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Join Date: Jan 2007
Posts: 163
Good Answers: 7

Re: The Electric Car in America (Part 2)

09/24/2008 5:51 PM

Electric Vehicles Questions and Answers

  1. How much will it cost me to do the conversion?

Not counting the cost of the donor vehicle, you will spend between $6500 and $9500. It depends on the type of vehicle you are converting, which determines the size motor, controller and number of batteries. The total cost also depends on how much metal work you can do yourself. See the Bill of Materials page for cost estimates for major components.

  1. Which vehicles are the most commonly used for conversion?

· Vehicles that are most often converted have a 4-cyl. engine and a manual transmission.

  1. What driving range can I expect on a charge?

Of course it all depends on the conversion – vehicle type along with the number and type of batteries. However, most people who drive electric street vehicles say they get between 30 and 50 miles per charge, without saying what they mean by 'charge'. I believe it is only reasonable to state the range based on a 50% drop in charge capacity. You can go lower, but repeatedly going down to 40% and less capacity (remaining capacity) point will shorten the life of the batteries. We don't want that. I have found that my Chevy S10 pickup truck conversion, which has 16 six-volt golf cart batteries and weighs a total of 3700 pounds, has a maximum range of about 35 miles, 20+ miles at the 50% point. Keep in mind that driving habits impact distance.

  1. How fast will my converted vehicle go?

My converted Chevy S10 has a top speed of almost 60 mph using 16 batteries. Most people who convert a Chevy S10 use 20 batteries, have a top speed of near 80 mph and a range of about 40+ miles (not at 80 mph). I don't have a need to drive on the freeway, so a top speed of 60 mph and a range of 35 miles are just fine for me.

  1. How do I determine the charge state of the batteries?

A simple way to measure state of charge is to measure the voltage of the battery bank a couple hours after you have driven it – and before you start charging, of course. The chart below is the one that I use to determine the percent charge remaining. You can make your own chart for the number of batteries you use. The third column, Individual Bat. Voltage, is simply multiplied by the number of batteries to create the first column. Many say that measuring the specific gravity is the best way to determine charge level, but who wants to mess with battery acid!

State of Charge

Unloaded

Bank Voltage

(16 Batteries)

% Charge

Individual Bat. Voltage

Spec. Gravity

(80o F)

101.90 100 6.37 1.277
100.96 90 6.31 1.258
100.00 80 6.25 1.238
99.04 70 6.19 1.217
97.92 60 6.12 1.195
96.80 50 6.05 1.172
95.68 40 5.98 1.148
94.56 30 5.91 1.124
93.28 20 5.83 1.098
92.00 10 5.75 1.073
  1. How much does it cost to charge the batteries? What is the cost per mile?

The actual cost to charge your batteries depends on your overall design, your charger and your driving habits. In my case, the cost per mile ranges between 5 and 6 cents. I have devoted an entire page to carefully answer this question. Click here!

  1. What can I do to keep the cost per mile as low as possible?

· Use low rolling resistance tires and keep the tire pressure up.

· Don't be a lead-foot. It's the same as a gas guzzler - take it easy.

· Learn to coast a lot - you are traveling for free when you coast.

· Use a high-efficiency charger so as not to waste energy while charging.

· Plug into the neighbor's house instead of yours when charging. (I'm not serious.)

  1. How much do batteries weigh?

The 6-V golf cart batteries are around 65 pounds each. The 12-V deep cycle batteries are usually about 10 pounds more.

  1. How should I care for the batteries to ensure long life?

· Use a quality charger that has three charge phases: constant current, constant voltage with decreasing current and a lower constant voltage for the final phase. The final charge phase is often called the finishing phase or the soak-in phase. The charger should also provide a manual equalization charge mode that you can use at wide intervals to restore balance to your series connected batteries. Equalization removes sulphate build-up on the plates and helps restore performance.

· Keep the batteries charged.

· Do not routinely discharge the batteries down to 40% or less of remaining capacity .

· Check water levels in the batteries at least once per month, especially during hot weather. Only add water after charging, not before.

· Never add acid to the batteries.

· Inspect the battery terminals to ensure they are tight. A loose terminal connector has contact resistance that will create a large amount of power loss in the form of heat and even melt the lead terminal post down.

· More. . .

  1. How long will the batteries last before they must be replaced?

I don't have personal experience with this yet, but it all depends. Battery Service Life: How long will the battery bank last?

This is a tough question. There are many variables involved in the service life of a bank of batteries. Personally, I don't yet know how long my battery bank will last because of these variables. I have heard some people say that they should last about 3 years, if they are well taken care of – the following will give you an idea of what that means.

