electrical help

[Anonymous]

I have an elaborate ho scale layout in my mother's basement. She has Alzhiemer's and doesn't think she owes a power bill. Can I run my trains using a car battery hooked up to the terminals of my power packs labeled 12V constant? I am using 2- wire dc and not dcc. All my power packs are MRC golden ampacks model 500.

[edblysard]

Only if you want to start a fire....
Auto batteries are 12 volt, 200 to 550 amp,
they will cook your wires...take a look at the cables comming from the battery, you'r thin guage wires will not carry the amps, and even if they did, imagine what 400 amps at 12 volts will do to your model's motor...

Now, you can buy a d/c to a/c converter at radio shack, about $99.00, which will hook up to a car battery, and provide a 110 volts source for your power packs, they have clamps that hook to the battery terminals, and a 110/115 outlets...

Ed

[adrianspeeder]

Ummm, maybe your mother needs more attention than your trains do???

I wouldnt do that. you could use one of these.

http://www.donrowe.com/inverters/inverters.html?source=overture1

Adrianspeeder

[Overmod]

Ed, you better not send an application to IEEE any time soon...

Folks who have been around model railroading since the 'early days' may remember that batteries were commonly used to run model trains... that is, model trains made to run on DC. (You can do it for low-voltage AC trains, like Lionels, with an appropriate inverter, I think)

Voltage is a measurement of 'pressure', not current or power (which is a function only of current and resistance). It doesn't matter whether you have a 12VDC battery capable of delivering 10,000A into a load, THE CURRENT IS A FUNCTION OF THE RESISTANCE. If you have a load designed and spec'd for 12V (or 12V max through a rheostat or other voltage-regulating circuit) it does not care whether the 12V source is big or small.

Now, the current capacity of the power source, that's more important. There's a reason you can't run laptop computers off those little multivoltage converters Radio Shack and Wal-Mart sell... those are only rated up to 300 to 500 milliamps (that's about 1/3 to 1/2 an ampere of current). At 12V, and (for DC) E=IR, that gives you a maximum wattage of anywhere from 4 to 6W... including all losses; that's not the 'rated' draw of the device you have connected. Exceed this and you get heating and meltdown... of the power source, NOT the thing you have connected to it.

I could get nauseatingly boring by discussing how voltage sag can occur with excessive drain on some power-supply designs, etc. etc. etc. But I won't. Point is, you can hook a rheostat up to a car battery and run HO gauge trains all day long. Likewise, hook the output of a car-battery circuit up to the TRACK terminals that connect to those 12V terminals on your power pack... after you disconnect the existing power pack from those terminals, of course. (You can easily make a switchbox to go back & forth between plug-in power pack and battery with a DPDT switch rated for over 12VDC, of course)

Where you need to be careful using a car battery is that short circuits take on a whole new meaning with all that power available, if you don't have a really careful fuse arrangement in the wires going to the load. What will happen if you short across the rails, for example, is that you'll get extremely high current into the low resistance, and the 'weakest link' in the circuit... usually the little lead wires to the track... will heat up and burn out just like the wire you made glow red in grade school when you connected it across the dry-cell terminals. If that doesn't burn up, something else will. Car batteries are perfectly capable of heating 16-gauge stranded zip cord up to white heat in a VERY short time (pun intended) -- this melts the insulation, spatters hot copper in random directions, gives you burns, etc. At the same time, the rapid discharge heats the battery, and can cause it to fail spectacularly and dangerously in a variety of ways that warm the cockles of John Edwards' heart, or the place where it should be, depending on your politics. So go back and read what I said about fuses. Then read it again. Don't hook up a big battery to a train set without appropriate fuses or DC circuit-breaker protection (use the circuit breakers sold in auto-parts stores to replace fuses in car panels). A good value would be the value of the circuit breaker built into your existing power pack.

Don't try running your power pack hooked in 'parallel' with a car battery. Interesting things could happen... some of which don't bear thinking about much. REPLACE the power pack with the battery (and provide some sort of speed control on there).

Of course, having gone on at this length, the appropriate place to post this question would be on the MODEL Railroader forums, where you will probably find people who will tell you exactly what to build, where to get the parts, how John Allen would have done it, etc. etc. etc. Do that now.

[ericsp]

I recommend not messing around with car batteries unless you have experience as an electrician or electrical engineer.

[adrianspeeder]

Another way to say it is a load will only draw as much current as it needs.

My truck has two 1000ccamp batteries in parallel. This gives me 2000amps total but only at twelve volts. I can hook up a load that only draws one amp and it will be fine. As long as it is fused for one amp and can take 12 volts.
If i hook the batteries in series, i get 24 volts, which will fry any thing only designed for 12 volts. The extra volts will "force" themselves into the load weather the load wants it or not.

another tip: undo the neg. terminal on a car bat. first. If you try the pos. first like i did and your wrench hits the block or anything grounded, you create a short through your wrench. The wrench will turn cherry red in about three seconds. (Dont ask for the story how i know.)

If you hook a car battery to the outputs on you powerpack, it will explode. In a ball of fire. Possibly injuring you. Or burn the house down.

Adrian"almost starting my electricial engineering at Widener"speeder

[Overmod]

Oh, yes: about those car batteries: It's a good idea NOT to bring them inside (as they contain, and often spew, sulfuric acid), and when you charge them they release hydrogen gas, which is explosive in concentrations from about 3% to over 97% in air.

Theoretically... very theoretically... you could locate a computer UPS (uninterruptible power supply) with an internal battery voltage of somewhere around 12V, and then use a car battery (charged somewhere else) through the circuitry. This should work reasonably well to power your MRC circuitry. Again, there are people on the MR lists who know what Needs To Be Known about this.

