DC/DC converter - 8KW

May as well ask for a simple, low cost schematic to make a supersonic fighter jet.

Some things just aren't simple and low cost.

John

Nah, you can get a brand new one for $18.95:

Cheers

Phil Hobbs

:-) What do you think, how would you solve this ? I think that my approach is OK but i need some "confirmation" before i start the project.

Not being a big-iron power supply guy, I wouldn't make any design recommendations except to say that doing something that size is no joke, and not a job for an amateur.

Cheers

Phil Hobbs

The Right Stuff! Are batteries included?

John

That would be a monstrous and ugly buzzing transformer.

For this type of power/voltage, I would use MOSFETs and run at the frequency of 30kHz or so. The schematics would be an MCU controlled push-pull. Pay special attention to overvoltage/overcurrent protection, soft startup and shutdown, and stray inductances.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

It just struck me that this is a leftist weenie design (every which way but the right way ;-)

Is the end load _really_ an AC 8kW motor?

Why not directly make a DC motor (EC) on the 72V? ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Why not. I designed the contol part for that:

It is interesting to work with 800A of current. You can feel the straignt wires attracting or pushing away from each other like magnets.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

Hi Vladimir and thank you for your reply. I have some basic schematics so if you have some time i can send it to you. I can lower the frequency to 100hz or use 5-10Khz or 30Khz solution but if you dont mind i would like to talk this per email.

Can you share some mail address ?

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

What, like this one?

HI Jim. Why do you think that Vladimir has "the weenie design " :-) btw. i dont want to use DC motor because all my other control electronic is for AC motor. And yes, the motor is 8kw but the load will be in range between 3 - 5 KW.

Vladimir I have send you mail with photo.

since he mentions a Siemens micromaster variable frequency drive and an ac motor what else could it be?

for industrial stuff ac motors and VFD are more standard and he wouldn't need to change the mechanics

but looking at a place like this:

it does look like you could get a 72V motor and controller in that power range for not too crazy prices

-Lasse

Product discontinued. Pity.

Still, it didn't look cheap or simple.

John

I wasn't referring to Vladimir, I was referring to you ;-)

And if you can't control the speed of an EC motor, you need to go back to school ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Why did they discontinue it?

At >20kA you can see really thick braided wires move when pulsed :-)

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
--------------------------------------------------------------

Yes. I designed and tested several 500hp inverters (old McMurray-Bedford configuration). When a fault occurred (about 2000 amps), the 4-0 welding cables connected to the 3ph, 480V source would jump a foot apart or so. If you're standing near to them and got touched by them, you would almost need fresh underwear.

Well, first, to get 8 KW at 72 V, you need a current of 111 Amps. IGBTs are not a good choice until voltages get up above 200 V. So, some paralleled big MOSFETs like IFR260 or something might be the best. If you don't need DC isolation, for get the transformer, just use a big inductor and the classic boost regulator topology. Just 4 major components. A series inductor, a power transistor to ground, a series diode and a filter cap.

Jon

Oh, CRAP! I was focusing on the 72 V, not the 460. Yes, you may want to use IGBTs, but higher voltage rated MOSFETs could also work. MOSFETs are generally faster than IGBTs, so higher switching frequencies can be used, making the inductor smaller. That inductor (or transformer, if you do need isolation for some reason) is going to be a major thing to develop, so making it smaller may be desirable.

Jon