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I need to charge a small lithium power pack from a device that was originally charged using a 5v USB connection. The connector on the device is damaged so I need to charge the power pack directly.

I'm not very experienced with electrical stuff so I am not sure what kind of connection it has? I've taken a photo of it with a sharpie pen for scale.

I'm assuming a need something like this?

http://www.ebay.co.uk/itm/NEW-5V-Mini-USB-1A-Lithium-Battery-Charging-Board-Charger-Module-WST-for-Arduino-/251447228883?pt=UK_Sound_Vision_Battery_Chargers&hash=item3a8b6c39d3

The power pack has 4 wires. 1 Yellow, 1 Red, and 2 Black.

I don't want to strip or cut any wires so I ideally need to find a female connector of that type with wires I can solder to the USB charger.

Can anyone help with pointers on things to search for and which wires I need to solder to the + and - points?

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  • \$\begingroup\$ The connector looks like Molex PicoBlade. Here's a 4-pin male. \$\endgroup\$ – Nick Alexeev♦ Feb 13 '14 at 1:15
  • \$\begingroup\$ Yes, this is definitely the connection! I can't seem to find any pre wired female connectors though. I can't imagine being able to solder something so small. What would you recommend? \$\endgroup\$ – Plasticated Feb 13 '14 at 1:35
  • \$\begingroup\$ There are quite a few wires pre-crimped with PicoBlade female (this, for example). But you need a wire pre-crimped with a male crimp (electrical maleness and mechanical maleness can be confusing sometimes). Pre-crimped with male crimp may be hard to come by, I suspect. Give fine soldering a try. You could also look for a breakout board, which would accept a PicoBlade with 1.25mm pitch on one side and fan it out to a larger more manageable pitch on the other side. \$\endgroup\$ – Nick Alexeev♦ Feb 13 '14 at 1:45
  • \$\begingroup\$ I have a specialized crimp tool for PicoBlade. If you were in the US, I could crimp some wires and mail them to you. \$\endgroup\$ – Nick Alexeev♦ Feb 13 '14 at 1:51
  • \$\begingroup\$ Can you email me? shealan [at] plasticated .com Happy to pay for postage if you could create a wired female connector. \$\endgroup\$ – Plasticated Feb 13 '14 at 2:02
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The problems started when the USB connector of the original device got damaged. Would it be reasonable to repairing the connector? You could also try to bypass the original connector to feed the charger.

Separate charger approach

The proposed approach with separate charger is sound. However, I would look for a charger, with:

  • A bit less current. Lithium-ion cells should be charged at current of 0.2C to 1.0C. This means that capacity of the cell drives the charge current and charge time. 0.2C is a shorthand which means that the current in [Amperes] is 0.2 of capacity in [Ampere-hours]. Units don't quite match, but again, this is a shorthand. 1A is on the upper side of the range. I would look for something between 0.2A and 0.6A.
  • Published schematic or known part number for the charge controller IC. This improves the chances during troubleshooting.

At the same time, there's nothing fundamentally wrong with the charger, which you've found on eBay.

The battery pack connector looks like Molex PicoBlade. Here's a 4-pin male (p/n 53047-0410).

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It is likely that the black is ground and the red or yellow are the +V line for charging, while the other colored wire is a temperature sensor to avoid battery overheating during charging.

You need a specific kind of battery charging chip to charge this battery. You can't just hook +5V up to it and expect it to not explode.

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  • \$\begingroup\$ One can actually expect it not to explode (albeit at his own risk). A Lithium-ion battery pack must have a built-in circuit, which protects the cells from overvoltage. Then again, not every Chinese sweatshop knows that. \$\endgroup\$ – Nick Alexeev♦ Feb 13 '14 at 1:18
  • \$\begingroup\$ There are square lumps under the side of plastic wrapper of this battery pack which I assume are chips. Probably what that is? \$\endgroup\$ – Plasticated Feb 13 '14 at 1:23
  • \$\begingroup\$ Probably. It looks to me that the protection circuit is on the narrow side of the battery pack, which is the furthest in the picture. About where the wires enter the pack. \$\endgroup\$ – Nick Alexeev♦ Feb 13 '14 at 1:26
  • \$\begingroup\$ @NickAlexeev many battery packs have circuitry to avoid excessive discharge, but no overcharging protection. \$\endgroup\$ – Sparr Feb 13 '14 at 14:21

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