Basic DC Controllers

[Dave Cooper]

Hi All

I was given a new Hornby R965 controller for a xmas present. It seems to give quite good slow running for most of my locos (except the 20 year-old Lima ones).

On putting my multi-meter across the rail supply, it gives a steady voltage reading regardless of the knob's rotational position. From this, I deduce that it's a current-controlling device ? (My meter peaks out at 250 m.amps)

For the big Lima diesels, I need to use their train-set supplied controller (one of which only goes to '2' out of '5' power settings !) I can use the Hornby unit on these but it needs almost full power before the Co-Co shoots off at speed...

It would be nice to have one controller that does all properly (I do mostly shunting and slow-running). I have considered changing the pancake motors in the Lima stuff (eg DMU, Big Co-Co) for 5-pole ones ?

Generally, the 009 line is satisfactory - most of the problems are on the 00 (standard gauge) lines - there's a moral there somewhere.

Any ideas welcome[/b]

[Hobby]

The old Lima stuff was always bad to control so nothing new there. If you replace the motor you'll solve your problem. I've had the odd Lima N gauge chassis in the past but just got rid of them, they are not worth the effort.

Regarding control of N and OO locos for DC personally I'd get rid of your Hornby controller (yes, I know it's new) and invest in a Gaugemaster unit. The W if you want to have a hand held unit or 100 for a cased version. The W will control both N and OO locos but you need to make sure you get the right cased untit that says it's suitable for N and OO, some of theirs are made for O scale which wouldn't do. There are other makes as I am sure someone will point out, but Gaugemaster are known to be reliable and give good performance and their guarantee is second to none.

With controllers you get what you pay for, if you want to shunt you need a decent controller.

[Graeme Dunbar]

I'm afraid I don't have suggestions to tame the Lima diesels, but regarding the Hornby controller I suspect it gives pulsed output (confirmed on this excellent web site -
http://www.scottpages.net/ReviewOfControllers.html ) and pulsed output will confuse a DMM on both DC and AC settings.

[Dave Cooper]

Thanks both. I think I'll try a 5-pole on the DMU first. I have heard that the standard Lima wheels are not very good on pick-up so, may give these an upgrade at the same time..(I like the Bachmann 00 DMU's but they are pricey - mine was

[Graeme Dunbar]

It would be interesting to see how it compares with the 'scope trace in the web page I linked and if the design of the controller has changed since the web page was made.

[B.Meldon]

Surprisingly for a

[Dave Cooper]

Thanks for the warning(s) Brian. It looks like a Gaugemaster unit then !

Incidentally, is the "feedback" that's being sensed by the R965 the 'back-emf' generated by the dc motor ?
Just curious as I'm an electronics novice...
Regards,
Dave

[B.Meldon]

Thanks for the warning(s) Brian. It looks like a Gaugemaster unit then !

Incidentally, is the "feedback" that's being sensed by the R965 the 'back-emf' generated by the dc motor ?
Just curious as I'm an electronics novice...
Regards,
Dave

Yes I think it is, and I think the modern motors by design have vertualy no back-emf, hence the problem.
But I am no expert, others need to comment on this.

Brian Meldon

[Steve Facknell]

Have a look at the Morley Vector- I use it for several layouts, including Woody Lane, it has the option of operating from the control panel or either of the supplied handhelds. Oh, it also has a built in CDU for point operation. An excellent

[Dave Cooper]

Thanks Steve, I'll add that one to the short-list.

Graeme: forgot to say thanks for the excellent link - I'm still digesting the contents !
Dave

[Graeme Dunbar]

Regarding back emf, there are subtle differences between motors, but back emf is fundamental to the operation of brushed dc motors. When operating efficiently the back emf is a sizable proportion of the supply voltage. Only at the instant of starting or when stalled is back emf zero.

