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  #11  
Old 07-17-2012, 12:15 AM
lowcrawler lowcrawler is offline
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Default Re: How often to charge...

Quote:
Originally Posted by Jesse67 View Post
With such a short commute and charging only to 3.5V your cells should last a long time, unless you drag race to work and back everyday....
Haha... yeah.

Well, my new property (which I just bought) is only 3 miles to work... and it's almost all 65mph freeway (litterally, my workplace is the second building off the exit and my new house is like the 7th house off the exit)... so that's like a drag race.

(actually, that's one reason why my pack is so oversized -- so I can run on the freeway without being at too high of a 'C' rate)
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  #12  
Old 07-17-2012, 06:30 AM
Jesse67 Jesse67 is offline
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Default Re: How often to charge...

Well any environmentally minded person like myself (tree hugger) should be asking you why you don't bike to work with a 3 mile commute.... that said I understand the joys of biking in traffic through industrial areas and fully realize its not for everyone.

It would be interesting if there was some more hard data on this, pay more for a large pack to have lower C rates and theoretically longer cell life, or pay less initially for a smaller pack which is worked a little harder but may not last as long? With less weight though the actual current draw and thus Ah draw would be less and the cells wouldn't have to work as hard as you might think. I would say you want your cells to be worn out from use just before they become no longer useful due to age, but you want this to be far enough in the future so your replacement pack is only a fraction of the initial price with 3 x the performance...whenever this will be I have no idea.

The mini truck is using 2 1/2 year old (calander life) 100Ah TS cells, 24 of them, and our current limit is at 450A which gives reasonable acceleration but it's also about as much as I can draw without the cell voltages sagging quite low, normal draw is around 100A. I would say these are being worked pretty hard, the range is only 50 km by design to keep the cell cost low. They only have maybe 1000km on them so we'll see how they hold up. My daily commute uses between 25-30Ah (or about an extra 500 calories when I bike...) so I have the same choices you have. I can technically drive to work for three days on one charge but I'll likely charge every day. I personnally tend to do better with frequent snacks as well, I get much less grumpy.
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  #13  
Old 07-17-2012, 08:52 AM
lowcrawler lowcrawler is offline
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Default Re: How often to charge...

Quote:
Originally Posted by Jesse67 View Post
Well any environmentally minded person like myself (tree hugger) should be asking you why you don't bike to work with a 3 mile commute.... that said I understand the joys of biking in traffic through industrial areas and fully realize its not for everyone.
Yeah, it's 3 miles on the freeway... nearly 6 if I bike. Still reasonable distance-wise, but only when it's between 35-60 or so degrees. Hotter and I arrive sweaty, cooler and it's too cold. ... and only when there is no threat of rain all day ... and only when it's not snowing or icy. ... and only when I don't have a meeting where my appearance matters... etc.

Biking is a GREAT option, but it has limited use in a state like MN due to the weather extremes. (it was triple digits here yesterday with the high humidity (humidity is generally high in MN anyway)... and it's below freezing for roughly 4-5 months of the year.


Quote:
It would be interesting if there was some more hard data on this, pay more for a large pack to have lower C rates and theoretically longer cell life, or pay less initially for a smaller pack which is worked a little harder but may not last as long?
Even as-is, I'm pulling 2-4C pretty consistently. I felt 15kwh was about the smallest I could go and not be over-stressing the batteries.

Interesting idea, though. I wish we had SOME data on calendar life... I mean, as far as I know, we don't even have estimates... do we?

Quote:
less [cells] and the cells wouldn't have to work as hard as you might think.
My pack isn't a huge percentage of my entire car weight -- only about 15-20%. Removing cells is going to shrink pack size (and increase C) at a rate faster than weight is removed... no?


Quote:
I can technically drive to work for three days on one charge but I'll likely charge every day. I personnally tend to do better with frequent snacks as well, I get much less grumpy.
Yeah, I'm leaning that way too....
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  #14  
Old 07-17-2012, 09:08 AM
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dtbaker dtbaker is offline
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Default Re: How often to charge...

Quote:
Originally Posted by Jesse67 View Post
It would be interesting if there was some more hard data on this, pay more for a large pack to have lower C rates and theoretically longer cell life, .... I'll likely charge every day. ... much less grumpy.
extrapolating manufacturing estimates on cycle life as affected by C rate in either charge or discharge, and %DOD..... It is logical that designing with a pack 'oversize' on range to obtain average C discharge no more than 2C with only occasional accel to 4C or 5C to avoid internal heating, and %DOD no more than 50% or 60% with daily charge will likely provide *much* longer life.

HOW much longer under 'real use', I don't think we'll know for a couple more years, until the early adopters here start posting decreasing capacity on 'normal use' packs.... but the goal I think would be to find a pack size yielding 10+ year, or 100k-ish miles which would make the pack essentially a 'lifetime' pack for a given donor.
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  #15  
Old 11-17-2015, 12:15 PM
scott scott is offline
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Default Re: How often to charge...

Hi all, found this post and am interested in how things are going, or turned out. I just upgraded to a 180Ah 153volt lithium pack in Little Red, and would like to know.Thanks
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  #16  
Old 11-17-2015, 02:15 PM
jwiger jwiger is offline
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Default Re: How often to charge...

Quote:
Originally Posted by lowcrawler View Post
...it has limited use in a state like MN due to the weather extremes...

The wife's car (CMAX Energy) uses power from the J1772 port to turn on the heater/defroster/seat-warmer or A/C depending on the weather. Also considering the temperature happy zone of the batteries might impact your charging, charging could help prevent cold-soaking your pack. Charging them when they are warm (a hot parking lot) might cost you some cycles.

just my $0.02
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  #17  
Old 11-18-2015, 09:00 AM
lowcrawler lowcrawler is offline
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Default Re: How often to charge...

Mine worked great for about 10,000 miles....

Then it got too cold to charge (MN has winters cold enough that the batteries got way below the safe charge temp). Unfortunately, with the MiniBMS system there was no way to 'turn it off' all the way and the parasitic charge of the MiniBMS took my cells way, way down...

Long story short, trying to bring them back up did a little damage to some of the cells. I got some more milage out of it, but it no longer was 'fun' after the MiniBMS issues (the alarm was always going whenever it was connected).

Lastly, the breaks in the car went out and I haven't fixed them.
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  #18  
Old 11-18-2015, 10:28 AM
Moltenmetal Moltenmetal is offline
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Default Re: How often to charge...

The literature I've read doesn't agree. You're looking at only half the problem.

Time at high voltage, and especially time at high voltage while hot, are both bad for the battery capacity. Two bad things happen at high voltage: thickening of the solid electrolyte interface on the anode, and electrolyte oxidation at the cathode. One eats lithium, tying it up in species that don't store energy while also making a thicker layer for the Li+ ions to diffuse through on their way to the anode. The other does more or less the same thing at the cathode. Both of those add up to degraded capacity and increased effective internal resistance under load.

Cycles AND calendar life are both ticking away at the life of each cell. Shunt charging is definitely something to avoid in my opinion, as it has minimal effect on the useful pack capacity at a risk of much longer time at high voltage.

There's a difference between high voltage during charge and high voltage during storage. Voltage during charge is a few tenths of a volt higher than the resting voltage post charge, and that few tenths of a volt mean a lot in electrochemical damage terms.

What's better: to recharge at 10% DOD to 0% DOD three times, or to recharge from 30% DOD to 0% DOD once? I'd guess the latter. What's the optimum? I'm sure the answer is "it depends".

Tony Bogs posted some excellent links on the ripple charging effect thread that are well worth a read.
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