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When to Use a Rectifier for Lighting
Tony M posted this question for readers:
“My question is about adding lights to buildings on my layout. The bulbs I have are 1.5v and my power packs are 19v ac output. My buildings I have that already have lights work ok, but the 1.5v bulbs blow when I hook them up, which is because of voltage difference. I am just a bit unsure how to fix this problem. Do I need a rectifier?”
14 Responses to When to Use a Rectifier for Lighting
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What you need is a voltage regulator, no a rectifier. I made mine but there should be some one selling just what you need. Please remember the power rating of the regulator is important, if you put more “loa” (watts) than the regulator the voltage will go down and the lights will go dim. Look for an adjustable regulator or power supply if you want to use it as a stand alone.
Recommend that you use LED lights, not incandescent. LEDs typically require 2 volts DC (polarity sensitive) and are about 20 ma maximum, but work down to less than 5 ma depending upon how bright you want the light. A simple rectifier bridge can be purchased to convert the AC voltage to DC, then use a resistor to reduce the voltage to limit the current, one per LED. Assuming 19 VDC output from the rectifier and 2 volts LED drop, you need a resistor of:
R = (19 – 2) V / 10 ma = (17 / 10) x 1000 = 1700 ohms. Have assumed 10 ma for the LED but you can vary depending upon your requirements. Adjust values as you need.
http://www.ebay.co.uk/itm/1-5-35V-10A-Adjustable-Step-Down-Buck-Power-Supply-Module-Display-XL4016-Winners/182389722782?_trkparms=ao%3D1%26asc%3D20170912102017%26meid%3Db738782b38dc4012a0a6df7b2b7ba0e1%26pid%3D100706%26rk%3D1%26rkt%3D1%26&_trksid=p2045573.c100706.m4781
The above is step down module that should run the lights but you will also need a rectifier as the input is dc hope this helps Dave
You could add resisters before the bulbs. The value of the resister would depend on how they’re arranged: series or parallel.
You have a difference in voltage. The bulbs are designed for 1.5 volts and you are sending 19 volts. Need a circuit that will break down voltage to 1.5 volts. Think of it like your lamp on the desk. The rectifier, diode will only allow DC voltage to flow one way. This does not create the voltage drop you need. I would look up basic electronics and designing a circuit for 1.5 volt recommendations.
You do not need a rectifier but you will have to use resistors to drop the voltage to 1.5V from 19V. It will be easier for you to connect the bulbs in series so that they add up to 19 V total. You will need a minimum of 13 bulbs joined in series, so that 13×1.5V=19.5V. This is OK as the power supply is just under the 19.5V and will not burn the bulbs. The only issue is if one bulb gets disconnected or fails, all the rest will be also off. Also, if you don’t have the need for that many bulbs it will be a waste of power. You will have to make sure your transformer can supply enough current to power that many bulbs!
The other method is to use a regulator circuit which you can find on Google easily. You will need a a few components including a bridge rectifier, regulator, a few resistors and capacitors based on which circuit you choose.
Hi Tony M,
The bulbs blow because the voltage (19VDC) is too high.
You need to put resistors in series with you bulbs.
Hope that helps.
Dennis
Tony, globes are expensive, especially if you keep blowing them. LEDs (Light Emitting Diodes) are cheap and almost everlasting. You do not need a rectifier, but you do need to ensure your globes only get the 1.5v for which they are rated. There are a number of retailers who can help you, and the hobby literature of recent times has run articles about using LEDs.for lighting buildings and rolling stock.
If you’re using a regular filament-type light bulb, as opposed to an LED, you don’t need a rectifier since they work equally well with AC or DC. What you need is a resistor in series with the bulb to drop the voltage. The question is, do you know the amount of current the bulb is rated at? If you do then you can use these two formulas to determine the resistance and wattage for the resistor.
Resistor Ohm Value: R(res) = (Vtrack – Vbulb) / Ibulb The ohm value to drop the voltage.
Resistor Watt Value: W(res) = (Vtrack – Vbulb) * Ibulb The heat the resistor will generate.
As a starting point, if you don’t know the current rating, try a 1.5K ohm resistor rated at 1/2 watt. The higher rating the resistor is, the less voltage be will available to the bulb. Once you have something that works you might try adjusting the ohm rating for the resistor to get brighter or dimmer light. Also, if the resistor gets hot replace it with a 1 watt version.
Tony, if you look at a Chinese site called alixpress and search for voltage regulators.
I have bought many from this company.
They are adjustable, often in the input side as well as the output and work very well. They are also very cheap.
Have fun
Hi Tony
The power supply that you are using has far to much power for the lights 17.5 volts in fact what you need to do is wire the lights in series where one of the leads from one light bulb is joined to the power supply and the other lead is connected to the next light and so on you will need to connect 13 lamps this way so that the each draws it right amount of power. The down fall of this system is that if one bulb blows all the lights go out so you would need to find which light has blown. I would suggest that you get some 12 volt grain of wheat bulbs and an old phone charger that gives out 12 volts or do as i do run them on a 9 volt charger they are not quite as bright but the bulbs last a lot longer. I hope this answers your question.
If you wire up enough in series, or put an appropriate resistor in the circuit?
Howdy Tony,
You need to get rid of all those ac/dc filament lights and go to LED´s. I purchased a 12 volt supply from e-Bay, 5 amp supply and use a 480 ohm current limiting resistor hooked to one of the LED legs (doesn´t matter which leg) and wire them to a block fed by the 12 volt supply. They work very well, just don´t try to hook em up without the current limiting resistor. Ask me how I know???? I blew about 10 LED´s in a row before I remembered the current limiting resistor. I have even changed out the headlights in all my HO and O scale engines from filiment lamps to LED´s. They work very well. On my HO engines I used 3 mm LED´s and on my O scale I used 5 mm LED´s. I even drill out the fake lamp housings on the engines and hook an LED backwards from the front light to use as backup lights. The headlight LED burns when the engine is going forward and the back LED burns when I reverse the engine. Wiring is not very difficult and the LED´s last soooooo much longer than filiment bulbs. Just remember to use some heat shrink on the LED lead wires to keep from shorting out on the engine frames. Hope this will work for you. LED´s are the best technology for lighting in any scale. Just remember the current limiting resistors. If your power supply is lower than 12 volts you can use 220 ohm current limiting resistors for 9 or 5 volt applications. Good luck.
Retifier will change it to 19 volt dc there is a 6 volt drop so it will only be 13 volts dc try to put a 1k ohm ristors in line for each bulb to lower the currant