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PostPosted: November 30, 2014, 9:48 am 
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I have thought about an electric vehicle for my next project, But only casually. Let me do some BOE calculations on this:

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the Nissan leaf uses between 280-350 watts per mile, with the average person pulling 302watts per mile. I am not sure how that converts over to generator output numbers as they do not specify that but they talk alot about DC charging at Battery voltage with 8-10Kwh generators.. One of the common generators tossed around on the forums that people seem to favor is this little guy


Well, from what I can read, the generator you mentioned is a ~3KW generator (28.2Volt/105 Amp) It is powered by a ~3.5 KW gas engine. If the Leaf uses 300W per mile, then 1 hour of charging with this generator will get you enough electricity to get you 10 miles down the road. If you hope to use this for long distance driving, that would mean if you do not want to discharge the batteries, you could travel as fast as 10 MPH continuously until you run out of gas.

The gas generator consumes as much as 400g/KWHr. So at 3.5 KW (Engine output) 1 hr of running at full load would consume 1400g of gasoline per hour. At .75Kg/ Liter, that would be ~2.6 Kg or 5.72 lbs. At 6 lbs per USG, that would be ~.95 gallons yielding ~10.5 miles per gallon on gasoline.

Now maybe there is something wrong with my math, But the generator/trailer doesn't make any sense to me. It adds weight, lowering the range of the vehicle on battery alone, Doesn't provide enough power to run the vehicle by itself. The only possibility for it,, is if you have enough battery to get you from point A to point B. Once at point B, you would have a way to recharge the battery overnight, before you have to get back to point A.

BTW, don't forget to add the driver's weight when calculating the range on the batteries. Driver's weight in a 600 lb vehicle will make a significant difference in range.

Keep up the research. It would be fun to follow your build log.

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PostPosted: November 30, 2014, 2:11 pm 
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rx7locost wrote:
I have thought about an electric vehicle for my next project, But only casually. Let me do some BOE calculations on this:

Quote:
the Nissan leaf uses between 280-350 watts per mile, with the average person pulling 302watts per mile. I am not sure how that converts over to generator output numbers as they do not specify that but they talk alot about DC charging at Battery voltage with 8-10Kwh generators.. One of the common generators tossed around on the forums that people seem to favor is this little guy


Well, from what I can read, the generator you mentioned is a ~3KW generator (28.2Volt/105 Amp) It is powered by a ~3.5 KW gas engine. If the Leaf uses 300W per mile, then 1 hour of charging with this generator will get you enough electricity to get you 10 miles down the road. If you hope to use this for long distance driving, that would mean if you do not want to discharge the batteries, you could travel as fast as 10 MPH continuously until you run out of gas.

The gas generator consumes as much as 400g/KWHr. So at 3.5 KW (Engine output) 1 hr of running at full load would consume 1400g of gasoline per hour. At .75Kg/ Liter, that would be ~2.6 Kg or 5.72 lbs. At 6 lbs per USG, that would be ~.95 gallons yielding ~10.5 miles per gallon on gasoline.

Now maybe there is something wrong with my math, But the generator/trailer doesn't make any sense to me. It adds weight, lowering the range of the vehicle on battery alone, Doesn't provide enough power to run the vehicle by itself. The only possibility for it,, is if you have enough battery to get you from point A to point B. Once at point B, you would have a way to recharge the battery overnight, before you have to get back to point A.

BTW, don't forget to add the driver's weight when calculating the range on the batteries. Driver's weight in a 600 lb vehicle will make a significant difference in range.

Keep up the research. It would be fun to follow your build log.


I am not doubting your math and what not, but i am not understanding it... there are plenty of people on the EV forums claiming that these trailered setups give them sustained highway driving.. when loads are very minimal...then there is prime example car that i am looking at BMW i3 and then looking at your statements and not understanding it all.. please explain it more to me plz so i can understand it..

