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When charging a lipo:

  1. Is there a max current you should recharge at?
  2. Does the protection circuit on the lipo correct for the amount of current that should be going into the battery?

I'm looking at solar lipo chargers, I see the seeed studio lipo rider has a output current of 300mA. (Not sure if that's referring to the usb interface or the battery JST), but how do I know this will accurately/safely charge my 3.7v 270mA lipo.

Does anyone have a resource that's in laymen terms on lipo charging? Don't know why but the whole battery situation scares me a bit with safety concerns, as I feel like I've never been able to get my head completely around how to safely charge a lipo, despite products like the "seed lipo rider"

seeed lipo rider

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  • \$\begingroup\$ All your questions have been addressed in prior SE answer. Search on LiIon (functionally same as LiPo). Add User:3288 (me) in search if desired to narrow it down. | Ma <= mAh usually. 300 into 270 PROBABLY OK. | Do not rely on protection cct to treat cell well. | ANY chather worthy of the name fully stops charge current at end of CC/CV process. \$\endgroup\$ – Russell McMahon♦ Jul 31 '15 at 9:06
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Generally you want to charge at "1C" or less unless your battery datasheet says otherwise; for a 270mAh lipo cell that's a max charge current of 270mA. Your protection circuit won't limit the charge current going into the battery- it would only open a FET to prevent charging in an overcurrent condition. You have to limit the charger current yourself. Many battery charger ICs will do this for you with a simple jumper or I2C register setting.

Packs usually come with a datasheet for the pack and a datasheet for the protection circuits. Both should be considered when setting up your charger. I just did this for the first time and set the limit on my Linear Tech (LTC3567) charger to a 100mA mode to be safe. It works like a champ and I don't need to worry about overcurrent on my pack (470mAh). Yes it takes a little longer to charge but that was okay for my design.

Sparkfun has some good charger examples (they are fairly cheap to buy if you want to go that route). Note that for this simple charger IC there is a "PROG" resistor that you can change to set your charge current limit.

Some of the RC forums/merchants have some decent reading on the subject. Here's one example: http://www.rogershobbycenter.com/lipoguide/

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  • \$\begingroup\$ Thanks for the help. I'm not sure if this effects the setup, but I'm using the lipo to power my arduino project. My project sleeps a majority of the time, and pulls microamps of current on average. Is the lipo charger and/or protection circuit smart enough to control for this small need? Also, how does the lipo charger know when the battery is full? \$\endgroup\$ – JW2 Jul 31 '15 at 3:58
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    \$\begingroup\$ @jmwagg When charging, the charger decides on the current limit. Most lipo/li-ion chargers will charge at a constant current (limited by the mechanism discussed above) until the battery voltage hits a predetermined level. Once this voltage is reached, the charger will automatically switch to "constant voltage" mode and charge the battery more slowly until it has finished charging. The battery is fully charged when the battery voltage reaches ~4.2v and your single-cell charger knows when to stop. For discharging, your circuit dictates the draw. If you only draw a few microamps that's fine! \$\endgroup\$ – mhilden Jul 31 '15 at 4:05
  • \$\begingroup\$ When you say charger in the first sentence, do you mean the board between the solar panel and the battery, or a wall charger? It sounds to me like I need to buy a lipo charge controller specifically rated for my 3.3v lipo (so it knows to stop charging at x volts and switch to constant voltage. Do you have any specific resources you used to learn about this? Thank you very much, you've been super helpful. \$\endgroup\$ – JW2 Jul 31 '15 at 4:10
  • \$\begingroup\$ @jmwagg When I'm talking about a "charger" I do mean a dedicated lipo/li-ion single-cell battery charger that would sit between the solar panel and the battery. I'm hoping that the single cell you have is a standard lipo cell and can be charged with a charger like the Sparkfun one I linked to in the answer. Take a look at your battery datasheet to see if you can use a standard lipo/li-ion charge profile. Specs for the battery should match the specs for charger that you choose. Make sure that the lipo charger you buy is rated for the max voltage output from your solar panel! \$\endgroup\$ – mhilden Jul 31 '15 at 4:25
  • \$\begingroup\$ In regards to buying a lipo charger rated for my panel - is it also possible to use a constant current/voltage circuit to take down the voltage and amperage of the panel, knowing its wasteful? Or if the voltage was too high, using an lm7805 to regulate? \$\endgroup\$ – JW2 Jul 31 '15 at 14:50

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