Low Cost CC/CV Power Supply Idea - Page 1
Forum section: electronics / projects

author: electro_pt
author_rank: Newbie
timestamp: September 01, 2016, 11:45:41 pm
content: Would like to do a little bit of electrolysis, which generally requires low voltages (2-14V) and high currents (10-100A). I've been playing with this idea, but it seems too easy for it to actually work. The concept is to get a cheap ATX power supply which will serve as the 120VAC to low voltage high amperage DC converter. Then I could parallel a number of those really cheap Chinese constant-current/constant-voltage buck-boost converters you see all over Amazon and eBay.Seems like if I were to put a high amperage diode on the outlet of each buck-boost converter, to prevent back flowing currents if each power supply isn't exactly matched, I would be good. If they don't quite match in voltages that's OK because whatever is the highest set voltage would peg-out and get limited from it's CC mode, drop voltage and the next lower voltage would start to add current. Obviously this wouldn't do very good current sharing, but I'm OK with that.I would love to hear advice on how I could do a central CC and/or CV control pot instead of having to trim each buck-boost separately. Also, I'm a little fuzzy on how a CV setup would work, the CC being more easy for me to visual. CC being more important in electrolysis anywise, however CV would be a fun addition if possible. Also, ATX PSU's are known to have a bit of ripple, but for electrolysis applications 10 mV is fine, though could probably run without issue even at 50 mV.I could even parallel two or more buck-boost converters to increase amperage to whatever is needed. Thoughts? Suggestions? Problems I have overlooked?

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: September 02, 2016, 12:48:08 am
content: I use an old Dell ATX power supply to power my stuff. So far I´ve been getting along fine with this since it has all the preset voltages and amperage you need for the most interesting experiments. Hell, it even as a -12 volt rail which combined with the +12 volt side gets me up to 24v. If thats not enough it has a current sense impute for supplying voltage accuracy. You idea is a good one but it may go to far if your´like me and am interested in practical application but not having alot of things to fiddle with.To your question.The other way to go is re wind an old MOT for a linear power supply since you mentioned that in your post. Get a big ass capacitor and a 10 amp rectifier. It should give you the umph to supply a bunch of smps like you mentioned. Better yet get several MOTs, they will provide more isolation and put them in an old computer case. While your at it pick up some no hacked up connectors from the junk microwave ovens. You would be amazed what quality stuff is in those junky MOT´s. Using old MOT´s will save you a ton of shipping costs and they are free or almost so.Anything else you need get on aliexpress and you will probably be pleasantly surprised, most of the time, about what cool stuff comes from China.Good luck.nico

author: MosherIV
author_rank: Super Contributor
timestamp: September 02, 2016, 09:34:41 am
content: Please stop calling it a Constant Current (CC) power supply, unless you do actually mean a CC PSU.You probably mean a Current Limit.A CV PSU sets the Volt and supplies the current upto the current limit depending on the load.A CC PSU sets the current and varies the voltage depending on the load, upto the volt limit.QuoteThe Chinese retailers miss represent what they sell in order to sell to as many people as they can. Most of them have a Current Limit NOT Constant Current.You cannot do both at the same time, it violates Ohms Law !They can be reconfigured to do Constant Current if you need to (hence they sell them as both).

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 02, 2016, 11:49:16 am
content: Quote from: MosherIV on September 02, 2016, 09:34:41 amThis is the second post I've seen from you harping on this so I guess it needs to be pointed out that when two phrases are joined by a slash one can interpret that to mean "phrase A" OR "phrase B". A common example is AC voltage ratings for motors: "208-230/460," which means 208 to 230VAC with the windings in parallel OR 460VAC with the windings in series.Thus, "Constant-Voltage/Constant-Current" can be interpreted to mean that either regulation mode is operating at any given time.Now as to whether those cheap little buck converter boards from China actually do constant current regulation, well... that's a whole 'nother argument. I've bought a couple on a lark - heck, at $5 why not? - and have been thoroughly disappointed in their performance, even considering the price paid.

author: Cerebus
author_rank: Super Contributor
timestamp: September 02, 2016, 03:22:48 pm
content: Quote from: MosherIV on September 02, 2016, 09:34:41 amHe said "electrolysis" so he almost certainly does mean setting a specific current, usually specified in terms of amps/area of electrode.You really do have a bee in your bonnet about CC versus CL don't you? You do realise that it's beginning to make you look likethatkind of pedant?

