Update: We went with Custom Arduino-based LVD solution for this project.
The LVD Project is great, but relatively complex -- overkill for some applications. A more static circuit could be made with a zener diode, a signalling LED, and possibly a relay (for actual switching)
This is a zener-based circuit. An interesting reference is at http://pubpages.unh.edu/~aperkins/pdf/Misc-devices/unijunction.pdf --- highly recommended, but a bit technical.
A subset of an LVD (or a starting point) is just the "detection" (signalling) portion:
A prototype is about the area of a dime, with only 6 components:
This working model lights up right at 10.7v, indicating sufficient voltage for a specific application (SLA batteries with 15w fluorescent load).
Parts
| P/N | Description |
|---|---|
| 743550 | 10v zener diode, 5240 |
| 38359 | 3904 NPN transistor |
| 333201 | small LED (t1) |
| 691340 | 100k Ohm resistor |
| 691104 | 10k Ohm resistor |
| 690865 | 1k Ohm resistor |
Wire the LED-side of the transistor over to an appropriately-sized relay and you get the actual protection circuit. For better usability, green and red LEDs can be added on the open/closed size of the relay as well, to indicate low/high voltage conditions.
For lower-power applications I found a Bestar BS-102B relay -- 12V SPDT, switches 2A, and draws less than 200mW.
This email address is being protected from spambots. You need JavaScript enabled to view it. (or comment in G+) if you're interested in this as a kit or working unit. The PCB is annoying to source, but the rest of the parts are $18 for qty 100 via Jameco
