Hanmatek Power Supply issue?

Thread Starter

RebelJD

Joined Nov 25, 2018
12
I recently purchased a Hanmatek HM305 power supply. It has some nice features but it has an "undocumented feature" I don't understand. Perhaps someone knows a little more about this.

It works fine stand alone, but when I connect other devices like a scope or lap top to the circuit I building/testing I've had a lot of issues damaging components. I thought at first I might have an issue with the 120vac source to the power supply being wired wrong, but it is fine. So I took a DVM and measure the DC output of the power supply to the earth ground of the 120vac source and what I found was surprising. With neg lead of the DVM on earth ground I get -10dc on the neg output post of the power supply. (the power supply was set at 10v). And, I get a solid 0v on the pos output post of the power supply. So it seems the pos output of the power supply is tied to ground. Not an issue when the power supply is floating on an isolated circuit, but when combined with other equipment its a problem. I did the same measurements on my old analog DC power supply and did not measure any voltage on either post.

Has anyone out there had an issue like this? Am I doing something wrong?

Smoking mad.......
Jim
 

MrChips

Joined Oct 2, 2009
22,505
Laboratory bench supplies ought to be floating.

Use an ohmmeter and check resistance between the AC plug E and all three banana posts.

Look to see if there is a grounding strap installed somewhere between + and GND.
 

MrChips

Joined Oct 2, 2009
22,505
I see that the Hanmatek HM305 PSU does not have a GND post.
In any case, test for isolation from the AC earthing prong.

1609779269962.png
 

Thread Starter

RebelJD

Joined Nov 25, 2018
12
Thanks Mr. Chips, I should have made that test before I posted. There is a dead short from the positive post to the earth ground prong. This is not a problem when using it stand alone, but when using in a circuit with a scope, signal generator etc it is a problem. I bought this thru Amazon which makes it tough to contact the OEM directly.

Thanks for your help.
Jim
 

MrChips

Joined Oct 2, 2009
22,505
Thanks Mr. Chips, I should have made that test before I posted. There is a dead short from the positive post to the earth ground prong. This is not a problem when using it stand alone, but when using in a circuit with a scope, signal generator etc it is a problem. I bought this thru Amazon which makes it tough to contact the OEM directly.

Thanks for your help.
Jim
There should not be a short from +ve to GND.
Open the unit and look for the short.

We find a lot of strange things out there. We bought 15 power supplies and all of them came with power cables with L and N reversed from standard.
Another brand PSU came with the fuse on the N side of AC LINE connection on all units.
Always check your power wring before using.
 

Thread Starter

RebelJD

Joined Nov 25, 2018
12
Amazon is sending me a replacement. Bad thing is I fried two Arduino Nano's and possibly a USB port on my laptop before I figured out what was going on. I did check to make sure the neg post was not tied to ground when I got it, (make sure is was floating) never thought to check the positive post.

Like you said, check everything before you use it. Maybe others can learn from this.....

Thanks again,

Jim
 

DickCappels

Joined Aug 21, 2008
6,788
AG Again, please stop bashing China. I have developed several products that were successfully manufactured in high volume and high quality in China. The trick is to know your vendor, and where applicable provide suitable training and oversight. China, Korea, Taiwan, Thailand and probably many other countries can all produce excellent products if given incentives and oversight.
 

Audioguru again

Joined Oct 21, 2019
2,374
Many "Western" companies have their excellent products made in China. Their designs are done in The West and are reliable and work well. Quality control is also good at their Chinese factories.

I worked mostly with European and American companies.
In 1982 I worked with a product made in Korea by Goldstar that had the worst design and worst hand-soldering I have ever seen. Goldstar designs and production have improved tremendously over the years and now it is called LG Electronics. LG means Lucky Goldstar.

My new large screen 4k TV has the Western name Westinghouse on it and has failed during its one year warranty. The customer support people have bad English on the phone and on e-mails and they say they do not repair the TV. I am told to make photos of its nameplate, serial number and photos of it thrown away in the recycling trash then they will send me a refund. Its Nameplate says it is designed and made by a Chinese company.
 

DickCappels

Joined Aug 21, 2008
6,788
In that case Westinghouse should be ashamed of the poor job they did while cultivating their partner and the design.

I worked with LG on a few things in the 1990's and while there were funny moments on the production line and one of the labs I was very pleased at their willingness to learn and try new things, change their procedures and to cooperate to take care of our needs, so as you said they must have improved a lot. One of the members of out team had some really bad experiences with them earlier and was quite discouraging to talk with.

