Power Supply Desgin HELP ! - Page 1
Forum section: electronics / beginners

author: Albatroon
author_rank: Contributor
timestamp: April 20, 2013, 10:20:57 am
content: Hello All,I am designing a power supply for a project I am building.This power supply will drive a lot of solenoids. they need about 20 AMPs. any they will open & close a lot in secondsI watched Dave's Youtube blogs about the differences between SMPS and linear regulators.I suppose that Its better for my project to build a SMPS one. Than i watched Dave's tutorial about designing a SMPS circuit.This one made the design a lot easier for me.. Thanks Dave!But what about this high current situation!According to Datasheet, I can add a external current boost to the IC. But what transistor I can use can handle this high current without any problems ?Thank you all ( :

author: Alana
author_rank: Frequent Contributor
timestamp: April 20, 2013, 12:41:51 pm
content: What is voltage of those solenoids? If its 12 or 24V ATX PC PSU or 2 of those may be your friend.

author: Albatroon
author_rank: Contributor
timestamp: April 20, 2013, 12:56:09 pm
content: Alana,Thanks for your replay.They Are 24v.I'll use a 30v transformer for this with a 50 a Bridge Rectifiers.And I can't find here in local market a good quality PC PSU that I can depend on. Thats why I need to build my oneThank you

author: Strada916
author_rank: Frequent Contributor
timestamp: April 20, 2013, 01:19:49 pm
content: Are the solenoids AC or DC?

author: Albatroon
author_rank: Contributor
timestamp: April 20, 2013, 01:24:04 pm
content: Quote from: Strada916 on April 20, 2013, 01:19:49 pmThey all are 24v DC 6.5WThank you

author: Albatroon
author_rank: Contributor
timestamp: April 20, 2013, 01:42:32 pm
content: Quote from: AcHmed99 on April 20, 2013, 01:38:55 pmMy Power source is 220v AC. converted to 30v AC via a transformer.I am trying to build one. not to buy one.Thank you

author: Alana
author_rank: Frequent Contributor
timestamp: April 20, 2013, 05:59:06 pm
content: Quick and stupid question. Are you sure that this voltage for solenoids must be regulated? Maybe 24V transformer with bridge rectifier and 10000uF of filtering caps is all you need?I have seen this kind of setup for powering stepper motors in DIY CNC - regulated voltage only for control, rest unregulated.And your transformer? Can you easly unwind few turns to make it 24V AC. I did that on toroid transformer not even by unwinding but by counting turns [they are usually visible from outside] and making a tap. How much turns i had to count - i wounded up 10 turns of simple insulated wire and mesured what is voltage per 10 turns. Simple maths [there was topic on transformers recently] and i know what to do.

author: Albatroon
author_rank: Contributor
timestamp: April 20, 2013, 06:09:09 pm
content: Quote from: AcHmed99 on April 20, 2013, 01:48:03 pmThanks for trying to help me!Its first time I hear about Buck converters..I Watched Dave video about The MC34063 Switch Mode Regulator ()..Can I use this ? All parts are around and its easy to buildBut what about this high current situation!According to Datasheet, I can add a external current boost to the circuit, But what transistor I can use can handle this high current without any problems ?Quote from: Alana on April 20, 2013, 05:59:06 pmAlana.. this is a beginners section.. So you must know that anyone here not asking stupid questions.. all questions here is for learning. So Please don't tell any beginner that he asked a stupid question.. Thank you ( :And about the rest answer,It's a good hint i just learned from you.. Thank you !

author: c4757p
author_rank: Super Contributor
timestamp: April 20, 2013, 06:12:10 pm
content: Quote from: Albatroon on April 20, 2013, 06:09:09 pmQuote from: Alana on April 20, 2013, 05:59:06 pmAs in, "Are you sure that ... must be regulated?" is a "Quick and stupid question".

author: SeanB
author_rank: Super Contributor
timestamp: April 20, 2013, 06:14:28 pm
content: If it is solenoids you only need unregulated voltage, preferably regulated to 24V with an allowable range of 18-28V. You will be dissipating 360W in whatever linear regulator you use, it will be much better to have a transformer of 18VAC to simply use with a bridge and 10000uF of capacitance as a supply. with 70 odd solenoids you will probably be better off using a few standard 24V industrial power supplies to provide power, 4 5A units with a number of solenoids for each will work well.If you want to make a buck converter you can use almost any controller likehttp://www.ti.com/lsds/ti/power-management/step-down-buck-controller-products.pagefor example.There are plenty of appnotes and design ideas there for use as well, though you will be best served by looking at older lower frequency devices, as the power devices will be easier to find substitutes for.

