# Circuit breaker questions



## Phishead (Sep 19, 2008)

I have heard that heading to Napa and asking for the lowest rating circuti breaker they have will do the trick.

Well my local Napa only stocked 20A breakers.

What is the recomended rating for a breaker or fuse system?

Any help would be greatly appricated.

Thanks,

Jasen


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## rbrunne1 (Sep 22, 2007)

What's the circuit breaker for? Are you adding a branch circuit for AC power or is this for DC track power?


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## Phishead (Sep 19, 2008)

Useing the breaker at the driver stations. 

The power supply I will be useing down the road will be 0-20v 10A.


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## rbrunne1 (Sep 22, 2007)

Each lane would need a 2 or 3 amp breaker or fuse. Mouser Electronics has one 3A, 50VDC panel mount circuit breaker for $13.97 (see link below):

http://www.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMtOvozo//68GEIe4OTCK%2bYXt1TNz1cLg5A=

Another option is to use a panel mounted fuse holder with 1-1/4x1/4" fuses. Each fuse holder is $1.99 at Radio Shack (http://www.radioshack.com/product/index.jsp?productId=2062230) and a 4-pack of fuses are $1.99 at Radio Shack (http://www.radioshack.com/product/index.jsp?productId=2102743).


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## Phishead (Sep 19, 2008)

Thanks much for the info


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## E-Force-1 (May 31, 2007)

Phishead,
You didn't mention what kind of circuit breakers. Hopefully this is what you are looking for.

Try giving Lucky Bob's Slot Cars a call at 414-327-4003. I think he has what you are looking for. I don't know where he gets them from, but he has low amp inline blade circuit breakers. NAPA and other auto parts stores have 20 Amp and on up. We use these as a resetable fuse in our controllers instead of a standard blade fuse.


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## Phishead (Sep 19, 2008)

Yea those are what I was talking about. Planning on useing them at the driver stations to protect the controllers.

It just seemed to me the Napa ones at 20 amp might be to high.


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## GoodwrenchIntim (Feb 22, 2005)

Phishead said:


> Yea those are what I was talking about. Planning on useing them at the driver stations to protect the controllers.
> 
> It just seemed to me the Napa ones at 20 amp might be to high.


you still have to be care full with those, they sometimes wont trip before its to late, I had 3 or 5 amp on my track an went back to fuse after a couple of controllers got fried. I use 5 amp fuses an have had no controllers fried since


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## Phishead (Sep 19, 2008)

I decided to go with the fuse route. Picked up the fuse holders from Radio Shack and some 3 amp fuses since the power supply I have now is only the BSRT 12 volt, 2Amp one.

The fuse holders support up to 10 amp so I have some room to expand when I finally get a bigger power supply.

I might put one of the resetting breakers inline with my trackmate system when I get more juice just in case.

Again, thanks everyone for their input on this. 

Jasen


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## brownie374 (Nov 21, 2007)

Jasen do not go with fuses if you run the flat shoes like on some if the xtactions they will blow like crazy.Thats what I used to have now I have 6 amp circuit breakers.I bought the at bowman electronics in valpo.I believe I gave you thier card.


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## Phishead (Sep 19, 2008)

I totally forgot about that place Rick. I believe I still have the card in my slot car box, gonna have to dig through it.

Do you think useing the fuses will cut it on this small power supply I am running (12v 2A) and upgrade to the 6 A breakers when I get the bigger supply? Or should I just get them now?


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## AfxToo (Aug 29, 2003)

Newark electronic distributors has DC compatible breakers in a wide variety of sizes, mounting styles, and form factors. Go to this site and select the DC voltage and current rating you want and you'll get a number of available choices.

http://www.newark.com/circuit-breakers_thermal

Select a voltage that's around 1.5X higher than your maximum track DC voltage, say 32 VDC or 48 VDC, and then select the current rating you want, say 3A (I use 5A because I run hotter cars on occasion). Then pick the style you want. If you are mounting the breaker on a panel, make sure the part of the breaker that protrudes through the panel is long enough for your panel thickness. There is a datasheet associated with most of the products that lists the detailed characteristics of the device. You can get automatic or manually resetting versions. I prefer the manual style because they alert you to the overcurrent situation.

