High power DC/DC converter 12 V to 360 or 720 V 10kW

Just a quick note. Your trannies will see 48V on their drains when the other "side" switches in a 24V system . For a 12V system the IRL2203N will probably be ok but not for a 24V system. This is assuming I have not misinterperated what you are doing. Cheers Rob

The only suggestion I really have is to start with the 48V - the switching transients will be higher, but you'll only have to deal with 1/4 the current.

Good Luck! Rich

CT-PP will be copper inefficient, and getting rid of heat from the transformer will be, umm, important.

Where are you going to get 12 volts at 1000 amps?

John

I will probably make the first prototype for 12 VDC source and 360 VDC output at nominal 1 HP (750 W). I already have the 240 VAC VF controller, IRL2203N transistors and a 12 VDC SLA battery, which should handle the

50-60 amps. I also have several 240 VAC motors of 1 to 2 HP.

Once I prove the concept, and work out any unforeseen bugs, I will be able to scale up the design to the next step, which would be 24 VDC to 720 VDC, and about 4 HP (3 kW). I will need to obtain or make a 480 VAC VF controller. I found some on eBay for under $100, but the one I was most interested in (7620803063) has a date of 1988 and I wonder how good it would be. I want a 480 VAC controller to see if I can double the HP of the

240 VAC motor by running at 120 Hz. I might use this system to make an electric powered lawn tractor, which will also be a "vehicle" for testing other concepts.

My final goal is a controller and motor system for an electrically powered car. My original idea was to rewind a motor for low voltage and run it directly from a battery pack of 48 or 72 VDC. I figure about 10-15 HP per wheel should be OK. I was going to use 3 HP 600 or 900 RPM motors and then push the HP to 4x or 6x, and use two motors on the rear wheels. That may prove to be the best final solution, but I wanted to try some ideas with standard motors first, before investing in rewinding. I did rewind a small

3/4 HP motor for 8 VAC with 12 poles and it runs at least up to 1800 RPM at 180 Hz, and I will do some experiments with my low voltage VF drive using that motor before I rewind a larger one.

I'll let you know as I progress. I appreciate your comments and suggestions.

Paul

You are a fun guy!

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Unfortunately your transformer will likely start smoking before you even hook up your load. If you 10X your frequency, that should allow you to 10X your applied voltage before hitting your saturation limit. Unfortunately, the transformer won't be saturation limited, it will be thermally limited long before you apply 10X the volts/turn.

If I understand my magnetics correctly, 10X-ing the applied voltage and

10X-ing the frequency should 10X the core hysteresis loss. Core hysteresis loss is basically independent of load power.

That won't be your real problem though. The real problem will be core eddy current loss. If I understand things correctly, all else being equal,

10X-ing the volts/turn should 100X (a factor of 10 squared, from the formula V^2/R = Power) the core eddy current loss. Core eddy current loss is also more or less independent of load power.

So, all else being equal, the net result will be your total core loss will likely increase by some factor between 10 and 100.

There is a small advantage to using square wave excitation compared to sinusoid excitation on the transformer however. I assume your 0.4V/turn figure is an RMS AC value. For an equivalent RMS voltage value, a full duty cycle square wave will subject the core to less volt seconds/cycle than the equivalent sinusoidal RMS voltage. Nevertheless, this small advantage will not keep your transformer from smoking, the above still applies.

You can still rewind the transformer for more power than the original 1kVA if you use 600Hz, but 10X-ing the power level is not realistic (at least not without much improved cooling).

55

The center tapped push pull topology is not a very good choice for such large current levels. Any leakage inductance on the primary will contain tremendous amounts of energy at the moment of MOSFET turn off. This energy must go somewhere, and it will have to avalanche the MOSFET in that topology (unless you use a couple of huge RCD snubbers across each half of the primary). The energy will likely destroy the MOSFETs.

The H-bridge topology would be much better suited to this task. In particular, the H-bridge topology allows energy stored in the leakage inductance of the primary to be returned to the DC input rail.

As John Larkin cogently pointed out: 12V at 1000 amps That is excellent as it would give you about 83 % conversion efficiency. While not state of the art, it was a good point. Leading to: mucho problems. Without proper insulation, you could turn your golf cart into a

4 wheel MO BYLE BBQ pit!

I designed inverters at Ford Motor as part of their electric vehicle program

1kW 2kW 5kW with about 85 % efficiency in the early 1990's. Current state of the art is about 92 % efficiency.

Due to mistakes made at various manufacturing stages, we saw a lot of components go Fzzzzzzzzzz and up in smoke, sometimes with serious damage!

Also, during the development of the 5kW inverters, EMI issues really surfaced. A nearby Ford EMI lab told us that we were generating fields strong enough to "confuse" some the on board electronics on automobiles. They said it took about a month and some direction finding equipment to track us down before the FCC was able to find us. We had to build a shielded lab.

At this point, the manager had finally agreed that simulation was an important ingredient on the development process. But these always work in simualtion.

Good luck, Dave

I have assembled the first prototype, and it seems to work OK. The toroid core is actually 1 volt per turn, and about 2 kVA nominal at 60 Hz. I used

6 turns of #10 AWG for the two primary legs, and two secondary windings of 30 turns each of #15. I use two MT60N06 MOSFETs for switching, with snubbers across each. I am using an SG3526 PWM IC. I have a FWB on one of the secondaries, into a 1500 uF 450 VDC capacitor.

