I have a Lionel Pacific engine from the 1990's with all it's electronics removed that I had installed a bridge rectifier in to run the DC can motor off of AC track power. My problem is that in doing so the engine now runs way too fast. I tried using resistors to solve this problem but all they did was slow the engine way down for a short time before getting extremely hot and burning up. Is there a way to do this properly? I would like to use this locomotive but need it to run more normally and not so fast. I certainly would appreciate any help.
gandydancer1950@hotmail.com
You might want to try a half-bridge design. That might slow it down. Search the internet for half-wave-bridge circuit.
A dc to dc converter would probably be the most efficient way to reduce it.
The cheapest way would be to use a higher wattage resistor, say 20 watts, with a heat sink. Not very efficient but it would do the job.
The half wave would help too as it would reduce the output voltage.
A half-wave rectifier is just a single diode in series between the supply and the load. So you probably won't find much searching for "half-wave-bridge", since there is no bridge at all. Unfortunately, the half-wave current waveform includes a large DC component, which will tend to saturate and overheat your transformer. You can get away with it if you have a large transformer, like a Z, ZW, or 30B.
A better approach is to stay with the bridge but put extra diodes in series with either the supply (transformer) or load (motor). You can use individual diodes for this or adapt bridge-rectifier module(s). I recommend putting them on the load side of the bridge (between the bridge output and the motor), using the + and - terminals (and leaving the ~ terminals unconnected). Note that these modules are not being used as bridge rectifiers but just as a compact source of diodes for voltage dropping.
Bob Nelson
I would pick up a Williams engine and strip the electronics out of it. You can find new Williams locomotives for under $100. Trainworld has 44-toners for $75. The electronics contained within will operate your DC can motors and give you forward and reverse.
The problem with resistors is that they limit current, not voltage. Use diodes instead:
Dropping Voltage With Diodes
Rob
The general idea is correct; but there are some mistakes on that web site. In particular, half-wave rectification drops the voltage by about 29 percent, not 50 percent. (It looks like 50 percent if you use a common voltmeter intended for sine waves.) The power goes down by about 40 percent, assuming incandescent lamps.
And anti-parallel diode pairs in series in an AC circuit generally drop the voltage by somewhat less than the diodes' forward voltage. The exact amount is a complicated function of the AC voltage used.
BigAl 956 I would pick up a Williams engine and strip the electronics out of it. You can find new Williams locomotives for under $100. Trainworld has 44-toners for $75. The electronics contained within will operate your DC can motors and give you forward and reverse.
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