Author Topic: Constant Current Power Supply  (Read 576 times)

Offline edwire

  • Expert
  • Participant
  • ***
  • Posts: 114
  • Likes: 3
Constant Current Power Supply
« on: March 04, 2021, 11:48:24 AM »
I found this Constant Current Power Supply Module, Regulated Power Supply Board DC Converter Module AC 15-24V to DC 0-30V 2mA-3A

https://www.amazon.com/gp/product/B07W2W1W4N/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&psc=1

How can I test for the correct mA output?
Chemistry is the melodies you can play on vibrating strings

Offline edwire

  • Expert
  • Participant
  • ***
  • Posts: 114
  • Likes: 3
Re: Constant Current Power Supply
« Reply #1 on: March 04, 2021, 11:12:27 PM »
This power supply is sort of like kit DIY. I'm going to put it together.
Chemistry is the melodies you can play on vibrating strings

Offline edwire

  • Expert
  • Participant
  • ***
  • Posts: 114
  • Likes: 3
Re: Constant Current Power Supply
« Reply #2 on: March 04, 2021, 11:14:53 PM »
forgot the pictures.
Chemistry is the melodies you can play on vibrating strings

Offline edwire

  • Expert
  • Participant
  • ***
  • Posts: 114
  • Likes: 3
Re: Constant Current Power Supply
« Reply #3 on: March 04, 2021, 11:31:07 PM »
There is a sort of manual to operate the power supply.
Chemistry is the melodies you can play on vibrating strings

Offline Rancher55

  • Participant
  • **
  • Posts: 8
  • Likes: 0
Re: Constant Current Power Supply
« Reply #4 on: March 14, 2021, 02:00:46 PM »
I know nothing of your power supply but I do have background in electronics.  My power supply is very simple.  I have an unregulated 30 volt DC power supply that can be found on ebay, amazon, etc.  The current supplied with any power supply you can find will almost always exceed our needs here.  What needs regulated is the current.  When you regulate the current, the voltage output changes so that the preset current is not exceeded.

I am using a 3 pin positive regulator IC with part number LM317.  This IC is good for up to 35 volts input and can be programmed as a fixed current regulator with a single resistor.  It can also be adjustable by simply using a variable resistor (potentiometer) in place of the aforementioned resistor.  Lots of data sheets for this device online.  Its very simple with a single INPUT pin and an OUTPUT pin and the current is precise and stable.

Attached is a screenshot of the schematic you will find on any data sheet for this IC.  For our applications here, this IC is well worth investing your time in getting to know.  You don't have to have a degree in electrical engineering to make this happen.

Offline Gene

  • Expert
  • Participant
  • ***
  • Posts: 1269
  • Likes: 91
Re: Constant Current Power Supply
« Reply #5 on: March 15, 2021, 04:25:32 AM »
You might want to look around here first before posting stuff thats already been discussed MANY times over many years. The LM317 is nothing new to all of us and many here use it.

The problem with the LM317 in the TO-220 package is that the stated minimum quiescent current (which in a current limiter must flow through the load) is about 10ma. You <might> be able to get it 20-30% lower due to process spread but its not getting down much farther.

A better solution I've talked about many times is the LM317LZ in the TO-92 package. It has a maximum output current of 100ma BUT it has a quiescent current around 2ma maximum which puts this variant of the regulator squarely in the adjustability range we want for Colloidal Silver production. I don't know anyone here who runs as low as about 2ma but some guys make cold and do run 3ma. Its also cheap as dirt from China. Though prices have gone up some more recently, I bought 20 of them a while ago for less than $1 (thats for 20 of them!)

For a power supply even an old laptop charger works. Most are 19.3V which is plenty. This is what I currently use.

The LM317's headroom is 2.5-3V meaning VIn must be 2.5-3V higher than maximum VOut of the regulator itself. Given we set our cell to 10-12V, even 15V works with the LM317 (but barely). 19.3V is plenty, usually.

The 2 transistor limiter as an alternative, has a headroom maybe around a volt so with this, for sure an old 15V laptop supply works.

There are many other solutions MUCH smaller than using a power supply or laptop supply and no, unless you're making bathtubs full of Colloidal Silver, you don't need 30V.

You can buy tiny boost converter modules from China (adjustable from 2-28V) which have also been discussed here a few times before over the years and a few guys are actually going this route, for less than 50 cents each, and you can get them with a micro USB power in jack so a $1 cost from dollar tree wall plug cell phone charger (5V, 1 amp) if even you don't already have one you can use which most of us have a drawer full of cell phone chargers already, which is TINY, is all you need beyond the boost converter, USB cable and your limiter.  That'd all fit in a box about the size of a pack of cigarettes if even that big. That boost converter can put out 2 amps so even if you set it to the maximum 28V, given the chip on the thing is 90% efficient, with 1 amp input (what most standard wall chargers can supply), you'd be able to supply about 160ma to the cell.  Normal use isn't even close to this.

