Laptop Power Supplies used for accessories on your layout

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railBuilderDhd

Active Member
I've started this thread so not to take over the original thread this discussion started on. The original discussion was about calculating Ohms and can be found here http://www.modelrailroadforums.com/forum/showthread.php?39658-Calculating-Ohms/.

This thread is to further discuss how to utilize alterative power supplies such as an old laptop power supply to run accessories on your layout. The initial discussion was about controlling a DC motor with a power supply that has a higher volt output then the motor is rated to accept. I felt this discussion was better as a separate discussion as I can see there could be interest in this as well as I didn't want to overrun the other discussion.

I was asking if I could use a power supply that has an output of 19 volts to power a DC motor that was rated at 12 volts.
So far we just started discussion the use of a small adjustable power regulator board like those found on eBay.

We can pick up this discussion from this point.

Thank you.
Dave
 

railBuilderDhd

Active Member
Now that we have distinct discussion going I can carry on with my question about the use of the laptop power supply and not feel like I’m stem rolling over O-Henry’s thread.
I was looking on eBay for the step power reducer for the use of a DC motor with the laptop power supply. I found on the cheap end one of these located here http://www.ebay.com/itm/LM317-DC-DC-Converter-Buck-Power-Module-Linear-Regulator-Step-Down-Adjustable-/162255283139?hash=item25c72b23c3:g:29YAAOSwUEVYECcs.

Now, with this little knowledge I’m buzzing with ideas on what I may be able to do with this little power supply. Now that I have the Laptop power supply that kicks out 19volts dropped down to a more usable voltage for models I would like to know more about this. After you get the volts to a point you don’t fry the motor can you have more than 1 motor, how many would be max? Now that the power is getting to the motors how what about the signal to operate the motor when you want the motor to run? Would this only work for something running in a loop or could you use a button or even DCC to activate the motor(s)?
And then would this work for running servos? I’m thinking of this for my turnout controls.

Now, that’s a loaded post so let’s see where this tread goes. I may have just killed it. LOL

Thanks.
Dave
 

Red Oak & Western

Active Member
First, the answer to most of your questions is yes.

I was looking on eBay for the step power reducer for the use of a DC motor with the laptop power supply. I found on the cheap end one of these located here ...

Regarding the DC-to-DC converted you showed: an LM317 is not the best choice for your use. The LM317 is a very inefficient device. If used for servos, which (mostly) operate on 5v (4.8), it could get really hot, depending on load. A much better alternative is an LM2596 based converter ( http://www.ebay.com/itm/10-pcs-DC-D...877446?hash=item461c33f386:g:ssMAAOxyeR9TIV7q ) I only picked that listing since it was the first to come up. Note the price per unit is only slightly greater $1.20 vs $.99. These are 2 amp units, capable of up to 3A with an added heat sink. The heat sinks run about $.50 each, also from eBay: http://www.ebay.com/itm/5pcs-Heatsi...536621?hash=item2816e101ad:g:Qj4AAOSw~oFXINsD

After you get the volts to a point you don’t fry the motor can you have more than 1 motor, how many would be max?

That depends. You need to know the current output of the laptop and the current draw of the motors. The easy answer is lots: 100,000,000 or so. :p That's because the motors only draw current while running. If you have a ladder where 40 or so motors are controlled from one switch, you might start to warm up the board.

Now that the power is getting to the motors how what about the signal to operate the motor when you want the motor to run? Would this only work for something running in a loop or could you use a button or even DCC to activate the motor(s)?

This depends one many more factors than you have provided info on. Are they just bare motors? Do they have some type of control circuit on board (Tortoise switch machine, PFM style stall motor, etc.). What is the function of the motor: continuously operate a Ferris Wheel? run a cinder conveyor round and round?

And then would this work for running servos? I’m thinking of this for my turnout controls.

Here again the answer is yes and no. Yes, it could be used for the base power for the servo, but remember, servos need both operating power and a control signal. You cannot just flip a switch and have a servo operate without some form of controller.
 

railBuilderDhd

Active Member
Thanks Kevin,

You have some great information here. Now I have more questions and I'm thinking I need to focus attention on basics to be able to figure the solutions to these questions myself. Yeah, back to college or trade school in my free time - LOL That's a joke son! LOL

First, the answer to most of your questions is yes.



Regarding the DC-to-DC converted you showed: an LM317 is not the best choice for your use. The LM317 is a very inefficient device. If used for servos, which (mostly) operate on 5v (4.8), it could get really hot, depending on load. A much better alternative is an LM2596 based converter ( http://www.ebay.com/itm/10-pcs-DC-D...877446?hash=item461c33f386:g:ssMAAOxyeR9TIV7q ) I only picked that listing since it was the first to come up.

