Buck converter for dropping 350V DC to 48V DC

Re: Buck converter for dropping 350V DC to 48V DC

Dave,

Historically, Semi companies, like National made Buck and Boost PS controller chips "all" that one would have to do is to is come up with a couple handfulls of transitors, a couple of large inductors, some large fast diodes capacitors heatsinks fans... etc, etc ...

Bet one could let out lotta smoke in the development process.

You might want to look for a 240 VAC Solit-phase input 48 Volt Power Supply. Perhaps you could hack it to accept the 350ish volt input.

I am assuming that the input might be PV strings, but it might just be rectified 240 VAC Split Phase line current. 240 Vac THROUGH A fwb INTO A cAP BANK IS ABOUT 350 VDC, but that simple circuit would NOT be PFC.

Many large switchers were used in the Telecom industry. It would be much better if MPPT was not required, and your 50 V WAS 50 V, not 46 to 64 V. Many of these Telecom PSes have a fairly low Vout max range.

boB knows all. Vic

Re: Buck converter for dropping 350V DC to 48V DC

Dave,

OH, frgot about the Volts.

Yes, the XW 600 80 (is that it ??) came to mind.

BUT, if the Volts were mine, I'd probably leave those Amps inside. Dunno, backup gensets sure work well, and there is your large On-Grid PV array ... .

I had wondered about trying to build a large (75-ish A) 2,4,6, 12 volt charger (no, not the cars) , but any of these projects just take a lot of time. Currently use a home brewed Variac - transformer - bridge - capacitor, manual job that works fine. Just not automatic.

Good Luck, Vic

Re: Buck converter for dropping 350V DC to 48V DC

The most readily available switching converter would be a flyback based power supply. One that runs on 120/240 vac would produce a high voltage DC.
When running on 240 vac the rectified filter cap will have about 340 vdc. The flyback switcher then converts this 340 vdc to its designed output voltage. This type of power supply is used is just about all computer power supplies. There is optical or transformer feedback coupling on the output voltage sense to provide isolation between primary and secondary side of transformer.

You have to find one with a 48 vdc with current limited output. You can modify the resistors on the output voltage feedback sense to raise the output voltage slightly to the 52 vdc necessary for floating a 48 vdc lead acid battery.

The problem with flyback power supplies is their efficiency is rarely above 80%. The flyback transformer is actually storing energy and discharging it to secondary winding.

It is possible to make a conventional buck converter but the voltage input to output ratio is such that the switching duty cycle becomes very small. This requires very low resistance MOSFET's to avoid too much loss in the switching device. It would also lack safety isolation between input and output.

The most efficient method would be a push-pull switching transformer converter. It can achieve high 90's% efficiency. You can get the duty cycle up on the switching devices ratioing the power transformer. The transformer is transferring power, not storing energy as it is in the flyback design. The potential issue with this type of switching power supply is any slight difference in push-pull switching times results in DC magnetic bias building up in the power transformer which can push the peak power transfers into transformer core saturation which causes the current to shoot up potentially damaging the switching devices. This type of converter is used is all low cost DC to AC inverters to convert input battery voltage to high voltage DC which is then chopped to produce modified sinewave or PWM'd and filtered for true sinewave inverter. Xantrex and Outback use this type of converters in their designs.

Re: Buck converter for dropping 350V DC to 48V DC

Here is what I found:
https://www.powerconversion.com/assets/aif12w300_ds_1191524409.pdf
http://www.meanwell.com/search/rsp-2000/RSP-2000-spec.pdf
Non stock item with Mouser.com minimum buy of 8, $316 ea

Re: Buck converter for dropping 350V DC to 48V DC

I did the Prius thing, works well. You really need to measure the min-max voltage fluctuation on the battery pack before you commit to anything. Just because it is rated for X doesn't mean it won't go down to Y or up to Z. My Prius battery is rated for 201.6 volts, but I measured it as high as 244 just before the engine shuts off and as low as 190 as it starts the engine. Details in the link in my signature.