Is my cheap amazon benchtop variable power supply floating?

Thread Starter

NotNu4U

Joined Jul 3, 2023
9
Hello I have taken 2 electronics class in university and find myself not knowing really what I am doing when it comes to selecting and using my own equipment.

I bought myself the 70$ Nankadf power supply on Amazon product number WPS3010H/B. I know it's cheap but im limited with money while in school.

It is a switch mode power supply and has three plugs in the front one ground, then POS and NEG. When I put my multimeter in continuity mode it seems the outputs are not connected to ground on the input chord that plugs into the outlet. I want to make sure this model is floating unless I tie it to ground. The user manual doesn't say anything about it.

The reason I want it to be floating is so I can practice using my oscilloscope and don't want to create a ground loop and blow my equipment up.

I am aware there are isolation transformers but when reading reviews online they are still referenced and connected to ground.

Pls lmk if I can do anything to better assist you with my question. Thank you
 

crutschow

Joined Mar 14, 2008
34,392
Isolation of a power supply does not refer to whether it is connected to safety/earth ground, it's whether the output is isolated from the main's power connections.
So if you measure no continuity between the power supply outputs and the main's plug connections then it is isolated.

The supply can be connected to the main's safety ground, which is okay, since that is a safety function to protect against accidental loss of isolation between the mains and the circuit.
 

dl324

Joined Mar 30, 2015
16,898
Welcome to AAC!
It is a switch mode power supply and has three plugs in the front one ground, then POS and NEG.
When there's a separate earth ground, the output should be floating.

I say should because there's no stopping manufacturers from doing something stupid. Like putting earth ground between the POS and NEG jacks. Back in the day, they put earth ground on the outside and made it easy to short it to NEG. They also made the spacing between them 0.75" so dual and triple banana plugs could be used.
HP6228B.jpg

The terminals on this power supply are about 0.8" apart, so dual banana plugs can't be used...
velleman3003.jpg
 

Thread Starter

NotNu4U

Joined Jul 3, 2023
9
hi NNU,
This is what an Amazon user reports.
E
Thank you for help, never h
Welcome to AAC!
When there's a separate earth ground, the output should be floating.

I say should because there's no stopping manufacturers from doing something stupid. Like putting earth ground between the POS and NEG jacks. Back in the day, they put earth ground on the outside and made it easy to short it to NEG. They also made the spacing between them 0.75" so dual and triple banana plugs could be used.
View attachment 297581

The terminals on this power supply are about 0.8" apart, so dual banana plugs can't be used...
View attachment 297582
Thank you for the help I really appreciate it, yes the power supply has the green plug in the middle. What is your opinion about probing around the circuit with the oscilloscope as if it's a battery while using this power supply, could I even safely put the prob on the positive terminal and reference clamp in the neg, or will I get fried.
 

Thread Starter

NotNu4U

Joined Jul 3, 2023
9
hi NNU,
This is what an Amazon user reports.
E
Thank you for the help. I see I have alot of technical language to catch up on. I never heard the term split phase dc power supply. I did some research and my interpretation of what that means is if the power supply can create positive and negative voltage. I tested it and it does is a ground positive terminal and measure the neg terminal to ground. Is there a relationship with this and oscilloscope safety?
 

ericgibbs

Joined Jan 29, 2010
18,835
hi,
OK,
Set it for Low Resistance measurement.
Unplug the power plug of the PSU from the mains power socket.
Measure the resistance from Earth pin of the power plug to the GREEN socket on the front of the PSU. note the reading.
Repeat
Measure the resistance from Earth pin of the power plug to the BLACK socket on the front of the PSU. note the reading.

Post your results.
E
 

dl324

Joined Mar 30, 2015
16,898
What is your opinion about probing around the circuit with the oscilloscope as if it's a battery while using this power supply, could I even safely put the prob on the positive terminal and reference clamp in the neg, or will I get fried.
If the scope is line powered and the circuit is using a grounded power source, you need to be mindful of where you put the ground lead.

If the scope is battery powered, the ground lead is isolated so you can put it wherever you want. There's a way to do that with line powered scopes, but not recommended for beginners.
 

Thread Starter

NotNu4U

Joined Jul 3, 2023
9
hi,
OK,
Set it for Low Resistance measurement.
Unplug the power plug of the PSU from the mains power socket.
Measure the resistance from Earth pin of the power plug to the GREEN socket on the front of the PSU. note the reading.
Repeat
Measure the resistance from Earth pin of the power plug to the BLACK socket on the front of the PSU. note the reading.

Post your results.
E
About 0.6 ohms green socket to the earth pin and open line from black to earth pin
 

ericgibbs

Joined Jan 29, 2010
18,835
hi,
That would indicate the comment from the Amazon user, the GREEN is at EARTH potential, is correct

Now check the resistance from the BLACK socket to the case of the PSU, any of the metal parts, lets know what you measure.
E
 

Thread Starter

NotNu4U

Joined Jul 3, 2023
9
hi,
That would indicate the comment from the Amazon user, the GREEN is at EARTH potential, is correct

Now check the resistance from the BLACK socket to the case of the PSU, any of the metal parts, lets know what you measure.
E
Open line again
 

ericgibbs

Joined Jan 29, 2010
18,835
Hi,
I would use the RED and BLACK sockets for powering Low Voltage projects, say up to 30V.
Until you are more are experienced, don't consider using the GREEN , EARTH socket.

Without any load connected set the PSU output to say 12V, you should measure, {with your DVM on Volts], 12V between the RED and BLACK sockets.

E
 

Thread Starter

NotNu4U

Joined Jul 3, 2023
9
Hi,
I would use the RED and BLACK sockets for powering Low Voltage projects, say up to 30V.
Until you are more are experienced, don't consider using the GREEN , EARTH socket.

Without any load connected set the PSU output to say 12V, you should measure, {with your DVM on Volts], 12V between the RED and BLACK sockets.

E
Yes that's almost exactly what I get. So to verify the concensus seems to be I can use the oscilloscope on it as long as red and black sockets are used and I ignore the green? However if I used the green (which I wont for now) great care needs to be taken to make sure the probe is connected correctly since it's not a battery oscilloscope?
 

ericgibbs

Joined Jan 29, 2010
18,835
Hi,
Check that your Scope 0V AND/OR chassis is connected to Mains Earth, use the same method as post #9.
Lets know
E

Footnote: @NotNu4U
I use an RCD [residual current detector] plug/socket] on all my domestic project workbenches and installations.
Well worth the small expense for that additional safety mains cut off in the event of a person inadvertently grounding a 'live' project using mains powered equipment.
 
Last edited:

Thread Starter

NotNu4U

Joined Jul 3, 2023
9
Hi,
Check that your Scope 0V AND/OR chassis is connected to Mains Earth, use the same method as post #9.
Lets know
E
Still waiting on it to be sent, it comes today. Youtube videos do show that it is connected to mains earth via the bmc connector. It is the 2 channel Hantek
 

MisterBill2

Joined Jan 23, 2018
18,442
Thank you for the help. I see I have alot of technical language to catch up on. I never heard the term split phase dc power supply. I did some research and my interpretation of what that means is if the power supply can create positive and negative voltage. I tested it and it does is a ground positive terminal and measure the neg terminal to ground. Is there a relationship with this and oscilloscope safety?
Neither have I ever heard "split phase" in reference to a DC supply. There certainly are dual supplies, even some where both positive and negative adjust at the same time. They may be called "split", but never split phase. That would be used by the unknowing while pretending to know something.
That "ground" terminal on a supply is there if one chooses totie an output to the safety ground pin connection of the power plug. I have never had the need to connect to it.
 
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