A friend of mine is looking to power his N scale train from a 12 volt car
Anyone know of some where to buy a control that will allow this?
I made him one using a LM317 voltage regulator, but it's minimum output is 1.2
volts and the friend is looking for something that will go from 0 volts to the
full 12 volts of the car battery.
Any help is greatly appreciated.
Please email responses to:
A 12 volt automobile battery cannot easily kill you. It CAN under some bizarre
circumstances cause death or serious injury but it cannot "easily" kill you. The
Volt 60Hz stuff in your breaker box can kill you a whole lot easier and quicker
any 12 volt car battery. The battery can only kill you with the greatest of
difficulty. You must help it along quite a bit to achieve such an end. The most
probable injury is a minor burn caused from being part of a short circuit.
If you burn your skin off or stab through it then the resistance across the whole
body under the skin is only about 500 ohms; even less, if you stab deep enough.
you take a couple of sharp probes, connect them to a 12 volt car battery, and
them into your chest, you'll be in a bad way.
However, if you do that it is evident that you were already in a bad way to begin
Now, while it may be possible (perhaps) to show documented proof of death as a
result of electrocution from a car battery, it is not something that is a serious
problem. Batteries are no more dangerous than the electrolyte inside and the
they outgass as a result of their function.
As anybody who's managed to jam his stainless steel watch bracelet between the
positive terminal of his car battery and the negative-ground frame will be able
tell you, car batteries can deliver quite a lot of current.
Automotive starter motors operate on 12 volts DC, and can draw hundreds of amps
the (with any luck) brief period when the engine's cranking. Let's assume the
delivers exactly 12 volts, and exactly 240 amps is being drawn. With that
information, you can use Ohm's law to figure out the resistance of the circuit
(including the starter motor, its wiring, the internal resistance of the
cetera). R equals 12/240, or only 0.05 ohms. And the circuit power, mostly
for by the motor, is 12 times 240 - an imposing 2880 watts.
If 240 amps passes through any significant amount of a human body for any
period of time, investigators may have to employ DNA analysis to determine who
stuff they found all over the place used to be. You really don't want to make
yourself part of a 240 amp circuit. Actually, only about 30 milliamps (0.03 amps)
across the human heart has a good chance of stopping it.
Where people go wrong, here, is by thinking that if you disconnect one battery
in your car, hold the end of that lead in one hand, touch the battery terminal
the other hand, shout "Je ne regrette rien!", and then get a partner in
exploration to turn the key, you'll be deader, faster, than someone who's already
started his skydive when he discovers that the thing on his back actually
some chocolate and a sleeping bag.
What will actually happen in the above situation - the car situation, not the
skydiving one - is nothing.
The reason for this is that the human body has quite a lot of resistance of its
If you've got a good contact - the terminals are big enough that the whole palm
each hand can touch them - then the resistance across your body is likely to be
between about 2,000 and 50,000 ohms. The thinner and wetter your skin, the lower
resistance will be.
Even if your resistance is only 2000 ohms - which it probably won't be - that's
enough to drop the circuit current to about 6mA. You may be able to feel that.
Since your resistance is actually likely to be much higher, the current through
body is likely to be trivially low. And since your body is part of the circuit,
current through the whole circuit will also be trivially low. Hence, the car
start, and you will not die.
But beware! You can most certainly fry one of those little flea sized N scale
locomotives if you do not include some kind of over-current protection such as a
or a crowbar curcuit. Fuses are OK and they are cheap. Crowbars are more
and expensive but work much quicker. You may still ruin a locomotive even if you
a fuse. Not really very likely, but the slim possibility does exist.
Don't open the batteries and expose yourself to the electrolyte. It's not a
but there's no future in it. You can get nasty acid burns if you're careless or
Don't allow hydrogen gas to accumulate in closed spaces unless you live in
New Jersey or your name is Hindenburg. and be sure to vent the inevitable acid
that are an integral part of lead-acid batteries. You can buy sealed batteries
days that cannot be opened and that will not spill. That is what I would
but I would still vent them to the outside if possible
NOTE: some of the comments above were C&P from http://www.dansdata.com and some
truly my own. I have messed about with automobile batteries for fifty years and
never been killed by one.
Not even injured.
While I agree with what you say, there's a LOT glossed over in your last
sentence. "Batteries are no more dangerous than the electrolyte inside
and the hydrogen they outgas as a result of their function."
