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Old 10-19-2015, 07:21 PM   #1 (permalink)
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Ideas for my first EV.

Hi.
My name is Alex.
I'm in the process of building my first ev.
So i have a couple of ideas for those of you who have do e something similar please feel free to shime in.
My donor car is a 1991 mexican build vw beetle.
Here is one of my crazy ideas.
I want to extend the range of the battery pack or bank.
Since a gasoline engine is less efective in stop and go traffic.
I decided to take a look at the gearing in the transmission to try and take some load off the electric motor and in theory extend the range.
So since i have been a vw nut for many years.
I would try to explain my best.
1st gear ratio is 3.8 to 1
2nd gear ratio is 2.06 to 1
3rd gear ratio is 1.32 to 1
4th gear ratio is .89 to 1
Ring and pinion is 4.37 to 1

So what this means is that on 1st gear you need 3.88 turns of the engine to do one complete turn of 1st gear only.
And to get one turn at the wheels you'll need 16.60 turns of the engine or electric motor.
You may be wondering how i ended up whit this number.
Is real easy.
Just multiply the gear ratio by the ring and pinion ratio.
1st gear 3.8x4.37=16.6 turns to 1 at the wheels
2nd gear 2.06x4.37=9.00 turns to 1 ar the wheels.
3rd gear 1.32x4.37=5.76 turns to 1 at the wheels
4th gear .89x4.37=3.88 turns to 1 at the wheel.
So my idea consists in adding 1.26 to 1 reduction gear boxes at the wheels like the ones used in early vw buses to relieve stress or load on the electric motor.
1st gear on reduction boxes
3.80x4.37x1.26=20.92.
So in theory instead of the electric motor turning 16 times under regular load to get 1 turn at he wheels.
It will require 20.92 turns under less load to get one turn at the wheels.
Second crazy idea is to get one electric motor that has shaft's on both end's
The idea is to use one of those shaft's to powe 1 12v alternator
To keep the main accesorie battery fully charged while driving.
And 2 or 3 36v marine alternators to try to extend the range.





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Old 10-19-2015, 10:30 PM   #2 (permalink)
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Skip the alternator all together, get a dc to dc converter to take care of your 12v needs.
Then the question is, are you building a hybrid, or an EV?
Your stock gearing should be perfect for a EV as the the stock VW engine maxed out at around 4,500rpm
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Old 10-19-2015, 10:37 PM   #3 (permalink)
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Is gonna be electric.
The point of using 2 36 volt alternators is to charge the battery pack while the electic motor is running so i culd extend the range.
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Old 10-19-2015, 11:05 PM   #4 (permalink)
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Old 10-19-2015, 11:17 PM   #5 (permalink)
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How come?
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Old 10-20-2015, 09:29 AM   #6 (permalink)
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Hi Alex,

Frank is the resident skeptic. Don't worry about him.

First, let me advise you not to tell us about car basics. We understand how transmissions work around here. You wasted some time telling us about the gear ratios in your VW transmission. We're already pretty familiar with stuff like that.

Second, completely throw away the idea of adding an alternator to your EV's electric motor. Just dump it. I will explain:

Assume you have 100 watts worth of energy coming out of your battery to go into your drive motor.

The drive motor is - I'll be optimistic - 90% efficient. (Some are better, but not under all loads at all speeds, and we're talking about a variable load/speed application).

That means your motor can generate 90 watts of output.

Now imagine that 90 watts of power is devoted entirely to turning the alternator.

A very efficient alternator is about 75% efficient. Good luck finding one that good, by the way, they mostly exist as prototypes. 90w x .75 = 67.5 watts.

All of this assumes you are only spinning the motor to run the alternator. That's the only thing we're looking at here.

Now we have 67.5 watts to send back to the drive battery to extend the range of the vehicle.

You pulled 100 watts out of the battery so you could send 67.5 watts back. It's better to just leave the power in the battery for moving the car.

If you wanted to be able to use the alternator for regeneration braking, don't worry about it. That's pretty easy to design in, especially if you're using an AC motor. And if you can't afford an off-the-shelf motor controller, don't worry about that either: Welcome to PaulandSabrinasEVstuff.com Electric Motor Controllers These guys are Ecomodder contributors, and evidently just really avid EV homebuilders. If you can follow instructions and solder you can probably build a pretty good motor controller on a tight budget.

If you need the power to run the usual 12v accessories in the car, don't worry about it. That just takes a DC-DC converter.

As for the transmission, you can choose to leave it in or design a vehicle that doesn't need it. Skip the gear reduction at the wheels (also called "portal" axles), that adds a LOT of weight at the wheel, which makes for a really rough ride. You could strip out all the unessential parts to lighten the transmission, leaving in only the ratio you need, or even choose a really low (numerically higher) final drive ratio and drive the axle directly. That would be the most efficient option; every gear reduction you go through wastes some of the motor's power in friction.

This is part of why the Tesla has a single-speed transmission.

VW Beetles are popular for conversion to EV because they're so common and it's easy to find parts if you need to make changes. With the rapidly improving battery technology you could build one with a decent amount of range, certainly enough for modest daily commuting.
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Old 10-20-2015, 12:35 PM   #7 (permalink)
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the alternator setup is to generate enough juice so i dont drain the battery to quikly.
not to power the dc motor

Last edited by Alex77tj; 10-20-2015 at 12:40 PM..
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Old 10-20-2015, 12:48 PM   #8 (permalink)
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also what reduces the life of a battery is the amount of times you drain them
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Old 10-20-2015, 12:50 PM   #9 (permalink)
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High Output Alternators

High Output Alternators manufactured in the USA by ZENA, Incorporated
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Old 10-20-2015, 01:13 PM   #10 (permalink)
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Quote:
Originally Posted by Alex77tj View Post
the alternator setup is to generate enough juice so i dont drain the battery to quikly.
not to power the dc motor
You take energy you take out of the battery to run the car. Say it takes 30 HP to run your car at 55 mph (which should be close)

If you run an alternator as well, the power it 'generates' is less than the extra power you use. Say the high output alternator 'uses' another 5 HP OUT of your batteries. elhigh was trying to explain that you will only GET BACK 3.5 HP worth of power to put back into your batteries.

The Controller on your car, that takes the accelerator input and puts out power to your motor, ramps the power up and down to get the speed you want to drive.

I can only think of one way that your configuration of using an alternator to 'put back' energy into the battery will sorta work - if you have NO controller at all, on a DC motor that you just TURN ON (no throttle ramp) and you use the alternators to load the motor heavily so that it goes slower. This does not work well on a series DC motor (it has more torque as it slows down) and it is horribly inefficient (reference elhigh's explanation of the alternator efficiency) as well as kinda dangerous (it's easy to have a contactor fail closed when you are switching such high currents).

Every time you take energy and convert it - mechanical to electrical, chemical to electrical, etc - there are losses. Most of it shows up as heat.

You posted your ideas and asked for feedback. You have received the feedback. It is your choice to listen to it or not. In my opinion, you will not convince more experienced people that you are right.

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