six pulse rectifier - Page 1
Forum section: electronics / beginners

author: SG-1
author_rank: Regular Contributor
timestamp: February 19, 2017, 04:46:14 pm
content: I am looking for the equation to determine the 3-phase current into the rectifier circuit & the DC current out. No filtering is used.let's say I have 10A DC load. How many amps ac will be present ?I have made some measurements & the ratio seems to be about .8 AC Amperes to 1 DC Amperes.

author: Zero999
author_rank: Super Contributor
timestamp: February 19, 2017, 06:29:32 pm
content: Are you talking about the peak or RMS current? The peak input current will be the same as the peak output current. KCL.

author: SG-1
author_rank: Regular Contributor
timestamp: February 20, 2017, 04:27:50 am
content: Thanks hero999, that is interesting. Do I not have to account for the efficiency of the diodes ?I am interested in the RMS current in vs the DC current out.Supposed one wants to limit, fuse, a DC power supply to 10 Amperes, one could place the over current protective device with just an ac rating before the rectifiers or an ocpd with a DC rating after the rectifiers. It appears the ocpd would have to be different values depending upon location.

author: Ammar
author_rank: Regular Contributor
timestamp: February 20, 2017, 05:50:00 am
content: Hopefully that helps.

author: Ian.M
author_rank: Super Contributor
timestamp: February 20, 2017, 06:39:20 am
content: Here's a LTSPICE sim to play with. Its set up for one cycle of 50Hz, and uses near-ideal diodes. You can use it to confirm numerically the results for the circuits Anmar posted.

author: Zero999
author_rank: Super Contributor
timestamp: February 20, 2017, 09:03:25 am
content: Quote from: SG-1 on February 20, 2017, 04:27:50 amNot for the current draw. The diodes only drop voltage.QuoteThen that's more tricky, since the current is drawn in pulses, the power factor will be poor.QuoteI'd strongly recommend putting the over current protection before the bridge because, f the bridge fails, the input power supply and wiring will be protected.

author: SG-1
author_rank: Regular Contributor
timestamp: February 21, 2017, 05:32:56 am
content: Quote from: Ammar on February 20, 2017, 05:50:00 amThank you, there is a lot there for me to digest.

author: SG-1
author_rank: Regular Contributor
timestamp: February 21, 2017, 05:35:24 am
content: Quote from: Ian.M on February 20, 2017, 06:39:20 amThank you, I have been trying to simulate this in LTSPICE for a few weeks now. I can finally see what I am doing wrong.

author: SG-1
author_rank: Regular Contributor
timestamp: February 21, 2017, 05:40:55 am
content: I'd strongly recommend putting the over current protection before the bridge because, f the bridge fails, the input power supply and wiring will be protected.We have had some failures on some 1950 vintage DC supplies. The diode bridge / volt trap failed & damaged the variable auto-transformer feeding it. I agree it is better to place the protection ahead of the bridge rectifier.

author: digsys
author_rank: Unknown
timestamp: February 21, 2017, 06:11:14 am
content: If you want even lower ripple output, you use 2 sets of secondaries - 1x star and 1x delta. It's double the diodes, but incredibly low ripple, 0.5%, and therefore ACcurrent peaks. We use it a lot for much higher currents, but it will work for any power. Obviously, depends on what you require.