Pages: [1] 2 3 4   Go Down
Author Topic: Constant current power supplies  (Read 5474 times)
0 Members and 1 Guest are viewing this topic.
New River, Arizona
Offline Offline
God Member
*****
Karma: 19
Posts: 928
Arduino rocks
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Has anyone else noticed that there are a ton of constant current power supplies out there for extremely low prices that are very small and quite powerful?  I've got a couple I'm experimenting with that supply 6-11 volts at 350ma.  I take it that that means they go as low as 6V and as high as 11V trying to supply 350ma to a fancy led or string of leds.

Well, why can't we hook one of those up to an arduino and have it run just fine.  There's already a regulator on the arduino that will take the incoming voltage and hold it at 5V for the board, so it shouldn't matter that the CCPS (constant current power supply, I just made that up) is varying its voltage as the current load changes.

Right???  Thoughts.
Logged

Trying to keep my house under control http://www.desert-home.com/

Manchester (England England)
Offline Offline
Brattain Member
*****
Karma: 602
Posts: 33371
Solder is electric glue
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

I have no idea what you want to acheave by connecting an arduino to a constant current supply. You will just end up supplying the maximum voltage into the arduino's vin pin.
Logged

New River, Arizona
Offline Offline
God Member
*****
Karma: 19
Posts: 928
Arduino rocks
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

The supplies are amazingly cheap, on the order of a couple of bucks a piece and small, on the order of 1/2 x 3/4 x 1/2.  They hook directly to wall power, 85 - 265 VAC is not uncommon.  And, they're available all over the place.

One could put an entire arduino, power supply and all in a wall wart size package to do some project or other.

Such an item (cheap, small, common) doesn't exist for constant voltage supplies unless you gut one of those tiny wall warts, and that's a pain sometimes.
Logged

Trying to keep my house under control http://www.desert-home.com/

New River, Arizona
Offline Offline
God Member
*****
Karma: 19
Posts: 928
Arduino rocks
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

go to ebay and take a look at LED power supplies.  There should be about a thousand or so.  Here's the link for the first one I found:

http://www.ebay.com/itm/Led-Driver-6-12x2W-Inside-Driver-Power-Supply-for-E27-GU10-Led-Light-Lamp-2pcs-/110982585621?pt=Lamps_US&hash=item19d713dd15

And, that was just a basic search.  Alibaba, sourcingmap, etc have many, many of these at prices that made my jaw drop.  I have two that I bought (quantity 1) for 3.95 free shipping.  If I bought ten of them and redeemed the coupon I got I would have gotten them for about .80 cents each (still free shipping).
Logged

Trying to keep my house under control http://www.desert-home.com/

Left Coast, CA (USA)
Offline Offline
Brattain Member
*****
Karma: 361
Posts: 17262
Measurement changes behavior
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

go to ebay and take a look at LED power supplies.  There should be about a thousand or so.  Here's the link for the first one I found:

http://www.ebay.com/itm/Led-Driver-6-12x2W-Inside-Driver-Power-Supply-for-E27-GU10-Led-Light-Lamp-2pcs-/110982585621?pt=Lamps_US&hash=item19d713dd15

And, that was just a basic search.  Alibaba, sourcingmap, etc have many, many of these at prices that made my jaw drop.  I have two that I bought (quantity 1) for 3.95 free shipping.  If I bought ten of them and redeemed the coupon I got I would have gotten them for about .80 cents each (still free shipping).

Well check out what I bought a few days ago in the power supply regulator section of E-bay. Five buck switching regulators for $1.53 each. At that price I bought 5. Plus free shipping  smiley-wink

http://www.ebay.com/itm/251066005460?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Lefty
« Last Edit: November 30, 2012, 08:36:32 pm by retrolefty » Logged

New River, Arizona
Offline Offline
God Member
*****
Karma: 19
Posts: 928
Arduino rocks
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

taken from the web (as usual):

LED Drivers: are current control devices that replace the need for resistors. LED Drivers respond to the changing input voltage while maintaining a constant amount of current (output power) to the LED as its electrical properties change with temperature.

And, that's why they are rated with varying voltage and a single current rating.  The point is not to argue about the definition of constant current, or whether or not a particular device fits one's definition completely, the point is they are incredibly small, cheap and available.  After I get done with some testing, they may represent a really cheap and small method of powering small smart devices from wall power without a wall wart and a bunch of circuitry that takes up space.

