Farnell power supply help please.

[Oldmanandhistoy]

Hi all

Need help with a Farnell power supply .It was given to me by a friend whom knows about as much as I do about electronics.
What I need to know is, can I plug it straight into my Xylotex board with out modification.

Info I have is.
On back Plate
Input 240v
Output 20v
10A
Model Num 30/10SCD

It has a cap in it 22000uf and when testing voltage it reads 28Vdc and it has output Adjust and Current limit.

Back plate says 20v but it is reading 28v on my meter is there a problem?

Might be a strange question but do I need to worry about the cable length between the power supply and the Xylotex board?

I would appreciate any help given and would like to say thanks in advance.

John

[H500]

If it has an output voltage adjust, then it just mean someone has cranked it up. If it's unregulated, then it's not unusual for the voltage to be higher than the spec when it is not loaded down.

28v is actually closer to the ideal voltage for the xylotex than 20v. The higher the voltage, the better your speed, but if its too high you might damage the driver.

In general, you should keep the power wires short (ie: several inches rather than several feet)

[Oldmanandhistoy]

Hi H500 and thanks.
The only detail I missed was that it is stabilised. Would that make a difference to the 28v reading?
Can I take it that other then that I can connect it without modification?

John

[jseiler]

some linear power supplies will not accurately regulate unless connected to a load of some sort. Since its a 20V 10A ps, one might connect a 1K ohm, 1W resistor accross it and see if it drops your voltage into line.

regrds,
John

[Oldmanandhistoy]

Hi jseiler and thanks.

I will try that and see what happens. I’m hoping it stays at 28v for my Xylotex board.
Still need to know if it will need modification?
Also if it stays at 28v and has been cracked up would there be a problem using it for prolonged periods?

Regards, John

[Oldmanandhistoy]

Ok I put a resistor across it and still get 28v measuring either side of it?

John

[Al_The_Man]

Originally Posted by jseiler some linear power supplies will not accurately regulate unless connected to a load of some sort. John

I think you will find that is generally switching type that may exhibit this, all the linear ones I have used have been dead on unloaded.
Al.

[Oldmanandhistoy]

Hi Al

How can you tell which type you have the only info I have on this is what it has on the plate on the back, Info in my first post?
Still don’t know if I need to modify it for my Xylotex?

John

[H500]

John,

Without specs, it is difficult to know for sure what voltage is "safe". What is the voltage rating of the 22000 uf capacitor?

If you have a digital camera, you could take a picture of it and post it. It shouldn't be hard to determine what type it is from the components on board.

[Oldmanandhistoy]

As requested I have added 2 photos .
Info on the cap is 22000uF, 50VDC and type 36D.

John

[lerman]

From the photo of the terminals, it appears that there is a separate feedback connection. The plus feedback connection should be connected to the plus output voltage connection AT THE LOAD. The minus feedback connection should be similarly connected to the minus output voltage connection.

For test purposes (and when measuring the voltage), you can connect them at the terminal strip. By connecting them at the load, the power supply can compensate for voltage drop in the connecting wires.

If they are not connected, that would explain why the output voltage is so high.

Ken

[Oldmanandhistoy]

Hi lerman
There is a connection via metal strips to the + output and the +feed back. There is also a connection between the –output and the – feed back.

John