Running trains with 9V DC battery?

I wanted to test some DC locos the other day and instead of dragging out my old DC power pack, I simply set the locos on a test track touched a 9V battery to the track and watched them go.

This got me thinking about using a small portable system ran on 9V batteries. But I had some questions.

First, is a 9V battery going to destroy an N scale locomotive moter? I ask this because when I was a kid, we would regularly convert Stomper trucks from AA to 9V battery for races and basically fry the motor in about 2 minutes. I guess I'm not sure how much voltage and amperage an N scale engine can handle.

Second, If a 9V battery is feasible how long will it last running an engine?

Third, Can I make a very basic circuit that puts a potentiometer in line with a 9V battery and a DPDT switch to make a usable power pack.

The simplicity of my imagined setup sounds very appealing to me, as I am building a very simple layout to demonstrate model railroading to preschoolers. I was thinking that the simpler it is, the easier it will be to keep them focused on running the trains. I also like the portability factory of not having to plug in.

Any thoughts?

 

The 9v battery is the cheapest DC power pack you can buy!

It will not damage a motor. in fact many people use a 9v battery to test an N scale locomotive in the absence of a power pack.

 

AAs are 1.5 volts, so if you have less than 6 of them in series, you've got less than 9 volts, and your motor probably can't handle 9 volts.

All N scale loco motors are surely able to handle at least 12 volts, probably quite a bit more in most cases, although unless you are modeling high speed passenger rail you definitely wouldn't want to run them that fast.

 

You could very easily get a variable resistor/potentiometer and hook it to something larger - a lantern battery or even a car battery - and run everything off that. Heck, even the battery pack from a cordless drill would work, and you'll have a spare recharging while you play!

I've used a 9V on the chassis of a locomotive when fiddling with it, trying to rule out something. Word to the wise: keep it far away from the lightboard. If you touch the wrong section, the LED will go off like an old-fashioned flashbulb.

 

Tested 9V power not too impressed

I wired up a potentiometer to a 9V battery to test this idea out.




I didn't wired in a DPDT reversing switch.

The results were less than impressive. First I tried a newer DCC ready Atlas locomotive. It ran, but started to smell like smoke real quick.

I also ran a couple of older DC Bachmann locos and they ran slowly with fits and starts and lost DC power fairly shortly from the source.

Maybe I'll just give up on this idea. Too bad, because it sounded pretty cool to have a little battery powered throttle/power pack that I could hand to a preschooler. I'll probably use the parts for a Zephyr jump throttle.

 

From the look of the size I'd think that pot is on the weedy size for that job, which would account for the 'smoke' and other problems. Looks like it may be a 10k resistance as well.

Off the top of my head I'd be thinking of using a 1k pot with 3 or even 5W power rating. (Say 300mA at 5V = 1.5W ... BUT that may only be applied across half the potentiometer surface if it is turned halfway, so is equivalent to 3W for the whole device.)
Or maybe using what you have there but with a power transistor to handle the output to the track.

 

Thanks Mike.

So you're thinking maybe the pot was giving the smoky smell? It is a 10K ohm, I'm not sure exactly what power rating it is, but Radio shack didn't have anything bigger than a .5W. I'll have tho go look at Alphatronics for something that can handle more power. How many amps do you think an N-Scale locomotive will draw?

Should I be thinking about a lower voltage also?

If I do make this work, I want to keep it simple. I have no idea what a transistor is, but dividing voltage and reducing currents are concepts I am comfortable with.

Greg

 

Put you multimeter in the DC amps selection and measure the current being drawn by the loco. Put the meter leads in series with one wire that goes from one battery terminal and to the motor connection.
Use the highest scale and work your way down.
Then use the below on line EIRP calculator to calculate wattage
I would guess at around 0.2 to 0.3 amps. Do not have any N scale locos.


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Many pots I like I see are usually around 2 watts. I have used many over the years.

Some even less wattage.

Take time to look closely at this if you are gong to work at the component level as I call it.
I usually use a rheostat but I have a lot of stuff in my electronics junk box I have robbed out of old electronics gear.




Rich

 

Yep. Can't see 9V DC smoking an N-scale loco.

Not sure, but I used 0.3A in my example and lexon concurs, but there are others here who know better and NEED TO SPEAK UP
But you need to build this for the worst likely case, not best or average, otherwise one 'heavy' loco could smoke your controller.

No - see first point above.

Definitley KISS it.
As you have it in your photos there will always be current flowing through the pot, even with no loco on the track which is wasting the battery; and this will be even more so with a 1k pot than a 10k. (It's a 'cost' of using a voltage divider.) You need to put your on/off/reverse switch between the battery and pot, NOT pot and track ... and remember to use it

 

I just took a 9 volt battery and a 2500 ohm, 2 watt pot with a motor mounted in a steamer.
At a slow speed, I measured 6.94 volts across the pot and the pot measures 60 ohms. That calculates out to 0.8 watts. 0.115 ma current.

The case of the pot I used is about one inch in diameter and I know the wattage.

The more I look at your pot, the more I think it "might" be a one watt or maybe half watt. No idea what your loco draws for current. Maybe the gears where locked up and maybe the loco used more current than usual.
Also, this will run down the battery quite rapidly. Bring a supply of 9 volt batteries.

Rich

 

The below battery usage chart should put this in perspective.
Battery Capacity

Rich

 

Thanks for the help Mike and Rich. I guess I won't give up the quest yet. Just gotta get down to Alphatronics or Fry's and find beefier components.

I ran that DCC readt Atlas loco I thought I had smoked today. It ran great using an old Model Power power supply.

If this works, it'll be for my sons preschool layout. I built a 2x4 foam top over the last few weeks, and added legs and Unitrack today. Right noew my 2 year old and 4 year old are going nuts playing trains. Model Railroading is awesome.

 

I went to both on line and only Fry's has some potentiometers. The average current to be drawn from a 9.6 volt battery is about 15 ma and running these locos will drain the battery quite rapidly.
I you really want to go down this path, Fry's has a four D cell holder and a two D cell holder. That will give you 9 volts. Fry's has 3 watt pots.
With the test I did, use a 100 ohm, 3 watt or maybe a 1k, 3 watt. With the 100 ohm, you will get more resolution of the control. This is guess work as I do not know what your N scale locos draw for current.
I was looking at a chart of popular N scale locos and I see 300 ma to 400 ma running current at 12 volts DC. Since you will have 9 volt max, I think a 100 ohm pot will work. If you are not sure, a 1k will work.
Find a suitable project box.

Rich

 

e-Z Throttle

I found a 9V Z Scale Throttle.



http://www.stonebridgemodels.com/electronics/index.html

Thinking about ordering one to see if it works with N-Scale.

 

Throttle

Very good. Thanks for getting back to the forums with an answer. I have kept the link.
Let us know the results.
Rich

 

N Scale with 9 volt

Some years ago, just before the advent of DCC there was a fellow here in the northwest that tarveled the swap meet circuit trying to sell his operating system. The system called for locomotives to be battery powered and and controlled in a way much like r/c cars were then. Seems to me that he used 9 volt batteries and in demonstrations the system was pretty impressive. But it seems to me that it waqs HO only. Perhaps a forum member with a sharper memory (and there must be some!) can recall more details on this.
Old Fat Robert