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c-cat
12-30-2007, 08:02 PM
Can a brushless moter be used as a generator?If so how effeicient would it be?

kaindub
12-30-2007, 08:34 PM
Yes it can.
It will be about as efficient a generator as it is a motor. Depending on speed and load from 60 to 80%.

c-cat
12-30-2007, 09:30 PM
So if Im starting for say a turbine with a brushless when all fired up the starter motor can gen. power for two more?I love the brushless sound just can't get past the whole lipos costing as much as a turbine...almost.

Insomniac
12-31-2007, 12:52 AM
What sort of turbine are you talking about? One that runs on fuel or one that spins when air blows into it?

c-cat
12-31-2007, 01:12 AM
Regular fueler like simjet, wren,etc.Potential project i guess for a large rc boat.I know i'm off topic but i figure if i wanted opinions about elec.rc stuff i'd better post on this forum.I've seen the turboprop turbines but two brushless powered by a turbine/brushless generator seems to be easier to me (no transmissions & easy to counterotate).thanks for your input.more would be great.

flybird
01-01-2008, 12:05 AM
When I was into gas planes I bought a Genesys generator system to install . They charge your rx battery, servos , accessories.as you fly working off your engine. Crashed before I could install it. Now I'm into electric planes I can fly at the park. Much cheaper and less time consuming, something that fits my lifestyle for now . I still miss the sound of gas though. I put it on e-bay , I don't have any use for it anymore. Its more for gas or glow planes. I don't know if it would work for electrics, maybe large ones.

c-cat
01-02-2008, 07:19 PM
Maybe now I should be more specific.What kind of power loss could I expect to see when powering two brless.with one brless twice the size?

Larry3215
01-03-2008, 06:41 AM
Why not just power the thing directly with the turbin? If you have a turbin its going to be putting out gobs of power any way.

Assuming ideal conditions, if the losses in the "generator" were 20% and the losses in the drive motors were another 20%, you would end up with a max of 80% of 80% of the turbins output power or about 64%.

I suspect you would actually end up less than that because the generator would be AC output, so you would have to rectify and smooth it out to feed the esc's. Probably more like 50% at a max.

Then you have the complexity and weight and cost of a turbin, fuel and associated support equipment, it has to be way more $$$ and weight than a set of lipos.

Interesting idea tho :)

Larry

c-cat
02-09-2008, 11:25 PM
Ok so maybe not a turbine,thinking deisel/elec. locomotive type drive system so any power source to generate elec really, would be nice to throttle up or down the source to regulate power to drivin (consuming) motors. is this possible with brushless motors supplied by another brushless generator?

Larry3215
02-10-2008, 04:18 AM
Its may be possible, but I very much doubt its going to be practical.

Part of the problem is you cant run one brushless motor directly from the output from the "generator" motor. You will need to rectify it and run it thru a speed controller anyway. So that defeats the main goal of using the deisel to vary the speed - just use the esc since you have to have one anyway.

Its going to end up being far less efficienct, more complex, cost more, take up more space and weigh more.

Im quite positive you wont be able to come even remotely close to equaling a simple battery pack and speed controller.

If you dont want to use lipos because they cost too much, try the A123 cells or even go NIMH or NICAD for less cost.

Good luck!

Larry

Larry3215
02-10-2008, 04:30 AM
By the way - with diesel/electric systems they do not slow down/speed up the diesel engines to vary the speed on the electric motors.

They vary the voltage output from the generator section to controll the speed.

The motors they use are called traction motors and are very different from our 3 phase brushless motors. Not even close to the same operation or how they are built.

Still, you could probably make it work but not easily or in an efficient way.

The reason trains use a diesel/electric system is jsut for the raw power they need - we're talking hundreds of thousands of watts at thousands of amps - enough to run a small city! Way more than batteries could ever produce. Directly driving the trains with the diesel engens would require masive trabsmissions and it works better and is cheeper and more reliable to use the electric motors.

If its a large RC boat and you already have a diesel engine, just run the prop directly from that. Far easier and mor efficient. :)

Larry