# 30V 10A 110V Precision Variable DC Power Supply to find short to ground(sort of newbe)

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#### gica69

##### New Member
I am trying to find a short to ground in a battery backup and surge protector and I saw a video on YouTube
where the guy placed a current through the contacts of an inductor that was removed to check the board for shorted components causing the short, he put a 3.5V and the full 10A that his expensive HP 6542A could handle. He found the heated component by finger touch and then used alcohol to pin point the culprit. My question is should I buy a 30V 10A 110V Precision Variable DC Power Supply or is a 5A max enough? Some people use like quarter amp to do the same thing. Any advice would be appreciated. Thanks for the input.

#### Nigel Goodwin

##### Super Moderator
Well for a start you don't need any 'precision' - this technique is akin to 'bashing it with a rock' - you just need sufficient current capacity.

Generally you'd just 'use what you have', but the higher the current the better, I doubt 1/4A would be enough.

#### spec

##### Well-Known Member
While I agree with Nigel, if you wanted to get a bench power supply for short testing and possibly for general use too, I would recommend one of the 0V to 30V, 0A to 10A linear power supplies linked below. They are a reasonable price- I have three.

I have seen quite a bit of short testing over the years using high constant current power supplies and infra red cameras. At one time we received a large batch of multi-layer printed circuit boards that had shorts.

spec

http://www.ebay.co.uk/itm/10A-0-30V...id=100005&rk=4&rkt=6&mehot=ag&sd=111711917619

#### JLNY

##### Active Member
While I agree with Nigel, if you wanted to get a bench power supply for short testing and possibly for general use too, I would recommend one of the 0V to 30V, 0A to 10A linear power supplies linked below. They are a reasonable price- I have three.

I have seen quite a bit of short testing over the years using high constant current power supplies and infra red cameras. At one time we received a large batch of multi-layer printed circuit boards that had shorts.

spec

Is that one linear? Unless they are specifically billed as being linear, I think they are usually switching PSUs inside. Probably not a big deal either way for the OP, but I usually go linear when I can to avoid RF noise. I have a linear one (a Tekpower TP-3003D) that's rated to 3A, although I think they have ones rated to 5A now. I have had mixed results with these cheapies over the years: I've used the aforementioned linear one for years and I've never had a problem with it, but I once ordered a 50V-rated switching supply ("Skypower," I think) and it started arcing and billowing smoke the second time I turned it on.

After that, I ponied up the cash for a monstrous 0-60V, 0-15A HP 6274B linear supply. I still use the Tekpower sometimes, though.

HP tends to be overpriced but good quality. The cheaper HPs tend to have puny current capacity, though. I think Kepco and Lambda are other good brands of lab supplies, and they don't go for too much on ebay. I also recently got a massive 600V Sorensen unit for some high voltage work with tube amplifiers.

The great thing about lab-grade supplies is that they are built like tanks, so they often outlive the labs they are used in. If you can deal with the slightly larger size and ugly appearance of some of them, getting a used power supply can be a decent idea.

After a couple minute of searching:

http://www.ebay.com/itm/Hewlett-Pac...740393?hash=item3ab8ee7ca9:g:qD0AAOSwf-VWbMK-

http://www.ebay.com/itm/NEW-Kepco-J...369941?hash=item35ffd44c55:g:lRgAAOSwIUNXFmMW

http://www.ebay.com/itm/Lambda-EMI-...242052?hash=item51f4225684:g:L1IAAOSwOgdYrNbC

http://www.ebay.com/itm/Kepco-JQE-5...730018?hash=item27fe925f22:g:NpcAAOSwrklVQ6oZ

I'm sure there are lots more that would be better suited to your exact criteria if you ran a search of your own.

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#### spec

##### Well-Known Member
You certainly can't complain about the price!
Yes, and they are nice to use and much smaller than the pictures would suggest.

The other thing is that accessibility is good and they use standard technology components so if you do get a problem they are easy to fix.

There is also a switch mode version which is built to a high standard and design and is even smaller, lighter and cheaper.

If you were wanting to charge batteries or light up some LED, drive a motor etc, I would go for the switch mode version.

spec

#### spec

##### Well-Known Member
Is that one linear?
see post #3

Unless they are specifically billed as being linear, I think they are usually switching PSUs inside.
When you buy anything from any source you have to do your homework

Probably not a big deal either way for the OP, but I usually go linear when I can to avoid RF noise.
That is why I recommended a linear power supply

I have a linear one (a Tekpower TP-3003D) that's rated to 3A, although I think they have ones rated to 5A now.
UPDATE: My response was in error and has been deleted- apologies to you.