author: mariush
author_rank: Super Contributor
timestamp: April 20, 2013, 06:32:50 pm
content: 24 v, 6.5 watts ... that's about 0.3 A per solenoid. Since you say you need about 20 A, I can only assume you have about 50-60 solenoids.Might sound silly, but it would probably be cheaper to just get a bunch of 7824 voltage regulators .. they're 0.3$ a piece in 100 quantity.24v transformers are readily available and might be cheaper than a custom 30v transformer. This is rms values, so the peak dc voltage would be 24x1.41 = 33.8v , drop about 2v for the bridge rectifier and you have 31v peak.As long as you have a minimum of 26.5v or so at the input of the linear regulators, they'll do just fine giving 24v output.You can size up the bulk capacitors to get that.. C = I x Cduty / ( V ripple x frequency ) I is 20 Amps, C duty is about 70% or 0.7 , Vripple is Vpeak - Vmin = 31-26.5 = 4.5v , frequency is 2 x ac frequency or 100 or 120HzC = 20 x 0.7 / 4.5 x 120 = 14/540 = 0.025925 F so you would probably need 26000 uF at least. 27000 uF is a common value and a 50v rated capacitor is about 10-12$ a piece, less in quantity. You could probably use 2 x 15-18.000 uF 50v instead, they're also 5-6$ a piece.So you can probably easily power 2-3 solenoids from a single 7824 linear regulator, they probably won't be all enabled at the same time and even if they are they still won't reach the 1A current the 7824 can do. You'll just need a cheap heatsink for the 7824 to help it dissipate the 2-3 watts at 1A it would do (or use a larger heatsink to connect several 7824 on a single heatsink since it's not important to have each of them isolated) and a couple of 100uF or so capacitors at input and output.

author: kxenos
author_rank: Frequent Contributor
timestamp: April 20, 2013, 08:09:42 pm
content: This is serious power for a switch mode DIY solution. I would suggest not to waste money & effort in designing it. You can use something like thishttp://export.farnell.com/emerson-network-power/lcm600q-t/psu-ac-dc-600w-single-output/dp/2115741if you absolutely want regulated voltage (Datasheet:http://www.farnell.com/datasheets/1624416.pdf). If you really want to design something, try an unregulated linear PSU as others suggested. If you want to regulate it, you should consider some (at least 3-4) transistors in parallel.Very quickly, to calculate thermal demands you go something like this:Ok, I have a, say, 230/24V transformer. Worst case is 230 +10% so 24 + 10% = 26,4VACrms. That is (26,4 * 1,41) - 1,4 = 35,8VDC (worst case). Your regulator will output 24VDC so you're going to have 11,8VDC voltage drop. The maximum worst case power dissipation therefore will be 11,8V * 20A = 236W. If you use, say 8 transistors, each one is going to dissipate 236/8 = 29,5W.If I use TO247 transistors like thesehttp://www.st.com/web/en/resource/technical/document/datasheet/CD00001165.pdfthey typically will have Rjc = 1C/W. In this I have to add, say, Rch = 0,2C/W typically. So we have so far thermal resistance from junction to case and from case to heatsink is 1,2C/W. So, I'm going to have 29.5*1,2 = 35,4Cabove ambienttemperature for my transistors. But I haven't calculated the resistance from heatsink to ambient. If I use a 2 heatsinks like thishttp://export.farnell.com/fischer-elektronik/la-6-150-12v/heat-sink-fan-cooled-12v/dp/1222507I'm going to have (236/2) *0,175C/W = 20,6C in every heatsinkabove ambient. So, total increase in temperature should be no more than 35,4 + 20,6 = 56C. For the specified transistors I see that the maximum temp. is 150C so the maximum ambient temperature my circuit could work safelly is 150C - 56C = 94C Which I guess is fine. But also there is something else. You have to derate the maximum power of the transistor as temp. goes higher. This is usually specified in the datasheet. For example, if my transistor has maximum power 150W with a power derate of 1,5W/C above 25C that means the maximum power for this transistor at 100C whould be 150 - ((100 - 25)* 1,5) = 37,5W. So, in our example, if my transistors have characteristics like this, 150W max., 1,5W/C that means 150 - ((Ttr - 25) * 1,5) = 29,5W -> Ttr = 105.3C and since this includes the 56C then the maximum ambient temperature will be 105,3 - 56 = 49,3C.From the above you can see that 2 heatsinks like that will cost about $130. Plus $24 for transistors plus maybe $100 for transformer you're easily above $300 for single quantities. The EMERSON NETWORK POWER - LCM600Q I suggested above goes for about the same price.Hope that helped.

author: cwalex
author_rank: Frequent Contributor
timestamp: April 21, 2013, 04:04:25 am
content: Quote from: Albatroon on April 20, 2013, 06:09:09 pmAlana wasn't implying that you were asking stupid questions, she was just saying that she was asking you a stupid question. It is a common way for people to politely ask something that may be obvious without causing offense. I think it is just a language barrier so no need to be offendedGood luck with your project

author: Strada916
author_rank: Frequent Contributor
timestamp: April 21, 2013, 05:37:28 am
content: simple idea. two car batteries in series. can power all the solenoids you need.