The service life of lead acid batteries depends on many factors. . .

Charge Cycles

Service life is often expressed as the number of discharge and charge cycles. I have read figures ranging from 300 to 1000 cycles for lead acid batteries. The reason for the wide range of number of cycles is because depth of discharge (DOD) and operating temperature directly affects the number of discharge and charge cycles, along with other factors. Many battery manufacturers specify the number of charge cycles at a DOD of 80%, which is quite deep.

Note: I go through 6 charge cycles per week, or 312 times per year. If I can only get about 300 charge cycles, I have to replace the battery bank every year. However, DOD does factor in here. I should get many more than 300 charge cycles because I operate the batteries in the 0 to 60% DOD range.

DOD

The service life, and number of charge cycles, can be extended if the batteries are not repeatedly deeply discharged. Many experts recommend that the batteries be used in the 0 to 60% DOD range. The rule of thumb is: the deeper the discharge (on a regular basis), the shorter the service life will be.

Charge Rate

Do not exceed the manufacturer's maximum charge rate specification. Lead acid batteries cannot be quick charged like NiCad and some other battery types. Usually, lead acid batteries must be charged over a minimum of a 6-hour period. Exceeding the maximum charge rate will deteriorate the plates, reduce capacity, unbalance battery voltages in the series string and shorten the life of the battery bank.

Temperature

Battery service life is also related to temperature. Service life for lead acid batteries is usually specified at 77oF or 80oF. If the battery operates in an ambient temperature higher than this, the service life is shortened. Summer high temperatures are hard on lead acid batteries, but cooler seasonal weather brings relief and may equal out.

Water Maintenance

Another factor that affects service life is water maintenance. The water level (electrolyte level) in the batteries must never fall below the top of the lead plates. If this occurs, the exposed plates will corrode and degrade the capacity of the battery. Always use pure distilled water to replace what has evaporated from the cell. Using any other type of water will degrade the cell. (See the Battery Watering System page.)

ADD DISTILLED WATER ONLY AFTER THE BATTERIES ARE FULLY CHARGED.

If you add water to a discharged cell, the water/acid will actually overflow while the cell is being charged by expanding and coming out under the cap seal.

Charge Maintenance

Good Charger - A good charger makes a big difference in the length of service life. Charging at too high a voltage will deteriorate the lead plates and charging at too low of a voltage will allow sulfates to build, increasing internal battery resistance and preventing full charge. Good chargers have three stages of operation: (1) bulk stage during which a constant charge current is applied and voltage increases, (2) constant voltage stage during which charge current decreases and (3) finishing or soak-in stage during which the voltage is decreased and charge current continues to decrease. The charger should have either manual or automatic equalization capability.

Equalization

Use a digital voltmeter to measure the terminal voltage of each battery in your bank. Ideally, all terminal voltages should be the same and remain the same over time. In practice, terminal voltages will not be the same as the batteries age. This causes some batteries to get a higher charge than others. To combat this, either each battery must be individually charge-managed using electronic circuits in a method called 'active equalization' or the overall bank charge voltage must be increased for a period of time to force a higher charge voltage across the low-terminal-voltage batteries in a method called 'passive equalization'. In each case, equalization forces a higher charge voltage on the batteries to 'melt' away the sulfation and restore the cells of the batteries to 'normal'.

You cannot constantly charge the batteries at the high equalization voltage level. Not only will they dry out, but the plates will quickly erode from the frantic chemical activity. Over time, at normal charge voltages, sulfates will slowly buildup, requiring an equalization charge session.

The best method to use is active equalization, but it requires an electronic circuit for each battery whose purpose is to even out the terminal voltage for all of the batteries as they charge. This method ensures that stronger cells are not overcharged and weaker ones are not under charged.

During passive equalization, a great amount of bubbling and some water evaporation will take place, so the water levels in the cells must be monitored. Also, during equalization, some hydrogen gas may escape the cells, so make sure this process is done out in the open, not in a closed area.

Steps for Passive Equalization

  1. Using the normal charge cycle, charge the batteries to what appears to be all they will take.
  2. Check the water levels in all cells of the batteries to ensure that the level reaches the bottom of the fill ring. Add distilled water as needed.
  3. Apply the equalization voltage to the battery bank. This voltage should be between 7.4 and 7.8 V per battery (assuming 6-V batteries).
  4. Monitor the terminal voltages with a digital voltmeter during the equalization process. When the terminal voltages of all batteries closely match, equalization is complete.
  5. The length of time for equalization may be many hours to several days. For long equalization cycles, keep an eye on the water levels. Keep the caps on the batteries (cells closed) during equalization except to check water levels.
  6. When equalization is complete, add distilled water to each cell as needed.
  7. Reapply the equalization voltage for about 30 minutes to allow the bubbling action to mix the distilled water into solution, evening out the density of the sulfuric acid throughout the cells, top to bottom.

