.

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No. The charge current only determines how long it will take to charge. Once the battery is charged, it will last just as long (when powering the same circuit) regardless of what current it was charged at.

Charge current can also have an affect on the number of total charge/discharge cycles you will get from it. Charging at a lower current is generally better for the life of the battery (within reason).

Another thing that affects the life of LiPo cells is the amount of charge and discharge. It’s better to only charge up to about 80% of a full charge and discharge down to about 10% of empty. However this is difficult to accomplish with the circuitry used by the Arduboy.

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Is the instantaneous current relevant to arduboy? if we’re going to be powering the circuit for more than short pulses, shouldn’t we be focused on constant current? Or do I misunderstand something?

Right, the load will change the discharge current, which is what I was trying to get at here, just poorly worded:

I think this is why the source I was looking at said that 300mA is an ideal “goldilocks” zone for 600mAH lipo, even though it’d be slow, it wouldn’t really risk the battery’s shelf-life or overheat. Although that begs the question, how much current could you charge a 600mAH lipo at before risking its life? Is it just anything above 1C?

Oh. I remember reading something that was saying that lipo batterys slowly die or something.

Yeah, I guess it is the “goldilocks” zone.

The only thing related to battery mAh capacity that is of concern in relation to the Arduboy is the average current that will be drawn and whether the battery is capable of providing it and whether it can provide it for the desired amount of time.

For the Arduboy, the average current is usually about 30mA to 40mA but can go to around 60mA if most of the display pixels are on and you have sound and/or use the RGB LED. So even a 80mAh cell would work but would only run for an hour or two. The 180mAh battery in the Arduboy is plenty. Anything higher gives you longer run time between charges.

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For the most part, with LiPo the lower the charge current, the longer the life but it isn’t a linear curve. As you lower charge current you get diminishing returns for cell lifetime.

As you initially implied, a general rule of thumb is to charge at or below 0.5C (300mA for a 600mAh cell) for best life. Anything below 0.5C probably won’t gain you much in terms of total battery life. Above 0.5C, lifetime decrease may be noticeable and somewhat linear as you approach the maximum 1C safe rate. However, it’s not like you’re going to see a huge loss of lifetime. Even always charging at 1C might only drop your lifetime to 80% of specified.

Given the cost of these small cells, I would consider charging between 0.7C and 0.85C to be a good compromise for charge speed and battery life.

Note that all of this is general advice. The battery manufacturer’s specifications are the final word.

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Hmm. That said, I think maybe for the charger I’m using, 600 mAh may not be a good amount. As you stated, to generaly charge at 0.5C, do you maybe think I should get a 1000 mAh battery and then convert the charger to charge at 500 mA?

I think you should stick with the 600mAh cell you have and covert the charger for 500mA, which would charge at 0.83C. This won’t reduce the life of the battery by much.

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What battery life would I get with the 600 mAh and also how long will the battery last at 500 mA?

There are many factors that will influence overall battery lifetime. Charging at 0.83C instead of 0.5C probably won’t make much of a difference. Only the manufacturer can say for sure.

What do you mean by “how long will the battery last”? If you mean total life before you have to discard it, then you’ve asked the same question twice in the same sentence.

If you mean how long will you be able to use it after a full charge, before it’s empty and you have to charge it again, then assuming a 35mA draw, a 600mAh battery would last about 17 hours. Whether you charge at 300mA or 500mA or anything else doesn’t affect this.

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I mean that if I charge it at 0.83C how long will the battery stay in peak condition, before it starts to get too bad?