Resistor to operate 4.5v motor on 12v

[Paul Walton]

Hi I recently bought a very tiny chassis from Japan to make a sort of freelance track inspection trolley. It is a TGW TU-9A, and the only info on the box that isn't in Japanese is (1v-4.5v), now I appreciate I will need a risistor to operate this on the normal 12-14v but I haven't a clue what resistor is required can anyone who has used a similar chassis help.?

the

[Hugh Norwood]

150 ohms should do the job.

[B.Meldon]

I have never had much success with these tiny chassis. I found that adding the resistor just sapped most of the power out of the motor, and they were never very powerful in the first place.

These tiny chassis also suffer from what is known as 'cogging' (I think?) this is down the high gearing.
What I found was that you had to turn the controller up higher to get them to move and only then could you turn the controller down, so they run slower.
That would be ok for a continuous run on a circuit, but it is not so good if you stop in a station and very poor if like us you do a lot of shunting.
That said I think others may have had better results than me, you will have to see how you get on with it.

Brian Meldon

[Paul Walton]

It is really a novelty item to use for a couple of laps per hour on the club narrow gauge layout Brian

[Scottish Modeller]

Hi all,

My advice is not to follow the resistor route.

Instead buy a power supply that matches the max voltage of the motor.

If you want to run other power units on the same track then all that is needed is a DPDT switch to change between the power supplies.

Check with MERG to see what power options you have.

Thanks
Phil H

[Stefan Krebs]

The resistor required is dependant on the resistance of the motor, and not just any value, i.e. 150 Ohm might be a good start or not.
More importantly, you also need to have the right Amperage, too small and the resistor will die (overheat melting your body), too large takes up a lot of space: check what the motor is rated for and match that (on the generous side).
For example, the 9V Maerklin Z motors are rated 2,5 A! (But I wouldn't push that).

An electric motor's torque is proportionate to the voltage, i.e. at 4,5V the torque is not very high and the slightest mechanical binding can cause stalling. That's why you can't control Busch's Feldbahn properly, running at 3V it's on at full speed, or off.

However, there's are 2 electronic 'cheats' available: Pulse-Width-Modulation (PWM) and Phase-Chopper-Control (PCC). In theory PWM should be better, but practically the difference is hardly noticeable. Both use the same trick: as the 4,5V rated voltage is for the effective voltage, a higher voltage may be used if the voltage is switched on and off fast enough, e.g. 50 times per second. Thus, for example 9V may be applied if it is only applied for 50% of the time. That way better speed control can be achieved, as with twice the torque the motor is less sensitive to mechanical binding.

If your controller gives acceptable performance, count your blessings, no need for such trickery. But if you try one and like it, go for it; the performance improvement can be impressive (but doesn't necessarily work with all motors).
Note 1: If you use engines with 12V motors, you still need the resistor to par down to 4,5V (and buy the PWM/ PCC for 12V).
Note 2: The internal resistance of your 4,5V motor is different running PWM or PCC, as opposed to DC. Therefore, a different resistor is required!

To find out which resistor you need, use the controller of choice, run the engine with an adjustable resistor in series, and set the controller to 12V, adjusting the resistor (from high to low of course) so that the voltage across the motor is 4,5V. Measure the adjustable resistor after shutting down the set-up.


Hope this helps
Waldschrat

[JulienW]

Paul, as an alternative to trying to obtain an adjustable resistor, faffing about wiering it in in series along with a volt meter and another meter to measure resistance or working it all out from first principles and wondering why you bothered with all the hassle for what was meant to be a bit of fun you have probably taken the better path in asking what resistance others have used in the small chassis coming out of Japan that seem to be equipped with 4.5volt motors.

I've converted several of these chassis by fitting a 150ohm resistor and they run OK  whereas a 270 ohm was a bit too much (unless you wanted very slow running!).

When I say OK what I really mean is that the magic smoke stays within the motor where you want it as if it escapes then the motor will not run anymore and I've never worked out how to get it back in (let alone catch it when it comes out!).

I suspect that the running qualities will not be as good as with a motor designed for 12volts (a bit of a faff given that the replacement motor will probably cost as much if not more than the chassis) or by using a controller designed with a 4.5volt output (again more expense to buy it and faff to fit it just to run one loco), but for a novelty item the resistor should suffice (but bear in mind when it comes to bodywork they go get a bit warm).

[Graeme Dunbar]

I would go with Hugh's and Julien's suggestion. It is what Nigel Lawton sells with his motors, but they are 6 V. It is going to be a bit of a compromise anyway. You don't have to yank the controller up to full voltage and the resistor is there as a bit of protection in case you forget.