Electrical burns are only part of the problem with short circuited car
batteries. The internal resistance of the battery will limit the current
to some finite value ... in the process it will generate a LOT of heat
IN the battery. This can be enough to boil the electrolyte and cause a
steam explosion of the battery case. This sprays scalding-hot battery
acid and hydrogen gas all over the place, along with plastic and lead
'shrapnel'. NOT good! A secondary hydrogen 'explosion' (see below) is a
More typically, however, hydrogen is vented during the charging process.
If not well ventilated, this can also cause risk of a hydrogen ignition.
Unless tightly confined (in a battery 'box' or similar), this is
unlikely to result in much of an explosion, but could easily ignite
other nearby items. It might also burst the battery case, with results
similar to those above.
A car battery can certainly be used for the suggested application. It
was common to do so in the 1930's and 1940's. As many have stated,
caution and proper use is necessary. A fuse MUST be fitted to the
battery, as close as possible to one of the main terminals (probably to
the positive one, as the negative is usually considered 'ground'). The
main terminals, and ANY wiring ahead of the fuse should be well
insulated and protected from accidental contact with (dropped?) metal
items. The battery should be in location away from where most persons
frequent, and well ventilated (especially during charging). The best
ventilation is to OUTDOORS! Perhaps a screened back porch or similar
might make a decent location (depending on the climate, but batteries
work well to below freezing temperatures).
As a side issue, hydrogen gas vented by the battery can build up in
space as large as an entire home. Probably not to dangerous levels, but
it can still cause problems. For one thing, it will set off
carbon-monoxide detectors (BTDT) ... this can lead to moments of
excitement until the problem is correctly analyzed. :-(
========Froggy@The, Pond.com wrote:
Well, yeah, that's right, but I'd already written a dissertation on the subject
my fingers were starting to get raw. So, I wrapped it up.
I have never, ever, never exploded a battery. In fifty years not one. While such
possible, the likelihood of it happening is quite small.
The point is, that it is highly unlikely that a car battery will kill you unless
dropped on you from a high altitude. Properly used they pose no threat to your
Improperly used.........well..........there is no defense against stupidity,
ignorance or carelessness. I would suggest that if one thinks he might be
ignorant or careless that he refrain from doing things that require intelligent
thought and planning. Of course I fully realize that such a suggestion is
Of course, in a more perfect world, you would have an 18 Volt 10 Ampere
with a 250 Watt capable rectifier on the output. This would feed a regulator
built around an LM7812 voltage regulator controlling a 2N3055 pass transistor.
a steady 12 volts with up to 10 Amps if needed. Enough current to run a
scale railroad, but not enough to weld trucks and motors to the track.
Never the less, it is entirely possible to use batteries with sufficient safety
run a model railway. It merely requires a bit more thought and planning than
the power company and a transformer.
Volta Cell, GA.
such is possible, the likelihood of it happening is quite small.<
Two points, years ago I saw my cousin explode a car battery, he was
trying to jumper it in front of the house. Lost a good suit, lucky he wore
Second point, mechanics always used to take off all rings. A possible
short could really produce a bad burn on the ring finger.
But the real point with model railroading is you must fuse it to the
layout. Other wise any short _could_ be exposed to a few hundred amps.
That's _hundred_ again.
They will burn the living snot out of you if you wear metalic objects that can
provide a current path. Sometimes they will "bite" you if you are wet and
however the odds of being fatally injured are too small to be overly concerned.
Absolutely. You can "fatally injure" an N scale locomotive with an unfused auto
battery under some conditions
One dark, rainy night too many years ago to count, I was working as a switchman
Inman Yard in Atlanta. I had to couple to a TOFC car that was wet from the misty
and also was leaking something. It was steaming as I approached it in the dark
confines of the class yard tracks. As I drew closer I could make out the
unmistakable odor of sulfuric acid fumes. The lead trailer was facing doors
the car and one of them was bulged out. A steady trickle of oil of vitriol was
dribbling out of the gap at the bottom. The temperature and humidity was stifling
that night. The very air was thick with foggy vapor, and now, sulfuric acid
As it had been raining for most of the evening I was quite moist. My clothes,
consisted of a 100% cotton shirt, cotton briefs, cotton denim jeans, cotton
leather shoes were likewise considerably moist and limp.
I coupled to the car with the vapors swirling all about and signaled to the
driver to back out of the track. I caught up on the car ahead of the TOFC flat
rode out on it. The evil fluid continued to seep out.
I dropped off as I passed the north-end conductors shack and walked inside.
"Hey Ragman", I called to conductor Wells, "You need to bad-order that first pig
this cut. It's leaking acid from one of the trailers."
