voltage changes when connected to load - Page 1
Forum section: electronics / beginners

author: VickySalunkhe
author_rank: Regular Contributor
timestamp: September 22, 2017, 07:27:42 am
content: There is a problemAbout Which i am not sure why it is occurringI have connected my power supply with my motor controller and throttleWhen the key is switch off of throttle i am getting 61v as output((IMAGES ATTACHED))But as soon as i switch on the throttle voltage drastically drops down to 4.8V ad outputWhy such behaviour is happening?How to resolve this issue?I have also attached circuit diagramPlz help sirThanks

author: Ian.M
author_rank: Super Contributor
timestamp: September 22, 2017, 07:36:25 am
content: Your power supply cant supply enough current for the motor.

author: VickySalunkhe
author_rank: Regular Contributor
timestamp: September 22, 2017, 07:39:38 am
content: But i am using 5A transformerWhy isn't it generating the current thenIs there anything wrong with the circuit?

author: VickySalunkhe
author_rank: Regular Contributor
timestamp: September 22, 2017, 07:42:58 am
content: Sir i faced a new scenarioI have directly taken supply after the capacitorNot from the output after voltage regulationSo now the motor runsSo what is the actual problem???

author: Ian.M
author_rank: Super Contributor
timestamp: September 22, 2017, 08:02:37 am
content: What's the DC resistance of the motor? Divide the rated voltage by the DC resistance to get the stall current. That's what the PSU has to supply at startup unless you ramp the voltage up gradually.

author: Brumby
author_rank: Unknown
timestamp: September 22, 2017, 09:12:44 am
content: Like most voltage regulators, the 338 has overload protection. If you want to pull excessive current it will limit the output to ensure the regulator can survive.AsIan.Mhas said, If the motor is being started from stationary, then the stall current could easily exceed the limits built into the chip. The chip limits the output and your motor never gets the power it needs to get up enough speed for the current to drop back.I'd put my 2 cents on that.

author: MAD MACRO
author_rank: Regular Contributor
timestamp: September 22, 2017, 11:03:09 am
content: You should power the chip from regulator output to the chip and another connection directly from power source to a transistor or a relay (controlled by a chip) to the motor.

author: David Hess
author_rank: Super Contributor
timestamp: September 22, 2017, 07:40:41 pm
content: The surge current is causing one of the 338 to current limit. When the voltage drop across the 338 rises, it *lowers* its current limit further to prevent secondary breakdown. Usually this would not be a problem but the second 338 maintains the current through the first one preventing it from recovering.I am surprised you did not destroy the 338s because operating them in series like that can force a reverse voltage across one if it current limits. The solution is to add a reverse protection diodes capable of carrying the maximum current across each output. Dual tracking regulators include these diodes internally as shown below as D10 and D12. In an extreme case, tracking might be implemented so that the regulators share the output voltage.Motors are not usually run from regulated outputs.

author: 2N3055
author_rank: Super Contributor
timestamp: September 23, 2017, 09:52:03 am
content: Lm317 350 338 have problems starting with inductive load.. Plus motor start current that others already mentioned..

author: IanB
author_rank: Super Contributor
timestamp: September 23, 2017, 10:10:47 am
content: It is still not clear to me why you are including the voltage regulators at all. As you have observed, the motor runs if you take the supply directly from the capacitors. And you don't even need the capacitors. The motor will run if you take the supply directly from the rectifier.

author: VickySalunkhe
author_rank: Regular Contributor
timestamp: September 23, 2017, 11:16:04 am
content: But wouldn't it create a problem to motorAs too much ripple will be present if output is taken directly from rectifierAnd sirOne thing i noticedWhen i started using the throttle the voltage started to decrease why did that happen i have no clueBut that limited my motor to run more as thr motot doesn't run after voltage is lower than 30VI really want to clear the concepts hope so you'll help me outHelp will be really appreciatedThanks all of you

author: IanB
author_rank: Super Contributor
timestamp: September 23, 2017, 11:30:26 am
content: The motor doesn't care about the ripple. It is not important.The supply voltage will decrease if you try to draw more current from the supply than it is able to provide. Either your motor is too large or your supply is too small.

author: VickySalunkhe
author_rank: Regular Contributor
timestamp: September 23, 2017, 11:36:59 am
content: Sir does connecting 1st and 3rd wire as output from center tap transformer gives half of the current as an outputFor ex say12-0-12v 5A center tap transformer is thereIf i use 1,3 wire and connect it with bridge rectifier does the output has 24v 2.5A as an outputI am clear about the voltage part i am not aure about the currentI have heard someone sayconnecting 1,3 wire-> half of the total rated currentConnecting 1,2 or 2,3 -> same rated currentIs that true?Thanks

author: IanB
author_rank: Super Contributor
timestamp: September 23, 2017, 11:45:21 am
content: If you connect the two outer wires of a 12-0-12 V, 5 A transformer you will have 24 V and 5 A available.Also, the transformer will not stop at 5 A, that is just the continuous rated current. You can take more current for short periods as long as the transformer doesn't get too hot. With every increase in current there will be a decrease in voltage.

author: VickySalunkhe
author_rank: Regular Contributor
timestamp: September 23, 2017, 01:05:47 pm
content: Sir i just got an idea.What if i make same power supply one more timeThen connect that psu with previous oneSo I'll have 2 psu with 51v 5A eachAnd then I'll connect it in parallel so that i can double the output currentI.e I'll get 51V 10A right?But the only doubt i was having is whether it will create a major problem to the motor or notIf it is going to create a problem how to prevent it ?Thanks

author: David Hess
author_rank: Super Contributor
timestamp: September 23, 2017, 01:39:13 pm
content: Quote from: VickySalunkhe on September 23, 2017, 01:05:47 pmThis will work however the regulators will not share current well when paralleled unless their design is changed. Diodes placed in series with the output should be sufficient to allow parallel operation. A single 51 volt and 5 or 10 amp regulator would be better.

author: Spaghetti_142
author_rank: Newbie
timestamp: September 24, 2017, 02:19:05 am
content: COMMON

author: IanB
author_rank: Super Contributor
timestamp: September 24, 2017, 02:37:09 am
content: Quote from: Spaghetti_142 on September 24, 2017, 02:19:05 amDo you mean "Come on" ?

author: Brumby
author_rank: Unknown
timestamp: September 24, 2017, 02:53:51 am
content: You tell me and we'll both know.Quote from: Spaghetti_142 on September 24, 2017, 02:19:05 amWe aren't mind readers - and while sometimes a single word might communicate something immediately useful ... this does not.We can't see your face or hear the intonation in your voice. We can't see how your arms are waving around, nor can we see the doodles on the notebook in front of you.Can you at least try to put together a whole sentence?