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Electromotive

Feb 14, 2018
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Gentlemen and Ladies:

Just discovered this fine Forum. This is my first Thread.

I am building 5A regulated power supplies for my O-Scale 2-rail layout. I have built two using LM317T regulators but need to increase the power, as the existing ones only deliver a little more than 1 Amp @ 12V. Fine for HO, but not O-Scale. I will be using the LM338K w/heat sinks.

I am looking for two OKURA LP580 24VCT 5A transformers or equivalent. The closest I can find are generic 4A.

Anyone have any hints as to where these may be obtained? I have tried the internet and the larger brand component suppliers.

Thank you.... Tom Electromotive




 
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Electromotive

Feb 14, 2018
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Have you tried AnTec? He builds toroidal to order http://www.antekinc.com/
M.
Thank you Minder. Very interesting. Pricing appears very reasonable for made to orders. I would imagine I could use a larger current stock one of 8,3 Amps (200VA) and that wouldn't adversely effect my need for a 5 Amp or 120 VA transformer. I am assuming that the circuit determines the power consumption, not the transformer.

Thank you.... Tom E.
 

Minder

Apr 24, 2015
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Yes, the circuit demand decides transformer size of which is usually based on the core size and wire gauge and in turn determines (K)Va.
M.
 

dave9

Mar 5, 2017
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Why do you need a linear regulated supply with a toroidal transformer?

Why a transformer that's 24VCT instead of just 12V? I mean you state it's 1A @ 12V you're looking to increase current on?

Seems like something a basic 12V SMPS (switch mode power supply) would do well at lower cost, even virtually free if you have a spare computer PSU lying around. If you want to go that route and it's an ATX PSU, just short the connector PS_On signal line to ground and you may need a slight load on the 5V rail (maybe 1A load) to make 12V rail regulate within bounds with only 12V otherwise loaded, OR with simpler ATX PSU designs you could just alter a resistor or two in the feedback loop to keep 5V a bit lower so 12V doesn't drooped too much under load.

Or of course just buy a 12V, 10A PSU. Random example, $13:
https://www.ebay.com/itm/DC-12V-3A-...r-Power-Supply-For-LED-Strip-USA/322674598974

However yes the transformer does determine the power consumption to some extent. If you get a larger current transformer than needed, the AC, then rectified DC to your linear regulator will be higher so the LM388's are shedding more heat.

Several watts of heat, will require a significant heatsink, enclosure, and/or fan, transformer, fuse, etc. Seems more compact, efficient, cheaper, to just use a SMPS.

Then again I don't know what you're doing with it. Are you setting this up with a potentiometer for locomotive speed? Even then there are SMPS controllers to step down to voltage with an (analog control) pot instead of the waste power/heat of a linear regulator stage.
 

Electromotive

Feb 14, 2018
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dave9

Regulated power supplies using transformer, bridge and filtered regulator is pretty much standard in the Model Railroad Industry. DCC users may be able to utilize a 12V PSU, as they depend on a digital controller in each locomotive to tap from the full applied voltage to the track.

I am going more "old school", as DCC systems are expensive and you have to have control units in each locomotive, as space will allow. I'm even going with analog amp/volt meters. Yes, I will have variable voltage thru the regulator. I believe this method includes the motor in the regulation that you don't get with a potentiometer.

I am going 24 Volts in order to get 0 - 17 volts on the track. I am in O-SCale, 2-Rail, and motors and current requirements are very different from HO Scale, which is half the size. I will be going with the 4 amp tsfr. My 1 amp existing power supplies utilizing the LM317T only put out 1 amp. Fine for HO, but not for the larger motors in O-Scale, 2-Rail. I keep mentioning 2-Rail. These are not Lionel. Then again, I could be all wrong but I can troubleshoot the below system and replace components if needed because I understand it. I guess I am old school, as I also repair and restore antique tube radio's. Even have all the components, test equipment and a tube tester. I do have a Fluke DMM but can't use it to tune an old radio.

Thanks.... Tom E.

variable-power-supply-lm338k1.jpg
 

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dave9

Mar 5, 2017
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It has been a long time since I tore apart and repaired a train controller, and the one I did might have even been low end (no idea, had only the one occasion to repair one) but from what I recall it did not have a linear regulator, just the two separate discrete transistor implementation of a darlington transistor for output.

It might have been roughly like the Kato circuit at the bottom of this page:
http://www.sumidacrossing.org/LayoutElectricity/ModelTrainPower/DCTrainControl/

However for higher current I might replace the transistor with a TIP142 or something else TO-247 sized. Supposedly some prefer this pulsed power over filtered linear regulated power because the peak pulses help to start train movement, the moment when peak power is needed so it reduces the overall power supply capacity required.
 
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