# 5kw pmbl motors - any suggestions? hybrid...



## mattW (Sep 14, 2007)

So you would have a (bio)diesel engine- pushing a permanent magnet motor to give charge the batteries to give power to the hub motors? Why not make it a parallel hybrid and use the pancake motor both to charge the batteries and power it at low speed? How big a battery pack were you planning?


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## greg123 (Apr 10, 2008)

Hey Matt, 

Thanks for the reply!

NO batteries, none. It's electric, but 100% of the electric comes from the biodiesel (actually biooil technically) engine direct to the hub motor.

The reason I don't want batteries is they weigh, and weight makes for inefficiency and they are very inefficient in taking charge, okay if you are plugging in at home but this is a fully stand alone machine used for motorway work/long trips as well as commuting, eg range is a factor. 200mpg or so should be possible easily, given a less efficient engine with an old fashioned 4 speed box with 20% transmission loss, running at variable engine speeds which lowers efficiency, still gets 170mpg.

So essentially it's a good efficient high power (5kw or more) hub motor, and some help finding or making a pancake generator to fit on the back of the engine (rotor running on the end of the crank, so no more bearings needed and no pulley/belt losses and nice and compact).

I hope someone can help me and please criticise my idea if you can, I'd like to overcome obstacles at the design stage....

Greg.



mattW said:


> So you would have a (bio)diesel engine- pushing a permanent magnet motor to give charge the batteries to give power to the hub motors? Why not make it a parallel hybrid and use the pancake motor both to charge the batteries and power it at low speed? How big a battery pack were you planning?


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## mattW (Sep 14, 2007)

Well if you weren't going to use batteries then why would you use electricity at all? You'd just be converting mechanical energy->electrical->mechanical again. Even if it was 90% efficient you'd still be throwing away 10% of your power...


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## greg123 (Apr 10, 2008)

That's right.

Considering the average transmission loss in a mechanical transmission is 20 - 25% and requires the engine to speed up and down (engine is peak efficient at only one revs and up to 50% less efficient at other revs) maybe you see why virtually all trains and many boats use a diesel engine to drive a generator to drive motors and why I want to do the same.....

My efficiency would, as you say, be up in the 90% compared to an average of 70% in a clutch/gearbox traditional setup..... Take a look at a few dyno HP print outs, the the difference between crank HP and HP at the wheel is SHOCKING.

The most efficient CVT belt drives come close to 90% efficiency, but they still have the issue of rigidly fixing where I can have the engine, which in this application I want to use prohibits me having a virtical crank engine which would fit best. With a generator on the engine, who cares where I put it!

Add it when ultracapacitors get cheaper I can put a regenerative braking system in and save 30% mpg in town (or accelerate 30% faster for free, depending what you want) and the system has future potential, a mechanically geared engine to wheel is never going to have an easy way of regenerative braking.

I know this is a bit blue sky thinking but I have never thought in a box and usually find that something like my ideas eventually come out in motor show prototypes or patents. I'm totally fed up of not making any of them, when I know the technology is all there. I read about permanant magnet axial flux motor/generators with 98% efficiency in prototypes/solar racers/university/patents which would give 96% overall efficiency, but buying one or how to make one... there I fall down.

Hope that makes sense?
Greg.



mattW said:


> Well if you weren't going to use batteries then why would you use electricity at all? You'd just be converting mechanical energy->electrical->mechanical again. Even if it was 90% efficient you'd still be throwing away 10% of your power...


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## mattW (Sep 14, 2007)

I would go with at least a small Ah battery pack to smooth the difference between the generator and the motor. If you are accelerating quickly but want the generator to stay at the same rpm you are going to have problems, but if you have batteries then they can discharge and get topped up once you start cruising again...


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## greg123 (Apr 10, 2008)

Thanks - I don't quite understand that, why would I have problems?

The engine govener keeps the engine at 3,000 rpm regardless of load. Lets say it's built to push 72v at that speed.

Correct me if I'm wrong, but a 72v motor connected to 72v will accelerate smoothly - why would it make a difference if the 72v is being fed by a generator or battery?

