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A few basic Questions (Warning: Noobie + ideas)

2742 Views 11 Replies 5 Participants Last post by  todayican
Ok first up if this is in the wrong thread I apologise whole heartedly. Please feel free (like I have a choice lol) to move it to an appropriate section if need be.

Right, to my question - this is important for me to fully understand because it will greatly affect the direction I take with my (hopeful) build. How to provide power to the engine.

I’ll have to put this down in point form because I really can’t seem to convey what I mean in structured sentences! Yes I’ve re-written this post about 6 times now and my bed is calling me...and the Mrs too.

1) Why can’t a small and efficient ICE engine be used to run a generator to directly power the main drive engine? Size and weight are obviously the potential issues I see, but I can build a 12kW wind powered generator that outputs that much power at as little as 1000rpm.

2) If this sort of arrangement were possible would batteries still be needed to link between the generator and the motor? The way I see it if you’re cruising then the generator is not working very hard and providing the main engine with enough power to keep the car moving at a decent pace....put your foot down and the generator firs up and the main drive engine moves a little faster. Some cleaning up of the power from the generator would be required of course.

3) To expand on question 2, I am assuming that if the driving motor was to be run at its peak rating, the generator would need to be able to provide exactly the right amount of power to do this and for the period required. So if you out your foot down the ICE would need to spin the generator rotors faster to provide the engine with the right amount of juice. Highly improbable anything like this would respond fast enough or even fit inside a car?

I’m asking these questions because while I care about the green potential of EV’s, I think the potential range improvements of this approach is better suited for the time being. Hell if you used a small displacement Diesel ICE to power the generator it’ll produce far less emissions than a normal car, but depending on power you will get blistering performance. Theoretically.

Depending on the ICE/Generator solution you could potentially save weight and cost over a similarly powerful battery configuration.

I clearly won’t have been the first to bring this up and to clarify I’m talking fast cars here, not Volt/Prius nanny cars....

I also could very well be talking out of my a** so that’s why I’m asking here now before I invest serious time and effort into a solution that is doomed to failure. Someone with the knowhow and experience to set me straight would have my full attention.

Any information would be greatly appreciated.


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If this sort of arrangement were possible would batteries still be needed to link between the generator and the motor?
If you don't have an energy storage, the only thing you change to your car is adding a few extra losses. So your range goes down, and your price per km goes up, as a nett result.

With a right sized battery pack you could use a smaller sized generator that spinns at its most economical rpm to keep the battery pack charged. And of this pack you can run a electric motor with the available power that the battery pack can give. So theoretically you can pull up much faster, and have a much higher top speed. But for a short time periode. The lower powered generator must catch up again as the battery pack drains.

But this generator, battery, electric motor powertrain is a lot of weight and complexity. And already available at your local car sale company.
Actually the Leaf is a pretty peppy little car. It could be peppier but that will come later. You could run a generator and directly power your main drive motor but you are limiting yourself and you still burn fuel. OUCH. Can your windmill generators belt out 156 or better volts and 2000 amps with the power a small gas or diesel could manage? If it can then you have one hell of a generator and one powerful little gas or diesel engine to power it.

Figure out the reality of what your system can produce and then you will truly see what your system is able to dish out. I am thinking you need to stick with the tried and true all electric vehicle for your needs. What are you planning on doing with your FAST electric car? Grocery getter or play with the children and their gas cars between green lights? Race track? Why do you need FAST? What type of vehicle? Can the diesel generator even fit? Lots to really check out before you make those decisions. If its a truck maybe you can get it to work. You will need space.

Pete :)
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OK, so after ingesting this information and doing a bit more reading up on how electric motors work (how conditions effect there power drain etc) I have a much better understanding of what I am asking/reading.

As far as I can tell it is, like everything in life: a trade off.

a) Nothing but batteries and you can have as much power as you need until they’re dead.

b) Only a generator and you are limited at all times to the output of the generator.

If you want gang buster performance, then (a) is the way to go but if you want to get from your house to work and back a few times then (b) is the best bet.

***I’m about to make some numbers up, so please ignore them from a technical perspective and just look at it theoretically…humour me basically ;-)***

Say and engine will give you a top speed at 24V and 10A. The batteries need to be able to supply the engine with this power. Depending on how long you want this power to be available for will determine how big your battery pack is. What would be ideal would be a generator that can supply the same power back into the batteries at the same time. Theoretically you’d be able to maintain the top power output of the motor as long as you have the generator running.

Let us say that [email protected] allows the car to travel at 200km/h. That’s great, but in every day use 100km/h (here in Australia anyway) is as fast as you can legally go. So why not have a battery pack that allows for this top speed for say 3 or 4 minutes, and then use a smaller, lighter and more fuel efficient generator to provide say, half the power needed for top performance. If the engine is pulling enough power for 100km/h, and the generator is capable of providing this power then again, you can drive for as long as the generator is churning it out.

Slow down but keep the generator running at the same speed and it will charge the batteries. Do this long enough and you can have your top performance back again – and because of the smaller battery size you should get that back fairly quickly.