One day our project team arrived at their factory and their sales guy said "We aren't Lucky Goldstar after this week. Out new name is 'LG". One of the team asked "Then what does LG stand for?" And the sales guy said "Nothing, its just LG". Lost in translation.
 

metermannd

Joined Oct 25, 2020
82
...by Goldstar that had the worst design and worst hand-soldering I have ever seen...
That just reminded me of the Goldstar monitor I had for my C64 for a while... it had extremely flaky vertical linearity. It started out OK when cold, but as it warmed up, there was some bad jitter, then when it finally reached 'end stage', the top of the screen was off the CRT with visible gaps between the scan lines. The tech I bought it from couldn't understand why I had so much trouble with it... my dad wound up buying a small 13" TV to use as a monitor instead.
 

Thread Starter

RebelJD

Joined Nov 25, 2018
12
Did not intend this to be a discussion on China, but here is my recent experience. I wanted to contact Hanmatek directly but could not find a website. So I contacted Amazon via a chat session. They tried to contract the seller while I waited, but had not luck. So they gave their phone number in China. I told the Amazon rep I was not making a phone call to China so they agreed to just exchange the power supply. I got the new power supply and it is fine, no short to earth ground from the pos terminal.

It's becoming more and more prevalent for hardware design to come out of China, and I don't see that changing anytime soon. If I was enrolling in college today (I'm an retired EE) I would lean towards a software career not a hardware career. Just an observation.

This is actually a very nice power supply for the price. Unfortunately with all the stuff that comes from China and sold by places like Amazon, customer service is basically non-existent. So you struggle thru things like this the best you can.
 

rsjsouza

Joined Apr 21, 2014
266
If possible, would you mind sharing photos of the power supply's internals? It would be interesting to see it.

In my opinion, the major reason for the bad reputation is two-pronged: this is a very niche market and the scattershot approach to resell a product under many brands is not conducive to invest in production refining and quality control. The original project may be a really good design, but it becomes watered down through the chain of manufacturing houses with varying degrees of workmanship and stable supply chain of parts. That is also reflected on the scant customer service and official representation outside of the home country. This is obviously not applicable to the larger manufacturers (Siglent, Rigol, GWI, etc.).

This also happens on the long term production - something that is good today may be poorly made in a few months or years. That has happened with anyone and not only China, however.
 

MrChips

Joined Oct 2, 2009
22,505
That is a nice PSU. One thing that is missing that you should have on every lab bench PSU is a banana GND post connected to earth ground. With this one can choose to have a floating supply, a positive supply voltage, or a negative supply voltage.
 

Thread Starter

RebelJD

Joined Nov 25, 2018
12
If possible, would you mind sharing photos of the power supply's internals? It would be interesting to see it.

In my opinion, the major reason for the bad reputation is two-pronged: this is a very niche market and the scattershot approach to resell a product under many brands is not conducive to invest in production refining and quality control. The original project may be a really good design, but it becomes watered down through the chain of manufacturing houses with varying degrees of workmanship and stable supply chain of parts. That is also reflected on the scant customer service and official representation outside of the home country. This is obviously not applicable to the larger manufacturers (Siglent, Rigol, GWI, etc.).

This also happens on the long term production - something that is good today may be poorly made in a few months or years. That has happened with anyone and not only China, however.
Here are some photos of the new power supply. I was hesitant to remove the cover on the old one for fear of voiding a warranty.

My first thought was positive banana plug some how came in contact with the hole in the case, but the front is plastic. I don't really see any place where the red wire comes closes to the chassis, but then again I didnt look inside the old one.
 

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rsjsouza

Joined Apr 21, 2014
266
Thank you very much for the photos. From the photos, it seems quite decently built.

In the past I had problems when one of the bypass transistors shorted itself with its heatsink, which created a ground loop and eventually blew an expensive setup of mine. Perhaps I would take this line of investigation.

All in all, it is great that Amazon set this scenario straight for you.
 
A bench power supply is certainly something you don't want to cut corners on, however attractive and cheap the equipment might look.
A lot of the stuff by the big names in electronic equipment is bought in or manufactured in the Far East, but we always assume that it has passed all the local regulations and that things like the CE mark is genuine, plus the company that puts their name on it has also done the checks.
The tale by Mr Chips highlights some of the dangers of unseen manufacturing defects.
Whether it's a bench supply, a soldering iron or a plug top power supply, you aren't far away from 240V AC or whatever.
If it has already cost the user a couple of Nano's and a laptop port, that should be lesson enough.
Anything that goes near mains electricity, be it a bench supply or a multimeter really needs to be up to scratch.
 
FYI: The setpoints are usually derived from the + of the supply. External setpoints and measured values on power suppleis that I have purchased (Xantech) have their 0-5 inputs (Setpoint) and 0-5 outputs (measured value) common to the (+) binding post.
You either need to buy it with isolated I/O or use it with an isolated output.

A power supply from Kikisui had a very visible strap on the front to a ground post. Negative was grounded as purchased.

Both of these were like 40V, 30A supplies.
 
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