Thoughts on GW-Instek 3303S Supply?

[FastEddieFelson]

I'm a software guy who's been gradually getting into the hardware side of things the last few years. Got hooked by Arduino and have moved on (back?) a bit and am now trying to teach myself analog electronics and fundamentals. I don't have any equipment other than a multimeter. I'd really like to get a benchtop power supply and eventually I'll build one myself but for now I'm looking for recommendations on a commercial unit.

I've read a lot on the forum about the "cheap" Chinese PSUs but then I came across the threads on the ITT auction and all of the equipment on sale on eBay. Does anybody have any experience or thoughts on the GW-Instek 330S Supply? For ~$150 USD shipped it sounds like a good deal and presumably is better than the budget triple outlet Chinese supplies. Is this correct? Would a used one of these be a better investment for a newbie like myself than a new Chinese model? I'm interested in anyone's thoughts on it's quality, reliability and noise level.

Thanks!

[bitseeker]

Welcome to the forums, Eddie. There was another thread where someone reported seeing significant voltage overshoot on one of the channels. You may want to check that out by searching for the model via https://www.eevblog.com/forum/search/

Since you're in the US, you may want to explore used A-brand power supplies as well. There are many threads in the forum with power supply recommendations.

[saturation]

The prior model 3303 was a workhorse and was often reviewed and torn down in the forum, so you can see what's in it;  the 3303S is the successor and should be too.  Its common to use in schools because its durable and performs well, so long as the auction units are in good shape.  You can hold Instek to its spec sheet, and new units are $400+.

[Gary350z]

Here's my post about this supply (as mentioned by bitseeker):
https://www.eevblog.com/forum/chat/what-did-you-buy-today-post-your-latest-purchase!/msg1117271/#msg1117271

Edit: fixed my bad url.

[nctnico]

Fixed the URL for you (USE THE URL TAGS OR CLICK THIS BUTTON ):
https://www.eevblog.com/forum/chat/what-did-you-buy-today-post-your-latest-purchase!/msg1117271/#msg1117271

I have been eyeballing these power supplies as well. However the output spike is an absolute no-go for me (even though on the auxilary 5V output). It can and will damage circuits! What happens if you connect an extra capacitor -say 470uf- at the output? If that fixes it the PSU may be worth a look after all.

[Gary350z]

Fixed the URL for you (USE THE URL TAGS OR CLICK THIS BUTTON ):
https://www.eevblog.com/forum/chat/what-did-you-buy-today-post-your-latest-purchase!/msg1117271/#msg1117271

I have been eyeballing these power supplies as well. However the output spike is an absolute no-go for me (even though on the auxilary 5V output). It can and will damage circuits! What happens if you connect an extra capacitor -say 470uf- at the output? If that fixes it the PSU may be worth a look after all.

Thanks for the url fix and your opinion.
Please see my new post:
https://www.eevblog.com/forum/testgear/instek-gpd-3303s-power-supply-overshoot-opinion-wanted/

You can buy a version of this supply without the 5V channel. It's also cheaper.
A 470uf cap on the output fixes the overshoot problem, but you shouldn't have to do that with a brand new supply. Do you think the 470uf cap could cause any unwanted side effects?

[nctnico]

Thanks for testing. IMHO it wouldn't need a new thread.
Anyway if I buy one I'll probably get a used one from the ITT school through an Ebay seller. So I wouldn't mind adding an extra capacitor.

[Gary350z]

nctnico I just noticed your post count; 10485. Wow.

[nctnico]

FYI: I have limited myself to only one electronics related forum and the other two fora I visit see maybe 1/100000 of the activity EEVblog has  No Facebook, instagram, twitter or the likes.

[Gary350z]

So I wouldn't mind adding an extra capacitor.

What are your thoughts on adding the capacitor. Any bad side effects?
I put a 1000uf cap on the output which reduced the turn on spike even more, but it appears that as the spike reaches it's peak, and the cap is fully charged, when the spike starts falling after the peak, it drives the output negative; about -0.6V. What do you think?

