5 ~ 10 watt variable current/voltage PSU for breadboarding? - Page 1
Forum section: electronics / testgear

author: nbritton
author_rank: Frequent Contributor
timestamp: September 26, 2015, 01:00:25 am
content: Ideally I'm looking for a digital display variable current & voltage PSU for use with breadboarding. It would be nice if it had pins that I can plug directly into the breadboard power rail and it also needs to be isolated from the mains so I can hookup my computer based analog discovery, arduinos, and raspberry pis. Extra features that would be cool are built-in USB power jacks and two outputs for +5V and +3.3V.

author: Aodhan145
author_rank: Frequent Contributor
timestamp: September 26, 2015, 01:06:20 am
content: Why not a proper bench PSU?

author: nbritton
author_rank: Frequent Contributor
timestamp: September 26, 2015, 01:16:02 am
content: Quote from: Aodhan145 on September 26, 2015, 01:06:20 amThe cheapest digital bench PSU with more than 1 output is $150 on tequipment.net. If I went to the effort to get a bench PSU I would get the Rigol DP832. However, that thing is a monster relative to my needs at the moment.

author: nbritton
author_rank: Frequent Contributor
timestamp: September 26, 2015, 01:36:50 am
content: I did find the MB102 breadboard power supply for $2, here:http://www.amazon.com/Breadboard-Power-Supply-Module-Solderless/dp/B00BXWV2F6However, this leaves a lot to be desired. One issue it has is power can backfeed through the board (even if the switch is off) if your using multiple power sources, for instance the +5V USB coming from the computer. Also only rated for 700mA. Furthermore, it has no current limiting feature or display.Looking for something in the $20 price range, in kit form or fully assembled.

author: sarepairman2
author_rank: Frequent Contributor
timestamp: September 26, 2015, 01:51:37 am
content: ebay some old linear dual supply for 50$

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 26, 2015, 01:55:25 am
content: If you're really just starting out, I'd suggest any kind of supply for several fixed voltages (3.3, 5, 9, 12, 24, whatever), maybe an ATX supply with the output enable strapped on. Then when you need an adjustable voltage, reduce it with resistors, or use an emitter follower or LM317 circuit, or any number of other approaches. Later on, you can get a proper adjustable supply when you've outgrown your use of this method.Tim

author: nbritton
author_rank: Frequent Contributor
timestamp: September 26, 2015, 02:11:23 am
content: Quote from: T3sl4co1l on September 26, 2015, 01:55:25 amI just recalled that I have an LM317 power supply sitting in storage, I would have to go hunting for it though. I have a crap ton of stuff in storage but I haven't had the time to go through it, just moved across the country.I would like current limiting so I don't blow my circuits up.

author: liquibyte
author_rank: Frequent Contributor
timestamp: September 26, 2015, 02:20:01 am
content: I like playing around with op amps so I came up with this. You could probably bodge in an adjustable limiter but this one's set at a hard limit of 1A due to the transformer. I've had it loaded down at 200mA and it produced less than 5mV ripple but I'm waiting on the boards to come in before I take it all the way to 1A.

author: ez24
author_rank: Super Contributor
timestamp: September 26, 2015, 02:31:57 am
content: How about a laptop PS (like Toshiba) that is 19v 90watts and use Aliexpress bucks and 317s to make the voltages you want in step down steps.As an alternative and if you have time to shop, a Power Designs power supply such as this onehttp://www.ebay.com/itm/Power-Design-TW347D-Dual-Output-Power-Supply-0-16V-5A-0-18V-3A-/151825062210?hash=item23597a9942There are several models, some which are very cool lookingThey are very well built and this means you have a good chance of getting a good one on ebay.An Aliexpress model buck:http://www.aliexpress.com/item/Wholesale-Price-C-D-C-CC-CV-Buck-Converter-Step-down-Power-Module-7-32V-to/32339838120.html?spm=2114.01020208.3.72.w6361q&ws_ab_test=201556_2,201527_2_71_72_73_74_75,201409_2these have current control and I have had good luck with them so far. Notice this one has large heat sinks and coil. This can handle 2 amps with no sweat.One more thing that others have told me - the max current for a breadboard should be 2 amps

