# Help understanding Power supply

I am setting up a steeper motor. My spec reads need fo a 24 V source.
I have a power source supply that reads -12, -5, 0, +5, +12. Does grounding the output lead -12 and the positive to +12 will give me 24 volts?

I want to make sure I dont smoke my power supply or my motors!!

Image attached

Firstly that supply might not be isolated, in that 0V may be grounded, in which case you can only use the +12.
Using a multimeter will indicate if the 0V output is grounded or not.

Secondly if you drive a positive supply direct to a negative supply like that you may need to add protection
diodes to the supply to prevent the +12V supply pulling the -12V rail higher than 0V or vice-versa.

cathode to +12V, anode to 0V
cathode to 0V, anode to -12V

These diodes need to be able to handle the full output current.

A supply like this would often be assuming all its outputs are relative to ground and may not have
protection for reverse-polarity on the rails.

Can you post a link to the motor?

jecalderon:
I am setting up a steeper motor. My spec reads need fo a 24 V source.
I have a power source supply that reads -12, -5, 0, +5, +12. Does grounding the output lead -12 and the positive to +12 will give me 24 volts?

Assuming your arduino is all connected up (and almost ready for operation) but is left DE-energised.... ie. no power of any kind switched on just yet. This means leave every power supply turned off. Connected up....but turned OFF. No power to anything just yet.

Now.....if 'grounding' means connecting the 'gnd' pin of the arduino to the -12V rail of the power supply, and assuming you have arduino 'GND' already connected to the -12V rail (but no power is turned on yet), then you should use the multimeter to do a 'continuity test' between the GND of the arduino and the '0V' rail of the power supply. If it turns out that there is a very low resistance path between GND of arduino and the 0V rail of the power supply, then do not go ahead with it ----- because .... as MarkT is saying..... the 0V rail of the power supply might be (for safety reasons etc) internally (electrically) connected to arduino GND. This would mean .... if you were then to connect arduino GND to the -12V rail..... then it would equivalently mean connecting the 0V rail of the power supply to the -12V rail of the same power supply, which is not desired at all.

This could mean that you would need to get or buy a 24V DC supply.

My thought was that the OP's motor may run on 12V, albeit slower and with less torque.

Hi jecalderon, I looked at the Minebea website, in particular the 17PM series. The torque/frequency data given there is done at 24 volts, but it doesn't say that is the only voltage they will run at. They do however all require a bit over 1 amp, so your power supply (rated at 1 amp) is lacking there. So I'd suggest getting a more robust (V and A) power supply.

OK, there's the picture. What you have not supplied is the web page detailing the power supply.

First step, take your multimeter, set it to various resistance ranges and measure between "G" and "FG". If there is any continuity at all, you can not use it with the -12V terminal as your "ground".

ChrisTenone:
Hi jecalderon, I looked at the Minebea website, in particular the 17PM series. The torque/frequency data given there is done at 24 volts, but it doesn't say that is the only voltage they will run at. They do however all require a bit over 1 amp, so your power supply (rated at 1 amp) is lacking there. So I'd suggest getting a more robust (V and A) power supply.

No, that doesn't actually follow, stepper drivers provide more current to the motor than they take from
the supply when the supply voltage is significantly larger than the product of motor winding current and
resistance.

Typical NEMA17 steppers use about 5W, so 24V at 1A is likely to be enough.

ChrisTenone:
Hi jecalderon, I looked at the Minebea website, in particular the 17PM series. The torque/frequency data given there is done at 24 volts, but it doesn't say that is the only voltage they will run at. They do however all require a bit over 1 amp, so your power supply (rated at 1 amp) is lacking there. So I'd suggest getting a more robust (V and A) power supply.

Thanks man!!!!! Did overlook this!. You just safe me a lot of smoke, trouble, and embarrassment. Thanks

Paul__B:

OK, there's the picture. What you have not supplied is the web page detailing the power supply.

First step, take your multimeter, set it to various resistance ranges and measure between "G" and "FG". If there is any continuity at all, you can not use it with the -12V terminal as your "ground".

The Supply oddly has no labels other that what is seen in front panel. The resistant between FG and G reads 6.7 MOhms. Will this render useless to try to supply 24V from -12 to +12?

jecalderon:
The resistant between FG and G reads 6.7 MOhms.

Then it is probably safe to ground the -12V line.

It is unclear with any given power supply, whether it will operate correctly with no load on the 5 V - primary - output. Whilst this supply is clearly intended for driving 5 V logic, its general-purpose nature and lack of documentation suggests it will need to be OK with no 5 V load. The 12 V supplies may not be accurately regulated, but for a stepper motor that does not matter.

The G label probably means 'earth'. And 'FG' is the 0V for isolated supply (not earthed). This is just a 'maybe'.

Get a multimeter in DC voltage reading mode.... disconnect everything from the power supply except for AC mains cable....turn on the supply....and measure the DC voltage between 'G' and the 5V terminal of the supply.

Then measure the voltage between 'FG' and the 5V terminal.

What values do you get for the measurements?

Later... if your AC cable has three pins when you observe it after disconnecting the mains plug from the wall socket...... you can use the multimeter to carry out a continuity test between 'G' terminal and the earth pin. And do the same for the 'FG' terminal and the earth pin.

Also ..... read post #3 if you haven't done it yet.

The issue is due to no user guide or tech manual for this power supply. Lack of details.

One more note or observation ...... the AC mains connection to that power supply looks ridiculous --- in that the AC mains wires are just connected to the terminal step on the front panel. Doesn't look like a good idea in terms of safety. I know some power supplies sold in shops are like that too, which is also ridiculous.

Southpark:
Later... if your AC cable has three pins when you observe it after disconnecting the mains plug from the wall socket...... you can use the multimeter to carry out a continuity test between 'G' terminal and the earth pin. And do the same for the 'FG' terminal and the earth pin.

I am puzzled - did you read my reply #7 and his answer in #10 which cover these details?

His picture shows the three pin (because it has a green/ yellow ground wire) power cord connected to "FG".

Paul__B:
I am puzzled - did you read my reply #7 and his answer in #10 which cover these details?

I did read it. I now see that 'FG' stands for 'frame ground'.......and the wiring shows 'FG' is connected to earth.

That supply looks like an accident waiting to happen with the mains connected to the front block like that.

Anyway..... would be nice if there is one extra FG terminal..... so that G and FG can be conveniently bridged when needed.

Ah, yes, mea culpa - I presumed that "FG" was self-explanatory.

Boy, that 12+ hour forum outage was unpleasant - I wonder if anything has been fixed?

Southpark:
That supply looks like an accident waiting to happen with the mains connected to the front block like that.

That's entirely standard for open-frame supplies which are intended to be always be sealed inside equipment.
Many do have removable transparent plastic covers over the terminal strip anyway.

Paul__B:
Ah, yes, mea culpa - I presumed that "FG" was self-explanatory.

"FG" can also stand for 'floating ground'. But I eventually checked out the photo of the supply more carefully, and everything started to become clear after that.

Boy, that 12+ hour forum outage was unpleasant - I wonder if anything has been fixed?

It certainly was a long outage. If only somebody could have pushed the rest button earlier, or get a txt message on their mobile earlier to push restart.....would have been nice. At least seems to be under control again. Back in action.