Powering AC SMPS from HV DC  - Page 1
Forum section: electronics / projects

author: firepower
author_rank: Regular Contributor
timestamp: April 11, 2015, 04:18:24 am
content: CHAdeMO fast charging should use 50V to 500V DC 125A to charge EV, but many charging stations only do 300V to 500V DC which is fine for cars, but too high for motorbikes which usually need 50V to 200V DC ,one solution is using AC SMPS and feeding DC into the input, this will allow it to be used at home on mains power and AC charging stations, but I think it also work with CHAdeMO DC charging stations.Most AC switch mode power supplies (SMPS) can run off high voltage DC (you dont need seperate DC to DC), It just means it be using 2 out of the 4 rectifying diodes, so as long as the 2 diodes can handle full load it should be good. IF we can get CHdeMO to supply the high Voltage DC to use instead of high voltage AC, It may be even more efficient with higher voltage than 110VAC/230VACHopefully can use our muliple Meanwells , Elcons, (or cheap server powersupplies, etc) in series for high voltage and currentThe same technique using cheap laptop style AC to DC power supplies powered from 116DC from battery pack to generate 13.8VDC 10A for bikes instead of buying the expensive ZERO 12V DC kit.Below is from wiki pedia"If the SMPS has an AC input, then the first stage is to convert the input to DC. This is called rectification. A SMPS with a DC input does not require this stage.""A SMPS designed for AC input can usually be run from a DC supply, because the DC would pass through the rectifier unchanged. If the power supply is designed for 115 VAC and has no voltage selector switch, the required DC voltage would be 163 VDC (115 × ?2). This type of use may be harmful to the rectifier stage, however, as it will only use half of diodes in the rectifier for the full load. This could possibly result in overheating of these components, causing them to fail prematurely. On the other hand, if the power supply has a voltage selector switch for 115/230V (computer ATX power supplies typically are in this category), the selector switch would have to be put in the 230 V position, and the required voltage would be 325 VDC (230 × ?2). The diodes in this type of power supply will handle the DC current just fine because they are rated to handle double the nominal input current when operated in the 115 V mode, due to the operation of the voltage doubler. This is because the doubler, when in operation, uses only half of the bridge rectifier and runs twice as much current through it. It is uncertain how an Auto-ranging/Active-PFC type power supply would react to being powered by DC."To upgrade the rectifying diodes is simple just replace the 4 diodes (or diode bridge)with higher voltage/current specs if needed.

author: DanielS
author_rank: Frequent Contributor
timestamp: April 11, 2015, 04:45:11 am
content: If you are going to mod a power supply to run off DC, you can simply bypass the rectifier bridge altogether instead of upgrading the diodes.If the power supply you are modding has a 115/230V switch, then it only uses one diode on alternate half-cycles to charge the top and bottom on each half-wave, which doubles the total voltage. If you put 160V DC on the 115V position, only the top capacitor will get charged and the PSU might not work properly, if at all. You need to set it in the 230V position to use the full bridge on AC and then you would need to feed it 300V DC. For PSUs with PFC (no switch), you would need 300-350V DC too.

author: firepower
author_rank: Regular Contributor
timestamp: April 11, 2015, 05:24:10 am
content: We still want to use the SMPS on AC too, but have option to use high voltage DC too. If these SMPS use switching mofet rectifiers, Would feeding them DC cause issues?here is a thread about the SMPS AC to DC fast charging to give you info about what type of SMPS are in use.http://electricmotorcycleforum.com/boards/index.php?topic=4523.0

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 11, 2015, 08:02:34 am
content: Active PFC circuits may not necessarily be happy with an unexpectedly static input. I've seen at least one PFC controller chip (but I don't remember which) that stated something to this effect in the datasheet.I would guess 90-98% of the power supply modules currently on the market would be happy with DC input. Some even say so on the label. Make sure it's fused by an approved device, that is capable of clearing DC of the stated voltage!Tim

author: DanielS
author_rank: Frequent Contributor
timestamp: April 11, 2015, 08:22:26 am
content: Whether synchronous rectifiers will be ok with DC depends on whether the bridge driver will start driving the appropriate MOSFETs regardless of how the controller gets powered on. If the driver chip waits for zero-crossing or something else to start driving after it has enough supply voltage to start up, then the rectifier will still work through the FETs' body diode, albeit at reduced efficiency due to the forward voltage drop not getting shorted out by the channel.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 11, 2015, 03:00:17 pm
content: Synchronous rectification is rarely done at mains voltages as it offers little improvement.

author: DanielS
author_rank: Frequent Contributor
timestamp: April 11, 2015, 04:18:52 pm
content: Quote from: NiHaoMike on April 11, 2015, 03:00:17 pmIt is becoming increasingly common in Platinum and nearly mandatory in Titanium 80+ rated power supplies and all sorts of high-efficiency supplies over a few hundred watts where every 1% efficiency gain counts.Some power supplies even combine the PFC function with synchronous rectification for even better efficiency and reduced component count.