Note: If you only select the desired current rating, say 3A, then you'll get a larger selection. As long as the rated DC voltage is 1.5X your max supply voltage you are good to go. 

When using thermal breakers on a per lane basis, you will still want to put a fast-acting fuse inline with the main power feed going to the drivers stations. The fuse should be rated for whatever max current limit you want for your whole track and to protect the main supply and wiring. I have a 10 amp supply so I use a 10A fuse on the main feed and each drivers station has a 5A breaker. A 3A breaker on each station probably would have worked just as well. If you are using batteries the fuse becomes even more important since batteries can generate enough current to melt the wiring.


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## Dslot (Sep 2, 2007)

AFX Too,
Let's talk the basics of fuse/breaker protection. I'm pretty hazy on the subject, never having protected a circuit for a slot layout, other than whatever breakers the packs may have inside.

In the following cases (see illustrations), assume cars are basic T-jet/AFX/Magnatraction/Tomy SRT/Tyco 440-2, pulling - what? - maybe 1/2 to 3/4 Amp each, max? No super-performance mods, etc.

In *Case A*, (separate circuits), I guess you'd fuse each circuit 1.5 x 20 = approx. 30V. So, a 32V-1A fuse in each circuit, right?

In *Case B*, (common return), would you fuse the common return line with a 32V-2A fuse, or fuse each lane input at 32V-1A?

In *Case C*, (single power source), would you fuse each lane at 32V-2A, or 32V-1A, or would you fuse the common return line at 32V-2A?

Are there any other characteristics to look for in fuses or breakers, such as slow-blow, fast-blow, or whatever?

Would brake circuits complicate the issue, requiring additional fuses?

Thanks for your expertise.
-- D


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## Dslot (Sep 2, 2007)

How do you decide at what amperage to protect the circuit? I assume you take the component with the lowest amp-tolerance and base it on that.

So if the circuit contains diodes, say, that are rated for 1 amp, do you use a 1-amp fuse? Lower? How much? And how do you know how much amperage, say a slot car or controller will take without being damaged?


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## AfxToo (Aug 29, 2003)

The protection devices you choose should be based on what you are trying to protect. The protection devices you choose should be based on the manner in which the devices that you are trying to protect react to over-current and/or over-voltage conditions. How you apply the protection devices depends on the nature of the threat. I'll try to explain...

In each of your diagrams, there are 6 things potentially at risk if you add a car to the circuit and ignore secondary effects (like fire): 

1) Your Home Wiring

Your home wiring is potentially at risk depending on how the power supply reacts to an over-current situation. At higher than normal current load the power supply will draw maximum power from your home wiring on that circuit. If you've put an unusually large power supply on an undersized circuit and your home's protection circuit is inadequate or defective, the home wiring could heat up and cause damage. If you have an over-current protection device on the power supply output, a fuse or circuit breaker, or if the power supply has internal protection, the power supply would be disconnected from the load and draw minimum power from your home wiring.

2) The Power Supply

While most power supplies have some sort of integrated short circuit protection, like fuse or crowbar circuit, some do not. The most concerning one that does not have protection is a battery. If something conductive shorts a battery, very bad things usually happen. If you are lucky, something in the short circuit path melts and opens the circuit. If you are very unlucky the battery overheats and explodes. Using batteries without a protection device in the circuit to protect the battery is insane. In fact, because circuit breakers are generally slower to react than are fuses, using a fuse is the preferred way to protect a battery. Just keep in mind that the fuse is there to protect the battery or power supply, so don't size it too small. Use secondary protection devices to protect other things in the circuit from currents that are less than what are harmful to the power supply/battery. 