Start simple and only make something more complex if simple isn't doing it for you (wink).

Offline edwire

  • Expert
  • Participant
  • ***
  • Posts: 114
  • Likes: 3
Re: Constant Current Power Supply
« Reply #6 on: March 15, 2021, 01:09:32 PM »
You might want to look around here first before posting stuff thats already been discussed MANY times over many years. The LM317 is nothing new to all of us and many here use it.

The problem with the LM317 in the TO-220 package is that the stated minimum quiescent current (which in a current limiter must flow through the load) is about 10ma. You <might> be able to get it 20-30% lower due to process spread but its not getting down much farther.

A better solution I've talked about many times is the LM317LZ in the TO-92 package. It has a maximum output current of 100ma BUT it has a quiescent current around 2ma maximum which puts this variant of the regulator squarely in the adjustability range we want for Colloidal Silver production. I don't know anyone here who runs as low as about 2ma but some guys make cold and do run 3ma. Its also cheap as dirt from China. Though prices have gone up some more recently, I bought 20 of them a while ago for less than $1 (thats for 20 of them!)

For a power supply even an old laptop charger works. Most are 19.3V which is plenty. This is what I currently use.

The LM317's headroom is 2.5-3V meaning VIn must be 2.5-3V higher than maximum VOut of the regulator itself. Given we set our cell to 10-12V, even 15V works with the LM317 (but barely). 19.3V is plenty, usually.

The 2 transistor limiter as an alternative, has a headroom maybe around a volt so with this, for sure an old 15V laptop supply works.

There are many other solutions MUCH smaller than using a power supply or laptop supply and no, unless you're making bathtubs full of Colloidal Silver, you don't need 30V.

You can buy tiny boost converter modules from China (adjustable from 2-28V) which have also been discussed here a few times before over the years and a few guys are actually going this route, for less than 50 cents each, and you can get them with a micro USB power in jack so a $1 cost from dollar tree wall plug cell phone charger (5V, 1 amp) if even you don't already have one you can use which most of us have a drawer full of cell phone chargers already, which is TINY, is all you need beyond the boost converter, USB cable and your limiter.  That'd all fit in a box about the size of a pack of cigarettes if even that big. That boost converter can put out 2 amps so even if you set it to the maximum 28V, given the chip on the thing is 90% efficient, with 1 amp input (what most standard wall chargers can supply), you'd be able to supply about 160ma to the cell.  Normal use isn't even close to this.

Start simple and only make something more complex if simple isn't doing it for you (wink).

Gene, thank you. Somehow I missed the LM317LZ, after reading your post and other posts I'll go that route.
Chemistry is the melodies you can play on vibrating strings

Offline Argentum

  • Participant
  • **
  • Posts: 179
  • Likes: 11
Re: Constant Current Power Supply
« Reply #7 on: March 21, 2021, 05:58:09 PM »
The problem with the LM317 in the TO-220 package is that the stated minimum quiescent current (which in a current limiter must flow through the load) is about 10ma. You <might> be able to get it 20-30% lower due to process spread but its not getting down much farther.

This isn't entirely true. If you check the data sheets the maximum minimal current is at a 40V input to output differential. At lower differential voltages (in vs out) the minimum required load current is much less.

Since we aren't running more then say 15 - 20 volts of in/out differential. The minimum required load is much less then the max of 10mA..

This is from a Nat-Semi data sheet:

Minimum Load Current (VIN − VOUT) = 40V:    3.5 mA(typical) 10 mA(maximum)

And an interesting graph from same data sheet (there should be an image attached to this post):

And from a TI data sheet:

Minimum Load Current VI – VO = 40 V:  3.5mA(typ) 10 mA(Max)

The data sheet for the TI LM317L has more information to bear this out:

Minimum load current: (VIN − VOUT) ≤ 40 V:   3.5mA(Typ) 5mA(Max)
Minimum load current: 3V ≤ (VIN − VOUT) ≤ 15 V:  1.5mA(Typ) 2.5mA(Max)

Notice how much lower the minimum required current is once the input vs output differential drops.

Argentum

Offline Gene

  • Expert
  • Participant
  • ***
  • Posts: 1269
  • Likes: 91
Re: Constant Current Power Supply
« Reply #8 on: March 21, 2021, 07:53:19 PM »
Your forgetting something. That chart is TYPICAL, not guaranteed. The only number we have thats guaranteed is 10ma for the LM317.  If you want to go for it, by all means but I don't design to TYPICAL specs.  No engineer worth his salt will.  Thats why I said you may be able to get lower but nothing is guaranteed.

Oh, and the TI datasheet I'm looking at for the LM317L part says 35V, not 40 and the only spec here is typical 1.5ma, max 2.5ma and there is NO chart. Again, the ONLY spec you can design to is 2.5ma if you want to guarantee its always going to do the same thing regardless the device, regardless which wafer or wafer lot it came from,...

