Using Lionel's TMCC cab-1 power master question..... using a rectifier for DC operation..

That could work. I wonder how well the rectifier will smooth the chopped sine wave of the Power master output.

Great thank-you  my prewar 256 dual motor LOVES the DC power .. ...daniel

@bmoran4 posted:

I wonder how well the rectifier will smooth the chopped sine wave of the Power master output.

Not at all. The chops and spikes will still be there, but will all be on the same side of the zero line.

@RoyBoy posted:

Not at all. The chops and spikes will still be there, but will all be on the same side of the zero line.

If the rectifier is just a straight rectifier, yes, but I presume that if @DanssuperO is going through the trouble of rectification for any perceived performance enhancements, he is seeking clean DC and is not simply satisfied with abs(sin(x)) and thus has more going on.

well all i got was a heavy duty  square bridge retifier been working great..

did not know of any other rectifier or that theirs a better one ?

if their is a better product if u could please let me know part name type or item number than my brifge retifier i have now

thanks....

Well, you are not really getting any benefit of "DC" then... you don't have the flat line of true smooth DC:

What you really want is this idealistically:

As such, your rectifier isn't doing much of anything for you at all. Might as well just be running straight AC.

thanks for the explanation... bmoran4

now to find the parts or components I only see this on the bay but its from china 

Power Supply Rectifier AC-DC Converter Board Input 0-220Vac Rectifier Board

This is what I bought and using

Bridge Rectifier, Single Phase, 50 V, 25 A, Module, 1.1 V, 4 Pins GBPC25005+

thanks for the help...daniel

What you need in addition to the rectifier is circuitry to smooth the DC which principally is a properly sized smoothing capacitor.

Any chance you know of a commercially made unit pre-made  item name or part number

or part number(s) of components needed

thanks

If you are content with how things have been operating, there is probably no need to have rectification at all You are just loosing some voltage through the diodes.

I like to add   a smoothing capacitor to my bridge rectifier to control the prewar  Lionel 256  twin motors on DC  would a

1000uf at 35  volt Capacitor   be sufficient..?   My understanding is too little or too much could be a problem            thanks

According to the calculator I linked you to, it seems as if you would need something in the range of a ~5.5mf capacitor rated for at minimum 24V. For a smoothing capacitor, you can err on the larger side.

@bmoran4 posted:

According to the calculator I linked you to, it seems as if you would need something in the range of a ~5.5mf capacitor rated for at minimum 24V. For a smoothing capacitor, you can err on the larger side.

Thank-YOU ...

any chance would this work?

@DanssuperO posted:

any chance would this work?

1 mF = 1000 uF

.0033 mF is no where close to 5.5 mF

OK... I can't find a part number typing in the

~5.5mf capacitor rated for at minimum 24V. any chance you know a part number for them

I found the 1000uf at 35  volt Capacitor   but not sure if its the same as what you posted

thanks...

You can take 5 or 6 of those 1000uF capacitors and wire them in parallel to get the desired total capacitance.

1000uF x 5 = 5000uF = 5mF

O I found these close to me

50pcs 1000uF 25V Electrolytic Capacitor 10×18mm Radial

I  hoping that is what you recommend thanks! 

OK... I think I found something close..

6800UF 25V 16X30mm Electrolytic Capacitor       top picture 

thanks again daniel

So, I got my 6800uf 25v capacitors. today

I only wired one to the bridge rectifier  ..  positive to dc and neg to dc neg on the rectifier.

Before I would crank the cab-1 and get the prewar 256  doubled motor to run .

With the capacitor installed  light movement made my 256 move very smooth and low voltage as seen by the lights.

However,... after a short time @1 to 2 laps it would make the cab-1 flicker  red light and stop power . If I wait @ 2-3 seconds in will reset and when I turn the cab 1 knob it works fine. until again it stops...

any idea what's going on ? again its fine without the capacitor. but honestly it does run way way  better I have not bypassed the cab -1 in hopes someone knows or can tell me what to do..thanks daniel

When using 6.8mF capacitor, you have increased the amperage draw too much causing the PowerMaster to trip its circuit protection. However, that would cause the light on the PowerMaster to flash, not the CAB-1.

@bmoran4 posted:

When using 6.8mF capacitor, you have increased the amperage draw too much causing the PowerMaster to trip its circuit protection. However, that would cause the light on the PowerMaster to flash, not the CAB-1.

YOUR right! that's what's happing!

Thanks! I know you said 5K  did not know the 6.8K too high

Think 5 k is too much?  I can order more . just not sure  what I need.. thank! you for letting me know.. (again) ..

when it does run it is SMOOTH! though!

