Someplace in South King County; October 2008 --
Late last summer, the Grand Mother and I finally decided to upgrade our home heating system with an air-to-air heat pump, using our existing oil-burning furnace as a supplemental heating source (necessary when our damp outside air gets lower than about 32 degr F.). One contractor gave us a reasonable bid, but was ultimately unable to satisfy Grumpy's requirement to exploit the full capabilities of the three-speed air-mover included in our existing furnace. Thus, the development of a single-module relay logic package was conceived.
Having the advantage of access to a family member who contracts to do various kinds of electrical wiring and module manufacturing, Grumpy undertook the design of the electrical schematic of the relay logic module (RLM) and depended on the skills of his trusty son-in-law, Chief Manufacturing Engineer, to figure out how to package it into a unit that would install in a small space (2.25" x 4.50" x 7.50") within the blower compartment.
The electric input signals (32 vac, nominal) into the RLM all emanate from an electronic interface unit provided as part of the heat pump installation. The outputs of the RLM are 120 vac power, controlling the three speeds of the air-blower (fan) and powering the oil-burner of the furnace.
The photo above shows the RLM as it was received from the manufacturer. Its overall dimension is about 2.00" x 3.00" x 4.25" -- well within the maximum specified dimensions of the space into which it had to be installed. The input signal wires are contained in a seven-wire (two spares) bundle 60" long, permanently attached to the RLM. This input signal cable had to be snaked through a 5/16" hole from the blower compartment, to the electronic interface unit mounted on the outside of the hot air bonnet. The manufacturer provided 24" lead wires with mating connectors attached to one end of each; these lead wires were of #14 gage stranded wire to provide the electrical power to the three different speed windings of the blower-motor and to the furnace burner. One of the lead wires provides 120 vac power into the RLM, which the relays then switch to the appropriate output lead wire.
The last photo shows the RLM sitting cozily in its final resting space; the wires on the right with the orange twist connectors, are the connections to the three speed windings for the blower-motor. The orange twist connector just left of center is the connection for the furnace burner. The mass of wires seen on the extreme right of the photo are mostly unused, being the remains of relay and power wires installed by the heat pump contractor; these will all be removed eventually. Grumpy also intends to use cable ties to "neatenify" the multiple wires that currently are wending their way loosely about the compartment.
The manufacturer and Grumpy are considering making a standardized version of the RLM for sale to Heating, Ventilation & Airconditioning contractors who might be faced with a challenge such as was met here. We are currently looking at improvements to the design, such as time delays (to prevent the blower from starting until the heat-exchanger has gained some heat -- the Grand Mother has already raised serious, potentially LMP-limiting objections to the cold blast of air she felt when the "heat" came on in the bathroom!) and provisions for alternative motor configurations, such as capacitor-run (versus capacitor-start) type single phase, multi-speed motors.
Having the advantage of access to a family member who contracts to do various kinds of electrical wiring and module manufacturing, Grumpy undertook the design of the electrical schematic of the relay logic module (RLM) and depended on the skills of his trusty son-in-law, Chief Manufacturing Engineer, to figure out how to package it into a unit that would install in a small space (2.25" x 4.50" x 7.50") within the blower compartment.
The electric input signals (32 vac, nominal) into the RLM all emanate from an electronic interface unit provided as part of the heat pump installation. The outputs of the RLM are 120 vac power, controlling the three speeds of the air-blower (fan) and powering the oil-burner of the furnace.
The photo above shows the RLM as it was received from the manufacturer. Its overall dimension is about 2.00" x 3.00" x 4.25" -- well within the maximum specified dimensions of the space into which it had to be installed. The input signal wires are contained in a seven-wire (two spares) bundle 60" long, permanently attached to the RLM. This input signal cable had to be snaked through a 5/16" hole from the blower compartment, to the electronic interface unit mounted on the outside of the hot air bonnet. The manufacturer provided 24" lead wires with mating connectors attached to one end of each; these lead wires were of #14 gage stranded wire to provide the electrical power to the three different speed windings of the blower-motor and to the furnace burner. One of the lead wires provides 120 vac power into the RLM, which the relays then switch to the appropriate output lead wire.
The last photo shows the RLM sitting cozily in its final resting space; the wires on the right with the orange twist connectors, are the connections to the three speed windings for the blower-motor. The orange twist connector just left of center is the connection for the furnace burner. The mass of wires seen on the extreme right of the photo are mostly unused, being the remains of relay and power wires installed by the heat pump contractor; these will all be removed eventually. Grumpy also intends to use cable ties to "neatenify" the multiple wires that currently are wending their way loosely about the compartment.The manufacturer and Grumpy are considering making a standardized version of the RLM for sale to Heating, Ventilation & Airconditioning contractors who might be faced with a challenge such as was met here. We are currently looking at improvements to the design, such as time delays (to prevent the blower from starting until the heat-exchanger has gained some heat -- the Grand Mother has already raised serious, potentially LMP-limiting objections to the cold blast of air she felt when the "heat" came on in the bathroom!) and provisions for alternative motor configurations, such as capacitor-run (versus capacitor-start) type single phase, multi-speed motors.
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