I'm wiring a signal controller and one of the resistors they provide gets very hot (the documentation states this). What can I put around it to keep it from making other things hot and possibly melting the foam base? Would tinfoil wrapped around it help keep the heat contained or would that make things worse?
The N scale section of my website is now uploaded with a lot of various things. Check it out: www.CarlettaTrains.com
To expand on what Mel said, the resistor wattage rating is in "free air." It sounds like it might be close to its rating, so it is important to keep it in free air. Mel's suggestion to extend the leads and move it away from the components is right on the money. The last thing you want to do is cover it with anything. If you do, it will only get hotter.
The resistor will be continously generating heat and it must be able to disapate that heat. Covering it will have exactly the opposit effect. It will cause the resistor to get hotter and may result in damage to one or more components.
It may be that the "hot" resistor is not all that hot and no extraordinary efforts are required. Perhaps if you post more details, others with exerience with the same equipment can chime in and offer their advice.
i repaired a Tecktronics scope this way. I was fortunate to find a web page describing the problem I had which was a failed resistor. So I mounted it as Mel describes, with longer leads so that it is away from the circuit board allowing more air around it to cool it. It's worked so far.
greg - Philadelphia & Reading / Reading
Not a suggestion, but a follow-up question for the electronics guys... Why not replace the offending resistor with one that will support a higher wattage or even one of the fancy ones that's built into its own heatsink?
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The company states that the resistor may even turn red, but I didn't see that happening. I'll just have to be sure to keep it away from ever else.
KisNapturn red
as in "red hot"?
regardless of what the resistor is rated at, the current thru the resistor dictates how much power it needs to dissipate and how hot it may get. A 1W resistor is likely to be hotter than a 1/2 resistor running at rated power.
Obviously, a resistor is likely to fail if it has to dissipate more heat (watts) than it is rated at and presumably the board is designed to tolerate the heat it needs to disspate as well as the other components.
the best thing to do it mount the board where there is adequate air flow (vertically is the best orientation).
If the manufacturer states that the resistor may get red hot - then I'd consider a different controller, becuase that is some poor design. Either the resistor needs a heat sink, or it needs some active cooling. Or, it needs to be repalced with one with a higher wattage rating. If it's going to get 'red hot' then it's probably running right at its rating, say a 5 watt resistor dissipating 4.9 watts. That's where the bad design comes in, a better choice in that case would be a 10 watt resistor rather than trying to push a 5 watt one right to the limit. Or whatever the value happens to be, my numbers are just an example.
I assume this is more than just a signal controller - nothing in signalling or detection should have anywhere near that much current flowing to generate such heat levels. Is this one of those automatic train shuttle things where as it approaches the yellow signal it gets powered via the resistor so the train slows down, and then if it passes a red the power is cut off?
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
KisNap I'm wiring a signal controller and one of the resistors they provide gets very hot (the documentation states this).
I'm wiring a signal controller and one of the resistors they provide gets very hot (the documentation states this).
It sure is interesting that it's acceptable for a resistor to get "very hot". Since the manufacturer planned it that way, I suppose it's alright to trust them that there won't be any, uh, problems.
What can I put around it to keep it from making other things hot and possibly melting the foam base? Would tinfoil wrapped around it help keep the heat contained or would that make things worse?
I'm a little anxious about the phrase "possibly melting the foam base". I surely hope "the foam base" is not supplied by the people who also like hot resistors. Assuming YOU'RE the one supplying the foam base, you are right to be concerned. The other folks are quite correct that you want the heat from the resistor to dissipate in the air. But you do need to be careful about the foam. It would certainly make sense to monitor the area for awhile. Touch the foam and try to judge if it's getting too hot. If it is, the foam (as opposed to the resistor) might need an application of some protection. One thing might be a layer of foil that would, again, dissipate the heat before it gets into the foam.
But please keep an eye on that foam.
Ed
KisNapThe company states that the resistor may even turn red
If "The Company" you are refering to is Logic Rail and you are talking about wiring the infra-red emittor and collector for detection, you don't have anything to worry about.
I have over a dozen Signal Animators on my layout. The 180Ω 1 watt resistor gets warm but no where near HOT. All my Signal Animator boards are mounted to a small lauan plywood sub base to make installation neater and easier. The resistor is in free air only because I have it coming directly off the terminal strip so there's about a 3/4" rise off the board.
Read the instructions a little more carefully:
The manufacturer states that "When properly wired the emitter will have a very faint red glow coming from it.
The emitter is NOT the resistor. There is a barely visible glow coming from the IR emitter.
Instructions for some of Logic Rail's I-R wiring specify a 150Ω 1W resistor and there is no warning about the heat. Maybe they made a revision and didn't update the documentation?
I believe in this day and age of quick and easy litigation, manufacturers are prone to put warnings on the warnings to warn you that if you don't read the warnings, well, you have been warned!
I have a jar of peanuts that has a warning stating that these peanuts were processed in a facility that processes nuts! I wonder just what kind of nuts they were refering to?
Still doesn't hold up in court.
Don't worry about the resistor.
Regards, Ed
Now that makes a little more sense, although still seems like a LOT of current for an IR emitter. I'm sure it's in spec but if that much current is needed to drive the emitter then I'd think a constant current source would be a better option than having to waste nearly 1 watt of power in a series resistor. Plenty of effective IR emitters out there that use less than 20ma, too.
Just don't put the resistor in the foam - stand it up vertically off the board, then attach the wire to the emitter, and run just the wire through a whole in the foam, no reason for the resistor to touch the foam. It just has to be in the circuit - it doesn;t have to be soldered right to the emitter. There can be wires to either side of it, it's all the same circuit:
board|-------<resistor>-------<emitter>
board|<resistor>------------------<emitter>
board|-------------------<resistor><emitter>
all are the same electrically.
KisNap:
Another option would be to glue the resistor tight to a small piece of brass sheet. The brass will act as a heat sink (in other words it will absorb the heat) and the surface area of the brass will dissipate the heat much better than the resistor will just by itself.
Make sure that the resistor leads can't come in contact with the brass. You suggested wrapping the resistor in tin foil. That would be a bit risky because if the tin foil shorted the resistor leads you would probably fry the detector.
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
Thanks everyone and thanks GPPullman for straightening out my confusion. It makes sense now that the emmiter glows and not the resistor. I thought that seemed a bit extreme. I have it mounted with the resistor bent down to keep it away from the foam so all should be good. Thanks again.