Diode Strings vs. Series Wiring

You only need one string to the motor or motors in parallel. Here is a pictorial post.

LINK

Dale H

It is a great circuit and I am a big fan of Dale Manquens. Still series wiring limits pulling power as each motor can get only a maximum of half throttle or 9 volts maximum.

The diodes only reduce maximum speed or top throttle voltage. The downside of the diodes is wasted heat and power,not an issue in most cases.

Dale H

A Williams F3 at 9-10 volts is like a speeding bullet.

You got that right, Rob. Because I use a ZW for power, I don't like the way it performs. Much better with the series wiring, but as I mentioned, I get motor stall, so I'm going to go with one of the above methods.

Roger

Ok.......I went with the diode string method. Rob's method is probably good as well, but I couldn't figure out the schematic. Anyway, I just finished it up and took a couple of photos of it (below). It runs very well and I no longer get wheel slip. However, I've got a major concern. Heat buildup. I've got a Fluke Infra Red meter. After I ran it for about 10 minutes, I popped the shell off to measure the temp. First I felt the diodes and the head was alarming. The measurement I got was 160 degrees. To me, that seems way too hot. I purposely did not wrap it in the tape and mounted it above the reverse unit on an old battery pack from a Miller sign (to get airflow around it). I'm thinking if I ran it for 20 minutes I'd be in shell melting territory. Anyway around this issue?

Roger

It didn't seem to get as hot when I was testing it (alligator clipped in). I didn't run it as long, however. Is it possible that I've got the polarity wrong?  I'm thinking it wouldn't even work if that was the case, but......just throwing it out there.   One thing for sure....I can't run it like this.

Roger

Six amp diodes shouldn't be getting hot, you're talking 71C in just a few minutes!  Looks like it's melting that battery box it's sitting on!

It's not wired wrong, what you have looks fine.  I'm assuming this is in one of the motor leads, right?

Hi John,

Thanks for popping in. The battery box isn't melting (yet). I Gooped the diodes to the raised edges of it. That's what you're seeing. 

I have to two yellow wires from the board to the motors cut. Board yellows to one end of the string. The other two  yellows (that go to the motors) are connected to the other end.

Glad I checked the temp. Buying a new shell is expensive.

Roger

And it's not shorting.  I've got a 91 circuit breakers on both feeds of the ZW. They trip instantaneously with a short. 

Roger

If you have a meter, measure the current in that circuit.  Heating those diodes up like that takes a lot of energy!

It's funny.....that's exactly what I was doing when your message came in. I connected my clamp on to that circuit. It's drawing 5 amps. That's high. It's pulling a heavy load, but my PW stuff doesn't draw that unless I double them up.

Roger

Well, I see why it wasn't getting hot on the test stand. Just ran it by itself and it was pulling 1.5 amps.

Roger

Five amps is WAY too much power through the motors, something is seriously wrong!

Well, here's part of the problem. That passenger consist is very heavy. 5 MTH Madisons plus the F3 B unit and 2 C units. I put my newly restored GG1 in front of it and it tripped the 91s.   5.8 amp draw. The GG by itself draws about 2.78 or so.  So, I'm thinking with the reduced power and efficiency of the motors, it's lost it's effortless pulling power (the Williams).   Strange, though. Wired in series, it pulled that consist (with some wheel slip) if started on a curve.  Maybe I should put this back to it's original wiring scheme.

Roger

And I thought I had a LOT of circuit breakers. You've put me to shame here.

Oh, I see from a later post that is a reference number for the breakers, I feel better now. Should have added, good luck with the diodes too. 

I've used diodes in a similar manner, and I've never had those kinds of results.  My usual 2-motored locomotives will pull a dozen cars on about 2 to 2.5 amps at 55 scale MPH.  Also, if you have five lighted passenger cars, those are pulling a couple of amps unless you've converted to LED lighting.  These are running in command mode, and they have additional electronics pulling some power.  My Lionel scale JLC GG-1 with nine lighted passenger cars draws 2.8 amps, including the passenger cars.

Either it is not wired correctly or one of the trucks is binding. I have diodes in nearly all my engines and have not had a problem.

