Advanced electric vehicle conversion project

The battery.

Manufactured by Thunder-sky
Cost $8,960 as a part of the large group purchase
Available directly from manufacturer or US distributors.

No matter what anyone claims, just remember this: your EV will be only as good as its battery. It has always been the Achilles Heel of any EV. Needless to say, if you plan to keep your EV for a long time and have as versatile EV as possible, you should get the absolutely best battery you can afford. And trust me: being on my fourth pack and fourth charger, I can tell you that saving money on batteries and especially charger now will cost you more money, time and frustration in very near future. Now, you may ask to define "the best". Well, it is just as impossible as to define  the "best" car - all depends on individual needs and wishes. While today we still don't have the choice of getting any battery manufactured for an EV we'd like (for availability, affordability or political reasons), the selection is much better than, say, 20 years ago.

The basic guidelines for selecting the battery and points to consider are as follows (money aside):

- The purpose of the vehicle: is it quick racer or moderate performance long ranger (sorry, you can't quite have both yet!) or something in between
- Required system voltage (depends on the controller and the motor you will use)
- The weight limitation imposed by the suspension and handling of the donor vehicle and the size limitations
- Availability of the suitable charging and equalizing hardware (based on the battery chemistry and parameters)
- Maintenance

Ideally, my own preference today would be this:

1. Li-Polymer battery. While still quite rare if scaled up to usable in EV size and up front expensive, at least it became available. Treated right, can be less expensive in a long run than lead acid batteries. Require sophisticated BMS (battery management system).
2. Li-Ion battery. Not as expensive and LiP battery above, but the next best thing. Technical requirements are the same as for LiP battery. Advantages (to me) are worth trying these. Require sophisticated BMS (battery management system).
3. NiNaCl Zebra battery. Expensive, looks like sold to OEM only, and limited selection (well matched to AC system requirements though).
4. NiZn battery - relatively new player on the market - comparable to NiMH and NiCd and (recently became) far less expensive.
5. NiMH battery. Not available for non-technical reasons and may never be available to you and to me.
6. NiCd battery. Realistically available from SAFT (France) or its subdivision ALCAD (Sweden). Expensive up front, but cheap over its long life time.
7.  PbA Gel Cell battery - quite a few choices.
8. PbA AGM sealed deep cycle battery - quite a few choices
9. PbA flooded battery - many choices.

About NiZn batteries. At 3 times energy density of a lead acid battery, NiZn may prove to be a good alternative to NiCd battery. So far some real life tests performed by EVers show that NiZn holds to the promises, the only unknown is life time. I personally know the of at least one EV conversion (and know the owner) done with these batteries. Coincidentally, it also uses Siemens AC drive system.

While other battery chemistries exist (like NiFe or Zinc-air), the ones above have been actually manufactured and demonstrated to be capable of propelling an EV. Please beware that this kind of information gets outdated pretty quickly, so do your home work. Choosing the battery is very individual thing - as choosing the car make and model itself, so no particular recommendations can be made. In my case, after dealing with lead for few years, I chose to try LiIon battery manufactured by Thunder-sky (China).By the time Zebra will be available (if ever), there will be plenty of experience accumulated regarding these LiIons, so I will be able to make educated choice.

 Worley Energy Cells (aka Thunder-Sky) Lithium Ion cells and batteries
 Zebra NiNaCl battery
 GM Ovonic NiMH battery
 SAFT NiCd battery
 ALCAD (now SAFT's subdivision) NiCd battery
 Evercel NiZn battery (monoblock, single cells also available)
 Evercel Evertroll NiZn battery (with optional charger which isn't worth much)
 PbA Optima D950S AGM batteries.

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The purpose of my vehicle is zippy one person commuter. Occasionally I can give a ride to a passenger, but 99% of the time drive alone; no heavy loads. So the calculations should be based on the minimum capacity (so the weight, size and the cost) still providing desired performance. Siemens system accepts near 400V DC input, so for the best acceleration and lowest possible battery current, the voltage should be as close to that as possible. However, I should remember that  during regen the pack voltage is pushed toward inverter high limit quite quickly. Once at that limit, inverter cuts the current into the pack (to keep the voltage at pre-set level) so regen effectively disappears.Taking all this plus the size, weight, cost and other factors in consideration, I chose to use 96 Lithium-Ion cells 90 Ah each. 3.6V nominal each, making it 345V pack. Specification stating that the max cell voltage on charge should not exceed 4.35VPC (Volts Per Cell). I'll stick with 4.25VPC, so the max pack voltage on charge will be 4.25*96= ~408V. On the low side, the recommended minimum is 2.5VPC or 240V, but for the short duration the voltage can be allowed to sag below that. Manufacturer recommended continuous max discharge current is 0.8C, and peal max should not exceed 3C or 270A to maintain specified life time.

My inverter is currently programmed for:

-220 VDC - min pack voltage
- 380 VDC - max pack voltage
- 240 ADC - max pos. (drive) pack current
- 50 ADC - max meg. (regen) pack current

The loose cells cannot be just thrown in the box, even lined up in nice rows. They have to be assembled in blocks and each block strapped together with stainless steel strips and aluminum "book ends" - flat plates entirely covering outer sides of the first and last cell in a block. The reason is, internal pressure builds up as the cells are charged, and relatively soft plastic case may swell if not confined. Too much swelling, and the case may crack. In a stack of the cells they keep each other from swelling, and the aluminum ends keep first and last cell's outer side straight as well. It is convenient to use no more than four cells in a block if all the blocks fit in the box, so it is light and easily changeable if needed. But, this is not a requirement. Five, six, eight, or any even or odd number of cells can be strapped together, and as long as the ends of the block are protected, it will be fine. Extra thickness of the book ends, however, takes up some space, so in my case 3 blocks of 4 cells each (so total 6 book ends for that row were used) didn't quite fit across the box. So, I re-arranged these 12 cells in two blocks of six cells each, so only four book ends were needed. This fit nicely, but barely. Well, the front box narrows even more toward its rear side, so two blocks of 6 cells didn't fit in last fifth row of the cells either. Again, I re-arranged this row in one block of 12 cells, so only two book ends were needed. This allowed whole block to fit, however it becomes heavy and bulky to deal with. If one cell will ever need replacement, it will be a major job - since they all are strapped together, I will have to pull out whole 12 cells block, disassemble it, take care of whatever the problem is, and put it all back together. I hope I won't need to do this often. But even then, let me tell you, an entire block of 12 LiIon cells it is still easier to handle than one 75 lb Trojan 5SHP 12V lead acid battery I used to have before - my 12 LiIon cells strapped together weigh 66 lb total.

Finally, it's worth to mention that the red cables interconnecting the front and rear boxes are routed through the special glands preventing movement and making sure the cable insulation never touch the metal. 

 The batteries came in banks of four strapped together.
 Before re-packaging all 96 cells were connected in parallel to keep them in perfect initial balance.
 Disassembled bank and new stainless steel strips prepared for the larger banks. Aluminum book ends are re-used.
 Assembling 12 cells bank.
 After straps are tight, it is convenient to perfectly line up the cells with large grips.
 Assembled 12 cell block.
 This is how the cells will sit inside the box.
 Trial fit. The fuses visible inside the front box ended up being outside the box.
 Finally, interconnecting straps are bolted in and the pack is ready to be used in actual driving. Later the cables will be re-routed neatly and equalizing modules will be bolted on top of each cell.

Read more...
http://www.metricmind.com/ac_honda/main2.htm

Don