Mini review: Tenma 72-8350A small footprint bench power supply - Page 1
Forum section: electronics / testgear

author: zapta
author_rank: Super Contributor
timestamp: June 03, 2015, 03:28:34 pm
content: I got recently this little bench power supply and l like it a lot so I thought I should share.This is the Tenma 72-8350A which the 20V/5A version of the power supply Mike reviewed herehttps://www.eevblog.com/forum/reviews/tenma-72-8345-bench-psu-review/This is an upgraded model (hence the 'A') suffix and the original version seems to be discontinued. The display is now white on black with excellent contrast, it shows the current limit setting without having to short the output and a click or two on the voltage and current button gets you into one of two course adjustment modes. Internally it looks just the same as in Mike's review.Fro reference, I tried the Korad KA3005D and didn't like it. Bulky, complex panel, and once every few times I turned it on the top cover made a loud sudden noise, probably from magnetic field change in the transformer below it.Like:* Compact, light, small footprint* Large clear display* 100W output (way more than I need, Mine is 20V 5A, they also have 60V 1.6A and 36V 3A versions.).* Accurate voltage/current settings and readings.* Simple and intuitive to operate.* Output on/off switch (my HP E3610A doesn't have it).* Good construction overall.* Reasonable price (~$160).Doesn't like:* Can't set current limit below 150ma (I often goes down to 40ma limit when bringing up boards).* No post binds. (I am using thesehttp://radioshacklb.com/index.php?route=product/product&product_id=2656)* Handle (removed).* No UL certification.Overall this power supply is a very good fit for my hobby needs. I think I will put my HP E3610A and Protek 303 for sell, and use only this one.

author: echomancer
author_rank: Contributor
timestamp: June 07, 2015, 03:13:55 am
content: I purchased one of these today but have noticed an odd behavior. If I set the voltage to say 5.00, the unit will show the output voltage as 5.32. it's as though the set point isn't calibrated the same as the actual VO. This happens whether there is a load or not. It seems no matter what, it is always displaying .32V above the set point. Have you noticed this? Have you discovered any type of calibration point? I will get my Fluke 287 out tomorrow to compare values. A third of a volt over is no fun.

author: zapta
author_rank: Super Contributor
timestamp: June 07, 2015, 05:57:54 am
content: Quote from: echomancer on June 07, 2015, 03:13:55 amI just tested mine at 5V and 20V, no load. I get at most one or two digits discrepancy between the set voltage and actual voltage (the voltage display and my Fluke are in close agreement). 0.32V seems way too high.It reminds me one of Dave's episode about the disconnected sense line. This power supply also has internal sense lines, visible in one of the pictures I posted. I wonder if one of them disconnected. That's a long shot.BTW, I just found that if I just click once on the voltage or current knobs it display the set value for a second or two. Very nice. Before, I used to turn them a click to see the set value.

author: GlowingGhoul
author_rank: Regular Contributor
timestamp: June 07, 2015, 06:36:19 am
content: The "A" in the model name stands for "approximate".

author: zapta
author_rank: Super Contributor
timestamp: June 07, 2015, 06:54:40 am
content: Quote from: GlowingGhoul on June 07, 2015, 06:36:19 amI assumed it stands for "awesome".

author: rolycat
author_rank: Super Contributor
timestamp: June 07, 2015, 08:45:11 am
content: Quote from: zapta on June 07, 2015, 06:54:40 amI have an older version of this PSU. It is also a 20V 5A unit but only has three-digit meters. On the other hand, the current limit works down to 3mA.It's definitely not "awesome", though. It's not a bad unit while it's working but it has packed up twice, on both occasions due to failed capacitors on the low voltage side. From your pictures it appears that you have the same C(r)apXon brand, so be prepared to replace them.

author: GreyWoolfe
author_rank: Unknown
timestamp: June 07, 2015, 11:50:50 am
content: I am amazed that CapXon is still around. They have to be the world's worst capacitors. I don't think I would get rid of my E3610 for the Tenma. By the way, Zapta, if you really want an output on/off switch, just add one.

