Can switch mode PSUs work from DC 300V? - Page 1
Forum section: electronics / general

author: elektrinis
author_rank: Regular Contributor
timestamp: August 05, 2020, 08:27:00 pm
content: Modern PSU incorporate a PFC, which expects AC to be fed.However... Will it work fine from DC source? From first glance ir kinda should, but I guess things are smart now and may think of reasons to go in to faults, etc.Shouldn't all modern PSUs run from DC just fine?

author: tom66
author_rank: Super Contributor
timestamp: August 05, 2020, 09:19:09 pm
content: Most will work well. With some exceptions.Some active PFC units will not boost without seeing a real sinewave or at least an AC input. With only 300V DC in, the full rated power output may not be available, or the PSU may stay in an undervoltage lockout condition or have a lower output voltage from nominal. The benefit of APFC is that the input:output voltage ratio of the main transformer can be much closer than one with a universal or even normal line voltage input, because it only has to work from 390V +/-20V; the consequence is that it may not work correctly with a low DC input.In certain power supplies the APFC circuit generates the low-voltage DC to power the rest of the power supply (via a tap on the PFC inductor) - without this, the PSU will not work. This is quite uncommon, generally only seen in PSUs without a standby circuit.The bridge rectifier may get hotter or fail if only two diodes are permanently conducting; heat/current is not spread across two devices.Some power supplies feature AC detection so that they can shut down as soon as line voltage is lost (this is common on TVs or audio amplifiers to avoid a "pop" when powering off, although it's much less common nowadays.) If there's no AC signal, this circuit may not work.

author: elektrinis
author_rank: Regular Contributor
timestamp: August 05, 2020, 09:23:16 pm
content: OK, so I guess DC powered home will have to wait then.. It would be nice to switch to DC when we already have solar power and most of electronics is almost ready. I know, circuit breakers are not compatible with DC, other things likely as well. I was just wondering how long this switch with take.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 05, 2020, 11:04:09 pm
content: Quote from: tom66 on August 05, 2020, 09:19:09 pmLargely offset by the lower average and peak currents with DC. That's especially true with "universal input" supplies that are very common nowadays.Quote from: elektrinis on August 05, 2020, 09:23:16 pmPulsed DC is compatible with AC switches and has most of the advantages of plain DC. Also trivial to make from plain DC with just one solid state switch.

author: Seekonk
author_rank: Super Contributor
timestamp: August 06, 2020, 12:05:40 am
content: Quote from: elektrinis on August 05, 2020, 09:23:16 pmMy PFC HP server power supplies work with 140V DC, won't start with 60. have heard 80 will do it. I have several old inverters where I ripped out the H bridge and just feed 140V DC to power DVD players and other electronics. I have a large capacity LG clothes washer running with a modified MSW inverter that I feed 140V DC with right off the panels. My dishwasher heating element runs off array voltage. Heat water off array at power point and I know someone who runs his clothes dryer heating element off array DC voltage.How long will it take? The microprocessor toilet won a IEEE prize in the early 70's. That only took 40 years to happen.

author: tom66
author_rank: Super Contributor
timestamp: August 06, 2020, 07:34:54 am
content: So, running your whole house on DC is a no go.There are plenty of things that will not take well to this, such as transformers and AC motors (especially ones with speed controllers, like those in washing machines.)Most active PFC supplies will work, as will almost all non-active PFC supplies, but it's hard to say without testing what will and won't work. I know some datacenters have moved to 380V DC distribution within, which is backed up by large DC UPSes, but these will be custom appliances.

author: fourtytwo42
author_rank: Super Contributor
timestamp: August 06, 2020, 08:25:58 am
content: Quote from: elektrinis on August 05, 2020, 09:23:16 pmIMOP high voltage DC in the home is extremely dangerous primarily because of arcing that will continue potentially unnoticed under the floor or inside a wood framed wall creating a fire hazard. Just go for the double conversion (DC-AC-DC) and accept the tiny increased losses.

author: Berni
author_rank: Super Contributor
timestamp: August 06, 2020, 11:04:44 am
content: Most switch mode supplies will indeed run fine from 300V DCBut running an entire house from 300V DC is not a good idea. Some things still use oldschool transformers and those will get blown by having DC input. Any motors that are not universal brushed motors will also blow up if connected to DC, any variable speed controled brushed motors will run full power because they generally use triacs to control them. Light dimmers also use triacs and will be stuck at full power Things powered by capacitive droppers such as some standby cirucits, low power loads, or mains powered dropper LEDs will not work at all. Anything with a resistive heating element will be under more stress because its running at about 35% higher power.And finally the circuit breakers and fuses used on mains are not designed to interrupt high voltage DC. So when one of them trips there is a large chance they will draw an arc internally, continue passing current and soon after catch fire. So very bad idea.Its fine to run a few computers from 300V DC and make a special IEC cable for them rather than a power strip so that it is harder for someone to just plug a random device into it, also fuse it with proper DC rated circuit breakers.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 06, 2020, 01:00:00 pm
content: Quote from: fourtytwo42 on August 06, 2020, 08:25:58 amOr do pulsed DC or slew rate controlled square waves for lower losses and lower cost than sine wave AC.

author: ocset
author_rank: Super Contributor
timestamp: August 06, 2020, 01:32:51 pm
content: Here is some previous discussion on this topichttps://www.eevblog.com/forum/projects/powering-ac-smps-from-hv-dc/https://www.eevblog.com/forum/projects/computer-power-supply-on-dc/..there's quite a few other forum posts on this aswell.....it comes up quite often...sorry i could not find more for you.

author: jbb
author_rank: Super Contributor
timestamp: August 09, 2020, 11:58:42 pm
content: Sorry to be a killjoy, but... insurance. I expect your fire insurance would be voided by running nonstandard electrical supplies.I feel so middle aged right now :-(If you make an unrelated claim (eg burglary) and your insurer is a real asshole, they might even try to say “you’ve broken our agreement and we’re voiding the whole policy.”

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 10, 2020, 04:47:20 am
content: Quote from: jbb on August 09, 2020, 11:58:42 pmHow would they ever know? In that case, the only investigations that would make sense on site would be checking that reasonable security measures are in place (e.g. that a door is not left unlocked or wide open all the time) and possibly collecting fingerprints.

author: tom66
author_rank: Super Contributor
timestamp: August 10, 2020, 08:43:52 am
content: It's certainly not a thing in the UK. If you mod your vehicle illegally, and it is stolen, while the insurer isn't liable to pay out for any modifications you've made (as they're not declared) they're still liable for the vehicle itself. There is some wiggle room if they can demonstrate the modifications made the vehicle considerably more attractive or easy to steal, but e.g. adding a stupid spoiler or changing the rims, would not usually count.Now running 300VDC in your own home presents fire risks and insurers are always going to investigate the cause of a fire. I would ensure you get it declared with them, whatever you do.