| Electronics > Beginners |
| Confused with about my new Lab/Bench PSU C.C. & C.V. Is it working correctly? |
| (1/5) > >> |
| castingflame:
Hey all. I just purchased a PSU from Amazon which is the following model... https://www.amazon.co.uk/gp/product/B00BCPTG66/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1 I am a little confused about the Constant Current (C.C) and the Constant Voltage (C.V.). I have read and looked at videos etc about using c.c . and c.v. but my PSU is not behaving how I would expect. It is always only ever showing 'C.V.' on the display. If I hit the button to switch between C.C. and C.V. The display does not change (Still displays C.V.) and the current is not constant. I can not change the current via the CUR ADJ buttons either. This is with or without a load. The manual is really no help. I am thinking it is faulty. Thanks for any help. |
| Circlotron:
Say you have the voltage set at 15V and the current set at 1A. If you load it more and more, it will stay in CV mode until the load current reaches the 1A setting. Any further increase in load will cause the voltage to decrease (not CV anymore) and the amps will go no higher than the 1A setting - CC. |
| rstofer:
I have always had an issue with the definition of Constant Current as it relates to power supplies. I prefer to think of it as Current Limit. For example, if I set the current to 1A, will the power supply raise the output voltage enough to deliver 1A to a 1K resistor? Of course not! In fact, it won't raise the output voltage at all; I have to set a sufficiently high voltage to allow the device to throttle on current. Simply put, all it does is reduce the output voltage to prevent more than 1A from flowing. It does NOT maintain a constant current regardless of load. Set the PS to 10V with a 100 Ohm load. The current should be 100 mA. Now, keep reducing the current setting until the voltage begins to drop. That should put the PS into CC mode and, if you parallel another 100 Ohm resistor, the current will stay at 100 mA but the voltage should drop to 5V. |
| jeroen79:
--- Quote from: rstofer on August 10, 2018, 05:25:30 pm ---I have always had an issue with the definition of Constant Current as it relates to power supplies. I prefer to think of it as Current Limit. For example, if I set the current to 1A, will the power supply raise the output voltage enough to deliver 1A to a 1K resistor? Of course not! In fact, it won't raise the output voltage at all; I have to set a sufficiently high voltage to allow the device to throttle on current. Simply put, all it does is reduce the output voltage to prevent more than 1A from flowing. It does NOT maintain a constant current regardless of load. --- End quote --- By that logic there are no constant voltage supplies either. Just voltage limited as none of the would increase the current enough to maintain 10V over a .1 ohm resistor. |
| james_s:
How do you expect to get a constant current into no load? Do the math, as the load approaches zero (open circuit), the voltage required to maintain a constant current approaches infinity. |
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