A very long piece of resistance wire acts as a very low power heater. It has three sections of heating long coils spread over the whole blanket. By using 4 throws selector switch to make those coils joint in parallel or series to achieve simple high,medium and low heating. Inside also enclose a temperature cut off switch in case blanket is overheated.
An electric blanket has a long resistance wire. The amout of power or heat generated depends on the switch setting. The switch causes the phase of SCR (or triac) firing to change and thus increase or decrease the RMS current.
What is changed by the switches is how the heater wire or wires in the blanket are connected to AC power.
There are several ways to install heater wires in the blanket, here are two :
1. Two heater wires are in the blanket, spread out so either one can heat the blanket. Each heater wire has two connections to the blanket connector, so there are four connectors in the blanket connector and four wires in a cable going from the blanket connector to the switch. The heater wires are not connected to each other.
High - the heater wires are connected in parallel by the switch, within the switch.
Medium - one heater wire is electrically connected by the switch to AC.
Low - the heater wires are connected in series by the switch, within the switch.
Off - no connection to any heater wire
2. Two heater wires are in the blanket, spread out so either one can heat the blanket. One end of one heater wire is connected to one end of the other heater wire. The free end of each heater wire, and the dual-connection end of the two heater wires, is connected to the blanket connector, so there are three connectors in the blanket connector, so there are three wires in a cable going from the blanket connector to the switch.
High - the heater wires are connected in parallel by the switch, within the switch.
Medium - one heater wire is electrically connected by the switch to AC.
Low - the heater wires are connected in series by the switch, within the switch.
Off - no connection to any heater wire
There is no requirement the heater wires be identical, but for manufacturing simplicity, they should be.
An old blanket probably has separate elements and High runs both of them, Low the smaller one, and Medium the bigger one.
A new one might have a TRIAC control I suppose
I just read a question about the power and voltage of an electric blanket. Two people worked the formulas and gave a good number. A real blanket has a High, Medium, Low and Off switch: so what is really changed by the switches?