[FastEddieFelson]

Here's my post about this supply (as mentioned by bitseeker):
https://www.eevblog.com/forum/chat/what-did-you-buy-today-post-your-latest-purchase!/msg1117271/#msg1117271

Edit: fixed my bad url.

Gary, does the overshoot problem just happen on the auxiliary 5V output when you turn it on? Any issues with any of the outputs after they're on? I'm assuming you measured this with an o-scope. Since I don't have one would there be any way for me to see this spike on the output of a unit I buy? The super quick spike you describe wouldn't show up on my DMM I'm afraid.

My other big question is how is the fan noise on yours? I tend to be sensitive to droning noises and I don't want something that's going to sound like an Airbus taking off if I can help it.

Thanks for responding guys. I certainly appreciate any advice I can get. I've got about $150 to spend on a PSU and I'd really like something that's relatively small, triple output and somewhat quiet. I'm thinking a used unit would get me more of these features than a new Chinese made unit. I've been waiting about 8 months and with the ITT sale it seems like now's a good time to buy.

[Fgrir]

My other big question is how is the fan noise on yours? I tend to be sensitive to droning noises and I don't want something that's going to sound like an Airbus taking off if I can help it.

Basing this on my 4303S, but the fan is pretty quiet when the supply is idle.  Not silent but no louder than any of the other fans in my office.  Put a moderate load on it and the fan does spin up and it gradually becomes the loudest thing in the room.  Not quite Airbus levels, but nobody would call it quiet.

[Kleinstein]

There are circuit schematics available for this supply. From this the channel 3/4 regulation is relatively slow and it look like it has a circuit intended for a controlled start up, that does not really work. So adding another 470 µF or so is not really fixing the root problem, but only dampen the spike. 

A true fix would need a more in depth change in the circuit (not necessarily large, but changing the control circuit) and thus needs a detailed simulation first. My first guess would be something like changing the CV mode compensation for output 3 and 4 in a way it is no going into deep windup any more. This could be as little as changing a capacitor (e.g. 10 nF -> 1 nF), adding a resistor in series with the old 10 nF cap to a different position.

[bitseeker]

I'm not sure if the older, GPC-3020, is better. It's the same channel configuration, but with analog meters. If it doesn't overshoot, there are a bunch of them on eBay right now for around US$45.

[Fgrir]

Interestingly, I don't see much difference between channels 3 and 4 on the schematic, but on my 4303S the behavior on channel 4 is just as well-controlled as channels 1 and 2.  Only channel 3 shows the initial spike and plateau on turn-on.
If my unit wasn't brand-new I'd probably crack it open to see if there is a missing component on channel 3...
Attached traces are for all four channels set to 5V 1A.

[calin]

Hah, right in time. My trusty GPS-4303 has started misbehaving yesterday evening. If I set CH2 to say 10V when output is off behaves OK, then I turn it on and it drops to something like 1-2V , the meter shows the correct 1-2V as it is but it is annoying.  Does anyone has the schematic for these power supplies ? If you do, please let me know if you can share it.


In rest, to stay on the thread topic, these are solid and nice power supplies. The 4303 was my work horse for long (4+ years) and I got it used. I have other more fancy but this was always on my bench, quiet, easy to use no fuss

[Gary350z]

Here's my post about this supply (as mentioned by bitseeker):
https://www.eevblog.com/forum/chat/what-did-you-buy-today-post-your-latest-purchase!/msg1117271/#msg1117271

Edit: fixed my bad url.

Gary, does the overshoot problem just happen on the auxiliary 5V output when you turn it on? Any issues with any of the outputs after they're on? I'm assuming you measured this with an o-scope. Since I don't have one would there be any way for me to see this spike on the output of a unit I buy? The super quick spike you describe wouldn't show up on my DMM I'm afraid.

My other big question is how is the fan noise on yours? I tend to be sensitive to droning noises and I don't want something that's going to sound like an Airbus taking off if I can help it.

Thanks for responding guys. I certainly appreciate any advice I can get. I've got about $150 to spend on a PSU and I'd really like something that's relatively small, triple output and somewhat quiet. I'm thinking a used unit would get me more of these features than a new Chinese made unit. I've been waiting about 8 months and with the ITT sale it seems like now's a good time to buy.

