22 replies to this topic

[Alan Draht]

I acquired this vintage "Pro" - built (Eddie MacDonald/ Texas) Retro chassis with a Mura CCW-rotation motor installed in lieu of a race-legal JK Hawk motor.

 

The frame has "MAC-5" inscribed on the bottom and its construction is very similar to a handful of other "MAC-5" Retro chassis I acquired about ten years ago.  (I refurbished and tested them briefly on Mike Swiss's flat track last year and they all handled very well).

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[Alan Draht]

I know next to nothing about solid state electronics so when I see a semi-conductor (which I think is a resistor?) soldered across the +/- braid clips on the guide flag, I have to ask,

 

 

**     What is it?  What does the number "103" signify?

 

**     What is the purpose of soldering a resistor into a slot car's power wiring harness?

[Wink Hackman]

Almost certainly a capacitor. Stops your slotcar from radiating radio frequency interference and messing with the locals' TV and radio reception.

[zipper]

10 nF ceramic capacitor. I wouldn't mind to tinker with those.

[MG Brown]

Almost certainly a capacitor. Stops your slotcar from radiating radio frequency interference and messing with the locals' TV and radio reception.

 

Frequently found on 1/32 - 1/24 "homeset" slot cars for this exact reason.

[John Luongo]

years ago, i experimented with a similar sized capacitor (0.5 mu i think) in paralell to help minimize brush arcing trying to reduce heat at the comm. after turning on an armature lathe, if the comm hasnt been under cut adequately, the brushes can arc as they "bounce" over the insulator. best regards

[Tom Thumb Hobbies]

The main purpose was not to reduce RF but to try and reduce arcing. I don’t think anyone could absolutely say they worked. But I can definitely tell you when they “popped” it was interesting.


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[Bill from NH]

Capacitors like this one were used back in the 70s in an attempt to eliminate AC ripple often found in the DC power supplies of the time. They weren't very effective & soon disappeared. I would think this newer retro chassis used one to eliminate RF  interference with electronic devices as others have said. I never heard or read anyone saying how effective they were at doing that. Alan, if that was my chassis, I'd remove that capacitor & forget about it..

[elvis44102]

Capacitors like this one were used back in the 70s in an attempt to eliminate AC ripple often found in the DC power supplies of the time. They weren't very effective & soon disappeared. I would think this newer retro chassis used one to eliminate RF  interference with electronic devices as others have said. I never heard or read anyone saying how effective they were at doing that. Alan, if that was my chassis, I'd remove that capacitor & forget about it..

 

Yes AC leakage from charger/power supply..but that small of capacitor would seem to have little capacity to do much of anything

[Alan Draht]

Thanks to everyone for their input!  Very interesting and informative.  I didn't know that capacitors looked like that; more familiar with cylindrically-shaped capacitors.

 

I have seen capacitors used in R/C electric on-road race cars and never fully understood their application there either. 

[Bill Seitz]

10 nano-farads is only going to have an effect at high frequencies. An RF filter makes some sense. You'd need a larger value than that to reduce arcing or ripple not practical to mount on the chassis but maybe on the control panel. However, capacitive ripple filters do not work well when the load current is high as in a slot car. An inductive filter works better, but a high current inductor is large and heavy, so would be totally impractical for mounting on a chassis, again only feasible for the control panel, and then not very.

[Phil Hackett]

At one time racers installed electrolytic capacitors in their controllers, something like 3500 uF @ 25v. Those seemed to work very well against AC ripple... but they could be used to drive the car further during a track call and, well, that wasn't something that the USRA thought was a good idea... also *if*  you connected the controller wrong, a 2500uF capacitor is a pretty good firecracker...

[Phil Smith]

Don't batteries work well to reduce AC ripple?

[old & gray]

Don't batteries work well to reduce AC ripple?

