Coldgunner Posted July 29, 2012 Share Posted July 29, 2012 My Gresley Buffet car has been sitting on my DCC circuit for around 20 mins and picked it up, only to find the roof is very hot to touch. I've only got one of these coaches so can't compare to another unit. Is this normal, should I be worried about it? Link to post Share on other sites More sharing options...
Orion Posted July 29, 2012 Share Posted July 29, 2012 Could just be that everyone's ordering toasted sandwiches? Link to post Share on other sites More sharing options...
Baby Deltic Posted July 29, 2012 Share Posted July 29, 2012 It depends how hot it is. Some of the ultrabright LED's can give off a fair amount of heat aswell as light. If it is 40 - 50°C I might not be too worried. If it is hotter, it might need bigger resistors to limit the current a bit more. Link to post Share on other sites More sharing options...
RMweb Premium Nile Posted July 29, 2012 RMweb Premium Share Posted July 29, 2012 The LEDs shouldn't be generating any heat, they are too small.I suspect a fault elsewhere in the circuit, such as a short circuit or wrong value component that is causing something to overheat. Link to post Share on other sites More sharing options...
M Graff Posted July 29, 2012 Share Posted July 29, 2012 I have updated a lot of older passenger cars to modern specs when it comes to resistor values. If the electronics are made for DC, and being exposed for the high voltage of DCC, problems WILL show! My guess is that you have either old equipment or faulty electronics...... Link to post Share on other sites More sharing options...
Dr Al Posted July 29, 2012 Share Posted July 29, 2012 The Dapol light bar doesn't use resistors as far as I'm aware, but a voltage regulator instead. I'd check the current consumption, and also clean any flux off the circuit board. I've seen several Dapol PCBs and light bars that seem to semi- short circuit because of this, but work fine once cleaned up. Cheers, Alan Link to post Share on other sites More sharing options...
Edwin_m Posted July 30, 2012 Share Posted July 30, 2012 What's your DCC track voltage? Link to post Share on other sites More sharing options...
Coldgunner Posted July 30, 2012 Author Share Posted July 30, 2012 No idea, I'm linked up through a SPROG II, which draws power from the 18v AC on my HM2000. Link to post Share on other sites More sharing options...
Vonzack Posted July 30, 2012 Share Posted July 30, 2012 I use a Sprog II as well, I have fed it with 17V DC from a Lenz Power Pack and at the track it looks like 21v (because of the square wave DCC signal), which was IMHO a little too high for N, so I switched to a 14v DC supply which gives me 17v at the track. Allowing for the error in reading a square wave with a multi-metre, I'm probably getting around 16v to the track. You should be feeding the Sprog via DC, then it converts into an AC DCC signal. I'm not sure how the light bar limits or regulates the supply, but it may be that your track voltage is higher than it's design maximum and this is causing it to heat up. Cheers, Mark. Link to post Share on other sites More sharing options...
Elvinley Posted July 30, 2012 Share Posted July 30, 2012 I had a couple of light bars get so hot they melted the coach roofs. Get in touch with Joel and he will sort it out for you. In my case he sent me replacement light bars and replaced the damage coaches. Most of the light bars work well, but there are a few out there with this fault. Link to post Share on other sites More sharing options...
Gordon H Posted July 30, 2012 Share Posted July 30, 2012 The LEDs shouldn't be generating any heat, they are too small. Not strictly true, and It has nothing to do with size as such. When lit, LEDs have voltage across them (Vf), and are passing current, therefore power is being dissipated. However, this can normally be taken as negligible on individual LEDs. A typical white LED might have a Vf of 3.2V, and be set to 10mA current, so it would dissipate 32mW. Once you start putting several of these together in an enclosed space (as with a light bar), plus any associated current regulation circuitry (typically a number of resistors), when they are all added up the overall power consumption can start to become significant. Series connection of the LEDs helps, but you then have to be careful about the supply voltage to ensure there is sufficient headroom for the current regulation to be effective. Link to post Share on other sites More sharing options...
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