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42-Month Electric Truck Evaluation (Dec. 18, 2006 to July 17, 2010)

July 17, 2010 marks the end of a little more than 42 months of service for my S10 conversion. The odometer reading is now 202,293. During the past 42 months, I drove the S10 a total of 14,441 miles.

$2.70 average per gallon over the 42-month period. $2.70 pg / 20 mpg = $0.135 per mile compared to an average of what is now $0.065 per mile for electric.

14,441 miles X $0.07/mile = $1011 savings.

Comparing the savings to the last journal entry below, you can see that the increase in savings was not very much. This is because gas prices have decreased while the cost of electricity continues to increase. Also, a savings in fuel cost over the past 42 months of only $1011 is not adequate when the cost of lead-acid batteries is taken into consideration. However, if we expand our view of total cost of ownership beyond just the cost of fuel, electricity and batteries, we see a bigger picture that includes maintenance.

Maintenance on my electric S10 over the past 42 months has been mainly the replacement of a few relays, 12V battery and wiper blades - all low-cost items with no labor charges. I can only estimate the maintenance of a standard S10 over the same 42-month period, which surely would have included oil changes, radiator flush, at least one belt, one or two air filters, at least two oil filters, fuel line filter and maybe a water pump, alternator, plugs, new plug wires and even perhaps a radiator and power steering pump. All of these can and do add up. If not having these problems saved me an additional $1000 over the 42 month period, my total savings to date would be just over $2000. That's still not enough to cover batteries.

My first set of 16 batteries cost me about $1200. My second set of 24 batteries cost about $2000. I had to replace those under warranty last year at no cost to me. Unfortunately, that set, which is my current set, is on its way out. A couple weeks ago, I replaced two of them under warranty. The remaining 22 batteries are close behind. How long will Sam's Club replace these batteries for me?

The Sam's Club batteries are Eveready branded and made by Johnson Controls. This current set was installed the beginning of August 2009. They are now almost 1 year old. I have used them 6 days out of every week, charging them 6 times per week. With each use, the depth of discharge was only about 30% with 70% charge remaining. That is very shallow compared to the 80% DoD that this class of batteries is rated for. In other words, I should get 300 or more charge cycles even at the extreme amount of discharge of 80%. The number of charge cycles to date at only 30% DoD is approximately 300. These batteries should be giving me a lot more charge cycles at only 30% DoD.

As you may have read below, I thought the problem with these batteries was because of charging method. However, this latest set of batteries has been charged according to the profile recommended by one of the Johnson Controls engineers.

I noticed that the end-of-life for these batteries has also been concurrent with the onset of Summer temperatures in the last half of their life. Note that I have installed the last two sets of batteries in August, then there are a few hot months, cool Fall weather and winter, which is mild in Florida. Then comes a cool Spring with temperatures rising to Summer. By the time these batteries are back in hot weather, they have deteriorated somewhat. Something has changed in them to make them very temperature sensitive. I notice early on that I had to turn down the charging voltages for the hot weather. We all know that temperature compensation is important for the life of these batteries. During these summer months, I have allowed the terminal voltage to rise to only a little over 15V at the end of the bulk charging stage. Then, the voltage is cut back to less than 14V for the absorption and finishing stages. This seemed to help reduce the rate of deterioration. In addition, the worst ones of the bunch are thermally running away even at these low voltages. One pair of batteries will not go below 4A of charge current and they get very warm - that continues to rise. Many of the others are showing the same trend.

My conclusion, based on my experience with these Sam's Club batteries is that they are not suited for EV use. They are more for golf carts that are only used occasionally. Everyday use in a road worthy EV is tough on them.

Even so, they do not meet the 300 charge cycles for 80% DoD rating.

Despite the frustrations with the lead acid batteries, I still like my EV. I like the fact that I understand everything about it and can work on it if needed without being at the mercy of a mechanic or dealership. I like that it is clean - clean under the hood and clean to drive. I like that I don't have to stop for gas.

