1

I just got in a LiPo charger (ptr-10401) and I want to use it to (yes I know slowly) charge a 24.8 Whr Lithium Polymer battery.

My question is pretty simple. Does this device contain the required logic to safely charge this battery? Meaning, if I were to plug it in and leave it would it be safe (I am not going to do this)

I was looking for laymen documentation or a tutorial but the only thing I could find was the VERY detailed documentation for the LiPo charger.

It's still to far beyond me (but I am trying, I just got Circuit Analysis for dummies)

Below are the parts and the links

I haven't hooked anything up. I want to make 100% sure this is a safe method for charging before I do this.

https://www.sparkfun.com/products/10401

enter image description here

http://www.ebay.com/itm/New-Internal-Battery-replacement-dajn-fit-for-iPad-1st-gen-/231044587897

enter image description here

Community
  • 1
DotNetRussell
  • 289
  • 2
  • 7
  • 19

2 Answers2

1

LiPo chargers have 3 stages and is completely safe on bigger batteries of same cell voltage.

The CC stage is 1st will limit current and just be a much longer duration. Safe.

The CV stage is 2nd and stay there until current drops below expected leakage thresholds. Safe.

Shutdown or charge-completed is the 3rd stage. Safe.

CC means constant current and some fast chargers will be designed for say C/10 or C/20 meaning Ah capacity /10 or /20, for example. There is no universal current value for all LiPo batteries.

Just be sure the cell string voltage is the same before stage 2.

user28288
  • 11
  • 1
  • So what you mean is get out my multimeter after stage 1 and make sure that the reading is equivalant to the labeled voltage of 3.75? – DotNetRussell Aug 31 '13 at 22:51
1

Having used the Sparkfun battery charger you listed (and in general designing with the Microchip MCP73831 battery charger), I have found that while it is supposed to be be safe, the Sparkfun device will get alarmingly hot when charging a large, almost empty battery from 5V USB power. I suspect this is simply due to the linear nature of the battery charger and the small un-heatsinked package., but I would be a bit weary of leaving it plugged in unattended because of this.

Zuofu
  • 4,168
  • 2
  • 21
  • 36
  • would you suggest dialing down the voltage from the 5V with some resistors before feeding it into the charging unit? – DotNetRussell Aug 31 '13 at 23:05
  • also, given what we know about how resistance works wouldn't you say that the device getting hot is a natural bi-product of it working and controlling the flow of voltage? (not playing devils advocate or trying to snark you I am actually asking because I know nothing about this stuff) – DotNetRussell Aug 31 '13 at 23:07
  • In theory the device has an internal thermal shutdown (which is supposed to kick in at 150C) and programmable charge current. The way it is used in the Sparkfun charger, Rprog = 2K, so the charger current seems to be at the maximum specified limit of 500mA. It is probably fine, but for a large battery, you can change Rprog to something bigger to limit the current (Ireg = 1000V/Rprog) – Zuofu Aug 31 '13 at 23:12
  • Do you know if there is a suggested operating time frame? – DotNetRussell Aug 31 '13 at 23:12
  • According to the datasheet: "The MCP73831/2 devices limit the charge current based on die temperature during high power or high ambient conditions. This thermal regulation optimizes the charge cycle time while maintaining device reliability." So I guess it just gets up to 150C, and then it shuts down. It seems like an odd way to operate, but I guess it's "just supposed to do that". – Zuofu Aug 31 '13 at 23:15
  • this seems to be charging at an alarming rate. It is going at about .010 every ~7 sec does this sound right? – DotNetRussell Aug 31 '13 at 23:35
  • If my math is right ((3.75/.01)*7)/60 then it seems this battery will charge in ~43 min – DotNetRussell Aug 31 '13 at 23:36
  • it seems to have slowed down now. Once it hit 3.1 on both batteries it is going at about .001 ~7 sec now – DotNetRussell Aug 31 '13 at 23:39
  • 1
    That seems about normal, if the initial cell voltage is low, it will just be current limited. Once it goes into constant-voltage mode, it will slow way down. – Zuofu Sep 01 '13 at 00:12