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 Post subject: Re: Electric Power????
PostPosted: October 31, 2017, 4:41 pm 
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Johnny Tsunami wrote:
Anyone tried a fully electric powered se7en? Looking for info on layout, type of motor, controller, batteries and setup.


Here is another kick at the can: why not look at hybrids.

http://www.carbuzz.com/news/2017/3/7/Ge ... a-7738150/

What would come to mind (at our level) would be a small high revving (possibly 2 stroke injected) engine or microturbine running an alternator, charging a bank of hydrogen batteries (not on the market yet). Power would be delivered to two AC motors with no differential... should I go on? :cheers:


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 Post subject: Re: Electric Power????
PostPosted: November 1, 2017, 1:04 pm 
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I think a series hybrid hotrod/Locost would be cool.

Cummins/Onan makes some diesel generators that can be configured to start up automatically when battery voltage gets low. A 30 to 34 amp diesel generator has a full load 100% duty cycle fuel consumption of 1.04 gal/hr. In a Locost, I doubt it would run at 100% duty cycle, even at 70 mph.

The math is fuzzy. 746 watts per HP, how much HP will it take to push a Locost to 70 mph?

Even better, put the generator in a small, Locost-shaped trailer. Run on batteries around town, hook up the trailer/generator for long trips.

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 Post subject: Re: Electric Power????
PostPosted: November 1, 2017, 1:50 pm 
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RickAllen wrote:
I think a series hybrid hotrod/Locost would be cool.

Cummins/Onan makes some diesel generators that can be configured to start up automatically when battery voltage gets low. A 30 to 34 amp diesel generator has a full load 100% duty cycle fuel consumption of 1.04 gal/hr. In a Locost, I doubt it would run at 100% duty cycle, even at 70 mph.

The math is fuzzy. 746 watts per HP, how much HP will it take to push a Locost to 70 mph?

Even better, put the generator in a small, Locost-shaped trailer. Run on batteries around town, hook up the trailer/generator for long trips.

There was a discussion of a similar project on here maybe a couple years ago, using a harbour freight gas engine generator. There was a lot of math thrown around, and it ended up that it would get pretty terrible fuel economy and not go very fast at all on the generator, but a bigger diesel one might work out better. A large enough generator to maintain cruise speed or a bit better, and a small battery bank or large capacitors for acceleration.
Kristian

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 Post subject: Re: Electric Power????
PostPosted: November 1, 2017, 2:41 pm 
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RickAllen wrote:
...how much HP will it take to push a Locost to 70 mph?


Seems to me Jack had MAX topping out at about 70 before going to the LALO body. And this was with 32 HP. Might want to double check these numbers. Can't guarantee the veracity of what comes out of my senior citizen brain these days. :?

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 Post subject: Re: Electric Power????
PostPosted: November 2, 2017, 4:11 pm 
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ngpmike wrote:
RickAllen wrote:
...how much HP will it take to push a Locost to 70 mph?


Seems to me Jack had MAX topping out at about 70 before going to the LALO body. And this was with 32 HP. Might want to double check these numbers. Can't guarantee the veracity of what comes out of my senior citizen brain these days. :?



It seems that Rick is not entirely looking at the whole picture. IMO the electric motor does not need a hell of a lot HP to move a car. I was told by someone who sells electric conversions for VWs that a 35HP would be plenty for a seven. The maximum speed does not depend much on the HP figure but on torque and the gear box. Take the maximum given motor rpm multiply it by the circumference of the rear wheels and you get the maximum speed on the road for a direct drive, ie motor to wheels. Introduce the gear box ratio and you will modify the speed figure accordingly. In what ever little research I have done on the subject I arrived at the conclusion that a 3 speed from anywhere may be plenty to achieve 70 mph. By that's just me. :cheers:


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 Post subject: Re: Electric Power????
PostPosted: November 2, 2017, 11:15 pm 
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I don't need a bigger picture than "how much HP does it take to maintain 70 mph".
Many slick sedans require less than 19 HP to maintain freeway speeds. It doesn't matter what engine/motor is providing it. Weight doesn't matter either.
I know all about the difference in power delivery electric vs IC, rated HP vs peak HP, the electric motor developing peak torque at 0 rpm, the gas engine's need for transmissions because, well, they can't do that. It's the main reason hybrids work so well, the electric motor supplying torque where the gas engine can't.
In this case, it's not the rated HP of the electric motor that drives the math.
The problem here is the generator has to supply enough power to maintain maximum cruise speed on flat level ground. And what is it's fuel consumption under those conditions?
From there the math is crystal clear.
You mention a 3 speed gearbox. Even better is a single planetary such as a Lenco or Powerglide.

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 Post subject: Re: Electric Power????
PostPosted: November 3, 2017, 11:48 am 
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phil wrote:
ngpmike wrote:

Seems to me Jack had MAX topping out at about 70 before going to the LALO body. And this was with 32 HP. Might want to double check these numbers. Can't guarantee the veracity of what comes out of my senior citizen brain these days. :?



It seems that Rick is not entirely looking at the whole picture. IMO the electric motor does not need a hell of a lot HP to move a car. I was told by someone who sells electric conversions for VWs that a 35HP would be plenty for a seven. The maximum speed does not depend much on the HP figure but on torque and the gear box. Take the maximum given motor rpm multiply it by the circumference of the rear wheels and you get the maximum speed on the road for a direct drive, ie motor to wheels. Introduce the gear box ratio and you will modify the speed figure accordingly. In what ever little research I have done on the subject I arrived at the conclusion that a 3 speed from anywhere may be plenty to achieve 70 mph. By that's just me. :cheers:


Simply stated: HP = Torque x RPM ÷ 5252. HP and torque are intimately related.