author: echomancer
author_rank: Contributor
timestamp: June 07, 2015, 11:57:36 am
content: I'll be heading back to MicroCenter today to exchange this for the other one they have in stock - hopefully this is just a bad sample and not indicative of the whole line. I've also made a video to demonstrate the issue (linked below). I also learned that even though the unit appears to come up with the output turned off, voltage is infact present during startup.

author: Fraser
author_rank: Super Contributor
timestamp: June 07, 2015, 12:50:49 pm
content: I bought one of these as a customer return a couple of years ago. The fault was pretty obvious...... the switching controller has self destructed in a big wayI bought a replacement chip (thankfully its a COTS device) and new capacitors, but I have yet to bother fitting them. Other priorities came higher up on the 'to-do' list.I do like the small footprint and it will be a useful little power supply to have around for those occasions when you just want to quickly apply power to a circuit without having to go to the garden office to do so. Lazy I know, but convenience is kingAurora

author: zapta
author_rank: Super Contributor
timestamp: June 07, 2015, 12:57:07 pm
content: Quote from: rolycat on June 07, 2015, 08:45:11 amI don't mind doing it now as a preventive measure. Which capacitors should I replace?

author: GreyWoolfe
author_rank: Unknown
timestamp: June 07, 2015, 01:21:15 pm
content: All that say CapXon.

author: artag
author_rank: Super Contributor
timestamp: June 07, 2015, 03:44:32 pm
content: Quote from: zapta on June 03, 2015, 03:28:34 pmMy Farnell B30/10 makes a loud crash when it's switched on, as the top steel plate rattles in the extrusions. It's one of the things I like best about it.

author: zapta
author_rank: Super Contributor
timestamp: June 07, 2015, 03:53:02 pm
content: Quote from: echomancer on June 07, 2015, 11:57:36 amI tested it on mine, and this is the output voltage when powering on with 20V setting and no load. I think I can live with that.Quote from: GreyWoolfe on June 07, 2015, 01:21:15 pm

author: nctnico
author_rank: Super Contributor
timestamp: June 07, 2015, 04:06:06 pm
content: Such a spike can be big enough to kill components. What happens with 3.3V or 5V at the output?

author: rolycat
author_rank: Super Contributor
timestamp: June 07, 2015, 04:10:10 pm
content: Quote from: zapta on June 07, 2015, 03:53:02 pmIt was the large caps on the low side that failed on my unit, but I have a little pot of failed/bulged capacitors of various sizes and voltages from several boards and 90% of them are CapXon.They must be unbelievably cheap to be so infamously useless and yet so common.

author: zapta
author_rank: Super Contributor
timestamp: June 07, 2015, 05:02:02 pm
content: Quote from: nctnico on June 07, 2015, 04:06:06 pmIt's going down to -0.4V on the negative side and 2.6 on the positive.Quote from: rolycat on June 07, 2015, 04:10:10 pmI am lucky in general so chances are I got good caps that will not fail. I can also tie to it a rabbit's foot just to be on the safe side.BTW, can I predict the failure using a IR camera? Do caps get hot before they fail? If not, can I test the caps in circuit? For example with DE-5000?

author: echomancer
author_rank: Contributor
timestamp: June 08, 2015, 01:42:07 am
content: I returned my unit today for a new one and all is right with the world again.

author: kopashoff
author_rank: Newbie
timestamp: December 21, 2017, 12:21:58 pm
content: Hi everyone!I have recently purchased 72-8350A. It shows voltage, but it does not show current consumption. What it can be?I have opened it, but have not found any visual defects.I can not return it, as i purchased it on ebay without warranty.Thanks

author: Fraser
author_rank: Super Contributor
timestamp: December 21, 2017, 12:56:31 pm
content: The output to the terminals is switched on and off by a MOSFET. Possibly the MOSFET has died.I have some schematics for these power supplies. If you PM me an email address I will send them to you.Fraser