Battery + Pot. = DPDT?

[Benjamin Maggi]

So I have a couple of small engines (LGB Stainz and two switch engines, each one powered by one truck of a Bachmann 45 tonner) and I am wiring them up for battery power only in a trailing car. Essentially, each will be isolated with just a pair of wires running out the back to the battery car. My Stainz has no lights, and the lights on the two scratchbuilt switch engines will be LEDs controlled by a 9 volt batter on the engine itself... basically, what I am trying to say is that the battery in the trailing car will only be used for the engine's motor, not lights, sound, etc.

I am new to battery power, and thought I would just pick up an Aristocraft Li-Ion battery and build up something. Their battery says it is 21.5 volts on the outside, and I don't know the amps. Even though this might be overkill, Li-ion batteries are light (important for a small engine pulling a trailing car containing a heavy battery) and last a while. I don't want anything fancy, and I have made an HO throttle circuit described in the Dec. 1986 Model Railroader, so I thoght I would try that again and put that in the trailing car too. I wanted to have the battery run to the throttle, and then have the output go directly to the engine. 

Here are my questions: 

1. Would this work? Can I just take a potentiometer designed for 21 volts and wire that, along with a toggle switch to change polarity/direction, and put that in between the battery and the engine for a simple control circuit? Is there anything I should know about this? Is there an easier way?

2. If my small engines described above only pull 12 or 14 volts (I am guessing, but since it seems most G-scale transformers put out that output... some do 18 volts) would 21 volts be overkill? Or would the engine still just draw 12-14 and the remaining 9 volts be reserved and cause the circuit to last longer?

3. If the Aristocraft Li-Ion battery is too big/powerful for my engines, what would you guys recommend for my battery car? There is a local Hobbytown that has lots of R/C stuff so I could ask them, but I would rather first talk to people who are more familiar with battery applications in trains. 

I guess I just want a simple circuit that is one step above the "power switch, direction switch" route. I want one that is "power switch/direction switch" and some speed control. 

Thanks 

[cabbage]

1: NO! Most modern potentiometers are rated at 0.25Watts maximum -you would need something like a heavy duty wire wound rated at at least 25 watts. If you put that much power through a typical plastic potentiometer the risks of fire and even parts of the pot flying off are just too dangerous to contemplate. It would be far simpler to buy a cheap PWAM controller. (circa £15) MFA sell a good one

2: The amount of voltage supplied by your Lithium Ion pack will not change until the end of its capacity and will not materially increase your run times.

3: The best answer I can give you is to look at the 7.2Volt Tamiya "Race Packs" so beloved of my son and his cousins. I use Sealed Lead Acid batteries because they are heavy and cheap -I know the sizes well and I can design my locos internals around them

regards

ralph

[Benjamin Maggi]

Thanks for the response. After looking around, I am thinking maybe a couple of batteries that, added up, will equal around 12-14 volts. I will not use a pot then if that is the resulting outcome. Excuse my ignorance, but what is a PWAM controller?

[Del Tapparo]

You may want to consider "Critter Controls". They are a step above a battery and a switch.

 

WWW.GScaleGraphics.net 

[cabbage]

A PWAM is a Pulse Width AMPLITUDE Modulator Controller. Unlike the std pulse width modulator which "chops" a square wave -so the motor gets full voltage pulses at (say 14Volts) a PWAM "chops" a rising SINE WAVE thus the voltage is continually increasing as the pulse is "on". Added to this the frequency of the sine wave normally rises as the length of the "on" pulse increases.

The net result is that it pulses slowly at low speeds, (better traction), and higher at high speeds, (better battery life). These have been around now for over 15 years to my knowledge -but are more commonly found on high power variable speed DC motor systems (like a lathe). The one I normally use is actually for a small bench drilling machine -but is nearly perfect for this application!!!

http://www.mfacomodrills.com/gearbox_accessories/multi_gearbox_accessories.html

(an example is at the bottom of the page). If you sort through the down loadable pdf catalogue you will find one to suit your needs.

regards

ralph

[Benjamin Maggi]

Del,

It has been a while since we have last talked. Your vinyl letters have really made my cars look great. With the spring weather here, I will be able to finish my fourth car (painted part of it this morning) and hope to have it completely done up by this weekend. Then, I will send payment for the LNER decal order.

I have seen your critter control unit before, but not being a battery-fan until this week I never took notice of it. I will take a closer look, and perhaps that is the solution.

Ben

 
Cabbage, what you said was pretty much over my head, but I will ask around at my local R/C shop and see what they say. I appreciate your comments, though. 

 

[altterrain]

Hey Ben,

I sent you a PM over on the Aristo board. My 7/8's trains will be using simple battery with a speed controller from quikar electronics (http://www.quickar.com/tkit.php?session=ckEjuiIm - ML-804). Its a $10 kit that works well -

cables and knob from allelectronics.com  battery from allbattery.com

-Brian 

[Benjamin Maggi]

Altterain,

I will check out my message on the other forum. I think Del's product looks really nice, but it is probably too nice (meaning more than I can afford right now) for me; I know his got good reviews in Garden Railways. 

[davidarf]

I have recently installed the Syren10 board from Dimension Engineering - http://www.dimensionengineering.com/SyRen10.htm

It is more expensive, but copes with any current load I throw at it, and can be controlled manually by wiring a simple Pot. or can be hooked to a radio control receiver to give full remote control.

 

Regards

David 

[izzy0855]

Check out Cordless Renovations, their a battery manufacturer in Iowa that build custom battery-packs for G-Scale trains.  Check out their website at www.cordlessrenovations.com.