Since a motor has close to full torque at 0 speed, no transmission is necessary.

I think 32-35 hp for 70 MPH is about right for a Locost book chassis, slightly more that that for a 442 chassis as it has a larger area to push down the road. Bear in mind that in Jacks case, the transmission looses some energy that a non-trans vehicle would then have available to push the car (less mechanical loss). That is for continuous operation. For longevity, one should de-rate the electric motor some amount so maybe use a 40HP motor?

Assuming a engine-generator set for long term hauling, the engine for the generator might be ~110-120% higher than the 35HP in order to account for conversion losses. The generator itself would have to be appropriately sized for continuous operation; slightly over 26KW.

This is all somewhat theoretical.

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 Post subject: Re: Electric Power????
PostPosted: November 3, 2017, 12:07 pm 
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Bear in mind that steady-state highway driving is not what our cars are made for - between the aerodynamics and the fact that tossing the cars around is the most fun use, I have very little use for that particular calculation.


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 Post subject: Re: Electric Power????
PostPosted: November 3, 2017, 1:46 pm 
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kreb wrote:
Bear in mind that steady-state highway driving is not what our cars are made for


Exactly. Two different equations.

Size the electric motor for sporty acceleration. Even uphill.

Since an unloaded (or partially loaded) electric motor draws less current than a loaded one (DC by reducing voltage, A/C from back EMF/higher impedance), steady cruise is the second equation, and is an average.

Tesla roadsters are what, 200 HP?

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 Post subject: Re: Electric Power????
PostPosted: November 3, 2017, 3:49 pm 
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RX7

Simply stated: HP = Torque x RPM ÷ 5252. HP and torque are intimately related.

Since a motor has close to full torque at 0 speed, no transmission is necessary.

I think 32-35 hp for 70 MPH is about right for a Locost book chassis, slightly more that that for a 442 chassis as it has a larger area to push down the road. Bear in mind that in Jacks case, the transmission looses some energy that a non-trans vehicle would then have available to push the car (less mechanical loss). That is for continuous operation. For longevity, one should de-rate the electric motor some amount so maybe use a 40HP motor?

Assuming a engine-generator set for long term hauling, the engine for the generator might be ~110-120% higher than the 35HP in order to account for conversion losses. The generator itself would have to be appropriately sized for continuous operation; slightly over 26KW.

This is all somewhat theoretical.[/quote]

Thanks,
I agree with your points regarding the transmission and when I was contemplating to turn my first locost to electric this is where my mind was. For what it's worth however I was told by most of the folks who have done conversions (including vendors) that an electric car with a transmission will be more versatile; ie will get to highway speed more easily and offer better regenerative power downhill. Direct drive however will work and save weight. :)


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 Post subject: Re: Electric Power????
PostPosted: November 3, 2017, 4:20 pm 
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RickAllen wrote:
I don't need a bigger picture than "how much HP does it take to maintain 70 mph".
Many slick sedans require less than 19 HP to maintain freeway speeds. It doesn't matter what engine/motor is providing it. Weight doesn't matter either.
I know all about the difference in power delivery electric vs IC, rated HP vs peak HP, the electric motor developing peak torque at 0 rpm, the gas engine's need for transmissions because, well, they can't do that. It's the main reason hybrids work so well, the electric motor supplying torque where the gas engine can't.
In this case, it's not the rated HP of the electric motor that drives the math.
The problem here is the generator has to supply enough power to maintain maximum cruise speed on flat level ground. And what is it's fuel consumption under those conditions?
From there the math is crystal clear.
You mention a 3 speed gearbox. Even better is a single planetary such as a Lenco or Powerglide.



Yes GM Powerglide being a 2 speed transmission it would be one of the best options on the electric car. As a plus ,Powerglides can be bolted to rear transaxles such as the Corvair's. An attractive system. :cheers:


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 Post subject: Re: Electric Power????
PostPosted: November 3, 2017, 5:35 pm 
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Doesn't the powerglide typically have a pretty sloppy torque converter? It's also pretty heavy. Not my idea of a great choice.


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 Post subject: Re: Electric Power????
PostPosted: November 3, 2017, 6:17 pm 
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The torque converter would be the first thing to go. Electric motors can run direct drive, and the Powerglide has been run in direct drive by roundy-round racers for years.

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 Post subject: Re: Electric Power????
PostPosted: November 3, 2017, 10:09 pm 
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kreb wrote:
Doesn't the powerglide typically have a pretty sloppy torque converter? It's also pretty heavy. Not my idea of a great choice.


Point well taken. At 150 lbs including the torque converter Powerglide may not be the best choice indeed. I have taken another look at the various conversations among electric car conversion forums. My impression is that there is a wide range of opinions out there but the main theme seems to be that a manual transmission 3 or 4 speed offers a greater variety of settings which translates in better amp economy, better regen, and greater top speed.


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 Post subject: Re: Electric Power????
PostPosted: November 6, 2017, 3:24 pm 
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Thanks to all who commented this certainly cleared it up for me. What I can tell now is that it has been done before, but there is no cook book recipe. Therefore I am going to stick to gas motor power as I understand this. ZiiiiiipppppP never sounds as good as BELOOOooowww wap wap wap anyhow.

Move to adjourn the thread.


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