High power buck converter 36v output for electric vehicle.

[EWorkshop1708]

I'm designing a buck converter to allow charging of 36v of batteries for small electric hybrid vehicle from an onboard ac generator. The generator will be modified with variable throttle to save fuel.

Before this thread gets moderated, I understand the voltage risk involved, this is not a novice project. All dc rails will be isolated from frame (ground)

The questions I have regard heat of the output inductor for the conversion ratio....
Variable throttle I assume 80v-200v rectified dc from generator, so that's why I'm choosing buck instead of push pull, also because I have a large iron powder core, much larger than my ferrite cores. Also wider range of regulation.

Power goal 1500w+ and wrap as much 12awg coil wire as possible on 2 inch x 0.75 inch yellow/white core. I'll be using paralleled old 500V 100A darlington transistor modules for switching.

Would this be efficient enough to convert power without too much heat or power loss?

[!]

Excuse if I am wrong but the project doesn't seem to make sense and I wonder if you are using confusing terminology.

"Generator"? Don't you mean an onboard switching charging circuit? That would not normally be called a generator. "Fuel"? Unless there is a fuel cell to convert fuel to electricity, it doesn't seem likely any fuel is involved.

Now about the project making sense... you propose to use a 36V battery pack and step that up to 80V-200V to drive a motor(s)? It makes no sense from an efficiency standpoint. Use a battery pack with (summed) voltage equal to what the motors need for full throttle. If you don't do that you suffer a conversion loss twice if you are boosting to 80V to 200V, then buck(ing).

Large iron powder core? What about weight?

Paralleled darlington transistors will be too inefficient. Use mosfets, then your heat level drops too.

What is the need to use a 200V motor? Perhaps if we knew more about the fundamental design of the system, and apparently what parts you need to use to save on construction costs, then we could come closer to realizing whether what you are asking is the best way to get from point A to point B.

What I propose for efficiency, safety, and reliability, is to follow the path of those who are already building small electric vehicles. Determine the torque you need, motor wattage, and pick one with a voltage range suited to a battery array. Something around 48V perhaps. Pick a ready made throttle controller. Pick a ready made charge controller.

In audio we DIY to achieve good sound at a fraction of the cost of audiophile amps but with DIY electric vehicles you will end up spending more money to achieve what is probably going to be an inferior result unless you spend between months and years debugging, refining, rebuilding the project... and perhaps risking power loss on the vehicle while operating it which is in itself a risk to safety the more often it happens.

[EWorkshop1708]

Dude, you misunderstood my post so severely, I don't know where to begin....

I'm not a newbie, I don't confuse terminology, I meant every word I said word for word!

Anyway, I mentioned nothing about controlling the motor at all with this circuit.

I'm just talking about 1500w smps buck converter, high voltage in, low voltage out to charge the 36v battery that powers the vehicle, and want to know if buck converter heat of output inductor and/or transistors may be a problem.

A typical mini 120vac generator puts out 80-200v DC after bridge rectifier if throttle is adjusted above or below stock 3600 RPM.

[!]

Generator?

If this were a foreign language translation, I could understand why the terminology is off, but this?

It makes no sense.

Your project is not using reasonable, available tech, trying to DIY is not wise. Can it be done in theory? Yes, but that does not mean it is reasonable to do.

[EWorkshop1708]

Your opinion of reasonable means nothing, this is my project, not yours, its reasonable because I say so.

What a close minded, ignorant response, shame seeing such on diyaudio forum.

I could think plenty of reasons to make a 36v battery charger, dont need some fool trying to determine how to use such a battery charger.

If you have nothing useful to contribute, then don't post.

I will just build the damn thing and see how hot it gets, figure it out myself.

[luka]

what part of generator don't you understand?



anyway, who cares, he already said he had 80-200v DC to work with... doesn't even matter where he gets it from

200v seems to me, a bit high for buck, can you somehow limit with generator to 200v or below 100v?

full bridge might be the way to go instead of buck...

[EWorkshop1708]

Well, I will limit in rpm, so I might not actually get full 200v, in actual use it will be about 160v or somewhat less, just like to design heavy duty.

Why is 160-200v kind of high for buck conv?...... just wondering.

Would a high number of turns on the output inductor help?

[benb]

He means a gasoline-operated engine that runs an electric generator that outputs "standard" 120VAC.

[CBS240]

If you're using somthing like in post 6, some small engines can overheat if used under load at low RPM. If the cooling fan fins are on the flywheel then using it for work at low RPM may not move enough air across the head and cylinder. If its a problem I suppose you can use an electric fan/w thermal sensor.

[flatheadmurre]

The fuel effiency of cheap small engines is a bigger problem then the effiency of the converter.

If you´re going to use this vehicle as transport search for a 1-2cylinder liquid cooled Yanmar/Kubota/Izusu engine from a salvageyard for small construction equipment.