The things that do vary widely are the number of windings, thickness of wires, dc resistance, geometry, magnetic field strength and so on and associated with that the inductance of the windings. Along with that, the relative proportions of back emf and the voltage dropped by the resistance will change. When stalled all the voltage is dropped across the winding resistance. When the motor has no load, very little of voltage appears across the resistance and most is back emf, opposing the supply.

In general small motors in small (i.e. 009) models are probably not run very efficiently and running closer to being stalled than in their most efficient or maximum power transfer region. Small motors are high-speed low-torque machines but we want low speed and high torque. I guess there is a trade-off in gearing as the gearing saps the power through friction and manufacturing cost is also a factor.

A difficulty is in developing a controller that can give good performance across a range of motor types and sizes. The better it is optimized for one the worse it may be for another. I guess this is were DCC wins out. It would be interesting though probably uneconomic to design a DC controller that could adjust its parameters on the fly through sensing the motor response.

[B.Meldon]

..............It would be interesting though probably uneconomic to design a DC controller that could adjust its parameters on the fly through sensing the motor response.

I think the 'Fidelity' controllers from New Zealand that are no longer produced, did just that?
But I could be wrong.

Brian Meldon

[Hobby]

It was one of those that was the only other controller that would give fine control of my TTe locos (powered by Rokuhan Z loco mechanisms) other than a Gaugemaster W, all the rest just wouldn't hack it. David Churchill has one and we gave it a try, if I hadn't got the W I'd have had to borrow his!

[Stefan Krebs]

From my experience you are faced with 2 problems, and before throwing out the baby with the bath I suggest you investigate and solve each problem on its own.

The Lima pancakes are renown for their quality problems. As it starts only at high speeds it appears to have mechanical problems. To verify that use a simple transformer and check which voltage is the minimum it starts, engine in the cradle upside down with wires to the wheels. If you can borrow a 2nd multimeter measure the current, it should be around 100mA tops. If much higher there's some binding somewhere.
Before taking things apart I would reduce the spring-pressure on the brushes as this is a common problem, it's often to high.
if that doesn't help take out all gearwheels and deburr them, another Lima issue. Run a sharp knife/ scalpel along ALL edges of each wheel (that's every tooth on both sides and the centre bore)
Before putting the gearwheels back check that the wheels turn freely.
Electric pick-up wipers pressing too hard onto the wheels can prevent free running, another thing to adjust.
Check the anchor revolves freely. It might be necessary to loosen the screws on the brush holder and move that slightly so the motor runs freely. Use a pair of wires from your controller to run the motor. If you can't put an Amperemeter in line you can roughly gauge how freely it runs with the voltage setting needed for start-up.
Now put the gearwheels back, if possible one at a time, and check that everything is moving freely at each step. There should be the slightest slack only in each gear-mesh, and no teeth must touch the bottom of the gap they go into. Oil only most sparingly after completing assembly.
Yes, Lima has always been very economical with electric pick-ups, but if the engine runs smoothly along the track that is not your worry. Certainly no harm done by adding electric pick-up from all wheels. The old metallic silver wheels were nickel-plated, and if that plating is not worn away everything should be fine (Maerklin, Trix, Fleischmann all used nickel-plated wheels). Re-plating worn wheels is not difficult, you can find the instructions on the web.

There ought to be no back-emf issue with the Lima motors, so if you have such a controller it should work.
To investigate I suggest you run one of your locomotives that run well on your controller and measure the current it draws at 3 or 4 settings. Repeat with the Lima and see what the difference is. Very cheap starter pack controllers, and those with transformer in the plug, can't deliver high current, i.e. their voltage just collapses. Most Lima motors require fairly high currents, so try a 1,5A or 2A controller (borrow one, or take your Lima to a club or exhibition). That way you'll know whether you really have a compatibility issue, or whether your Lima is just a ad performer. The latter is a good idea before you buy anything: try before you buy!

Hope this helps
Waldschrat

[Dave Cooper]

That's my homework sorted out for a while then !