Are Lionel trains AC or DC? That’s a trick question. Traditionally, Lionel trains run on AC but there are exceptions. And even when Lionel trains run on AC, they sometimes do some DC trickery. Let’s explain.

Traditional Lionel trains from before 1969 can generally run on either AC or DC, but are better off running on AC. Some Lionel trains sold in discount stores in the 70s and 80s did run on DC, as a cost reduction measure.

AC and DC on traditional Lionel trains vs modern

are Lionel trains AC or DC

Traditional Lionel transformers like this KW emit AC power for the train, and DC power for the tender when you use the whistle controller.

Traditional Lionel trains used an open-frame motor that technically will run on either AC or DC. This was important early in the 20th century. Most homes that had electricity ran on AC, but there were some parts of the country that had DC power. Some houses didn’t have electricity. In those cases, kids would run their trains off a car battery, which was DC. That’s clever. Not very safe, and I wouldn’t turn my kids loose with a car battery, but it’s clever.

Now, in the 70s and 80s, things changed. Small, cheap DC motors became available. Lionel trains were no longer the hottest thing going, so Lionel wanted to move downmarket to try to increase sales. To that end, Lionel tried putting cheap DC motors and power packs in their inexpensive trains intended for discount stores like Kmart and Zayre. This introduced incompatibility with the higher-end Lionel trains sold in hobby shops, which still ran on AC. It also didn’t revitalize the brand the way management wanted, so Lionel discontinued this practice by the late 1980s.

Attempting to run a DC-powered Lionel on AC causes malfunctions. It’ll make a ton of noise, but it won’t move. If you have one of those trains, power it with an HO scale transformer to keep from burning up the motor.

One downside to using DC on a traditional open-frame Lionel motor is that it can magnetize the reverse unit over time and eventually cause it to stick.

Another downside to using DC is it interferes with the whistle unit in the tender.

The Lionel whistle and DC

Lionel used a clever trick with its whistling tender. Once AC was firmly established as the household standard, Lionel pulled a MacGyver move to control the whistle in its tender. The tender contained an electric motor, a relay, a fan, and a whistle. By injecting DC power on the track in addition to the AC, Lionel could activate the relay, which in turn activated the motor in the tender to blow the whistle. The motor in the engine didn’t mind the DC and continued to run, and the motor in the tender ignored the AC.

The problem with this is that if you use DC power to run the locomotive, the whistle in the tender blows all the time.

Modern Lionel trains and DC

Modern Lionel trains generally use the cheaper DC motors, but include electronics that rectify AC power to DC. In theory these trains should be able to run on DC as well. In practice, I’ve heard people say not to do it, and I’ve heard people say they do it. Having not done it myself, and not knowing who to believe, I recommend using modern Lionel AC transformers on modern engines.