Someday, I will purchase a set of LiFePo4 batteries. Right now, the theory is that these batteries will last more than 8 years and will give service well beyond that. All of the automotive manufacturers are betting on that. For now, I see another set of Sam's batteries in my very near future.

Added July 18 - After writing the above, I decided not to wait any longer to seek a warranty replacement for this failing set of batteries as the 1 year period was coming to a close. My local Sam's club general manager informed me that the warranty was on the original set only, not on the replacement set. Despite that, he was gracious to replace the set anyway, saying that this would be the last time. He said that the batteries were intended for golf carts, not for EVs. That's what I found out through experience. Naturally, I was satisfied with his generosity in replacing the set yet again.

Basically, I received three sets for the price of one when I should have received only two sets for the price of one. The current price per battery is $77 plus a $9 core charge. That adds up to $86, add tax, for the first two years, which should include one replacement set. There is no additional core charge after the first set because you are exchanging old for new. Other brands of batteries and their corresponding cost can be compared to this to see where the cost value is. I have no personal experience with Trojan or Exide batteries, so I can't do this analysis.

A theoretical comparison can be done to LiFePo4 batteries, which are supposed to last at least 6 to 8 years. However, 8 years is a very subjective claim that will vary depending on usage and charge cycles. If the LiFePo4 batteries are rated for 2000 charge cycles at 80% DoD, then how many charge cycles could I get if the DoD is only 30%? I don't know. I am cycling 300 times per year, so that means I will get at least almost 7 years. Because my DoD is shallow, I should get much longer use.

My current cost for the Sam's batteries is $43 per 6-V battery per year for the first two years, taking into consideration the warranty replacement batteries. For 24 batteries, that comes out to $1032 per year. Assuming that the cost will stay at $77 per battery and no further core charges, the cost will be $38.50 per battery per year or $924 per year for 24 batteries after the first two years. For a 7-year period, my cost for the Sam's club batteries is $2,064 + 5 X $924 = $6684.

What I have read about LiFePo4 batteries is that their charge cycle rating is conservative and the usefulness of the LiFePo4 batteries goes on well past the rating, in other words, they don't just quickly die like lead acid batteries do. So, let's factor is another 2 years. That would be 9 years total bringing the Sam's Club battery cost for 9 years to $2,064 + 7 X $924 = $8532. Now, can I buy a 144-V, 200Ah set of LiFePo4 batteries for that amount? Almost! A friend of mine is pursuing that now and has pricing in the $9600 range, then add shipping.

So if the cost of owning LiFePo4 is nearly the same as owning the Sam's Club Eveready branded batteries, I would rather have LiFePo4 and drive a much lighter and faster vehicle without the hassle of yearly battery replacement - I lifted 2500 lbs in batteries at Sam's while changing them out.

What do you think?

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36-Month Electric Truck Evaluation (Dec. 18, 2006 to January 2, 2010)

January 2, 2010 marks the end of a little more than 36 months of service for my S10 conversion. The odometer reading is 199,609. During the past 36 months, I drove the S10 a total of 11,757 miles.

$2.80 average per gallon over the 36 months period. $2.80 pg / 20 mpg = $0.14 per mile compared to an average of $0.06 per mile for electric.

11,757 miles X $0.08/mile = $941 savings

Now for the bad news - but you can learn from my failure. The new battery bank, put into service on October 31, 2008, lasted only 7 months due to my failure to complete the design of my charging system. I was not charging them properly and they sulfated so badly that they partially shorted, all of them nearly at the same time. Sam's Club was kind enough to replace them all at no cost to me as they were still under the 12-month warranty. Note that battery manufacturers do not provide charging instructions with the purchase of their batteries, so charging requirements are not part of the warranty.

I had not finished my charging system when I placed the new batteries into service. I needed to add a higher boost voltage to the design to either reach a higher voltage at the end of the bulk charging stage or to reach a higher voltage during the second stage of charging, the absorption stage. Johnson Controls recommends that you frequently allow the terminal voltage to reach as high as 8 V per battery during the absorption stage as a means of battery maintenance. Flooded deep-cycle lead-acid batteries must experience the higher charge voltage for a short time during each charge or for extended times (3 to 6 hours) a couple times per week after normal charging. As you probably know, there are two main reasons for this: 1) to remove sulfation and 2) to keep the acid mixed evenly top to bottom in the cells. The acid stratifies quite easily with a higher concentration near the bottom. This encourages sulfation and sulfate bridging near the bottoms of the cells.

