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 Post subject: 1.5 volt battery powered led - used for an ho train diesel h
PostPosted: Jan Sat 26, 2013 3:53 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Cold Spring Kentucky USA
can someone help me with a circuit to use to build a simple led headlamp for a model train? run by a 1.5 volt battery?

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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sat 26, 2013 4:07 am 
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If it's a regular LED, all you need is a resistor of the proper value and wattage.
You need to know the forward voltage and current drain of the LED.

If it's a high-intensity LED it might require an actual power supply; much more complicated.

- Leigh

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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sat 26, 2013 4:19 am 
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Location: Tehachapi, CA - Bottom end of the Sierras
The problem is that a red LED has a forward drop of 1.7V. Other colors, higher. Even with a fresh 1.5V battery, that red LED just turns ON. You want a much higher voltage source, then use a limiting resistor, to take up the slack.

One option, if you only have that 1.5V battery, is to rig a blocking oscillator, which has a winding that will step up the voltage. I'll have to scribble one out, but its a simple circuit. Down side, is that you'll need to wind your own little transformer. I've done it with Amidon toroids, and not too many turns of magnet wire. 26 to 30 awg is good enough.

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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sat 26, 2013 5:52 am 
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Here's a little circuit I just got working:

Attachment:
LED_1V5.gif
LED_1V5.gif [ 13.78 KiB | Viewed 3927 times ]


And a photo of it working, with its waveform:
Attachment:
LED_1V5phs.jpg
LED_1V5phs.jpg [ 41.81 KiB | Viewed 3927 times ]

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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sat 26, 2013 6:02 am 
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Mike,
Boy, that didn't take you long to come up with a circuit and a working prototype... How many volts on the secondary side... yikes!

On another note, I like your mini oscilloscope, which one is it?

Sal

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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sat 26, 2013 6:14 am 
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Roughly 7Vpp. I'd like a transformer with a lower impedance, but its what was sitting on my work bench. The AA battery leads are held on with a rubber band.

The scope is a Seeed Studios DSO Quad. Bandwidth is decent for non-RF stuff. Users interface, however, sucks big time ! Its good for the field, and even has a built in signal generator. Oh, don't tie to a tube circuit. It won't survive those kind of voltages.

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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sat 26, 2013 6:36 am 
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I was thinking buying this one http://www.ebay.com/itm/New-Mini-Nano-A ... 0313006408, price is right. Do I need it, no, but do I need all the toys I have.... no :-)

I have enough Tek scopes to last a few lifetimes..

Sal

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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sat 26, 2013 9:51 am 
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Sal Brisindi wrote:
price is right.

http://www.nkcelectronics.com/digital-s ... y-kit.html

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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sat 26, 2013 5:15 pm 
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Joined: May Tue 30, 2006 4:46 pm
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Location: Santa Rosa, CA
Since LEDs need 1.7 to 3.7V, depending on color, one battery won't cut it.

The blocking oscillator idea is a proven solution. Most of the "garden lights" that sell cheaply at the home stores utilize this circuit.

Search the web for "Joule Thief." This is a popular, cheap, and easy-to-build circuit that will allow you to run a white LED from a 1.2 V rechargeable battery. The circuit works even when the battery gets down to about 0.7 V, so it steals all the available "juice" before it ceases to operate.

http://en.wikipedia.org/wiki/Joule_thief

http://www.instructables.com/id/Make-a-Joule-Thief/

I've built a couple of Joule Thief versions and they work well.

Rich

PS: I put a scope on my solar-powered garden light (one NiCd battery) and it oscillates at 518 KHz.
Image


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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sat 26, 2013 10:29 pm 
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Joined: Feb Sun 24, 2008 4:21 am
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Location: Sedona, AZ/ Placentia CA
This year I was working on my little steam powered carousel. The little steam engine turned an old slot car motor (for those of you old enough to remember them). The little motor run as a generator only produced about .9V at the speed I wanted to run the steam engine. Not enough to run 3 LED lights for my project. I had some great guidance from this forum and was introduced to the concept of the joule thief. I will attach a link to the "Mad Scientist" which is where I purchased two of their nice little boards, each would supply enough voltage and current to run nicely a total of 6 LEDs off my wimpy .9V. One of this little boards should take your 1.5V AAA voltage and run your LED (you can take the one off the board and move it to your locomotive head light) and it will run it forever. Your are on your own to figure out how to turn off the battery of course but no matter what, you probably would do that any way. The other option is to pick up the track voltage running your motor and use it. This is assuming that your running an electric motor.
Let us know and show some pictures of your train.