BMW i3 2,799lbs without REX, 3,064lbs with REX
Rex Specs:
7.4 kW continuous (25 kW MAX)
647 cc, two-cylinder generator
7.2 L (1.9 US gal) in the U.S

How does 7.4 kW continuous output able to power a 3,064lb SUV up to 70-80ish mph on the highway, but a smaller 10kw generator setup is unable to power a ultralight bike around 700lbs?


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PostPosted: November 30, 2014, 2:24 pm 
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What about building my own generator using an off the shelf motor of similar voltage to generate matching voltage since the size motors i am looking at are all around $200-500 range and 3 of them would be roughly the cost a decent R1 engine off Ebay in the end... then use a off the shelf small motor to power the motor to produce the output voltage i need...Here is a good vehicle that uses this technology also and they scale the charging motor to 60% of the drive motor size and claim that at flat land highway driving the charging motor would recharge the 40 mile range battery pack in 100 miles of gasoline operation while maintaining highway speeds...
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PostPosted: November 30, 2014, 2:46 pm 
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I believe the 7.4 kw continuous/ 25 kw peak rating is for the traction motor, that sounds about right for a fairly low drag vehicle.
As I recall the Ford Tempo only required 12 or 13 hp to maintain 60 mph on flat ground.
Getting there in an amount of time that doesn't piss of other drivers takes the peak rating of 25 kw at minimum, even assuming that 80% of torque rating is available at any rpm.

Do you know the output rating for the genset? 650 cc gasoline, no turbo, can provide as low as 7 hp or as high as 50 hp (36 kw) depending on state of tune. ..

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PostPosted: November 30, 2014, 4:50 pm 
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The genset on the i3 doesn't power the car to 80 mph. It only charges the batteries. It simply slows the discharge rate, extending the range a bit.

Not interested in anybody's justification/claims. Just build it.

If you want to be practical and greener, get an echo, festiva, aspire, metro, or similar vehicle to drive to work.

Burning fuel to turn a generator to charge a battery to discharge into a motor to drive a vehicle is not more efficient than burning fuel to drive a vehicle.

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PostPosted: November 30, 2014, 5:49 pm 
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Many of the statements you are pointing at are sort of mixing units and don't really say anything. For instance I can say I am 5'8" and my younger brother is taller than me, he weighs 200 lbs.! I haven't said anything wrong, and you might have a guess what my brother looks like, but you don't have real data.

Saying a Leaf uses 300 watts per mile doesn't mean anything, if it does that mile in 10 hours is very different than if it does it in 1 minute at 60 MPH. In your ad picture above the battery pack is described as 23 kWh, so that's kilowatt / hours. That's a useful number and tells us that it can produce 30 hp for one hour. It sort of implies it could go 40 miles at 40 MPH, but that may or may not be true. There is much less air drag at slow speeds so it takes more work to go quickly somewhere than slowly. For instance it takes only one horsepower to travel at a few miles an hour using an actual horse.

Building a trike is a project in itself, so I think you should pick which is most important and either go EV and a locost book chassis or just do a trike. The car chassis will be more adaptable and give you room to change ideas etc. When you do something unusual finding some area to simplify things lets you concentrate on what's important.

Above you mention the BMW / REX thingie. It has 7.5 kW output. That is 10 horsepower. Weight is of little issue with speed on level ground. It is all about friction and aero drag. When you say 70 - 80 MPH that is a huge difference. Speed relates to the cube of the power. So 80 MPH takes %50 more power than 70. That is a problem with how numbers that you see are being presented to you. Much of what you are reading is just hype or crap. That's just life.

So what this adds up to is it will take you some effort just to get to the point of learning how to read and discard some stuff and figure out what is being said. It's not that people have malicious intent, but they don't always understand what they are talking about.

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PostPosted: November 30, 2014, 5:51 pm 
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MV8 is right. The stuff you are talking about doing will make you generate more pollution then a whole bunch of the cars around you put together... Those little motors generate 10x the pollution of a modern car engine...

