Quite impressed. Like most typical US based Americans, I only know one language. My hat is off to both of you.
I apologize again for the off topic Garry.
Really? I thought I'd be pushing the limits on the converter's amperage output. Which converter exactly do you have dave_? I appreciate your testing for me! If I power my drivers off the regulator, what voltage would I adjust the regulator to output? Does it matter?
By the way, your English is just fine!
-Garry
The nice thing is that your drivers are buck converters too if i see it right (the inductor would indicate that). So their input current will be lower than their output current.
E1320 says they will deliver 2.5 amps to the emitter at 12V input, so in a perfect world they would have about 700mA input. Lets say they have only 75% efficiency, so they take 850…900mA current each. So let’s say 1.8A for both in parallel.
You say you have 18.25V AC, makes 25.8V rectified. Minus two diode drops for the bridge rectifier, you will end up somewhere near 24.5V DC at the input.
Now we look at page 26 of the datasheet (http://www.ti.com/lit/ds/symlink/lm2596.pdf#page=26&zoom=100,0,427.5).
The bottom graph shows temparature rise of an PCB mounted converter chip.
25V input, 12V output at 2A will give a temperature rise of ~62K. We know we draw less current, but it’s still quite some heat.
The upper graph shows the chip in another package on a little heatsink.
25V in, 12V out at 3A will give a rise of ~44K. We know we will draw way less current than that, so heatwise a little heatsink will be fine.
Output current is also within limits.
My fear is that the inductor has a to low saturation current, but there is only one way to find out :D. The caps are very likely to be crappy, maybe the diode too, but with a little luck they are good enough.
I have this converter http://www.ebay.de/itm/330882678355?ssPageName=STRK:MEWNX:IT&\_trksid=p3984.m1439.l2649 which is basically the same, just minus the rectifier and big input cap.
Well, best output voltage depends on several variables. How much will the input voltage drop under load? Do the drivers change output current with changing input voltage?
If all assumptions made so long are correct, 12V seems save. The drivers will output nice current then and the converter is in save operating area.
Thank you two!
English is a beautiful language and combined with modern technology a great opportunity to connect with all people in the world who have similar interests.
Well, we are forced to learn other languages here. Within a day’s drive I can get to places with maybe 6 or 7 different languages. Draw a 1000km circle on the US map and you barely will see it. 
English connects!
Thanks again… It is great that we can be connect for almost any part of the world and share, help and talk with other peoples…
This is a nice forum… With nice peoples…
Now I am that take my hat is off…
This is the right method to connect it with a perfect explanation…
Thank you dave_! So if your module works out (English link to dave_'s item) than your suggesting I can use this one which incorporates the AC to DC rectifier? Now what about going back to this one in the waterproof case rated 12V 2A max? That one would be really ideal already being in a case and waterproof (or at least water resistant)!
Thanks!
-Garry
By the way, here is RaceR86's test/review of the driver I have (I'm pretty sure it's the same). Be sure to look at post#9 though - it may not put out the 2+ amps I was expecting.
-Garry
Well, it has not the same inductor and caps, we have to trust the seller that they are good enough on that.
I can at least test heatsinking.
This waterproof module looks really nice!
If the manufacturer’s claims are accurate, it will fit perfectly.
Oh, it’s a shame the driver’s output ist that low. (But to be fair, product description says 1 to 1.2 A)
I found the waterproof one quite a bit cheaper. So you believe I could use one of these and connect my two drivers parallel off of it? I don't need two of these? Too bad we don't know what is on the inside of these to get an idea of quality.
-Garry
Nice, that’s really cheap!
RaceR86 measured about .7A input at ~12V, so two of the drivers in parallel will only be 70% of the max current it can deliver.
Should work really nice!
Even if you one day change your mind and want more light output, you could drive two LEDs in series at 2A with a linear driver or choose a different switching driver for even more. So I would say it’s hard to get more versatility for 8 bucks. 
