Reducing track voltage feeds to ancillary ligt bulbs

Ralphmp

Ralphmp

Registered
Country flag
Apologies if this has been covered before but I couldn't find anything when I searched.

I have a few LGB point lanterns that came with 18v bulbs. I'd like to get them working but as I use Massoth DCC (24v) I'm assuming this will either blow the bulbs or at best reduce their life.

I've previously replaced all of the bulbs in my signals with LEDs plus suitable resistors, and these work fine using track voltage. I'm therefore wondering if I could also use resistors or other electronic component(s) to reduce the voltage going from track to the point lantern 18v bulbs?

If so, how would I work out which components to use (all the resistor calculators I've found seem to be tailored to LEDs, not regular bulbs).

Thanks.
 
Edit:
 
Last edited by a moderator:
Any idea of the wattage of the 18v bulb? From that you can derive the current draw and the resistance, which would then give you an idea of what value of resistor you'd need to put in series with the bulb. Effectively you'd need a resistor value 1/3 that of the bulb to drop 24V down to 18V across the bulb.

It's likely to be quite wasteful in that even a small bulb is no doubt drawing quite a bit more current than an LED would in the same situation. The resistor would need to be suitable wattage to handle the current through it.

Is it not possible to replace the lantern bulb with an LED and resistor as you've done with your signals?
 
As far as I am aware the max voltage with the 1210Z is 22v, but the output is adjustable between 14v and 22v so you could just set it to 18v which would be the simplest solution. It would of course be possible to use resistors to drop from 22v to 18v and the calculation is quite simple.
 
It is also possible to but E5.5 LED's for use at 18¬24v with an inbuilt resistor. I bought a bunch of these to replace the bulbs in some Belico and LGB street lamps. They are or course more expensive than filament lamps but I guess their life is considerably longer.
 
Thanks for helpful suggestions. Looks like a number of options to consider so I'll work my way through them.

Best wishes
 
Whilst I'll probably have a go at converting the lamps to LEDs at some point, I think in the short term I'll try and find a similar thread bulb capable of handling higher voltage.

The LGB part number for the current (sorry!) bulb appears to be 68501 which is an 18v, 15mA with E5,5 thread. If I remember my school physics correctly (Watts = Volts x Amps) then this means the bulb is around 0.27 Watts. So am I right in thinking if I look for a 24v replacement, I'll need one that draws around 11mA to give a similar wattage to the original bulb so will be of similar brightness?

Thanks
 
Ralphmp said:
The LGB part number for the current (sorry!) bulb appears to be 68501 which is an 18v, 15mA with E5,5 thread. If I remember my school physics correctly (Watts = Volts x Amps) then this means the bulb is around 0.27 Watts. So am I right in thinking if I look for a 24v replacement, I'll need one that draws around 11mA to give a similar wattage to the original bulb so will be of similar brightness?

Thanks
Click to expand...

Really, just 15mA? I always thought they were nearer 50! I recall allowing for 20 per amp. Maybe LGB have gone over to reduced power bulbs like the high street?

Just checked and I have in front of me a sealed packet of 25 x 5050/1 18v 50 mA bulbs. Someone has helpfully writen 68501 on the packet.

If someone has a link for the E5.5 LEDs I would appreciate them posting it. The only downside I can see there, after the cost, is that the LES type screw threads tend to vibrate loose and the super dooper LED would not be immune to that.

James
 
Last edited:
I got the 68501 part number from the instructions which came with my point lantern (LGB 12040); champex-linden LGB database shows ==> upload_2016-8-5_23-20-44.png

Maybe this is a typo?
 
Must admit I thought 15mA sounded a bit low for a bulb (though reasonable for an LED) but various shops and sites seem to be quoting it for the LGB 18V bulbs. The 24V E5.5s I've found in searches are rated at more like 1.2W (50mA)
 
Last edited:
Ralphmp said:
James

I found these - is this what you were after? (and would they work for my point lantern?)

http://www.ebay.co.uk/itm/10PCS-War...5-12V-14V-Spur-OO-HO-TT-N-Gauge-/311468614305
Click to expand...

Phil,

I was wondering that. Lost in translation perhaps? Thanks for the link on the LED LES units. They would certainly fit, but an electronics whiz would need to pass judgement on if/how well they would work with the higher voltage. They are being advertised for lower voltages than the 18v AC I use.

James
 
Ralphmp said:
Whilst I'll probably have a go at converting the lamps to LEDs at some point, I think in the short term I'll try and find a similar thread bulb capable of handling higher voltage.
Click to expand...

You may well find that the original lower voltage bulbs still have a reasonable life at the new higher voltage. If this is the case an intermediate replacement before LED conversion may prove unnecessary.
 
You must log in or register to reply here.
Back
Top