Keith Lofstrom wrote: > On Fri, Feb 19, 2010 at 10:01:25AM -0600, Fred James wrote: > >> "but not with a 0V battery" - I don't know - from the documentation one >> might expect the BBU to shutdown leaving some "reserve" power in the battery >> Now, Verizon "tech" did say the aux port wasn't hooked up, but APC >> couldn't understand that statement - i.e.: APC's documents contradict >> Verizon's statement - but I don't know how to verify that either way? >> > > Verizon is not in the business of telling the truth. They are in the > business of keeping their equipment safe from hardware hackers like us. > Obviously, there are risks, starting with some clown hooking a car > battery backwards into that port. If I was programming an Indian call > center, I would have them say whatever was necessary to keep people like > us from fooling with the customer equipment. I'm grateful that they > were willing to help me plug into the ethernet port on the ONT, rather > than route through the Actiontec cable modem as originally installed > (another story). They could have told me to jump in a lake. > > The aux port does hook up to the aux indicator light, and there is a > 12.5V threshold, so it is not just a matter of an otherwise-unconnected > LED and resistor. I imagine that under the right circumstances, the > port will provide power though the BBU. > > I'm guessing that replacing the good battery with an almost-but-not-quite > discharged one will cause the main BBU to draw power from the aux port. > The BBU control circuitry that does the switching may be powered off the > main internal battery, drawing a trickle of current. > > If the external APC unit has a charger, then that is good news, because > it means the main APC unit is not trying to charge it, and probably > does not care how big the external battery is. Car batteries are much > cheaper per watt-hour than the small gel cells, and you can keep them > on a trickle charger. In extremis, you could even power the unit from > the battery in a car, BUT DO NOT CONNECT IT WHEN THE CAR IS RUNNING, > the ignition spikes would likely kill the APC BBU. > > If you're looking for inexpensive lead-acid batteries for this service, look to deep discharge marine, RV or golf cart batteries. Car batteries are optimized to generate LOTS of current for a short time, and are presumed to rarely get deeply discharged. This is because that current is needed, and they generally still have considerable remaining capacity when they're too 'dead' to turn an engine. As a consequence of being optimized for low price and high current output they don't do a good job controlling where the material plates on during charge after a deep discharge, so they tend to suffer an early death if they go through too many deep discharge/charge cycles.
There is considerable collected wisdom on this subject in the amateur radio literature, from folks building emergency-power stations suitable for the aftermath of fire, flood, and earthquake. They all say "don't use car batteries". Anything called "deep discharge" will (well, should) be designed to be deeply discharged -- and recharged -- on a regular basis, and will probably severely compromise cold cranking amps while doing so. -- Tim Wescott Wescott Design Services Voice: 503-631-7815 Cell: 503-349-8432 http://www.wescottdesign.com _______________________________________________ PLUG mailing list [email protected] http://lists.pdxlinux.org/mailman/listinfo/plug
