Voltage regulation

[lor_kev]

Greetings all, I am a first time poster looking for help on a project I am working on. I am building a slot car track and I am nearing the end, but I have one last item I would like to rig up. I am supplying power to the track with an adjustable power supply. I am operating the track at about 10VDC for the kids, 18VDC when the grown ups are playing and up to 24VDC after the grown ups have had a couple of pops. I always have the power supply set to the maximum 10Amps. What I want to do is supply power to my Infra-red timing system without having to plug in an extra adapter. I have an adapter rigged up right now that has an output of 12VDC with a max current of 300mA. Is there any way of tying into my variable power supply and keeping it at a constant 12VDC, regardles of what I have the input voltage set at on the track. I have tried to dig up info on voltage regulators but am not sure if this is what I am looking for or if this can be done at all. Looking forward to any input , Kevin. (a cabinetmaker with a solder gun in his hand )

 

[ikalogic]

mhh.. i find it very difficult to understand what you need to do exactly...

Do you want to get a stable 12V output from a voltage that may vary from 10 to 24 V... am i right?

 

[Torben]

Can you post the schematic of what you already have? Without that we're guessing at what exactly your setup looks like.

That said, I'd say you could probably just tie into whatever is feeding your adustable power supply and get your juice there.


Torben

 

[stevez]

You probably would like to use the supply that delivers between 10 vdc and 24 vdc as the source for your relatively low current 12 vdc needs.

Does your timing system need 12 vdc or can it run on much less?

The problem (if you want to keep it very simple) is that your source will be well below 12 vdc to start with and if you really do need the 12 vdc from 10 vdc you'll need some means of boosting the voltage. While not complex for the experienced it's not something easily done by a beginner.

If you were to find that your IR timing system can operate on something like 6 vdc then you could use a simple 3 terminal regulator to take 10 to 24 vdc in and hold it at a steady 6 vdc out. A heat sink and other issues might have to be addressed but only if this is even possible.

If you could steal a few hundred milliamps from the supply before the 10 to 24 vdc output, that would always be 14 vdc or more you might use an LM7812 to make the 12 volts - with due consideration for heat and other limits. That might be something you leave for the more experienced.

 

[KMoffett]

Though not cheap, this buck/boost regulator should do exactly what he needs...and so simple even a "cabinetmaker" could wire it in:

https://www.dimensionengineering.com/AnyVoltMicro.htm

But at $20 a pop, I'd opt' for a wall wart.

Ken

 

[lor_kev]

Thanks for the input guys. Torben, I could draw a schematic, but that would end up looking lika a cabinet and muddying up the water. Steve, I could drop the input voltage to my IR's without too much trouble, I just happen to have a 12V supply available when I was playing around, and worked eveything off of that. If I change the resistor that I have now I can get down to a 6V Input. If you could sketch up something (remembering who you are dealing with here) that would be great. This is all really about asthetics and the fact that I am being a bit anal about too many cords sticking out of my track. It is a portable unit and I am trying to keep it as neat as possible. I like what you have there Ken, the $$ isn't the issue (see anal above). Looking at the specs for this unit though, I am concerned that the max input for this unit is only 14V and we might fry it when we crank up the juice on the power supply.

 

[stevez]

An LM317 is a 3 terminal regulator that is fairly easy to find. With a couple of resistors the output could be adjusted to 7 volts allowing 3 volts across the regulator. An LM7806 would not need the resistors but is harder to find (I have some but that does you no good unless you live nearby). The output of the LM7806 is 6 volts - you could adjust the 317 to 6 volts. Take a look at the datasheets. You'll need a few parts but not many and except for the resistors the value isn't critical. Others here on the forum may be able to advise on low dropout regulators. I think the key for you is obtaining parts. The 317 can be aquired from Radio Shack.

What we really don't know is the current requirement. We can make the assumption that is equal to or less than 300 ma. Where it will matter is in the requirement for a heat sink. If I were building it I'd attach the LM317 to an piece of aluminum that might be an inch square or so - keeping in mind that the tab and therefore the heat sink may be part of the circuit so it needs to be isolated.

There are others here would have more expertise than I however if things don't work out IM me and I'll give you what help I can.

 

[lor_kev]

Steve, I guess that is something I have not considered is the amperage. The 4 LEDs are each rated at 150mA. Being that the power supply is set up to 10A, is that something that has to be regulated as well? Bear with me here, but if I have 4 LEDs at 150mA each, do I require a total 600mA to run them at the optimum level, or does 150mA do the trick. The Wall Wart that I am using now is only rated at 300mA, they seem to work fine but perhaps not as well as they should.

 

[stevez]

It sounds like you are satisfied with the 10 to 24 vdc supply and the way it operates now. If that is true then my advice would be to leave that part alone - let's not try to fix what isn't broken.

Somehow you'll need to determine the current requirements for your timing circuit. If all 4 LEDs are in series then the total current is for the LEDs is only 150 ma. I am not sure what else you might be powering. I could be wrong but if the 300 ma wall wart is running ok, not getting hot, etc - it suggests but doesn't prove that the load is less than 300 ma.

If the current requirement is signficantly more than 300 ma then it might overload your 10 to 24 vdc supply. You said it's set for 10 amps but we don't know what it's running at. There is nothing mysterious about 300 ma - it's just an opinion that adding 0.3 amps to a 10 amp load is trivial - but at some point you could overload your 10 to 24 vdc supply.

Do you have a DMM with a current range that would allow you to measure the current on the wall wart? Ideally you'd want to measure it in a way that reveals the current requirement when operating at 6 vdc.

Bear with me on all of the questions. I realize that some of this might not make sense right away.

 

[lor_kev]

stevez, The cars I am running on this track will draw a max of 1-1.5 amps at full load. I run 4 cars so at the max I will be drawing 6 amps. I have nothing else running off of this power supply so overloading the supply is not an issue. I guess what I was curious about is if there is too much amperage available, will that fry the LEDs or do they just draw what they need. I am not familiar with how that works. Regardless, it seems to me that the way to go is to change the resistor to my LEDs to allow for a 6V supply. I have an industrial electronics distributor nearby that has had all of the parts I have required so far, so if I am reading this right, if I can find something similair to the LM7806, I should be in business, or at least going in the right direction. Is there anything else I should be aware of?