ElectroClassic EV
Classic Cars Reborn into the Electric Future

Battery Goodness

These Lithium Iron Phosphate (LiFePO4) batteries were ordered from Calib Power, which is the authorized US branch of CALB, the Chinese Aviation Lithium Battery Company. Shipping time from China is anywhere from 1 to 3 weeks from the date of order. Sitting above on a palette in Calib’s Pomona warehouse are the 36 cells that will live in the Porsche. Now they are mine, and I can stop lusting after them.

.

Calib Power has an enormous warehouse space, with large batches of batteries shipping all over the US through this facility. My measly little order is put in perspective by this shipment for a single client, for use in UPS backup power systems for cellular and radio transmitter towers.

.

I saved a couple hundred dollars in shipping by picking up the batteries myself, which was one of the reasons for purchasing them from CALB. Their warehouse is within an hour’s drive from my home if there are any problems. Another plus is CALB cells don’t swell up like most LiFePO4 prismatic batteries, which need to be strapped tightly together in modules of 3 or 4 to prevent expansion that can impact performance. Above we see Calib staffer Annmarie in her heels and dress, hoisting the batteries onto my truck with her forklift.

.

Calib also sells the terminal bolts and copper bus bars, which are commonly used to tie multiple cells together into battery banks for custom applications. I unexpectedly discovered that the distance between battery terminals is slightly longer when cells are arranged end-to-end rather than side-by-side. Because of the configuration of my pack, 23 of the connections needed the longer bus bars. Calib told me that a new order would take several weeks to ship from China, which led me to investigate alternatives. I’ll speak more to that in a later post.

.

All these go inside there. The crates were heavy and even with a dolly I could only handle one at a time. Each individual cell weighs 12.3 lbs, multiplied by 36 for a total pack weight of 444 lbs. It seems like a lot, but lithium batteries are a third the weight of common lead acid cells, which would have added nearly a ton to the car’s weight, and taken up twice the space. Speaking of weight, removing the 1.8 liter gas engine relieved the car of 277 lbs, and the full gas tank and 16.4 gallons of fuel removed approx 110 lbs, for a total reduction of 387 lbs.  So the weight of the above lithium cells only exceeds the combined weight of the gas engine and full tank by about 57 lbs. However, the weight of the AC50 motor, adapter, controller, charger, and battery racks should also be factored in. That final figure is posted HERE.

.

Checking the cells with a multimeter is a way to confirm they are healthy and holding a charge. I expected a plus or minus variation of at least a tenth of a volt, but the meter showed them all perfectly holding their factory charge at 3.31 volts DC. This erased any lingering fear of a bad cell in the batch, and reflects well on quality control in the CALB Chinese lithium battery plant.

.

Despite all of the cells reflecting the same voltage, I still checked with CALB about balancing the battery pack before administering their first real-world charge. Balancing is essentially distributing the overall charge evenly, so any cell that is initially over or undercharged has the opportunity to adjust to the average pack charge. The simplest technique involves wiring all of the positive cell terminals together, and separately wiring all of the negative terminals together for a couple days. This lets all cells normalize to an average pack voltage, sort of like tilting an ice cube tray to evenly distribute the water. Charge balancing makes utmost sense if the plan is to run the pack naked, but CALB asserted any benefit is irrelevant if a battery management system (BMS) will be used, like mine. However, an individual cell with a high state-of-charge (SOC) could still shut down the charger prior to the rest of the pack being fully charged. Furthermore, even though all my cells already show an identical voltage, it doesn’t mean they all share the same SOC.

Pack balancing can become quite technical if individual cells are discovered to have widely varying charges. This procedure published by CleanElectricAuto describes how to diagnose and remedy such an imbalance with an installed BMS. Even though I’ve barely unpacked my batteries and I’m hardly to that stage yet, a little voice kept telling me to gang them all together so they can achieve electrochemical group mind. These cells are a litter of puppies that need to commune for a while, prior to being connected in series like a dogsled team and run for years, completing their life cycle when that same little voice shepherds them off to doggy heaven. It’s pure science.

.

Advertisements

One Response to “Battery Goodness”

  1. […] Connecting all cells in parallel is called static balancing, but there are also dynamic methods, such as bottom balancing. This involves discharging all cells to the same floor level, so they begin their next charge cycle equally at the bottom of their capacity. Top balancing requires bringing all cells to their maximum level, so they start their next discharge cycle equally at their fullest capacity. CleanPowerAuto recommends top balancing as the only method to use with their MiniBMS. […]


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: