Hi



Over the last 6 months, I have shorted 3 controllers. It took a while to clue in what was happening. I use a 10AMP power supply set at 18 volts, for a 4 lane routed track with braid (as opposed to rails, really increases shoe life!!!).



The power supply is fused, but I do not have an inline fuse for the power supply. I have been painfully repairing my Parma’s, replacing the fried resistors with 90 ohm Parma resistors (painful b/c soldering irons and "lectricty" in general are not my friends). I tried an HO world 120 ohm resistor but it was a piece of crap that fell apart as I tried soldering it to the controller wire. I am not the best at soldering but the Parma resistors held up and the HO world one didn’t.



Anyway, I did put 1 amp in line fuses in the black controller wire for each controller. got 4 of them wired up last night and did some racing. As I was testing, I began to notice that during a slide that didn’t result in a de-slot, but did cause the car to end up not contacting the power braid, about 1/5 the time would blow a fuse. Now, a fuse is cheaper than a resistor, and the in line fuse kits worked well, but I am wondering if there is something wrong with my setup (besides my driving!) that causes these shorts. I was using JLTO, JLXT, and AFX magnatractions, last night, and at various times each type caused a short. During one short, I had 4 controllers hooked up to different lanes, and 3 of the 4 controllers blew a fuse (the one that didn’t had a slightly larger fuse, 1.5A vs. 1A).



So, here are some questions:



1) How large of a fuse can I use and still protect the resistors?

2) Is there another cure for these shorts?

3) Should I put an inline fuse to the power supply (which already has its own fuse? If so, how large?





Thanks

Mike

Mike,

Your braid has a wider contact area than regular rails, therefore when your car slides the bottom of the Pickup shoes is shorting across both braids.

On the Magnatraction style cars, the solution is easy. Just get some Aurora Small Step shoes that they made and retrofit your runners.

For the Tjets, I don't know anyone making a small step shoe. The Very early tjets had a small step, but they went to long step shortly after release so I doubt you will find a supply of NOS of those.

Another thing you can do is go to a 1.5 Slow Blow fuse, they can take short spikes without blowing. Radio Shack should stock them.

Good luck,

Keith

Without seeing your wiring schematic I'm guessing that the underside conductors and shoes on those pancake chassis are shorting across the track conductor braids when the car slides out. The same thing can happen with "ski" shoes. Try running a magnet car chassis with short step shoes. Then try taping over the underside of a pancake chassis to insulate it. Just use masking tape for the experiment.

An alternative to fuses are low voltage DC circuit breakers. These are used on boats and some RV vehicles. They usually have a reset button on them to restore them after a trip but some of the smaller amperage ones are auto resetting. Don't use home AC style circuit breakers, they won't provide the protection you think.

Ideally what you should have is a fast acting high current fuse (10A for your setup) on the main power lead and individual lower current DC breakers or slow blow fuses on each individual lane, say 5A or 6A.

Never count on a power supply's built-in protection circuitry to protect your equipment. The short circuit protection (or crowbar circuit) on a power supply usually clamps the current to a fixed high value (like 10A) if the outputs are shorted, it does not open the circuit unless there is a breaker or fuse on the power supply unit itself.

If it's a shoe problem, BSRT makes a "thunder shoe" that has a shorter step. Since you are using braid and your shoes last a long time and have less friction on them you could also try painting over part of the shoe to reduce the contact area. Same goes for the underside electricals other than at the contact points. Cellophane tape may work too.

for the very insightful replies.

i agree the issue is that the braid is wider than rails, so slides can result in shorts. i have been to RS for some slow burning 1.5-2Amp fuses, as well as an * Amp fuse for the power supply.

ive got too many runners to worry about replacing shoes, so i will just stock up on fuses!

thanks again

mike