[PLUG] experiments - OT: FiOS auxiliary power for BBU
Fred James
fredjame at fredjame.cnc.net
Fri Feb 19 16:07:55 UTC 2010
Tim Wescott wrote:
> Fred James wrote:
>
>> Keith Lofstrom wrote:
>>
>>
>>> I fiddled a bit with the "Auxilliary Power Supply DC 12V" input to
>>> my FIOS BBU.
>>>
>>> The barrel connector seems to be a 0.15 inch barrel (approximately
>>> 6mm), center positive. I clipped the connector and cable off an
>>> obsolete wall wart, and proceeded. This is the same power connector
>>> as some of the older Nokia cell phones, IIRC.
>>>
>>> I set up a lab bench power supply with current and voltage limits,
>>> and connected it to the cable. When I increased the voltage above
>>> 12.5V , the "Auxilliary Power Source" light on the front panel lit
>>> up. The BBU drew less than 10mA. I dialed it up to 13.5V, about
>>> what a car battery puts out, and set the current limit to 5 amps.
>>> Since the unit draws 20W from the line in normal operation, I
>>> assumed that would be enough.
>>>
>>> I pulled the line power input to the BBU, the unit went on battery
>>> as intended. I pulled the internal battery connection, hoping it
>>> would use the auxiliary power instead of the internal battery,
>>> and the BBU shut down, without drawing current from the auxiliary
>>> jack and bench supply. It might have been a startup surge, so I
>>> tried again with 0.086 farads across the supply. Again, shut
>>> down, no current from the bench supply. I don't want to try a car
>>> battery directly, too much current if something shorts.
>>>
>>> So - a mystery. Perhaps there is some protocol on the wire to the
>>> approved external device. For extended life, use an external UPS
>>> on the line input, I guess.
>>>
>>> Keith
>>>
>>>
>>>
>> Keith Lofstrom
>> According to what I have read (online manual for the unit I have
>> (CPL28U12) - you didn't mention your model) ... you are/were almost
>> there ... there is (again, on my model) a button marked "Battery
>> Emergency Use" (next to the Alarm Silence button), which (although
>> Verizon fails to mention it in their documentation) is intended for
>> emergency use as follows ...
>> "Press the button once to use the reserve battery capacity and/or
>> the auxiliary battery capacity after low battery shutdown. The unit
>> will emit a confirmation beep."
>> ... as an additional note, the battery is a 12 V 7.2 AHr battery - I am
>> not sure what that would equal in amps from a bench power supply,
>>
> Amp-hours vs. amps isn't entirely meaningless, but it's not terrifically
> meaningful in a battery vs. bench supply shoot-off. Battery capacity is
> rated in amp-hours, which along with the voltage tells you roughly how
> much energy is stored in the thing. A battery's ability to deliver
> current is measured in amps. All else being equal, a bigger amp-hour
> rating indicates a greater ability to deliver current, but there are
> potentially huge differences in construction from one battery to the
> next which drastically affects the capacity vs. current-delivering
> capability trade off.
>
> (Having said that, most sealed gel-cell batteries for equipment power
> use are mostly designed for a minimum 10-hour discharge time, meaning
> you wouldn't want to pull more than 720mA out of that 7.2A-hr battery,
> and you could expect it to last 10 hours in that service).
>
> Putting a bigger battery on there will give you a longer discharge time,
> but may confuse the heck out of any charging circuit they may have built
> into the thing.
>
>> but I
>> don't think that was the cause of the NoGo in your test, as you didn't
>> mention pushing the Battery Emergency Use button.
>> Thanks for the input - that sounds (correct me if I am wrong) as if one
>> were to connect the free ends (say with alligator clips attached?) of a
>> cable of the description you gave above to a fully charged 12 V 7.2 AHr
>> battery (i.e., the same type as the one in the unit itself), and the
>> barrel end of that cable to the BBU auxiliary port provided, one could
>> be good to go? First making sure polarity on the cable was correct, of
>> course.
>> Regards
>> Fred James
>>
Tim Wescott
Thank you for the clarification
The APC documentation indicates stringing one or more "battery packs" to
the BBU - if one were to try to duplicate this with just batteries and
wire, I am assuming (pardon my ignorance here) that one would want to
wire those extra batteries in parallel - is that true? IIRC parallel (+
to + and - to -) delivers the same current but for longer, and series (+
to - as in a flash light) delivers a higher voltage but not for longer?
Thanks again
Regards
Fred James
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