I recently bought a used Tripp-Lite power supply at a trin show. It was listed at 12 vdc, but when measured with a volt meter, it is actually putting out 13.7 vdc. Since my Tortoise switch machines require 12 vdc, what sized resistor should I use in my supply connection to the power distribution block to reduce the voltage?
RicZ
Tortoise are designed to operate at 12 volts but many modelers feed them less than this to slow them down even more for more realistic operation.They are slow motion turnout motors at 12V but many find them still too fast.
Add two doides in series to the output. This will lower the voltage 1.4 volts and not be dependent on the load as a resistor will be. Wire the diodes head to tail-head to tail. A 1N4001 diode will work.Still 12 volts may be to fast for the Tortoise.
Sounds like this power supply might put out a common voltage for electronics operated by a car system which is usually about 13.6 VDC.
Build or buy a voltage regulator that puts out 9 vdc. A common voltage for the Tortoise. It consist of two resistors, two caps, a voltage regulator IC, usually a LM317 regulator. This is a better option.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
richg1998Sounds like this power supply might put out a common voltage for electronics operated by a car system which is usually about 13.6 VDC.
i think you need to measure the voltage under load at the specified current.
greg - Philadelphia & Reading / Reading
The actual voltage you get will vary some when you use a resistor as it depends on the load.
A regulator will give a constant voltage.
The complete regulator on a PC board are sold for about $10..00. I have seen them at an online shop and on ebay. They are based on the LM317 voltage regulator and are usually adjustable.
This way, any circuits that require around 12 to 13 VDC can be operated.
You can even adjust them down to 1.5 volts for low voltage 1.5 volt light bulbs.
A guess, open the case. There might be a potentiometer to tweak the voltage.
Instead of diodes inthe power supply, you can also put LEDs in series with the Tortoise motors. This will cut voltage byt he drop of the LED - about 2.1 volts for a typical red or green LED. Plus you get panel indicators. Or even two sets of LEDs (or 2-lead bi-color LEDs) - one on the panel and one as a trackside dwarf signal.
If this is a power suppyl meant for a computer, it may just need a certain load to regualte properly. Although every computer pwoer supply I've used and converted to other uses had the 12V line LOWER than 12V until a load was applied. The 5V side usually runs high under no load.
The 1N4001 will work - you might want to make multiple circuits though - a 1N4001 is rated for 1 amp, which is a lot of Tortoises, 50 of them at 75% load, absolute max of about 60 of them, so unless you rlayout is HUGE, it's probably enough however you could get 4 diodes, using two pairs off the 12V lone, one to half the Tortoises and one to the other half. If the power supply is only rated for 1 amp or less, then no point, just add a pair of diodes and be done. Or 4 of them - Tortoises seem o work best with around 9 volts getting to the motor, quieter than at the 12V rating, yet still fast enough and enough power to move and hold the turnouts. The motor in a Torotise is actually highly efficient and will actually move with less than 6 volts, but it will be extremely slow and not have a lot of power.
Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Hey Randy
Small question, Does the Tortoise sit there drawing power all the time, or only when it is activated?
Thanks
Lee
yankee flyer Hey Randy Small question, Does the Tortoise sit there drawing power all the time, or only when it is activated? Thanks Lee
You only have to ask the question, once.
Yes, it is always drawing about 10 to 15 ma. Take time to do a Google search for tortoise machine operation. The machine is called a stall machine. That is what keeps the points in place.
You can put a red/green LED in series with one lead of the machine to see which direction the points are in. Our club does that and we use 9 VDC from a voltage regulator that is connected to the 12 VDC buss.
To clarify, the Tripp Lite is a PR-3A with an out out on 13,7v and 3amp.
The computer power supply is from a Sony VAIO laptop and is rated at 19.5 v and 4.7 amps. I was going to use the brick to power the atlas sanp swich machines through a capaticance discharge unit in my staging yard.
The Tripp Lite is to support the Tortoises and lighting in the main layout.
Thanks for all your help guys.
The below voltage regulator is very easy to use. You can set it to run the Tortoise a little slower which many like to do. About 9 VDC which gives a more realistic point speed.
You can use another one to dim the layout lights, in one section. Use your imagination.
Another one to use just 1.5 volt lamps.
Just parallel them off the big power supply.
Our club has block signals with LED's and we adjust one to 5 VDC to operate the signal logic chips.
http://www.bakatronics.com/shop/item.aspx?itemid=638
They can be made much simpler if you can work with the components. LM317 Regulator, potentiometer, a resistor, two caps.
Simple enough to just use an LM78xx regulator to get the desired voltage. Digikey sell them singles for 70 cents a piece. just wire one in to the supply circuit for several tortii. Your Trippe power supply has a regulated output already. LM7809 (9 volts) would be ideal. LM7812 will give you 12 volts if desired. I'd keep the load on each regulator under 1/2 amp. They will be fine without a heat sink that way. Heck they're almost cheap enough to use one on each tortoise.
Martin Myers
mfm37 Simple enough to just use an LM78xx regulator to get the desired voltage. Digikey sell them singles for 70 cents a piece. just wire one in to the supply circuit for several tortii. Your Trippe power supply has a regulated output already. LM7809 (9 volts) would be ideal. LM7812 will give you 12 volts if desired. I'd keep the load on each regulator under 1/2 amp. They will be fine without a heat sink that way. Heck they're almost cheap enough to use one on each tortoise. Martin Myers
With the 7809, all you would need to add are two 0.01 ufd, 25 VDC ceramic capacitors. One on the input and one one the output. The big supply has a filter cap. Does not get any simpler.
http://www.researchcell.com/general/7809-pin-and-circuit-diagram/
Hmmmm
Not sure if it was the computer or me that posted twice.