Obviously I wouldn't always feed full power to the motor, I'd be hoping there is some sort of PWM controller to control power I can use - when the PWM is wide and low power to the motor, less torque is required by the generator and the diesel engine automatically backs off the throttle thus keeping a rigid 3,000rpm and maintaining the voltage.

I see what you mean about batteries but I can't use them, the inefficiency in charge and discharge would just kill my idea dead. I have to use the same system as other efficient diesel electrics, straight from generator to motor.

How unsmooth is the generator going to be anyhow? I can't see it being any more unsmooth than the output of a PWM controller at half or quarter throttle, and there is the inertia of the wheel and tyre to smooth out power when it gets up to speed.

Thoughts appreciated,
Greg.



mattW said:


> I would go with at least a small Ah battery pack to smooth the difference between the generator and the motor. If you are accelerating quickly but want the generator to stay at the same rpm you are going to have problems, but if you have batteries then they can discharge and get topped up once you start cruising again...


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## mattW (Sep 14, 2007)

the voltage will stay the same (as will the rpm of the motor) but the current draw will increase, increasing the load on the generator. Motors usually go to higher revs for more power but you will be stuck at 3000 rpm. I don't know how much play you can get in the power levels of diesels at a given rpm but I don't imagine there is much... which means your electric motor is only going to get 1 level of amps. You could always have the generator at peak power and block the excess when you didn't need it but that throws your efficiency and with no batteries you couldn't do anything with the excess.

As an example lets say your diesel motor puts out 3.5kW at 3000rpm @ 72V. That means you have about 50A going from the generator to the motor, which will give you a specific cruising speed. If you want to accelerate you need more amps out of the generator but how are you going to get it without changing the rpm? If you were constantly charging some batteries then they can give power on demand; 50A when its needed, or 0 or 100A. What is your generator going to do with the power it generates when you're at a traffic light? That could be going into the batteries... Do you see what I'm getting at? If you just want to cruise at 1 speed your idea will work but you need to think of the other variables.


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## greg123 (Apr 10, 2008)

You have missed out the pwm motor controller, what you said would make sense if it was always wired to the generator.

The diesel engine has a range of 0-12hp at 3,000rpm, it throttles up as you load it.

The voltage would be constant.

The PWM controller would feed current to the motor 10% of the time when you are on 10% throttle, giving a 10% average load on the generator and 10% power from the motor.

When you want to cruise at half throttle, it feeds a 50% duty cycle to the motor, and thus 50% of the max output is taken from the generator and 50% the max motor output is given to the wheel.

When you want to accelerate, the PWM will feed 100% duty cycle, and as you say this is now limited to the current and volts the generator produces at 3000rpm. I'd need to make a generator which can suit the maximum output of the engine. As you point out, to go faster, I'd now need to increase my revs, but this is max power and the generator would be on full load to the engine - so no more power, full throttle pushing around 10kw out to the wheel motor.

It's the same as an electric drill, that has a 12v motor which only works on 12v and a 12v battery which only works on 12v, but the PWM controller feeds it 12v for a fraction of a second, then turns it off for a fraction of a second, then back on for a fraction of a second, all so fast that you can't tell, to make the overall percentage of 'on' time when the battery is connected to the motor anywhere between 0% and 100%, depending how much you press the trigger. 

My idea is the same, just replace battery with a static voltage generator. The duty cycle of the PWM governs the load on the engine and the power output of the motor.

I thought this was standard pratice with EV's? I thought the days of inefficient resistor shunting were gone?

If it makes it easier, forget I have a generator. Just say I have a battery, with a max power load at it's given voltage of 10kw, the only difference that this battery will never go flat.

Now am I making sense, or am I potty 

I could make a very small version of this, with a small RC engine set at the correct rpm to make 12v from a dynamo, then hook it up to an electric drill and trigger. I'd have a variable torque/speed output from the drills 12v motor from a generator input. Presuming I have a govenor on the engine, or when I opened up the trigger, it would load the generator more which would drag engine rpm down which would lower voltage which would.... etc. So a governer on the engine and a maximum load that the engine is capable of sustaining (I wouldn't try and shunt 50 kw off it, it might stall the engine with that load - or at leas slow it right down) at the needed rpm to maintain the required voltage would be the setup.

