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Capacitor flywheels

Collection of posts to HOn30 Mailcar RE “Capacitor flywheels”

Circa 1996/1997 – Compiled by Prof Klyzlr.

From: Brick Price
Hi all:

This may be old hat for many of you, but I have been performing a cheap,
simple trick on my locos lately which seems to help immensely. I took a
capacitor from one of my Katos and wired it across the leads of the Bachmann
motor on my Forney conversion. Interference has been eliminated on my short
wave radio and wheel arcing seems non-existent. The motor runs cooler and
smoother at all speeds. In fact, I would swear that running noise is
reduced. As memory serves me, from my Hughes Aircraft electronics days, the
capacitor acts like a tiny storage device. If the motor is recieving
electricity, it stores the excess. If there is a dirty spot on the track,
the capacitor bleeds off power to the motor until it receives power again.
It also serves to smooth out AC pulses providing cleaner DC to the motor.
I wish I could tell you what rating (ie size) to use, but I didn’t see a
number. I’m going to experiment with different sizes and see what happens
Any electronics whizzes in the group? Is this accurate reckoning or wishful
thinking? I would like to hear about more such tips, use of diodes, etc.

Brick Price

Cool! Capacitors are basically electricity reservoirs. Powersupplies for
electronic devices use capacitors to help filter out noise and to help
maintain a constant voltage. MR throttles use capacitors to simulate
momentum and braking. I have never heard of someone directly mounting them
in the loco though, but I see no reason why this can’t be applied to motors
as well.

There is indeed a threshold for a minimum working value, and size would
limit the maximum. I would experiment with a value somewhere in the 200uF
(micro farads), with perhaps a maximum of 1000uF. A larger value will just
store more juice, which would mean a longer runtime once when the power is
lost. Note that this would affect stopping distance of your loco, and
starting time will be slower as the capacitor has to fill-up before the
motor will begin to work. Also note that capacitors are rated for a
specific voltage. It is okay to use a higher voltage rating, but not one
that is lower than your source voltage (12V). Typical ranges are 16V and
25V, either one being appropriate for MR use. Radio Shack has many sizes
and styles.


this has got to be one of the all-time best pieces of information I have ever
picked up on the internet. It even beats out several years worth of 4
different railroad magazines I subscribe to. Brick please keep us informed
of the results of your experimentation.

I have used constant lighting units for a similar effect, but I think they
only increase the needed voltage by providing resistance. With a resistor,
since there is more voltage flowing to the track, electricity is more likely
to jump small bits of dust to reach the pick-up wheels. Adding a capaciter
serves as an electrical fly-wheel which when combined with a smooth mechanism
and a brass fly-wheel could provide very slow operaton.

Thanks for the idea!! Jim Pasquill

For the past 5 or so years, I have collected N scale equipment (often
blindly, and ending up with all sorts of odd stuff – stuff that will likely
become HOn30 motive power…!) and have found that almost all European and
most of my Kato stuff include capacitors. The caps are used on both
expensive items and “low end” items.

I have a Kato powered railcar in front of me right now, model number 614-1
[M]. This appears to be an inexpensive model intended for the lower end of
the Japanese market; I paid about $30US for a two-car set (one powered, one
not). The powered unit has a capacitor mounted in the body, connected to
the motor with copper clips. This “cheap” railcar runs like a charm – I was
surprised when I got it home and found that it ran just as smoothly as a
Kato F3.

There is no capacitance value marked on the cap, but it does have “104Z”
printed on it. Maybe someone out there can tell us what the code indicates.

The cap measures 8.65mm in diameter, 2.71mm thick, with approximately 26mm
leads. Having (sort of) worked in the electronics industry and seen a lot
of bits and pieces, this appears to be a common size for many different caps
- so there’s likely a wide range of caps suitable for locomotive applications.

If anyone out there is looking for some cheap yet reliable Kato motive power
that lends itself to conversion to HOn30 stuff, check out the 614-1 [M] – I
highly recommend it for its running qualities. I intend to convert mine to
a rail car of some sort.