3) The Controller

Controllers are typically the first casualty in an over-current scenario. This is also where having brakes wired raises the threat level considerably. The brake connection is attached to the negative terminal on the power supply. The brake band in the controller is attached to the control rail on the track. When the controller is in the brake position you are placing a short circuit, or a small brake resistance value (brake pot), across the track rail. This is true for all controllers with brakes. If you hookup your controller wrong, notably by placing the positive controller lead (white) on the positive power supply connection (white) at the drivers station and the controller track control lead (black) on the brake connection (red) - as soon as you pull the trigger you will be routing the full power supply current through your controllers track control circuit. If you bury the throttle quickly enough you will be shorting out your power supply, and if it is protected you may be lucky and it will open and you will still have a functioning controller. If you ease on the throttle your controller and your power supply can source many amps, your controller will probably be damaged. On a resistor controller the resistor windings will typically melt. On a transistor controller, the power transistor will usually blow. To prevent controller damage you should either have a current protection device on the controller, the red lead is a good choice, or a current protection device on the drivers station. This is why I recommend a smaller circuit breaker or slow blow fuse on the drivers station, to protect the controller. 

4) The Track Wiring

The amount of current a wire can handle is related to its conductor material and wire gauge. Say you have a big fuse protecting your battery, smaller ones at the drivers stations protecting the controllers, and because you found a spool of free telephone wire at a yard sale you decide to wire your track with it the weekend before the big unlimited race. Everyone's smiling and happy, mesmerized by the sights and sounds of the unlimited beasts, when suddenly a puff of smoke appear from under your track table. No blown fuses, no cars stopped, but the smell of PCBs mixed with woody overtones wafts across the room. Then everything stops as you scramble for a fire extinguisher. The track wire just became the weakest link and if you are lucky, a fuse. I've actually seen this scenario, on a 1:24 scale track. If you have undersized wiring, check its current rating and size your protection devices accordingly.

5) The Track Rails

Same issue as track wiring. with sufficient current and inadequate protection, the rails can become a fuse. More likely however, something will short the rails, like a wire retainer on a T1 for example, and under full throttle and with sufficient current on tap, you end up with some nasty arc burns on your track rails. Don't ask me how I know.

6) The Car

Look at the size of the wires wound on your motor's armature. Not very big, almost as small as the wire in a fuse. Imagine your car wrecks, gets reslotted, but the rear wheels are now locked when you hammer the throttle. Inadequate current protection in the circuit and unwillingness to let off the throttle results in a little puff of smoke. Suddenly you're making funeral arrangements for your favorite motor. Hopefully, the track bears no scars from your little impromptu barbecue.

The concern here is over-current protection. Thermal circuit breakers typically use a bi-metal contactor to trip the circuit and it takes time to build up heat in the device. The heating effect is different for AC versus DC and that's why the voltage ratings are different for each current type. But within the specified voltage range, these are current protection devices. Picking a device that has a voltage rating 1.5X the expected voltage is just good practice, or engineering margin. 

Case A: Fuse each power supply (+) lead at 1A. 

Case B: Same as A. Putting a 2A fuse in the return line would give you the same total protection when both lanes are running, but when one lane is open you are now running the remaining lane with a 2A fuse. If you really want 1A limit for protecting each power supply, this does not deliver the protection you want.

Case C: Depends on what you are trying to protect. If you are only concerned about the power supply, you could fuse the return line at 2A. If you want to protect the controllers at something less than 2A them I would add a lower rated fuse to each power supply (+) lead.


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## brownie374 (Nov 21, 2007)

If you use the 3 amp fuses buy alot of em,My 6 amp breakers will click on occasian but havent popped yet.My power supply also has a fuse.I got tired of the fuses slowing up my races as you know sometimes I get a pretty big crowd 15+racers and only 4 lanes.


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## blubyu (May 4, 2008)

I use 5A at each controller station. Last race Red lane kept blowing until the racer removed his car with a axle retainer stuck to the bottom magnets from the lane,his controller (Lucky Bob's) was fine. I know what Brownie means when running Ski shoes on Pancake cars, slow acting fuse might help some?


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## AfxToo (Aug 29, 2003)

Read the data sheets on the protection devices you are considering, especially thermal breakers, but also slow blow fuses. The current rating of a thermal breaker, say 3A, is typically the max continuous current that it can take - without ever tripping. The trip current is much higher and is a function of time, a lot more time and current than you may be able to afford. 

A quick look at some of the trip time specs for 6A thermal breakers shows that current would have to be at 3X rated current, or 18A for greater than _10 seconds_ to trip the breaker. If you are drawing 18A continuous for 10 seconds on a single lane, something is seriously wrong and your controller is probably going to be toasted long before you trip the breaker.


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