Interesting Commentary on Modern Transformers

[prewardude]

I'd say this about sums it up:
http://prewartimes.blogspot.com

Regards,
Clint

[Anonymous]

OK, How many of us have old PostWar E-units that buzz like crazy from the AC current running through them, even when it's a "pure" sine wave? The modified output of SOME of these modern power supplies can cause problems. They also allow higher end units like the TPC's to perform pretty nifty tricks like allowing locomotives without built in cruise control technology to creep around a layout without modifiying the engine.

Transformers come in two flavors, ones that were designed/work well and ones that don't. This was just as true in the pre-war era, post war era as it is today.

chuck

[wrmcclellan]

I agree with Chuck. Many early transformers were dangerous. Those that have survived were the ones that were better designed.

[lionelsoni]

I have to disagree with you, Roy, about things running cooler. Take the HO case of a DC motor, for example. If the chopping is very fast, the motor inductance blocks it and the motor runs pretty much as if it were powered by DC equal to the average of the chopped waveform, so the motor runs neither hotter nor colder.

If the chopping is slower than that, however, the motor current is governed by the armature resistance, with the inductance playing a negligible role. Suppose that the motor has an armature resistance of 1 ohm and is driven from a supply with an average voltage of 6 volts. If the supply is DC, the current depends only on the motor's load and could be nearly zero. But, if it is a 50-percent chopped 12-volt waveform, the instantaneous supply voltage is always 6 volts different from the back-emf of the motor; so the motor is dissipating 36 watts at no load!

The situation is not so bad at very low speeds, which is where pulsed power is most useful. A great proportion of the power is still wasted as heat, but it is a large part of a small quantity.

One type, the Faulhaber coreless motor, is particularly vulnerable to burnout when used with other than straight DC. See http://www.worldrailfans.info/forum/viewtopic.php?t=448&sid=1fafdee837e22fc9a154e9db856474de

An incandescent lamp cannot run cooler and still put out the same light, since the brightness of the light depends on the filament temperature.

[wrmcclellan]

OK Bob - I'll edit my post. The lamps will run cooler as they are not putting out the same amount of light when pulsed.