DC distribution in the Home

As more "alternative" intermittent sources are added to the grid, stability and availability may become an issue. Due to horrible customer service, spam calls, and slow backhaul, we recently moved from Frontier FIOS to Comcast Business, and our phones from Frontier to Ooma.

A downside is that the Ooma Telo base station, and the base station for our cordless phones, and the internet access point will all fail if incoming power fails. Since our power is supplied via 70kV lines on poles along Beaverton-Hillsdale Highway, and traffic accidents are increasing as drivers flout traffic laws and distract themselves with dodopaddles, a 70 kV supply pole will come down sooner or later, which translates to a week or more without electricity while major repairs are scheduled, provisioned, and implemented.

To supply essential communications, we will need standby battery/generator power to these items:


Comcast Phone interface




Comcast Internet interface




WIFI access points



Power over ethernet to three buck converters






ALIX firewall



ethernet hub




cordless telephone base station




2 Laptop cradles



car charger adapters?

I would like to distribute 24V through a "standard" UL approved connector that cannot be confused with house AC power, and use buck converters to drop the voltage from 24V to the various low power appliances. WHAT IS THE STANDARD? One possibility is oddball twistlock plugs normally used for 240V; alternatively, the triangularly-arranged line plugs used in Australia are a possibility; they may be approved by Australian UL, but the Oregon electrical inspectors may disagree.


In addition, a "nice to have" would be keeping the refrigerators, a microwave oven, and the gas furnace motor and gas water heater running.

Smart Plug and Receptacle Standards

The Power Source Enforces Safe Operation, Not the Mechanical Connection

An emerging standard is Power Over Ethernet (POE), which moves current through ethernet signalling pairs, less than 100 watts. The setup uses signalling to negotiate the needs of the device and the capabilities of the power source; perhaps the signalling method can be generalized to any DC power source and device, and any plug/receptacle pair.

The circuit starts out unpowered. A low voltage (50 mV?), low frequency (200 KHz?) signal queries the receptacle continuously (500 millisecond intervals?), looking for "smart devices", perhaps just a cheap standardized piezo resonator as an indicator that a smart device has been connected. If one is detected, a slightly higher power modulated signal is sent to power and query a chip connected to the resonator, and extract a kilobit ID string (ICID?). The power source uses that ID to query a local database of devices and operating behaviors; if the device isn't found, or the database is stale, the source queries a server on the internet for an individual device's power needs (voltage and maximum current), behavior, and power-up testing requirements.

The smart power source turns on the circuit according to the power-up sequence specified by the device manufacturer. This sequence can be designed for safe operation, and adapt to recent information about device defects. This might run the powered device in a reduced capability mode, which is better than discarding it if it still be operated safely.

This can be exceptionally safe and abuse-resistant. The receptacle will be unpowered and inert until a compatible device is plugged into it; the baby can stick a fork or his fingers into the socket without drawing more than a few microamps of low-voltage low-frequency AC. Rewiring the device plug for an oddball, insufficiently powered socket could result in baking the connector - but why not build a second resonator into the plug, to indicate whether it has been monkeyed with?

Library books - none satisfying yet

Multnomah County Library, 2018 January

Battery Chart


Gassing Voltage Bulk Charge

14.2 to 14.6

Absorption Voltage

13.6 to 13.8

Full Battery at Rest

12.8 to 12.9

Half Empty Battery


Empty Battery


DChouse (last edited 2018-02-01 22:40:50 by KeithLofstrom)