author: Albatroon
author_rank: Contributor
timestamp: April 21, 2013, 10:21:15 am
content: Quote from: cwalex on April 21, 2013, 04:04:25 amOhhh.. Thank you for making everything clear!And Alana, Thanks again.. sorry for this misunderstanding..Quote from: Strada916 on April 21, 2013, 05:37:28 amNice add. thank you.. But I need something better than a battery !Quote from: kxenos on April 20, 2013, 08:09:42 pmYou helped me a lot !!! But the problem is I need 3 of this power supply for 192 solenoids.. each one is 20a minimum. So it will cost much money.That's why I am trying to build my switch mode power supply.On other side.. I prefer regulated power for a reason.. all solenoids must open at the same time! if one of the transformers voltage not equaled the others.. the solenoids connected to this transformer may open slower (I Think !).I have another solution.. maybe better and easier.Those solenoids already connected to driver I built with shift registers & ULN2803. each board have 8 output, Can I use a MC34063 switch regulator on each board with a transistor current booster ? it only need less than 3 ampsAnd for more information about the project I am building.. This is my 1st prototype:Now I am making it bigger and better..If anyone have a better idea Please tell me..Thank all for your effort !

author: Albatroon
author_rank: Contributor
timestamp: April 21, 2013, 11:44:03 am
content: Quote from: AcHmed99 on April 21, 2013, 11:24:44 amThis project is a water fountain for indoor decoration.. I just watched it online and I insisted to build one..About the transformer, this transformer will be a manual one. so I can control any the output voltage to be close to the value I need.I just said 30v for any voltage drop in Bridge Rectifiers & Regulators, I can reduce the voltage if needed. I found a very small factory builds any transformers as needed, They just are too primitive and can't give a precisely output.But, If a 25v transformer will do the job. I can ask him to build it 25v instead of 30v.I'll use this Bridge Rectifiershttp://ram-e-shop.com/oscmax/catalog/redirect.php?action=url&goto=www.ram-e-shop.com%2Fds%2Fgeneral%2FKBPC5010A_Bridg.pdf.What is voltage drop for this one .. and what's is the safe input to 34063 to out 24v ?Thank you

author: mariush
author_rank: Super Contributor
timestamp: April 21, 2013, 11:48:20 am
content: By the time you buy the parts for the MC34063 ( mc34063, shottky diode, inductor capable of the peak currents, under 1 ohm resistors), the pass transistor, making a pcb so that the mc34063 will be stable (it's often unstable even on breadboards), you'll get to about 2-3$ for a 24v 3a "dc-dc converter"Even with the pass transistor, the mc34063 won't be 100% efficient, so you're probably looking at 3.5-4A to get 24v 3A - you're just increasing the transformer size.So you'd still have 2-3$ x 24 = 48-72$ , let's say if you're lucky maybe 50$, and you still have to buy the big transformer, that's gonna be about 250$.You can buy industrial power supply rated for 24v on eBay relatively cheaply, for example just search for "meanwell 24v" - meanwell is a relatively good brand of switching power supplies.Saw this for example:350w for 55$ :http://www.ebay.com/itm/Mean-Well-MW-24V-14-6A-350W-AC-DC-Switching-Power-Supply-NES-350-24-UL-Brand-New-/350666712199?pt=LH_DefaultDomain_2&hash=item51a55d6487500w for 50$ :http://www.ebay.com/itm/Mean-Well-Power-Supply-SP-500-24-In-100-240-VAC-24V-20A-Out-Used-WARRANTY-/171019689462?pt=LH_DefaultDomain_0&hash=item27d1915df6500w for 70$ :http://www.ebay.com/itm/MEAN-WELL-DC-POWER-SUPPLY-24V-SP-500-24-INPUT-100-240V-/180954887238?pt=LH_DefaultDomain_0&hash=item2a21c074461000w for 200$ :http://www.ebay.com/itm/Mean-Well-SE-1000-24-24V-1000W-Power-Supply-New-/330832718278?pt=US_Radio_Control_Control_Line&hash=item4d072aa9c6If you keep the load under about 300 watts, I'm sure it's going to be just fine... so if you get three 500w psus for 150-250$ in total, you're going to have 1500w available (62A), enough for those solenoids.And these are not even the cheapest on eBay, I just sorted by Price (highest first) to get the bigger wattage psus on top, if you search carefully you're going to find better deals (less dollars per wattage)later edit:The bridge rectifier you link to has 1.1v voltage drop per diode, so 2.2v in total.What do you mean manual transformer? You mean a variac ? If so, that's a bit dangerous...

