Drawing power from a rectified DC signal from a DC load? - Page 1
Forum section: electronics / projects

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: April 14, 2020, 07:38:12 pm
content: I have a programmable DC electronic load and I'd like to draw power from a fully bridge rectified AC signal but I'm not sure if this may cause damage to the instrument.Are they only able to draw current from stable DC voltages such as batteries, power supplies, capacitors etc or can they also do PWM, and rectfied signals?

author: Shock
author_rank: Super Contributor
timestamp: April 14, 2020, 08:12:21 pm
content: I'd suggest mentioning what electronic load you are using and how you are setting up your test circuit and what voltage it is etc. If you are also testing circuits to the point of failure you have to consider what happens when a component fails as well.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: April 14, 2020, 08:51:30 pm
content: Quote from: Shock on April 14, 2020, 08:12:21 pmThe load is a Gwinstek PEL-3031e.This is just a theoretical question. I have no use for it currently but would like to know if it is possible in case I ever decide to make my own power supply and would then load the full bridge rectifier after dropping down the voltage via a toroidal transformer.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 14, 2020, 09:01:21 pm
content: The electronic load can get upset by the dropping voltage. Below some 0.2-1 V the load will not be able sink the current as planed. This can upset the regulation: either cause a drop out - turn off with a error message, more or less significant overshoot when the voltage comes back and probably some error in the average current.It should not cause damage to the load - at least this is the plan and how it should be.Things should better if the is a filter cap after the rectifier, just like i the real circuit.

author: Shock
author_rank: Super Contributor
timestamp: April 14, 2020, 09:30:00 pm
content: Minimum 1V according to the manual.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: April 14, 2020, 10:06:17 pm
content: Surely a large value cap will bring at 0V crest up to an average voltage and then I could surely load the rectifier.Should I give it a try either way? I doubt there would be any damage to the unit as there are no negative wave cycles.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 15, 2020, 09:35:16 am
content: One does not need a lot of capacitance, just enough to keep the voltage over the 1 V limit. So more like 1/10 the normal filter capacitance (but also sufficient ripple rating - so one may need more for this reason).Normally there should be no damage - but the current may be off from what is expected and not representative for a normal load.

author: Vovk_Z
author_rank: Super Contributor
timestamp: April 16, 2020, 08:03:33 am
content: "Classic electronic load" means using CC (constant current) mode for DC with low pulsations.To load rectifier (with large pulsations) we need CR (constant resistance) mode.I don't know if there is such mode in Gwinstek PEL-3031e, but usually industrial devices have it (all modes - CC, CP, CV, CR).

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: April 16, 2020, 10:00:38 am
content: Quote from: Vovk_Z on April 16, 2020, 08:03:33 amI thought about putting it in CR mode as that does not force CC or CV.The load has dynamic loading capability so it is able to switch between two current values at frequencies of up to 20 KHz or such so I don't think it will have trouble with the pulsating DC voltage.

author: David Hess
author_rank: Super Contributor
timestamp: April 16, 2020, 05:25:29 pm
content: Except for the obvious issue with dropout at low voltages, there is nothing inherent which should prevent any electronic load from operating with rectified AC.

author: Gracep
author_rank: Newbie
timestamp: April 20, 2020, 05:22:31 pm
content: Quote from: Kleinstein on April 14, 2020, 09:01:21 pmthanks, i found i very helpful. i'm a newbie and since i'm still learning, that's not very easy for me to find it out all as easy.i'm still having some questions and i was wondering if i could ask you, sir, some questions? anyway, thanks a lot as you already helped

author: Shock
author_rank: Super Contributor
timestamp: April 20, 2020, 06:18:38 pm
content: If you have a question just ask, or post a new thread if it's unrelated.