DC converter 200v->12/24/48 - Page 1
Forum section: electronics / general

author: Dankoozy
author_rank: Contributor
timestamp: August 31, 2022, 11:48:46 pm
content: I have an array of 4 solar panels connected to a grid tie inverter but it would be nice to be able to charge some batteries with it too especially if we get all the black outs they are promisingSo I am thinking of building a charger to charge some batteries at 24v. I built a few buck converter based MPPT chargers before but only for a single panel (50v/10A) but I'm wondering would it be silly to use buck topology for such a large step down? I could do away with 12V charging if I want but probably want to keep the ability to charge at 24, should I look at building a flyback converter with custom made transformer instead?

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 01, 2022, 02:26:53 am
content: Just get a common switching power supply and hack it to throttle back the output in order to hold the input voltage near MPP.

author: Faringdon
author_rank: Super Contributor
timestamp: September 02, 2022, 04:46:49 pm
content: i once had to bring up a buck for 300v to 100v at 300w...it was using sic fets...which obviously have sic parallel diodes in them.....btu use a low side sic if you want too, for safety in case.In fact it was a dual cascaded buck...so two bucks with their fets controlled by the same controller.....if you want ill send you the schem etc?The cascade made it easier to handle the high voltage and big step down.The circuit was originally for 300v to 24v 300w....but we adjusted it.Top fets were driven by pulse transformer.....hi side current sense via current sense transformer.Worked well...just used a uc38c43.You can get high pwoer by paralleling any number of converters...just add a current clamp to the outptu of each......ie opamp to pull down error amp if goes over nom max current...then no converter will hog more than its max.

author: Dankoozy
author_rank: Contributor
timestamp: September 03, 2022, 09:54:05 pm
content: Quote from: Faringdon on September 02, 2022, 04:46:49 pmKewl ya it would be interesting to see it anyway

author: Faringdon
author_rank: Super Contributor
timestamp: September 03, 2022, 10:44:05 pm
content: Thanks, here is the dual cascaded buck in the free LTspice.Sorry it does some messing about with full load to no load transient at the startSo is it 200V, 10A that comes out of your panels now?I dont see why you coudlnt do it with a buck, or a cascaded buck, or a few cascaded bucks in parallel.Since you are charging batteries , you are reg'ing the output current, so you can just put smps in parallel if you want.There are boost converters as PFCs that do 2kW, with 400v output, and 0v input when mains is at zero cross, so sure you can do a buck to go from 200v to 12v (or cascaded buck is better) at 2kw.Yes you are right though, 200v is high and you would be best to use sic diodes in the buck/cascaded buck.If you use a sync buck, then you will be best using sic fets , as non-sic-fets dont have sic diodes inside them.(You need sic to avoid overheating and noise due to severe reverse recovery)

author: Siwastaja
author_rank: Super Contributor
timestamp: September 09, 2022, 03:46:41 pm
content: Buck is, if not perfectly optimum at low duty cycles, quite acceptable. Think about CPU power supplies which buck 12V to 0.8V or so despite large ratio and low duty cycle. They deal with that by multi-phase design.For 12V target, you probably want synchronous buck. 24V or 48V I wouldn't care, schottky diode drop is then OK.But remember, 200V is already beyond safety extra low voltage, and being a non-isolating topology, you should consider the whole circuit dangerous HVDC!Flyback would allow designing for more balanced duty cycle and avoid the fundamental problem of buck: having to dimension transistors for combination of high input voltage and high output current. But flyback is another can of worms with added complexity, costs and losses.TLDR: do the math and if the cost of MOSFETs with Vds_max>300V and low enough Rds_on to handle I_out isn't prohibitive, then buck is fine.

author: james_s
author_rank: Super Contributor
timestamp: September 09, 2022, 05:40:41 pm
content: I would just use an off the shelf SMPS, many of them are wide voltage range and will run off 90-265VAC, should work just as well off 200VDC. Just don't get one that has active PFC, but most smaller ones don't.

author: Seekonk
author_rank: Super Contributor
timestamp: September 09, 2022, 11:33:54 pm
content: I use those 110-220AC 12V 10A LED switching power supplies on solar at 60V DC and easily get 8A out of them @14.3 with resistor change. I like them being isolated rather than buck. Many were picked up on auction for only $9 shipped. Can't build for that even if you double them up. Most solar applications have the panels floating. Some changes on the input to save every volt and accommodate extra current. You can go up to the 180W units. Over that the do voltage doubling on the input. The voltage doubler ones like a lot of voltage. 175DC didn't get a lot of power out of them.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 10, 2022, 01:32:28 am
content: Quote from: james_s on September 09, 2022, 05:40:41 pmThe PFC can be hacked into a MPPT boost converter. Then cap the duty cycle of the main converter and you basically have an isolated solar charge controller.