It will be the current that kills the motor, if it does, not the voltage. The resistor is as much to limit the current to the motor as to drop the voltage.

[Hugh Norwood]

I would go with Hugh's and Julien's suggestion. It is what Nigel Lawton sells with his motors, but they are 6 V. It is going to be a bit of a compromise anyway. You don't have to yank the controller up to full voltage and the resistor is there as a bit of protection in case you forget.

It will be the current that kills the motor, if it does, not the voltage. The resistor is as much to limit the current to the motor as to drop the voltage.

There you go! :)

[Elmgate]

I too have used a similar chassis (TU7 - but basically the same mechanism in a different configuration) with 150 ohm resistor, and I concur with Hugh and Julien. Regarding controller, you cannot expect to get good control from a "basic" train set controller, but need one that works by varying voltage (not simply adding resistance). With a good controller, you can get slow running, but only at the lower end of the range. Although my skills are limited, I have constructed my own controllers, which are made to operate at lower voltage (12 volts is rarely necessary except for very old high current mechanisms), even from the "standard" 15 volt a.c. supplies. However, much has been written about the "best" electronic contollers, and I will leave my comments at that!  :D

[Stefan Krebs]

Err, '... you cannot expect to get good control from a "basic" train set controller,...'?  ???   ???

I beg to disagree, the Eishindo controller comes in every of their basic train sets, and it not only provides surprisingly good control (at their low operational voltage), but even includes connectivity for 2 infrared sensors to operate the shuttle unit integral to the controller. As 'basic' controllers go I can't fault that!   ???
The ROCO digital controllers, even as supplied with starter sets, I can't fault either. And where starter sets from Fleischmann and Trix contained half-wave controllers (Fleischmann MSF; Trix Vario), I'm content to rate those providing 'good control'.

But I agree that MOST cheap and cheerful controllers, as COMMONLY found in starter sets, but also from controller-only suppliers, fail to excite. And as set out elsewhere, rheostat controllers are a different kettle of fish, i.e. much more likely not to provide satisfactory control.


Cheers
Waldschrat

[Graeme Dunbar]

Are there many controllers currently in production that still use resistance mats?

I wonder what the least expensive of the currently available commercial controllers is?

[Stefan Krebs]

Depends how you frame your question: rheostats are still the weapon of choice for slotcars (unless digital), and they appear to be still fairly common in that country South of Canada.

The cheapest commercial controllers I have bought were on ebay 2nd hand, 99p plus postage (=

[Graeme Dunbar]

Yes, I did wonder about slot car controllers (if ever there was a good illustration of the limitations of speed control of rheostat type controller, look no further) but I was thinking specifically about what is commercially available in model train controllers. That would be actual train controllers, not including ones adapted from other things such as generic motor speed controllers, home-made, second-hand and special offers.

I was thinking specifically of a newcomer to the hobby wanting a basic "shop bought" (actual or online) DC controller. Also, not to worry too much at this point about "controller X doesn't work well with locomotive Y", though that would be an important consideration for making a purchase. Also, the cost of a power supply should be factored in, if not part of the controller itself.

I suspected many candidate controllers would come out at about the same price so I thought I'd do a quick search. I'm sure prices will vary quite a lot and I've not considered delivery charges (or the cost of travel to a shop). There is an element of recommended price and shop price and perhaps old v.s. newer models to be factored in too.

So for DC controllers:

Kato 22-018 https://www.traintrax.co.uk/22018-power-pack-standard-p-1660.html ~

[Stefan Krebs]

Digitrax Zephyr; - basic? Whow, that is one of the best digital controllers on the market. Okay, it might be their no-frills 'basic' unit, but their control electronics are certainly good, anything but basic.

You do not state, why, or rather what for you want the controller.

I have the late 1960s Fleischmann starter pack controller, and it has only 5 (fixed voltage) speed settings; fine for certain testing, e.g. comparison testing of engines as you always have the exactly same voltage at the setting you select.
I have the (modular) Fleischmann tin-box controllers, excellent speed range as they kick in at below 1V, and they can handle serious amperage (for Playmobil and LGB; they were designed for their 0-gauge range) up to 19V!
I have the Playmobil/ LGB (both made by Titan again) starter-pack controllers for the kiddywinks to play with; simple and rugged; fine-control? What for, they are digital drivers, stop or full throttle.    ;D
I have the Trix Vario and Fleischmann MSF (both Titan again), which I use for train running and shunting in H0 and H0e, and they work okay.
And I have my home-built walk-around controller, which is my preferred shunting controller, especially in H0f. That's because it hasn't got a dial knob, you control with simple push buttons, giving much finer control.

I only ever bought the MSF, the Vario, and the Minitrains, to trial them, because I won the auctions at