DC-DC Convertors

240 VDC are you sure you don't mean 240VAC? (Not pickin, just want to make sure of the facts!)

Enter the words "buck converter" into any internet search engine, and press enter.

Many of the buck converter designs on the net don't have stepping down a 240 V DC. Usually they step down voltages from say 4 to 60 V DC to a lower value.

You may want to search "240 V buck converter" or "High voltage buck converter" and check the maximum voltage for input on the buck converter design. Here is a nice design offers even isolation from high voltage but it uses a lot of circuitry and transformers and gives 5 V output, not 24 V.

http://cds.linear.com/docs/Design%20Note/dn260f.pdf

NB: If you are trying to work with the mains its not a 240 DC, its an AC voltage. Which is why the first comment on this tread.

buck converters are great , but is there one which can be used on electric cars which allows reverse flow for regenerative braking ?

ie having 140 VDC batteries , convert up to 450 VDC to input at the motor controller THEN also allow reverse conversion from 450 VDC down to the 140 VDC so the regenerative power recharges the vehicle batteries during braking cycles ?

that would be useful

How many tera-watts of power will you be applying at 24VDC?

How much of a load do you need to handle? We use DC-DC power supplies by Converter Concepts in some of our scada equipment. The VT50-181 model takes an input of 100-350VDC (or 90-250VAC) and gives 28VDC at up to 2A. They must have models that will provide 24V. Check their web site for standard versions or for contact info:

http://www.ccips.com/Products/Industrial/industrial___commercial_power_.html

First convert to ac...http://powtech.en.made-in-china.com/product/YbNJzerKgEIc/China-240vdc-AC-Inverter-1phase-.html

Not needed, but then again its not my money.

We use a lot of Vicor modules here; I think you'd have a hard time building one any cheaper than you can purchase one for, but I guess that depends on how much power you need, and what you might have on hand already.

Here's a link to their DC-DC converter page:

LINK

Hope that helps,

Tom D.

Most any standard universal voltage type switching power supply will work. They simply take the incoming AC voltage and rectify it to DC then use a high frequency switching system to step it down then re converter it back to DC voltage again.

Odds are you wont be able to build anything for the price and reliability that you could by a off the shelf unit for regardless of the power level you may need.

Have a look at Victron brand battery chargers their solar grid tie products include a 240V input charger that can handle DC input and you can select a 12V 24V or 48V charger. In effect this gives you 240V Dc to 24V DC conversion.

Plenty out there to choose from.

Did you try an internet search?

A switch mode power supply can run on DC input and works nicely as a DC DC converter.

What do you need it for?

I still think it would be wise to know if the 24V current will be closer to 50 milliamperes or 50 kilo-amperes.

Problem belong Normbourne.

By all means build your own. First purchase book by Marty Brown on power supply design.

When you've read it, consider whether you might have better put the book price towards buying a ready-made unit. Tesla made good stuff, but cost.

As we still don't know how many amps he needs at 24 volts, we also don#t know if he meant 240 volts aC or DC either, I think this guy could kill himself working with the mains supply.......

My suggestion is a 240 to 24 volt Toroidal transformer and an LT1074 chip, which will give him up to 5 amps in an 85% efficient circuit......I even have a circuit (contact me via CR4 email, with your normal email address) using two of the chips for a 10 amp supply.....far safer for someone just starting out working with the mains......and very few components in total.

I am guessing this is for a DC battery array. You could try Meanwell, Powerbox

Meanwell or Powerbox should have something suitable.

Also, don't forget that many modern switchmode power supplies can operate from both an AC or DC source, so don't forget to check those out either.

Okay guys, I seem to have stirred up a hornets nest, anyway, here is the good oil..!!

My mate has had installed a solar cell array, the output of which is sold to the supply electrical authority, this amount is then credited against his electric bill.

He has asked me, if it was possible to tap onto the the output from the said solar array, to charge a set of batteries, which will provide him with lighting only in his residence, in the event that he loses power, which often happens, as we live in a cyclone prone area.

I confirm that the output from the array, is 240volts DC which will be the input to the convertor, the output from same, will be 24volts DC. This will be used to provide charging current to the batteries, which will be no more than 10 Amps.

To those of you who have expressed concerns about my credentials, I advise that I am a time served electrician with 50 years experience, 35 of which, I was director of my own company dealing in electrical installations, at both 415volt & 11,000volt levels, so am fully aware of the various safety factors involved.

Thanks everyone for your input.

Norm.

talk to powerbox.

you would want a DC/DC converter that also has a charge controller and turns off when the batteries are fully charged so it doesnt waste any additional power from the retail end of the equipment after charge is complete.

something to be _very_ careful of , is to make sure that whatever you choose will not affect the operation of the anti islanding circuit in the inverter which is connected to the grid.

You will know what they are and their function , utility companies get very niggly about their functionality.

other way to approach it is to look at the grid tied inverter , and just run a 24 volt truck battery charger off the 240 V mains on that side .

but that wont work if the power grid goes down , because the anti-islanding circuit will also turn off the inverter...... ooops ... no 240 volt supply

so i understand why you want to take power off the DC side before the inverter now

Talk to Powerbox technical :)

cheers n good luck

You need 24V at 10A, that's 240 watts, a modest level of power. One thing that can be pointed out is that ordinary AC-line to low-voltage DC-output power supplies can be used with DC rather than AC input power. And AC power supplies are much more common than 240V DC-input supplies.

Internally they use a bridge rectifier to convert the AC to DC anyway, charging a "bulk" capacitor, before isolating and downconverting, so if you present it with DC power, the bridge rectifier simply passes this on to the bulk cap in a redundant manner.

A 220 or 230V AC line has at least 300 peak voltage on the sine wave, so the bulk capacitor gets charged to nearly that voltage DC, which is higher than the 240Vdc you have available. But some AC-line supplies work over the input range from 105 to 240 Vac, without changing a switch or tap, etc. If you find one of those, it'd be happy to work at around 240Vdc. One caution, you'll want to make sure that your proposed 24V supply doesn't have some type of small auxiliary AC transformer inside. If it advertizes a wide AC-input voltage range, it's likely it does not, but I'd open it for inspection anyway.

Another caution, I'd suggest that you not wire up your DC to an ordinary 230Vac socket to plug your 24V power supply into, but rather I'd suggest you change the plug on its power cord to something completely different from your AC-line connectors. We don't want anybody coming along later and plugging the wrong thing into your connector!

When I hear you asking for a diagram without telling us which power the device has to have I believe its no such good idea to build it on your own ...

G'Day Guys, All sorted, thanks everyone for your help & support. Norm.

What did you end up going with?

Wal, Powerbox have the answers, surprisingly, I have dealt with them before, whilst an Electrical Contractor, but I had forgotten all about them. (Age...????)

Once again, many thanks..!! Norm.

Nice one Norm

Cheers mate.