. . .

  1. Why can't I just use deep-cycle 12-V batteries to save space and weight?

Assuming that your goal is to have the same voltage either way, you will have less capacity and range using the 12-V batteries. However, if the vehicle is small and light, 12-V batteries are the best option because of lack of space and the need for less weight. Many Geo Metro and VW Rabbit conversions use 12-V batteries. Realize that these are not 12-V automobile batteries. They are deep-cycle batteries intended for golf cart and other electric vehicle use. 8-V golf cart batteries are also available as a design option.

  1. Why don't you use Lithium-ion batteries?

Lithium-ion (Li-ion) batteries are very expensive and they require an expensive charger and protection electronics for each battery. A company I investigated recently offers 12-V Li-ion batteries for vehicle applications at a cost of $2500 each plus another $500 each to cover the special electronics and charger. Compare one of these to two of my 6-V golf cart batteries at a cost of only $130.

  1. What size cabling should I use for the high-current connections?

#2 should be the smallest cable size that you use to interconnect the batteries, high-current fuse, circuit breaker, high-current contactor, current shunt, controller and motor. #4 and #6 are smaller diameter sizes that should not be used – too much power loss and heating. Visit your local welding supply store to obtain a flexible welding cable of size #2, #1 or larger. I used #2 and it is just fine for my application.

  1. For battery terminal connections, should I use the wing-nut bolt on the terminal post or should I use terminal-post clamps?

Terminal-post clamps are best because they offer more contact surface area to handle the high current and will stay tight. If you decide instead to use the wing-nut bolt on each terminal post, make sure you use the correct size cable terminal end, usually a 5/16" hole and that you use a spring-type lock washer under the wing nut. If you fail to use the lock washer, the wing nut will become loose, contact resistance will increase rapidly, heat will increase dramatically and the terminal post will melt – not pretty.

  1. Can I use an automatic transmission?

An automatic transmission will use more energy than a manual transmission, which means less range. I have heard it done, but not very often.

  1. Why do I need a transmission at all?

If a transmission is not used, a gear ratio that allows the motor to start easily under load must be used. The idea behind this is to ensure that the motor is not over burdened when moving the vehicle from a dead stop. With such a starting and fixed gear ratio, the vehicle will reach a top speed that corresponds to the top safe RPM of the motor. For example, I can start off in 2nd gear and accelerate to about 30 mph. If the ratio of my second gear is to be used for a fixed gear ratio, my top speed will be about 30 mph. To get higher speeds, gear shifting is needed. Gear shifting allows for increased speed as the electric motor stays within its rpm design range.

  1. What kind of meter(s) should I install so I can monitor as I drive?

Most people install both an ammeter and a voltmeter. The ammeter helps you determine when to shift gears and how to optimize the use of the 'gas' pedal and conserve energy. The voltmeter is of little use at all because it will vary widely as you accelerate and coast. The voltmeter cannot tell you the true state of charge until the vehicle has rested for a couple hours. Unless it is a digital voltmeter, it won't be accurate enough anyway. So, an inexpensive multimeter can be used to measure your bank voltage until you are familiar with the discharge and range capabilities. If you have some extra money, you may be able to find a computing meter that keeps track of discharge and shows you what is left.

This photo shows how I embedded the ammeter in the instrument cluster, replacing the fuel gauge.

  1. After the conversion, will the vehicle be heavier?

Yes. My Chevy S10 started at 3,040 pounds and ended up being 3700 pounds. The good news is that it is below the chassis and suspension ratings and the weight ended up being evenly distributed front and rear. I did add height-raising extensions (shackles) to the back of the leaf springs and a set of air shocks. The reason I did this is because the front of the vehicle was now lighter and caused the front to be higher than the rear. I wanted the rear to be slightly higher. For smaller vehicles, the suspension system will be challenged, especially with passengers. Add booster springs or shocks with coil springs.

  1. Are conversion vehicles really reliable?

My experience thus far (see 6-month Evaluation), and the experience of many others, says yes! Build it well. Keep an eye on battery water and terminal tightness. Still an unknown to me is exactly how long my battery bank will last until I am forced to replace it (see Battery Service Life).