author: nbritton
author_rank: Frequent Contributor
timestamp: September 26, 2015, 03:19:13 am
content: Quote from: ez24 on September 26, 2015, 02:31:57 amPer rail. Hence my frustration that the MB102 breadboard power supply is only rated for 700mA.What about something like this?:http://www.amazon.com/gp/product/B00GZG7X9Y

author: ez24
author_rank: Super Contributor
timestamp: September 26, 2015, 04:59:24 am
content: Quote from: nbritton on September 26, 2015, 03:26:23 amToo bad about eBay. From my experience buying power supplies has been my only successful test equipment purchases.I would buy these (what you picked) and test it at 2 amps. Absolutely do not believe specs of 5 amps. But it has the big inductor.The 2 amp rating of breadboards came from several members, so I think this is a trust worthy number.If you got three of these and a laptop PS supply you could come up with 3 different outputs all rated at 2 amps max and still be under the 90 watt rating of the brick.And you have a voltage and current meter for each supply plus current limiting. Remember you will need some power resistors to test and set these up based on Ohms law.I may buy your selection and put together a 3 output power supply myself.You would have dual displays for each voltage and current limiting, good selection.Do you have a Harbor Freight IR meter? If so you can test the heat ratings of the chips and heat sinks.These things have high ripple, do you have a scope to test it with? But from what I have found out, even though the ripple is relatively high, it is not a problem. But I would place a 317 at the end of each to reduce the ripple a little just for fun.

author: nbritton
author_rank: Frequent Contributor
timestamp: September 26, 2015, 06:01:13 am
content: Quote from: ez24 on September 26, 2015, 04:59:24 amYeah! I have an ancient 200W 19.5V power brick that I can cannibalize. The only issue is it has a grounded plug. How should I deal with that?

author: ez24
author_rank: Super Contributor
timestamp: September 26, 2015, 06:09:39 am
content: Quote from: nbritton on September 26, 2015, 06:01:13 amTake a pair of pliers and pull it out of the plugEdit: Since my house is old and has no ground, this is what I do. If you have a ground then do as others have suggested and then ignore it. You should have a neg wire that goes to the neg terminal on the buck and a positive that goes to the pos on the buck, as determined by a multimeter. (unless it is a Dell ps). Then the neg will become the ground for your circuit. This should be ok unless you start to deal with AC main voltage then all bets are off.What I like about the laptop supply is all AC mains - remain on the floor and you will not have high voltage on your bench

author: bitseeker
author_rank: Super Contributor
timestamp: September 26, 2015, 06:12:36 am
content: If there are only two leads on the output, check if there's continuity between the ground prong and the negative side of the DC output. If there isn't, then the ground might only be there for the sake of the supply, not the device after it (i.e., laptop).

author: CustomEngineerer
author_rank: Frequent Contributor
timestamp: September 26, 2015, 06:44:14 am
content: Quote from: nbritton on September 26, 2015, 03:19:13 amThats not a PSU, just a Regulator. If you get that you will still need something to supply it with the 5V-30V DC that it needs. I also wouldn't trust that thing at 5 Amps, though you'd probably be ok with 2.

author: nbritton
author_rank: Frequent Contributor
timestamp: September 26, 2015, 08:18:58 pm
content: If you had to choose between these two, which would you choose and why?:http://www.amazon.com/gp/product/B00GZG7X9Yhttp://www.amazon.com/gp/product/B013STFDTC

author: ez24
author_rank: Super Contributor
timestamp: September 26, 2015, 09:04:44 pm
content: Quote from: nbritton on September 26, 2015, 08:18:58 pmTuff when the price is so differentThe one with the fan probably can do 3a. The caps are low rated at 35v and I cannot see the coil. If the coil is 101 then it is past my pay grade.Why don't you buy both then report back to us on your review of them? If you buy the $37 one it is not that much more to get the $17 one.The $17 adjusts with a pot and from what I have been told they do not hold up to much usage. So if you are only going to buy one and plan to change the voltage or current often then get the $37 because if you keep making changes to the $17 it is likely to fail early. So the $37 makes for a better adjustable supply.So my suggestion is get both and use one as a fixed supply and the $37 for an adjustable supply.Mounting is also an issue to think about.

