Jens Groot and Li-ion Battery Testing

For years now I’ve lamented that there’s no real academic source for lithium battery testing.  Well, thanks to a Mr. Jens Groot (Division of Electric Power Engineering, Department of Energy and Environment, CHALMERS UNIVERSITY OF TECHNOLOGY, Göteborg, Sweden 2012) as well as my friend and Electric Chronicles commenter Jarkko Santala, I gots me one to read…

Here it is: State-of-Health Estimation of Li-ion Batteries: Cycle Life Test Methods

Since stuff on University sites moves around a lot, I’ve taken the liberty of posting it here too: JensGroot_batterytesting

From the study:

The purpose of the work presented in this thesis is to investigate how different load cycle properties affect the cycle life and ageing processes of Li-ion cells developed for use in HEVs. In particular, Li-ion cells using graphite anodes and LiFePO4 cathodes are to be studied.

Furthermore, a target is to perform extensive laboratory testing of commercial Li-ion cells to develop and evaluate test methods for cycle life tests. The cell ageing analysis is combined with results from field testing of cells performed by Scania CV AB and research tests performed by KTH and UU.

Finally, an objective is to initiate the modelling of SOH which are to be developed in the continuing phase of this
investigation.

Here’s a little more about Mr. Groot, a PhD student, as well as a list of other work he’s done at Chalmers.

OK, gotta go.  Got me some readin’ to do.

LiPo Packs, Fires and Facts

So, if you’ve looked into lipo chemistry at all, you have no doubt read all the warnings about their volatility and the potential for fires and explosions.  Repeatedly I’ve been told they’re acceptable for experimental use, but not safe for daily commuters.

I call bull.

First, I know a few guys who are using them, daily, and have been for a good long while.  Second, I did this video, trying to do my own lipo fire with some failed cells, and, you can see for yourself, the result was a little disappointing.

.

I have, since then, got a lot of advice on how to get a better result, that is, a better fire and explosion, which basically comes down to this.  First, work with a cell with a maximum charge, even hugely overcharged.  Pierce the cell with a conductive material, like a nail, that will short the cells and not burn up.  Heat the cells, best, by discharging them.  Then they may burst into flames and even explode, but maybe not.

So, if you have fully charged or overcharged cells, and you’re running your bike really hard, and you lay it down and something conductive pierces casing an then the cells, then you may be in trouble.

Reminds me of…  gasoline?

In fact, from a post on ElMoto.net, LiveForPhysics, AKA builder of the Death Bike and Guy Who’s Blown Up More Lipo Than Anyone I Know said “The modern RC LiPo packs are fairly shockingly stable. I’ve had some that required overcharging past 8v, taking in 3x the cells rated capacity before getting fire balls (though most blow around 5.5v). It can be difficult to get fireballs on a healthy cell from any amount of physical trauma (including stabbing with conductive materials) anymore with modern RC LiPo. “

To be sure, lipo is touchier than most any other chemistry, and by that I mean you can junk the pack a lot easier than others.  Overcharge it, over-drain it, there’s a host of care and feeding instructions I’ve posted.  Treat them badly, they will repay you by failing.  But burst into flames for no apparent reason?  I’m beginning to think this is, at best, old news, and bad information.  At worst, it’s internet hype and hysteria fed by maybe nothing more than people’s love of a good explosion video.  Actually, there is a worse scenario, that people are actively trying to harpoon lipo chemistry for their own nefarious reasons…  or maybe it’s Space Aliens from the Future trying to corner the HobbyKing lipo market…  who knows?

Here are a few links to some “Care and Feeding of lipo” that I found helpful.

One thing is for sure…  lipo chemistry and radio-control lipo packs have gone through some very rapid development in the last few years.  I suspect a lot of the “exploding lipo” comes from early packs and “sketchy suppliers.”

So, my next step is to order and build a bigger pack, something around 30ah, so I can get a little more mileage out of it, and a little more current at full-throttle…  and I’m going to stick with the Turnigy hardcase lipo.  Stay tuned…

Care and Feeding of LiPo

I have been wondering about storing my bike outside in the cold New England winters.  Here’s a great post that talks about that, and other storage, temperature and charging issues with lipo batteries from none other than the RC aviation community.  Who else?

He focuses on getting the most life out of lipo, and the secret is in not abusing them…  knowingly or not.

Lithium lifetime is based on several factors:

1. Temperature while in use
2. Temperature while in storage (for our purposes, “storage” is the same as “maintaining a constant voltage level”)
3. Percentage of “full charge” (4.20v/cell) to which a cell is charged
4. Percentage of “full discharge” (depending on chemistry, somewhere between 2.5v and 3.2v) reached by a cell
5. Rate of charge (depending on chemistry, between 0.3C and 3C may not be excessive)
6. Rate of discharge (depending on chemistry, up to 20C may not be excessive)
7. Charge level while in storage

In particular, there’s the issue of charging when the batteries are cold. And by cold, he means around 32F.  If you top out the battery at that temperature, you’ve overcharged it.  When it gets warmer, your 4.2V charge is going to go well over that, apparently, so you may have taken as much as 10% off the life of the pack.

Here’s another very informative post on lipo use in general: Lipo Usage Best Practices.

Finally, none other than Battery University:

Many battery users are unaware that consumer-grade lithium-ion batteries cannot be charged below 0°C (32°F). Although the pack appears to be charging normally, plating of metallic lithium can occur on the anode during a subfreezing charge. The plating is permanent and cannot be removed with cycling. Batteries with lithium plating are known to be more vulnerable to failure if exposed to vibration or other stressful conditions. Advanced chargers, such as those made by Cadex, prevent charging Li-ion below freezing.