And, Lefty, that was a heck of a find.  NIce job.  I love using those little things to battery power devices.  My problem has always been that I have exactly zero skill at making low power devices.  I can measure and control 440V three phase welders with the best of them, but I can't make a darn battery last over night......sigh.
Logged

Trying to keep my house under control http://www.desert-home.com/

New River, Arizona
Offline Offline
God Member
*****
Karma: 19
Posts: 928
Arduino rocks
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

That yellow thing is the transformer that's normally used on a switching power supply, not a step down transformer.  And, as for price, I already told you the deal I got on two of them by just searching around a little bit.  The example I cited was simply the first one I came across on ebay; there's tons of them out there in many, many configurations and prices.  Once again, these things are constant current supplies and would require a voltage regulator to keep the voltage correct for a processor circuit; maybe an extra 50 cents or so if the board doesn't already have one.  The ones I have supply a constant 350ma until the load resistance drops enough to cause it to shut down.  On the high side, they max out at a little over 11V and don't go any higher.  Carefully hooking it to the VIN on an arduino (UNO), they seem to work fine.  The problems may come when the combination of arduino and other devices need more than the 350ma and the thing shuts down.  But I won't trust it until I have much more experience with it.

It's obvious that you only want to argue rather than look into possibilities for cheaper smaller devices, so get the wall wart and be happy with it; I have dozens of them and they work fine if you want that kind of thing.  I also gut them and use the power supply inside directly for some projects.

However, if one wants a self contained device that just plugs into the wall and works in the smallest possible size, there may well be better solutions.  That's what I'm exploring.
Logged

Trying to keep my house under control http://www.desert-home.com/

SF Bay Area (USA)
Offline Offline
Tesla Member
***
Karma: 124
Posts: 6647
Strongly opinionated, but not official!
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I don't see the point.

1) Arduino is designed to be connected to a constant voltage power supply.
2) Constant voltage power supplies are equally common and cheap.

Essentially, you're buying "wall wart guts", but not the type that Arduino was designed for...

You can add that a supply designed for LED lighting may not provide isolation from the house power wiring, making it suitable for self-contained lamps of various sorts, but NOT for an experimental device like an Arduino with exposed wiring that you poke your fingers at.

Also, cheap Chinese import power supplies (of all types) are getting significant publicity recently for being poorly designed, lacking safety certifications (and in fact having poor safety design aspects that would make it impossible to get safety certifications), and having very questionable performance (poor regulation, high ripple, etc)  For example
Logged

New River, Arizona
Offline Offline
God Member
*****
Karma: 19
Posts: 928
Arduino rocks
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

westfw, that's the kind of response I was looking for.  Good point about the isolation, I'll check that in the next few days, but I suspect you're right in that there may well be a potential difference that sets the Arduino above ground and could cause problems.  Regarding Chinese manufactured power supplies being crappy, I've see good ones and bad ones.  However, I haven't seen wall warts or small power supplies that were made anywhere else.

Every cotton picking one I have in the house was made in China, even the ones that are 10-15 years old and are stored in a box in the garage.  The one that powers my Japanese alarm clock was made in China???  So, it appears that we're stuck with Chinese devices until we start building our own in the garage.

The point I'm trying to get to is that I'm tired of the power supply for the device I'm building being twice the size of the device itself and having a big lump that plugs into the wall.  Things got a little better when Apple came out with their small USB supplies (also made in China), but it's still annoying.
Logged

Trying to keep my house under control http://www.desert-home.com/

Dubuque, Iowa, USA
Offline Offline
Edison Member
*
Karma: 45
Posts: 2468
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

The ones I have supply a constant 350ma until the load resistance drops enough to cause it to shut down.  On the high side, they max out at a little over 11V and don't go any higher.  Carefully hooking it to the VIN on an arduino (UNO), they seem to work fine.  The problems may come when the combination of arduino and other devices need more than the 350ma and the thing shuts down.

But isn't that an important issue? These LED drivers are sensitive to the load they're driving; too little load and they shut off, too much load and they shut off. Only under fairly specific circumstances would you have a circuit that could keep that constant load.
Logged

SF Bay Area (USA)
Offline Offline
Tesla Member
***
Karma: 124
Posts: 6647
Strongly opinionated, but not official!
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
I haven't seen wall warts or small power supplies that were made anywhere else.
Good point.  The danger sign is probably "cheaper than it seems possible", rather than "made in China."
Although "shipped direct to you from China, bypassing regulatory approval processes" is probably also a bad sign.
The Apple USB-supply cube is impressive engineering (much smaller than the LED supplies you linked), now widely (and sadly) "faked" with a much less worthy/safe circuit.  Much of the recent publicy has surrounded fake Apple chargers.  http://www.youtube.com/watch?v=wi-b9k-0KfE
http://www.arcfn.com/2012/03/inside-cheap-phone-charger-and-why-you.html
(Real Apple or Amazon chargers aren't "inexpensive.")
« Last Edit: December 01, 2012, 01:33:15 am by westfw » Logged

