Accucraft K-27

[rusty spike]

I’m installing battery R/C DCC to my Accucraft K-27. The decoder/receiver & battery install is all going well. Anyone owning one of these locos will know the electricity is picked up from the track on one side of the loco and returned via the opposite side from the tender wheels. Isolating the motor was straight forward, it just entailed undoing the connecting wires from the terminal below the cab floor.
My question is: can I wire the head and marker lights and cab light (no tender light fitted to this particular model) directly to the Zimo MX699 KS decoder. I took a look inside the smoke box and it looks like some electronics are present to perhaps turn off the light while reversing? Also I’m guessing some form of voltage regulator?
Here’s the terminal below the footplate before removing the wiring.
Any help gratefully received

 

[maxi-model]

I have recently done a DC battery conversion, with an old Sierra sound card included, to my Accucraft K-27. It had the same pick up configuration as yours. The voltage regulator for all the loco (not tender) mounted incandescent lights is housed in the smokebox. That light system takes its power from the buss showing in your picture. Carefully pull away the smokebox front plate, it's only an interference fit, from the smokebox barrel and you will be able to get at the voltage regulator mounted there. The voltage regulator circuit board is bolted in place on an insulated mount on the smoke stack post. If you damage the board in any way let me know as I have a couple of spares, courtesy of the generosity of JohnS on here. Got share the love around

Just unbolt the cable tags from the buss and give them a gentle tug to identify which is which and then reattach as required in your new DCC setup. If you have not already found it make sure you isolate the wire from the driving wheel pickups that will be attached on that buss too on one of the posts. It'll be obvious which one it is when you give it a tug Likewise, just for safety, make sure you isolate any pick ups on the tender wheels and trucks. The loco and tender appear earthed through its body, although the loco's drawbar is isolated from the loco's chassis (or at least should be)

There is/would have been a separate voltage regulator in the tender that was attached to the reversing light. I assume there was some means there to activate that light when the current polarity was reversed. It still does on my set up. Others here, particularly Greg Elmassian and JohnS, will probably be able to give you more expert guidance, particularly in relation to the DCC aspect of your installation. Max

 

[rusty spike]

Hi Max,
Thanks for the detailed reply
From your response I’m guessing you are staying with DC control?
I was hoping to find if the voltage regulator is kept in the circuit when using DCC. I believe the tender on my loco originally came with the rear light on a tower, but at some point a previous owner has replaced it with a ‘dog house’ I removed the redundant regulator (shown below) and pick ups from the tender.
I’m concerned I may damage the decoder and or loco lights if the circuit board is left in situ?

 

[maxi-model]

I think you need to await advice from the electrical/DCC/RC experts on this forum. To get a fix on what you are intending what will you be using for your TX/RX/ESC/DCC ? I have an 18v battery pack fitted on my K-27. The loco's Pitman motor is rated at 19v and around 1.5 amp power draw under normal load conditions. The Accucraft manual supplied was bit sketchy on information and I was advised the factory issued no wiring schematics, at least for the earlier models with this wiring setup. I would advise that your RX is fitted with an aerial lead (it'll probably end up inside that metal tender with a metal lid) and you look for an ESC that can cope with up to a constant 100w power demand, the usual 30w might be a bit marginal. That's what came to light with my installation.

I note from your picture of the power buss that you still have the engineside pickup lead in place. It's the one with the tags doubled up on the 3rd pin from the left. The other, heavier lead, on that post, is one of the motor leads. You also have the wire connection showing from the tender on the 2nd post from the left with the other motor lead. Depending on how you install your RC/Battery/Sound/DCC equipment it might be advisable to delete/isolate these wires. On mine the, as designed, isolation of the tender and loco was a necessity. As to the use of the voltage regulators, lighting system and possible reinstatement of the reversing light I could not comment on that. On my K-27's tender the holes are already present for a doghouse to be fitted. I think in real life the rear light would have been centerset or offset and mounted further back at the tender's rear extremity, if a dog house was used. Max

You may be able to glean some ideas from this - Converting Accucraft K-27 to battery r/c - G Scale Central

 

[Greg Elmassian]

So spent some time looking around the internet for a nice primer on installing DCC decoders to answer the basic questions you are asking. The ones I found were not great, although someone somewhere should have written one.

Most give you the basics on find and isolate and test the power pickups.
Next do the same for the motor.

