PDA

View Full Version : choke box's



quakebo
03-26-2003, 10:35 AM
can anyone tell me what choke box's do

RomanK
03-26-2003, 10:40 AM
Simply put, a choke box is nothing more than a means of placing a length of wire between the white controller wire and the track.

"ie" the #10 on the choke indicates 10 feet of (usually) #18 Ga wire

Normal use is to tame down a hot wind armature to increase longevity and driveability.

BigDaddy
04-09-2003, 01:01 PM
A "choke" is another word for an inductor. An inductor is a coil of wire as Roman says. The beauty of a coil is that when an sudden change of current occurs in the wire making up the coil, a magnetic field is generated that induces a current in the opposite direction. Remember your high school physics "For every action, there is an equal and opposite reaction." The coil effectively resists any "sudden" change in current.

What this means to a slot racer is that it prevents any large sudden current spikes from reaching your armature as is the case with GRP-7s and other open classes. Once the current reaches a steady state, the choke does nothing except for an insignificant DC loss over the effective length of the coil.

The theory is that a choke protects high current arms from potentially damaging current spikes that occur when the driver pulls the trigger on the controller (and releases the trigger).

Hope this helps.

jake
04-10-2003, 06:31 AM
A couple of the guys at my local track have chokes that I have tried but I just don't like the delay in acceleration that they cause. When I want to go I want to go. Does this mean that the coil needs to be shorter (some of the guys have taps).
As far as the protection, what happens to your motor without the choke ? (..the health risks of unprotected slotracing )

Thanks and regards/jj

BigDaddy
04-10-2003, 06:55 AM
Jake,

The effectiveness of a choke is measure in Henry's or more typically milliHenries (i.e. H or mH). There are several physical parameters of the choke (inductor or coil) that can be changed that will change the behavior of the choke. Reducing the length of the coil by placing taps on it will lower the protection offered by the choke. Of course your are trading protection for a little more "snapiness" in the controllers performance. You can measure the choke by using a good multimeter with an inductance measurement capability.

Since I am primarily a Box Stock 12 racer, I don't have a lot of experience with the feel of chokes but I am an electrical engineer so I know the theory behind it. It seems to me that since a wing car is pretty much kept up to speed once the race is started, the little trade-off in snapiness is worth the protection afforded by the choke.

As far as what happens to the motor without the choke, smoke and flame is likely during periods of high stress on the armature. High stress occurs during acceleration and more so on higher load armatures (like the Group 7s and open classes).

Remember the law of physics "For every action there is an equal and oposite reaction?" With electric motors, once current is applied, the windings of the armature resist the immediate change in current because they are chokes themselves. This (equal and opposite reaction) resistance manifests itself as heat. Eventually as the motor starts to turn, the energy is translated into motion instead of heat. It is during the intial startup that your risk of damage to the armature is highest and the choke will provide the most protection. Did you ever wonder why light bulbs seem to burn up when you first turn them on? Same theory. A bulb that is never turned off will sometimes run forever!

I hope I made sense....

RomanK
04-10-2003, 09:23 AM
Rumor has it that you are making the trip south to do some wing car racing this weekend........that right?

Cya there!!

BigDaddy
04-10-2003, 11:55 AM
Yes sir! And I am better preapred this time. Last time was a real learning experience for me seeing how the big boys play. I built a couple of fast motors so I have little more depth this time. With better weather, I can hang out longer too!

I'll be there tomorrow after noon so I can help out marshalling the Grp-12 Pros tomorrow night. I am looking forward to the Spec-15 and Box Stock Am on Saturday.

I'll see you there...

jake
04-11-2003, 05:54 AM
Hey Big Daddy
Thanks for the info. Sounds like the old tradeoff of reliability for performance again (an equal and opposite reaction...)
Regards/jj

GearBear
04-13-2003, 02:53 PM
The side affect that Big D didn't mention is that when you are running a really hot motor using a "few feet" of choke will often make it a lot easier to drive the car. We use chokes quite a bit with the Group 12 IRL cars in the PNW AMCA servies because the cars are so over powered in comparison to their handling that without a choke you tend to over drive the cars. The choke will help you smooth out the car making you faster. Any time you can keep the tires from just spinning when you hit the power you are better off! :)

BigDaddy
04-15-2003, 01:17 PM
Gary is right. It just goes to show you that all the theory in the world doesn't replace track experience. Roman showed me a choke at the Nats warm up this weekend. One of these days I need to try one so I can get the feel of one.

Roman, thanks for a great time this weekend. It looks like team Del pulled through!