On a related topic: can people on the group suggest affordable and readily
available N scale locomotives that are useful for HOn30 projects? I’d like
to put together a list and keep it handy so that when I come across a “gotta
have it” plan in the Gazette I’ll have an idea of which mechanisms can be
used. The Kato 614-1 [M] is one suggestion for possible HOn30 use – anyone
have any others?

Thanks -
Jon Piasecki

That is a 0.01 Micro farad capacitor (probably 50V to 100V working). It is
really not acting as an energy storage device, just eating up the high
frequency noise that the motor makes as it turns and turns on and off its
coils. I am surprised that any small DC would be shipped without one one


Jan 96

Hi Jorgen:

The instruction sheet shows different chassis and where to cut them to work
in the rail car. I happen to like the Arnold, Kato and Atlas chassis for
these types of setup. The Bachmann unit should work as well. Simply cut
off the chassis in front of the motor. Cut off the forward flywheel and
shaft with a cutoff wheel. Frankly, I don’t see any advantage to a flywheel
over a capacitor across the motor leads.


The capacitor will help reduce electrical noise such as radio
interference and if big enough will act as a sort of short term battery
to get you over electrical discontinuities while the flywheel helps
the motor overcome friction in the mechanical system to smooth out
the operation and minimize the effect of small binds.

If you can, keep the flywheel. It is a good thing.

Joerg Seiler

Well, I see some advantages with the capactitor; it definitely helps
at slow speed if you have pickup problems, and could also eliminate
those abrupt ‘jump stops’. On the other hand – the big advantage with
flywheels is that you can apply a lot more power to a rough mechanism
and still get a smooth start.

Adding a resistor to the capacitor solution could also give you
smoother starts, (i.e. let the capacitor charge trough the resistor),
but I’d rather have a flywheel if possible…

Up here we have another gizmo available; the combination of a
flywheel and an advanced centrifugal clutch system. When you start
the engine, the motor initially runs free, and doesn’t engage before
it has picked up some speed. Then the clutch softly engages, and the
loco slides away in an incredible way. Viola, no more jump starts.
Of course, the combination of sound and movement is best enjoyed with
Diesel electric locos, but it helps on steamers too…
The inventor also has modified the clutch so that when you remove the
power, the clutch disengages, and the loco floats to a stop without
the motor braking.



Jan 97

Brick a while ago, mentioned using capacitors as a electronic versus a
mechanical flywheel. The idea being that the capacitor stores an amount of
electricity the helps in the exact same way as a flywheel. A capacitor or
around 100mF 16V would a good starting point, and are small enough for our


Funny, I thought this size (and bigger) capacitors are polarity sensitive.

Please correct my if I’m wrong or just washed up.


Tobias Giles
Mtn. View, CA

That’s a good point. There are many types of capacitors, the kind in
question here are “electrolytic”. The bulk of electrolytic capacitors are
polarity sensitive, but others are not (bi-polar). I just checked the
Digi-Key catalog and there are types with this capacity and miniature size.

Other capacitor types such a polyester, film, ceramic are usually not
polarity sensistive.
This may be what you are thinking of. These are not capable of storing a
large amount of current for a motor, but are good for filtering noise or
spikes from an electrical signal.


I can not remember, but was the presense of a constant lighting
unit in parallel with the motor roughly equivalent to a flywheel capacitor?


I thought I’d toss in my two bytes worth, about these types of circuits.

I have built a lot of different constant/flashing lighting circuits
(SHAMELESS PLUG check my WWW page for easy to follow diagrams and believe me, this type of thing
is probably much more trouble than it’s worth.

1) size: no matter how much you squeeze, unless you have a wave
soldering station to handle SMDs (surface mount devices) you would have
to mount these in a tender. In HO. Pretty much forget HOn30 or N. I was
personally proud of the fact when I crammed a dual flashing headlight,
blinking roof strobe and directional constant rear light in an HO scale
BL-2, but I wouldn’t want to do it again!