I have a soft spot for the Golden Ampacks... that was the first thing I ever ran a model train with. I still have it downstairs somewhere (complete with the punched-through red circuit breaker button that so fascinated a five-year-old...)

[Anonymous]

Hello fawfhamilton--

I won't bore you by repeating what Overmod is telling you, except to say that he's generally correct, except on one point, that I'll try to explain below.

But, I would also add that you should not set up any car battery system in an unventilated or poorly ventilated confined space (like your basement) if you ever intend to recharge (which I assume you will want to do eventually), because a standard lead-acid car, boat or motorcycle battery vents hydrogen, which is an explosive gas. It's a fire safety hazard!! If you use a battery, take it OUTSIDE or into a well-ventilated space, like the garage with the door open, away from anything combustible, before recharging it. And stand back. I've actually witnessed bad lead-acid batteries explode when they are put on the charger.

And (this is where Overmod and I differ), do NOT use an automotive breaker as your primary protection. Fuses and circuit breakers must be capable of safely opening in the presence of very large currents feeding a short circuit (called the interrupting rating because the device is attempting to interrupt and shut off the current). Instead, you will need a dc rated fuse or dc rated circuit breaker and enclosure that is rated for at least 5000-10,000 Amps interrupting current (listed as A.I.C. on the device) for just a single battery, as car and boat batteries, especially deep cycle batteries, can easily provide this very high level of current into a short circuit. The interrupting current is the amount of short circuit current a protective device can take safely while it is trying to open and turn off the power to the short. Note that the "Cold Cranking Amps" usually listed by the battery manufacturer is only a fraction of the current that the battery can dump into a direct short! The reason that this issue is critically important is that electrical switching devices like fuses and circuit breakers can fail catastrophically (read "blow up") if subjected to very high currents that exceed the interrupting rating of the device. And I would definitely not recommend using automotive breakers for this purpose--believe it or not, most of their A.I.C.s are not rated sufficiently high enough to take anywhere near what the battery can put out. The biggest automotive style breakers made (usually 150-200 Amp rated--much too large for what you want to do) are designed, tested and certified to safely interrupt only 2100 Amps! The smaller automotive breakers have even much lower A.I.C. ratings. That's why automotive systems usually have either a big fuse or a fusible link ahead of all the small fuses and breakers.

Therefore, I would recommend a properly sized DC rated fuse or a DC rated circuit breaker. Good news, though. Most household circuit breakers are rated for DC also and can usually take a minimum of 10,000 Amps--sufficient to handle a short circuit fed by a single car battery. Any good electrical supply house, electrician or electrical engineer who does commercial wiring design should have access to a Square D, GE or other similar catalog that lists the ratings for these breakers, and can tell you what will work. Tell them you need a 15 amp or 20 Amp breaker rated for 10,000 A.I.C. at 15 Volts dc or more.

And, DO run it into a properly rated inverter and then to your power pack(s). Make sure the inverter(s) is (are) properly sized for the total watt (power) rating of your packs that you intend to connect to them, plus about 25%.

Also, if you make this wiring permanent, you will almost certainly have to get a permit and meet the National Electrical Code. This, for most lay persons, means you will have to get an electrician to inatall and hook it up. DO THIS, UNLESS YOU HAVE SPECIALIZED ELECTRICAL KNOWLEDGE AND CAN UNDERSTAND WHAT THE CODE REQUIRES!!

If you have any questions, respond back on this string as there are obviously several people here (including me) who are willing to assist.

Adrianspeeder--good luck from somebody who has been on both sides of the lecturn in the EE lecture hall! Hit the books hard when you start and it'll only get harder from there (thought I was gonna say easier, didn't you??). But the time and effort spent are very rewarding if you continue to have an interest in the discipline. BBROYGBVGW.

[ericsp]

QUOTE: Originally posted by drephpe


BBROYGBVGW.

Looks close to ROYGBIV.

[Anonymous]

Close, but no cigar.

[adrianspeeder]

Hey drephpe, send me an email, got some questions for ya.

Another thing i thought of. Optima makes good sealed gel batteries that can be mounted anywhere in any positon. There is one that is upsidedown in my bronco because that is the only way it would fit when i added a second one. I'll need to do the same thing when I add two more batteries to my diesel.

Adrianspeeder

Adrianspeeder

[Anonymous]

just kidding guys....but it did bring up some great responses.It's easier to just pay the power bill and continue to enjoy running my trains as I care for my mother. Thanks to all who replied.

[lonewoof]

BBROYGBVGW.

black brownredorange yellow...
buster brown rode our young goat...
bad boys...

[Big_Boy_4005]

QUOTE: Originally posted by lonewoof

BBROYGBVGW.

black brownredorange yellow...
buster brown rode our young goat...
bad boys...

Ah yes, color symbol for number, a very handy system for wire identification and resistor values among other things.

The pioneers in DC modeling used large batteries to run their trains 70 years ago. As the others have said, very doable. Just make sure to use a 3 to 5 amp breaker or fuse, and size your wire accordingly.

[CBQ_Guy]

QUOTE: Originally posted by Big_Boy_4005

QUOTE: Originally posted by lonewoof

BBROYGBVGW.

black brownredorange yellow...
buster brown rode our young goat...
bad boys...

Ah yes, color symbol for number, a very handy system for wire identification and resistor values among other things.

I'm thinking I first read this in a model railroad related article or book over forty years ago, except they used...Better Be Right Or Your Great Big Venture Goes West!

I still use that little memory jogger to this day!

[lonewoof]

You could also get a large 12-volt lamp (dual-beam headlight with one filament burned out) and connect to battery +, then run train controls off of the other side of the lamp. Limits current to a safer value in case of a short...
/WFA