The overshoot only occurs on the 5V channel (ch3). Look at the other posts here showing that. I think you will need a scope to see the overshoot.

The fan noise is a bit loud. I think you will always have fan noise on a big linear power supply to keep it cool.

There is a 2 channel version of this supply that does not have the 5V channel (ch3); Instek GPD-2303S.

[Gary350z]

Does anyone has the schematic for these power supplies ? If you do, please let me know if you can share it.

GPD-3303S User Manual:
https://wiki.ntb.ch/infoportal/_media/labors/gpd-3303-manual.pdf

GPD-2303S/3303S/4303S Service Manual (schematic):
http://www.eltest.hu/pdf/GPD3303SM.pdf

[bitseeker]

The fan noise is a bit loud. I think you will always have fan noise on a big linear power supply to keep it cool.

Depends on the design of the supply. Fans are significantly cheaper than large heat sinks. I have some small HP ones that are passively cooled, around 30W, and several Power Designs ones, include a couple of triple channel models.  The largest one is a single-channel Power Designs 3650-S -- 180W and no fan. You can see the double heat sinks in the back of it at the link, above.

[cdev]

It looks like a very nice supply.

[djnz]

So I wouldn't mind adding an extra capacitor.

What are your thoughts on adding the capacitor. Any bad side effects?
I put a 1000uf cap on the output which reduced the turn on spike even more, but it appears that as the spike reaches it's peak, and the cap is fully charged, when the spike starts falling after the peak, it drives the output negative; about -0.6V. What do you think?

A side effect of the capacitor could be that current limiting could be affected. The energy stored in the capacitor could be dumped into your circuit, which could be a problem. To minimize this, if you do put a capacitor, you want it to be as small as possible to just correct the overshoot problem to the degree you want, but not any larger.

Also, the responsiveness of the power supply will obviously be affected with a capacitor. This is usually not an issue with manual hand-operated operation, but if you want to use the supply where you want rapid voltage transitions (and you will program it for this), then it might be an issue.

[Kleinstein]

I have looked at the schematics and did a simulation of the simplified (only CV mode) circuit for channel 3.

There are already 200 µF at the output, so adding another 500 µF is not so bad, as the regulation is slow anyway. However at least in the simulation the simple circuit for channels 3/4 is not regulating very well with a large capacitive load. Depending on the ESR it shows some ringing. The simulation also reproduces the spike on turn on from the output enable - the size depends on the ESR of the output capacitor. However a  cap with much lower ERS is not a real option as this would reduce stability.

In the simulation it works to add the usual phase boost to the feedback network, much like in the faster channels 1 and 2. For channel 3 this would be something like 50 nF in series with 1.5 K parallel to R712.
At least in the simulation this also improves stability and the speed of regulation. The spike on turn on is essentially gone (only about 1 V and thus usually below set voltage).

[henken]

In the simulation it works to add the usual phase boost to the feedback network, much like in the faster channels 1 and 2. For channel 3 this would be something like 50 nF in series with 1.5 K parallel to R712.
At least in the simulation this also improves stability and the speed of regulation. The spike on turn on is essentially gone (only about 1 V and thus usually below set voltage).

So, who will be first to test a fix like this? 

[calin]

Thanks Garry, I got these too also but the service manual no match. Mine is a GPS-4030 not programmable.  GPD series are programmable and all so I think the schematic (especially on the settings and control side of things are pretty different). I did not had the time to open it to check (too busy fidling with my Frankenstein style GPSDO

Quote from: Gary350z on Yesterday at 08:10:33 PM

GPD-3303S User Manual:
>https://wiki.ntb.ch/infoportal/_media/labors/gpd-3303-manual.pdf

GPD-2303S/3303S/4303S Service Manual (schematic):
http://www.eltest.hu/pdf/GPD3303SM.pdf

[bitseeker]

GPD and GPS are different. The schematics and parts lists aren't interchangeable from what I've seen.