 

As I understand it, in order for a battery to charge the charger voltage needs to exceed the battery voltage. Any AC ripple would be on top of the charging voltage and provide the dreaded 60 or 120 hertz pulses which would fry motors. So raceways (which shall not be named) used automotive battery chargers with little to no filtering on the output. These chargers were designed to charge batteries outside a car where AC ripple would not be a problem.

[Phil Hackett]

Don't batteries work well to reduce AC ripple?

 

 

No. Batteries don't care. AC ripple is more like pulsating DC in reality. If there truly was AC the batteries would let you know very quickly.

[tonyp]

Capacitors like this one were used back in the 70s in an attempt to eliminate AC ripple often found in the DC power supplies of the time. They weren't very effective & soon disappeared. I would think this newer retro chassis used one to eliminate RF  interference with electronic devices as others have said. I never heard or read anyone saying how effective they were at doing that. Alan, if that was my chassis, I'd remove that capacitor & forget about it..

That was the Idea but nothing became of it.

Trinity kept selling them on our assembled wire as a way to keep from losing a clip on a crash.


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[Bill from NH]

I hadn't thought of that Tony. I don't recall losing a clip, but I've had a few broken leadwires over the years.

[Chuck Gibke]

Most home race sets back in the 60s had power supplies that were very simple (and "dirty"). I have a couple of old Revell power packs that are nothing more than a full-wave bridge to provide "DC" to the track. A cheap multi-meter will show an 18 volt AC component. This causes some motors to "buzz" and certainly is not good for them although it sometimes helps cranky motors to get started.

 

As mentioned, the attached capacitor is too small to provide any power supply filtering and was probably for RF suppression.

 

.......cg

[Rotorranch]

When we were racing in the late 70's,  caps were the thing. You either put one on every motor, or put one on the guide.

 

It was supposed to make the motor brushes last longer.

 

Roror

[John Luongo]

as heavy duty trucks were built with more and more electronics, very often a customers truck was ordered with a particular engine and/or a particular transmission depending on the job. not unusual for there to be 2-3 separate electronic systems all installed on the same truck chassis. computer and wiring for the chassis (freightliner, for example),engine (cummins)and (allison) transmission. we discovered many times that by routing the main wiring harnesses for each system along the same frame rail (easier to build at the factory), the close proximity of these harnesses would show a spike in rf interference between the harnesses causing weird codes and improper functioning. the fix was to separate the wiring harnesses and add shielding material around them. later, frequency controlled systems were less problematic. a properly sized capacitor on a slot car would often give one the impression that the motor had no drag from the brushes, and depending on how fast the car was going at the time of power shut down, it could easily roll a significant distance. but when power to the track resumed, regardless of your trigger position, it could result in a slight delay before the car accelerated losing any perceived gain from a free rolling car. best regards

[Mark Onofri]

So let me see if I have this. First, if I'm playing Patsy Cline I want to leave that in? Second, if I'm playing Jimi Hendrix I want to crank up the power for that tortured Marshall amp effect? Crackel,sizzle,pop,etc.

[smichslot]

Reducing high-frequency noise in electronic product of virtually any kind is a rule of the law today.
Its implemented because any noise emitted from one product might limit the performane of another product.
Even US an Europe are agreing on a set of ruleset, which then means that the asians (read: China) is forced accept, because of trade restrictions.
By a lucky strike no low voltage products are included in the ruleset, so no noisy slotcars have to use an inefficient capacitor. And it wouldn't work anyway.
Modern PWM-power-supplies are less noisy than the old linear PSU's.

Steen

[Horsepower]

Dallas Racer, on 24 May 2021 - 1:38 PM, said:

Don't batteries work well to reduce AC ripple?

 

 

"No. Batteries don't care. AC ripple is more like pulsating DC in reality. If there truly was AC the batteries would let you know very quickly."

 

No, batteries don't reduce ripple, they eliminate it. There is no A.C. output from any battery. Certainly the chargers have ripple, but we used to charge our track battery and then remove the charger for racing. Pure D.C. then.