Rectifiers and Postwar accessories

[nitroboy]

Has anyone used rectifiers to quiet down the noise on some of your postwar accessories? There was an article in one of the CTT magazines a few years back about it, but I can't find it. If I remember correctly they used a rectifier on a gateman to quiet the soleniod down.

Thanks!!!
Dave

[lionelsoni]

This is essentially the same problem as quieting an e-unit. You can put a small bridge rectifier between the solenoid and the rest of the world. The + and - terminals of the bridge go to the solenoid and the ~ terminals connect to whatever the solenoid used to connect to. This may do the job; but the DC waveform that results is still fairly bumpy and some noise may remain. This can be smoothed out with an electrolytic capacitor across the + and - terminals. The capacitor will increase the voltage that the solenoid sees; so you might have to lower the supply voltage to the accessory. The current rating of the bridge will depend on the current drawn; but a 4-ampere bridge should handle just about anything. The capacitor's voltage rating should be about 25 volts. The capacitance will depend on the current and the degree of additional smoothing needed, if any.

[Anonymous]

A bridge rectifier will work with some accessories but keep in mind that some rely on the vibrations to make the unit work. Accessories that use a motor with brushes, a magnet that atracts and holds an armiture, or a solenoid will work on the DC that results. Also be aware that using DC with magnets or solenoids can lead to magnatizing them and result in their sticking and not releasing. This can be a serious problem with the solenoid E units in engins.

[lionelsoni]

I believe that this magnetization problem is a myth. Here is what I said about it a while back:

"It is very unlikely that an e-unit run on AC would ever get magnetized at all. I have rectifiers in my locomotives and no trouble with magnetized e-units. Screwdrivers are very often deliberately magnetized to hold screws; so they are not so good for testing e-unit armatures.

"As e-units wear, they develop notches in the ***es of the drum teeth, which tend to catch the pawl, keeping it from releasing. I suspect that, if you look very closely at the drum, you will see these notches. The vibration of AC-powered e-units tends to mitigate this, giving the impression that magnetization has something to do with it. However, a little whittling to straighten out the plastic teeth or replacing the drum every 40 years or so will also cure the ***-notch problem."

I was surprised to see the asterisks bowdlerizing what I think is an innocent word in this context. Its definition is

"1 : a pole with a forked end used especially as a prop
2 : an angle formed by the parting of two legs, branches, or members"

[4kitties]

I have used full-wave rectifiers for years (since 1999) to quiet my 252 crossing gate and the 145 gateman, with no ill effects. If the solenoid plungers were going to become magnetized, I think they would have done it by now.

[Anonymous]

I am glad that so many of you have had no problem using rectifiers on E units. I have repaired this things many times and have found out that on about 5 percent of them, when all else fails, demagnetizing the plunger and frame would cure the sticking. The same is true for Whistle relays. The problem does exist, if you have not encontered it great for you. If you wi***o use a rectifier, I think it is unnecessary, go ahead but this problem can develop in possibly a small number of cases.

[lionelsoni]

I can understand sticking in a whistle relay, which I have also seen. The relay armature can come into intimate contact with the core, where a very small amount of magnetic charge can produce a large force over such a small distance as a result of the fact that the force between two charges is inversly proportional to the square of the distance. This is the reason for the dropout current of relay to be so much less than the pickup current. A simple cure for the whistle relay is a piece of masking tape to keep the gap from closing quite to zero.

With solenoids, there is no possibility of anything like close contact. Furthermore, the normal operation of the e-unit closely resembles a demagnitization episode: A strong alternating magnetic field is gradually reduced to a low level, albeit not fully to zero. It seems unlikely to me that any residual magnetization of the circuit would be noticeable unless the operation were right on the edge of failure for some mechanical reason (like notches in the drum teeth). If such a second cause accounts for some few examples that can be improved by demagnitization, it would be better to find it.

Why aren't whistle relays demagnitized in the same way in normal operation? The copper slug at the armature end of the core shields that area from the alternating magnetic field, so that the relay does not actuate until DC is added to the transformer's output voltage. And their very different mechanical arrangement is peculiarly sensitive to sticking.