Korad KA3005P outputs less then set? - Page 1
Forum section: electronics / beginners

author: VenHeelun
author_rank: Newbie
timestamp: January 10, 2019, 07:25:15 pm
content: HiI do understand a very little about electronics but i still did buy a Korad KA3005P to do some small projects.I did buy a ledstrip & controller about one year ago and want to see if they work.The controller is a SP108E Wifi controller witch can be operated with a phone.The ledstrip is a 5mtr UCS1903 rgb ledstrip witch is adressable per led.The SP108E: DC5V - 24V, 20mA - 130mAThe UCS1903 ledstrip: DC12V, 14,4W/Mtr (so total 72W / 6A)Q1:If i set the powersupply to 12V at 1A (witch is to low) then the voltage is only ouputting 9.5V.At 5A (the highest on the powersupply) it outputs 12V, 2,1A.Why 9,5V on 1A? That's 2,5V lower.Q2:Can i connect both controller (130mA) & ledstrip (6A) on one 12V, 6A powersupply?Can i damage anything (on the controller) this way?Thank you

author: ataradov
author_rank: Super Contributor
timestamp: January 10, 2019, 08:00:25 pm
content: Quote from: VenHeelun on January 10, 2019, 07:25:15 pmPower supply enters into constant current mode, so it start to lover the voltage until current consumption is at the set level.Clearly your device consumes 2.1V. So any current limit setting will result in a reduced voltage.Quote from: VenHeelun on January 10, 2019, 07:25:15 pmYes, 130 mA is an insignificant additional load, it should not cause any harm.

author: tooki
author_rank: Super Contributor
timestamp: January 10, 2019, 08:20:22 pm
content: Quote from: ataradov on January 10, 2019, 08:00:25 pmYou mean 2.1A, right? And thus that any current limit setting below 2.1A will result in reduced voltage.

author: ataradov
author_rank: Super Contributor
timestamp: January 10, 2019, 08:22:43 pm
content: Yes, just a spelling error

author: tooki
author_rank: Super Contributor
timestamp: January 10, 2019, 08:32:02 pm
content: Quote from: VenHeelun on January 10, 2019, 07:25:15 pmThe key to remember is that the voltage and current settings arelimits. (You cannot force a certain current through something. Ohm's law explains the relationship of how a voltage "pushes" current through a load.) And the voltage limit takes priority over the current limit. (For the sake of understanding, pretend that without the setting, the power supply would output infinite voltage. So the setting keeps it down where we need it.)So when you set the power supply to 12V/1A, what you're saying is "do not exceed 12V, AND do not exceed 1A". Since the voltage's primary control is the setting, then it will remain at 12V,unlessthe current limit (1A here) is exceeded, in which case the current limiting kicks in and takes over, lowering the voltage until the current limit is no longer exceeded. Note that at any given time, EITHER the voltage limit OR the current limit is in control, but not BOTH at the same time! This is what the CV and CC* lights on the power supply indicate: which limit is in control right now!*Meaning "constant voltage" and "constant current", though those names are IMHO not very good, but they're what the industry uses. I think "voltage-limited" and "current-limited" would be better, but lab PSUs tend to use "limit" to mean turning off once a limit is breached.

author: VenHeelun
author_rank: Newbie
timestamp: January 10, 2019, 10:38:18 pm
content: That's something to sink in!So what i understand is that the lower i set the current the lower the voltage will be because the Amp-limit does also limit the voltage so you get a voltagedrop.

author: ataradov
author_rank: Super Contributor
timestamp: January 10, 2019, 10:49:52 pm
content: You generally should not set the current limit lower than the rated consumption of your load. The reason current limit exists on lab power supplies is to prevent accidental damage to the device, since lab power supplies often used during development of new products, where mistakes are quite possible.Voltage, current and resistance of the load are related using Ohm's law: I = U / R. If R is fixed, then given a limited current, you have to lover the voltage to satisfy that equation.Power supplies first limit the voltage and allow the current to do whatever it wants to do depending on the load. But once the current is over the set limit, they start lowering the voltage.