Help me with Power supply - Page 1
Forum section: electronics / beginners

author: sleepy_platter
author_rank: Newbie
timestamp: May 01, 2014, 07:18:04 pm
content: Hello!So I need to buy a variable power supplyI need one that can give me variable 2 to 6 voltand variable amp. I need sometime to set it a 0.18 amps and max 1 amp(for electroplating)I bought one but after I got it I realise only the volts where variableSo nowIf I buy something like this will I be ok?http://www.amazon.ca/Tekpower-HY1803D-Variable-Power-Supply/dp/B000CSQK5EI just don't understand thisLine regulation: CV <= 0.01% + 1 mV, CC <= 0.2% + 1 mALoad Regulation: CV <= 0.01% + 3mV, CC <= 0.2% + 3 mAThanks everybody!

author: Jeroen3
author_rank: Super Contributor
timestamp: May 01, 2014, 08:00:21 pm
content: If you short circuit a lab power supply*, it turns into an variable amp supply with a maximum voltage specified by the voltage setting.So yes, the thing you linked should do*.I do not think the regulation accuracy and stability is of any concern when you are using it for electroplating.Find out for yourself. eg: is 1.1 Amp with 6.5 Volt still ok? Then you have 10% on amps and 8.3% on voltage error.The one you linked says there probably is (less than) 0.01% error in voltage mode and (less than) 0.2% in current mode.*please make sure your lab supply is specified to thecontinuousshort circuit condition and load conditions prior to using.Some are only capable of maximum current for (less than) a few hours due to thermal issues.

author: Fank1
author_rank: Regular Contributor
timestamp: May 01, 2014, 08:41:49 pm
content: Just add a 3 terminal regulator, LM7805 or so and connect it to be a current regulator.There are plenty of circuits in the data sheets.

author: grumpydoc
author_rank: Super Contributor
timestamp: May 01, 2014, 09:42:33 pm
content: Short answer - it will probably be OK.Long answer - well I think some understanding of CV and CC mode in power supplies is called for.First lets recap Ohms Law.Ohms Law (paraphrased a bit) says that the current through a resistance is linearly proportional to the voltage across the resistance. In fact the current is given by the relationshipI = V/RWhere I is current in amps, V the voltage in Volts and R the resistance in ohms.So if you have a 2ohm resistor and connect it to a 10V supply 5 amps will flow (5=10/2).Ohms law can also be re-arranged to give other useful equations eg V=IR.Note that only two of these quantities are independent - once you know two of the values in the equation the third takes on a fixed value which is given by solving the equation.That means that no matter how you try you cannot get 6 amps to flow through a 2 ohm resistor if there is 10V across it.Now, power supplies typically have two modes. constant voltage(CV) and constant current(CC) mode.In CV mode the output voltage is regulated. Using the values above if I take my bench PSU and set it to 10V and put a 2ohm resistor across the terminals then 5A will flow - assuming the PSU can supply that much current.If it can't the PSU will protect itself from overload. Cheaper supplies such as the one you linked to will normally lower the output voltage to limit the current to their maximum output - so a supply capable of supplying 3A would drop the voltage to 6V at which point the current will be 3A. More expensive supplies might turn the output off depending on how they are set-up.In CC mode the current is regulated by the PSU adjusting the voltage. If I take my PSU and put it into CC mode and ask for 10A, then connect a 2ohm resistor then the PSU will increase the voltage to 20V. If the PSU doesn't go that high - such as the HY1803 which only goes to 18V - then it will never be able to get 10A to flow into a 2ohm load - even if it was rated for a 10A output.If you look at the power supply you won't find a button which switches between CV mode and CC mode - what you will find is a voltagelimitcontrol and a currentlimitcontrol. If you set the voltage and current limits and connect a load which draws less than the current limit the supply will operate in CV mode, if the load draws more than the current limit it will operate in CC mode.For cheap supplies (like the HY1803) the recommended way of setting the current limit is to short the output - even at low output voltages this will draw a high current (as the resistance is low) and so you can see (and adjust) what current is flowing. To use the supply you thenremove the shortso you do not need to worry about the PSU being able to supply a short circuit continuously1.So - it is actually impossible to say whether the HY1803 will work for your electroplating. You can certainly set the output in the range 2-6V, and it will be able to supply up to 1.1A. The thing I can't say is whether it can cause 1.1A to flow through your electroplating solution. The resistance of your set-up will vary according to the electrode size and the concentration of the electroplating solution. You mentioned 2-6V and 0.18A - now if your set-up draws 0.18A at 2V the resistance is 11.1ohms, in which case this supply would be able increase the output voltage so that 1.1A flows (in that case 12.22V is needed). If, however your set-up draws .18A at 6V then the resistance will be 33.3ohms and this supply will not be able to give you 1.1A since you'd need the output to go up to 36.7V which it doesn'tSo, to decide you need to look at your electroplating set-ups and take some measurements of voltage and current. Then you will be able to work out whether the supply will work for all of the scenarios that you want. Although if I buy a "3A" PSU I expect it to be able to supply 3A continuously at up to it's rated output voltage FFS, anthing else is a waste of time.