  1. Can I make my own adapters, one for the motor shaft-to-clutch plate and one for the motor-to-transmission mount?

A few people have done so. However, you need access to a metal lathe and other precision tools. It is a difficult process that requires a precision outcome. Balance and alignment are critical. My advice is to buy these parts already precision manufactured and ready to bolt on.

  1. Should I make a new bed for my truck like you did?

I discovered that the truck bed on my Chevy S10 weighed 320 pounds. The truck weighed 3,040 pounds with the bed and 2,720 pounds with the bed off. I made a light-weight bed using 2" square aluminum stock, used for patios, and ABS plastic sheathing (3/16" on the sides and ¼" on the bed floor). That saved me a couple hundred pounds. It allowed me to make a nice compartment with a lid to cover the batteries. Some people make simple flatbeds, add trailer lights and call it done.

  1. Why didn't you put your batteries in multiple racks under the truck frame in front of and behind the rear axle?

I have seen some truck conversions that place 8 batteries under the frame behind the rear axle – that's 500 pounds of weight behind the rear axle. It not only places a great strain on the rear springs, but it also adds a lot of outward force when going around a corner – not good on wet or icy pavement. Placing the batteries in a secure steel rack behind the cab and resting on the frame yields an even balance of weight front and rear and provides great handling.

  1. Can I still have air conditioning?

Some people do try to keep the air conditioning. They use a motor that has a shaft sticking out of both ends. The front shaft interfaces with the flywheel and clutch assembly. The shaft sticking out the back end is used to mechanically connect to the airco compressor. Keep in mind that if you do this, you will have no airco when the motor is stopped, which as it turns out is a lot of the time during stops and coasting. Also, the energy needed for this airco comes from your battery bank, shortening your range.

  1. Where can I purchase all of the components I will need?
    See the Resources page.
  1. Why don't you add a gasoline generator to keep the batteries charged all of the time?

This is a very common question. The short answer is that the generator would have to be fairly large to constantly replace the energy that is being used. The gasoline engine on the generator would be large enough to run the vehicle directly without the generator or electric motor. That brings you back to a conventional vehicle.

The long answer involves some math. In round numbers, let's say it takes 16 kWhrs of energy to replace what is used from the batteries over a 1 hr period (average speed of around 35 mph). It means that a 16 kW+ generator must be used over that 1 hr period to replenish the used energy. At 100% efficiency, it takes 1 horsepower (hp) to create 746 watts (W) of electricity. In reality, the conversion process is not 100% efficient, meaning that it is more like 1 hp can create only 634 W (0.634 kW), a safe estimate at 85% efficiency. Now, we divide 16 kW by 0.634 kW and we get 25.2. That means we need a 25.2 hp gasoline engine to drive the generator to produce 16 kW of electrical power. Over the 1 hr period of operation, that's 16 kWhrs of electrical energy.

The advantage of such a system is that you have a limitless range of travel, like a conventional vehicle, as long as you don't exceed an average speed of 35 mph or run into other circumstances that would increase the battery drain beyond what the generator can replace. If you plan on driving at a higher average speed, the kWhr energy usage will be higher and a larger generator and engine will be needed.

The disadvantages include the extra weight, system complexity, noise, increased maintenance and being once again tied to gas pumps and prices.

  1. Can I add a generator, or several generators, to my EV to keep the batteries charged?

This is a very common question, but it requires a detailed answer

Adding Generators to Your EV

This is a very frequent topic. Many people believe they can add generators to their electric vehicle and run around town for free, never exhausting their batteries.

Note: I am not talking about a gasoline-powered generator here. I am talking about mechanically connecting the generator to the vehicle in such a way that it generates electricity as the vehicle is in motion. The energy to crank the generator comes form the vehicle itself - from the electric motor and batteries or from the inertial mass of the vehicle as it is in motion.

Richard wrote to ask if he could add three 90-V generators that produced between 250 and 500 Amps each.

Here is my answer:

Richard,

You are not alone in thinking that you can add generators to replace electricity in the batteries while you drive. In fact, there is a very small car company making claims that they have such a vehicle and will make it available soon. These are scam artists.

Let's look at the issue scientifically. Assuming 100% efficiency in motors and generators, the conversion of power is 1 horsepower to 746 Watts of electricity. In your email, you mentioned that you have some permanent-magnet alternators (PMAs) that produce 250 to 500 Amps at 90 Volts. Let's use the 300 Amps you are hoping to get to calculate the actual wattage and required mechanical horsepower needed to produce it. Again, for the time being, we will assume 100% conversion efficiency.

Power = # Watts = # Amps X # Volts, So, in this case we have 300 Amps X 90 Volts = 27,000 Watts.