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PostPosted: November 30, 2014, 6:46 pm 
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I think alot of yall are misunderstanding my statements.. I have asked multiple times already to explain it more so i can LEARN from this confusion.. i am admitting that i am not fully understanding all of this and willing to learn..

I was originally planning out to go the R1 engine route on a "tadpole" design and have read a lot of threads using that engine to make notes of the requirements and such.. but then lately i had a friend get an EV (Tesla Model S) and after taking it for a test ride blew me away with the torque you feel instantly and smooth power.. so my thoughts changed and i actually almost bought a EV car myself after test driving the BMW i3 and Chevy Volt, but decided to keep the money i have been saving up for my locost build switch over to EV power on the build.. so i have been trying to understand EV power and components needed to propel it..

I completely understand that the generator will be inefficient and burn more oil than just going with an R1 engine from the beginning.. but i am not looking to utilize this generator very often.. its more of an hand full of times a year usage kind of deal.. i am planning the range for transport to and from work with some room to spare and im actually seeing that with the use of lighter more expensive batteries i could easily move that range out to 50+ miles without adding much weight.. it would just add up in the wallet as batteries are not cheap for the good quality ones..

I would charge the bike at home for everyday use via a charge controller utilizing some of the free energy i get from my solar system on the house, my area in Florida no longer purchases excess solar unless i switch my panels out for ones on the APPROVED list and those units are just stupid expensive and i already own 18 x 300 watt units now that the previous owner had installed.. so during the peak of the day on most days i am wasting free energy that i could use instead of getting a lousy credit.. i pay 12 cents per kwh flat for power, but if i have excess i only get 10% (1.2 cents) per kwh which turns out as a bonus to go EV... plus if i build it EV i can use the batteries for house backup power in emergency cases for short term usage..

My original understanding of EV motors and picking 2 very small 48v units is starting to change as i believe it would be super slow since most of the EV go karts i have been reading about run between 300-500amp rated motors and the ones i was looking at were max like 80 amps..


Last edited by storx on November 30, 2014, 7:24 pm, edited 1 time in total.

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PostPosted: November 30, 2014, 7:22 pm 
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Don't get me wrong, I think that an EV would be a great project. But to DIY, you have to have a handle on the difference between KW and KWH. Volts and Amps; WHr and AHr battery ratings, to say nothing about knowing your expected loads, at least within the right ballpark. You talk about a 600 lb vehicle and the range therof. But neglect to add any driver weight. Even a light driver at 150# will add 25% to that weight, reducing your expected battery range.

The generator you referred to has a DC output rating of 3KW. That is the equivalent of 4 HP. See the mfgr's specs for yourself> http://www.soleadopower.com/html-en/pro ... lecom.html. How fast do you think 4HP will get you rolling down the road?

The DC motors you are considering, 48Volt/80Amp are 3840Watt motors each (~5.12HP). 2 of them would draw 7680 Watts if used at full load. The generator can only put out 3000 Watts so sustained driving cannot be attained with this setup. These are very rough, basic calculations.

Do you have any idea what CdA aerodrag your vehicle will have? This will greatly affect your highway speed and range. It is not enough to only consider weight for calculating this. And comparing it to a Leaf or I3 is even more unrealistic. These vehicles will, I suspect, have a Cd of 0.3 while comparing it to the typical Locost of around 0.6 to 0.7. Who knows what your vehicle's CdA will be.

To get you started, here is an online calculator that will tell you how many watts (HP) is required to push a given vehicle at a give speed. Play with some realistic numbers of Cd and frontal area (say 0.5 CD and 15 sq ft frontal area to start) and see what you get. http://ecomodder.com/forum/tool-aero-ro ... stance.php

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“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766


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PostPosted: November 30, 2014, 7:44 pm 
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rx7locost wrote:
Don't get me wrong, I think that an EV would be a great project. But to DIY, you have to have a handle on the difference between KW and KWH. Volts and Amps; WHr and AHr battery ratings, to say nothing about knowing your expected loads, at least within the right ballpark. You talk about a 600 lb vehicle and the range therof. But neglect to add any driver weight. Even a light driver at 150# will add 25% to that weight, reducing your expected battery range.

