Full Version: Convert an AC model To DC?
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Hey guys,

As I model the late 1970s, there were a few interesting prototypes out there that I'd like to represent. One such prototype is Amtrak X995, the prototype Swedish engine that would become the AEM7. As it turns out, Marklin produces this model, and they show up fairly frequently on Ebay.

However, the main challenge would be making it work on 2-rail DC. I am sure someone here has experience with Marklin AC engines, and I am curious if they know the details of the construction of AC powered HO engines.

What I'd like to do, is order the guts of an Atlas AEM7 and adapt them to the Marklin engine. However, I think I was told that the wheel sets in the AC engine are a single electrically conductive piece, and are not insulated from each other. This would prevent me from simply rewiring and re-motoring the model.

Can anyone shed some light on this? would this be too much of a headache to rebuild?

jwb

I think in addition to the AC uninsulated wheelsets, you've got a problem with the wheel profile -- some of the German guys on this board can probably speak to this, but I'm not sure if the Maerklin wheels are even compatible with US code 100 track. I've heard Maerklin motors will run on DC, but you'd have an additional issue with any DCC conversion. You mention the idea of getting an Atlas mechanism -- would there be a potential for just chucking the whole Maerklin chassis, dremeling out the body, and just putting the Maerklin body on the Atlas mech?
That's kind of what I'm doing with a Marklin AC powered Reichsbahn Class 05 steam loco.
But I have a Lilliput DC powered Class 05 drive train that I'm going to use. Both are tender drives.
The only reason I'm switching it out is the shell of the Marklin,, is in better shape than the Lilliput. Both were given to me.

The Marklin has "shoes" in the middle to pick up the staples in the middle of Marklins AC track. I don't know if the AEM7 Marklin makes is the same, but I'm guessing it is.
So, its probably better just to switch the drives.
Yep, I say just do a body swap..
The main complication with just swapping shells is that some of the details are different, and I'm not sure if the Marklin shell will fit over the Atlas frame. As I understand it, the X995 is a tad smaller (indeed, the "Americanization" of the body shell for safety purposes is the one reason that the X995 and the AEM7 don't entirely resemble each other).

I have a spare motor and I can get spare trucks, and hopefully I might be able to adapt them to the X995 frame. I suppose it doesn't make a difference until I can acquire such an engine for close up inspection, but I wasn't sure if it was worth the effort or not.

jwb

I would think that either way, that's what Dremels are for! Remember that guys have hacked away at old Alco Models brass diesels to install Atlas motors, trucks, bolsters, etc. I assume something similar could be done here -- even at worst cutting some heavy sheet brass as a new frame.

If you're able to cast your own bodies for various projects, I would assume you're capable of this.
Sure enough, I have recently acquired a model of X995 for my roster. It is a Marklin model from almost 20 years ago.

I will have to post pictures of this thing when i get a chance, but its going to be tricky. half the body is part of the metal frame, so I can't do a body swap with the Atlas AEM7. Even if I could, the body shell is too short for an AEM7 frame, though the wheel base is the same.

Internally, the drive mechanism has more in common with the old "pancake" truck-motors than the typical Athearn style drive. The motor truck has traction tires on all wheels, while the dummy truck carries the third rail pick up show for the Marklin track. It is actually quite spacious in the model, with the only other thing in the body shell being the "Delta" digital control electronics.

As I understand it, I cannot convert the AC motor to DC (or can I?), so I will need to totally remove the drive as it is and replace it with something new. I have no Idea how I would this, but there is a lot of empty space in the hood outside of the body shell mount screw.
Well, here are some pictures of the model and what we are dealing with. It seems that a swap between the AEM7 and the RC4 is not going to work.

Here they are posed together-

[Image: PC111791.jpg]

One of the first problems is that the wheel base didn't match as closely as I first thought.

[Image: PC111812.jpg]

Another problem is that the shells split differently. The entire body shell is one piece on the Atlas unit, while the "lower" part of the Marklin model is part of the metal frame. Further complicating things, part of the truck sideframes are cast into the frame of the model, and are not separate like on the AEM7 model.

[Image: PC111801.jpg]

The frame doesn't really support a typical drive, so even if did have a spare AEM7 drive and trucks, it looks like I'd only be able to get one end running.

In reality, i do have a really old SEPTA AEM7 that hit the floor that had one truck with a broken king pin. I might be able to use these parts on this model, but I'll have to gut it.

[Image: PC111797.jpg]

I haven't yet disassembled the trucks, but I assume none of the wheels are insulated, and that I can't rewire the motor in this model to work under DC power, making this drive useless.

[Image: PC111793.jpg]
Any AC motor should work on DC. What happens is that the field magnet is an elecromagnet and the poles flop back and forth 60 times a second, just as the poles on the armature fop back and forth. If you run it on DC, the poles do not flop, but the armature poles cycle as usual.
Now, the electromagnet motor has to have the field magnet reversed for the armature to run in the other direction.* There is a contraption in the loco that does this. In Lionel it's called an E-unit. If you replace this with with a bridge rectifier, it will set the field magnet the same way at all times and you can change direction by reversing the armature, using track power.

*(Of course, they may have done it bt reversing the armature poles...)

That's the easy part, compared to changing the wheels, dropping the 3rd rail pickup, ...