Kato 10-173 651系 'Super Hitachi'
So, you have just purchaed Kato 10-173 651系 (651-series) “Super Hitachi”, and want to know how to convert it to DCC. I’ve just begun this process myself; here is part one (of many!) of my report.
The 651系 is factory-fitted with interior lighting, a nice touch. But, being bulbs, those lights have to go. For one, they draw a ton of current—55mA/bulb @ 9 bulbs = almost half an ampere!—which limits the number of trains that my Digitrax Zephyr can drive simultaneously from two to one. For another, bulbs get hot when powered by AC, and DCC is AC. Some people have reported that Kato’s bulb-based interior lights cause meltdowns when run on DCC. I don’t have a link, because I think this claim is largely apocryphal, but Kato nevertheless cautions against using their bulb kits with DCC. Or at least they did until they discontinued those sets. Anyway, Kato’s LED interior lighting kits aren’t compatible with the 651系. You’ll see why below. This means we’re going to have to improvise something new if we want to run out 651系 on DCC.
Ngingeering's tiny rectifier, with the resistor I'm about to solder to the other side.
The key to the conversion is replacing the bulbs with roughly-similar sized LEDs, and providing an LED driver, a small circuit that rectifies the DCC signal into a flat DC source. For an LED driver, I chose Ngineering‘s N8101 bridge rectifier circuit. This is a tiny board that combines a full-wave bridge rectifier and a small capacitor that work together to provide a smooth DC signal at whatever voltage your booster uses (14V, I think, for the Digitrax Zephyr). It can be used as is to power bulbs, even over DCC. So, in some sense, you could stop here by finding a way to just install these things as is. But I want to bring the total power consumption down, and that means soldering on a resistor, and swapping the bulb for an LED.
I didn’t take any photos of the LED I used. My choice was this 2mmx3mm LED from Digi-Key. It’s the right size for replacing a 3mm bulb, it’s a warm white, it’s amazingly bright, and it’s dirt cheap (56¢ each).
This is the light unit diassembled. The whole thing is held together by one screw.
The carriage comes apart easily, by pulling the sides away from the frame, and the frame down. One open, a single (large and easy to spot) screw holds the entire lighting assembly together. There is a long clear light pipe, a metal clip thingy, a plastic bulb holder, the rest of the frame and the screw. The objective is to get the N8108 and LED installed without having to break or cut any of this. Thankfully, Kato made this easy.
Bulb and bulb holder. Notice how the bulb leads are wrapped around two bobbins on the sides.
The bulb attaches to the plastic holder very simply: It’s leads are wound around two small bobbins; the bobbins are designed to press the leads against two brass pickup rails mounted in the frame. Very clever! Remove the bulb and discard it or set it aside.
30AWG magnet wire wrapped around bobbins.
N8108 hung from magnet wire wrapped around plastic bobbins.
I used 30AWG magnet wire wrapped around these bobbins—with the insulation scraped off so that they will make electrical contact with the brass rails—to hold the N8108 in place. In the photo, I’ve wrapped the wire around the bobbins, and then bent the wire upwards to support the N8108; the kinks in the wire tell me where to cut, and where to scrape off more insulation so that I can solder the N8108 in place just like this.
LED glued on the bulb holder, with 38AWG magnet wire leads soldered to the LED.
The next step was to remove all this wire (note to future self: Try to do things in an order where you don’t have to undo completed steps! Which means maybe this step ought to come first?) and glue the LED into place. Actually, first I soldered 38AWG wire leads to each terminal of the LED. Then I used a little PVA (white) glue to hold the LED down, routing the wires through the sides of the bulb holder. Be careful to route the leads so that the metal clip, which nestles into the V-shape the LED sits in does not interfere with or sever the leads.
The LED leads are fed directly to the outputs of the N8108. Be sure to leave enough slack in the leads so that you can rearrange them.
Finally, I wrapped the 30AWG wires back around the bobbins, and string the LED leads to the outputs at the bottom of the N8108. I actually tied the very thin leads to the solder points, and since this wire is meant to be stripped with a soldering iron rather than a hobby knife, I just soldered the knot in place without trying to untie the knot to strip and tin the wire. Very handy.
A final note on installation, be sure to put a little tape along the metal clip when you reinstall it, to avoid having your wires short against it. That would be a real problem.
Comparison of final result with original bulbs. LED on left, bulb on right.
The new LEDs are dimmer than the original bulbs. This is by design. I found the factory-fitted bulb lighting too bright to be realistic, so I chose a resistance value to tone it down a bit. In the end, I used a 2.2KΩ ¼W resistor (in an 1206 SMD pacakge, Digi-Key part no. RHM2.2KERCT-ND—just 41¢ for 10!), but if you prefer a brighter light, you could use perhaps a 1.6KΩ resistor. These values are dependent on the LED I’m using, and will vary if you pick a different LED. Finally, although the LED is quite warm, it is nowhere near as warm as the original bulb. Again, I found the bulb to be just too orange for my taste, but you may want to consider applying a thin coat of Tamiya X-26 clear orange paint to warm up the color even more. With a smaller resistor, the LED I’m using will still be plenty bright even under a coat of paint.
One down, six more to go! In the next part, I’ll show you how to replace the headlight/markerlight bulbs with proper LEDs, which will be a little tricky. In the final part, I’ll install the motor decoder, which should just be easy-peasy.
Ahhh…very interesting. There’s a lot of applications here that go beyond this specific model. I’ve always been intimidated by all those fancy doo-hickey’s like the N8101! Question: With the capacitor, will it store enough current to avoid flickering?
‘Struth, you could rig a lighting system from scratch this way. Were you thinking of something in particular? And no, the capacitor won’t do a thing for flicker; it’s designed only to even out the almost-but-not-quite flat DC signal the rectifier produces. You need a much bigger cap to reduce flicker.
Ah…okay. Actually, I have some double-decker cars that need lights and there are no kits that will make it work, but this would do it. It actually seems like this is a much less expensive way to add lights than the Kato sets, or am I under-estimating the time and/or costs of all the parts together?
The time costs are not trivial. The first car took me two hours, but that includes a lot of experimentation. I expect I could get the remaining 6 done in about three to four hours total, if I do an assembly line. The costs are somewhat less; each N8101 is about $4, for a total of about $4.60 for each car; Kato LED lighting units are about $30 for 6, or $5 each, so the cost savings are not significant; the extra time required makes this route more expensive is the cars can be fitted with stock Kato units.
But in your case, this might be worthwhile. Using these same LEDs, and throttling the current down to about 4mA each means that the N8101 could drive something like 50 of them, if they were all wired in parallel. At 12V, you could probably put three or four to a string for a total of maybe 200 LEDs? That should be more than ample to light a passenger car! I would take some tiny LEDs, solder up leads as I did, and glue them to strips of thin styrene, affixing the styrene to the inside of the roof and under the top level seats. That could be pretty easy, really. And about the same cost as commercial solutions that, as you say, won’t fit.
But why are we so attracted to light? We obviously ain’t any butterfly but still… light triggers something in us.
Nice job Don. I’m quite amazed by the amount of time and energy you put into this.
Light especially triggers something in Quinntopia
Thanks for the complements, but in fact not so much time, and even less energy went into this project so far. When you have a relatively small roster, you can afford to obsess over details, I suppose!