I thought I could get away with not having the higher charge voltage until I could buy the parts I needed and had the time to finish the design. Unfortunately, time got away from me while the batteries died a slow death - a death that was not obvious to me until it was too late. The loss of the set after only 7 months was a huge wakeup call for me. I replaced the set and scrambled to come up with a quick fix. The design is still not complete, but all battery pairs receive a boost voltage toward the end of the bulk stage of charging. I have a voltage comparator circuit that monitors the voltage on one of the chargers, which relay-controls all of the other charger settings. When the terminal voltage of pair #12 reaches 15.5 V, all of the chargers drop back to a regulated 14.4 V to finish the charge. I apply the boost voltage on Saturdays for an hour or so or anytime that I add water, which isn't very often.

My next step to finish the design is to make each charger independent of the others so each charger will have its own voltage comparator circuit. That isn't so important now, but it will be as they continue to age.

I have had this new set since the beginning of August 2009. So far, they are charging well and are staying well balanced. Time will tell and I will tell you.

Update: (written April 2, 2010) - I completed my distributed charging system in January 2010. Each charger has its own battery voltage threshold detection circuit that changes the charge mode from Stage 1 Bulk to Stage 2 absorption. Each charger has a switch to place it in the Boost mode for desulfation. You can just about see these switches mounted along the top and bottom of the cabinet. There is also a master switch (red-handled toggle, top right) that places all chargers in the Boost mode. Stage 1 lasts until the battery terminal voltage reaches 15.5V for each pair of 6V batteries. Stage 2 is presently set at a constant voltage of 14.4V. I will soon decrease this voltage for the hot summer months.

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30-Month Electric Truck Evaluation (Dec. 18, 2006 to June 20, 2009)

June 20, 2009 marks the end of 30 months of service for my S10 conversion. The odometer reading is 197089. During the past 30 months, I drove the S10 a total of 9239 miles with an approximate energy cost savings of $879 (15 cents per mile on an average $3/gal over this time period on gasoline and average of 5.5 cents per mile on electric over the same period).

9239 miles X $0.15/mile = $1386 for gasoline as compared to 9239 miles X $0.055/mile = $508 for electric

The approximate energy cost savings is: $1386 - $508 = $878

The new battery bank, put into service on October 31, 2008, now has a modest 1758 miles on it. I have been using my distributed charging system to charge the batteries from their time of installation. I have added water only 3 times to date and each time only a small amount. The charging ammeter indicates only a small amount of sulfate buildup on the plates as the finishing current is only 0.1 A higher than when first installed, taking temperature into account. All batteries appear to be healthy with no noticeable deterioration. However, this is to be expected with only 9 months of use and so few miles driven. No form of desulfation or brute over-charging has been applied to date.

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22-Month Electric Truck Evaluation (Dec. 18, 2006 to October 31, 2008)

October 30, 2008 marks the end of 22 months of service for my S10 conversion. During the past 22 months, I drove the S10 a total of 7481 miles with an approximate savings in energy cost of $800. On this day, October, 31, 2008, the entire battery bank has been replaced with 24 batteries instead of just 16. The odometer reading is 195331.

The early demise of the 16-battery bank is attributed to having too few batteries in the bank to begin with and having to add a few new batteries along the way (see log below). With only 16 batteries, the overall voltage is too low, forcing the batteries to supply more current for a given amount of power and range. This causes a greater depth of discharge (DoD) and shortens the battery life. With more batteries, performance is improved and battery life is extended.

In addition, charging an entire string of batteries with a single high-voltage charger is far from ideal. A single charger cannot do anything to maintain charge balance from battery to battery - thus the market for add-on devices for balancing the terminal voltage of the batteries. The total cost of a single charger and a balancing scheme is quite high. A distributed charging system that provides a dedicated charger for at least every two batteries is the better way to go for both battery care and overall cost.