I 'm thinking of plan B ...   leave the 6.8K capacitor with the bridge   rectifier without the TMCC control

reason is so far with just the setup and the KW  it runs so smooth and with very little throttle.

If I could ask again will this be ok without the TMCC control using the 6.8K   capacitor

I 'll use the TMCC for my other AC control units with a double throw switch to keep the AC/DC from ever being on the same time!

thanks...daniel

If you're going to go the conventional route why not just try a DC Transformer and see if it makes a world of difference or not

You do realize that the 25V rating is marginal at best.  The KW peaks at 20VAC output, let's be charitable and call it 18V.  The bridge rectifier will pass a peak of 1.414 * the RMS output of the transformer, that's 25.5 volts. Let's assume you go for full voltage on the KW and have 20VAC.  Now the cap is seeing 28.3 volts, exceeding it's maximum rating.

You really should consider a 35V rated cap for this function, electrolytic caps don't like to be pushed to their max voltage ratings.

Hi...gunrunnerjohn

Thanks for the info so far the prewar 256 uses very little throttle...  but I have NO problem getting what I need but honestly I don't know what to order    I see a 35volt  with 3300uf think that would do it? if not could you please at least tell me what you would order THANK-YOU...daniel

Anything with a 35V rating would be good, that one would be fine.

@gunrunnerjohn posted:

You do realize that the 25V rating is marginal at best.  The KW peaks at 20VAC output, let's be charitable and call it 18V.  The bridge rectifier will pass a peak of 1.414 * the RMS output of the transformer, that's 25.5 volts. Let's assume you go for full voltage on the KW and have 20VAC.  Now the cap is seeing 28.3 volts, exceeding it's maximum rating.

You really should consider a 35V rated cap for this function, electrolytic caps don't like to be pushed to their max voltage ratings.

Agree, 35 volt is better for the life of the electrolytic capacitor. However, the math above lacks the diode voltage drop within the rectifier before the capacitor and also the additional 1 or so volt drop introduced by the TMCC PowerMaster. This still puts the voltage rating on the edge to the max, but depending upon what is on the shelf or in the bin, very usable. Hence the wording "at minimum".

@bmoran4 posted:

Agree, 35 volt is better for the life of the electrolytic capacitor. However, the math above lacks the diode voltage drop within the rectifier before the capacitor and also the additional 1 or so volt drop introduced by the TMCC PowerMaster. This still puts the voltage rating on the edge to the max, but depending upon what is on the shelf or in the bin, very usable. Hence the wording "at minimum".

If you assume the 20V maximum output of the KW, the 2.4 volt total drop still allows you to exceed the 25V rating.

Like I said...

@gunrunnerjohn posted:

Let's assume you go for full voltage on the KW and have 20VAC.  Now the cap is seeing 28.3 volts, exceeding it's maximum rating.

I'm not saying it'll blow up tomorrow, but one point of these forums is to point out things like this so future design decisions are based on solid design principles and margins. Anyone that tells you that a 25V rating on the cap is correct for this application is wrong, at least IMO.

@gunrunnerjohn posted:

Anything with a 35V rating would be good, that one would be fine.

THANK-YOU I ordered it and hoping it might "might" work with the TMCC cab 1 and not overload it time will tell, I apricated the info ...daniel

Just expounding upon the math here showing it eeks by with 20V and acceptable with the traditional 18V input for the PowerMaster:

20-2.4=17.6
17.6*1.414=24.8864
24.8864 < 25

18-2.4=15.6
15.6*1.414=22.0584
22.0584 < 25

We are splitting hairs and conflating making what you have at your disposal work well enough and engineering a product. I don't believe the math or datasheet to be wrong. We can argue all day long about what de-rating parameters are appropriate for a given product design, but I choose to play trains instead

My 35v 330uf capacitor came early today. sort of fitting .. being New Year's Eve something old ..

I put the new capacitor on and turned up my KW to @ 18 volts and used my TNCC cab -1 , but one pass it still kicked the thermal breaker in the Power Master .So all I did was switch the switch on the side of the power master from 135 to 180 AND it all works fine...

Just wanted to again thank the above guys for sharing and  giving me advise on what I would need to make my tribute for my  Dad possible,,  I can now use DC power for rally low speed and smooth operation for this prewar  electric loco and use   TMCC for  control... and move on to the New Year ahead... daniel

Glad you got it working to your satisfaction! Just a clarification -  you used a 3300uF, not 330uF correct?

oh boy i need  to take a electronic course OR buy more trains lol .......thank-you yes 3300uf