So, as long as I get the volt and amps correct the LM2596 based converter will be a better option(?).

Note the price per unit is only slightly greater $1.20 vs $.99. These are 2 amp units, capable of up to 3A with an added heat sink. The heat sinks run about $.50 each, also from eBay: http://www.ebay.com/itm/5pcs-Heatsi...536621?hash=item2816e101ad:g:Qj4AAOSw~oFXINsD
To get the heat sink to work properly it will need to be attached to the board or the LM2596 chip?

That depends. You need to know the current output of the laptop and the current draw of the motors. The easy answer is lots: 100,000,000 or so. :p That's because the motors only draw current while running. If you have a ladder where 40 or so motors are controlled from one switch, you might start to warm up the board.
If I understand correctly I need to have the volts at the correct needs of the motor and the amps will need to be the least amount needed or they can be more. If I would like to run more then one motor the volts need to match the max load no matter how many motors I'm running. If to many at one time draw on the power supply it could heat up? But the amps need to be enough to equal the total of all motors. So, 2 motors at 5V and they both use 3A I would need a power supply of 5V and at least 6A to run the motors. (I hope I'm getting this now. If not it's time to give up or start the college class)

This depends one many more factors than you have provided info on. Are they just bare motors? Do they have some type of control circuit on board (Tortoise switch machine, PFM style stall motor, etc.). What is the function of the motor: continuously operate a Ferris Wheel? run a cinder conveyor round and round?
I've not provide all details as I'm not working on a particular project and know the answer to all the questions. I'm more trying to understand how it works and what I need to know in order to be able to build electronics into my models.
Here again the answer is yes and no. Yes, it could be used for the base power for the servo, but remember, servos need both operating power and a control signal. You cannot just flip a switch and have a servo operate without some form of controller.

I understand that all we are talking about here is the power to run a servo or many and not how you get that servo, a motor or other device to operate. No matter you use a switch or a control board and your DCC system. Dose it seem like any of this is sinking in my thick head at all? The controller and DCC discussion will have it's own thread as I'm sure it will be a lot of questions of it's own.

I hope someone else is getting something from this and it's not just me being stupid and wasting other members time.

Ok, What about regulated or unregulated power? Would this be something I need to worry about or does one need to research from the power supply used if it is unregulated? I have no ide if the laptop power supplies are regulated or not.

Thanks,
Dave
 
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Iron Horseman

Well-Known Member
To get the heat sink to work properly it will need to be attached to the board or the LM2596 chip?
To the chip. All the heat sink does is transfer heat from the unit (LM2596 chip in this case) to the air to keep it cool. One can see the component screwed to the heat sink on the first unit (LM317) you linked to.

If I understand correctly I need to have the volts at the correct needs of the motor and the amps will need to be the least amount needed or they can be more. If I would like to run more then one motor the volts need to match the max load no matter how many motors I'm running. If to many at one time draw on the power supply it could heat up? But the amps need to be enough to equal the total of all motors. So, 2 motors at 5V and they both use 3A I would need a power supply of 5V and at least 6A to run the motors.
I think you're getting it. The supply voltage cannot exceed the max of the motor (or other unit for that matter). The supply current (amperage) must be at least enough to meet the demands of all the units attached. The current can be much greater than demand because each unit will only consume what it needs. Think of when you plug something small (like a night light) into a wall outlet. All the current available to the circuit (usually about 20 amps) is available, but the night lite only sips its tiny .05 amps.

Ok, What about regulated or unregulated power? Would this be something I need to worry about or does one need to research from the power supply used if it is unregulated? I have no ide if the laptop power supplies are regulated or not.
regulated power supplies are very nice. They will produce the same voltage regardless of the load (current) put on them - up to their designed maximum of course. An unregulated supply the voltage will vary with the load outside of its rated capacity. For example the old Tyco toy train transformers at max throttle when measured straight off the screws will show about 18 volts. As soon as one connects it to the track and adds a locomotive the voltage will drop into the 13 volt range.

That is a good question about the power supplies that come with lap tops. Normally a computer's power supply is regulated (5 & 12 volts). But a laptop might depend on its battery (like a capacitor) to regulate the supply, so the so called "power supplies" might really be just battery chargers and would not have to be regulated. Any one know for certain? I'm throwing out ideas. On the other hand I have a laptop supply that also has a USB power connector. The USB has to be regulated.
 