author: MosherIV
author_rank: Super Contributor
timestamp: September 02, 2016, 03:36:14 pm
content: QuoteWhen I see CV/CC in the same heading - I do worry about the miss-understanding and the perpetuation of the miss-understandingBack to Topic :QuoteNo - sounds like a good way to blow up the cheap buck-boost converters.Diodes will not help.If the output voltage is within a few milivolts of each other, it may be possible to use high wattage resistors. Look at some reference designs for paralleling up by-pass transistors in Linear Regulator application notes.If one of the switchers output voltage change by volts compared to the others - it probably will get destroyed or destroy one of the others, since they will all be trying to regulate the voltage.QuoteInstead of trying to parallel lots of them up, try looking at how to increase the output of a single switching controller. It usually involves using much bigger FETs and inductors and adjusting the current sense.Look at the datasheets and application notes.

author: ebclr
author_rank: Super Contributor
timestamp: September 05, 2016, 08:51:36 am
content: 'Please stop calling it a Constant Current (CC) power supply, unless you do actually mean a CC PSU. You probably mean a Current Limit.'A current limit is what a Constant current power supply do, no objection on the name. A constant current power supply is nothing more than a Constant voltage power supply on the maximum voltage and operating on the constant current limit zone, is not wrong with that name is a CONSTANT CURRENT until the load permit's that

author: MosherIV
author_rank: Super Contributor
timestamp: September 05, 2016, 09:00:53 am
content: QuoteI could not disagree moreA CV PSU in current limit will lower the voltage to maintain the current limit.A proper CC PSU will raise the voltage until it meets the CC set point.Fundamentally, one controls voltage and the other controls current.

author: ebclr
author_rank: Super Contributor
timestamp: September 05, 2016, 09:07:42 am
content: And this will be exactly what will happen, because the initial voltage is set to maximum, and tyhe voltage will go to a point to maintain the current, any decrease on load will reduce voltage, any increase on the load will increase voltage, exactly like a perfect constant current generator works limited to maximum voltage / load ratio

author: ebclr
author_rank: Super Contributor
timestamp: September 05, 2016, 09:13:03 am
content: The point that you are losing, is that those power supplies are 'mutants' they can be both, if the led CV is lighted is operating in constant voltage, if the led CC is lighted is operating in constant current. It's mathematical impossible to deny that

author: MosherIV
author_rank: Super Contributor
timestamp: September 05, 2016, 09:21:47 am
content: QuoteI am not missing anything. I am trying to point out, main for beginners, that yes a bench PSU can have a mode where it controls current BUT this is aCurrent LimitNOT Constant Current.The fact that some manufactures call it CC, even HP, is just marketing. The PSU is actually in Current Limit mode.There is a difference between the way a CV PSU with Current Limit works compared with a dedicated CC PSU works and that is what I am trying to point out.

author: ebclr
author_rank: Super Contributor
timestamp: September 05, 2016, 09:32:31 am
content: This difference does not exist, If the power supply is made on the correct way, You are making a point where isn't possible. OMHS Law supporting the reality

author: MosherIV
author_rank: Super Contributor
timestamp: September 05, 2016, 10:28:37 am
content: It sounds like you are not aware that there are CC PSUs

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 05, 2016, 11:40:39 am
content: Quote from: MosherIV on September 02, 2016, 03:36:14 pm+1. imagine they bought a PSU in ebay indicating CC/CV that turned out to be CV/CL. they start to mourn in every forum they can imagine, and then it turned out the designer of the PSU is the OP, or some kids who was reading the thread. so then they got bitten back right in the ass, worst if some other poor educated guy is the victim of the circumstances. its like in another thread where people loved to write MegaHertz as mHz. i dont get why when one tried to do a good thing just to be called a pedantic its like they never went to school to experience how fierce the teacher/lecturer/mentor/educator tried to maintain the quality to avoid this misconception... let alone in life threatening situation...

author: ebclr
author_rank: Super Contributor
timestamp: September 06, 2016, 08:45:28 am
content: For the Kids that guess they are mans read thishttps://en.wikipedia.org/wiki/Source_transformation

author: dom0
author_rank: Super Contributor
timestamp: September 07, 2016, 05:14:54 pm
content: Quote from: ebclr on September 06, 2016, 08:45:28 amIf you have read that article, then you may have noticed that voltage and current sources usually have rather different impedances. The same goes for power supplies; a design that has very low output impedance, typical for CV supplies, will require large amounts of feedback to exhibit a large output impedance in current limit (this applies to both linear and switched supplies). Therefore for "real" CC application a dedicated CC supply with an output network that has inherently high output impedance is preferable.Note that that doesn't really matter for applications where no serious regulation to speak of is required, like simple DIY electrolysis. Here a current-limited supply will work just fine due to the low regulation, accuracy and bandwidth requirements.Even voltage-mode control will work just fine (ie. controlling output current by influencing the voltage set point of the PSUs regulator). This is reasonably easy to implement with oldish 60 mV current shunts on top of existing cheapo ATX or server PSUs (higher quality or more modern parts often have quite intricate protection circuits that make this kind of thing hard to pull off, since sometimes multiple monitors/MCUs monitor the supply and shut it down -hard- if anything is off).