FS Class E646 - Technical Details

Technical Details

Class E.646 does not follow the standard Italian class numbering rules where the last digit indicates the number of motors, as it mounts 12 two by two mechanically coupled 82-333FS type electric motors, each providing {{convert|360 kW, fed from the 3000 V catenary. These motors are more powerful than those mounted on the predecessor E.636 class and able to improve performance up to 50% with only a 20% increase in weight; this also increases the mass available for adhesion, giving it better hauling ability.

Maximum speed is 140 km/h (87 mph) for the E.646. The E.645 has a different gear ratio — 21/68 instead of 25/64 — which reduces the maximum speed to 120 km/h (75 mph), while increasing tractive effort. The locomotives weights 110 t (108 long tons; 121 short tons) (E.645: 112).

To reach higher speeds, the motors can be connected in four ways:

Due to the ability of the DC motors to absorb very high currents at low speeds, a rheostat needs to be connected in series to the traction motors when starting the train, to avoid drawing excessive current. The rheostat is gradually excluded as speed builds up and is also reintroduced when a transition to another is made; like almost every Italian electric locomotive since E.626, rheostatic exclusion is commanded through a controller (formed by a lever mounted on a curved notched support, commonly called respectively maniglione and roncola in Italian) subdivided into several notches, each representing a portion of the rheostat, plus four (one for each combination) special intermediate "end combination" notches.

The driver gradually excludes the rheostat by rotating the lever counterclockwise, paying attention to not exceed the maximum allowed current (in this occurrence, the "maximum current relay", and consequently the "Main Breaker" (IR, Interruttore Rapido) opens), until he reaches the end combination notches, meaning that the rheostat is fully excluded for that combination; at this point, he can pass to the following combination or insert the field weakening shunts to further increase current. There are 31, 11, 9 and 8 notches on the roncola, each representing a portion of rheostat in the respective combinations.

In the 1960s the E.646 locomotives were updated with the standard 78-wire cable, fire extinguishing system and automatic rheostatic exclusion system (Avviatore Automatico) to permit remote commanding by driving coaches on commuter push-pull passenger services.

Air production is granted by two 1000 l compressors, that fill the main tanks used by the braking system and other components (horn, whistle, contactors etc.).

Main auxiliary services also comprehend the 3000 V motor cooling fans, which also are used as generators to produce current used to recharge the 24 V DC batteries, that feed the low tension devices (lights, relays, solenoid valves, etc.).

Some units have also been fitted with static converters to feed auxiliary services and recharge batteries.

Like all non-electronic Italian locomotives, E.646 are technically simple; driving personnel can often easily fix problems and get the locomotive moving for enough time to end the service or at least free the tracks.