As a first try, I was able to get 81 VDC with a 15 VDC supply, at about 400 mA with about 20% PWM. Then I adjusted the PWM to near 100% and got 56 VDC with 10 VDC at 1.3 amps input. I added a load of 900 ohms, and got 54 VDC at 1.5 amps input. I'm running at about 450 Hz. The current goes up if I reduce the frequency.

From this, it looks like there will be a minimum loss of about 13 watts. I was able to get 3.4 watts of power out for an additional 2 watts input. I will need to apply much heavier loads to get a true idea of the efficiency. I thought most of the power was lost in the forward conduction of the transistors, but with 0.016 ohms at 1.3 amps that is only 0.03 W. It is probably lost in the transformer. If the transformer is rated for 2000 watts, 13 watts loss is better than 99% efficiency, and if it is rated at

10 KVA at this frequency, it is much better. At 600 watts, with 50 amps being switched at 12 V, the forward drop in the MOSFETs would be about 40 watts, so efficiency would be about 93%. I will probably need better MOSFETs or a lot of them in parallel to get my 10 kW.

Of course, higher currents will also result in copper losses. I have room to add another set of primary windings and another set of secondaries. I would expect the no load primary current to double with two in parallel. With four secondaries, I should be able to get 260 VDC at 12 VDC. I may need to remove one primary turn to get 320 VDC which is about minimum to run a 208/240 VAC motor, but realistically I expect to use 24 VDC for 240 VAC, and 48 VDC for 480 VAC. It looks like the output voltage is just about

5 times the input voltage, which is the winding ratio of 30 to 6.

I will need to package this monster a bit more carefully to do higher power testing. I think the concept is proven enough to proceed to the next step. I'll let you know what sort of results I get.

BTW, what ever happened to Ford's electric car program?

Paul

Like all other major auto manufacturers they have realized that battery technology has a *long* way to go before even coming close to the performance of the current generation of hydrogen fuel cell electric vehicles, with their 65 kW fuel cells, 60 kW motors, and 400 kM range. While others are busy talking about how impractical fuel cells are the auto manufacturers are busy developing them. I guess all af the major auto manufacturers must be clueless :-).

Fuel cells are insanely expensive and short-lived. There's no practical way to store a useful amount of hydrogen on-board a car, and no way to manufacture the hydrogen that's not polluting, absurdly inefficient, or both.

The thing that electric and hydrogen-powered vehicles almost always have in common is that they're small, light, and very aerodynamic. So it makes a lot more sense to just make small, light, slippery cars and power them from gasoline engines, maybe with hybrid electric boost.

John

Bad, bad math. Sorry.

Sure will. Without copper losses, a megawatt transformer would fit in your pocket.

No, magnetizing current and core loss wouldn't change.

As you increase primary voltage, you must increase primary turns to avoid core saturation. More turns of thinner wire blows up the copper loss. The only way out of that dilemma is to keep the pri turns constant but increase frequency, which has a set of problems of its own.

Mother Nature was in a very bad mood the day transformers were invented.

John

Yep, pretty much so. The clue that they have is that there is big bucks in researching hydrogen vehicles (Hey, the government is giving away free money!) but that there is NO MONEY WHATSOEVER in actually producing the expensive, short-lived, short range dangerous things for commercial sale.

However, there might be a reasonable market for electric vehicles for commuters, but these might take away sales from SUVs and other profit centers, so they put them on a back burner.

Charlie

I agree. My 1998 Saturn SL1 5 speed bare bones car averages 36 MPG and can get 45 MPG on the highway. Ten years later and you probably can't get a non-hybrid that will do as well, because the commercials push ZoomZoomZoom. For the manufacturers, it's all about immediate profits, and they move so slowly that they won't be able to come out with an economical vehicle to meet present demands, due to fuel costs, for about five years. Also, people will not really "demand" a lightweight, efficient vehicle until gasoline reaches about $5/gallon. And there is the question of safety, which will make it hard to reduce weight while there are still so many heavy cars, SUVs, and trucks, being driven by increasingly aggressive, cell-phone distracted drivers.

I am still considering adding rear wheel drive electric boost to my other Saturn SW1, which has a failing motor. Maybe I'll go all electric, which is probably practical for my usual 25 mile commute and other trips which usually are less than 100 miles a day. About 500 lb of batteries should give me that, and the energy cost will probably be about $2.00, compared to about $10 for gas at 30 MPG.

Ultimately, I think hybrids will be designed that use ethanol or veggie oil. Another possibility is to add a modular motor/generator pack to an electric vehicle for long trips, so you leave the extra weight at home when you are just commuting. There are many ideas floating around that can solve our energy crisis, but we need public acceptance and government support to make them work on a large scale. Eventually, I hope, battery technology will make EVs viable for 90% of all transportation needs.

Paul

I'm hoping to meet a witch who knows some physics, and create a Zero Point Daemon for unlimited free energy. ;-)

Cheers! Rich

That's because Mother's energy is magnetic, and She doesn't like being pushed around by cold, unfeeling electricity.

Thanks, Rich

Be careful what you wish for. Such a thing would be built into a terrible weapon long before it was put into any transportation machine. Availability of unlimited free energy would be the the beginning of a very quick end of the human race, and possibly the planet.

No, you see, we'd create a daemon who would refuse to let his powers be used for evil. :-)

Take the Rich Grise/Insert Name Here power unit, and try to make a bomb, and it would say, "Fuck You." Or maybe just azp the individual evil person. ;-)

Cheers! Rich

Geez, you sure sound like a person who has no kids.

John

Don't blame Grease. It's hereditary.

--
  Keith