Greg.



mattW said:


> the voltage will stay the same (as will the rpm of the motor) but the current draw will increase, increasing the load on the generator. Motors usually go to higher revs for more power but you will be stuck at 3000 rpm. I don't know how much play you can get in the power levels of diesels at a given rpm but I don't imagine there is much... which means your electric motor is only going to get 1 level of amps. You could always have the generator at peak power and block the excess when you didn't need it but that throws your efficiency and with no batteries you couldn't do anything with the excess.
> 
> As an example lets say your diesel motor puts out 3.5kW at 3000rpm @ 72V. That means you have about 50A going from the generator to the motor, which will give you a specific cruising speed. If you want to accelerate you need more amps out of the generator but how are you going to get it without changing the rpm? If you were constantly charging some batteries then they can give power on demand; 50A when its needed, or 0 or 100A. What is your generator going to do with the power it generates when you're at a traffic light? That could be going into the batteries... Do you see what I'm getting at? If you just want to cruise at 1 speed your idea will work but you need to think of the other variables.


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## MrCrabs (Mar 7, 2008)

From the Wikipedia article on Stationary Engines.
http://en.wikipedia.org/wiki/Stationary_engine

"On a medium size engine such as a 6hp, the engine can be adjusted so that it only fires every 10 seconds or so when it is not under load. These engines generally drove a wide flat belt to run a firewood cutoff saw, a pump, a reciprocating log saw, etc."

Would the engine you plan to use have the ability to do this? If so then it sounds like it could work without having a battery pack to store electricity.


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## ww321q (Mar 28, 2008)

greg123 your idea would work . The motorcycle would also accelerate just like a train to . J.W.


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## greg123 (Apr 10, 2008)

I don't get it - why would I want to??? That's 100 year old technology!!!!

A standard stationary engine can hold any rpm with an infinately adjustable power output as needed to hold that rpm, from 0hp to max hp, whatever is needed to keep the rpm constant.

Why would I want it firing every few seconds?  What's the object, what do I want to do with the engine? I thought it was keep it at a constant rpm regardless of load, which I can do fine, the PWM controller taking care of the power sent to the motor.



MrCrabs said:


> From the Wikipedia article on Stationary Engines.
> http://en.wikipedia.org/wiki/Stationary_engine
> 
> "On a medium size engine such as a 6hp, the engine can be adjusted so that it only fires every 10 seconds or so when it is not under load. These engines generally drove a wide flat belt to run a firewood cutoff saw, a pump, a reciprocating log saw, etc."
> ...


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## greg123 (Apr 10, 2008)

Thankyou JW!

It works well enough on the train yes!

Question is if I can get anyone to point me in the right direction or help me make the generator & motor at a good efficiency. I can do it right now with alternator /field winding motors, but the efficiency would be way down and not worth it.

Greg.



ww321q said:


> greg123 your idea would work . The motorcycle would also accelerate just like a train to . J.W.


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## mattW (Sep 14, 2007)

Ok, I didn't realise diesels could vary their power output so much while at the same rpm... In that case your system would work fine. I was just thinking you would have one set power output, so one fixed current level to the controller so all the controller could do would be to throw away some of the energy or put it all straight in the motor... Which is wrong, sorry.

Your system will be very efficient for all situations where you require power such as accelerating and cruising, but what about when you are coasting or decelerating? Will you do something with the energy it produces while idling or switch it off?


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## MrCrabs (Mar 7, 2008)

greg123 said:


> I don't get it - why would I want to??? That's 100 year old technology!!!!
> 
> A standard stationary engine can hold any rpm with an infinately adjustable power output as needed to hold that rpm, from 0hp to max hp, whatever is needed to keep the rpm constant.
> 
> Why would I want it firing every few seconds?  What's the object, what do I want to do with the engine? I thought it was keep it at a constant rpm regardless of load, which I can do fine, the PWM controller taking care of the power sent to the motor.