2) complexity: besides the usual headaches of day-to-day operation, you
would now have an electronic circuit with 4 to 6 additional components,
all prone to failure. Not to mention loose wires, shorts, cold/broken
solder joints, etc. The BL-2 mentioned above still works, but I’ve had
much simpler circuits fail for no good reason.

3) time: I have enough trouble finding time to work on my trains,
without neglecting family, friends, work and household maintenance. I
personally feel the time is better spent on other things.

The capacitor mentioned (use a 0.01 Micro farad capacitor, 50V to 100V)
is not acting as an energy storage device, just eating up the high
frequency noise that the motor makes as it turns and turns on and off
its coils. It will make a motor run smoother.

BTW a flywheel will help in almost every case. The stored energy allows
the engine to move forward a minute fraction of an inch, to overcome a
dead spot on the track.

The moral of all this — I think — is to use a non-abrasive track
cleaning method. Use it often, especially before entertaining friends
(“why do you have to keep pushing that train?”).

And as always, keep smiling!

As for the “Capacitor Fly Wheel” I did a quick test using the Car Works
Forney and a few flat cars. For the loco to coast across a dead piece of
track half an inch long you need a capacitor of 10,000 mf, 25 volt.
Unfortunately the one I used was a normal
electrolytic type, for each loco you would require two such items and a
filter network. It is possible to use a Bi-Polar type but I don’t think
they come in values above 2,000 mf. Oh yes the size of a common 10,000
mf 25 volt cap is about 9 feet in HO and about 20 feet long so each loco
would have to be permantently coupled to 2 cars.

NWSL has a good range of flywheels to fit any can motor. I have a mack
railcar, similar to the Brick Price unit, it will roll about 1/4 of an
inch when it runs onto dead track. After fitting the smallest NWSL FW it
will roll 1 and 1/2 inches under the same conditions.




I originally started using capacitors across HO motors to assist with
smoothing the output from Zero-1 command control modules 10 years ago, and
following much experimentation, have concluded that (1) the downside is that
capacitors do not replace the effect of flywheels, but (2) paired capacitors
of the appropriate value *do* provide a *significant* improvement in
performance and ‘dirty spot’ avoidance.

Plain ordinary 35V electrolytic capacitors (the polar variety) are ideal,
but the trick is to mount them in pairs, with the negative leads direct
connected to each other and with the positive leads attached to the two
motor leads. The rule of thumb is to use capacitors with around the same
value as the current draw of the motor – i.e. a 200mA motor should use 200
uF capacitors, a 500 mA motor would use 500 uF capacitors etc. This gives a
smoothing which helps the motor with ‘short term’ performance (i.e. a cycle
or two), but does not interfere with ‘rolling’ capabilities. That’s where
flywheels come in.

I have used this technique for years now on a variety of motors from Mashima
/ Sagami low-power can motors to Athearn brutes, and the results are well
worth it in all cases. We’re not talking high tech here – just a pair of the
simplest ‘electronic’ devices around.

Hope this is of help,

Peter Knife

Third – capacitor size (I have some dirty thoughts . . .;- )
Yes, electrolytic capacitors come in all sizes, voltage ratings, and of
course, capacitances. First, voltage ratings. Don’t be fooled into
thinking the following: well, my power pack only puts out 12 voltages (or
whatever) and so I only need a 12 voltage capacitor across my motor.

First, back EMF (electro motive force) will spike higher than the
supply voltage and blow a hole in the dielectric of the capacitor. What
did he just say? On a standard run-of-the-mill 3 pole or 5 or 7 pole
motor, as the armature turns, the brushes make and break contact with the
segmented ring. As the contacts break, the magnetic field collapses and
creates a high OPPOSING voltage across the coil (the coil is one of the
poles on your motor). This higher voltage spike will exceed the capacitor
voltage rating and pow. (I’m really glossing over some details here so
forgive me.) This is also what creates noise on the TV or radio.

Second, again electrolytics have polarity. If you had an
electrolytic across your motor and you reversed your power pack, then you
have reversed the voltage across the capacitor. When you hear a small
explosion – it’s time to replace that capacitor.