I have had mixed results with these cheapies over the years:
That is a sweeping statement.

At work we had all sorts of problems with famous-make power supplies that cost the earth. Two common faults were the output lurching up to around 60V at switch on and the other was that the output capacitance stored such massive charge so the power supply cant respond to an overload current before the device under test got damaged. Another big problem was input output isolation. My son has recently bought two famous name and expensive power supplies- both were faulty.

I've used the aforementioned linear one for years and I've never had a problem with it, but I once ordered a 50V-rated switching supply ("Skypower," I think) and it started arcing and billowing smoke the second time I turned it on.

After that, I ponied up the cash for a monstrous 0-60V, 0-15A HP 6274B linear supply. I still use the Tekpower sometimes, though.

HP tends to be overpriced but good quality. The cheaper HPs tend to have puny current capacity, though. I think Kepco and Lambda are other good brands of lab supplies, and they don't go for too much on ebay. I also recently got a massive 600V Sorensen unit for some high voltage work with tube amplifiers.

The great thing about lab-grade supplies is that they are built like tanks, so they often outlive the labs they are used in. If you can deal with the slightly larger size and ugly appearance of some of them, getting a used power supply can be a decent idea.
Not sure what the basis of this is

You appear to be countering my recommendation without any good reason.

spec

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#### JLNY

##### Active Member
You are being a nuisance and hanging on the shirt tails of my recommendation without any sense.
Whoa, hey, I'm sorry, that's not what I meant by that. I was suggesting an alternative, not trying to bash your recommendations.

1. I said Tekpower, not Tektronix. I bought it brand new for maybe $40 or so on amazon. I don't know if that exact model is sold anymore, but there are lots of very reasonably priced ones available. Tekpower as far as I know is a more budget brand very similar to the one you mentioned. It is a 3A-rated supply specifically billed as being linear. Here it is pictured below: 2. If the supply you linked to is a 10A linear supply, then why is the weight listed as only 6 lbs? That seems really light for a 300W linear supply, hence why I think it might be a switcher. I weighed my 90W TP-3003D, and it weighs 7.75 lbs. 3. Unless the OP is doing RF work or something similar, it is probably irrelevant whether they get a linear or switching PSU, but I thought it was worth mentioning the difference and why one would choose one over the other. 4. How is relating a bad experience I had with one a sweeping statement? saying something like "all cheap power supplies are bad" would be a sweeping statement, but that's not what I said. I agree that the OP should do his homework before buying anything. 5. I recommended the idea that the OP might also consider a secondhand lab supply. I know plenty of folks who use older lab PSUs that are 30-40 years old without issue, and the OP mentioned the person in the video using an HP The drawbacks, as I mentioned, are large size The OP mentioned the person in the video using a HP supply. I apologize if I came across as dismissing your suggestion. I was merely mentioning this as something to consider alongside getting a new one. Sincerely, JLNY Last edited: #### spec ##### Well-Known Member Most Helpful Member Whoa, hey, I'm sorry, that's not what I meant by that. I suggesting an alternative, not trying to bash your recommendations. To answer you questions, though: 1. I said Tekpower, not Tektronix. I bought it brand new for maybe$40 or so on amazon. I don't know if that exact model is sold anymore, but there are lots of very reasonably priced ones available. Tekpower as far as I know is a more budget brand very similar to the one you mentioned. It is a 3A-rated supply specifically billed as being linear. Here it is pictured below:
View attachment 104562

2. If the supply you linked to is a 10A linear supply, then why is the weight listed as only 6 lbs? That seems really light for a 300W linear supply, hence why I think it might be a switcher. I weighed my 90W TP-3003D, and it weighs 7.75 lbs.

3. Unless the OP is doing RF work or something similar, it is probably irrelevant whether they get a linear or switching PSU, but I thought it was worth mentioning the difference and why one would choose one over the other.

4. How is relating a bad experience I had with one a sweeping statement? saying something like "all cheap power supplies are bad" would be a sweeping statement, but that's not what I said. I agree that the OP should do his homework before buying anything.

5. I recommended the idea that the OP might also consider a secondhand lab supply. I know plenty of folks who use older lab PSUs that are 30-40 years old without issue, and the OP mentioned the person in the video using an HP The drawbacks, as I mentioned, are large size The OP mentioned the person in the video using a HP supply.