The Lipo Project: Balance Block and the Mini Bus Bullet Block

As is often the case when I’m in the middle of a project I put all this stuff together and kind of forgot to post it here.  Sorry.

Here’s what I ended up with for connections and wire management for the lipo packs.

First, with the help of David O’Brien, I got these little things together for paralleling the balance tabs:

After we got done, he found some boards that were set up as strips in the bottom of some drawer, but watching him solder this thing was like watching Leonardo paint.

Here’s what I came up with to parallel the 9mm bullet connectors on the Turnigy packs:

A simple chunk of copper, drilled with holes to accept the connectors.  Add a little heatshrink and you gotcha Mini Bullet Bus Block.

Connectors working loose is a huge issue, so I wanted to figure out some way to mount them, lock them, and help manage the cables.  I made up a simple ABS plate with some cutouts and ridges that does the trick.

Here’s what it all looks like in the bike:

Enertia at 60mph vs 50mph- range/consumption test

(or… Brammo vs. Rt128 Part 2)

OK THAT was interesting…

In my bold commuting attempt on the infamous Route 128, I was pretty impressed by the Enertia’s range running at a fairly extended section- oh, maybe 8 miles or so- at 50mph. This naturally led me to wonder what the range might be at a full-bore 60mph, a speed that would avoid any death and dismemberment, or worse, tickets, from going too slow on “America’s (death) Technology Highway”.

My Mom always said I don’t know when to stop.

Anyway, the testing plan I hatched was simple. Run the bike on a nice, quiet Saturday morning from my exit at a nice, even 60mph until I get to 50% charge levels as shown on the panel. Turn around, run it back at 50mph, and see where I sit for charge.

The exit is about a mile and a half or so from the house, so I started the run with the meter showing 98%. I made the run. After an almost even 8 miles I hit 48% charge. I sat for a bit by the side of the road, and the level dropped to 45%.

I came back at an dead-on 50mph speed, and at my exit I showed 18% charge- netting a 27% battery draw. Somebody do the math for me, will ya? 60mph for a 50% drain vs. 50mph for a 27% drain. I hate math.

Oh, lemmee see, I can do this. For 20% more speed, you’re draining your batteries at almost twice the rate. 1.85% to be more precise. (27% capacity x 1.8 = 50% capacity… is that right?) …oh crap I hate math.

Let me see if it makes sense in a mileage reference. If I’m going 60mph, I’ve got about 16 miles of range. 50mph gives me (at a 30% discharge) more like 24 miles. 20% more speed cuts my mileage down to around 60% of my range.

There, that’s better…

I think.

One funny thing, though.  When I got off the exit after the 60mph run I was reading 48% charge, and by the time I got into the cloverleaf it had dropped to 45%, and stayed there.  When I got back to the exit after the 50mph segment it was reading 18%, but when I got on the road home, it had rebounded to 19%…  only to go up to 20% on the road home cruising at 30mph or so.  I did not stop to let the batteries rest, or anything.  When I got home, it was still at 20%.  I can’t figure this out- it doesn’t seem like the batteries had any chance to rebound, and the rebound I expected after the first leg didn’t happen, in fact, quite the opposite, they drained another 3%.

I blame Math.

Rechargeable Zinc-Air Batteries

I say again. WOW.

via physorg.com, the manufacturer’s site here- ReVolt Technology.

more lists…

This, from “tech”, at Electric Motorsport:

If you are riding this thing across the country I would have to say it is a first.

Since you like to compare drive and battery systems here is something for the website. This is a breakdown of the Isle of Man and Mid Ohio TTXGP Electric Motorcycle race results (w/ Type of Motor used and battery pack size) Also which bike hit the highest top speed at the race.

Isle of Man TTXGP team results – motors used – Size of battery

Best buy Pro Class

First place- Team Agni – 2 Agni motors – 10.5 kwh
Second place -Team xxl – One Seimens AC Induction motor – 9.5 kwh (highest top speed 105 mph)
Third place -Brammo – One liquid cooled brush-less Perm permanent magnet motor – 8.4kwh

Open Class

First place – Electric Motorsport – One AC Induction motor – 6.5 kwh
Second Place – Bare foot motors- On AC induction motor – 10 kwh (89 mph not confirmed)
Third place – Team Tork- one Agni motor – 6.5 kwh

TTXGP Mid ohio team results – motors used – Size of battery

Pro Class-

First place – Electric Motorsport – One AC induction motor – 8.4 Kwh (highest to speed 108+ mph)
Second Place – Nortan Electric – One AC induction Motor – 7.4 kwh (also hit 108 mph)
Third place – Enertrak – One Enertrak BLDC motor – Approx 5 kwh

Tech

ThunderSky Batteries

ThunderSky LiFePO4 Batteries.
…Cedric’s choice.

Comparisons to come.

Holy crap.

TS-LFP90AHA x 18 = 72V, 90AHh @ 77.6#
And the winner is!

WAIT this just in:

TS-LCP92AHA x 18 = 72V, 92AHr @ 56.9#

OMGOMG!!

Battery answers

OK, in the spirit and tradition of our sponsors, Head-2-Head Reviews, here’s the battery matchup- just gimmee the facts, m’am…

…seems clear enough. (To get maximum range on the things, we’re looking for the best amp-hour rating per pound. Check the AHr/lb column.)

BionX Sony Lithium Manganese battery