I’ve seen a few motors with capacitors (I think) on them. How does this help the motors?
A capacitor supplys a start “boost”, nothing more.
No. Capactor’ were put across the motor brushes to cut down EMI - Electro Magnetic Interference - common with electric motor’s. EMI puts ‘noise’ on analog Sound System’s, and makes TV’s jump when on the same household circuit.
Got a portable TV? Try watching football and running train’s, sometime.
Well, I learn something new everyday.
Actually it depends on the motor. If it’s a DC motor, they might have a small capacitor to supress noise. But if it’s an AC motor, the capacitor does store a charge to help in starting.
On an AC motor it shifts the phase of the current to aid in starting.
The capacitor on a DCC motor will act like a small battery of sorts, storing enough juice to power over small gaps or dirty track and allow the motor and decoder sound effects to continue without interruption.
A capacitor in parallel to a DC motor is ther to absorb EMI, nothing more. A capacitor parallel to the motor on DCC will do the same, but it also absorbs some of the high frequency drive pulses, making for less smooth operation, which is why it is usually recommened to cut the leads on such capacitors when installing DCC. Some Bachmann locos also have inductors (coils) in the motor circuit. A combine inductor/capacitor circuit (since inductance is represented with the letter L, they are called LC circuits) resonates at cerain frequencies, which is helpful in tuning a radio but when you want to supply a high fequency pulse to the motor for silent running, it interferes.
None of this has anything to do with keeping power applied over short interruptions of pickup.
–Randy
Bachmann Spectrum G-scale motors have a small circuit board mounted on the top with two capacitors on them. These are purely for radio frequency interference (RFI) or electro-magnetic interference (EMI) filtering to keep the sparking within the motor brushes from traveling back through the power pack into the house wiring and interfering with radio and TV reception.
When battery power is going to be used instead of track power, as I do with all of my G-scale engines, this circuit board must be removed from the motor because the capacitors can interfere with the AirWire900 decoder’s output and cause poor performance from the locomotive.
As Randy indicated in his post, capacitors on the motor can degrade DCC performance.
SoundTraxx recommends that the capacitors on Bachmann Spectrum HO-scale steam engine circuit boards be removed when installing their decoder, and other decoder manufacturers may make similar recommendations.
You’ve got it right on AC motors. It’s called a motor starting capacitor, and is pulled out of the circuit by a relay as the motor comes up to speed. You’ll often see them on air compressor and table saw motors.
You’ll also see some capacitors by motors in industrial settings to help correct the power factor of the motor.
Mark in Utah
I suspect that the real reason why you should not put a capacitor across the motor in a DCC aplication is that the cap looks like a dead short for very high frequencies, which will overload the decoder until the capacitor charges during the current pulse.
You can also creat a tuned circuit wherein a large voltage spike is created every time you stop the motor, possibly damaging the insulation in the motor windings. This is much more a factor for AC motors.
I guess Digitrax, Soundtraxx, Lenz, Allen Gartner, Joe Fugate, and everybody else who says it does work are wrong? All of the above have advised to use the capacitors. Even on this very forum this subject has been brought up right here…
http://www.trains.com/community/forum/topic.asp?page=-1&TOPIC_ID=44569&REPLY_ID=476047
Everyone agreed it works. I’ve been doing this for six years. IT F’ING WORKS. If you want to give out misinformation, go do it somewhere else. You think you know more than Allen Gartner? Digitrax? Soundtraxx? I think you’re full of yourself. I know you’re full of something else.
They’re putting the cap across ponts on the decoder, to keep the decoder powered during those brief outages, not acroos the motor that I know of.
As for your civility and foul mouth, check it at the door. It stinks and shows your lack of intellect and education.
Mark in Utah
On30Shay;
YOU had better go back and re-read the post that you provided the link to. It is not about capacitors attached to motors, it is about a capacitor in the power circuitry of a sound decoder. The are two entirely different things.
It seems the cap is probably going on the decoder after the DCC signal is rectified. Actually, theremust be something along those lines already, providing the power for the decoder. The additional cap probably just helps keeps the voltage a little longer.
Randy, I’m having trouble closing the loop. I got the part about why and how of capacitors, even the (ahem) where, … but if, as stated elsewhere above, that the capacitors should be snipped when going to DCC, how does this impact on our 100LC groaning problems? Is there a relationship?
I completely understand what this post was about. I was pointing out that the correct place for a DCC equipped loco to have a capacitor would be in the decoder power supply. I guess I took too much for granted on some peoples’ comprehension skills.
[quote]
QUOTE: Originally posted by nfmisso
On30Shay;
YOU had better go back and re-read the post tha
Not really, since the older Sountraxx sound and motor decoders don’t use silent running or any sort of high frequency drive, a capacitor across the motor should make no difference. That’s yet another thing the Tsunami ‘fixes’. Theoretically you could build a circuit to smooth out those slow pulses which would help silence the motor noise, at the possible expense of top speed.
–Randy
I think we are comparing apples and grapefruits here. A capacitor big enough to have an appreciable effect on keeping a motor running is going to be pretty large (150 microfarad will give maybe a 10th of a second); one to keep brush “hash” from interfering with radio/TV is going to be MUCH smaller (around .01 uF) and will have basically NO effect on the motor.
There are decoders that can use a capacitor to cover for momentary losses of track power - Lenz Gold decoders can have a power storage unit (basically a capacitor) soldered to them that will do this, it costs the same as the decoder which makes it something of an upmarket option. The capacitors soldered across the terminals on DC motors are intended to reduce RF interference.