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railBuilderDhd

Active Member
What would be added to the power supply from a laptop to regulate the power for our uses. I'm thinking something like a LM7805 Voltage Regulator Chip. Would this be something you can just add to be safe. Would this go on the wires from the source before anything is attached.

I'll keep reading.

Dave
 

railBuilderDhd

Active Member
I was just thinking about the thought of adding a regulator to the laptop power supply and cam up with a new question. Would it cause a problem adding a new regulator to the circuit and cause a problem if you added a second regulator to the power supply?

Dave
 

wvg_ca

Well-Known Member
I was just thinking about the thought of adding a regulator to the laptop power supply and cam up with a new question. Would it cause a problem adding a new regulator to the circuit and cause a problem if you added a second regulator to the power supply?

Dave

Nope, no problem .. If your donor laptop supply doesn't have an output voltage close to what you need, you can easily add additional voltage regulators .. fixed [ like 7805 style], or adjustable to get what voltages you need .. as long as they are capable of the current for the end devices / lights / etc ..
 

Red Oak & Western

Active Member
The LM317, LM2596, 7805, etc. ARE regulators. I just did a little testing on the bench. I have and use an old laptop power supply for quick setups. It's no load output is 19.2V, its full load output (4.5A) it dropped to 18.9V. Very little ripple at no load, about 25mV at full load. (Dave: ripple is something you absolutely do not need to worry about!) Using an LM2596 down converter set to 5.0V, no load was 5.00V, 2.0A load was 4.94V. I didn't bother to check it at max load, since I never run them that high. At the price, its easier to use two or three and not worry about load capacity. And yes, you can connect two or three or more to your "high" voltage supply, so long as the total load doesn't exceed the available output. And remember, unlike a laptop, where the load is fairly large and constant, the items we connect only occasionally consume power. (The term load refers to the current {amperage} demand.)

The heat sink I linked to is actually applied to the back (non-component side) of the regulator board. There are heat sinks that attach to the regulator itself. Either will work, the cost is about the same, and its easier to add the board sink.

You're not wasting time by asking questions. Even if it was only you and I, I enjoy sharing knowledge and it is worth it. I agree with Horseman --- you are getting it.

Added: You can string a bunch of regulators in series SO LONG AS... A bit more "education": the input voltage to the regulator must be greater than the output voltage for the regulator to work. So if you had your power supply, then a 12 volt regulator, then a 5 volt regulator, that would work. But if you tried power supply, 5 volt regulator, 5 volt regulator, you'd have a problem in that the last regulator would not be able to regulate. So adding step down regulators to a regulated power source is not a problem so long as...
 
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railBuilderDhd

Active Member
Agreed Kevin, even if this thread is only you and I it is worth it. I'm learning and I'm sure someone else will get something from all this at some point.

I guess the only ripple I need to worry about is the one in the bottle and how much of that I have before I mess with wires. LOL

On a serious note I have one question; in your last post that's not totally clear to me. You said:

At the price, its easier to use two or three and not worry about load capacity. And yes, you can connect two or three or more to your "high" voltage supply, so long as the total load doesn't exceed the available output. And remember, unlike a laptop, where the load is fairly large and constant, the items we connect only occasionally consume power. (The term load refers to the current {amperage} demand.)

"At the price" are you referring to the cost of the laptop power supplies or the added power regulator boards (LM2596...)? I do have a bunch of these old power supplies so I'm sure I don't need to load down just one with everything on the layout. I guess it's ok to keep adding to one power supply as long as I have more AMPS from the power supply then used by whatever is attached.

For now it seems the use of a laptop power supply will be a good option or at least an option for running accessories or even the turnout servos.

I have placed an order on eBay for all kinds of part and will share with so you can see what I'm working with to better understand what I'm asking. I don't have projects in mind but many have been passing by as I think of what I could do with these little motors and new found knowledge. I will try to get the whole Arduino. We will have to have separate post for all those fun projects later. I do look forward to doing many thing with this knowledge.

Dave
 

jdetray

Well-Known Member
The LM2596 voltage regulator boards from eBay are really interesting and useful. I've been experimenting with the ones that include a voltage display:

power_converter_750.png


These are a little more expensive than the version without the display but still less than $2.00. You can choose to have the display show the input voltage, in which case the device functions as a DC voltmeter. Or the display can show the output voltage.

- Jeff
 

Red Oak & Western

Active Member
I guess the only ripple I need to worry about is the one in the bottle and how much of that I have before I mess with wires. LOL
Oops, showing your age there!

"At the price" are you referring to the cost of the laptop power supplies or the added power regulator boards (LM2596...)?

