Revision A of the TOY battery board did not have a cutoff circuit, to stop the Lithium battery discharging beyond its allowed level if the MicroVAX was left unpowered for too long.
So, a new board was designed and built, that uses a AP9101CK6-ANTRG1 battery protection IC.
In addition, arrangements have been added to allow the board to be fed power from a standard power supply – using a Molex hard-drive type connector. A “battery output” connector was added so the TOY board can be connected to any main board that expects a 3.6V NiCad battery. So – it can be used with machines such as the MicroVAX 2000, MicroVAX 3100, and numerous old PCs (286/386/486) that use a 3.6V NiCad rechargeable, often called a “BIOS” or a “CMOS” battery.
The TOY Battery Board includes a diode (actually two BAT54C diodes in parallel) connected in series to the Lithium Ion battery positive terminal, so whatever charge circuit is present on the motherboard side is disabled, and charging is taken care of exclusively using the MCP73833 IC on board, which is fed 5 Volts from J2/J3, or from the Molex connector (P1) .
Below you can find photos of the finished board, all production files have been placed on github.
A Quick roundup of the TOY Battery Board Features:
- Modern Li-Ion battery replacement for old rechargeable NiCad 3.6V batteries
- Drop-in replacement for KA630/KA650/KA655 FUNCT SEL/SLU MODULE battery board
- Also usable on any other main board with a 3.6V rechargeable battery pack connection arrangement
- Uses one Lithium-Ion type 14500, 1200 mAh rechargeable battery
- Expected battery backup time calculation:
Assuming MC146818 RTC chip and a typical 14500 1.2Ah battery:
- Conservative: 0.75Ah usable, 110uA discharge: 9 months
- Typical: 0.9Ah usable, 85uA discharge: 14 months
- Discharge cutoff to protect battery from over-discharge (at ~ 3.3-3.4V)
- Charge time: approx. 3 to 4 hours to full charge