How current works under load(repost) - Page 1
Forum section: electronics / beginners

author: isaacsong23
author_rank: Contributor
timestamp: April 14, 2017, 03:15:52 am
content: Hi!!Quick question!!If my power supply is putting out 5V 4A for my four tp4056 modules in parallel, and lets say i wish to only use one of the four tp4056 module to charge a single 18650 battery , i am seeing two scenarios, first Will the tp4056 still put out 1A for the single 18650 battery ? Second, Or will the battery try to pull.more current causing the TP4056 Module to exceed its current rating of 3A and than boom. Thank you!! If you are curious my batteries are LG H2 18650 batteries Thank you!!:) TP4056 Chips can only handle a maximum of 3A before spoiling btw. Thanks!!Sent from my SM-G935F using Tapatalk

author: sleemanj
author_rank: Super Contributor
timestamp: April 14, 2017, 03:31:53 am
content: If you configure your TP4056 to have a maximum 1A charge current, it will draw a maximum of approx 1A from the power supply and it will supply a maximum of 1A to the cell, during the CC phase.

author: Rerouter
author_rank: Super Contributor
timestamp: April 14, 2017, 04:41:34 am
content: A load and a supply are different, and this seems to be a common confused concept for beginners, your power supply tells you the most it can safely provide, (how much it can supply), while a load is described by how much it wants to consume (how much it will take if the supply can meet demand)To flip in on its head to help you understand, with nothing connected to your 5V 4A supply, and you measure across it with your multimeter, you will get something in the ball park of 5V, even though it can supply 4A, does not mean it will try and feed 4A into your multimeters inputs (1 Megaohm * 4A = 4,000,000V, so obviously this is not the case)Equally to add a slight bit of confusion, the TP4056 modules are a "constant current" charger, which means they limit how much they can supply, so even though the battery your charging can potentially demand 20+ Amp to try and equalise, this chip limits the supply and its output voltage falls in turn to just a tiny amount higher than the batteries internal voltage to limit it to only consuming 1A.

author: Brumby
author_rank: Unknown
timestamp: April 14, 2017, 06:38:16 am
content: Quote from: Rerouter on April 14, 2017, 04:41:34 amThis is a basic bit of knowledge that needs to be well understood - but it is not hard.A powersupplythat is rated at 12V, 5A willprovidea fixed 12 volts and becapableof providingupto5 amps of current at that voltage.Aloadthat is rated at 12V, 5A willrequirea fixed 12 voltsand5 amps of current at that voltage.In all cases, the voltages must match and the currentcapabilitiesof the supply must always be equal to or greater than the demand of the load.Examples. Let's continue to use the 12V 5A supply for these examples.....- A circuit (load) requiring 12V 1A will work happily. (In fact, you could run 5 such circuits.)- A circuit (load) requiring 12V 200mA will work happily.(In fact, you could run 25 such circuits.)- A circuit (load) requiring 12V 5.5A(it's just a little bit over)continuously**would be a problem. Itmightwork, but the supply is overloaded. Depending on the supply, this could cause overheating, a drop in voltage or activation of protection mechanisms and your load may not function correctly. If you have a supply that can still deliver the power, then it will be under a greater stress than it was designed to handle - and it may suffer a shortened life.- A circuit (load) requiring 12V 20A continuously**will not work. The supply will just cave in with either overheating and a drop in voltage or activation of protection mechanisms. Depending on the supply, this could be a serious fire risk.**Often there are circuits that perform different operations at different times and their current requirements can fluctuate.One example is a temperature controller with a heating element. When monitoring, it may draw very little current which is well within the capabilities of the supply - and during these periods, all will be well. But when the element is switched on, the current draw will go up dramatically. If the total current required by the load now exceeds the capabilities of the supply - problems will arise.

author: IanB
author_rank: Super Contributor
timestamp: April 14, 2017, 06:56:06 am
content: Quote from: Brumby on April 14, 2017, 06:38:16 amConsidering the battery charger/LED module in the first post, there is also an opposite case to this. A 1 A lithium ion charger is also a kind of power supply, except in this caseit will provide a fixed 1 A to the load andbe capableof providing up to 4.2 V at that current.The constant current supply can be thought of in this way: if you were to place a short circuit across the output terminals the current would be 1 A and the voltage would be zero (more or less). If you were to slowly increase the resistance across the output, the current would remain at 1 A and the voltage would increase towards the maximum of 4.2 V. But if you should increase the resistance too much the voltage would hit the limit at 4.2 V and then the current would decrease below 1 A.

author: Brumby
author_rank: Unknown
timestamp: April 14, 2017, 07:06:32 am
content: Yes ... batteries and charging circuits are another level.

author: isaacsong23
author_rank: Contributor
timestamp: April 14, 2017, 11:40:03 am
content: Thank you so much guys!!Helped me a ton , now i am much clearer haha thank you!!!Cheers!Sent from my SM-G935F using Tapatalk