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Risk of damage using an unregulated power supply

Carlos Oliveira

Jul 4, 2015
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Hello to all,

I have an unregulated Power Supply with output specs of 1.5-3-4.5-6-7.5-9-12V an 1000mA 12VA (max). As with all unregulated power supplies, when I measure its output at 9V setting, I get about 14V. I understand that with this power supply when the device consums about the 1000mA, then I would get the 9V output.
What I would like to know if it's Ok to use this power supply to power a device that needs to be powered at 9V, with a consumption of no more than 80mA, or am I having the risk of damagind the device? Should I use the power supply at a lower output voltage so I can get something more around the needed 9V?

Thank you very much in advance.

Cheers!
 

Arouse1973

Adam
Dec 18, 2013
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No is the answer if as you say the 9 Volts is only attained with a 1 Amp load. Load it with a resistor to produce 80 mA of current and then measure the voltage. This will tell you what the output voltage will be when you connect your load to it. If it's higher than 9 Volts then look at using a 9 Volt regulator and set your power supply to 12 Volts.
Adam
 

Colin Mitchell

Aug 31, 2014
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Use the 7.5v or 6v tapping. Simple. I just completed a 6 year degree in electronics and it only took me 35 minutes to work that out. !!!!
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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Unfortunately, Colin's disdain for education often obscures an otherwise useful (if incomplete) answer.

The simple answer is to switch the unregulated power supply to a setting which provides a voltage closest to the required voltage at the normal operating current of the device.

This can normally be determined experimentally by trial and error, setting the power supply to the tap which produces the voltage closest to the operating voltage unloaded, then powering the device. If the voltage falls substantially (often indicated by the device not working correctly), try the next tap up.

Most devices can handle a reasonably wide range of voltages from an external power supply without immediate damage, but it's generally best to err on the side of a lower voltage.

If the device has a wide range of power requirements, the input voltage will go up and down as the load changes. This may cause problems if the original adapter was regulated.
 

Colin Mitchell

Aug 31, 2014
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"Load it with a resistor to produce 80 mA of current and then measure the voltage." He has already done that and the voltage is 14v.
Why go to all the work of repainting the outside of the Taj Mahal and use a 9v regulator, when simply changing the tapping is all that is needed.
"(if incomplete) answer." What is incomplete with switching to 7.5v or 6v. ????
Do you want me to add a precision regulator and 100,000u electrolytic ??
 

Arouse1973

Adam
Dec 18, 2013
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"Load it with a resistor to produce 80 mA of current and then measure the voltage." He has already done that and the voltage is 14v.
Why go to all the work of repainting the outside of the Taj Mahal and use a 9v regulator, when simply changing the tapping is all that is needed.
"(if incomplete) answer." What is incomplete with switching to 7.5v or 6v. ????
Do you want me to add a precision regulator and 100,000u electrolytic ??

Blimey Colin, more than one sentence..... I am impressed. Where in the original thread did he say he had connected a resistor?

We don't know what he is powering unfortunately he doesn't say. Although I agree that changing the switches could be an option. What we don't know is the tolerance in the working voltage of the device. I played safe and the cost of a regulator is probably cheaper than a replacement piece of equipment if it were to get damaged by an incorrect voltage setting.

Who on earth would want to paint the beautiful white marble of the Taj Mahal :)

Adam
 

Arouse1973

Adam
Dec 18, 2013
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Perhaps you could give answers that don't take a swipe at other contributors.

It's ok I think we are all guilty of this to some respect. I am guilty of having a pop at Colin at times, but it's out of frustration rather than anything else.
Adam
 
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