Print
Category: Hardware hacking
Hits: 3692

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/NDescription
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