Worst state in America
Offline Offline
God Member
*****
Karma: 32
Posts: 792
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Has anyone else noticed that there are a ton of constant current power supplies out there for extremely low prices that are very small and quite powerful?  I've got a couple I'm experimenting with that supply 6-11 volts at 350ma.  I take it that that means they go as low as 6V and as high as 11V trying to supply 350ma to a fancy led or string of leds.

Well, why can't we hook one of those up to an arduino and have it run just fine.  There's already a regulator on the arduino that will take the incoming voltage and hold it at 5V for the board, so it shouldn't matter that the CCPS (constant current power supply, I just made that up) is varying its voltage as the current load changes.

Right???  Thoughts.

A constant current source (theoretically) would supply infinite voltage if it were open circuited. Of course, real-world current sources are limited by their design. The maximum open circuit voltage is called the "compliance" voltage.

If you tried to power a voltage regulator (like the input to an Arduino board) with a constant current source, one of two things would happen:

(1) if the Arduino needed more current that the CC source supplied, the voltage would be too low and the Arduino would not even boot up.

(2) If the current source was set to a higher current that the Arduino required, the current source would swing right up to it's maximum voltage (the compliance voltage).

Since both 1 and 2 are worthless smiley You see that you don't want to power an Arduino (or most anything else) with a constant current source.

What they ARE good for, however, it powering LED's and LASER DIODES. These devices have a nominal forward voltage drop, but it varies from part to part and varies with temperature. You NEVER want to power an LED or laser diode with a constant VOLTAGE source.

A constant current source is like an "electronic spring". It will flex - give and take a little bit to accommodate the LED or laser. The nominal voltage drop across the LED or laser, times the constant current equals the input power to the device. As the device warms up, it's forward drop will change slightly, and the current source will simply adjust itself and keep providing the correct current to the device.

Without the electronic "spring" to take out fluctuations in operating parameters, the device could work fine one minute and burn out the next.

That's why, in simpler setups, you always use a resistor in series with an LED... to limit the current. The resistor acts like an electronic "spring".

Did all this make sense?
Logged

Gentlemen may prefer Blondes, but Real Men prefer Redheads!

SF Bay Area (USA)
Offline Offline
Tesla Member
***
Karma: 124
Posts: 6647
Strongly opinionated, but not official!
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

The little transformers provide ("are supposed to provide") as much isolation as the traditional large "step down transformer."  They can be smaller because they operate at a much higher frequency.  You can think of a switch-mode power supply as modulating the high-voltage side of the supply so that the frequency and waveform are varied in a way that causes them to provide exactly the right amount of power needed by the load.
Logged

Worst state in America
Offline Offline
God Member
*****
Karma: 32
Posts: 792
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

The little transformers provide ("are supposed to provide") as much isolation as the traditional large "step down transformer."  They can be smaller because they operate at a much higher frequency.  You can think of a switch-mode power supply as modulating the high-voltage side of the supply so that the frequency and waveform are varied in a way that causes them to provide exactly the right amount of power needed by the load.


So George Westinghouse was right after all?  smiley
Logged

Gentlemen may prefer Blondes, but Real Men prefer Redheads!

Offline Offline
Full Member
***
Karma: 3
Posts: 244
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I read this stuff and wounder is this for real. Constant current supply's Are mainly used for driving Led's or led displays, Now there no way anyone can tell the OP any thing about his supply that's not a guess. Now if he would run down the chip used on this we would have a place to start. I use a constant current led driver you set the dang thing to 25 mA which is changeable in code to a point meaning you can change the range a little up or down to hit the 25 on the head.

Let's see a show of hands how many of you have used cel phone charger even like the iphone charger  or any of the newer smart phone chargers. Well how may hands are up in the air Guess what there constant current supply that do to things one
there output is fixed at 5 volts till you over load them then it drops off to a point that they shut down.

So the bottom line is if this doesn't put out more then the happy 7 to 12 volts it would work fine as long as it doesn't need to be loaded.

But you may have to add filtering and a regulator to keep the power clean and under the happy zone of 12 volts to 7.  
Logged

Pages: [1] 2 3 4   Go Up
Jump to: