# Series vs parallel hybrid.



## Vwbeamer (Jun 16, 2008)

I see no real benefit to a series hybrid. yet on every forum, the majority of people see it as The hot set up. I open to the idea that I'm missing something, but first let me explain how i see it.

I see several disadvantages to the series -

*Less efficient.* mechanical energy is turned into AC electrical energy, which is converted to DC energy, which then converted back in mechanical energy. Every step of the way power is lost.

*More complex*. You need an extra generator, a battery charger.

*More weight*. You have to carry around the generator and the charger. The extra weight could be used to carry more batteries,

*More expense. *You have to the generator and a charger capable of quickly charging the batteries. A charger like that will cost more the standard charger needed to charge over night..

The parallel system has none of those disadvantages-

*More efficient.* Mechanical energy developed by the ICE is delivered direct to the drive system. No power is lost being converted to electrical energy, and back to mechanical energy.

*Simpler*. An 8- 10 hp ICE can be couple direct to a dual shaft traction motor with a simple centrifugal clutch or belt driven torque converter.

*Cheaper*. A clutch or belt driven torque converter is $1000's cheaper than a gen set and high rate battery charger. a high quality 8-10 hp ICE can be purchased for $500.00. the clutch or torque converto is only a few 100 more.

*More power*. With both the traction motor and ICE directly coupled to the drive train, you have the combined HP of both to drive the car.

I would like to hear what the advantages to the series set up is, because i see very few.


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## ga2500ev (Apr 20, 2008)

Vwbeamer said:


> I see no real benefit to a series hybrid. yet on every forum, the majority of people see it as The hot set up. I open to the idea that I'm missing something, but first let me explain how i see it.


There are at least two other active threads on the subject around here.

My position is all hybrids have issues.



> I see several disadvantages to the series -
> 
> *Less efficient.* mechanical energy is turned into AC electrical energy, which is converted to DC energy, which then converted back in mechanical energy. Every step of the way power is lost.


Agreed.



> *More complex*. You need an extra generator, a battery charger.


Well the charger isn't as much an issue as the generator.



> *More weight*. You have to carry around the generator and the charger. The extra weight could be used to carry more batteries,


This is my biggest issue. The objective of a Plug-in EV or hybrid is to not use fossil fuels. The extra weight limits the BEV range even more.



> *More expense. *You have to the generator and a charger capable of quickly charging the batteries. A charger like that will cost more the standard charger needed to charge over night..


That's generally not the idea. The idea is to have the generator pump its power directly into the motor. This either limits the amount of battery power required, or if there is enough power left over to charge the batteries too while moving the vehicle.



> The parallel system has none of those disadvantages-
> 
> *More efficient.* Mechanical energy developed by the ICE is delivered direct to the drive system. No power is lost being converted to electrical energy, and back to mechanical energy.


Of course the real issue is that the power efficiency to the wheel is well less than 25%. This is a major issue.



> *Simpler*. An 8- 10 hp ICE can be couple direct to a dual shaft traction motor with a simple centrifugal clutch or belt driven torque converter.


But now you limit the range of power bands that the electric motor can operate in right? And a torque converter is going to lose energy too.

I have to disagree here. Applying electrical power directly to either batteries or a motor is much simpler than a mechanical coupling.



> *Cheaper*. A clutch or belt driven torque converter is $1000's cheaper than a gen set and high rate battery charger. a high quality 8-10 hp ICE can be purchased for $500.00. the clutch or torque convertor is only a few 100 more.


Um exactly how much power are you expecting to get out of a 8-10 HP ICE? ICE HP is generally rated at peak power. 8-10 HP is pretty weak.

Also what are the emission standards on such a motor?



> *More power*. With both the traction motor and ICE directly coupled to the drive train, you have the combined HP of both to drive the car.


That's rarely an issue. A decent electric motor has all the power necessary. The primary purposes of any hybrid system is to add range and fast energy recharge. Additional power generally is not the issue.



> I would like to hear what the advantages to the series set up is, because i see very few.



I see a lot of the same issues with the parallel setup. Simply throwing in an ICE into the drive train isn't as simple as you think it is. Also you still have the same weight issues in purely EV operation.

The best compromise that I've seen is the ICE EV pusher concept. Simply put you attach an ICE trailer to the EV. It's a disconnected parallel hybrid. You get all the advantages of direct mechanical power to the road without any of the disadvantages of coupling in either a parallel or series model as you've outlined above. The hookup is a small set of simple electrical controls. It functions pretty much as a cruise control.

The best part is that you only attach it when you need it. Around town, just leave it home. Long trip, just attach and go. When you get to your long range destination, detach and have a pure plug in EV again. without any additional weight to lug around.

It's the best of all possible worlds.

ga2500ev


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## ww321q (Mar 28, 2008)

I don't really like hypothetical discussions but . But if I was millionaire I guess I would buy a $100,000 EV . It would have gobs lifepo batteries a $25000 AC drive and go 300 miles on a charge . Oh! wait . If I had that kind of money I could care what gas cost . Actually I think the oil companies have the right to charge what ever they want or sell as little as they want . The 10 hp diesel motor and enough fuel to go 300 miles would weigh 165 lbs. Thats about the weight of 2 or 3 batteries . As far as a drive to couple the 2 drive systems , a cog belt or chain to a clutch would work . Just so happens that the diesel I have is designed to run under load at 3600 rpm . I think that is close to what most series run (sweat spot) . I'm not a environmentalist. I am building an EV to have a choise to who I spend my money with . The reason I want to build a parallel hybrid is for economy. My new Clark forklift motor and new diesel motor cost me about $850 for both ! I got plenty of room for batteries , over 20 . I might even be able to use the 72 volt Curtis controller I got for $300 . With the extra 10 hp provided by the diesel motor I may be able to go 70mph or more on the freeway . As far as what the pollutants that motors put out . The system that they use is flawed so it means nothing . They are measured in "parts per million" not "parts per minute" . Now where did I put that bucket of money I saved ?  J.W.


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## Vwbeamer (Jun 16, 2008)

agree, in the end it is about cost per mile for me.



ww321q said:


> I don't really like hypothetical discussions but . But if I was millionaire I guess I would buy a $100,000 EV . It would have gobs lifepo batteries a $25000 AC drive and go 300 miles on a charge . Oh! wait . If I had that kind of money I could care what gas cost . Actually I think the oil companies have the right to charge what ever they want or sell as little as they want . The 10 hp diesel motor and enough fuel to go 300 miles would weigh 165 lbs. Thats about the weight of 2 or 3 batteries . As far as a drive to couple the 2 drive systems , a cog belt or chain to a clutch would work . Just so happens that the diesel I have is designed to run under load at 3600 rpm . I think that is close to what most series run (sweat spot) . I'm not a environmentalist. I am building an EV to have a choise to who I spend my money with . The reason I want to build a parallel hybrid is for economy. My new Clark forklift motor and new diesel motor cost me about $850 for both ! I got plenty of room for batteries , over 20 . I might even be able to use the 72 volt Curtis controller I got for $300 . With the extra 10 hp provided by the diesel motor I may be able to go 70mph or more on the freeway . As far as what the pollutants that motors put out . The system that they use is flawed so it means nothing . They are measured in "parts per million" not "parts per minute" . Now where did I put that bucket of money I saved ?  J.W.


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## Manntis (May 22, 2008)

Vwbeamer said:


> *Less efficient.* mechanical energy is turned into AC electrical energy, which is converted to DC energy, which then converted back in mechanical energy. Every step of the way power is lost.


That presumes you're using a DC motor.



Vwbeamer said:


> *More complex*. You need an extra generator, a battery charger.


Parallel hybrids carry a generator too. Have a look at a Prius, Escape, or Camry hybrid sometime.



Vwbeamer said:


> *More weight*. You have to carry around the generator and the charger. The extra weight could be used to carry more batteries


Parallel hybrids also carry a generator and charger. See above.





Vwbeamer said:


> The parallel system has none of those disadvantages-


au contraire 



Vwbeamer said:


> *More efficient.* Mechanical energy developed by the ICE is delivered direct to the drive system. No power is lost being converted to electrical energy, and back to mechanical energy.


Instead of an engine running in its peak power band, transferring to electrical, then to the motor you have a larger engine (in case you need higher HP, no peak power band option as it has to run at required propulsion RPM) transferring mechanical energy through the required 5 speed transmission. Six of one, hanf-dozen of the other.



Vwbeamer said:


> *Simpler*. An 8- 10 hp ICE can be couple direct to a dual shaft traction motor with a simple centrifugal clutch or belt driven torque converter.


Simpler? Ask yourself why production parallel hybrids are so complex then 




Vwbeamer said:


> *Cheaper*. A clutch or belt driven torque converter is $1000's cheaper than a gen set and high rate battery charger.


Again, parallel hybrids still have generators and chargers. That's how the ICE recharges the pack.



Vwbeamer said:


> *More power*. With both the traction motor and ICE directly coupled to the drive train, you have the combined HP of both to drive the car.


True - but only an issue if you went with a smaller electric motor to begin with.


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## ww321q (Mar 28, 2008)

I think that each one of us has our own individual needs in a vehicle . Some Gas is the way to go because of the long range and structure in place to refuel at a whim . Some of us want to get away from the oil industry . And some are concerned with the environment . What ever fits the individuals needs is what he will see as best . No one version of vehicle is better than the rest just some fit one persons needs better than others . You can go tit for tat and no opinions will change , well unless your needs change . I am building a vehicle that fits my needs . I don't think that it may fit anyone else's needs necessarily . On another string they were talking about the importance of current control in an EV . In my case I know the cars I drive , a good amp , volt and maybe temp gauge is all the control I need . But that's just me . I have almost all the components for the EV I'm going to build at a cost under what most spend on motor alone . I have enough money in the bank to buy what ever I want but that's not me . I'm a scrounge and good at it . Give me box of junk and I'll make something out of it . I just think arguing over what is better is pointless . Time better spent helping the ones with ideas that would help them with their EV . Maybe even the free energy crowd . .....J.W.


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## Woodsmith (Jun 5, 2008)

ga2500ev said:


> The best compromise that I've seen is the ICE EV pusher concept. Simply put you attach an ICE trailer to the EV. It's a disconnected parallel hybrid. You get all the advantages of direct mechanical power to the road without any of the disadvantages of coupling in either a parallel or series model as you've outlined above. The hookup is a small set of simple electrical controls. It functions pretty much as a cruise control.
> 
> The best part is that you only attach it when you need it. Around town, just leave it home. Long trip, just attach and go. When you get to your long range destination, detach and have a pure plug in EV again. without any additional weight to lug around.
> 
> ...


Is that an ICE driven trailer that literally pushes the EV along?
I have thought about the possibility of an all electric system but, for the longer journeys where there is no place to plug in, carry a small ICE generator set in the boot/trunk to charge up during rest stops or at the destination. Not the most fuel efficient method but perhaps as an occasional use.


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## Vwbeamer (Jun 16, 2008)

*The parallel hybrids use the traction motor in regen mode to generate electric power*, they do not have separate generator/ chargers. if they do then they are series hybrids. by definition.

Besides, we are not talking about what Toyota or Gm has engineered. This what we can " DIY".

It is my contention that simply adding a simple 8-10 hp ICE coupled to the traction motor has the advantage over a DIY series set up using a commercially avalable 110/220 VAC gen set.

Great forum, and i'm not trying to troll, just wanted to see what others think.


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## Tesla (Jun 27, 2008)

ok well i've been crunching numbers trying to figure out the perfect system for my needs and i'll share some of my figures with you along with my thoughts on the subject.

average car efficiency = *24%* (30% engine (liberal) 80% auto transmission) for a series hybrid using ac motor and diesel engine = ~*36%*
(gen head 92%, motor 93%, charger 90%, manual transmission 94% and battery charging (nimh) 66%)

between series hybrid and standard car there's a ~50% increase in efficiency.

with a parallel system i averaged the efficiencys of the gas system using a cvt and the electric drive train to come to ~41% (correct me if my math is wrong with that one, it sounds correct)

but with a parallel system on long hauls when your battery is depleted you are then taking power from the engine to charge the battery. i figured the efficiency while charging is about 13% (that's taking a ~25% efficiency and then taking more off that for charging). i averaged those two together to figure what the overall efficiency would be but in real world it would take much longer to charge the batteries than it would to discharge them so for more than probably 3/4 of the time it would be in charging mode. i averaged the charging and driving efficiency and got about *27%* (2% more than standard engine drive train cars). this sounds kind of low but gm discontinued their parallel hybrid silverado and sierra trucks because they only got a +2mpg from standard so i feel these figures hold water fairly well.

even with all numbers set aside its also a fact that gasoline engines perform the most efficient at one rpm which is exactly what the generator does so series hybrids already use gas the most efficiently.

so with all this said i believe that series hybrids offer the best efficiency while also allowing for an all electric skip to the store with very little complexity in building.


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## ga2500ev (Apr 20, 2008)

Tesla I have just one question:

What percentage of the time/miles do you plan to use the gas part of your system?

Just curious.

ga2500ev


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## skullbearer (Jul 9, 2008)

Tesla said:


> ok well i've been crunching numbers trying to figure out the perfect system for my needs and i'll share some of my figures with you along with my thoughts on the subject.
> 
> average car efficiency = *24%* (30% engine (liberal) 80% auto transmission) for a series hybrid using ac motor and diesel engine = ~*36%*
> (gen head 92%, motor 93%, charger 90%, manual transmission 94% and battery charging (nimh) 66%)
> ...




30% is a good avg. efficiency, but that is across normal driving rpm's. Piston motors designed for high efficiency purposes are designed in two ways:

Consumer method: 

Low rpm, high compression, so good solid torque for the weight of the vehicle (not in a sport sense, but in a real need sense) across the lower band, and longer gears for greater speed but slower acceleration. What this does is it encourages near wide open throttle at lower rpm because the people with these vehicles tend to freak out when they hear anything above 4k rpm and the fun times whine of bearing just entering their real operational range starts.

This is my experience with people at least as a mechanic for Toyota for a while.


Sport/Race method:

I've only seen this in a few designs for normal consumers, largely mazda and honda 4 bangers.

At max throttle (un-enriched if you want economy, obviously) and in full power band range, the motor is under its greatest mechanical stresses of its life, but the funny thing is these two factors actually give it a LOWER mechanical resistance to movement, and its overall thermal and volumetric efficiency are UP. These motors often tend to be a little bit lower compression so they won't wear down at constant heavy throttle, but honda doesn't seem to agree with that statement (they just like replacing valve seals on Si models  ).

Anyway, max throttle = 0 crankcase vacuum of pressure thanks to our wonderful emissions systems, this means 0 vacuum on the bottoms of cylinders going up. You'd think the pull on downward moving cylinders would cancel that out, but cylinder blowby provides enough to make that upwards vacuum count. Not to mention that when a cylinder fires, another is often on the intake stroke, which provides further vacuum forces to the crank via ventilation. Likewise, by having ventilation we avoid a pressurizing crank, and because of ecology reasons we don't want to have the old 'vent to the air' method either (though that actually gives us the efficiency bonus)

High rpm and max power put massive stress on crank, rod, piston, transmission, etc bearings. High load = bad, right? WRONG! Bearings of the kinds using in these components don't know the meaning of 'easy work', and have this backwards way of thinking that 'as the going gets tough, the tough get going'. Bearings actually meet peak efficiency the instant before they break from load.

This is one of the reasons in racing engines they carefully monitor their loads and select bearings which, under full power, are as close to breaking as the builders feel comfortable with. This frees up as much power in the max power points as possible. To give you a reference, if you take a ball bearing from a car wheel, from a motorcycle wheel (scooter is even better), and from a good road bike (if you have the 'zero friction' bearings for bicycles that's even better), you can compare.

Take an axle bolt or rod that will fit through it, spin it without pressure, then start adding weight. Funny think happens, if you can get the bicycle bearing with about 100-160 lb's on it, it is EVEN EASIER (but only if you can get it spinning decently, kind of hard to do with your hands alone, but bear with my example). Same deal with the scooter/bike bearing at 180-300lb (for small bikes, like 250's). The car bearing however won't get really buttery compares to no weight until you get a good loaded sedan weight on there, as much as 40-800lbs. (800 for your big dodge baby murders with the fat family option).


Round about way of coming to my point: Smaller engine on a hybrid gives you a constant max throttle high load option for efficiency, not talking about the cost of engine rebuilds and replacements, just straight fuel economy. The Toyoto Prius was initially designed with a small new motor running just like this, but it wasn't something Toyota already had off the assembly line, AND the sound of a small motor in that situation is hard to completely muffle from the passengers, who wouldn't like it. Comfort won out over design.

If you're going to put a small motor in there, figure out your hp need by studying your driving habits, or if you can store your power use on your EV over a week, study your true average power requirement. Get a motor rated for your true average during daily driving, and it should charge enough while cruising or at lights for your acceleration, but not be too much so you couldn't run it at max efficiency the bulk of the time it was running.


SORRY FOR THE EXTRANEOUSLY LONG POST! This is just the area I'm going into. I love it! 


PS EDIT: See if you can get an old turbine accessory power generator through army surplus. Sometimes I see them there but people grab them quick... these come off helicopters and sometimes even converted humvees and such needed a high efficiency high power output generator for command center type work. Most would be in some foul condition but the manufacturers are private and it is a publicly available tech (albeit at ridiculous cost). You can get 80-90% power efficiency out the shaft on these turbo-shaft turbines, and they are smaller than a 1.0L piston pounder in most cases. Just beware, getting parts is a difficult and expensive process of dealing with the manufacturer (and no listed prices, so its all al la carte), and my experience with the three different companies I know of that were doing that sort of thing was they are extremely rude unless a blank check falls in their lap, although they DO sell to the public. There are also Turbine repair/rebuild shops around the U.S. that deal with these, and for a solid kick to the wallet you can get a rebuild, or have one rebuilt. DONT EVER RUN IT UNINSPECTED. They aren't in surplus unless it was cheaper to take a new one off the shelf rather than fix it.


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## Tesla (Jun 27, 2008)

thank you a lot the info and wisdom. i was actually looking the other day for a turbine after finding they're very efficient. most i could find were model airplane turbines and home-made turbo turbines which efficiencies were just wrong. it's understandable on a business aspect but just sad that Toyota would do that, maybe an active noise cancellation system integrated into the speakers could deaden the engine noise in the passenger compartment. the parallel system i was comparing would be the power assist hybrid type that they used in the honda insight. which got 70mpg. and to digress a bit it got 58mpg with the ac on lol, a solar powered TEC system like in the aptera would really help and i do plan on developing that sort of system for heating/cooling. im still in the development phase but when i do build it i will log my "adventure" in full detail.


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## ricksmol (Jul 7, 2008)

I think the main point of a series hybrid is based on statistics. Most people drive within a certain range daily. Take for example the Chevy Volt (according to what I have read of course) it will go 40 miles without using one drop of gasoline. This means that a large percentage of the population could use this car daily and recharge it at home or work and avoid the use of gas. If your driving range is more than 40 miles, then the ICE kicks in. 

If you drive 100 miles daily then the average between the battery driven distance and the gas driven distance would still average to about 100 miles per gallon plus the electricity used to charge the battery.

In contrast the parallel Hybrid is giving you an average mileage of 50 miles per gallon from the moment you start it.

If you have to go on a long trip with the series hybrid then you still get a very long range using the ICE to drive the electric motor and your average mileage would still rival that of a parallel hybrid of about 55 mpg.

How often do you go on a 400 mile trip? Most of the time you will be averaging between no gas at all and 100 mpg.

This I think is the advantage of the series hybrid.

Rick


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## Tesla (Jun 27, 2008)

I agree with you rick. In my situation I actually do go long distances frequently. Just in the last 3 months I've gone 400miles 5 times and every weekend I do about 200miles. So for me I wouldn't consider a parallel. A large advantage of the Series Hybrid is that it allows you to have a small engine that produces just enough energy to maintain freeway speeds. 99.999% of the vehicles on the road today are capable of producing a couple times of the energy they need to do legal speeds. The extra power is just for acceleration, and because of this they are much less efficient. With the series hybrid it produces what you need but it also allows a battery bank for acceleration making it that much more efficient. Another advantage is the fact that the ICE doesn't have to run constantly. If you decide to take the highway at 55mph and the genset produces the energy to do 70mph then the generator only needs to kick on once in a while to top off the battery (check out the pulse and glide technique for hypermiling, it'll boost mileage to astronomical numbers if done correctly and at low speeds (http://www.metrompg.com/posts/pulse-and-glide.htm)). And then there's the fact that with a generator you can fine tune an engine to be much more efficient than an engine that requires constant rpm change. I'm sure these things are ditto in this thread but they are very large advantages. They allow the vehicle to use a much more efficient engine and operate it in a way that just isn't really safely possible when the engine is driving the wheels.


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