The generator you referred to has a DC output rating of 3KW. That is the equivalent of 4 HP. See the mfgr's specs for yourself> http://www.soleadopower.com/html-en/pro ... lecom.html. How fast do you think 4HP will get you rolling down the road?

The DC motors you are considering, 48Volt/80Amp are 3840Watt motors each (~5.12HP). 2 of them would draw 7680 Watts if used at full load. The generator can only put out 3000 Watts so sustained driving cannot be attained with this setup. These are very rough, basic calculations.

Do you have any idea what CdA aerodrag your vehicle will have? This will greatly affect your highway speed and range. It is not enough to only consider weight for calculating this. And comparing it to a Leaf or I3 is even more unrealistic. These vehicles will, I suspect, have a Cd of 0.3 while comparing it to the typical Locost of around 0.6 to 0.7. Who knows what your vehicle's CdA will be.

To get you started, here is an online calculator that will tell you how many watts (HP) is required to push a given vehicle at a give speed. Play with some realistic numbers of Cd and frontal area (say 0.5 CD and 15 sq ft frontal area to start) and see what you get. http://ecomodder.com/forum/tool-aero-ro ... stance.php


Thanks for posting that link, i am going to play around with it some to see the numbers.. I think the first focus for this setup would be figuring out the correct motors for the application, then from there i could figure out a generator setup for sustained long highway rides.... heck if i had to i could just make a generator out of an old carb'd motorcycle engine that noone wants... maybe like a cheap 250-500cc bike or what not since a lot of the very small displacement engines sit and rot in the motorcycle bone yards with very minimal miles on them.. but ill worry about that later..


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PostPosted: December 1, 2014, 12:57 am 
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Spent a few hours today trying to figure out how to draw pipe work on sketchup and the fartest i could get was one corner before it kept giving me issues and going crazy so i just stick figured it out... the front is where the 2 motors would sit and the area behind the seat would be were the batteries would sit and controller
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PostPosted: December 1, 2014, 1:23 am 
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Lump the joints together so that they form nodes, it's much stronger that way.
For example, on your picture the side braces do not meet the floor braces, that puts a bending load on the main tubes which is a no-no.

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PostPosted: December 1, 2014, 9:01 pm 
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oldejack wrote:
Lump the joints together so that they form nodes, it's much stronger that way.
For example, on your picture the side braces do not meet the floor braces, that puts a bending load on the main tubes which is a no-no.


i drew it out in single line form because i watched some video's on how to use the Follow Me function to draw tubes among all the lines.. but as soon as i meet a connection with another line the follow me function would just stop and not let me continue and after hours of fooling with it i could not get any further so i just did some quick crude drawings of my ideas..


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PostPosted: December 1, 2014, 11:20 pm 
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I think alot of yall are misunderstanding my statements.. I have asked multiple times already to explain it more so i can LEARN from this confusion.. i am admitting that i am not fully understanding all of this and willing to learn..


Not trying to sound rude. I heard you say you want to learn. It's frustrating the things people write that you are reading, that's all. It takes a good effort to learn all this stuff, everyone here will be patient and we all learn things from each other.

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PostPosted: May 29, 2015, 11:53 pm 
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I actually did a design study of an EV A-Mod car for SCCA. It's similar to a Locost, but a little smaller and with gigantic wings.

Here's what I came up with:

4wd via 4 inboard pancake motors. $20,000
Motor controller: $7,500
Batteries: Quick swap battery packs (2 per run): $10,000 (6 packs)
Battery chargers: $2,000
Cabling: 350 MCM: $2,000

To get the 400 hp you need to compete, you'd be running the motors at 372 V and 400 A, well above their rating in both areas. You'd burn out motors on a regular basis, and would require a cooling system to get the 90 seconds you would need to an autox run.

Moral of the story is, EV stuff isn't cheap. If you want to compete with a modest IC setup, you're looking at $15k + for the power train.


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