Can I install a bridge rectifier from the AC track power source?

[statistician]

Hi all,

I have a Lionel engine with a universal motor and electro-mechanical e-unit  (very loud) that I want to run on DC to minimize the e-unit noise.  All of the posts I read suggest installing a bride-rectifier downstream (inside the locomotive).  I want to keep the engine as it is, but most DC transformers are not powerful enough and do not have a directional control button.

Can I just install a rectifier at the track power source from an AC transformer?  I'd be using an AC transformer for directional control along with the mechanical e-unit (no modification to engine) F-N-R running on DC to minimize noise.  MPC engine, has no whistle anyway so that's not a problem...

Thanks!!

[sir james I]

Yes you can add a rectifier between track and AC transformer.

If you want it both ways get a DP switch, run the track wires to the center. Run wires directly from the transformer to one side of the switch and run wires with a rectifier to the other side of the switch. Then just flip the switch to one side or the other.

[statistician]

great idea - thank you sir james!!

[lionelsoni]

Keep in mind that the track common will no longer be the same as the transformer common and cannot be connected to it.  If you are using any control rails for separately-powered accessories or turnouts, you will have to move them to a separate transformer or other power supply. 

 

 

 

 

 

 

 

 

 

 

 

[Dave632]

 I would suggest using a electrolytic filter capacitor, (100uf @ 50V would be OK), along with the bridge rectifier.

[Gray Cat]

Dave632

 I would suggest using a electrolytic filter capacitor, (100uf @ 50V would be OK), along with the bridge rectifier.

and the reason for that is to smooth out the DC voltage that the bridge rectifier produces.. choppy DC might still be a bit "noisy"

[lionelsoni]

I'm afraid that 100 microfarads will not make much of a dent in the ripple.  Even 1000 microfarads will result in about 8 volts peak-to-peak ripple for each ampere of load current.  I use 5000 for small locomotives and 10000 for big ones; but with half-wave DC.

[BigAl 956]

You will need a high wattage 7 amp rectifier. Also the whistle and horns run on DC so if you do this they will blow continuously if you do not disconnect them. Also, the buzz is part of the charm. Finally, how will you handle reverse? You would have to install a DPDT switch to reverse polarity. Would it not be easier to turn of the e-unit lever?

[sir james I]

E units still function on DC so the reverse procedure will still be the same. Way back when,  I read several times that when using DC,  the E unit plungers can magnetize over time but I cannot verify this.

S.J.

[gunrunnerjohn]

You will have lots more issues trying to do this without any mods to the locomotive.  It's easy to put a bridge rectifier inside the locomotive to handle the E-unit coil, and that will quiet the noise.  I've used a 1000uf 25 volt capacitor across it as well, and they are totally silent.

There are other ways you can attempt to quiet the E-Unit as well.  One I was successful by putting a small rubber bumper in the plunder cylinder to buffer the plunger, that really worked way better than I expected.

[lionelsoni]

I advise using no bigger capacitor than needed to quiet the buzzing when the bridge rectifier is powering the e-unit only and not the motor.  The problem is that the capacitor fills in the valleys in the rectified-voltage waveform, increasing the RMS voltage to the e-unit compared to the voltage at the motor and as much as doubling the power dissipation of the e-unit's coil.  So, if you can get away with less capacitance or none at all, you can reduce or eliminate the excess heat.