I apologize if I came across as dismissing your suggestion. I was merely mentioning this as something to consider alongside getting a new one.

Sincerely,
JLNY
Thanks for your reply JLNY- I obviously misunderstood the objective of your post and my apologies for that, especially as I find your posts generally constructive and informed.

But, can I assure you that the power supply I recommended is definitely a linear power supply and it has a sizable mains transformer too.

I also support your view that for a professional environment I would not even consider any power supply that was not from one of the mainline manufacturers. But for hobby work the recommended power supply is ideal- I would say.

spec

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#### spec

##### Well-Known Member
1. I said Tekpower, not Tektronix. I bought it brand new for maybe \$40 or so on amazon. I don't know if that exact model is sold anymore, but there are lots of very reasonably priced ones available. Tekpower as far as I know is a more budget brand very similar to the one you mentioned. It is a 3A-rated supply specifically billed as being linear. Here it is pictured below:
View attachment 104562

2. If the supply you linked to is a 10A linear supply, then why is the weight listed as only 6 lbs? That seems really light for a 300W linear supply, hence why I think it might be a switcher. I weighed my 90W TP-3003D, and it weighs 7.75 lbs.
Appologies again. I was in a rush when I reacted to your post and there has been some other things going on that influenced me.

Tekpower is a badge version of the generic power supply that is made by a big company in the east and is the basis of a whole family of low-cost linear power supplies, including the version that I recommended. The various versions are 0 to 15V, 0 to 24V.. with maximum current options of 0 to 1A, 0 to 2A, 0 to 5A, and 0 to 10A.

This generic power supply is badge engineered by many retailers, some well respected.

The control electronics are 741 opamps and 2N3055 output transistors, although this can vary. Some time, I will trace out the circuit, as a matter of interest.

The readouts are standard hi-tech boards, like you see on eBay etc.

The early readouts were LED, but LCD readouts are taking over- mine are LED.

As far as I can tell, the transformer is tapped and switched to reduce dissipation and the higher power versions have thermally controlled fans.

The standard of soldering/wire routing can be substandard on some examples of the power supply, but the majority are fine. Incidentally, there are a number of tear-downs on YouTube.

The calibration of the current and voltage meters can be out too, but it is a simple matter to calibrate them against your multi meter, using presets which are fitted to the power supplies,

As I said, I bought three of the power supplies expecting the worst. My plan was to re-engineer the electronics (the case, transformer, heat sink, fans, and controls are the expensive/difficult part of a power supply). But, I was pleasantly surprised by the units I bought, and they arrived within three days too. So I just use them as... bench power supplies.

I was planning to replace the fine and coarse voltage and current controls with ten turn pots, but the original pots are so nice to use that I probably won't bother.

On the down side, these power supplies do over volt to a degree at switch-on. I aim to get around that by fitting a switch that disconnects the output, like you see on some expensive power supplies

spec

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#### MikeMl

##### Well-Known Member
If the goal is to smoke everything in the shorted path, a 12V car battery (almost unlimited current available) works well. You can use an automotive headlight (either or both of the filaments) as a ballast resistor to prevent fires...

#### spec

##### Well-Known Member
This is the highest current switch mode power supply that I identified as suitable for home use in a mini investigation about a year ago The build standard and design are excellent, according to tear-downs on YouTube. Once again, it is a generic design from a big eastern company.

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#### Nigel Goodwin

##### Super Moderator
If the goal is to smoke everything in the shorted path, a 12V car battery (almost unlimited current available) works well.
The problem with that is if the S/C 'blows off' (which is quite possible) you then have 12V (with very high current capability) directly across your 3.3V supply line. This will destroy pretty well every I/C on the board, and perhaps a lot more stuff as well.

Incidentally, a common fault in these types of cases are SM capacitors S/C.

#### JLNY

##### Active Member
Appologies again. I was in a rush when I reacted to your post and there has been some other things going on that influenced me.

Tekpower is a badge version of the generic power supply that is made by a big company in the east and is the basis of a whole family of low-cost linear power supplies, including the version that I recommended. The various versions are 0 to 15V, 0 to 24V.. with maximum current options of 0 to 1A, 0 to 2A, 0 to 5A, and 0 to 10A.

This generic power supply is badge engineered by many retailers, some well respected.

