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Discussion Starter · #1 ·
Greetings, Scientist

Does anyone have an idea of the maximum voltage slot car motors put out when spinning at full speed while unpowered (where it acts as a generator)?

Is it very different for Scaley-type engine, Ninco NC5-Type Engine, ProSlot/Falcon/TSRF-type engine (4Amp jobbies)?

Very important to me.

Thanks in advance.

-Maltese
 

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Beppe Giannini
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If I'm not mistaken, under normal working conditions applied voltage equals back-EMF plus arm resistance x current

Since you're looking at full speed, current will be rather low - my guesstimate would be around 0.3 A for a Scaley (say 7 ohm arm)

If you unload the motor and spin it by outside means at the same speed, with zero current you should see pretty much 10 V - if you connect a load and use it as a generator, voltage at the terminals is again decreased by arm resistance x current

Hope this makes sense

Beppe
 

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This EMF also explains why dead strips are very unwise to use when using computerized lap timing... You do no want that EMF going backwards into your preciousssss compuuuter...

/Erik
 

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Julius Wilkko
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Hi!

Got max 2volts from NC1. More powerful motors surely give more. Just connect a multimeter to your motor and spin shaft with fingers. Tolerates no loading, voltage drops instantly.

Cheers!

Julius
 

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This EMF also explains why dead strips are very unwise to use when using computerized lap timing... You do no want that EMF going backwards into your preciousssss compuuuter..

Diodes stop that if it really is a problem.
 

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If that really is a problem?
Well, I didn't know they made computers in Soviet...

For those getting uptight here... A MIG can land on a plowed and frozen weat field - crosswise...

Yes, adding even more electronics.... Well, what I said was why not to use them. Just as reed and micro isn't a good choice.
And I wouldn't be to sure about that diod thing, it's a spike we are talking about, and not necessarily one we know which way it goes.
 

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Discussion Starter · #8 ·
Hey,

I sure appreciate all of your responses, chaps! 3 - 10> volts momentarily sounds about right.

BTW, the dead strip wires should be connected to a relay, not directly to the 'puter port. That would be baaaaaad, eh?

I shall proceed in building Frankenstein!

Thanks VERY much!!!


-Maltese
 

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Al Schwartz
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I have used dead strips with two different race managment systems (both of them using dedicated boards - not connected to parallel, serial or game ports) for years with no problem. Most commercial set-ups that I know of do the same -and, if there was ever a likely source of damaging back EMF, I would imagine that one of those 75,000 RPM, cobalt magneted flying doorstops would be it.

EM
 

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Al Schwartz
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1. Since the dedicated boards are designed to use with dead strips, the issue, if any, may have been taken into account in their design e.g a zener across the input, a diode blocker or a capacitor - since the dead strips are only switching low voltage DC at a very low rate. They clearly do not need to be a high impedance input

2. In any event, these boards are between the putative source of a volatge pulse and the computer bus and should serve to shield it.

Again, I do not know the details of the circuitry. I am merely reporting on my observations and, as are you, speculating.

EM
 

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No speculation needed. You can add diodes which are, crudely put, one way valves or just use an old computer. Computers that can handle lap counting software are easily found anywhere since they require so little CPU, RAM or HDD. Just whip out an ancient 486 or 586 and have at it. I've never heard of anyone killing a computer port by using a dead strip lap counter. People kill ports by bending pins, shorting pins and just plain dumb luck.

If the car is doing 10 mph, not an unheard of speed, then it covers 14.66 feet per second. If the dead section is 0.5 feet long (6") then the car will be on the dead strip for a total of 0.0347 seconds. That's IF the car is going that slow and IF the dead strip is that long. Most cars go faster and many dead strips are shorter so you'll be spending less time on the thing. My Scalextric GT40 is 5" long.

x = 1/14.66
x = 0.0347

You should double check my math as it's a weak point of mine. I'm not even going to try converting it to metric, my brain would explode.

