Lipo charging question - Page 1
Forum section: electronics / beginners

author: prebs
author_rank: Newbie
timestamp: September 12, 2013, 08:00:32 am
content: I have made a charging circuit using the famous MCP73831T-2ACI/OT.I does work (it seems) , but stops charging once it hits 3.6v. When the battery was new, I would start off at 3.8v. Is this normal, or should it charge it up again to 3.7/3.8?Im using a 2k resistor, so I should charge 500mAH (i think).Any advice would be appreciatedThanks

author: amyk
author_rank: Super Contributor
timestamp: September 12, 2013, 11:54:09 am
content: What is the voltage of the power supply? This a linear charger and requires at least the termination voltage (4.2V) to fully the battery. The datasheet gives 6V as the recommended maximum input voltage.

author: Zbig
author_rank: Frequent Contributor
timestamp: September 12, 2013, 12:01:18 pm
content: Proper Li-Po charging cycle is Constant Current phase until the cell voltage reaches 4.2V then Constant Voltage phase (so the voltage doesn't exceed 4.2V) while the current gradually lowers until it reaches termination value. If the cell voltages you posted are across open terminals, that doesn't tell you much as it drops quickly once disconnected from charger.

author: ovnr
author_rank: Frequent Contributor
timestamp: September 12, 2013, 12:12:32 pm
content: Quote from: Zbig on September 12, 2013, 12:01:18 pmLiPos don't drop to 3.6V, even when they've been disconnected for a long time. I've got ones that have been sitting in a box for a couple years, and even they are above 4V.

author: olsenn
author_rank: Frequent Contributor
timestamp: September 12, 2013, 12:28:28 pm
content: I got a lipo charger at MacDonald's today; it was delicious!

author: Zbig
author_rank: Frequent Contributor
timestamp: September 12, 2013, 01:21:47 pm
content: Quote from: ovnr on September 12, 2013, 12:12:32 pmYou're right it shouldn't drop that much but still the measurements should be performed during the charging. By the way, it's not a good practice to store the Li-Pos in fully charged state for prolonged periods. Optimal storage voltage is around 3.8V/cell.

author: Jibby
author_rank: Contributor
timestamp: September 17, 2013, 06:20:53 am
content: Single NiCd, NiMh or Lion batteries are 1.2 volts .So 3 numbers in series makes it 3.6V. It can get charged to n3.7 or 3.8 developing no problem on the batteries but once the charge is removed it goes back to 3.6 volt in.

author: dr_p
author_rank: Frequent Contributor
timestamp: September 17, 2013, 07:39:04 am
content: Quote from: Jibby on September 17, 2013, 06:20:53 amYou got this all wrong. AsingleLithium-xx cell has 3.2-3.7V and charges at 3.7-4.2V. Depends on the chemistry (ion, po, Fe).

author: Zbig
author_rank: Frequent Contributor
timestamp: September 17, 2013, 11:34:38 am
content: Quote from: Jibby on September 17, 2013, 06:20:53 amSorry Jibby, but that's not the case at all. Lithium-based secondary cells are very differrent to Nickel-based chemistry ones in almost all respects. Li-Ion/Po cells require very strictly controlled charging process, otherwise that's what happens:I found this website a very good resource on everything battery related:http://batteryuniversity.com/

author: amyk
author_rank: Super Contributor
timestamp: September 17, 2013, 11:55:25 am
content: Quote from: Zbig on September 17, 2013, 11:34:38 amAnyone who considers putting 10A(!!!) through a 1.2Ah cell deserves a Darwin Award... yes lion chemistry does have a really high energy density and require good voltage regulation at termination but charging them is less involved than the algorithms for nickel-based chemistries. Fireworks tend to occur only if you seriously act like an idiot with them.

author: peter.mitchell
author_rank: Super Contributor
timestamp: September 17, 2013, 03:07:58 pm
content: Lithium-Ion Polymer cells can be charged somewhat safely with a 4.2v power supply and a current limiting resistor of appropriate power rating and resistance.With that said, Lithium-Ion Polymer cells should probably not be charged with a 4.2v power supply and a current limiting resistor of appropriate power rating and resistance.