Martin Catt
April 19th, 2008, 09:42 AM
... an XL2 battery? I had one of my after-market BP930-equivalent XL2 batteries finally quit taking a charge after about a years' use, so being the inquiring sort of fellow, I decided to open it up and do a post-mortem.
DISCLAIMER: before any of you have a apoplexy, understand that I do similar work in my paying job, and am used to dealing with small, complex structures that contain potentially dangerous electrical charges and hazardous materials. I don't recommend people cracking open their batteries if they don't know what they're doing.
There were no real surprises. I used diagonal cutters to clip through the corners of the thin plastic cover. Inside are four 3.7 volt, 2000 mAh lithium cells, wired together in a series/parallel configuration to provide 7.4 volts at a listed 3600 mAh (don't ask me where the extra 400 mAh went to). Photo 2 shows the end view, where a small surface-mount PC board has two integrated circuits, plus four chip capacitors and four resistors. Based on the connections to the board, I'd guess they are part of the charging and charge-monitoring circuit. The remaining photos show different angles, plus the circuit board and paper insulator removed and next to a dime for scale. The whole assembly was held together with double-sided tape, which is actually just fine, considering how snugly everything fit inside the plastic case with nearly zero clearance.
The last photo shows the real prize: the bottom plate with the mounting lugs and power contacts. This is what I really wanted, so I can build a regulated adapter to convert 12 volts down to 7.4 volts to run the XL2 off a belt of lead/acid gel cells. I already made one that uses the AC adapter plate plugged into an external box, but the intention is to build the entire regulator circuit on the salvaged plate and run the unregulated 12 volts to the new adapter.
As for the cause of death, I found a small piece of metallic trash wedged between two pins on one of the integrated circuits, obviously debris that got sealed inside the housing when the unit was assembled.
Hope you enjoyed the tour. BTW, the old cells are going off to a recycle center.
Regards;
Martin
DISCLAIMER: before any of you have a apoplexy, understand that I do similar work in my paying job, and am used to dealing with small, complex structures that contain potentially dangerous electrical charges and hazardous materials. I don't recommend people cracking open their batteries if they don't know what they're doing.
There were no real surprises. I used diagonal cutters to clip through the corners of the thin plastic cover. Inside are four 3.7 volt, 2000 mAh lithium cells, wired together in a series/parallel configuration to provide 7.4 volts at a listed 3600 mAh (don't ask me where the extra 400 mAh went to). Photo 2 shows the end view, where a small surface-mount PC board has two integrated circuits, plus four chip capacitors and four resistors. Based on the connections to the board, I'd guess they are part of the charging and charge-monitoring circuit. The remaining photos show different angles, plus the circuit board and paper insulator removed and next to a dime for scale. The whole assembly was held together with double-sided tape, which is actually just fine, considering how snugly everything fit inside the plastic case with nearly zero clearance.
The last photo shows the real prize: the bottom plate with the mounting lugs and power contacts. This is what I really wanted, so I can build a regulated adapter to convert 12 volts down to 7.4 volts to run the XL2 off a belt of lead/acid gel cells. I already made one that uses the AC adapter plate plugged into an external box, but the intention is to build the entire regulator circuit on the salvaged plate and run the unregulated 12 volts to the new adapter.
As for the cause of death, I found a small piece of metallic trash wedged between two pins on one of the integrated circuits, obviously debris that got sealed inside the housing when the unit was assembled.
Hope you enjoyed the tour. BTW, the old cells are going off to a recycle center.
Regards;
Martin