Thursday, 21 May 2009

Decoder Comparison; TCS vs Lenz

Lets begin with the prices. Its an unfair comparison. A TCS MC2 costs under £20. A Lenz Gold plus USP module costs nearly £70. So, those with a restricted budget, stop reading now.

I have a 4mm scale railbus, its an Airfix kit with a Branchlines mechanism and interior. A Mashima motor drives one axle, the other has simple compensation. Wiper pickups on the top of the wheels. For a while this has run with the TCS chip; its seemed adequate for the job, but there have been shortcomings.

The biggest problem is not down to the chip, its the light weight four wheeled vehicle. The pickup can be erratic on all but the cleanest track. So, as an occaisional use vehicle on an exhibition layout, its a problem if it stalls on the crossing into the platform ! The TCS chip does exaggerate this problem to an extent; once power is lost, the chip restarts from speed zero, doing all the acceleration again. The TCS chip control is OK, the motor runs a little noisily, but its OK. The start speed is a little on the high side, but again, its OK.

So, why replace a £20 chip with a pair of devices costing £70 ?

One way round a pickup problem is a UPS capacitor to store power when there is a break in power to keep the chip alive. The store need only last for a tiny fraction of a second to overcome a microscopic bit of dirt. Zimo have solder pads for this and instructions on how to add the cheap components, some other chips can be end-user "hacked" to add a capacitor (your warranty is void when you start soldering bits onto most chips!). Lenz have a fairly expensive solution in the UPS module which fits Gold chips. It contains far more capacitance for the volume than is possible with the Zimo method.

The Railcar has potential to be used as an automatic train. If the layout operator wants a rest, or there are questions from a visitor, a train which shuttles into the platform, waits, then departs is very useful. DMUs and Railcars are ideal for this service. The Lenz Gold and Silver chips support automatic shuttles using ABC braking modules. ABC braking is very simple - four or five diodes per brake section - so a shuttle could be created on a layout for the price of a couple of on/off switches and about 20p worth of diodes, and the shuttle won't break anything else on the layout.

So, for both UPS and Shuttle features, the Gold is the chip for this particular loco.

Having fitted the Gold, the changes are significant.

The motor in the loco does run more quietly, though the slowest speed isn't massively better than the TCS chip (and its nowhere near the slow speed which CT and Zimo can achieve). I have tried various of the Lenz motor options (though there isn't any documentation to explain what they do, so changes are blind), and have gone back to the defaults as the best option.

The UPS module is the biggest improvement. I had expected this from my experience of similar units in Zimo equipped locos. Its now pretty much impossible to stall this locomotive.

The automation is taking a while to setup; the basics are fine - ABC plus Shuttle behaviour. Distance related stopping does what it is supposed to do, though it doesn't appear to be as well implemented as that on Zimo chips.

Getting the distance related stopping to stop smoothly seems to need tweaking of the decelleration (CV4) and possibly a custom speed curve, otherwise the loco decellerates quite rapidly (following CV4?) and then inches along to the stopping point. The Zimo method where the loco maintains its running speed until it needs to decellerate to the stopping point seems so much better (or optionally the Zimo can work out a braking curve depending on the approach speed). There may be a few CV's I haven't understood, but, in part, that must be the weak Lenz documentation compared to that from Zimo.

So, overall, for this locomotive, the Lenz Gold + UPS does the trick. Compared to other methods of building an automated shuttle train, the Gold/Silver features are quite cheap. The UPS is moderately pricey, but its the only way for a Gold. But, if not requiring the shuttle feature and only needing ABC braking, then I think a Zimo is a better chip than the Lenz; the low speed control is better, the distance braking control is much easier to understand and setup, the UPS capacitor is £1 or so, rather than £36. etc..