author: SeanB
author_rank: Super Contributor
timestamp: April 21, 2013, 12:12:32 pm
content: Wind transformer for 18-20V, then use unregulated. You will have to use 100v transistors to drive the solenoids and use 80v transorbs across the transistors to get the coils to operate fast enough. You might even have to run them at 48V with each being controlled by a current source to get the turn on time lower. Then you put a 120V transorb across each coil and use 200V rated transistors.For this you do not want a clamp diode, rather allow the coil to generate a high voltage at switch off so that current collapses fast in the coil. For turn on you need a high voltage to get to the required current faster, but current limited to prevent coil burn out. Likely you might want to use stepper motor drive chips as they have the required switching circuitry inside along with the high voltage rating, as steppers are often run from a high voltage to increase step speed. These often are run from a 60V rail but use a motor that is only rated to have 12V across it, the high voltage being used to turn the windings on and off faster.

author: Albatroon
author_rank: Contributor
timestamp: April 21, 2013, 12:36:33 pm
content: Quote from: mariush on April 21, 2013, 11:48:20 amBuying and shipping them to Egypt, And paying customs for them.. It will cost a lot of money.And meant by manual that the factory will wind the transformer as I request.. and on cheap too.And I'll make PCBs anyway for the control drivers boards (shift registers & ULN2803). So adding some parts to it will not be a problem.The max load on each board will be 2.4 amps..Can I use normal 7824. maybe 3 or 4 of them on each board with a 1000uf cap .. would it work good and stable ?It just will need more than 24v .. maybe 27v transformer to give out 24v.. Right ?Or just use the MC34063 with a pass transistor ..They both solutions are cheap to me, But which one is better for my case ?Thank youQuote from: SeanB on April 21, 2013, 12:12:32 pmI am sorry, Could you explain more ? What is the transorbs ??And the solenoids are 24v rated.. and have -+ 5% working range.. how I can them on 18-20 v ??I am sorry please explain more..Thank you

author: SeanB
author_rank: Super Contributor
timestamp: April 21, 2013, 12:42:21 pm
content: If you want the solenoids to switch fast you have to ramp the current in them up and down very fast. Typically solenoids switch on and off in the range of 50-200mS, and this will be a big issue if you are trying to switch them fast. Typically they can be run off half wave rectified AC without doing anything more than being a little noisy.

author: mariush
author_rank: Super Contributor
timestamp: April 21, 2013, 01:10:48 pm
content: Quote from: Albatroon on April 21, 2013, 12:36:33 pmCustom made PCB is kind of expensive for cm2, unless you go with SOIC or other surface mount components it might turn out more expensive than simply getting some prototyping boards:http://uk.farnell.com/roth-elektronik/re521-hp/pcb-eurocard-fr2-stripes-2-54mm/dp/1172138You can buy stripboards like the one from eBay more cheaply but they're of a bit less quality. Anyway, there's 37 lines so you can put 3 DIP 2803 chips in line AND have room on the side for a voltage regulator, and you can probably put about 3-4 pairs of 2803 + shift registers on each board (there's 57 holes vertically so you have about 18 vertical holes for each set, you only need about 12 so you have room to solder wires and maybe resistors)You just have to cut with an xacto knife or some other blade (or just use a drill to enlarge the holes and separate the strips under chips so the pins aren't shorted.If it helps and you trust me enough, I'd be willing to mail you some components you need and maybe as they'll come from a private person (me), you may not have to pay customs and other taxes. Since I'm in Romania, you'd get the parts in about 6-10 days compared to buying them from China or US, but on the downside, I'd have to pay VAT of my country (24%) if I buy parts from a store like Farnell (the linked above).Hit me with some components and quantity you need and I'll look up some prices for you if you want... but don't expect me to mail you 192 solenoids, I mean stuff that would go through mail as a thick A4 envelope, like dip chips in a cardboard boxes, pcb boards etc

author: Albatroon
author_rank: Contributor
timestamp: April 21, 2013, 04:33:49 pm
content: Quote from: mariush on April 21, 2013, 01:10:48 pmReally Thank you for trying to help me.. After what you said sure I can blind trust you.All parts I mentioned are available here.. expect this 20A SMPS !And I haven't problem with PCBs too. there's a good local PCB factory with very good price per cm2. My first prototype in video above used a custom PCBs..About the regulator.. which one is better in my case.. 7824 or MC34063. I think a switch mode reg is better.And what is best voltage input should I use if I used on of them ?And if I used the MC34063, What transistor should use to handle up to 2.4 amp at 24v ?Thank you again..Quote from: SeanB on April 21, 2013, 12:42:21 pmThe solenoids i used in first prototype was DC not AC. Also i used a DC power source and they worked great at 10 mS rate. which worked great.. Also 192 solenoid noise.. will be very loud !