Bridge rectifier sizing

That should drive 20 or so.

The 12 LED's are wired in groups of three, so they would consume 80ma at full intensity at 12 volts.

Thank you, Cjack and John

The guys answered the question you asked....but just to be clear, what is your AC voltage going into the bridge?  Are you only using this 1.5A bridge-rectifier between this source and your LED strip?

Stan asks an excellent question, the LED strips are designed to run on 12V max, if the DC voltage is greater by more than 1/2 a volt, I'd recommend a regulator to protect the LED strips.

I believe it was a Weller, but I forget the exact model.

Here's one that is temperature controlled at 60W, and it appears to take Hakko tips, a nice plus.

http://www.ebay.com/itm/Tenma-...;hash=item27e9a95b9d

I should have gone to Google before I asked you.  there is a lot of stuff to read and see on youtube.

Greg

Is this being powered by variable track voltage?  If so, have you confirmed there is enough voltage at lower track voltages (below, say, 10V) to light up the strip? 

There can be quirky situations such as lower-cost chopped-sine controllers working "better" wrt lighting up a strip than expensive pure-sine controllers.

It is variable track voltage and I have not checked to see how well they will work; however I did put a strip in one of the cars powered by a 9 volt battery and at 9 volts it’s right at the brightness I like.

I’m also thinking, if needed, I could short-out the built in resistor on the strips to have more of a voltage range.

Greg

Sounds like you're on top of the situation.

If shorting the resistor is not enough, you can instead short one LED from each section of 3.  At ~9VDC on a section you're driving each section at just a few milliamps...rather than the nominal 20 milliamps if driven at 12V.  At such a low current, the resistor does not eat very much voltage - less than 0.5V - whilst each LED drops about 2.9V.  So in this option, you'd drive 8 LEDs (2 per section instead of 3).  I believe you'll find this still has suitable uniformity/smoothness in lighting up a car.  And you'll gain about 2V of bottom end voltage range.

Remember, shorting out the resistor doesn't actually increase the voltage range, rather it lowers it in a very tight band.  With no current limiting, you can very quickly overcurrent the LED's with just a volt or two excess voltage and kill them.

It's really very important to have current limiting for LED's if you don't have precise voltage control.

Stan's idea is a good one to drop the voltage range, you still keep some current limiting capability but lower the minimum voltage requirement.  You'll probably not notice one LED from each group being missing as far as the lighting is concerned.

OK, when I get all the parts I'll set up a test set outside of the car, hook up the leads to the track, set the regulator to about 9 volts and run a 8-10 car train to see how it works. The LEDs sure look good in the car.

Greg 

That's the best way to see, I do bench tests all the time when there's a question of how something is going to work out.

I'll report back.

Greg

If you were to short the resistor and remove one of the LED's and jumper across the pads, you'd be able to run down to around 4.5-5.0 volts track voltage with a simple constant current regulator to drive the LED's.

I know how to short out the resistor but not to sure how to remove one of LEDs from the strip.. While I'm asking questions, what size cap. would be good on the DC output?

Greg

Thanks, John

Dale, did you miss the part about removing one LED and jumpering across it's contacts?

I tried the mod using one three-LED segment from a strip.  It requires 7 VAC from the transformer with the resistor and one LED position shorted in each three-LED group.  That gets you most of the way there with some intensity adjustment of the lighting.  At around 7.5 VAC, the regulator circuit is fully operational and very little change is noticed in the light output all the way to maximum voltage at 18 volts.  At around 6 volts the lighting is on pretty decent, but not at the set brightness yet.

Here's a version of a 12V strip where you can see the interconnections within a 3-LED section.  I realize most strips now have opaque coatings so you can't see what's going on but if you have a meter you can also confirm the interconnection scheme and of course once to figure it out for one section, that scheme is repeated on all other sections.

Sometimes it can be easier/faster to bypass an LED by adding a jumper wire rather than removing the LED and then shorting across the pads with a tiny wire.  In the photo the middle LED is to be taken out of the circuit.  Of course you don't get the unused LED to recycle into another project but you may save some a minute or two and since an LED is "worth" less than a nickel, the minimum wage police won't come knocking...