author: Rick Law
author_rank: Super Contributor
timestamp: September 27, 2015, 01:12:25 am
content: Why not get adigitally controlledB3603 at about the same price! (Around $13 to $15 USD)See the link below for a mini-review. If this looks interesting, make sure you read the whole thread since a lot of info has been updated along the way as the thread grew.https://www.eevblog.com/forum/reviews/b3603-dcdc-buck-converter-mini-review-and-how-the-set-key-could-be-fatal/Rick

author: ez24
author_rank: Super Contributor
timestamp: September 28, 2015, 03:00:06 am
content: Quote from: Rick Law on September 27, 2015, 01:12:25 amThis has the ability to check the temps on the heat sink and be able to change the settings without turning a cheap pot. I did not read the whole post because at the beginning there is a warning. That stopped me cold, if there is a way to screw something up, I will find it.

author: TMM
author_rank: Frequent Contributor
timestamp: September 28, 2015, 05:06:39 am
content: Quote from: T3sl4co1l on September 26, 2015, 01:55:25 amWouldn't recommend it for a beginner as most modern ATX psus are more than happy to output 20A+ on their rails. Also unsuitable if you need low noise.A low power unregulated DC wallwart/brick powersupply and an LM series regulator is what i'd recommend. Even without implementing a current control, you'll hit the internal current limit of the reg at 1-2A which is probably good enough to stop everything turning into BBQ.

author: ez24
author_rank: Super Contributor
timestamp: September 28, 2015, 05:12:00 am
content: Quote from: TMM on September 28, 2015, 05:06:39 amIn my case I do not want the AC component to be on the desktop, thus the reason I want to start with a laptop brick and that will sit on the floor. I know my scope is AC but I want the PS to be safe for children.

author: fivefish
author_rank: Frequent Contributor
timestamp: September 28, 2015, 05:15:16 am
content: Get an HP 6205C Dual Regulated Power Supply. Less than $100 on eBay, find some deals for $49.

author: TMM
author_rank: Frequent Contributor
timestamp: September 28, 2015, 05:32:55 am
content: an ATX psu doesn't have mains AC exposed, all the output connectors are low voltage DC. The issue is that an ATX psu is a high current supply and will happily make small gauge wires red hot. Also all the output grounds of an ATX psu are referenced to mains earth so you can't gang up multiple PSUs to create split rails, or do anything that requires a floating ground. If you put a linear regulator like an LM317 on the 12V rail from the PSU you can get a variable output from a few volts up to about 9V and it will be safer than using the psus outputs directly as there is an internal current in the linear regulator so you can't draw more than about 2A. You may still kill your circuit under test but at least it's not going to make things red hot or start a fire.Smaller brick supplies are usually double insulated instead of mains earth referenced, so you can float them (within reason...) e.g. create +/-9V rails, gang them up in series to get a higher voltage.

author: Flenser
author_rank: Regular Contributor
timestamp: September 28, 2015, 09:25:50 am
content: Quote from: nbritton on September 26, 2015, 08:18:58 pmJulian Ilett has posted a video review warning about a bug that the first module suffers from where the current limiting does not work when the voltage and current limits are turned down to near their minimum:

author: ez24
author_rank: Super Contributor
timestamp: September 28, 2015, 06:53:13 pm
content: I forgot about Julian's videos (isn't he a member?)Notice the plug.So I suggest to OP to go through themhttps://www.youtube.com/user/julius256/playlistsBesides videos on the bucks he has videos on using the bucks in different projectsThanks Flenser

author: Rick Law
author_rank: Super Contributor
timestamp: September 28, 2015, 08:42:45 pm
content: Quote from: Flenser on September 28, 2015, 09:25:50 amThis design flaw is probably common. I have it on two different different CC/CV board I purchased. It was not until I made my own that I understood where it may come from.The scenarioprobablyis when the short occurs, momentarily the main power source has a voltage sag. The op-amp dealing with current is not having enough volt to run properly allowing the run-away current draw, this in-turn locks the op-amp in the underpower/non-performing mode thus keeping the current at run-away level.On the one I made myself, I use a separate power source to run the control circuit. For the purchased stuff, I have some luck reducing it by using a "reservoir capacitor" at the op-amp. I have better luck with bigger power source (less sag thus not triggering the initial momentary run-away).Since I have seen it on more than one kind of CC/CV board, I think one should just be mindful that with this kinds of boards, a sudden big current increase could knock the control circuitry out of action. If you plan to use it as your PSU, testing this characteristic (using your intended power source) is important or you may be pumping 5A into your DUT giving you kind of a bad day.

