It’s cold here in Cape Girardeau for July. Actually, not. It has been over 100 degrees Fahrenheit every day and most of our shop is devoid of air conditioning, making EVTV a pretty miserable place to be, much less pinned to for two hours writing down battery measurements every minute on the minute.
But we are kind of on a mission here. Our enthusiasm for CALB’s new CA series continues to grow. As we look at these cells in more detail, we are finding ourselves quite taken with this latest offering of Chinese LiFePo4 technology. It is enabling for DIY car conversions.
In this episode, we undertook our first cold temperature testing ever. We’ve talked about doing this for years, but really never have actually put a number to the decreased performance we have noticed in winter months. In the event of the Escalade Project, we had decided to heat not only the passenger compartment with circulated ethylene glycol, but also the battery boxes. This so we could safely charge the vehicle in low temperatures but in the hopes of a more seasonal performance as well. Without really defining what happens to these cells in the cold, it is kind of a blind solution to an undefined problem.
Indeed, we still haven’t’ tested a 400Ah Winston battery in these conditions and I’m a little hesitant to undertake that on a battery that size. But one of CALB’s claims for the new CALB CA series is improved low temperature performance.
We rather failed to reproduce there results, but we didn’t use exactly the same methodology. Ours varied in five important respects:
1. Temperature. Implied in the CALB graph is a steady -20C or -4F. We cold soaked our cells to 0F, but during the test, held the cell in ice in a cooler. The temperature rose over the test for both cells from 0 to about 25.5 degrees F.
2. Discharge level. CALB discharged their cells to 2.0 v. We end the test at 2.5v. First, 2.5v is supposed to be 100%DOD. But second, we wanted to compare directly discharge tests we did last week at 88F ambient. Those tests were done to 2.50v.
3. Discharge rate. The CALB test was performed at 0.3C which in our case would be 60amps. We did our testing at a uniform 100A constant discharge which is a little over 0.5C by spec, and about 0.5C for the actual tested capacities.
4. We don’t know WHAT they meant by RETENTION by percent. Retained capacity in Watt hours? In amp hours? In physical weight? In geographic location?
5. We used the larger 180Ah cells rather than the unequal sizes of 60Ah for SE and 40Ah for CA. I find larger cells give longer, slower, larger results less affected by testing errors and noise.
Our first tests were of the familiar SE180AHA cell. This was a new cell which we had tested the previous week at 88F.
The actual decrease in amp hour capacity was about 10Ah or 5%. Not too shabby. But the voltage of the cell throughout the test was DRAMATICALLY lower than the voltage at 88F.
This would obviously affect our performance on the road and the feel of the car. It would not be as snappy or accelerate as well and this very much matches our observations during winter driving. So we really have two results here, diminished capacity and diminished performance.
Actually we don’t. They are one and the same but not apparent in this graph. We measure amp hours because the cells are rated in amp hours and that is what we have good tools to measure with. When your only tool is a hammer, all the problems begin to resemble nails.
Your car using electrical POWER. This is actually more properly measured in watts. As most are familiar, a watt is the product of one amp of current flow at one volt of pressure. And if that current flow is maintained at one amp by one volt for an hour, we can term it a Watt-hour of energy. A level of electrical energy expended over time. We often DO talk about our cars requiring 200 Wh per mile for example.
But a watt at 3/4 of a volt isn’t’ a watt at all. If we compare the voltage and current levels of our test in a minute by minute fashion, we find a cumulative test result of 621 Watt-hours from the SE180Ah cell as shown in the graph below.
As you can see, 535 watts at the lower temperature indicates 86.15% of capacity, a more substantial loss of very nearly 14% in cold weather. This is a very believable figure for me.
The CA series voltage comparison is quite similar:
This is an improvement to over 97% of amp hour capacity, but again, if we look at total Watt-hours it is probably a more accurate representation of “retention”.
This represents a decrease in total energy available of more like 7.75%. This is about 56% of the decrease we see with the SE series and so a pretty serious improvement over the SE series. If you live in an area with frequent temperatures below freezing, this represents a significant advantage to the newer CA series cells. If you live in Florida, Arizona, or California, the advantages are dubious here. But here in Missouri we would pay attention to that pretty smartly.
Raymond Harp joins us on camera here at EVTV with Brian Noto in beginning a small, and hopefully both easy and inexpensive project to convert a John Deere zero turn lawn mower to LiFepo4 power as well. We expect a good outcome here as it should dramatically reduce the noise signature of this heinous device and ideally the torque of electric drive will make it quite a grass thrower as well. We are using a used John Deere, have rebuilt what was actually a locked up junk motor discarded from a previous build, no controller, and probably a series of 10 or 12 survivor cells from my earlier test ministrations. Hopefully this little side project will not distract us too much from our main Escalade project.
The Escalade is not well. Yes, we can start and idle it and even rev it up impressively in neutral. But if we drop it into gear, it moves into gear quite smoothly, but then the ECU slams the throttle plate closed in quite authoritative fashion. It would appear not to like one of our sensor inputs. I’m guessing manifold pressure, which I’ve always thought should be ore tied to current than rpm. Back to the drawing board. I don’t see much reason to spend a lot of time on pumps, heaters and accoutrements when we don’t have it driving yet.
Royce Wood operates an automotive repair shop called K&R Automotive up in Ohio. He’s got a lot of GM experience and most notably with ECU issues. He’s offered to drive down this week with his GENESIS scanner to do an analysis on the Escalade and ascertain for certain WHICH ECU sensor signal is likely causing the issue. That won’t fix it. But it will point us more accurately to where we should be working.
We include a video update on Royce’s electric Mercury Cougar project. He has already signed up to bring the Cougar to EVCCON 2012.
We continue to enjoy kind of phenomenal response to our online components, and continue to work on additions. Our most serious omission is an ongoing problem in the EV community, and affordable and flexible charger.
We did quite a bit of discussion with Elcon. This is a very reliable and low cost charger, but curiously inflexible. You have to set the voltage and current levels at the factory and live with them forever more.
But there is a chink in the resistance this problem has presented. They do offer a CANbus controlled version of the charger. WE are looking at the feasibility of coupling a CANbus equipped Arduino to this otherwise excellent charger, to produce a configurable version of this charger. Any Arduino gurus who wish to assist are welcome.
I personally think this weeks video is about as good as we’ve done.