Is this theory even close?

Please correct any errant comments I have made as well – I don’t want to continue thinking something is right when it is clearly wrong…

What are you planning on doing with your FAST electric car? Grocery getter or play with the children and their gas cars between green lights? Race track? Why do you need FAST? What type of vehicle?
For the record this is not a “grocery getter”. It will (if I go ahead with it) a weekend cruiser. A car designed to go hard when needed but allow me to go cruising down/up the coast with my mates if the range allows for it. I probably would never be doing any extended circuit races (maybe the odd track day) and would hit the ¼ mile every now and then. But that is a long way off. On the other hand those ‘desirables’ will affect what I do right now.

And no I’m not hoping for the dream EV. I want peak performance for a time no where near as long as say, the White Zombie (or what ever it is called) - peak performance for 2 minutes at most. Normal driving conditions all other times.

I could be talking out my a** however, hence why I’m on here now getting my ideas into the ‘possible’ range. :p
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Hi Modern

First thing read some of the posts so you have some numbers that are reasonable!

24volt and 10Amps = 240 watts most cars will need 12,000 - 15,000 watts for 100Km/hr
(this is 16 - 20 Hp)

200 Km/hr will be between 4 and eight times as much - 50 Kw - 120 Kw

A gen set and IC engine capable of delivering this is quite meaty!

Most of us have decided that the extra complexity of an on board gen set is not worth the hassle

You can make a sprightly vehicle - I am expecting mine to be quite rapid! - with a decent range as long as you are prepared to pay for the batteries

Rough numbers

$5,000 = 10Kwhrs = 50 miles range = 100Kg of batteries
$15,000 = 30 Kwhrs = 150 miles range = 300Kg of batteries

If you want long range -
(my machine is a Lotus 7 type with aero-screens is not a good long distance cruiser)
Think about mounting the gen-set on a small trailer
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First thing read some of the posts so you have some numbers that are reasonable!
Lol my numbers were a bit of a bum pluck, but I knew that before I wrote them down...

If I can get/make a generator capable of maintaining the right power for highway cruising (100km/h) then I'll be happy as a pig in mud.

That been said I have been looking into this for exactly 2 days now, so I am a long way off deciding exactly what I am going to do!
I think what is being described is an electric transmission and what he is after is more of a thought exercise even if it wouldn't be easy to accomplish. No need to knock it down just yet:)

Allison already has a design out there that works on that principle. Diesel locomotives have been using them for decades as well, generally called EMD or Electro Motive Diesel. Thats why the hybrid automobile is not exactly a groundbreaking innovation since it works on principles that are not only well understood, but well demonstrated in commercial heavy industry.

There will be conversion losses when you try to run a motor off a generator - however, there are always conversion losses anytime you try to transmit energy from one location or form to another. That goes for mechanical means (bearings, gears, shafts, torque converter) or electronic means (switches, conductors, PWM, inverters etc).

The major advantage I always saw with the electric transmission is the ability to continuously vary the gear ratio without interrupting power flow and without being rigidly aligned to a fixed set of gear ratios. One major reason they used EMD in diesel locomotives was because they usually employed medium speed engines that would redline in the 1200 RPM range and ran efficiently in a narrow 200 RPM corridor. For such a vehicle to operate efficiently across a speed range as wide as 0-80 MPH, a multi speed transmission, along with complex CV shafts to deliver the power to the axles would have been extremely complex and subject to large amounts of parastatic losses. Not to mention horrible service intervals!

Some earlier diesel locomotives even used compound torque converter transmissions before 1st generation EMDs came along - also not efficient, but at least more dynamic. Early EMDs used relays to switch windings in the main generator to deliver different "gear ratios", but these days its generally done with electronics to produce a much smoother variable drive ratio.

Building something small and light enough while still being efficient to fit in a car isn't going to be easy though. Industrial drives that are powerful and efficient enough to be worth looking at are not meant to be lightweight. While small motors/generators are generally not meant to be efficient or powerful enough. If you have the ability to prototype this sort of thing from scratch, I feel it could be done and the results might be very impressive if you got all the variables just right. Being able to have low speed torque to crawl over rocks and logs then smoothly transition up to motorway speeds without changing gears is something worth looking at IMO. Besides, you could always add a battery later to get full plug in EV capability.

As a general rule, most automotive gearboxes eat at least 15% power (more if we are looking at older 2 and 3 speed open torque converter automatics). Getting a motor and controller setup into the 85% range is easy, but you have to remember that your losses are double since you have 1 motor and one generator. So that would bring your net operating effiency down to about 72%.

If you had access to a motor and generator that both worked at 90%, then net operating is 81%

For 95% efficient units, it works out to 90% (roughly)

This of course assumes that you can maintain that level of efficiency across the board. Most motors can't do this, and the ones that can, are usually experimental top shelf stuff that us enthusiests are never allowed anywhere near.

