NIK Posted January 21, 2020 Share Posted January 21, 2020 2 hours ago, Pete the Elaner said: If you want to find resistance, then surely it is easier to use the resistance setting on your multimeter? Who has a 10 ohm 5 watt resistor in their electronics box going spare? Who even has an electronics box? (actually I have 2 ... until I find another I had forgotten about, but many don't). I use the method described earlier by Crosland. We may not have a fat resistor but all have a spare piece of wire. Hi, If there are suspect joints through the layout the resistance may increase when the current a loco takes is flowing. The interest is normally is checking for good running so testing for DCC voltage at typical loco currents is a way to do that. I think if the DCC voltage were 15V then a 10 ohm resistor would have to be 22.5 Watts rating to be on the safe side (power dissipated = R * I squared, 15 volts /10 ohms = 1.5 Amps, 1.5 squared = 2.25, 2.25 * 10 ohms = 22.5 Watts). Regards Nick Link to post Share on other sites More sharing options...
Pete the Elaner Posted January 21, 2020 Share Posted January 21, 2020 11 hours ago, NIK said: If there are suspect joints through the layout the resistance may increase when the current a loco takes is flowing. But suspect joints will be revealed by a resistance meter anyway. If it says zero, then you don't have a problem. A joint's resistance will only increase due to current indirectly (because it gets hot..& it needs power to heat something up) & it will only get hot at normal running currents (up to 5A) if there is a measurable resistance in the first place. If you can't measure a resistance, you won't need a measurable voltage. Without voltage, you'll have no power. Without power, you'll have no heat. Without heat, the joint's resistance will be constant. & without music they can't dance & if they can't dance, they can't kiss, & if they don't kiss they can't fall in love & I'm history. So if your meter reads zero ohms, the joint or section will not gain resistance as the current increases. A joint/section which already has resistance (which is unwanted anyway) will ... but you will read this with a resistance meter. 11 hours ago, NIK said: I think if the DCC voltage were 15V then a 10 ohm resistor would have to be 22.5 Watts rating to be on the safe side (power dissipated = R * I squared, 15 volts /10 ohms = 1.5 Amps, 1.5 squared = 2.25, 2.25 * 10 ohms = 22.5 Watts). I agree with your calculations but where would you find a 22.5W resistor? These are not normal electronics products. Rapid don't seem to have one on their website. Multimeters are much more useful than just for reading voltages. I use mine for reading resistances far more often. Link to post Share on other sites More sharing options...
RobjUK Posted January 22, 2020 Share Posted January 22, 2020 (edited) 8 hours ago, Pete the Elaner said: But suspect joints will be revealed by a resistance meter anyway. If it says zero, then you don't have a problem. Agreed - but Nik has a point with "load", though mechanical not electrical. If a layout is relying on fishplates for electrical connections, the resistance may change slightly if the track can flex. If any problems are suspected, I'd meter it for resistance while running an unpowered truck over joints with a bit of finger pressure to see if anything changes with flexing. It's not something that would be a possible problem if all track sections have individual feeders. Edited January 22, 2020 by RobjUK Link to post Share on other sites More sharing options...
Paul80 Posted January 22, 2020 Share Posted January 22, 2020 Remember what confucius said about meters An electrician with one meter always knows the correct voltage An electrician with two meters never knows the correct voltage. Hat coat door 1 1 1 Link to post Share on other sites More sharing options...
NIK Posted January 22, 2020 Share Posted January 22, 2020 8 hours ago, Pete the Elaner said: But suspect joints will be revealed by a resistance meter anyway. If it says zero, then you don't have a problem. A joint's resistance will only increase due to current indirectly (because it gets hot..& it needs power to heat something up) & it will only get hot at normal running currents (up to 5A) if there is a measurable resistance in the first place. If you can't measure a resistance, you won't need a measurable voltage. Without voltage, you'll have no power. Without power, you'll have no heat. Without heat, the joint's resistance will be constant. & without music they can't dance & if they can't dance, they can't kiss, & if they don't kiss they can't fall in love & I'm history. So if your meter reads zero ohms, the joint or section will not gain resistance as the current increases. A joint/section which already has resistance (which is unwanted anyway) will ... but you will read this with a resistance meter. I agree with your calculations but where would you find a 22.5W resistor? These are not normal electronics products. Rapid don't seem to have one on their website. Multimeters are much more useful than just for reading voltages. I use mine for reading resistances far more often. Hi, RS do 25 Watt resistors. Regards Nick 1 Link to post Share on other sites More sharing options...
Pete the Elaner Posted January 22, 2020 Share Posted January 22, 2020 12 minutes ago, NIK said: Hi, RS do 25 Watt resistors. Regards Nick Never seen them on sale before, but at over £2 each, they are not something many would have lying around in a components box. & you couldn't plonk it across the rails them move it around...not without a pair of oven gloves anyway. Dare I ask...have you got one or is this just theory? ...bearing in mind you suggested 10ohms & they don't seem to have one available this size. Link to post Share on other sites More sharing options...
Crosland Posted January 22, 2020 Share Posted January 22, 2020 3 hours ago, Paul80 said: An electrician with one meter always knows the correct voltage An electrician with two meters never knows the correct voltage. With two meters you can know voltage and current. Perhaps Mr Heisenberg has something to say about that 1 Link to post Share on other sites More sharing options...
