Lipo Charging

Hey. So I was doing some research about lipo charging and batterys in general and, how do I know what mA my battery has/needs to be charged at? Is it even important?

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Usually the mAH is printed on the battery itself somewhere, but if not, this thread describes how to test the capacity of your battery, although you can’t exactly probe the battery and find out I think. It is important, though most lipo charging boards you find will work for most lipo batteries. It’s still good practice to check, though. If you wanna know a bit about lipo charging, I think this video is a pretty good one, it goes over some pretty sketchy charging schematics, so you can see what to avoid.

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Would an Adafruit micro lipo work for a 600 mAH battery? Also, does the mAH determine the mA?

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It could, but it would be slow. You want something that has constant current of 300mAH for a battery with capacity of 600maH. The adafruit micro lipo can do 100mAH OR 500mAH. Not quite the Goldilocks zone you’re looking for.

Yes, the mAH determines the amperage, but also it doesn’t. It determines it’s possible amperage. The other factor is the load. Amps are a measurement of how much current is going through a load. If you think of electricity like water, the amount of water you have collected is the voltage, and amperage is how fast that water moves through the pipes. how wide those pipes are can be thought of like resistance/impedance, or load. Milliamp Hours (mAH) is just how much current (amperage) it provides over a one hour period under minimal load. So in our water analogy, if we know know how long it takes to drain all of it at a constant speed, we know how fast that water was going.

tl;dr: Not really. A 600mAH battery can last for one hour if you draw 600 milliamps from it. but can also last 600 hours if you’re only drawing one milliamp.

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Mmm. So 100 mA or 500 mA. I see a 500 mA surface mount pad so does that mean that by default it charges at 100 mA? Also, how do I change it to 500 mA? Does it have something to do with that pad?

Rule of thumb is charge at 1/10 C (basically take the capacity of the battery and divide by ten to get a safe charge current). If you wanna go higher you can check the battery datasheet to see what the manufacturer specifies is ok to go up to. To change the current of charger ics you would change the resistor value on the current programming pin in accordance with the equation given in the datasheet.

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Not necessarily. A LiPo battery will be specified for a maximum charge current. This is usually specified as a percentage of its capacity. 1C is 1 times its Ah capacity in amps. 1C for a 600mAh battery would be 600mA. 0.5C for a 600mAh battery would be 300mA.

There is no “Goldilocks” zone for standard LiPo batteries as long as you stay below the maximum recommended current. This is typically 1C. Assuming 1C is safe, charging a 600mAh LiPo at 500mA (0.83C) isn’t going to be significantly worse for the battery than charging at 300mA (0.5C) or even 100mA (0.17C). The charge current used will determine how long the battery will take to charge. (Lower takes longer.)

No. The maximum amperage you can (safely) draw from a battery will be determined by its chemistry, construction and size. The mAh rating of the battery has nothing to do with the maximum current it can provide (although for a given battery series, the maximum current may be proportional to the capacity.)

The rated mAh capacity of a battery is stated for a given current but it’s not linear for all currents. At currents higher than that specified for the rating, you will likely get less capacity. At currents lower than the spec, you will likely get more capacity.

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For typical LiPo cells it’s more like 0.5C to 0.8C, assuming you have a “smart” charger that can follow the proper charging rules.

0.1C possibly could be used if you just blindly charged at that current, but even then wouldn’t be recommended after the battery reached fully charged state.

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Yes. For 100mA, leave the pads open, as is. For 500mA, put a blob of solder across the pads to short them together.

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I’m not the smartest cookie in the jar, but basically my 600 mAh battery should be charged at 60 mA? But is it safe to charge it at 100 mA?

I looked at the datasheet and all it says is it’s voltage (3.7 v) and the capacity. It says on the datasheet it’s a 650 mAh battery but on my battery, it’s empty, but there is a piece of tape that says everything on it so it could be a mistake and may be a 650 mAh battery.

As I said above, with a proper charger (such as the mentioned Adafruit Mico-Lipo) it’s safe to charge a 600mAh LiPo at 100mA or even 500mA. It will take much longer to charge at 100mA than 500mA. (Probably about 1.5 hours at 500mA and 7 hours at 100mA.)

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The 1/10C rule is obviously for cc/cv chargers as the min safe charging current when you don’t have a datasheet and may not know the exact chemistry of the battery. Especially if the battery has sat for an extended period of time and needs to be reconditioned! Like I said though if you have a spec sheet then just follow the manufacturer recommendations.

We’ve been discussing using a proper LiPo “smart” charger here. Not a cc/cv charger.

A proper LiPo charger will sense and properly recondition a battery if necessary.

What “smart” algorithm are we talking about? Just a variation of piecewise linear cc/cv states dependent on voltage and temp ranges? Or the higher end battery characterization chips that do soc/soh and coulomb counting then yes they are more sophisticated than cc/cv chargers, but they usually require a separate main controller to interface with for monitoring/configuration and would be wayyyy overkill for something like an arduboy.

In the case of the Adafruit Mico-LiPo Charger, discussed here, see the MCP73831 datasheet.

Yeah that’s an analog piecewise linear cc/cv controller. I wouldn’t really consider that a smart charger, but looks like it does uvlo and precondition trickle charging. Not sure though how safe it’d be on reconditioning unknown batteries without some sort of temp sensing to cut off in the event of thermal runaway.

Also, does the micro lipo have battery protection?

Were talking small, hundreds of mAh, single LiPo cells here. Not a Tesla Powerwall.

The Arduboy uses the same MCP73831 controller chip as the Adafruit Mico-Lipo. It should be noted that, due to a design mistake, the charge current programming resistor value is incorrect, resulting in an “unsafe” 2.8C charge current. See the discussion here. There have been no reports of any Arduboys overheating, blowing up or catching fire (although I’ve seen one report of a bulged battery).

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No, but most LiPo cells of the type you would use have protection circuitry built in. The Arduboy’s battery is an exception, which is why there’s a protection circuit on the Arduboy circuit board.

If you post a clear photo of your battery, we may be able to determine if it has its own protection.

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