Converted Fleischmann loco's lurching down the track at low speeds. Chip problems?

[Wear Valley Wanderer]

I've recently been converting some of my late father's collection of locos to DCC. The latest two are old Fleischmann locos. One is a BR 38, the other a BR 78. 

 

Both have been fitted with AE Models decoders and both are experiencing the same problem, if at slightly different degrees. At low power they are lurching, or 'jumping', badly in either direction until more power is applied. The problem disappears at higher speeds. Just for info, I'm using a Z21 controller. 

 

I've converted other locos and not really noticed this before, with the exception of when I tried Lais chips which weren't exactly the best on the market. I used to use Train-o-matic decoders, but these haven't been available for ages.

 

The common factor here seems to be the chips. I'm not sure if there's something I can do to 'smooth out' the running at lower speeds or if I'll simply have to buy more expensive chips.

 

Any thoughts welcome.

 

Cheers,

 

Mark

[WIMorrison]

The decoders may not be the best, but they will still provide the power to the motor consistently and, TBH sounds like the transmission is binding slightly somewhere. Common causes are the worm onto the pinion, or wheels not being quartered correctly. 

[BoD]

Were the locos running well at low speeds before you fitted the decoders?

[Wear Valley Wanderer]

14 minutes ago, BoD said:

Were the locos running well at low speeds before you fitted the decoders?

They were running fine.

[Wear Valley Wanderer]

15 minutes ago, WIMorrison said:

The decoders may not be the best, but they will still provide the power to the motor consistently and, TBH sounds like the transmission is binding slightly somewhere. Common causes are the worm onto the pinion, or wheels not being quartered correctly. 

One of the locos is tender drive and I hadn't done much to it other than to lubricate the gears and do the wiring. As you said, the quartering on the 'loco end' could be a problem, especially as this was the one that was jumping badly. Being a bit of a newbie, I don't tend to mess about with the wheel set, but this one did 'self disassemble' whilst working on the wiring. I don't really know how to quarter a loco, so I'll have a look into it. We all have to start somewhere I guess!

 

One other thing, was that I was told that the current draw on older locos is quite high and it could be the chip just isn't up to the job. 

 

A trip to my local shop may be in order!

 

 

[Hamburger]

On old Fleischmann motors often one pole is connected directly to the chassis and therefore to track voltage. This causes severe problems and can even destroy a decoder.

This has to be checked and fixed. Maybe you have to cut the respective connection directly at the motor shield.

Secondly, old Fleischmann motors often have built up a lot of dirt/abrasion in the gaps between the commutator plates so this has to be removed with a toothpick and the commutator  has to be cleaned with alcohol or similar.

[Harlequin]

If the suppression circuit is still connected to the motor terminals this can confuse the feedback detection of decoders and cause lumpy running. It can be safely removed.

 

[Wear Valley Wanderer]

12 hours ago, Harlequin said:

If the suppression circuit is still connected to the motor terminals this can confuse the feedback detection of decoders and cause lumpy running. It can be safely removed.

 

I followed the method used by HD Springer (German youtuber) who removed all the chokes etc. I've converted a couple of this type of motor before and not had a problem. If memory serves I used a Rails of Sheffield decoder. I found out yesterday that these are made by DCC Concepts and can cope with higher power draw. I may well try one and see if it makes a difference.

 

Regarding the quartering, I did try rolling the loco along the bench (!) before connecting it to the tender and there was no sign of any binding. Not to say something didn't happen when I put it all back together of course. Just hope I haven't inadvertently damaged any of the valve gear, but to be honest it ran smooth at higher speeds so I'll have to do more investigative work.

 

 

[Wear Valley Wanderer]

22 hours ago, Hamburger said:

On old Fleischmann motors often one pole is connected directly to the chassis and therefore to track voltage. This causes severe problems and can even destroy a decoder.

This has to be checked and fixed. Maybe you have to cut the respective connection directly at the motor shield.

Secondly, old Fleischmann motors often have built up a lot of dirt/abrasion in the gaps between the commutator plates so this has to be removed with a toothpick and the commutator  has to be cleaned with alcohol or similar.

I made sure to isolate everything properly. HD Springer on Youtube does a lot of old conversions and I followed his directions as closely as I could. I also cleaned the commutator, but it wasn't the best condition. A lot of fin scoring on there. I'll try cleaning it again, paying attention to the gaps in the plates.

[RobinofLoxley]

I have no specific knowledge on the locos in question, but this sounds very similar to a problem that afflicts tender drives that have little or no pickup from the loco. If only 1/2 wheel pairs are picking up then its easier to lose the contact momentarily at lower speed. At higher speed momentum carries the loco across dead spots to some extent. Running smoothly at high speed eliminates most of the potential mechanical issues. Even if its multi wheel pickup by design worth checking for bent contact strips, broken wires, etc.

[Wear Valley Wanderer]

SUCCESS!

 

Believe it or not the fix was incredibly simple. When you know how, naturally.

 

I was calling around various dealers/manufacturers, trying to find a chip capable of handling higher current draw, when I stumbled across the maker of the chip I've installed in the two locos (AE Models). The chap I spoke to was very helpful and suggested I try the following before going down the route of higher power chips :

 

1. Change CV 66 to value 1.

 

2. Change CV 61 to next smallest even number (In this case the original value was 1, so I changed it to 0).

 

I believe that CV 61 turns off Back EMF. Not sure what CV 66 does. 

 

The result was that both locos now run as smooth as butter and I am very happy indeed. The old motors are a bit noisy despite being serviced, but I can live with that.

 

Such a simple fix in the end, but I am very grateful to everyone for their help in this matter. Some of the tips regarding quartering, checking the commutator and so on are very helpful going forward. Now I'm off to convert the next loco (Fleischmann BR 03 161) with sound and firebox glow. Wish me luck 😀

 

Cheers,

 

Mark