| Don S 2005-05-22, 10:52 pm |
| In article <3d71919alco4nhjicgdh37atfldcoeu8sa@4ax.com>, moc.enilepip@ykkams wrote:
>Most of the sites here (I am in a rapidly urbanizing suburb which
>borders on rural areas) are served by sites which have slab-mounted
>enclosures which are weathertight without having a full pre-fab
>housing. These seem to have their own HVAC internally, but do not have
>anything more than the manual transfer switch and generator jack.
Sorry, in my earlier comments, I thought you were referring to a building with
a MTSO/CO/cell site. The Outside Plant Cabinets do have self contained HVAC
units. Usually, only critical locations have a gen-set.
>I'm not sure if there are batteries in there, as there doesn't seem to
>be much room. Even if there are, this couldn't run very long given the
>typical powe failure duration in these parts.
The cabinet contains power and batteries, usually in the form of
"mono-blocks". These are similar to a car battery, in that each unit contains
6 * 2V cells, for 12V. The rule of thumb is to provision for 8 hours
backup, but actual run time may be much less. As you noted, if it gets too
hot in the cabinet, the radio/telecom gear will shut down before the batteries
die.
>
>In the late 80's/ early 90's I did work in the AMPS cellular industry.
>This was a time when PCS was called "CT2." I understand things have
>changed. Back then, I was with a "B carrier" whose sites mostly AT&T
>equipment which had banks of glass jar batteries along one side of the
>wall. My impression is that these sites were built to remain up for
>several days.
Those are called wet cells. Valve Regulated Lead Acid (VRLA) batteries were
introduced as a "maintenance free" alternative to wet cells. They use a gel
instead of the water. Unfortunately, they have proved to have a much shorter
life span (~5 to 7 years) vs the 20+ years you can get out of a properly
maintained set of wet cells.
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