DC electronic loads: CV, CC, CR help me to understand better - Page 1
Forum section: electronics / beginners

author: mcinque
author_rank: Unknown
timestamp: October 15, 2013, 10:35:42 pm
content: Hi all,I'm not an owner of an electronic load, but I'd like to understand how this instrument could be used.Could you please explain em better the test methods used by these instrument?For CC I think I have very clear ideas (I hope), but I've some doubt on the behaviour for CV and I'm totally lost for CR.CONSTANT CURRENT= to test aVOLTAGEsource.In particular this method is used to investigate the ability of a power source (power supplies, linear regulators...)to provide a stable (or defined) output VOLTAGE under load condition.The electronic load will sink current and monitor the voltage.For example, I know that I can test a linear regulator loading it with the maximum current he can provide, and if the voltage provided drop under the expecting value, the regulator is bad.The same for a power supply, or to test a battery by monitoring its voltage drop with various load connected.I think that CC is very easy to understand, more or less it's basically like connecting a specific wattage bulb to a battery or a psu and measuring the voltage on its terminals. Am I wrong?CONSTANT VOLTAGE= to test aCURRENTsource.I know that this method can be used to test, for example, battery chargers: to see the exact amount of current they provide while charging and/or if they detects correctly the "delta peak" when the battery reach its terminal voltage.But what will be the behaviour of the electronic load in this method?I mean, in CC the load will sink CURRENT, but what in CV?It will PROVIDE current? How can a deviceprovideCURRENT??Can you list other tests that involves this method?CONSTANT RESISTANCE= ?Even If it's simple (I understand that the instrument will apply a defined resistance to the load connected), I can not figure any uses of this method. Can you suggest me a couple of them?Thank you all in advance!

author: AG6QR
author_rank: Frequent Contributor
timestamp: October 15, 2013, 11:10:17 pm
content: Quote from: mcinque on October 15, 2013, 10:35:42 pmNot quite. A specific light bulb will come close to obeying Ohm's law. As you decrease the voltage across a light bulb, the current will decrease. A CC electronic load will keep the current constant regadless of voltage, at least until the voltage drops to near zero and the supply can't provide the specified level of current.QuoteThe load won't provide current, it will sink whatever amount of current will provide the specified voltage.QuoteThe load will act like a big power resistor, where you can set the value. It may be useful for testing the behavior of a battery or supply against a constant resistance load like a light bulb (though many light bulbs have a high temperature coefficient of resistance, so they may not exactly behave like constant resistance loads).In all three cases, the load acts like a big adjustable resistor, but with an automatic system for very rapidly and precisely adjusting the value of resistance. In the CC case, the adjustment mechanism measures the current, and changes the resistance until the specified current is measured going through the load. In the CV case, it measures voltage, and changes the value of resistance until the specified voltage is present. In the CR case, it simply sets the resistance to a specified constant value.The CV and CC modes rely on the power supply to provide voltage or current. If you put it in CV mode at a high voltage, and your supply can't provide that much voltage, the load will ideally act like an open circuit. If you put the supply in CC mode at a high current, and your load can't supply that much current, it will ideally act like a short. For the actual behavior of your load under those limiting cases, see the specifications.

author: olsenn
author_rank: Frequent Contributor
timestamp: October 15, 2013, 11:20:18 pm
content: DC Electronic Loads are for testing power sources such as batteries. I will use a 1.5V AA-battery for example in each mode of operation."CC" = Constant Current: In this mode, the electronic load drains a specified (constant) amount of current.The voltage seen at the terminals of the battery will be 1.5V - (internal resistance)*(current)"CV" = Constant Voltage: In this mode, the electronic load drains the amount of current required for the voltage across the input terminals to be what the user specified (constant)The current through the battery will be (1.5V - setVoltage) / (internal resistance)."CP" = Constant Power: In this mode, the electronic load uses whatever input voltage it's given, and adjusts the current such that the power (V*I) is what the user set.In the case of the battery, the load initially tries to draw P/1.5V amps of current. However, due to the internal resistance of the battery, this causes the voltage to drop,so the current changes again, and this continues until a balance of P is achieved.

author: sync
author_rank: Frequent Contributor
timestamp: October 15, 2013, 11:30:26 pm
content: Quote from: mcinque on October 15, 2013, 10:35:42 pmTo test a transformer:transformer --- bridge rectifier --- DC load in CR

author: mcinque
author_rank: Unknown
timestamp: October 16, 2013, 11:38:17 am
content: Quote from: AG6QR on October 15, 2013, 11:10:17 pmok, now it is clearThank you AG6QR.Quote from: olsenn on October 15, 2013, 11:20:18 pmThank you too, olsennQuote from: sync on October 15, 2013, 11:30:26 pmThank you sync