The control electronics are 741 opamps and 2N3055 output transistors, although this can vary. Some time, I will trace out the circuit, as a matter of interest.

The readouts are standard hi-tech boards, like you see on eBay etc.

The early readouts were LED, but LCD readouts are taking over- mine are LED.

As far as I can tell, the transformer is tapped and switched to reduce dissipation and the higher power versions have thermally controlled fans.

The standard of soldering/wire routing can be substandard on some examples of the power supply, but the majority are fine. Incidentally, there are a number of tear-downs on YouTube.

The calibration of the current and voltage meters can be out too, but it is a simple matter to calibrate them against your multi meter, using presets which are fitted to the power supplies,

As I said, I bought three of the power supplies expecting the worst. My plan was to re-engineer the electronics (the case, transformer, heat sink, fans, and controls are the expensive/difficult part of a power supply). But, I was pleasantly surprised by the units I bought, and they arrived within three days too. So I just use them as... bench power supplies.

I was planning to replace the fine and coarse voltage and current controls with ten turn pots, but the original pots are so nice to use that I probably won't bother.

On the down side, these power supplies do over volt to a degree at switch-on. I aim to get around that by fitting a switch that disconnects the output, like you see on some expensive power supplies

spec
No worries. You flatter me with your praise, and I was honestly terrified myself that I had offended you. You are a good engineer, and I would feel badly if I were to get on bad terms with you or any of the regulars on this forum. Think nothing of it, and we can write off the whole thing as a miscommunication.

Yes, from my Tekpower I can definitely attest that the construction of many of these generics is generally pretty good. It has a similar construction, andI can hear it audibly switching taps on the transformer as the voltage is turned up. It is still my go-to supply for most things that don't need the massive power (and super-loud fan) from my HP supply. I've never really taken the time to examine them closely inside, so it sounds like you are fairly knowledgeable about them.

I've always wondered about the turn-on characteristics of these supplies, but until recently I didn't have a storage scope to test it. Interesting that they overshoot a little. I wonder if they also do that when switching ranges as well? Maybe I'll check that tonight.

I have no idea what made that one switcher blow up on me, but I do recall that it happened when I tested it connected to a fairly heavy load that probably would have tripped the current limiting. My only theory was that there may have been some issue with the current limiting on startup that caused the unit to go over current and fail.

The panel meters on mine are LCDs with a green backlight. I've found that the panel meters on mine are actually surprisingly well calibrated. I have found that it is generally within a tenth of a volt or so of my handheld, but force of habit has trained me to always check it manually anyway.

Actually, the reason this habit is so ingrained in me (although it is a good habit for anyone) was that the first real bench supply I learned on was, if memory serves, a crusty old Power Designs TW-5005 dual supply. The left panel read about 10% high, and the right read almost 10% low. IIRC, the feedback for the voltage regulation in that supply worked in such a way that if the wipers in the scratchy old pots for the voltage adjustments skipped and went open circuit, the supply would spike all the way to 50V and usually blow up whatever you were working on. Hehe, that's a subtle but important failure mode to keep in mind for anyone designing their own bench supply!

#### JLNY

##### Active Member
Okay, so I can confirm that my TP-3003D does have some overshoot on turn on. I tried measuring for any transients during the range switches, but I didn't find anything obvious.

Here is the TP-3003D at turn on, set to 5V, and no load connected:

Here is the range transition at around 8V or so (not a very accurate test, basically I just started the pot at about 7V and flicked it up as fast as I could turn it):

I'm not sure how I could do this test accurately without doing modifications to the supply. You could probably go into the case and splice a control signal in place of the pot to rapidly change the voltage setting. Either way, I couldn't see any sudden jump up or down in the output at the transition. I'm guessing that the caps on the unregulated side of the secondary are valued large enough that they can absorb the transition, but maybe I'll have to re-run the test when the unit is under a load. (EDIT: tried it under an ~2A load, a 4-Ohm resistor. no change)

And for a bit of comparison for the first plot, here is my HP 6274B for the same startup test with it set to 5V, and no load connected. I have no idea what that sudden drop before it climbs up is, but I tried turning it on multiple times and it seemed to happen pretty consistently. Hmm. On a side note, I think the trigger level on my scope may need to be recalibrated.

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#### gica69

##### New Member
While I agree with Nigel, if you wanted to get a bench power supply for short testing and possibly for general use too, I would recommend one of the 0V to 30V, 0A to 10A linear power supplies linked below. They are a reasonable price- I have three.

