What is a cycle?

thedman

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Batteries often advertise a certain number of cycles - many Lifepo4 are in the 3000 to 6000 rating.

But what defines a cycle? I get it from a full discharge to a full recharge.

But what about 'cycles' that drain 10 or 20% of available energy, and then gets recharged. is this also a cycle?
 

Mudd

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Batteries often advertise a certain number of cycles - many Lifepo4 are in the 3000 to 6000 rating.

But what defines a cycle? I get it from a full discharge to a full recharge.

But what about 'cycles' that drain 10 or 20% of available energy, and then gets recharged. is this also a cycle?
A cycle from my understanding is 100% to zero. For example eve cells say you can cycle 100% for 3,000 cycles and still have 80% capacity. So if you're cycling 90% maybe you'll get 5,000 cycles before capacity depletes to 80%.
 

Don B. Cilly

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Very good question. For LFP, if I never - well, pretty much never - discharge below 60% (as calculated by the Victron SmartShunt, but still, independent voltmeter audits ;·) seem to agree... and never charge to 100%, what sort of life expectancy should I get?
At a temperature range of, say, 8-40 ºC, with like 12-25 80% of the time?

[EDIT] 9:20 PM, quite a few cloudy days lately, SOC reported as 75%:

Screenshot_1007_212017.png

Yes, it got to 29V... once. That was before I told my controller to "not be a dick" ;·)
 
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Mudd

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Very good question. For LFP, if I never - well, pretty much never - discharge below 60% (as calculated by the Victron SmartShunt, but still, independent voltmeter audits ;·) seem to agree... and never charge to 100%, what sort of life expectancy should I get?
At a temperature range of, say, 8-40 ºC, with like 12-25 80% of the time?

[EDIT] 9:20 PM, quite a few cloudy days lately, SOC reported as 75%:

View attachment 67902

Yes, it got to 29V... once. That was before I told my controller to "not be a dick" ;·)
I'm guessing you'll expire before they do.
 

Messier11

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I was about to ask this exact question too.

I’ve started to plan an off grid solar system for my off grid cabin. It will be overdimensioned in the sense that I don’t think we will go into deep cycles more than say 10 times per year.

I know this can’t be easy to answer, but is there reason to believe that the batteries basically could work for like 30 years?
 

Mudd

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I was about to ask this exact question too.

I’ve started to plan an off grid solar system for my off grid cabin. It will be overdimensioned in the sense that I don’t think we will go into deep cycles more than say 10 times per year.

I know this can’t be easy to answer, but is there reason to believe that the batteries basically could work for like 30 years?
10 cycles per year should last you about 300 years. Haha..... 3000 cycles and they should still have 80% capacity after those 300 years. Yeah with that little use they're going to last a good bit.
 

Messier11

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10 cycles per year should last you about 300 years. Haha..... 3000 cycles and they should still have 80% capacity after those 300 years. Yeah with that little use they're going to last a good bit.

Haha :)

But there would probably be about 60-90 cycles to perhaps 50-60%.
 

S Davis

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Here is a page of the EVE LF280 specs, it says full charge to 2.5’volt cut off equals one cycle.
 

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Don B. Cilly

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So, if you never do a "full" charge either?
Victron's software (which I don't really understand anyway) says I've done 4 charge cycles in just over three months.

vshunt.png
 

RVLiFe

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Within the Victron app, a charge cycle is considered charging your battery between 60% and 90%. It's that simple. You have to drain your battery to below 60% and it needs to be charged back up to 90% . It will then add a charge cycle to the count.
 

RVLiFe

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SoC. but its based off of the battery size and current draw to determine how many Amps you've used. Not sure how much is actually learned from these devices without you inputting the correct values in the first place. You shouldn't use voltage to determine a batteries SoC anyway unless the battery has been sitting for a while. This is why these shunts are necessary if you want to really know a batteries current state of charge.
 

Don B. Cilly

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Victron shunts determine (more like guesstimate) SOC by measuring current in and out and applying some (more or less) clever algorithms to that.
After you've manually set your SOC a few times using other methods - they vary, but in my case, BMS giving approximate SOC, mini-voltmeters right on each battery terminal, and quite a bit of guesswork over some time - they get pretty good.

The software setup PITA is that if you disconnect the batter(ies) for any maintenance tasks, you have to start the teaching (yes, not quite learning ;·) process all over. Which is a bit silly, because, if it can remember the last... everything, in "history", why not the last SOC? Pfft.

On cycles... I guess fuzzy logic best applies. The shallowest you cycle, the best life-expectancy you can... expect :·)
By exactly how much, is anybody's guess, but as a rule of thumb, they're a bit like dogs. Treat them well, they're happier, they live longer. Obviously it's no guarantee they won't get sick and die "before their time",but there's better chances.

Now, if we take the dog simile to its extreme, one might argue that some exercise would also be beneficial, so too much mollycoddling might not be ;)
 

RVLiFe

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When using the victron shunt, if I ever need to disconnect the battery for any kind of maintenance task, I simply go into the battery setting and get the current soC setting as seen by the shunt which is accurate to the tens position. Then after I’m done with my maintenance task, I manually set the SoC setting to this previous value and I’m back in business without really loosing anything. If I do happen to forget to get the current SoC before I disconnect the battery, it really isn’t that big of a deal. The next time my SCC fully charges the battery and hits my charge values, the SoC will automatically reset to 100%. It really is a set it and forget it type of device and I would be lost without it and was happy to pay the premium for it over the Chinese brand that requires a lot more user intervention.
 
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