I would still like to build one if I could though.:)
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David85, it's scary but I started looking at EV's after I asked a question about rotary engines in another forum and someone piped up with the idea that a rotary engine specifically designed for use as a generator engine in an EV would be perfect (small displacement, uncomplicated design and less moving parts, much better power-to-weight ratio than a traditional 4-stroke etc). NFI how we got there though lol. Imagine a diesel rotary…

The discussion led me to Diesel electric locomotives and well….here we are.

I have been posting elsewhere in these forums trying to bring my understanding of EV principles up to speed and suffice to say I am getting there slowly.

What I am looking at now is a range-extended vehicle basically. But only on the assumption that I could build a generator small enough and light enough to effectively replace a large swathe of heavy and expensive batteries. There will still be batteries in there – just not as many as your typical performance EV.

I have found a design for a 10” Permanent Magnet Wind Generator that outputs 10kW at 1000rpm. The design is rough and overly bulky, but the way I see it if it is cleaned up and wound better (stronger magnets too) and combined with a lightweight ICE engine, I could easily approach 20kW – especially if the wind alone managed to turn this thing at 1000rpm. That’s idle for a normal ICE!

Lot of assumptions there, and I am a long way off anything starting yet. I ordered some insulated copper wiring today to test my winding technique last night lol.

Really it all comes down to the generator as to where I go from here.
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I would really like to see a diesel wankel but to my knowledge, no one has done this yet. There were examples of rotaries that can run multiple fuels but those were still low compression (around 9 or 10:1 I think) and used spark assist ignition with throttle body fuel injection. Essentially its still a petrol engine that had its fuel "spiked". Not really a diesel in my view. Some claimed to be able to run lean burn ratios as far as 2:1 though, which was impressive and one step closer to true diesel.

But a true high compression rotary (16:1 or higher) with direct diesel injection at TDC is something that I haven't been able to find yet. Maybe a quad rotor with staged turbochargers and enough power for a HD truck coupled to an electro motive transmission for perfect gearing in any situation. The generator would double as the engine start. I wonder what that would even sound like. Oh, wait, you said small and light - my bad:D

Yes, it seems you and I got here along similar trains of thought.:eek:
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There was a diesel wankel - I think it was RollsRoyce (as in tank engines) it used a two stage wankel
One rotor compressed air into the second smaller rotor - they called it a cottage loaf engine,
Expansion was the same two stages - that fixes the biggest problem with the wankel
Expansion ratio!
You can only expand so much then you run out of expansion - this is why wankels are low efficiency with very hot exhausts

When looking at your range extender -

You need 50 kg of batteries - for perfomance = 25 miles range

100 extra miles = extra 200kg of batteries
Generator = 300 kg+

If you need 100 miles range - batteries win
if you need 400 miles range - generators win
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Lot's I haven't thought about yet - hence why I'm here now asking questions before I get started!

if you need 400 miles range - generators win
I want range with a little bit of performance. We'll see what comes about from experimentation I guess.
Ive been looking at doing this for the trike Im building now and here is what Ive come up with:

Use a 10hp chineese diesel derated to 8 hp and have it run in its "sweetspot" of fuel efficiency (about half the fuel used if a motorcycle engine of about the same hp output) (the diesel would have been only 25% better except the BSFC jumps up in the "sweet spot"

Anyways, the etek style motors have always been 90% plus efficiency and they just (finally)! released a motor I beleive has enough umph to actually drive my trike to highway speeds the mars 1003

So here is what im thinking;

Gen) Mars 709 (known as etek rt) running at 96v and 55 to 60a constant
Drive) Mars 1003 (known as etek-s)

either 96v x 32 ah of 8ah headways or 96v of 100ah of prismatics (Possibly both) :)

For around town and shorter trips, just the batts driving through the controller.

For extended highway driving gen "passing through" the batts and on to the drive motor.

For charging at roadside cafe while having a cup of coffee, just run the motor im thinking. (I would LOVE to have a chat with someone smarter then me to see what im missing in the way of a charge controller? im thinking that the amp output from the gen wouldn't fry the batts, it would just need a hvc cutoff on the high side right?

So, if my math is right, assuming 91% on both motors by way of efficiency:

8hp diesel into gen = 7.28
7.28 going into batts and controller @95% 6.91hp
going into drive motor @91% = 6.28

5% for loss in the chain itself leaves 5.96 hp for moving the car (for my trike this should be fine)

so with 180 grams per hp per hour thats a whole lotta MPG

Using the 15% example for mechanical losses in the transmission (and the fact that you cant engineer a "sweet spot" for the gen because you would have to cycle through the gears and change throttle position 8hp in a motorcycle engine would show up as 6.8 hp at the rear wheel

at 354 grams per hp per hour (a standard 250cc motorcycle engine) the math starts to look better

assuming the car needs 5kwh to travel 70mph for one hour (6.67 "hp hour")

the diesel in example a is going to burn .46 gallons of fuel
the MC engine (non hybrid, just driving a rear wheel) will burn .91 gallons of gas.

Is my math right here, I did it fast and made a lot of assumptions, but it looks like BSFC is the key to this being viable (That and no voodoo hiding in a charge controller) lol.


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