Tomix/Atlas Track Cleaner (Vacuum) Car - Disassembly?

[C855B]

Not having much luck unsnapping the top half, which appears to be the point of entry. Too much force (or resorting to a screwdriver) appears to be on the verge of breaking something or otherwise screwing-up the plastic.

Any experience here? TCS used to have a decoder installation page on it; now gone.

[GaryHinshaw]

You need to unscrew the trucks.  @fifer (Mike Fifer) has a nice video on adding a Z2 decoder to one of these units:

[C855B]

Thanks, Gary! (And Mike!)

It's a because apparently I knew this from removing the trucks to install TSC. Including the important bit about not losing the springs. I had the bloody thing apart already.

I repeat, . Sheesh.

[C855B]

'Fessing-up, it turns out that the admonishment to "not use with DCC" is real. Both of mine stopped working after a couple of sessions, and I was concerned that the slightly higher DCC voltage had toasted the motor. After taking one apart, the bare motor ran fine on the bench, nary a problem. So I found a spare TCS M3, did Mike's upgrade, put it back together and merrily vacuumed the layout.

The failure I suspect was the voltage rating for the stock bridge rectifier and/or the electrolytic capacitor between it and the motor was exceeded. I'm away from the bench at the moment, so maybe tomorrow I'll test the parts to see what blew.

[peteski]

I'm surprised that there is a capacitor. Well, if it is a large value capacitor (100s of micro Farads).   But if it's a small cap then it is probably added to minimize Radio Frequency Interference (RFI) from the motor's brushes/commutator arcing.  I suspect that it is the bridge rectifier (one or mode diodes) which failed.  Again, I'm surprised that it did fail. Most common bridge rectifiers are able to withstand 50V or more. I wonder if the current (of a motor running full speed) and not the voltage which caused the failure.

[C855B]

There are three capacitors. There's a through-hole ceramic across the frame, the electrolytic I mentioned (SMD can-type), and a small chip cap across the motor. You can see them on Mike's video from 2:11 to 2:22. That last one is likely most of your EMI suppression. You've got me on purpose of the electrolytic; given its small size I would not be surprised at all if it has a 15V rating (maybe 25V?) and is why they say "don't do that!". I'll check tomorrow.

[peteski]

There are three capacitors. There's a through-hole ceramic across the frame, the electrolytic I mentioned (SMD can-type), and a small chip cap across the motor. You can see them on Mike's video from 2:11 to 2:22. That last one is likely most of your EMI suppression. You've got me on purpose of the electrolytic; given its small size I would not be surprised at all if it has a 15V rating (maybe 25V?) and is why they say "don't do that!". I'll check tomorrow.

I really don't see a need for a large value electrolytic cap for smoothing out voltage just for the motor.  Sounds like some overzealous engineer designed this circuit.  Whatever happened, (since the motor still works) must have created an open in the circuit. My bet is on the bridge rectifier. It could have been caused by excessive voltage causing one of the caps to short out, creating over-current, blowing the diodes.  What are the markings on the large cap?  We can likely find its rated voltage.  That yellow component could be a circuit breaker or a MOV ((Metal-Oxide Varistor, a device which camps voltage).  Depends on how it is installed in the circuit: If it is in series with one of the voltage rails then it is a breaker, if it is wired across the voltage rails then it is a MOV.

[C855B]

Ha! I went back to the studio to take measurements and on the way there also realized the "ceramic cap" across the chassis was an MOV. The MOV is bad, at 2Ω not quite a short but enough to keep things from working. Bridge and caps are fine. Electrolytic is 4.7uF @ 35V, a low enough value to make me think it's also there for EMI suppression. It would've been an easy fix, but I'm OK by removing doubt with the decoder solution, and will probably do the same to the other.

[peteski]

So this design actually worked - the MOV sacrificed itself to protect the motor. But did the motor really need that protection?    Also, if the MOV shorted out (which they do) why didn't the high current blow out the rectifier or trip the breaker in the booster (when the cleaning car is placed on live DCC track). I still think this design is an overkill.

[C855B]

Good question. I don't know the MOV's rating since it is house-marked; sadly there is no standard for marking these things. What's clear at this point is this is the reason they say don't use on DCC, they know the specs and that the MOV happens to be under-rated for DCC voltages. But you're right - overkill. Not quite sure what the objective is, maybe they're protecting themselves against layout operators doing something stupid like setting the DCC voltage high (O scale = 20V). In that case the track cleaner car is going to be the least of their worries. :shoulder-shrug:

Anyway, not a full short, at 2Ω it would have been just barely past the 5 amps of the booster, so it didn't trip. Interesting.

[peteski]

Good question. I don't know the MOV's rating since it is house-marked; sadly there is no standard for marking these things. What's clear at this point is this is the reason they say don't use on DCC, they know the specs and that the MOV happens to be under-rated for DCC voltages. But you're right - overkill. Not quite sure what the objective is, maybe they're protecting themselves against layout operators doing something stupid like setting the DCC voltage high (O scale = 20V). In that case the track cleaner car is going to be the least of their worries. :shoulder-shrug:

Anyway, not a full short, at 2Ω it would have been just barely past the 5 amps of the booster, so it didn't trip. Interesting.

And adding probably around 1.4V voltage drop across the rectifier diodes would reduce the current even more. Assuming that the MOV is on the DC side of the rectifier.  But then I'm surprised that the rectifier didn't fry (even if only 4A was passing through it).

[C855B]

The MOV is on the AC side of the bridge.

[peteski]

The MOV is on the AC side of the bridge.

Interesting . . .
If the MOV is now showing 2 ohms, then if you calculated 5 Amps @2 ohms, the voltage getting to the rest of the circuit should be 2*5 (or 10V)  The motor should still be running fast at 10V.

[GaryHinshaw]

So what's the bottom line now?  I have been running my units on DCC w/o a decoder for nearly 2 years with no issues.  Have I just been lucky?

[peteski]

So what's the bottom line now?  I have been running my units on DCC w/o a decoder for nearly 2 years with no issues.  Have I just been lucky?

I wonder if your DCC booster's output voltage is lower than Mike's?  Low enough not to trigger the MOV.