author: ez24
author_rank: Super Contributor
timestamp: September 28, 2015, 09:57:16 pm
content: QuoteCould you explain this more? Are you soldering components onto the buck's circuit board?Would this work:Julian's video shows that the buck can put out 5 amps when shorted. What if the buck's current was set to 2 amps with a resistor and then shorted. Would there be a problem? Or will the current stay at 2 amps?thanks

author: ez24
author_rank: Super Contributor
timestamp: September 28, 2015, 10:03:16 pm
content: QuoteCould you explain this more? Are you soldering components onto the buck's circuit board?Would this work:Julian's video shows that the buck can put out 5 amps when shorted. What if the buck's current was set to 2 amps with a resistor and then shorted. Would there be a problem? Or will the current stay at 2 amps?thanks

author: Rick Law
author_rank: Super Contributor
timestamp: September 29, 2015, 02:10:35 am
content: Quote from: ez24 on September 28, 2015, 10:03:16 pmYes, I am soldering components onto the buck board. Since you asked me to explain, let me do the explaining first so my solution description makes more sense.The whole issue that I came across, which is exactly like the one shown, was the sudden high current draw pulled the Vin too low for the op-amp (and the rest of the control circuitry) to function, thus the run-away condition. So, my attempted fix is to make sure that the control circuit is well juiced.Lowering the current limit likely would not have an impact since the control circuit is not in control. So, whatever you set doesn't matter.My experimental fix was then to solder in from 100nF to 100uF as near the op-amp (and control circuit) as possible. The idea is to provide enough juice for the control circuitry to run long enough to drive down the current enough before run-away occurs. "Drive down the current enough" means the Vin sagging is no longer too low for the control circuit by the time the capacitor is drained.That works, but not well. However big the capacitor, there is always a path to leak it out. When the unit is outputing 5A at near zero volt for the short, it is grabbing from everywhere since everywhere is likely > near zero volt.Assuming we are indeed talk about the same problemrather then two different problem but same symptom -- The best fix is of course to make sure the control circuitry has an independent power source. I found "fatter source" to be more reliable over a "reservoir capacitor" at the op-amp. After switching from the 9V1A to a 12V1A then a 15V3A source, I recall very rare occasions when I hit the problem with 12V1A source. I don't recall it failing since I up-ed it to 15V3A from either of my two CC/CV boards. It is a lot easier for the 9V to sag below what is needed for the control circuitry than to have 15V sag to below what is needed.I now switched to a digitally controlled B3603 as my main power source with a 15V3A Vin. I misplaced the 9V1A long ago, so I am not sure if this one too can be afflicted with that sagging - the same elements are there so the same issue may affect it.By the way,if this board is supplied by another bench PSU(with CC)like when being tested in the lab, that "power drop below necessary" situation for sure will happen. When supply PSU hits its CC limit, the Vout from the bench supply PSU will fall like a rock and this board will not have adequate volts to run the control circuit.- if you can attach a detail photo of each side of the board, I may be able to do some suggestions.- also, if you want to see how a CC circuit may work, take a look at this link where I added CC to a similar CV only board to make it a CC/CV board.https://www.eevblog.com/forum/beginners/adding-cc-to-a-cv-buck-to-make-it-cccv/

author: nowlan
author_rank: Frequent Contributor
timestamp: September 29, 2015, 03:07:28 am
content: Skullcom Hobbies did some mods for the DROK DC converter on youtube.

author: ez24
author_rank: Super Contributor
timestamp: September 29, 2015, 04:06:28 am
content: Quote from: nowlan on September 29, 2015, 03:07:28 amInteresting - thanks