'Exact Behavior' of Battery Chemistries?

[safe]

I'm sure this has been summarized elsewhere, but I like to get the same information many times so that it sinks in as "the truth".

When it comes to NiMH the major issue in charging is that you MUST do all charging in SERIES with no exceptions. (this action is "completed" at the design stage)

As for "balancing" you need to be sure that no one cell in a series is unable to take a full charge or drains too fast. You should be able to tell the ones that drain too fast by them being "low" after a ride compared to the other cells. As for the "full charge" you would test the cells at full charge to see if any fail to hold a normal amount.

Discharge is no big deal as long as your maximum discharge rate is within spec for the batteries. So if the batteries can do 3C be sure that you stay within that. (another action completed at the design stage)

That's about it...

So from my perspective once the cells are inserted into the "tubes" with paste between them all I need to do is test the whole "tube" first (10 cells) and if it's within acceptable parameters then I skip it, if not, then I take it apart and search for either an overly drained cell or one that can't hold a charge. My guess is that I check the "overly drained" idea first and if that doesn't work I slip the cells back in, charge them up, then check for a cell that can't hold a charge.

So that's the "routine checkup" that I would do every once and a while to keep tabs on the health of the cells.

Anything else? Did I miss something?

Is there such a thing as a single cell charger-tester that costs less than $20? (this might be asking too much?)

 

[Lessss]

One wonders what the performance of a 48V nuclear battery would be?
What size and sheilding required at what weight lasting how long. Too bad there is so much hysteria surrounding them.

 

[patrick_mahoney]

Patrick runs 8 of these cells in parallel, with the 20 amp controller for 1.13C, and has written that he's had no problem pulling 1.8C from them.

I did? When did I write that? I don't think I've ever pulled more than ~22A from my 17.6Ah pack. At least nothing that I can think of right now. When did I say that I did this?

 

[xyster]

Patrick runs 8 of these cells in parallel, with the 20 amp controller for 1.13C, and has written that he's had no problem pulling 1.8C from them.

I did? When did I write that? I don't think I've ever pulled more than ~22A from my 17.6Ah pack. At least nothing that I can think of right now. When did I say that I did this?

I thought you did in one of our emails. So I checked. It appears I'm probably confusing-together a couple different people's experiences with lithium 18650's. Between this group, the RC forums, the emails, the links... well, collating all the info in my brain promptly and properly often doesn't happen as good as it should. Sorry for the misquote. I'll print a front-page retraction ASAP!

 

[patrick_mahoney]

I thought you did in one of our emails. So I checked. It appears I'm probably confusing-together a couple different people's experiences with lithium 18650's. Between this group, the RC forums, the emails, the links... well, collating all the info in my brain promptly and properly often doesn't happen as good as it should. Sorry for the misquote. I'll print a front-page retraction ASAP!

No big deal. I just sat here and thought: my 20A controller seems pretty good - I've seen it go up a bit above 20A but not much. I haven't used my pack for anything other than the bike... so I couldn't think of why I would have said that I'd ever pulled more than 20A from it.



Details on my pack: it is supposed to be 17.6Ah. When I first bought it it measured exactly 17.2Ah at a 0.8C discharge rate (from 4.2V to 3.0) which I did using the discharge/cycle capability of my charger. I've cycled it approximately 70 times so far... approximately. Maybe a bit more than that. I've never discharged it above 22A. Typically it seems to sit around 15A when I'm riding. I've never checked the capacity since I bought it, but probably will check again in July/August when it's 1 year-old (after the party, and the cake with the 1 candle).

I have a indoor/outdoor thermometer on it so I can measure ambient and the wire probe in the heart of the pack. After riding, I have never seen it higher than 4Celsius. While charging at 0.5C to 100% - which is the highest charge rate that I ever use,I've seen the temperature rise at the end to 6Celsius above ambient. At my more typical charge rate of 0.3C, and my typical end point of 4V, the temperature after charging is usually 1Celsius above ambient. The batteries are taped, wrapped in bubble wrap and then stuff into a canvas bag from Wilderness energy. The pack in it's bag weighs 10lbs or about 4.5kg.

I always balance the pack when charging. I use a Hyperion LBA10 with the pack in a 6s16p configuration - I wrote a post somewhere on here where I talk about how I do this swap from 12s8p to 6s18p using plugs - if anyone is curious, I can write up details. At the end of a ride, one of my 1s16p blocks (#4 to be specific) is always 0.1V lower than the other five 1s16p packs. It's always been this way, and lately it's been taking longer to even it out. But it's not been enough of a concern to consider taking the pack apart to fix it. At least not yet.

My commute to work is approximately 9 miles roundtrip. I usually pedal hard - enough that I'm usually breathing fairly hard both ways. My average speed is usually ~30mph when I'm moving. I haven't tracked my real average speed which includes stoplights. I usually charge about 6Ah back in - very approximately. Sometimes 5Ah, sometimes as high as 8Ah. Never over 10Ah. I only try to charge to about 4V - although my cut off method relies on my paying a bit of attention to the beeps from the charger. Since my charging method relies on me arbitrarily stopping, I'm never quite sure how much capacity the ride uses (since it's almost never "full").

I wrote a build log of the pack over at the old visforvoltage. One of these days I'll rewrite it here. There's a bunch of things - particularly the way that I soldered it together - that I would highly recommend other people putting together 18650 packs avoid.

Batteries: all-battery.com's (LG Electronics) 2200mAh 3.6V 18650. Paid about $3.95 per cell, I bought 101 and used 96 (101 got better pricing, and I had a 12% off coupon). The price appears to have risen considerably since I bought mine.
http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=1643

Charger: Astroflight 109 - charges 1-9 lithium cells (3.7 - 33.3V) at up to 8A
http://aeromicro.com/Catalog/astroflight_109_deluxe_digital_battery_charger_discharger_2691678.htm

Balancer: Hyperion LBA10 - balances up to 6 cells, has overcharge shut off
http://www.aircraft-world.com/shopexd.asp?id=4283

 

[xyster]

At the end of a ride, one of my 1s16p blocks (#4 to be specific) is always 0.1V lower than the other five 1s16p packs. It's always been this way, and lately it's been taking longer to even it out. But it's not been enough of a concern to consider taking the pack apart to fix it. At least not yet.

That's a very significant, roughly 30% capacity drop compared to your other subpacks. During discharge, my 20, 15-cell subpacks stay balanced within 0.02 volts. I'd be concerned you've got a bad cell or two, that is if it shorts, is going to also short the others wired in parallel with it.

My problem is that my cheap B.S. chargers don't like to charge to the same voltage level -- the variance on charge ranges about 0.08V (4.12 to 4.20).