Jerry

Edit: I noticed Rich was making the same suggestion while I was typing. Sorry. You can buy the complete kit for a few bucks or the assembled for around 6 bucks. Winding the toroid for the kit was well, tough on my eyes!

http://www.madscientisthut.com/Shopping ... ting&xm=on

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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sat 26, 2013 10:41 pm 
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threeneurons wrote:
Here's a little circuit I just got working:

Attachment:
LED_1V5.gif


And a photo of it working, with its waveform:
Attachment:
LED_1V5phs.jpg


Wow,

Nice circuit and NICE scope. A 1K series resistor should be fine for a red led.


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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sun 27, 2013 3:02 am 
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Location: Tehachapi, CA - Bottom end of the Sierras
Rich, W3HWJ wrote:
The blocking oscillator idea is a proven solution. Most of the "garden lights" that sell cheaply at the home stores utilize this circuit.

Search the web for "Joule Thief." This is a popular, cheap, and easy-to-build circuit


Joule Thief Circuit:
Image

If you look closely, the "joule thief", is a blocking oscillator. Basically, the same circuit.

I only got one cobbled up so quickly, because its something I've built, many times since my childhood. A lot of the circuits in that old Radio Shack 100-in-1 kit were based around a blocking oscillator. I just had not heard the term "joule thief", before, or at least didn't make the association.

Well, today, I replaced the Xicon transformer with a little 1/2" (#77) Amidon toroid, and its lighting up that white LED.

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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sun 27, 2013 3:57 am 
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Location: Sedona, AZ/ Placentia CA
I don't know how much room you have in your little HO engine for stuff. I can't imagine you could build a joule thief for much less than the kit I suggested with a nice little PC board. You have to be cramped in that little engine. Might be better to just build something that would take your track voltage and regulated it down to running an LED.
Jerry

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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sun 27, 2013 3:58 am 
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There is actually a much simpler circuit used in the garden lamps. No transformer needed:

Image

http://www.joulethief.com/kit.php


Rich


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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sun 27, 2013 4:00 am 
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A single-cell LIPO is 3.7V and not 'that' much bigger than AAA.

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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sun 27, 2013 4:01 am 
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In the early '90s, when I was with Siliconix, we worked with Maerklin; they used a buck-boost circuit to keep the light output constant regardless of track voltage... of course, it was incandescent in those days.

Rich

http://www.marklin.com/


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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sun 27, 2013 4:11 am 
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Location: Santa Rosa, CA
Quote:
A single-cell LIPO is 3.7V and not 'that' much bigger than AAA.


Unfortunately, many white LEDs require 3.6 V, so your 3.7 Li may power them dimly or not at all or not for very long.

Rich
Image


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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sun 27, 2013 4:17 am 
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All of this begs the question, what is your track voltage from high speed to low speed?
Jerry

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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sun 27, 2013 4:55 am 
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JerryHawthorne wrote:
All of this begs the question, what is your track voltage from high speed to low speed?
Jerry


If you can pull the power off the track, and its DC, then:
Image

It regulates the current, over a broad input voltage range (line regulation).

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 Post subject: Re: 1.5 volt battery powered led - used for an ho train dies
PostPosted: Jan Sun 27, 2013 5:45 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 431
Location: Cold Spring Kentucky USA
Appreciate all of the help, but I just want a simple headlamp, with a on off switch and a little battery power source - totally seperate from the track or track voltage. Maybe I would be better off with a 0-16 volt dc track run regular small lamp?? how do you regulate the true voltage to the lamp if you do that? I guess im dropping back to what the companies actually use on ho trains, many or my engines have no headlamp and I just want to add something.

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