A dead heat as to whether you do your lawnmower first (think the momenteum has clearly shifted in your favor) w new lights or I do my snowblower for next season…?!
A quick call to any good power equipment dealer should get the answer (even though you tested) to whether you have AC or DC at the lights - I know only 12v DC in any lawn or outdoor equipment at the terminal* - and Dr’s suggestion to wire off the battery direct, w a fuse, is also the easiest and as noted, very reversible. I did this w my olde timey tractor mod for a friend, magnetic base LED lights, cigarette lighter style cords/plug ins and such… in business in a flash. And astonishing results.
- and aren’t the current bulbs 12v auto style?
Yes, the bulbs are #1156 12v bulbs (standard automotive bayonet socket). I don't know about the race to finish. I've been sitting on the other components since I started this thread (June 29th 2012)! Perhaps I'll take another look at the mower sometime and see if I change my mind on the direction to go with this.
-Garry
The automotive bulbs don’t mean that it’s not 18vac system. Hot wire bulbs work regardless of current feed to them. I regularly hook up 120vac bulbs to my 98vdc solar array. Drives them great. No regulator need for traditional bulbs because they provide the resistance themselves.
Why go through all the trouble and expense of using separate LED drivers and a buck converter? The unit I linked to does both. It is a buck converter with the ability to do constant current output.
It is a nice sullution, that’s for sure!
Since he already has the drivers and needs to add a rectifier & cap to this unit, trouble and expense are quite comparable I guess.
Your suggestion yields the opportunity to drive the LEDs quite hard if desired tho.
(But I guess in a watertight case one still would need a creative sullution for cooling)
I will consider your option if I need to drive the LEDs harder.
-Garry
I’ll continue following this…
I have a ’72 Elan (pull start, no battery) so if I go to an LED headlight I’ll probably need a similar solution.
It’s not that interesting of an option anymore, but since this converter is just under 2$ shipped I figured I could as well test the little thing anyway.
I testet it with an 12V halogen lamp that draws 1.5A at 12V.
Input: 24.6V
Output: 1.5A at 12.1V
Results: well, the whole board heated up within seconds. I was unable to hold the board for more than a few seconds.
Unfortunately someone took the temp probe, so I have no measurements on that.
Not that big of an suprise. 22.05W in, 18.15W out makes 82.4% efficiency, but the 4W still have to go somewhere. Difficult on a board you could put into a matchbox
I liftet the chip and clamped a heatsink on it very professionaly (:P) to test how much heat the other components contribute
Heatsink gets now really nice warm and you can hold the board. Inductor and diode still get hot, I would estimate ~50°C, but that should not be a problem. Input cap is in direct contact with the heatsink and gets hot, but since it’s no low-esr type it may without that too.
I will leave it on until tonight when I go home, but I already can say that I would not recommend it for use in a confined space. There is no use for a converter that eventually will go into thermal shutdown after some use. This is probalby also true for the more or less similar converters linked in this thread. With a heatsink and some moving air it will probably do fine tho. Nothing wrong with the board operating at 60°C or so.
I really would not want to operate it on higher power levels.
I will bring a second lamp the next days to see what comes first: thermal shutdown or self destruction.
But it’s a national holiday today and I am quite alone here. Don’t want to trigger the fire alarm without anyone to tell it was a false alarm.
Thanks for the info! It doesn't help that in my situation the engine's exhaust is right under the headlights (so it gets hot up front there). If used in my situation I'd likely have to mount it further away and run longer wires to the lights (not that bad to do, although I was trying to avoid it). I had already figured the boards like these need a heatsink added.
-Garry
Nice work dave_. Great pictures too.
Thanks!
I guess pictures weren’t really necessary. On the other hand, people can see than what one did and maybe spot an error.
Btw: output voltage ripple in this configuration as almost 200mV at 57kHz. One would have to make sure any following regulators can take that without going berzerk or add better output/input filtering.