Looking at your pic the motor wires are yellow and blue. Each pair should go from the motor to the board. Some boards just have one wire to the board. The motors should be in parallel with the diode string in series to one of the leads. You also have to wrap the diodes with tape,they can not touch the frame. 

Dale H

The voice of experience, I figured you'd drop in soon.   I can't imagine pulling enough power to get 6A diodes that hot, that's got to be hard on motors as well!

The drawing is a bit better if you click on it. Note the blue wires are not connected to the yellow wires. 2 blue wires to the board. 2 yellow wires to the diodes. 2 yellow wires from the diodes to the board.

Dale H

Dale,

That's exactly the way I had it connected. But I noticed a couple of things. I was getting very high readings with that heavy, lighted consist. If they are 6 amp diodes and it is running 5.5 or so, I would think they would be at the upper end of their ratings.    I also started getting shorts that were tripping my breakers. It seemed a separate issue. I tried to narrow it down by removing cars until just the engine was left and.....still it would trip. I finally found out why........a screw from a Garmin dashboard "bean bag" was wedged in one of my switches. No idea how that screw got there. Anyway, that ended the shorts. 

In reading a couple of other threads about series wiring, it was written that series wiring cuts the voltage and the amperage remains the same. That's not what I measure. With straight parallel wiring, the engine draws 1.71amps. When I put it back to series, it measures .75.   I verified this with another engine as well. In that one, I had installed a switch so I could go back and forth. Same measurements.....an amp less. The whole consist now runs at 3.71 amps. With the diodes in there, it was 5.3 and above. I have no idea why that is, but I don't trust it.   If anything was shorted, my breakers would have tripped. And the wiring was correct.   Was it due to the load of the consist?

Roger

You have been misled on series wiring.  If you wire two motors in series, all other things being equal, the voltage applied to each motor will be half of the applied voltage, and the current will also be cut in half.

I actually tried the series diode wiring on the bench with a single drive motor.  I don't get anything like the reaction you are describing as far as increased current just because of the diodes, I find that most curious.  Yes, I was putting a load on the motor by applying friction to the flywheel to simulate a real situation.  My experience was that I had to apply several volts additional to attain the same current under the same load conditions with the diodes.

I may experiment with it in the next few days (I put it back to series). I'm a bit gun-shy with it now. I'm so glad I took the shell off to test it yesterday. Could have been the boards as well as the shell.

On the positive side.....in trying to figure out where the amp load was coming from, I tested each car in the consist and found that one of the B -units (that I put an ERR sound system and big speaker into) was dragging a wheel pair. It was tight out of the box, but I thought the lube I put in there would loosen it. Nope.  Nothing I could do would loosen it. Must be a bent axle. Called Williams just now and they will be sending me a new truck. Nice!

Roger

I am curious how a diode string vs series wiring to cut motor voltage will affect "wheel slip and motor stall if I do a startup on a tight curve".

Earl

Roger

If the motors pull 3 amps,which would be a bit high if they are in good working order,a diode string of 4 pairs would consume about 7.5 watts of energy. That is comparable to the heat generated from 2, 4 watt light bulbs at 18 volts in a passenger car. They would be pretty warm but not hot. The passenger car pull does not affect the diode string,only the motor current. At 14 volts throttle this would add about a half amp to the current draw. 

All I can say is I use diode strings and really have no problems with them. It does add a bit more power requirements as noted which could be more than compensated for with LED passenger car lighting conversion.

Dale H

Dale,

I'm a bit hesitant to put it back in. What could have gone wrong in there to generate that kind of heat?  If there were any shorts, my breakers would have immediately tripped. 

Roger

Breakers are very slow if it is a slight overload and not a short. A binding or tight truck can pull more current,more than normal and not trip a breaker. This could account for your problem on curves with series wiring. One truck is stopped and one is spinning. Series wiring will tend to speed up the moving truck. The stopped motor would actually get less current. With parallel wiring they get the same voltage,unless one motor has a problem.    All I am saying is that if every things is working right the diodes should not get boiling hot. What transformer are you using? I assume it is a ZW. The diodes work best with pure sine waves. 

