maanantai 29. huhtikuuta 2013

Charge points

Just a quick update; I started a shared Google map of public charge points in Finland called Latauspisteitä. Let me know if you want to contribute and I'll invite you in. Otherwise, just enjoy. So far I've only got three points mapped in the Satakunta region.

Update: Found Fortum's charge point map for Nordic countries:

perjantai 26. huhtikuuta 2013

Porin Ässät!

In case you were wondering, I can't resist posting about the Finnish hockey championship winner, a team which my late grandfather made possible by negotiating the union of two local teams in 1967 and also came up with the name for the team, Porin Ässät. It's spade logo and team colors were then chosen to go with the name. It's a shame he passed away just a couple of years ago, especially since the last championship for the team was from 1978, just a few months before I was born.

The championship is ours and I was there! Go Ässät!

keskiviikko 17. huhtikuuta 2013

First ride of the season, car progress and more

Here's the bike after the first ride of the season. Only a little less than 20 km leisure cruise. Everything still works as before and top speed of the ride was 104 km/h. A total of 20.62 Ah or 1481.4 Wh was consumed. Max battery amps were 422.5 A and minimum voltage under load 57.2 V. The bottom fairing is missing because it needs cleaning and perhaps I will also modify it a little for hopefully improved aerodynamics. I also bought an extended front fender from ebay to reduce water and crap flying into the motor and batteries

My KP-K 2000 W charger doing it's thing. I just keep it in a large tank bag from Biltema. It just fits with enough clearance for air flow. All 20 amps going into the 40 Ah pack with no problem whatsoever. I'd charge faster if I had a bigger charger and was comfortable with pulling over 2000 W the usual Schuko plug. I had outlets with a 16 A fuse installed, but just the other day I noticed the charger's connector getting pretty hot. For faster charging better connectors would definitely be in order.

I also started putting together the motor with the flywheel, clutch and so on. It's a bit more ghetto than I'd like, but I'll have to make do with the time and the tools that I have. At least I'll have room for improvement later if I find myself bored and with too much time in my hands... Right, maybe in thirty years or so when I reach retirement.

A bit of news I actually picked up in the local newspaper, Fortum and Nissan along with the ABC! stations have teamed up to provide a network of 50 quick charge stations in Finland. With Nissan on board there should be no question of whether they'll be CHAdeMO or not. The good part is that it's the best option available right now. The bad is that it's highly proprietary and not available for free. However, I did find an open-chademo project which hopefully will make it possible for private converters to equip their vehicle with a CHAdeMO plug. Me included, I hope.

Update! Looks like the charging stations may actually have both CHAdeMO for 50 kW DC and Mennekes for 43 kW AC charging. At least according to this press release from last year. Nice!

maanantai 8. huhtikuuta 2013

Why you shouldn't fully charge your cells

In my previous entry I wrote about the Swedish paper on Lithium battery cycle life. I kept thinking about the results and came to an interesting conclusion on why you really shouldn't fully charge your cells.

Consider a scenario like the one in the paper where you would Top Balance your cells and fully recharge them to 100% state of charge every time and then discharge them to empty. You'd be at 80% capacity in about 2000 cycles as expected.

But if you didn't fully charge your cells, but instead chose to undercharge your cells like we do in addition to Bottom Balancing? You might not see the 9000 cycles that they got when they only charged to 50% SOC, but I'd bet you'd get to 6000 easy. Even that would be triple compared to Top Balancing.

In order to get maximum range a lot of people will Top Balance, use a BMS or try to find other ways to maximize their traction pack capacity, for example by trying to even the cell charges on the fly. What they don't realise is that if you try to push as much into the cells as you can you are killing them much faster than you could be.

By 1000 cycles of 100% charging you'll have less capacity in the cells that you would have had if you just undercharged them in the first place. And the loss is permanent. There's no way to get them back. Undercharge and those cells will have that 90% charge much longer than the fully charged, Top Balanced pack takes to reach 80% capacity.

Top Balancing might give you the maximum range right now, but after a couple of thousand cycles they guy who only charged to 90% will probably have longer range and healthier cells.

If you have more money than you can ever use, or happen to sell batteries, then Top Balancing is for you. Otherwise, in the long run, undercharging is the smart thing to do. Don't forget to Bottom Balance.

Update! Here's a link to the paper:

Disclaimer: All of my battery ramblings are based on my own experience and Jack Rickard's findings. They are applicable to CALB SE- and CA-series cells. Other cells and chemistries may at least require different voltages.

On swelling and battery life

Ok, I'll just steal that one from Jack's University of Batteries, but I do think it holds true. Swelling is telling and if your cells swell you are damaging them. Hence there is no need to bind them together tight, unless you want to destroy them by overcharging or, oh, let's say by Top Balancing, which really is just a form of doing that.

Another very, very interesting thing is the excellent paper from Sweden Jack is also kind enough to present to us. What's apparent is that to get the 2000-3000 cycle cell life (down to 80% capacity) you need to continously charge to 100% and discharge to about 10%. I think you'll get the same results by Top Balancing as well if you boil your cells at 100% SOC for extended periods of time. And every time you charge to 100% you're harming the cell, so it's really better to Bottom Balance and undercharge a little, say by charging to 3.5 volts per cell. It's the best way to take of your cells really. You only charge them to a voltage and stop immediately.

The test went on to 9000 cycles with LiPO cells in cyclic simulated EV use before the 80% capacity limit, if you didn't charge them over 50%. It didn't matter how fast you discharged. They lasted better if you went from 23 degrees Celsius to 35 degrees. I know it's LiPO cells, but they should be similar enough for all this to apply to LiFePO4 cells as well. Nothing whatsoever in there that would support anything the BMS people are claiming.

I'd go as far as claiming that if you only have 80% capacity left after only 2000 cycles you've probably been doing something wrong. If you are using a BMS then it's your BMS that is harming your cells.

Another thing to take home here is that discharge rate doesn't matter, which means I'm definitely going to remove any artificial current limits in my motorcycle right away. The SE40AHA cells can put out 400 A, that's 10 C, and I'm going to take it all. My AXE7245 controller could go up to 450 A. I will add some cooling though, I have a 8" fan and a 3" marine blower that I'll be experimenting with, but more on that later.