Size. Open a small radio and you can seen numerous electrolytic
capacitors. But the energy they store is very small. The energy potential
is just enough for radio signal level electronics. To move a motor takes a
surprising amount of energy. Place a small open framed motor sitting on
the table top, not connected to any drive shaft, and connect to it these
pencil eraser size capacitors (say 200 mf, maybe in the 20 volt range) .
If you’re lucky, you may see it do one or two turns and this has to a very
good motor. Typically the armature will pulse, wiggly, or barely turn a
120 degrees. To move a locomotive over a dead spot will require numerous
turns of the motor and pencil eraser size caps just don’t do it. I wish
had this technology.

Back-to-back electrolytics. This does get around the polarity
problem but it does effectively reduce the capacitances by half (assuming
the same values are used). Standard capacitance math. Read Electronics

Capacitors on constant lighting units. On DC powered lamps, LEDs,
etc., a capacitor in PARALLEL with the lamps will add a little more
illumining time when the train losses power for what ever reason. If you
put the cap in series with your constant lighting circuit, the cap will
block DC and not allow your lamps to light.

Wow, what’s a lot to write. If there are typos, forget me, I’ve got to get
back to work ;-).

Tobias Giles
Mtn. View, CA

Capacitors DO help (as stated by many of us). They wil NOT replace
batteries, nor will they continue to run a motor more than a revolution or
two, but that jolt is enough to carry you across a dead spot or dirty track
and therein lies the advantage. I did’t say that they would replace a
flywheel as that is a mechanical device with inertia behind it. So called
“flywheel effects” of transformers are diminished voltage being automatically
appled to the motor during startup and shutdown. Give the capacitors a
chance. The only cost a quarter or so each and are really easy to install.

Brick Price

G,day All,

There are two small points to add.

1. If there is a tiny space left in a loco I try and fill it with low
temp solder, this is worth a few hundred micro farrads.

2. The whole idea of using the capacitor as a flywheel relies on the
capacitor storing energy and discharging through the motor to keep it
running. The amount of charge is dependant on the voltage applied to the
capacitor. This depends greatly on the type of throttle used. A smooth
DC throttle would charge up to a lower voltage than a pulse type
throttle ………. I know someone will come back with “but pulse power
will heat up a small motor if used for a prolonged time”!!!!!!!

Our motors are rated for 12 volts but for scale speeds only run at 6 – 9
volts. A pulse throttle will deliver up to 15 – 18 volt pulses. This is
without the back EMF generated by the motor over dirty track. When a
small capacitor blows it can be quite spectacular maby we can use this
as an explosive effect on the mining section of the layout.

Well thats enough stirring for one day. The moral of the story — keep
your track clean, keep your wheels clean, use a flywheel and run your
trains regularly even for a few minutes on a test track.

My smallest running unit, which has run a few real miles in its life is
a Model T Ford pulling a 4 wheel truck with a can of weed spray on it.
Keeping the weeds off the track will also help!



I think I am going to try your approach of two capacitors linked head to
tail. I have a Heisler with only two wheel pick-up on each side that stalls
at times. Perhaps this would help it.

The question I have is: does this approach only work in commenad control.
I use cab control. I do not see how that would make
a difference, but am pretty ignorant in this regard.


Your guess is quite correct that it doesn’t make any difference. I only
mentioned command control because it was in experimenting CC with that I
found out about the capacitor trick. They work fine with any conventional

Having said that, though, if you have a loco which only picks up on two
wheels on each side, you will get better results by adding pickups to all
other wheels on each side. Improving pickup is always the first thing you
try and do. Adding capacitors will help with ‘little’ dead spots, but not
with ‘big’ spots such as dead frogs in turnouts etc.


Peter Knife

Sept ’07

Our friend Mr. Price suggests that the addtion of a capacitor will aid
in the operation of locomotives. I think I was sleeping during that
part of physics. Just how does this work? And how does one decide the
type/capacity of the capacitor.

Chuck Lie

Hi Chuck

Let’s see if I can explain this so that it’s understandable, _without_
confusing what is actually going on.

1st, there are two basic types of capacitors (In the size range that
will be useful).
(1) Non polarized (I.E. _no_ polarity markings on the part leads).