Here's where most advice kind of goes away... it's either just "hook up the lights", or change to LEDs

Other than model specific advice, here's some of the missing stuff:

1. first, before I even start the conversion process, I evaluate the lighting setup, and see what are LEDs, what are incandescents, and if there are any "special voltages" present. You can do this by putting it on rollers, run it on DC and max out the voltage and measure the voltages to the lights (forget LEDs here for now).

In your particular example, often Accucraft hides a 6 volt regulator somewhere. At this point you will also probably discover that the 3 terminal regulator has one of the connections "Grounded" the to metal chassis of the loco, a real warning sign.

So, my take is you have to develop the lighting "strategy" BEFORE you start cutting and ripping out stuff.

Once you know what you are going to do (change all to LEDs, or figure a way to support a 3 volt incandescent), then I proceed.

I disconnect the lighting, so whatever I do next won't blow it up.

At this point then I do the track pickups and motor, and then check out on programming track, and if that checks out (can program, motor "bursts" when programming), only then does it go on the mainline and get tested out.

Only when it runs perfectly do I go on to lights.

Now I normally try to go all LED, since they are low current, no issue with a decoder and all you need is a "current limiting" resistor inline with one of the leads to the decoder.

When I "keep" an existing incandescent lamp, I usually calculate the current (remember you measured voltages before) and see if I can use a big resistor (because they normally make heat, or I have to do something else to supply the voltage it wants. This is where you have to get creative but also calculate power.

Example, you have a 3 volt incandescent bulb, and it drew 200 milliamps, and you wanted to just power it from the decoder, and you have 24 volts on the rails, then your resistor needs to "use" 21 volts, you may have an issue. The resistor will draw 0.2 * 21 or 4.2 watts !!!! This means you need a 8 watt 100 ohm resistor!

So you need to find alternatives, and check things out before you just hook up lamps to a decoder. The regulator in your loco may indeed be for an incandescent lamp, or to allow the lamp to go to full brightness "sooner" on analog.

Anyway, there are solutions (in the above example, you can usually find a 5v common on the decoder and then the resistor only needs to drop 2 volts, and that only needs a 1 watt resistor since that setup only draws 0.4 watts.

So, after all that, the #1 thing you need to do is "survey" your lighting and see what kind of lighting you have and how it runs.

Greg

 

[rusty spike]

Thanks Greg, very sound advice.
I’m running on battery R/C so I have isolated the motor and lighting connections. I will do as you recommend and run just with the motor hooked up and get it running on the rollers. I need to change a couple of CVs to enable the ‘virtual chuff cam’ and once I’m happy I’ll crack on with the lighting. I would prefer to go with LEDs. I will need to check how to remove the bulbs from the front markers etc.

 

[Greg Elmassian]

Yeah, the markers might be ones you leave as bulbs in that LEDs usually don't have the dispersion a GOW bulb has.

Best of luck,

Greg

 

[Paul M]

Best of luck,

Lots of very useful advice Greg, I'm not into track or DCC power, more live steam and plain battery, but the way you seem to be able to explain thinks makes a lot of sense.

 

[idlemarvel]

Nice write-up Greg thanks for taking the time. Just a question from a dummy, could you use a diode to drop a few volts to the incandescent bulbs? Any pros and cons versus resistors?

 

[Greg Elmassian]

Yes, diodes are actually preferable since they are a constant voltage drop, as opposed to resistors where the drop is controlled by the current drawn.

The issue with diodes is getting enough of a drop at 0.7 volts each. Also, you need to be sure you are not overheating the diodes, but that compares with having to use high wattage resistors.

Greg

 

[idlemarvel]

Thanks Greg, that's what I thought. Going from 5v to 3v would be practicable, going from full track voltage to 3v not so.

 

[PhilP]

Thanks Greg, that's what I thought. Going from 5v to 3v would be practicable, going from full track voltage to 3v not so.

I would use a bridge-rectifier and 'buck' converter for that..

 

[Greg Elmassian]

The reason I do not just straight out recommend a DC-DC converter system, is that an adjustable regulator system CAN go out of adjustment, and fry things.

Simpler is normally more reliable... also these cheap DC-DC boards are just that, CHEAP, i.e. not the highest quality components... I like reliability.

Greg

 

[rusty spike]

I got the decoder wired from the tender via a plug and socket to the motor and lights. As I will eventually be replacing the light bulbs with LED’s, I felt confident to wire straight back to the decoder and trust the on board voltage regulator. To my relief the only adjustment needed was to adjust the exhaust to 4 chuffs per rev.
Thanks especially to Greg for the detailed information which will be invaluable when I replace the bulbs.