Technical Question

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Paul M

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I would like a piece of technical, electronic advice please!
For Christmas I received a Plateway Model tram. The motor supplied is z 1.5-6 volt job, at 1.5 volts the speed is quite sufficient for what I would probably need. I would like to have LEDs for directional headlights & tail lights. Most LED seem to have a forward voltage of 2-3V. So I can use the LEDs I would like to reduce the voltage to the motor. I know it can be done with diodes, but I've no idea how many or what sort I would need. Or would it be easier to use filament bulbs?
Thanks in advance for any suggestions
 
If it was mine I would try trial & error. Stick a couple of diodes in series & see how it goes. If still too fast stick a few more. Once you have found out how many you need put the same in the other way to allow the motor to go in reverse. Any diodes of adequate current rating will do. Diodes are cheap enough to by a dozen to play with.
 
Most common diodes drop 0.7 volts so two in each direction should work, but with a switch to by pass the diodes you could have a fast and a slow speed on your loco if you wanted.
 
Thanks, I'll give it a go. I just need to find a decent local shop to flog me the stuff. Redoing are local, but they never seem to have anything I need
 
Paul M said:
Thanks, I'll give it a go. I just need to find a decent local shop to flog me the stuff. Redoing are local, but they never seem to have anything I need
Click to expand...
If you get stuck let me know & I will send you some.
 
Another source of diodes is an old circuit board from a piece of electrical equipment, most have loads of them in.
 
Paul M said:
I would like a piece of technical, electronic advice please!
For Christmas I received a Plateway Model tram. The motor supplied is z 1.5-6 volt job, at 1.5 volts the speed is quite sufficient for what I would probably need. I would like to have LEDs for directional headlights & tail lights. Most LED seem to have a forward voltage of 2-3V. So I can use the LEDs I would like to reduce the voltage to the motor. I know it can be done with diodes, but I've no idea how many or what sort I would need. Or would it be easier to use filament bulbs?
Thanks in advance for any suggestions
Click to expand...
try one of these
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DC-DC LM2596 Adjustable Buck Converter Step Down Power Supply Module 1.23-30V | eBay

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  • Input voltage:3-40V.
  • Output voltage:1.5-35V(Adjustable)
  • Output current: Rated current is 2A, maximum 3A(Additional heatsink is required)
  • Module Properties: non-isolated constant voltage module.
  • Rectification: non-synchronous rectification.
  • Short circuit protection: current limiting, since the recovery.
Are you using track power or battery?

for track power put the LEDs across the input and connect motor across output.

for battery you would have to put the LEDs across the output after a reversing switch and put a diode or 2 in series with the motor lead. as said previously usual voltage across a diode is around 0.7V so at 2.2V output the diodes would light and the motor would get 1.5V.
Case of experimentation to get it the way you like it.
 
Note the minimum input voltage. - You would need 2 cells, but would get better runtime.

If you were to use track power, you would need a bridge rectifier before the module, to keep the polarity correct.

These modules are more efficient than a diode-string. If you are only going to use 1 cell, it is not a very big 'bucket' of charge, so will not last too long.

PhilP.
 
I hadn't thought of a buck converter. I'll have a look into it. PhilP, No track power, but I've been thinking about the wisdom of using only one battery, it seems a bit paltry.
 
Paul M said:
I hadn't thought of a buck converter. I'll have a look into it. PhilP, No track power, but I've been thinking about the wisdom of using only one battery, it seems a bit paltry.
Click to expand...
You could use 1 Lithium ion cell at 3.7V.
Something like this would give heaps of run time
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New 3.7V 4400mAh~6800mAh 1S2P Li-ion Rechargeable Battery Pack With XH 2.54 Plug | eBay

Capacity: 4400mAh~6800mAh. type : Lithium Cobalt Manganese Oxide (Li(NiCoMn)O2). The plug is positive. Auto & Motor Parts. Battery Application We accept customized battery plugs and capacities. Why Buy From Us.
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Diodes can be .3 or .7 amps. Depends on materials they are made of. Be sure to check all the specs before buying these.
Also for driving leds I use the cl2N3 (this unit does need polarized DC so a bridge rectifier need is needed) which is a current limiter so the supply voltage can be 5 volt up to 90 volts without using any resistors. I use single 20ma leds or 2 10 ma leds (10's are in parallel to give a 20 ma load). Using these lets trains run with bright lights at low running voltages in DC operations.
 
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