Well the way I understood it, when the engine had no load, it would only take 1 firing every few seconds to keep RPM up. Then when loaded it would fire normally to maintain RPMs... I wasen't sure what you were talking about when you said "stationary engine", and thats what wikipedia turned up.




mattW said:


> Ok, I didn't realise diesels could vary their power output so much while at the same rpm... In that case your system would work fine. I was just thinking you would have one set power output, so one fixed current level to the controller so all the controller could do would be to throw away some of the energy or put it all straight in the motor... Which is wrong, sorry.
> 
> Your system will be very efficient for all situations where you require power such as accelerating and cruising, but what about when you are coasting or decelerating? Will you do something with the energy it produces while idling or switch it off?


What we are getting at, is how much fuel is used by this engine you want to use, just to keep itself moving at 3000 RPM??
When coasting or decelerating you need 0 electricity generated... So any fuel used by the engine should be just enough to keep itself running... If the engine is using more fuel than this it is wasted fuel...

I am confused how an engine can have an HP rating of 0 at 3000 RPM, since HP = torque*rpm / 5252.


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## greg123 (Apr 10, 2008)

The hp I'm talking about is output hp. An engine idling produces no output hp, if you put any load on the the revs would drop, because it's current hp is equal to the friction/resistance of the engine at that speed, hence it's idling.

These engines do that, at any speed. They sit at 3,000rpm using virtually no fuel, idling - 0 output hp (all used internally to keep up the 3k rpm). When a load comes, the govenor throttles it up to avoid the engine bogging down and then you get the shaft hp output because the engine is now producing more hp than it takes just to turn the engine over.



MrCrabs said:


> Well the way I understood it, when the engine had no load, it would only take 1 firing every few seconds to keep RPM up. Then when loaded it would fire normally to maintain RPMs... I wasen't sure what you were talking about when you said "stationary engine", and thats what wikipedia turned up.
> 
> 
> 
> ...


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## greg123 (Apr 10, 2008)

These small direct injection diesels are incredibly efficient on part/no load. They will sit running with no load for several hours on a mug full of diesel, unlike a petrol which has significant pumping and heat losses so uses a LOT of fuel to idle in comparison.

So, practically, on no load I could pull down the govenor so it sits at idle rather than 3,000rpm (idle is 1,500rpm on a single cylinder - you are only getting a power stroke 1/4 of the time you do in a car 4 cylinder so it actually sounds pretty slow) and let it sit at idle when no electirc is being used. That would, in reality, work just find due to the ultra low fuel consumption on those conditions.

However.... till I got advanced with regenerative braking etc, it may be possible to rig up some engine braking for a very slight improvement in efficiency.

If, during decelaration (when brakes are applied) the rear motor FEEDS some power to the generator, and thus spins the engine, in that condition I could shut the fuel off, such that when you are braking slowly down a long hill the engine is still running but not using any fuel and it would provide some 'feel' like engine braking on a car.

Given the already fantastic efficiency at idle, if it's worth it is another matter...... I think I'd be happy enough just to get the gen/motor/controller worked out and make it work 

Engine braking/ultracap bank for regenerative braking... all these could be 'added on' later as developments, if I can get the base system working. Which hinges on getting an efficient enough generator and motor. I know it's possible, solar racers use PM motors built with 98% efficiency, wind generators are up there.... 



mattW said:


> Ok, I didn't realise diesels could vary their power output so much while at the same rpm... In that case your system would work fine. I was just thinking you would have one set power output, so one fixed current level to the controller so all the controller could do would be to throw away some of the energy or put it all straight in the motor... Which is wrong, sorry.
> 
> Your system will be very efficient for all situations where you require power such as accelerating and cruising, but what about when you are coasting or decelerating? Will you do something with the energy it produces while idling or switch it off?


