[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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