Gordon H Posted January 22, 2020 Share Posted January 22, 2020 13 hours ago, Pete the Elaner said: I agree with your calculations but where would you find a 22.5W resistor? These are not normal electronics products. Rapid don't seem to have one on their website. Really? How about this whole section of their website: https://www.rapidonline.com/power-resistors 4 hours ago, Pete the Elaner said: Never seen them on sale before, but at over £2 each, they are not something many would have lying around in a components box. & you couldn't plonk it across the rails them move it around...not without a pair of oven gloves anyway. Dare I ask...have you got one or is this just theory? ...bearing in mind you suggested 10ohms & they don't seem to have one available this size. How about Rapid 62-8112 or RS 157-550? Suggest you check the facts before making such sweeping statements. 1 Link to post Share on other sites More sharing options...
John ks Posted January 22, 2020 Share Posted January 22, 2020 Instead of using a 22.5W resistor why not use an automotive bulb rated at 20+ watts It gives an instant indication that volts are on the track & if it is dim then you know something is wrong In stead of putting your ohm meter next to the command station/booster & shorting the track at different places why not put the short at the command station/booster & measure the resistance at any part of the layout. On a large you wont have to continually go to & from the short to the command station to read the meter a lamp with a couple of alligator clips like these which may only be 5-10Watts John 1 Link to post Share on other sites More sharing options...
NIK Posted January 22, 2020 Share Posted January 22, 2020 1 hour ago, John ks said: Instead of using a 22.5W resistor why not use an automotive bulb rated at 20+ watts It gives an instant indication that volts are on the track & if it is dim then you know something is wrong In stead of putting your ohm meter next to the command station/booster & shorting the track at different places why not put the short at the command station/booster & measure the resistance at any part of the layout. On a large you wont have to continually go to & from the short to the command station to read the meter a lamp with a couple of alligator clips like these which may only be 5-10Watts John Hi, Sound like a good idea especially as it avoids having to find space on the tracks or scenery for a meter and it could keep your hands free for operating points, waggling connectors/wires etc. Could put a clear housing round the bulb to protect it from getting crushed in a tool box?. Regards Nick Link to post Share on other sites More sharing options...
Crosland Posted January 23, 2020 Share Posted January 23, 2020 23 hours ago, John ks said: In stead of putting your ohm meter next to the command station/booster & shorting the track at different places why not put the short at the command station/booster & measure the resistance at any part of the layout. On a large you wont have to continually go to & from the short to the command station to read the meter Even better Link to post Share on other sites More sharing options...
RAF96 Posted January 23, 2020 Share Posted January 23, 2020 Use a Mk 1 thumb run along the rails to check for hot spots, generated by high resistance joints like loose or corroded fishplates. Cheaper than a meter if you discount the cost of sticky plasters for the burns. Link to post Share on other sites More sharing options...
Anthony566 Posted February 5, 2020 Share Posted February 5, 2020 I see Dcc Concepts have now got the new meter in stock .... Link to post Share on other sites More sharing options...
WIMorrison Posted February 5, 2020 Share Posted February 5, 2020 But not useful for using to fault find a layout as it is designed to be a panel mount across the terminals of you command station to give you the command station output voltage and current draw. Could have been an excellent and useful additional to a modellers bag of tricks, however the current design is limited in usability. Link to post Share on other sites More sharing options...
Anthony566 Posted February 5, 2020 Share Posted February 5, 2020 39 minutes ago, WIMorrison said: But not useful for using to fault find a layout as it is designed to be a panel mount across the terminals of you command station to give you the command station output voltage and current draw. Could have been an excellent and useful additional to a modellers bag of tricks, however the current design is limited in usability. Hmm I was planning on buying the triple pack and mounting one in a box as that would make it extremely portable..... I can box mount it for less than the RRamp V2 cost plus i think it looks better coz lets face it ....it's all about the looks really. Link to post Share on other sites More sharing options...
WIMorrison Posted February 5, 2020 Share Posted February 5, 2020 If I was spending that sort of money I would expect it to come in a box with leads and have all the functionality without any effort from me - as it is you will need to bridge terminals somehow to make it work as it must have an input and an output side - it has to have that to be able to measure the current draw as an ammeter is in series with the circuit whereas the voltmeter is across the circuit. I will admit haven't seen one but that is how it has to work and if it as easy as you say why do they not sell it like that, or even advertise that it can be used like that? Link to post Share on other sites More sharing options...
Grovenor Posted February 5, 2020 Share Posted February 5, 2020 Quote plus i think it looks better coz lets face it ....it's all about the looks really. Yep, just a vanity item, hence the price. Link to post Share on other sites More sharing options...
Anthony566 Posted February 5, 2020 Share Posted February 5, 2020 2 hours ago, Grovenor said: Yep, just a vanity item, hence the price. Hmm not sure about that one... V1 is £3 less and the V2 is £28 more .... Link to post Share on other sites More sharing options...
arff999 Posted February 6, 2020 Share Posted February 6, 2020 Go take a look at the website posting, there to me anyways its pretty obvious it does amps. this is the spec Power – DC or DCC, 5-29V, 10 amps max. Power – AC, 5-20.5V, 7 amps max. https://www.dccconcepts.com/product/alpha-meter-for-dc-or-dcc/ John Link to post Share on other sites More sharing options...
WIMorrison Posted February 6, 2020 Share Posted February 6, 2020 Nobody has said it doesn’t do current ... Link to post Share on other sites More sharing options...
Anthony566 Posted February 7, 2020 Share Posted February 7, 2020 I see DCC Concepts have mounted one in a small project box and posted a how to ..... https://www.dccconceptsforum.com/post/alpha-meter-in-a-box-a-quickie-project-10423826 Link to post Share on other sites More sharing options...
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