CAR HEATERS.

Electric Heaters for warming cars in winter, consist of iron wire coils which are warmed by the passage of electric current through them. The heat so evolved varies as the resistance multiplied by the square of the current. The iron wire coils of the heater are mounted on non-combustible insulating supports, and are arranged so that there is a free circulation of air through them. The coils are surrounded with a perforated metal case, the object of which is to prevent injury to the coils and to prevent persons or clothing coming in contact with the hot, live wires of the coils. Heaters are sometimes arranged so that they can be connected in series or parallel to give different degrees of heat.

The diagram, [Fig. 29], shows the most common arrangement of electric heaters recently. The tap from the trolley should be taken off on the trolley side of the circuit breaker. After passing through a fuse the circuit goes to the switch. Each of the heaters contains two coils, one of higher resistance than the other. Two independent circuits are run from the switch, through the heaters and to the ground. One circuit passes through the high resistance coils of the several heaters while the other goes through the low resistance coils. The switch has three points. On the first point a circuit is made through the high resistance coils. The second point connects the low resistance coils while the third point puts both circuits in service. With this arrangement three gradations of heat may be obtained.

To avoid complicated wiring sometimes but one circuit is employed. In such a case the heat must either be all on or off, no gradations being possible.

The chief difficulty encountered with electric heaters is the breaking of the wires because of the scale of oxide that forms gradually when they are run at a high temperature or because of water striking them from passengers’ clothing on wet days, which causes the wires to snap.

The Consolidated Car Heating Company gives the following data on the current required to heat cars:

	Length of Car Body.	Amperes.
		Switch Positions.
		1	2	3
Average conditions	14 to 20 feet	3	4	7
	20 to 28”	3	6	9
	28 to 34”	4	7	11
Severest conditions	18 to 24 feet	4	7	11
Severest conditions	28 to 34”	6	8	14

In his Electrical Engineers’ Hand Book, Mr. Foster gives results of tests made on Brooklyn cars as follows:

Cars.			Temperature F.		Consumption.
Doors.	Windows.	Contents cu. ft.	Outside.	Average in car.	Watts.	Amperes at 500 volts.
2	12	850½	28	55	2295	4.6
2	12	850½	7	39	2325	4.6
2	12	808½	28	49	2180	4.3
2	12	913½	35	52	2745	4.5
4	16	1012	7	46	3038	6.
4	16	1012	28	54	3160	6.3

When not watched carefully considerable current may be wasted by allowing the heaters to remain turned on when not needed. Many companies hang out signs where motormen may observe them, indicating when the heaters shall be turned on and to what point.

Fig. 30. Electric Heater.

The best practice in electric heating is to have plenty of heaters and run the wire at a low temperature, rather than attempt to heat with a few at high temperature. The greater the number of heaters the larger the radiating surface around which the air can circulate and a given amount of car heating can be accomplished with less current than with a few high temperature heaters. The depreciation of the heater wires is less the lower the temperature at which they are operated. An electric heater is shown in [Fig. 30].

Hot-Water Heaters are frequently used on large electric cars. Hot-water pipes are placed along the sides of the car, and connected with a stove containing hot-water coils at one end of the car. The water, as it is heated in the stove or heater, expands, and consequently becomes lighter per cubic inch or other unit of volume; it therefore tends to rise when balanced against the colder water in the car pipes. Hot water leaves the top of the heater, flows up to an expansion tank and then down through the car piping, and back to the bottom of the heater. The car piping slopes continuously down from the top connection to the bottom connection of the heater. At the top, an opening to the atmosphere is provided through a small water tank, called an expansion tank. This prevents water pressure bursting the pipes as they become heated, and allows any steam that may have formed to escape. The most modern hot-water heaters for cars are completely closed except as to the ash pit at the bottom and a small feed door in the top. The latter is locked so that the fire cannot come out even if the car is tipped over in a wreck. [Fig. 31] shows the pipes of a hot-water heating installation.

Fig. 31. Pipes for Hot-Water Heating.