3 phase rectifier with single phase fallback - Page 1
Forum section: electronics / projects

author: oliv3r
author_rank: Frequent Contributor
timestamp: November 13, 2022, 09:42:23 pm
content: Hey All,I've been thinking of wanting to power a device from 3 phases. Now this is not due to power requirements, we're talking about 3 - 5 watts at the most. However, as this would be a monitoring device, and should function even if one (or two) of the phases drops out, or if the device is simply connected to a service with only a single phase (which should cover split phase easily then), it should 'just work'.As the PSU also needs to be as small as possible (while still being properly isolated, e.g. transformer) I am borrowing an idea I saw elsewhere, Rectify, filter, SMPS (i think) with a much small transformer.So at first, I was thinking, well simple, single phase, is a full-bridge-rectifier, and there are 3 phase full-bridge-rectifiers, easy? However I noticed, at with 3 phase rectifiers do not care about the neutral. So 3 phases go nicely into 6 diodes, and nothing ever comes back (other then via the phases themselves of course, AC still applies).But this would not work if I wanted to do single phase fallback. I did see a half-bridge-rectifier, e.g. just 3 diodes, which would work exactly how I expect, with the downside, that especially with single phase, we'd be having a typical single diode rectifier. Might still work fine, but with greater losses?An ugly alternative, would be different wiring schemes depending on what the setup is, but that then doesn't help with a 2 phase failure scenario.So is what I want, full-bridge rectification with support for single and triple phases even possible?

author: TheMG
author_rank: Frequent Contributor
timestamp: November 14, 2022, 12:56:53 am
content: For single-phase operation just wire the neutral to any of the bridge rectifier inputs. The bridge rectifier really won't care.I wouldn't worry too much about dropping 2 out of 3 phases in 3-phase operation, as that would be a very rare scenario. But if you do want to cover that possibility you can always add two more diodes to your bridge rectifier and wire the neutral to that.

author: Wolfram
author_rank: Frequent Contributor
timestamp: November 14, 2022, 04:59:09 am
content: You could either do a four phase rectifier, with the Neutral as the fourth phase as suggested, easily implemented with two full bridge rectifiers. Half-wave rectifying all three phases against the neutral as you mentioned is also a good option, with the advantage that you could use a standard input voltage SMPS in the case of using 400 V mains.

author: geggi1
author_rank: Frequent Contributor
timestamp: November 14, 2022, 05:59:12 am
content: This will work with 2 and 3 phases and is very common in a lot of industrial stuff.If you got 3 phases and nutral use the 3 diode circuit and if you dont use the 6 diode one.With loss of one phase (2 phase) you wil get a lower RMS on your DC.https://www.electronics-tutorials.ws/power/three-phase-rectification.html

author: oliv3r
author_rank: Frequent Contributor
timestamp: November 14, 2022, 09:12:31 am
content: Quote from: TheMG on November 14, 2022, 12:56:53 amThat would be a 'wiring alternative' right?Quote from: TheMG on November 14, 2022, 12:56:53 amIt is, but, it's the redundancy factorAlso, single phase solution at the same timeQuote from: Wolfram on November 14, 2022, 04:59:09 amAs I couldn't find a 4 phase bridge rectifier, I suppose that's the only wayI did a quick draw (see attachment) which is what would be the result then. Since a smd Full-Bridge-Rectifier can be had as cheap as €0.04 (in bulk) this isn't too bad.The wave form and all math still works out the same as a 3 phase rectifier, right? so at 240V per phase, we still have ~400V, and the ripple looks the same too? (Couldn't imagine it any other way anyhow). What about the current, not an issue with a 5Watt device, but generally speaking. Does anything even travel over the neutral or are there other issues to be aware of?I was thinking at our 3 phase fuseboard. Here we get 3 phases + neutral entering our home, and then each phase is used for different area's/devices. e.g. 1 phase is for the induction stove, one for the oven, one for an AC, so the loads are nicely distributed. However all current enters via one phase, and exists via neutral (e.g. standard single phase setup). But Somehow, I'd think all current is now 'leaving' through neutral, which means the neutral would need to be 3x as thick a cable to carry all that current!Quote from: Wolfram on November 14, 2022, 04:59:09 amOk this confuses me a bit, why wouldn't I be able to use a standard 400V SMPS in the case of the quad phase solution? Both produce 400V DC, albeit with a smaller/bigger ripple. I do just realize, the input of the SMPS will have to work with input voltages from 230 - 400V (well whatever RMS those equate to) to handle single, double and triple phases (ideally 100 - 400V to also deal with those 120V systems ....) Would be a truly universal PSU

author: Zero999
author_rank: Super Contributor
timestamp: November 14, 2022, 09:55:48 am
content: Quote from: oliv3r on November 14, 2022, 09:12:31 amThat configuration will produce 325V on single phase and 563V on three phase.

author: xani
author_rank: Frequent Contributor
timestamp: November 14, 2022, 02:13:32 pm
content: There are dedicated devices that do what you ask, they just pick a phase and switch to different one if that one dies. If all you need is to keep your automation/metering/whatever going that is most likely the simplest solution. The name to google is "automatic phase switch".

author: oliv3r
author_rank: Frequent Contributor
timestamp: November 14, 2022, 02:56:44 pm
content: Quote from: xani on November 14, 2022, 02:13:32 pmThat looks mighty expensive instead of just using 2 bridge rectifiers, also, I still need to monitor the 3phases, so all 3 phases are still entering the system ... Not sure what the benefit would be for that.Quote from: Zero999 on November 14, 2022, 09:55:48 amSo an SMPS chip that can take as input anything from 325 to 600V. Thanks!

author: DavidAlfa
author_rank: Super Contributor
timestamp: November 14, 2022, 03:25:03 pm
content: Quote from: oliv3r on November 13, 2022, 09:42:23 pmJust add another rectifier to the 3-phase?In fact, given the low power, just use 8x cheap 1N4007.Definitely a 600V smps IC is too close, 3-phase will give around 588V.

author: oliv3r
author_rank: Frequent Contributor
timestamp: November 15, 2022, 08:26:43 am
content: Thanks all! The double bridge rectifier seems like the cheapest solution (in terms of cost and PCB spaceNow the trick will be to find a 100 - 600V SMPS :p

author: Zero999
author_rank: Super Contributor
timestamp: November 15, 2022, 10:48:05 am
content: 8 diodes such as the 1N4007 or two bridges like the DB107S will do.A rating of 600V is marginal. The upper tolerance for the mains is 253V single phase, which is 438V three phase, giving 620VDC on the output of the rectifier. You'll have to use two capacitors in series for smoothing, because electrolytics top out at 600V. Add balancing resistors in parallel so they share the voltage.

author: Phoenix
author_rank: Frequent Contributor
timestamp: November 15, 2022, 10:55:17 pm
content: Quote from: oliv3r on November 15, 2022, 08:26:43 amOff the shelf power supplies that go that high can be hard to find. Were you planning to make your own? Infineon (and probably others now) make flyback controllers with integrated FETs up to 950V. If you're designing your own you need to consider line voltage surges and transistor voltage derating too.https://www.infineon.com/cms/en/product/power/ac-dc-power-conversion/ac-dc-integrated-power-stage-coolset/