Itsy, Bitsy, Spyder 550 and Battery Balance Myths: Unpacking the BMS Debate

In this week's episode, we assemble new mounts for the 2009 Mini Cooper Clubman drive train - somewhat colorfully.

We also wrap up our Vantage Green Van Battery Makeover. We have thrown out 775 lbs of AGM lead acid batteries and replaced them with 27 High-Power brand 200AH cells that I never liked well enough to put them in a car. The resulting pack weighs 350 lbs.

Because I had used some of the cells in some experiments in the lab, we were forced to bottom balance the pack, a three day adventure. Young Hauber subsequently drove the Vantage Green Van 103 miles on a single charge. This is a bit of an improvement over the 16 miles I had achieved during one test drive with the AGM's which only had 600 miles on them. Gentlemen. Lead is dead. Long live the LiFePo4. Get over it.

Also featured this week is Duane Ball's most excellent Spyder 550 build. And therein lies a tale.

Duane is about to take delivery of a Beck Porsche 904 from Special Editions Inc.

This is a fantastic new Beck reproduction. Just the roller will cost over $50,000. To raise funds for this project, Duane wanted to sell his beloved Spyder 550. So for a mere one Brazillion dollars, I bought it.

The car is a superb build with essentially duplicate components from Speedster Part Duh, but with a much better Brusa charger in it. Duane did use a PB-6 potentiometer box and a cable assembly to act as a throttle/accelerator, and everyone is pretty much unanimous that this was the one POS error in the car. It just feels awful. We'll be changing that.

In the meantime, the original Speedster is nearly 2 years old and has about 10,000 km on it. Duane's Spyder has 5811 km on it. So young Hauber and myself took advantage of a crisp, cool but beautiful October Sunday afternoon and drove on U.S. 61, a winding blacktop hilly highway to Perryville Missouri and back.

For some reason, this took more energy than it normally does. But to an interesting result. In the Speedster, we actually rolled to a stop just in front of our new shop at 601 Morgan Oak. We had to push the car inside by hand.

We had used a total of 195 AH out of the Speedsters two-year-old 180AH pack. And six cells were well under 0.5v STATIC once we pushed it inside and put a meter on it. This car has had NO BMS of any kind, other than a single CellLog8s misadventure for three days monitoring 8 cells and resulting in, you guessed it, a fire. It has been repeatedly run to full 100% DOD in testing. ANd we still managed 195AH from a 180AH pack (two strings of Thundersky TS-90AH in parallel).

So we've finally destroyed it. Well, at least we haven't done it any good. But as of last night, all cells were taking a charge and climbing in voltage. I'll check later today to see if any also LOSE their charge after the full charge. If they don't, this is incredible.

The Spyder 550 was also interesting. The cells are much easier to access, and we have young Hauber now to do the heavy lifting. It used 176 AH on the trip. It is much lighter (as is Hauber) accounting for the difference.

The Spyder is 1890 lbs with a 44% front and 56% rear weight distribution. As the cells were all still over 3.00v, I sent young Hauber for a couple of sleds of Stag Beer, his favorite housekeeping task here at EVTV. On return, the vehicle was showing 157 km total on the trip, 183.5 AH used, and a static voltage of just 95.65 volts or an average of 2.517 per cell.

After letting the cells rest and recover for a few minutes, I had Hauber take a reading of every cell in the car. Here's what we found....

Of course, the excellent news is that with NO BALANCE DONE EVER, and NO BMS EVER, a car with 5811 kilometers (3611 miles) on it was in excellent shape, excellent "balance" and all on the very vertical face of the discharge curve well below 3.00v and with 183 ah withdrawn from a 180 AH pack.

I have an odd ability at pattern recognition that is only occasionally useful for any thing. But the first 10 cells sort of jumped off the page at me. It raises a question.

The first 12 cells are arrayed across the front of the car, and so they may be getting dramatically more cooling than the cells in the rear of the car. But there are 12 of them. And cell 11 and 12 simply do not match the first 10.

I went to look at the overall pack voltage, and of course Duane had used a Xantrex. I recall the same problem on the Mini Cooper. I had originally used the lower 10 cells to power the Xantrex at the 35 volts it likes. Over time, this depletes the cells actually. The Xantrex doesn't draw much, but it draws enough. Duane had apparently used the first 10 cells, just as I had, and later went to a voltage divider across the entire pack to power the Xantrex, just as I had. It is eerie to see your MISTAKES replicated in somebody elses' build.

We put a charger on the 10 cells at about 30 amps for probably 5 minutes. They all fell right in line. And while we were doing it, with hit Cell 22 with a very brief shot to bring it up as well. I don't have a cogent theory for that one.

Here's what I DO get from all this. The "they gradually go out of balance" theory used to support the increasingly dubious case for the necessity of the BMS is just pure D Grade Bullshit. That is, bullshit that is not even very high grade bullshit. Here we have two cars that have NEVER been balanced in any direction, with a couple of years on one and 3600 miles on the other, where NONE of that has been done, and they both operate so well, that I can take 195 AH out of a 180AH pack apparently without mortal damage.

The BMS adherents, who increasingly start to look also like the BMS designers, who also look a lot like the people selling the BMS's are simply pumping BS for cash. Their products will actually DAMAGE your car, and the purported gain from using them is total nonsense. At this point, since we've made this information public numerous times, I believe that they KNOW or SHOULD HAVE KNOWN it was bullshit, and are actually lying to you for cash. There is no innocent "difference of opinion" going on here.

I have actually set out to cripple a perfectly operational electric car that I have well in excess of $70,000 invested in and have apparently FAILED to KILL IT. As I'm normally very good at these things, we'll see with some folow up tests that almost have to show some DAMAGE at least. But I could not kill the car, and did not drive any cells apparently into reversal.

If you top balance your cells, you CAN. And we have in the past done that empirically and publicly where anyone can duplicate the experiment.

ANd here is the problem with the online milieu, people have extended the right to "have their own opinion" to somehow include the right to have their own facts. It does not.

That said, they remain YOUR cells, do with them as you may.

The Rinehart controller we are installing in the Mini requires a switched ground signal to indicate the brake light is on. I don't quite get this. Brake lights run on 12v and you usually see 12v coming on when you apply the brakes. But it's easy enough to invert. A relay would work quite well, but we put on brakes a lot and so we're going to wear out the mechanical relay. Another way is simply to switch a transistor, which inverts the signal. A MOSFET is a good candidate because of very low forward resistance. We used a 75 Amp 30v MOSFET that is gross overkill to switch milliamps. But this will work quickly and probably won't ever wear out. This is the little diagram to invert our brake signal to a ground instead of 12v when we press the brakes. The 12v brake signal switches on the MOSFET applying ground to the output.

Jack Rickard