For the LM317, nothing below 10ma is guaranteed because there is no stated spec to use to compute what that value is for different voltage differentials.  The chart can't be.  And for the LM317L, nothing below 2.5ma is guaranteed for the same reason.

Offline Argentum

  • Participant
  • **
  • Posts: 179
  • Likes: 11
Re: Constant Current Power Supply
« Reply #9 on: March 22, 2021, 04:28:00 PM »
Your forgetting something. That chart is TYPICAL, not guaranteed. The only number we have thats guaranteed is 10ma for the LM317.  If you want to go for it, by all means but I don't design to TYPICAL specs.  No engineer worth his salt will.  Thats why I said you may be able to get lower but nothing is guaranteed.

Oh, and the TI datasheet I'm looking at for the LM317L part says 35V, not 40 and the only spec here is typical 1.5ma, max 2.5ma and there is NO chart. Again, the ONLY spec you can design to is 2.5ma if you want to guarantee its always going to do the same thing regardless the device, regardless which wafer or wafer lot it came from,...

For the LM317, nothing below 10ma is guaranteed because there is no stated spec to use to compute what that value is for different voltage differentials.  The chart can't be.  And for the LM317L, nothing below 2.5ma is guaranteed for the same reason.

Exact response I expected. Based on emotions, not facts. It is obvious that the input to output voltage differential makes a big difference in the minimum required output current to maintain regulation.

Use it to advantage based on how the device is being used.

Argentum

P.S. the data I posted was copy and paste from the data sheets. Not made up...

Offline Gene

  • Expert
  • Participant
  • ***
  • Posts: 1269
  • Likes: 91
Re: Constant Current Power Supply
« Reply #10 on: March 22, 2021, 07:26:48 PM »
OK, show me some data thats GUARANTEED or an equation to compute what the minimum required current for regulation is. That chart is TYPICAL. Engineers don't deal in "typical" because its a good way to get bitten in the ass by process spread,... or even the manufacturer changes the design and guarantees the same specs but now how it operates internally, its different. Oh yeah I've seen that before. TOO many times. Do they always get around to fully updating the datasheet? They should but I've seen plenty of instances over my career where they haven't which you find out from the manufacturer after talking to them... Oops.

Yes, the chart shows that lower voltage requires lower current but there is no spec for it nor any equation they guarantee that will allow you to compute it.

The ONLY spec you have is at 40V.

I worked in a chip development role for 25 years.  Process spread can have things varying by up to 60% one way or the other and no I'm NOT kidding!  Sometimes it doesn't get that bad but it can and I've seen it.

Go back to TI and ask them for their GUARANTEED datapoints.  If I were designing that part in and wanted to be guaranteed of a minimum operating current at my voltage operating point if that were less than a 40V differential across the part, I'd go back to the TI rep and ask them to provide it only I kind of already know they won't.

Statistics are nice (what that chart shows) but you can't design to it because it WILL vary from wafer lot to wafer lot and even from device to device across a single wafer.

"Typical" charts are no guarantee of anything.  And then too, different manufacturers show slightly different specs so for sure all LM317's are not the created equal but if they're a cross, someone in purchasing will buy them because they're cheaper and now if you're relying on a typical chart, you may wind up in trouble.

Thats why I said you should be able to get less but its not guaranteed in my posts. Because its NOT!

For onesies on a bench, sure, try it but be prepared that when you burn it out and replace it, things WILL be different but always within stated specs, here, the required current at 40V which is all we have.

The LM317LZ datasheet says that part only works to 35V and in that TI datasheet there isn't a chart.

Offline Argentum

  • Participant
  • **
  • Posts: 179
  • Likes: 11
Re: Constant Current Power Supply
« Reply #11 on: March 22, 2021, 08:34:19 PM »
LOL.

Argentum

Offline chrisflhtc

  • Participant
  • **
  • Posts: 88
  • Likes: 4
Re: Constant Current Power Supply
« Reply #12 on: March 23, 2021, 09:39:04 PM »
Use a higher amperage and don't sweat the small stuff. YMMV, JMHO, DYODD Listen to the ones who know!. :) Mine always comes out clear and not turbulent or cloudy. Read the Articles  ;D
Chris

Offline Pemf silver

  • Participant
  • **
  • Posts: 33
  • Likes: 2
Re: Constant Current Power Supply
« Reply #13 on: March 25, 2021, 10:35:55 PM »
This home made generator works excellent for me.
Good luck with your generator.

Offline Gene

  • Expert
  • Participant
  • ***
  • Posts: 1269
  • Likes: 91
Re: Constant Current Power Supply
« Reply #14 on: March 26, 2021, 08:20:35 PM »
Whats a PEFM and what has it got to do with making Colloidal Silver?

All you need is a constant current source, a power supply, a voltmeter and a timer or clock to time the run. There's no "frequency" involved. Its all DC.