# 300 hp 55 mpg series hybrid



## owensa13 (Dec 8, 2015)

Hi everybody! I am brand new and pretty clueless about mechanics in general.

I've read about the old GM Ev1 and how there was a concept that used a micro turbine as a generator that kicked in when the battery power dropped to 50%. There's a company called Wrightspeed that's been applying the same principles to garbage trucks.

I realize that micro-turbines would probably be cost prohibitive (pretty cool though!) but I was wondering how to build a similar series hybrid system that had a decent amount of power and got at least 55 mpg. (I know, it might be easier to just be full EV, but I'm just wondering how this would work in theory)

So,
A) What would be the cheapest option for a 250-300 hp electric motor

B) How large of a battery pack would be required 

C) What engine would generate the power to charge the batteries (keep them at 50%)

D) What kind of computer system would be needed to control when the engine "kicks on"? Does anyone make them

The cheaper any of you guys know how to do this the better! Thanks


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## madderscience (Jun 28, 2008)

There were several GM trucks and SUV models in recent years with a hybrid design, they have a standard V6 and/or V8 and another 100-150hp (peak) worth of electric motors. I don't know how big the battery is but probably not exceeding a couple kwh.

Its worth noting that these trucks while they get better mileage than their non-hybrid counterparts, don't get anywhere near 55mpg.

The project you are thinking about would be quite complex. Not impossible of course, but quite complex for a DIY, even one with a good mechanical / electrical and software background.

Your best bet to get a custom hybrid with the power and mileage you are thinking about might be to transplant a V6 drivetrain from one of these trucks into a corvette body to get the weight down and the aerodynamics way better. I'm not sure about getting to 55mpg (a prius gets that on a good day) but you ought to be able to get well into the 30's mileage with such a design. It might also be possible to build a bigger battery pack, or add a secondary battery pack (ala the old prius plug-in conversion technique) to increase electric only range.

IMO if you want a hybrid, there are many good OEM models to choose from in the horsepower OR (not and) mileage range you want.

Good luck.


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## miscrms (Sep 25, 2013)

Unfortunately I think this would be difficult at best on any budget, let alone cheap.

To build a series hybrid you basically have to build a full BEV plus have the added complexity (and weight) of an additional power source and control system. In theory the place you can back off is in battery capacity, as you don't have to meet the range target strictly through batteries. The problem with that is its hard to make smaller capacity batteries that can still put out enough instantaneous power. If you want 300hp, you not only need a motor that can put out 300hp, you need a controller, battery, etc that can do the same. You can reduce the instantaneous power requirement of the battery by using the engine/generator to supplement electrical power to the controller/motor, but doing so is likely going to cost you in terms of efficiency compared to running the generator in a steady state peak efficiency mode.

A parallel hybrid architecture solves some of these issues, reducing the instantaneous power required from motor, batteries, and controller by using the supplemental power source in parallel to help drive the wheels. And under many conditions it can end up being as efficient and even more efficient than the series architecture. However it generally requires a much more sophisticated control system to do so. The Prius uses a combination of series and parallel operating modes to optimize efficiency. The Volt was aiming to be full series hybrid (ie true range extended EV, like the i3) but also ended up with a parallel mode.

Microturbines are very cool, but in practice their efficiency doesn't seem to scale down well. The one vehicle scale example I'm familiar with, the Capstone C30/60 has about the same efficiency as the Prius Atkinson engine or a steady state diesel, at much greater cost and complexity.

You can start to get a sense of the challenge by looking at whats already out there. The Volt running in Charge Sustain mode is rated 37mpg EPA combined with an 80hp traditional Otto Cycle engine. The Prius is rated 50mpg with a 98hp quasi-Atkinson cycle engine. A similarly sized microturbine would likely put about the same power at about the same efficiency as the Prius. That's probably plenty of power to maintain battery SOC even at fairly high speed running steady state near peak efficiency, but would rely on the battery to provide most of the instantaneous power for acceleration.

To get ~300hp electric drive you're pretty much looking at Tesla class drive components. You _might_ be able to source parts from a wrecked Tesla for $20-30k, but would still face many challenges in being able to use them. Its being worked on, but I'm unaware of anyone yet getting all the major components (motor, inverter, battery, bms, charger) working in a conversion. You could probably source an engine and transaxle from a Prius you use as a generator for a few $k, which is probably the most reasonable path to a high efficiency high power unit. The control of the generator would not be too bad, in general its just on when you hit a certain SOC on the battery pack and off when it climbs to another set threshold. You could even just rig that up with manual control, though it will take a fair deal of CAN controller programming just to turn the Prius unit into an on demand generator.

Rather than starting out with an arbitrary power requirement, I would start with defining your real requirements. Acceleration, top speed, range, cargo, budget and go from there. Vehicle design is all about balancing trade-offs. If you can live with a motor cycle for example, you can get blinding acceleration and impressive range on a much lower budget than if you have to carry 5 and tow a boat 

My tradeoff space led me to the lightest, most aerodynamic two seater I could find to see just how much performance / range I could squeeze out of a Leaf drive system. It may be only 80kW, but it also only cost me $7k for a complete functional system. And since I should be able to get in under 2000 lbs, with very low CdA, it should also go 100-150 miles per charge, recharge in 30-45min with DC Quick Charge, and have <5s 0-60 acceleration. Though maybe not both at the same time...

Best of luck,
Rob


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## Moltenmetal (Mar 20, 2014)

Gas turbines aren't really all that efficient until you add a steam turbine to make use of the heat in the exhaust. The smallest vehicle likely to be able to use such an architecture is a seagoing ship.


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## Duncan (Dec 8, 2008)

Hi Molten
Gas turbines can be OK efficient (as good as an IC engine) if you use a re-gen system on the intake/exhaust - it about doubles the weight/bulk of the motor
Basically you use the exhaust to pre-heat the intake

it about doubles the weight/bulk of the motor


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## Moltenmetal (Mar 20, 2014)

By not that efficient, I meant about the same as a turbo diesel. Can you do better than that using the exhaust to preheat the combustion air on a gas turbine of engine size Duncan? I have no idea.


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## miscrms (Sep 25, 2013)

These Capstone 30kW units are the only production microturbines I've come across that were tried in mobile applications. Their claimed efficiency for electric generation was ~26% as I recall.


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## Duncan (Dec 8, 2008)

Hi Molten
No I don't think they can get as high an efficiency as a diesel,
But they can get a similar efficiency to a petrol engine


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