Capitol Park

Table of contents


This site is located at (47.623722°, -122.315161°) on an 11 story building, along the elevator shack.


Three sectors provide 360 degree coverage. Sectors are single polarity only (horizontal).



Long term plans for backup power are in flux, as we coordinate with other local users on a larger system for the gear on site.

In the meantime, a small amount of backup power is available on site, as a 24V 20Ah battery bank. AC power is managed by an APC7900 PDU, AC power is fed into a PoE PDU. The onboard power supply is set to 27.2V to appropriately float charge the lead acid batteries. Power from the PSU is fed to the distribution ports for the modems, and is fed to the battery bank via this simple circuit to provide trickle charging, and battery runtime in the case of mains failure.


The onboard PSU draws ~8mA of backfeed power in the case of an AC failure, apparently primarily for the status indicator LED. The resistors in the circuit limit charging currents to ~250mA when the batteries are at 0% SOC (10.65V per batt).

The PoE PDU will load shed modems as the batteries are drained, based on measured battery voltage. The diode bypassing the resistors for battery operation will cause voltage readings to be low by ~0.7V. The sectors will be disabled at approximately 50% SOC. Site router and backhaul link will be disabled at approximately 10% SOC. Power will automatically be reapplied once AC power is restored.

Battery voltage bypassing the current limiting resistors is wired into the ALT bus on the PoE PDU providing for direct voltage monitoring, and a rough indicator of current over the resistors by the voltage difference seen between the MAIN and ALT busses.


Filename Size Modified
capitolhill-240.png 450KiB 2016-08-05 22:35:14
capitolhill-120.png 463KiB 2016-08-05 22:35:14
HamWAN-CPark-Power.png 7.4KiB 2017-11-04 17:57:29