On Fri, Feb 19, 2010 at 10:42 AM, Tim Wescott <[email protected]> wrote:
> 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 > The more common term that I've seen used is "deep cycle." -wes _______________________________________________ PLUG mailing list [email protected] http://lists.pdxlinux.org/mailman/listinfo/plug