Normally, 20 batteries are sufficient for a light pickup truck conversion, but I wanted 24 batteries to be able to prove my 'Power Wheel' controller technology at the 153-V level (144 V nominal).

New bank of 24 - October 31, 2008

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18-Month Electric Truck Evaluation (Dec. 18, 2006 to June. 18, 2008)

June 18, 2008 marks the end of 18 months of service for my S10 conversion. During the past 18 months, I drove the S10 a total of 6791 miles with an approximate savings in energy cost of $700.

Problems Encountered

On January 26, 2008, I had to replace one of the original batteries because plates were shorted in one cell. Symptoms: whistling sound, spitting acid out onto top of battery case.

On March 15, 2008, I added a 'Hog Tamer' across each of 3 newer batteries to help the others in the string get a full charge. Click here for details.

Two of the original batteries are showing an increased resistance to charging. I occasionally use a separate 6-V charger on these to bring their charge up.

Overall Performance

Acceleration and distance have changed to a noticeable extent. It looks as though I will have to change the battery bank in the next 6 months or so. I will do all I can to stretch the life of these batteries into 2009 when most of the batteries will be over 2 yrs. old.

My 'Power Wheel' controller is still working great.

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12-Month Electric Truck Evaluation (Dec. 18, 2006 to Dec. 18, 2007)

December 18, 2007 marks the end of 12 months of service for my electric truck. During the 12 months I drove a total of 5,034 miles with an approximate saving in energy cost of $463.

Problems Encountered

I had to deal with a problem that started early on. When I first built the conversion, I used wing nuts on the battery terminals. Terminals on three batteries melted enough so that I could not use the terminal clamps that I had changed all of the other battery terminals (cable ends) to. One battery had to be replaced because the melt-down was complete. A couple months ago, I had to replace another one of the three for the same reason.

I didn't wait for the distorted terminal on the third battery to totally melt down. Using a short piece of aluminum tubing, I was able to make a mold and re-pour the terminal, restoring it almost like new so I could use a clamp-on cable end.

Recently, one of the batteries demonstrated that it had some shorted plates. The symptoms were whistling and spitting acid. In addition, the chain of batteries would not finish charging keeping the charge current high all night long. After replacing this battery, everything normalized. Fortunately, the battery was still under warranty and I got an even trade for a new one.

All but this last problem are related to the terminal meltdowns early on. If I had started with the clamp-on terminal connectors from the beginning, I would not have had these problems.

Overall Performance

Acceleration and distance have not changed noticeably. I really would like to get three years of service out of this set of batteries. Just two more years to go. Maybe.

My 'Power Wheel' controller is working great. I am now in the process of building an improved second-generation controller. The improvements have to do with making the controller smaller, more compact.

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6-Month Electric Truck Evaluation (Dec 18, 2006 to end June 2007)

The end of June 07 marks the end of the first 6 months that my S10 conversion has been in service. During that period, I added 2800 miles to the vehicle and a starting odometer reading of 187,852 miles. The following is my evaluation over that period of time and distance.

Problems Encountered

The only significant problem was with the battery terminals early on. I discovered that using the wing nuts to secure terminal lugs to the top of the battery terminals was not a good idea. The lugs offered insufficient contact surface area for the high current and could loosen to increase contact resistance, heat and meltdown. The solution was to replace the terminal lugs with terminal clamps, which provide much more contact area and remain secure. One battery had to be replaced because of severe terminal meltdown.

I had to replace the vacuum switch and relay on the 12-V vacuum pump. The company provided free replacements.

Overall Performance

The truck performs well with no signs of stress on any of the components. After driving, I can place my hand on both the controller and the motor and leave it there because these components are only warm, not hot. That's a good sign.

Early on, I replaced the tires that came with the truck with Michelin X radials that offer low rolling resistance. This made a noticeable improvement in performance - increased coasting distance and less battery drain.