Best way to make a Constant Power Load

[PeterFreedom]

What would be the best way to make a load that always draws the same amount of power whatever the voltage on it. For exemple, an load would draw 100 mA at 24 VDC, 150 mA at 18 VDC and 200 mA at 12 VDC. All I found is to use Nonlinear Dependant source.

Any easier way to do this? Thanks.

[lacy]

I have an idea that I just tested that may be suitable as a constant power load, but I will let you take a peek at it and see if it would be suitable to your application. I have read your other post about the leaky feeder and I do not have any idea as to why it is malfunctioning with the added component. The only way I did manage to get it simulating is to hook the last component up directly to the 24VDC, but I know this isn't the way it is arranged in your mine and you need to simulate it the way it is in reality.

In as far as this circuit I am going to post, I do not have any idea on how to go about incorporating this into your design. This will be something you may have to investigate on your own (sorry), but I will leave it out there for you to determine if you can use it or not.

[PeterFreedom]

Thank you very much Lacy. I can't open your file because I'm using Multisim 9. I don't know if you can save it as a Multisim 9 file. By this time I tried some other thing for a constant power load and I found that. See Constant Power Load1.ms9. This is working fine but, again I can't place too many of them.

You wrotew that you can make my last file work by placing the 9th amplifier at the end of the line on the 24 VDC. On my computer, if I do that, I have the same problem as before. The simulation aborts. Friday I tried to do it in an Excel spreadsheet and the iteration is working fine so why a Simulation software can't do it? I'm very disapointed by Multisim.

I'm only interested in knowing the steady state of the circuit, is there a way to simplify the simulation so it will not abort? Thanks all.

[lacy]

Sorry about the file mix up, I was anxious to get it posted for you that I failed to realize you were using a different version.

As far as the last "amplifier" in your Leaky Feeder design, I actually hooked it up to the 24VDC supply on the left and this was a direct connect before the first resistor.  I realize this is not what would be ideal for your application as probably you have only a certain place in the Leaker Feeder to tap off from. I would suppose this would be going into a different entry way off the main entry at an intersection so I do not know how my adjusting the placing of this would effect the results because it seems to me by doing this I have bypassed a bunch resistance in the Feeder cable itself (if that is what the resistors represent) and also bypassed a number of amplification stages in the process as well.

I will post a picture of my circuit for you to examine and try in Version 9.  This is the only thing I could come up with to where the power draw was the same no matter what the voltage input was. The only thing I can see as a drawback is that with this circuit the current remains constant but the voltage fluctuates. If I use a 24V regualtor and drop the input voltage to 12V the current remains at approx 118ma but the voltage drops to 12V when I plug it into your circuit.. I will let you try it and see what you may be able to do with it.

Message Edited by lacy on 04-28-2008 05:47 PM

[PeterFreedom]

The circuit that best fits is the one in my Leaky Feeder is the one I posted (see the image Nonlinear Dependant Source.jpg). This Source reacts the same way as the amplifiers we use underground for the mine communication. You enter the formula of your choice in it. Friday my simulation was not working and monday it was working even if I did not change anything. Stange things are happening...

I also tried something yesterday. I tried a version that was not working if I tried to add a 9tth amplifier at the end of the line on the right. Then I put the 9th amplifier at the beginning (on left side) and it was working. Then I moved it two amplifiers to the right, and it worked again, then I moved it this same way until I reached the end (to the right) and it was still working. Does Multisim as to be trained or what? See my other post

[lacy]

I can't understand that at all. It is weird to say the least. I am going to try what you outlined in Version 10 and see it it does the same. I wish there was some other component you could use to simulate these amps, but I do not have a clue as to how to create one. It was just a stab in the dark with the voltage regulator. I would have hoped it would work, but I was not very confident that it would.

I do have a question concerning the actual Leaky Feeder system you have. Doesn't the system have a way of monitoring itself, like say a computer terminal or master panel, that can warn the dispatcher/office when a fault occurs? I would think this would be something that would be built into any new system under the Miner Act and MSHA regulations as well as West Virginia MSHT regulations.

[PeterFreedom]

The Leaky Feeder system monitors it current consumption and we have a display on surface that will tell us if the current is out of normal operation and if the Power Supply on surface is within normal operation.

The goal of the simulation is to understand how the voltage will decrease as the communication network is getting longer and that new branch are added. The resistances in series represent the lost  in the cable due to its resistance (Ohms/km). Each amplifier draws around 100 mA when power at 24 Vdc. But their current increase when the voltage decrease. So the more current you draw on the network, the more voltage drop you have and the more current each amplifier will draw.... and so on. There is a point where it reaches stability.

The simulation can tell us if it normal that, for example we have only 21 Volts at amplifier # 7. So this way we can know if there is a problem with a damaged cable or something else.

Lacy, you seems to know a lot about Communication system for the mining industry and the Miner Act and MSHA regulations as well as West Virginia MSHT regulations, are you related to the Mining Industry?

[lacy]

I have over 10 years experience in  the mining electical/electronic repair field. You may be familiar with the company that I used to work for before they were bought out by United Central Indusrtial Supply. I worked for National Mine Service, Inc. here in Beckley, Wv. I was the a Class A technician mainly for electronic equipment: trolleyphones, pager phones, longwall phones, ground fault monitors, conveyor belt slip/sequence controls, deluge controls, S&S logic boxes, footswitches, A-5100 and A-3600 motor controls, fire suppression systems and the list goes on.

I have not been exposed as much to the Leakey Feeder, but I do know about it. At the time I was working for NMS Leaky Feeder was just coming around and there wasn't much demand for it in this area and what was in the mines was not very reliable. This was from 1992-2001 so I would assume that there have been a lot of improvements since that time.

I currenly work at Mato Corporation repairing Belt Lacer Machines and Tool Frames used for splicing belts.