(2) Polarized, There is a _DEFINITE_ + and – for the part leads. (This
MUST NOT BE IGNORED. Shorts, minor explosions, other bad stuff may

(1 & 2) exceeding voltage ratings will _also_ lead to the ‘shorts,
explosions, etc., mentioned above.

A capacitor across the motor leads, will allow the excess available
power (over and above what the motor is using), to have a place to go.

Result — The excess available power, is temporarily stored in the
capacitor, and supplies the motor with power when the power supply is
‘pausing’ in it’s job of supplying power. (Between ‘Pulses’ for ‘pulse
power, between spikes of the Pulse Width Modulation speed control for
those type throttles.[This is what DCC is supplying to the motor])
If you are running controlled voltage DC on the track, then the
capacitor, is essentially useless (except for flywheel effect over dirty

For both ‘pulse power’ and ‘PWM’, a capacitor will quiet things down
‘noise wise’, because it is clipping the top off of the rising voltage
spike (This is what is supposed to be supplying the mechanical ‘kick’ to
the motor armature to help it spin.) In this case, you win some, you
lose some.

As far as size (rating) goes, it’s really a ‘experiment and try’ thing.
I would try and start with AT least 20mfd, and would see if I could find
100mfd, or 500mfd that were physically usable.

This usage (motor smoothing) is not a normal usage for capacitors, and
there isn’t a lot of data available. They are more normally used for
electronic filtering, and signal transmission. Which are a completely
different mode of operation.


One more thing that I failed to mention. And it’s real important.

About the ‘polarity problem’.
The connections to the motor are sometimes one polarity, but when the
loco reverses dirrection, the polarity REVERSES.
This can lead to some spectacular fireworks if forgotten (ignored).

The solution, is to use two polarized capacitors in series. Use them


Actually, using capacitors to smooth out the current to a motor has become
very common. You’re right though, there isn’t much available data applicable
to our uses. The data that is available deals with either big industrial
motors, or little tiny precision motors (but not the types we typically use).
In the last twenty years or so, variable speed AC motor controls have become
very common in industrial applications. These are basically a bunch of
rectifiers that take the AC line voltage, convert it into DC, and with some
BIG transistors controlled by a small microprocessor, reassembles the DC back
into an AC waveform, but at a different frequency and voltage as required to
obtain the desired speed. The circuitry is almost identical to our power
packs! Since the new AC is being “built” from switching DC currents on and
off, it is anything but smooth. Capacitors are required to smooth out all
the spikes and unwanted bumps. AC motors especially don’t like non-smooth
current. They have this nasty habit of getting so noisy you can’t stand near
them, and get very hot otherwise. You would be technically correct in calling
them filter capacitors or smoothing capacitors. Both terms are accurate for
what the cap’s do.

I may have gotten a bit technical and off the subject, but I thought it might
be marginally interesting. I originally intended to note it is also important
to watch the voltage rating of the capacitors. I didn’t see where anyone has
mentioned that. At the voltages we use, the cap’s should be rated for at
least 35 VDC. Higher is okay, but less and they may do all all the nasty
exploding things you mention. If your lucky, they’ll just quietly pass away,
and then do nothing, leaving you to believe all the work you just went
through was a waste, since it didn’t work!

Ben Y.

If I recall, DC power supplies back in the “build it yourself era” were
often designed with large electrolic capacators (sometimes even
motor-start size) to smooth out the spikes to pure steady DC. And,
sometimes a VARIAC was added between the wall and the stepdown
transformer (or between the stepdown and the rectifier) for speed
control. Quite smooth and good, I recall. The smaller open frame
motors and pulse power (half wave DC) for slow speed operation ended
that concept. VARIACs are NOT cheap, so that didn’t help either.


Classic example of filtering! The Variac, for those who don’t know, is a
variable ratio transformer. It does an outstanding job of varying a voltage-
far better than the old-fashioned rheostat setups. Modern electronics
(transistors, etc.) could do the job better and far cheaper, hence they’re
not seen much any more.


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