I went about my business and in a few minutes we started into another track.
thereafter I bent over to throw a switch and the back of my shirt ripped.
later, as I stepped up onto the engine the knee of my jeans tore open, then the
one. In just a few more minutes I was in rags, my clothes literally falling off
body. It had started to rain again and I was dissolving like a sugar cube in a
I put on my rain gear and called Ragman. "Hey Rag, you need to call me a relief,
gotta go home."
"What's the matter, You sick?"
"No, I'm naked"
The acid vapors had literally eaten the damp cotton clothes right off my back.
Everyone except me seemed quite amused by the whole incident. The Terminal Super
told me to go on home and not wait for a relief, it would be OK, he said.
You are quite right about the rings. That is more a problem when
battery is installed in a car, and especially when the positive
the one closest to the fender wall. Also note that using wrenches
insulated handles keeps you from accidentally causing showers of
or welding tools to the car. Don't ask how I know that.
However, you should remember that the amount of current a wire
carry depends on its heat dissipation ability. Well, all right, you
theoretically blow a wire apart with electrostatic force but it's kind
hard to keep it from becoming a gas before you do that. My point is,
you will never get those 100 amps to the layout unless you hook the
battery up with a cable that can carry 100 amps. If you have a car,
look at it, and notice how large the battery to starter cable is,
that is if it is old enough that the SOB's didn't hide the battery
in some awful corner. If you use a cable like that to hook up your
yes, you can get 100 amps to the layout, but you'd be a meatball.
What WILL happen, if you hook the battery up with a more
wire, let us say 14 ga, and then lay a Crescent wrench across the
with power full on, is that something will overheat. It might just
quickly to smoke, opening the circuit. It might also just get red
and set fire to your Styrofoam mountains. Your fuse is simply there
overload before your wiring does. It doesn't matter how many amperes
your battery can deliver; one of those ridiculously huge DCC power
would cause a fire just as nicely if there wasn't any fuse.
I don't know if sealed batteries would be needed. Clamp the
down and it won't spill. I don't like sealed batteries for cars
because I take off the caps and lay a rag over the holes when I am
charging them, so any gas will be able to bubble out easily and the
battery can't overpressure. I
don't care how good the relief valves on sealed batteries are, an open
is still better.
Agreed. Lead-acid batteries in a car they rarely cause problems other
than dying with age. And also agreed that one does NOT want to drop one
on one's foot, for various reasons. :-(
I've never exploded a battery either, but I've seen some that HAVE
exploded, and it's not pretty.
The big issue is bringing the battery INSIDE, and keeping it in possibly
confined and/or poorly ventilated spaces. That is NOT good. In many
instances, charging is more dangerous than using the battery, as that's
when the most hydrogen is usually released.
And all wiring ahead of the fuse (mandatory) should be protected from
accidental contact with metal that may cause 'shorts'. Some kind of
ventilated hood or cover over the battery would be desirable.
========Froggy@The, Pond.com wrote:
On 4/27/04 1:36 PM, in article firstname.lastname@example.org,
A car battery provides 12 volts DC, pretty low voltage. However, the
current it can provide is about 240 amps. The car circuitry (starter motor
wiring, inside of battery, connecting wires) has a resistance of about 0.05
Ohms (12 v / 240 amps = 0.05 ohms). The power delivered to the starter motor
is 2880 watts ( 12v X 240 amps = 2880 watts). If you grab both terminals of
a car battery, the resistance of your skin (2000 ohms or more) will drop the
circuit current to 6 milliamps (I = 12/2000 = 0.006 amps), not enough to
feel or injure you. Take that same battery and use sharp probes to stick
into the chest under the skin to a lower circuit resistance (500 ohms) and
now you can be harmed (24 milliamps).
Is this the sort of thing that might probably happen to a model railroader using
batteries for a power source? Is it possible to accidentally stab yourself in
chest with a pair of sharp probes connected to a freshly charged automobile
I must confess, the thought of doing just that has occurred to me many times
This is beginning to read lke a Monty Python sketch.
Dead Parrot, GA
PS: I have always enjoyed sticking my tongue to both terminals of a nine volt
transistor battery too.
From my college days I have a recollection that a low current,
approximately 10 mA, passing through the chest can affect the
diaphragm causing it to stop. So while technically not electrocution
(you die of asphyxiation) it can kill. I do not remember the exact
numbers (hey, it was more than 50 years ago) but they are in that
Since most of us have messed around with 12 volts a lot it is not a
common cause of death but it has apparently occurred.
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