You could power each truck separately and meter the current flow. Might be a binding truck of bad motor winding. Williams can motors use little current in my experience if they are running right. 

Dale H

He's using fast-acting electromagnetic #91 breakers.

Dale,

Rob is right......PW 91 breaker......instantaneous. In fact, when I first started using them (mainly because of Rob's posts), I was getting a million nuisance trips. I solved all of those problems, but each time I get a new engine and run it through switches......always an adventure.

The engine pulls 1.7amps by itself and .75 when series wired, so I'm not thinking it's a motor problem. Spinning the flywheels by hand feels the same on both (but I'll check that again. Dale, if you could do me a favor and measure the resistance of the chain. I'm getting 12M ohm and reversing the probes.....around 6M ohms. I don't know if that's what it should be. Maybe a diode is bad (heat from soldering?).

Roger

You can't measure diodes using the standard ohms scale, it doesn't apply enough voltage to cause the diodes to conduct.  The way to check your diodes is either individually with the diode setting, or connect a DC power supply with a series resistor and the diodes.  Run it up to at least 1 volt for each diode and then check the voltage drop across each diode.  Since you have a bi-polar arrangement of diodes, you'll have to reverse the polarity of the power supply to check the second string.

John,

I tested all the diodes with my meter and they all came out ok. So, that wasn't the problem. 

Roger

Even if you had a bad or multiple defective diodes,the only way they could cause a problem is if somehow it conducted to common. That would be a half wave short and most likely not trip a breaker,even a magnetic one.

  In the string,if one did not conduct,half the chain would be broken and you would get half waved DC. It would cause the motors to run slower but not pull more current,in fact they would pull less.  If one was shorted the current would simply conduct to the next diode so you would have 4 on one side and 3 on the other. This would not be much of an issue either.

I guess it is remotely possible one or more had some forward resistance or a breakdown in reverse resistance. This would be very unusual but not impossible. I am assuming these are standard diodes and not some special ones like a Schottky or something.

If the motors pull 5 amps,that would not trip an 8 amp breaker,but the diodes would give off some heat,about 14 watts. That would be abnormal. Either one of the motors is bad or part of the diode string lead is touching the ground.

You can measure the diodes as John describes. Put the string in series to a load like a light bulb to a DC source,then turn it around. It should conduct both ways lighting the bulb and the light should be the same intensity. If fact you can measure the voltage across the bulb each time.  I am a bit baffled by your experiences. Barring using a scope this should give you an idea.

Dale H

I think Dale and I agree on one point, something is amiss in that installation.  There's no way that you overheat 6A diodes running without a load if things are working properly with that engine!

Ok......I'll try it again when I get a chance.  But with the chain alligator clipped in and the shell off.

Thanks!

Roger

Maybe his original problem of "wheel slip" and "motor stall" are related to the over-heated diodes.

Earl

Earl,

No.....the motor stall occurred when I had it series wired with no diodes. I have that consist in a side spur on my layout and there's a tight turn before the switch to the main line. Starting up there on the curve, I'd get motor stall. With parallel wiring, of course, it would blow through there. And no slip with the diodes either. But I have to figure out why they get hot.

Roger

Roger,

What I am trying to say is the same problem that was causing the motor stall and wheel slipping with the series wiring is causing the diode strings to heat because of excessive current draw. 

I assume you have two motors in the engine, as most Williams engines do.  I suspect one of the motors is drawing excessive current causing both the motor stall and the wheel slip with the series wiring and the hot diodes with the diode strings.  The motor with the wheel slip is most likely the good motor and the other motor has some defect.

Good Luck...

Earl

Earl,

Sorry I misunderstood. I'll see if I can check those motors. I'm thinking they are both ok. 

Roger

Actually, series wiring of motors makes the problem very easy to force.  Anytime one motor has more traction than the other for any reason, it'll lose power due to the fact it offers less impedance to the series current.  The motor with less traction will then likely spin.

This isn't a flaw with the motors, it's simply the nature of the beast. 

FWIW, this happens to locomotives with tach based speed control when the tach equipped motor loses traction, it stops requiring much power to spin at the command speed, and the other motor just stalls.