I have seen quite a bit of short testing over the years using high constant current power supplies and infra red cameras. At one time we received a large batch of multi-layer printed circuit boards that had shorts.

spec

I was looking at these models also. Any ide what the difference is between this one http://www.ebay.com/itm/201664929313?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649 and this one which has an additional AMP button I think it's a high and low amp http://www.ebay.com/itm/30V-10A-110...=8e2adfc3379145b48a0bc6efe5a9b32b&pid=100150&

#### gica69

##### New Member
The problem with that is if the S/C 'blows off' (which is quite possible) you then have 12V (with very high current capability) directly across your 3.3V supply line. This will destroy pretty well every I/C on the board, and perhaps a lot more stuff as well.

Incidentally, a common fault in these types of cases are SM capacitors S/C.

I agree, that's why I first need to find the actual voltage that goes through that particular circuit. Wasn't thinking of actually putting 12v through 3.3V. But the guy in the video used the 10A to have current drawn from it and that's why I asked if 5A would be enough, and it seems that 10A is a better choice. I already replaced the caps there were three bad ones, didn't check the diodes yet or the transistors. But I am basically experimenting with this project, and am buying up some equipment in the process, I am the eternal hobbyist when it comes to anything.

#### gica69

##### New Member
While I agree with Nigel, if you wanted to get a bench power supply for short testing and possibly for general use too, I would recommend one of the 0V to 30V, 0A to 10A linear power supplies linked below. They are a reasonable price- I have three.

I have seen quite a bit of short testing over the years using high constant current power supplies and infra red cameras. At one time we received a large batch of multi-layer printed circuit boards that had shorts.

spec

Was also looking at these http://www.ebay.com/itm/13205911261...me=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649 it offers many advantages, you can view the preset voltage, input voltage, output voltage, the preset current, output current, output power, etc. on the output state remind area, you can see that output opens or not, the state of constant voltage and constant current, output is normal or not, the key is locked or not, and the current data groups that is being used. On the setting data interface, you can adjust overvoltage value, overcurrent value, over-power value, data set and LCD brightness. And it's really well calibrated from the factory. Well worth the money.
My only dilemma is that it comes with a step down module and it needs an ac to dc supply to power it. So as it has Input Voltage listed at DC6-40V. Was thinking of getting a dc power supply that would allow me to use it with this contraption.
So I was looking at these http://www.ebay.com/itm/AC100V-240V...hash=item2825aed2a8:m:mpug97Vr562FptQfZdfX1RQ but it's not a linear one it's a switch. So waiting for more great advice. Thanks in advance.

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#### spec

##### Well-Known Member
Hi G69,

The two power supplies that you link are essentially the same generic 0 to 30V, 0 to 10A linear power supplies that I mentioned in post #3.

The AMP button on the second linked power supply simply changes the range of the current digital read out from Amps to miliamps (as far as I can tell). A miliamp read out would be useful for setting low currents, but a simple switch seems to double the price.

spec

#### spec

##### Well-Known Member
Was also looking at these http://www.ebay.com/itm/13205911261...me=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649 it offers many advantages, you can view the preset voltage, input voltage, output voltage, the preset current, output current, output power, etc. on the output state remind area, you can see that output opens or not, the state of constant voltage and constant current, output is normal or not, the key is locked or not, and the current data groups that is being used. On the setting data interface, you can adjust overvoltage value, overcurrent value, over-power value, data set and LCD brightness. And it's really well calibrated from the factory. Well worth the money.
I don't know about these units- you do know that they are switch mode? But I would expect them to perform well.

My only dilemma is that it comes with a step down module and it needs an ac to dc supply to power it. So as it has Input Voltage listed at DC6-40V. Was thinking of getting a dc power supply that would allow me to use it with this contraption.
So I was looking at these http://www.ebay.com/itm/AC100V-240V...hash=item2825aed2a8:m:mpug97Vr562FptQfZdfX1RQ but it's not a linear one it's a switch. So waiting for more great advice. Thanks in advance.
These switch mode power supplies are also generic. I have no experience of the specific power supply that you link, but base on other similar power supplies, it should be fine. Be aware though that you will then have two sources of switching noise.

Just three words about cost effective test equipment: keep it simple. I have experienced no end of test equipment with all the bells and whistles that has been a nightmare to use and the reliability has been a poor too- I am not talking about the superb instruments from the big test equipment manufactures though.

spec

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