author: madshaman
author_rank: Frequent Contributor
timestamp: May 01, 2014, 10:42:24 pm
content: I think the correct tool for the OP is a current source, either purchased used or it can be constructed from:A voltage referenceA potentiometerA power MOSFETA general purpose opampA sense resistor of some sort with a low valueMaybe make friends with an electronics hobbiest; most could probably build what you need in 30 mins from junk lying around their workshop.Edit: a linear regulator connected as a current source will also work but your control pot won't alter the current linearly and you'll be more limited by maximum current.

author: electr_peter
author_rank: Unknown
timestamp: May 02, 2014, 06:36:45 am
content: Quote from: madshaman on May 01, 2014, 10:42:24 pmAdd some power source to the list as well.Current source is viable option, but CC and CV mode power supply is just easier to deal wit for this application - it provides both power and constant curent regulation. Remember to check or test continuous power handling properties.

author: grumpydoc
author_rank: Super Contributor
timestamp: May 02, 2014, 08:05:37 am
content: QuoteIf the OP isn't sure how to work out whether an off-the-shelf power supply will do what he wants is it likely he can construct his own current source?He still needs to understand how to calculate how much voltage headroom he requires to get the current he wants.The HY1803 will probably do. An 0-30V 3A supply might add a bit of flexibility.

author: madshaman
author_rank: Frequent Contributor
timestamp: May 02, 2014, 12:45:36 pm
content: Quote from: grumpydoc on May 02, 2014, 08:05:37 amThat's why I suggested this:Quote from: madshaman on May 01, 2014, 10:42:24 pm:-)It could be a trade of sorts (e.g. The OP could electroplate things for the electronics hobbyist once they're set up), and in the process the OP can begin to learn some of those important basics.

author: madshaman
author_rank: Frequent Contributor
timestamp: May 02, 2014, 01:01:33 pm
content: Quote from: electr_peter on May 02, 2014, 06:36:45 amThat's been my biggest concern with this thread; electroplating can be a long unsupervised operation and I have serious doubts about the OP choosing a new supply (not designed specifically for electroplating) that won't melt or fail spectacularly.I'd trust my HP heavy duty system supplies to handle this safely and without worry, but the el-cheapo Yihua that sits on my build bench, not so much.If someone built the OP a simple current source, they'd (hopefully) heatsink the pass element(s) and ensure the thing could run on a continuous duty cycle indefinitely.It's just one suggestion, the more viable options the OP has the better; we don't know what social resource he or she has available.

author: sleepy_platter
author_rank: Newbie
timestamp: May 02, 2014, 08:10:36 pm
content: Ho wow!!! what a ton of amazing anwsers!I have a calculator for the amp I need no worries about thatthe volt just need to be around 3volt and to calculate the amps I go to this websitehttp://www.goldn.co.uk/tankcalc-new.phplike tichness 2,5 micron surface area 6cm gold concentration 1,5 per litter, solution used 500mlI just enter the size of the surface and it tell me how much amps I needThe problem with this actual machine that I bough the amps are too high, it plate too fast and then the gold fade faster because if kind of burn(if for a musical instrument part that have to rub on the face all the time)If the link I suggested is not good for me, do you have any sggestions?I will never need more than 10 volts and 5 ampsThanks a lot!

author: sleepy_platter
author_rank: Newbie
timestamp: May 02, 2014, 08:17:07 pm
content: and my electroplating time is never higher than 15 minuteI only do small thingsI really don't have any friends good at electricitybuilding the thing myself I would be affraid to electrocute myself

author: grumpydoc
author_rank: Super Contributor
timestamp: May 02, 2014, 08:50:03 pm
content: QuoteAmps and volts or amps and time?What calculator do you use?AFAICS a plating calculator can take the amount of material to plate - that's simple enough given the area of the surface you want to plate and the thickness of the desired plating and give you the "amount" of electricity that is needed to do the plating. The unit for the amount of electricity is the Coulomb (C). One Coulomb is one amp for one second so I can see that you could calculate the number of Coulombs required for a plating and turn that into a current and time.When you set up your plating there will be a resistance between the cathode and anode - that resistance will depend on the surface area to be plated, the surface area of the anode, the distance between the anode and the surface to be plated and the concentration of the plating solution. Whatever it is though will be fixed - so we now have current and resistance which means voltage comes from ohms law. Some of the parameters that affect the resistance might change as plating proceeds.If you connect your set-up to a PSU set with the current that you desire and max voltage the PSU willtryto achieve the current that you want but if it runs out of volts it won't get there.I can't quite see your calculator telling you volts and amps - but eletroplating's not something I've tried so I might be missing something.I can just see confusion ahead because you can't tell the PSU to output X volts and Y amps and expect that to happen because the PSU can't control the resistance of the load.If you say 10V and 2A for instance and then connect a 10ohm load it will operate in CV mode at 10V but you will only have 1A - if you connect a 1ohm resistor then it will operate in CC mode at 2A but drop the voltage to 2V - only if you happen to connect an exactly 5ohm load will you get 10V and 2A.You need to understand this otherwise you'll be scratching you head when your PSU apparently doesn't work the way you thought it should.

author: cellularmitosis
author_rank: Unknown
timestamp: May 06, 2014, 02:32:42 am
content: I've had good luck with the $50 CSI1802X, if you are looking for a cheaper supply.http://www.circuitspecialists.com/bench-power-supply-csi1802x.htmlAs a learning exercise I started translating the manufacturer's schematic into KiCAD.https://github.com/pepaslabs/CSI1802X