Now, to generate 27,000 Watts of electrical power, you will need at least 36.2 horsepower (27,000/746 = 36.2 hp). Two of these PMAs will require 72.4 hp and three will require 108.6 hp. This simply demonstrates that it takes real mechanical power to produce electrical power and vise versa.

Let's dig in now and see how much power the vehicle's electric motor is consuming from the batteries as you drive down the road. Assume the electric motor is using 90 Volts worth of batteries (15 batteries X 6 V each). Your average running current, without generators being attached, is around 150 Amps. So, the electrical power averages around 150 Amps X 90 Volts = 13,500 Watts. That is equivalent to 18.1 horsepower, assuming 100% efficiency. This is just the power that is needed to move the vehicle down the road.

With each generator you add, the power to drive them is going to come from the electric motor and the batteries. Now think carefully here, let's say that you add one generator to produce 150 Amps of current to replace what the motor is using. Sounds good so far, but wait - to produce the 150 Amps of charge current, the generator will require 90 Volts X 150 Amps = 13,500 Watts and 13,500/746 = 18.1 horsepower. So, the generator is requiring 18.1 horsepower from the electric motor and the batteries. Now, the electric motor must produce 18.1 horsepower to keep the vehicle moving plus 18.1 horsepower to drive the generator - that's a total of 36.2 hp that must come from the batteries.

Can we simply 'ask' the generator, or generators, to produce more current? Well, I think by now you are getting the idea - if the generator is asked to produce more current, it will take more horsepower, which comes from the motor and from the batteries.

What you are seeing here is that the generator can never make up for the power it takes to move the electric vehicle down the road.

What is more, neither the electric motor nor the generator are 100% efficient, which means you need much more than 1 horsepower to produce 746 Watts of electrical power and vise versa. In most cases, it's more like 1.2 horsepower to produce 746 Watts (as applies to the generators), where 1 horsepower produces only 634 Watts of electricity, assuming 85% efficiency. Looking at it from the Watts point of view (as applies to the electric motor), it would actually take about 878 Watts of electricity to produce 1 horsepower from the motor. This all means that you experience compounded losses that cannot be made up in the batteries-motor-generator circle of life.

Regenerative Braking

After having mathematically explained the above, in some cases it is still useful to have some kind of generating capability. Those are cases in which you wish to replace 'some' electrical power as the vehicle is slowing down to eventually stop or going down a long hill. This is called regenerative braking. Braking action is the result of the mechanical horsepower that the generator is demanding from the moving mass of the vehicle - it slows the vehicle down (assuming a flat surface) as energy is being removed from the moving mass.

Most hybrid vehicles today use regenerative braking to replace 'some' of the battery energy. This is a computer-controlled operation to ensure the smoothest and most efficient recapture of energy. Regenerative braking helps extend your range a little, not a lot. In your case, it may be useful to mechanically connect (toothed belt or chain) one of your PMAs to the back auxiliary shaft on the electric motor, assuming your electric motor has one. The electric motor I use does have one - the Advanced DC 9.1" motor #4001A.

You will need to add a high current diode and contactor between the generator and the battery bank. The diode should be a 150 V, 400 Amp Schottky diode available from DigiKey Corporation. The heavy-duty contactor is the same as used to connect the battery bank to the controller when you step on the gas peddle. Now you have two heavy-duty contactors, one for the controller and motor and the other for the generator. These two contactors must work opposite each other. When you press on the gas peddle, the motor contactor slams in and the generator contactor releases. This ensures that the generator does not generate electricity, and act as a powerful load, while you are trying to accelerate and cruise. When you take your foot off of the gas peddle to slow down, the motor contactor opens up and the generator contactor closes so the generator can pass current through the diode to the battery bank. The diode is needed to make sure that current will not flow from the batteries back through the generator - yikes. As long as the generator voltage is greater than the battery bank voltage, current will pass from the generator through the diode to the batteries. By the way, for this to work, you must leave the transmission in gear. In neutral, the electric motor and attached generator will simply stop as the vehicle continues to coast with no regenerative braking.

But wait! Why not use the motor as a generator to provide regenerative braking? Well, you can, but sometimes it is difficult. It is a complicated operation to get a series-wound electric motor to do that. It can be done, but it is very cumbersome. I decided it is not worth it. On the other hand, permanent magnet motors or parallel-wound motors make good generators. Unfortunately, there are not many available that have the starting torque to make good road-worthy full-size electric vehicles. In hybrid vehicles, the electric motor is specifically designed to also work efficiently as a generator to provide regenerative braking.

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