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## mattW (Sep 14, 2007)

I am really curious about how this will work out, you've certainly put a lot of thought into it. I'm impressed by the range of hp at 3000rpm and the low speed efficiency. If I were doing it I would use a small battery pack and continue charging it during deceleration and stopping but I understand your theory about the charging inefficiencies and idle efficiency... So your way is just as valid. The CSIRO here in Australia sell those ultra high efficiency hub motors but they cost about AU$11000... I guess you have a favourable exchange rate though. The power output is fairly low but you could have two giving you a very unique 2WD motorbike. Building an efficient generator doesn't sound too hard either...Very interesting indeed!


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## 3dplane (Feb 27, 2008)

Greg123! 
If you insist on building your own "pancake" alternator and you haven't already been there go to : otherpower.com .There is a wealth of knowledge and info there.However the main design feature there is focused around low rpm wind generators.Your idea would work no doubt but i'm afraid not at the efficiency level you expect.Dont forget the fact that just like ICE an electric motor has its peak efficiency at a certain load and rpm.There is going to be rectification losses as well besides other obsticles.Keep going at it though that's the only way to find out Barna


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## JimFritzMI (Jan 9, 2008)

I know that this doesn't really go with the whole electric car idea, but I've always found using the most appropriate tool always results in better results. So with that I would like to suggest you look into using a hydrostatic transmission of sorts. If you were to mount a variable displacement hydrostatic pump to the engine and then a fixed displacement hydraulic motor to the driving wheel(s) you would end up with a very light weight variable ratio trasmission.

It is exactly what you describe but using hydraulics instead of electric. 

---
Thanks,
Jim


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## greg123 (Apr 10, 2008)

Thanks guys for replies. As for most of us i cant afford 10k or so for a motor, im curious how a shaft, casing, neo magnets and varnished wire can ever be worth that much!I have looked into hydrostatic drive but all the commercial ones i see have terrible efficiency from churning fluid which is high loss. If u know of any that reach 90% or better please let me know. Otherwise a cvt belt drive is a couple hundred and around 90% efficient, though limits engine placement!Engine constant speed, dont know why a gen cant be built to suit it, then only variable efficiency of motor to worry about. But its a bit beyond me, i know the priinciple is sound thats all.GgGreg.


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## MrCrabs (Mar 7, 2008)

Its not the parts that cost that much. Its knowing how to put it all together!

Just keep an eye out for how all these conversions add up in series....
1 HP out from the engine * 0.9 CVT efficiency * 0.9 generator efficiency * 0.95 motor controller * 0.85 motor efficiency = 0.65 HP to the wheel.

I haven't looked at hydraulic pumps and motors myself, but if you could find a pump >= 80% efficient and a motor >= 80% efficient it would be better or equal to the electric option...


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## greg123 (Apr 10, 2008)

No no, the CVT would be an alternative to motor - it's 90% efficient and that's it, no more parts needed. So that's what I'm trying to beat, it's 2008 and I'm trying to beat a rubber band round two cones effectively, and seemingly having a struggle.

I'd need a 95% or better motor and generator to beat it.

Greg.



MrCrabs said:


> Its not the parts that cost that much. Its knowing how to put it all together!
> 
> Just keep an eye out for how all these conversions add up in series....
> 1 HP out from the engine * 0.9 CVT efficiency * 0.9 generator efficiency * 0.95 motor controller * 0.85 motor efficiency = 0.65 HP to the wheel.
> ...


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## MrCrabs (Mar 7, 2008)

Oh, ok I misunderstood what you mean with the CVT.

In the tradition of KISS a pure mechanical setup would probably be the best way to go. I don't think your going to find an affordable motor and generator that are > 95% efficient.


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## greg123 (Apr 10, 2008)

Yeah you are probably right  It's a real shame though as mounting possibilities and various other factors would make an electric drive much more attractive. Shame it's 2008 and I can find a relatively easy way to beat a rubber band....

Ah nuts!



MrCrabs said:


> Oh, ok I misunderstood what you mean with the CVT.
> 
> In the tradition of KISS a pure mechanical setup would probably be the best way to go. I don't think your going to find an affordable motor and generator that are > 95% efficient.


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