how does opportunity charging affect cycle battery life?

[monster]

so the life of a battery is measured in cycles right? if your "cycle" is actually just a 1/2 charge or 1/4 charge does that still count as a charge cycle and hence reduce battery life?

i have nicd and about 12 mile range but i usually charge at work after only 3.5 miles will this reduce life? should i try and use all the capacity before i recharge?

 

[Link]

Umm, sort of.

"Cycle" would be one discharge/recharge, but the life varies. If you discharge it to 80% DOD, you might see 100-150 cycles or so (making that up). If you only discharge it to something like 30%, you might see upwards of 300 cycles. 100% discharge is generally a no-no for cycle life.

Generally, it's best to discharge as little as possible, and charge immediately after riding (this is for SLA of course. Lithium is much more forgiving about waiting at 40% charge).

 

[TylerDurden]

NiCd has the dreaded "memory effect": shallow discharges reduce the capacity significantly, unless you periodically discharge completely and recharge. NiCd "conditioning-chargers" will discharge the battery before recharging.

http://www.batteryuniversity.com/partone-4.htm

:?

 

[Link]

What's the deal with that, anyway?

I hear all this crap about it, but I never have seen it. I've also heard that there never was a memory effect. It was just caused by crappy timer based chargers (which would account for everything).

:?

 

[TylerDurden]

I can't explain it from a chemistry standpoint, but it has been the primary issue with nicads since they first hit the street. Toxicity notwithstanding.

Otherwise, it is a damn fine technology for ebike use. Not the lightest, but great value for the $$$.

Even the better NiMh chargers will discharge prior to charging.

 

[monster]

i read that there was no such thing as memory effect too. it only happens under a very specific set of circumstances. i think if i vary DOD then i avoid memory effect.

 

[TylerDurden]

A periodic full discharge is so important that, if omitted, large crystals will form on the cell plates (also referred to as memory) and the nickel-cadmium will gradually lose its performance.

 

[Link]

Well, yeah. If I remember correctly, that wasn't just specific to NiCDs. It was just worse on them. And, like you said, you would never even notice it if you used the batts to their full capacity sometimes.

Think you'll be fine, in any case, Monster.

 

[Ypedal]

NIcads work great for ebike use.. the high-amp drain makes the memory effect a non-issue. and every cycle will be different DOD..

Good Cycle life on Ni based chemistry is acheived by not reversing polarity on cells by draining 100 % under high-load. I've drained Ni packs to 0v a few times, and always managed to get them back to full capacity after a few cycles.

SLA cycle life is best if kepts shallow, again, avoid deep discharges as much as possible and re-charge after every cycle, right away.

Lithium, Ballanced cells, good chargers, and calender life are the factors, DOD does not seem to be an issue as long as you keep the voltage within it's specific range.

50 % discharge x 2 = 1 full cycle in my eyes.

 

[monster]

excellent cheers for all your top replys!

 

[Freddyflatfoot]

I was just thinking about this myself in regards to LiFePo4, but probably early days yet.
Depending on which batteries you look at, they reckon you can get anywhere from 1000 to 3000 recharges.
I normally ride to work, about a 14k round trip, and then recharge. I even recharge if I have only ridden around the block!
If my normal range is 40k's per charge, that is only a ~33% DOD. So if I only get 100 charges, does this mean that my battery has only served me for 1/3 the mileage that I could have otherwise achieved?
Or will I get more life by charging at a lower DOD?
Or should I recharge, say, every second day?
Might be a moot point, coz even at 1000 charges, that's probably something like a 5 year life! Or even up to 10 years or more, if I get the 2000 recharges that some sites mention.
Hmmm 5 years 'free' fuel.
Anyway, might be worth seeing what others have found/discovered about getting the most out of LiFePo4.

 

[fechter]

Virtually all rechargeable batteries will have a longer cycle life if the depth of discharge is less. It would be nice to know if this is also true for LiFePO4. Other factors affect life, like storage state of charge and temperature. These factors might be more important than depth of discharge under some conditions.

 

[Ypedal]

Ni packs get HOT when charging, no way around it unless you want to trickle charge for days on end..

But Lithium does not get hot during charge ( unless something drastically wrong is going on ) and i feel that it's best to charge as often as conveniently possible to prevent over-discharge of any single cell in the pack.

A fully charged Li pack that goes back on the charger ( ever wonder if you charged that pack or not last night ? ) no harm done..

An already charged Ni pack that goes on the charger again can cause problems depending on the charger used..over-charge is a possibility.

 

[Bill Best]

I was just about to ask this question! Would this be the proper assumption for the various battery chemistries..

SLA = Charge after every ride + do not drain too low
NiCad = can charge after every ride, but must condition battery (full discharge/charge) once a month
NiMH = can charge after every ride, but must condition battery (full discharge/charge) once every 3 months
Lithium-Ion = can charge after every ride, but is not necessary + try not to completely discharge

How about LiFEPO4?

...EDIT

I just found the batteryuniversity.com page that talks all about this... DOH!

http://www.batteryuniversity.com/partone-21.htm

 

[Link]

How about LiFEPO4?

LiFePO4 = Jury's still out.

 

[safe]

Lithium Storage Charge

Lithium appears to prefer a "storage charge" that is in the middle. So it wears out from either end... either you charge above the middle voltage or you allow a discharge below the middle voltage and that causes wear. (so it's actually for the batteries benefit to keep it at half charge)

SLA always wants to be full.

NiMh and NiCad seem to not care that much, but you have to be careful to not overheat them when you charge. Since the signal of when the cells are full is hard to detect it's easy to get it wrong. Also, you have all the same problems that a "runt cell" can introduce. (actually all chemistries are vulnerable to the "runt cell" problem)