It isn't really EMF that you're worried about, it's voltage. Your car is actually generating electricity during deccelleration and putting it back into the braids directly, not indirectly. So you're temporarily generating X amount of DC voltage during deccelleration. An electromagnetic field exists whenever the car is running regardless of accellerating or deccellerating. That's how these cars move, each pole on the armature is an electromagnet that is switched on and off in a timed fashion by simple rotation of the commutator which is rigidly affixed to the armature. Not all of this field is contained within the motor can so there is a lot of EMF bleeding out.

EMF exists in your computer already. Your cooling fans, the power supply, the traces on the main board etc. You can't escape it. Your hard drive is not only generating EMF but it also has a large and extremely powerful neodymium magnet in the thing to control the arm for reading the disks.
 

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1 hp Trabant is not my real car
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QUOTE An electromagnetic field exists

Um, a Bill... re your definition of EMF:

EMF that we are talking about here is Electro Motive Force, not ElectroMagnetic Field. (Re the title)

EMF is normally expressed as Volts.
Back EMF is the energy generated by a motor that opposes the energy turning the motor..... or words more or less to that general effect.

But then I lost the plot on electrics when some wag determined that electrons actually flow in the opposite direction to the current


Cheers, Tom.
 

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Thank you Isetta.

Basically, you don't want these possible EMF spikes into your computer. And yes, I've seen fried cards. Luckily not fried computers.
The base is that the com-card is made to handle it's own signals (5V and almost no A). It's not made to handle the EMF.
You can surely try to minimize it with both resistors and diodes, I wouldn't. I would go back to basics and not allow it to even maybe happen.
But that's me, I'm the not perhaps cautios guy, I am the guy that tries to see it doesn't risk happening at all.
 

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hi, guys
as a mechanical type and not an electrical type...I am only half following this thread. one thing occurs to me though...is that part of the discrepancy is that some are thinking EMF is ElectroMotiveForce and others are thinking ElectroMagneticField. If I am wrong in this...please don't shoot me *grin*

meanwhile, I have a junky old 400 MHz machine sitting in the corner. Keep talking, maybe I need to hook it to my track?? now there's a thought...

cheers,
John
 

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1 hp Trabant is not my real car
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John,
The definition of the acronym EMF is just a small side issue.

The gist of the thread is that as the car passes over a "dead strip" made for lap counting, the sudden absence of applied volts will allow the motor to revert to its "alter ego" and become a generator (driven by the car momentum). The car will feed this voltage back to the track and thence to a computer connected to it.

I think all on the thread are in agreement that this voltage exists whatever we call it. The open discussion is about how much and is it a real, potential, or non-existant hazard to the health of your computer circuits.

All you want the dead strip to do is act as switch contacts, to be bridged by the car circuitry, not belt a bunch of volts into your poor PC.

I have no idea if it is harmful to the PC or not (although in theory it should be, and as we are dealing DC, it can be eliminated by diodes as mentioned elsewhere). But I am enjoying the thread and look forward to more opinions/theories.

Cheers, Tom.
 

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John, go for it
That computer is a rocket ship compared to what you need.

Electromotive force? I'll have to get back to you
All of these acronyms are killing me.

Does anyone have a track with a dead section that they can disconnect the lap counter/timer from and hook up a volt meter? Then we'd see exactly how many volts are being made by the motor. Unless you have a very high quality digital multimeter you should use an analog meter as they respond faster.

I really believe that the voltage is too low and for too short a duration to be of consequence. That and most tracks I've played on use dead strips with computer lap counter/timers and never failed.
 

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This issue has been discussed several times in Slot Adictos spanish forum.

Some people fried their parallel port using dead strips and 1/32 slot cars (SCX/NCx motors) Why? two reasons:

1) If motor is generating positive voltage compared to computer ground, more than 5v are applied and, if sensor is programmed to read low doesn't work now.

2) If motor is generating negative power to computer ground, less than 0v are applied and, if sensor is programmed to read high doesn't work now.

So first we install a 4v7 zener diode with the dead strip, cathode is positive in parallel port. Then me make sure all dead strips are correctly connected (polarity) to computer to make sure that all cars are detected.

That's our experience, hope it helps.
 
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