Again, it depends on what you're using it for. I was actually referring to the regulator boards, since at about a dollar each, there is no reason to push the capacity of a board, unless, of course, the load requires that much power. On a 3 amp power supply, I would use up to 3 boards, one for each application, e.g. one for signals, one for building lights, and one for servos. I would do it that way, rather than one power supply and one regulator per application, only to limit the number of plugs in the power strip. And yes, there is a power efficiency factor, but for us, its not really that important.
 

railBuilderDhd

Active Member
I thought maybe some will not get the reference of ripple. So what. after one bottle you just don't care. LOL

I agree about not pushing each board and I was already thinking I could keep these divided basted on what they are used for. I will use one for LED's and one for Servos controlling the track switches and then one more for other animations I will be adding as I go. That's my basic thought for now.

I am excited about doing these projects and now that I will be able to use the free power supplies I have that's one less expense pulling on my hobby budget.

Dave
 

railBuilderDhd

Active Member
So last night I got to thinking about this discussion. So far we talked about volts and amps but what about watts? I realize we haven't even talked about them. This makes me think we are not worried about them? That seems wrong. I know the resisters used for LEDs are based on watts. Right?
Just keeping the discussion moving.

I got the motors fromeBay yesterday. Wow they are really small. So mall I may need to get more that are bigger. That's something I don't normally say when buying for the hobby.

Dave
 

Red Oak & Western

Active Member
Watts. The formula is P=IE where P stands for Power, expressed in watts; I stands for Intensity (since C was already in use), expressed in amperes; and E stands for ElectroMotive Force (EMF), the early description of Voltage, expressed in volts.

So far we have ignored watts because, for the most part, it doesn't matter. About the only component we (model railroaders) are concerned with watts is resistors. And the most common are 1/4 watt, which defines the amount of power consumed by the resistor not the whole circuit, and are big enough for most every instance where we use them.

We focus on voltage and amperage because that is how our "devices", whatever we are using, are rated. A servo requires 4.8 volts and consumes 220 mA (milliamperes, or 0.220 A). A red LED requires 2.0 volts and consumes 20mA. etc. etc.

And on the subject of motors; servo, switch machine, or locomotive, I have ignored the differences between operating current and stall current.
 

railBuilderDhd

Active Member
Watts... ...And on the subject of motors; servo, switch machine, or locomotive, I have ignored the differences between operating current and stall current.

This sounds like our segue to our next chapter on electronic and model building.

Should I be looking up what is the difference between operational and stall current?

For now I'll not think about watts as it seems like I may be able to do all I need without knowing much about watts.

Dave
 

Red Oak & Western

Active Member
We can start with the 3 current ratings that apply to a (model) locomotive: operating, slipping, and stall. Operating is the amount of current to motor draws during normal operation. Then take hold of the coupler so that the wheels slip (duh). This is the amount of current you should use when determining the capacity (number of locomotives) a power supply / booster / etc. Finally, take your thumb and press on the top of the loco until the spinning wheels stop spinning. This is the stall current, that is, trying to run, but the motor is stalled.

The same operating and stall currents apply to things like switch motors, servos, etc. LEDs and incandescent lights only have their operating current.
 

railBuilderDhd

Active Member
So, now that we have discussed all about how to use the laptop power supplies I was thinking about the cheap power supplies you see all over the place. I was thinking about the output of these and the laptop supply and what would really be better to use. The power supplies from laptop or the universal power supplies? Would one heat up more then the other? Do you get more powered from a laptop power supply or the universal power supply?

Any thoughts on this guys? I just got my hands on a few more universal power supplies. I noticed one had an output of 100mA and I thought that's not bad, correct? Maybe these are better to use.

Dave
 

jdetray

Well-Known Member
Hi Dave -

A maximum current of 100mA is pretty low -- one-tenth of an Amp. You could use such a power supply to power perhaps 5 LEDs, but that's about all.

When you refer to "the cheap power supplies you see all over the place" are you talking about wall-wart type supplies or something else?

- Jeff
 

railBuilderDhd

Active Member
Hi Dave -

A maximum current of 100mA is pretty low -- one-tenth of an Amp. You could use such a power supply to power perhaps 5 LEDs, but that's about all.

When you refer to "the cheap power supplies you see all over the place" are you talking about wall-wart type supplies or something else?

- Jeff

My bad, it was 1100 mA not 100mA.

Other question for you guys. If there is a universal power supply that has an output of 15V and 1100mA do you need to have a power regulator to change this to 12v and when it changes to 12v will the 1100mA also change to less?

Dave
 




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