Tortoises draw power all the time. About 15ma worth, which is why you can just put LEDs in series with the motor wires with no extra reistors, the motor itself limits the current to 15ma.
--Randy
That laptop power supply - is it 19.5V DC or AC? If AC< checkt he rating ont he big capacitor on the CD unit you are planning to use. In feedign 19.5V AC into a CD circut, the recitifier plus charge pump action of the circtuit will result int he voltage across the capacitor exceeding 25 volts, so if the builder only used a 25V capacitor, you would be exceeding the rating and capacitors make nice booms when you do this. If it has a 35 volt capacitor, you are safe all around.
Measures 19.5 vdc when I used a multimeter.
Ric, as one person mentioned, you will not get an accurate reading of the power supply voltage unless it is supplying power to some load, however light. You appear (my guess) to be measuring the 'voltage' with nothing connected except your voltmeter. Most modern voltmeters have a megohm or more impedance, which means they look essentially like 'no load' to the power supply.
So you are getting a higher value than would be seen if some load were connected. That simple.
The Torti are a very small load at about 15 ma. Even so, 13.6 is a pretty standard open-circuit voltage for a "12-volt" supply, and probably will not damage the tort. This is only a guess, however, and you could check the voltage under load - quickly - with a 1k, half-watt resistor connected across the supply leads. This will approximate the 15 ma load of the tortoise. (13.6 / 1000 = approx 14 ma; power drawn is I*I*R = approx 0.2 watts, so you need a half-watt or greater resistor. It will still get hot quickly.)
That said, the full 12v will run a Tort pretty fast, and putting some resistance in series will lower the voltage seen by the Tort and slow the speed to something more realistic, as several have said.
Using a voltage regulator would seem to be overkill.
Dick Chaffer
RicZ Measures 19.5 vdc when I used a multimeter. RicZ
RicZ I recently bought a used Tripp-Lite power supply at a trin show. It was listed at 12 vdc, but when measured with a volt meter, it is actually putting out 13.7 vdc. Since my Tortoise switch machines require 12 vdc, what sized resistor should I use in my supply connection to the power distribution block to reduce the voltage? RicZ
Which model? Picture.
To my knowledge many of these are regulated power supplies.
Put a couple auto lamps on it and the voltage should drop very little if any with a load if the supply is regulated.
Many, many car radios, CB sets, music systems say for 12 VDC but the average car voltage is usually around 13.6 VDC when the engine is running. I have seen this for many years. Quite normal.
Voltage regulators are not overkill. They are quite normal and very cheap. Less than $1.00 each if you know what you are doing. This can easily be done with a 9 volt regulator. One item. Input from power supply. Output to what ever you power. Two wires in, two wires out. No resistors to calculate. In this case, you do not even need the two ceramic capacitors. He is powering some Tortoise machines. No complex electronics.
This is not my opinion. I am speaking from experience. I have used these regulators a lot over the years. I sometimes have used a couple capacitors on the input of the regulator and output if powering some electronics circuits.
Using a single resistor as a way to drop voltage to the entire rest of the circuitry is not a good idea, because the voltage drop will vary greatly with the load. If you only need a volt or two drop, a string of diodes is much better, the drop is consistent across the load range (ok, technically it will vary SLIGHTLY - at the extremes of load, since there is no such thing as the 'ideal diode', but for our purpsoes - it will drop .7volt with 2 or 20 Tortoises connected.).
Regualtors are fine, and also prety cimple, but they do need a heat sink to get clsoe tot he rated current capacity. ANd the greater the differential between the input source and the regulated output,t he more heat is generated. This may not be an issue if you need t run, sya, 10 Tortoises and use a 1 amp voltage regulator. It shouldn't even get warm, even without a heat sink. A nice thing about linear regulators, at least the 7800 series, is they shut down if overlaoded. This shouldn;t be an excuse to eliminate proper fusing, but typically the device will shut down until it cools down, with no harm.
Randy,
If you had read my post, you would realize I was suggesting a resistor in parallel as a means of checking the voltage drop of the supply under load.
Voltage regulators have become quite simple over the years, it is true. They are easily available at Rat Shack. But to call them 'cimple' in comparison to a standard resistor, found by experimentation, in series with each Tort is a bit strange. A newbie to elex might find the resistor an easier way to go. If he puts one resistor in series with each Tort, there is no 'variation with load' at all.
To each his own, I guess.
Dick
rrinker Using a single resistor as a way to drop voltage to the entire rest of the circuitry is not a good idea, because the voltage drop will vary greatly with the load. If you only need a volt or two drop, a string of diodes is much better, the drop is consistent across the load range (ok, technically it will vary SLIGHTLY - at the extremes of load, since there is no such thing as the 'ideal diode', but for our purpsoes - it will drop .7volt with 2 or 20 Tortoises connected.). Regualtors are fine, and also prety cimple, but they do need a heat sink to get clsoe tot he rated current capacity. ANd the greater the differential between the input source and the regulated output,t he more heat is generated. This may not be an issue if you need t run, sya, 10 Tortoises and use a 1 amp voltage regulator. It shouldn't even get warm, even without a heat sink. A nice thing about linear regulators, at least the 7800 series, is they shut down if overlaoded. This shouldn;t be an excuse to eliminate proper fusing, but typically the device will shut down until it cools down, with no harm. --Randy
I read the post.
A single 7808 or 7809 is all that is needed. That way the OP has a dedicated DC Tortoise buss. No need to calculate and go looking for resistors. Yes it can be done by resistors.
The TO-220 case is easy to bolt to a piece of aluminum if he gets a lot of Tortoise machines.
The OP can then have the 13.6 vdc buss for lighting.