Simple battery confusion

[dzl_]

Originally Posted by cadillackid

to me the charge shopws DOC i call that depth of charge. a battery at 100% is 100% depth of charge or 0% DOD depth of discharge.. are you saying DOC is depth of cycle????

Hmm yes, this is a rather confusing chart, in retrospect it was not the best to choose for an example. DOC is not a standard term as far as I know, I didn't notice it before (read it as DOD). My guess is that DOC is either a typo or it is synonymous to DOD (charge can be used as noun which has a different meaning than charge as a verb). If you look in the comments that seems to be the conclusion others arrived at as well. The chart is labeled depth of discharge.

but the gist it seems is to use as little of the battery as possible before charging it back up to full

Correct (as I understand it) at least from a simple cycle life point of view.

But it gets more complicated when you bring price into the equation. Shallower discharge = more batteries = more money but longer life. So you have to consider cost per unit energy over the lifetime of the battery bank. There is probably an optimal point for cost.

[cadillackid]

well in my case I have a pair of 100ah AGM's on average im dropping them down less than 25% thus far in the fall running heaters... the bus then drives and gets parked for awhile where the ycan get at least most of a charge put back before i use em again.. so I think ill be OK.. if im on a road trip the shore-charge is out of the question however the drive-time is longer so more alternator charge time..



being that im not going for Ultrea-Greenie-points if i see the Level getting down low I can always idle for awhile too and pump some juioce back in..



the batteries get very Little use in warm weather.. I dont use the A/C much when parked.. and its engine driven so no battery use if I do use it..



for those few summer overnights I do, my portable A/C gets used with a Genny..



the pack mainly runs my Telematics and parking-heat in cold weather when im occupying the bus..



it appears I can over-run my 12kw Diesel heater with 2 heater fans on higjh and a total amp draw of around 20 amps.. 5 hours to 50% ot 2.5 hours to 75%.. conditions such to need to run the heating systems on full blast constantly are not an every day occurance.. and in ohio when we reach temps that cold pretty much everyone is idling so i can idle as needed to keep my charge up if I choose to hang in my bus longer than say 3 hours..



yeah I think I got this setup..



Hail to the Victron products.. the BM712 and the new 25 amp IP67 smart charger... I really dont want to have to replace the batteries too often.. they are kind of expensive.. I also dont have room in my current setup to add any more batteries.. so I think for me using shore power at home and a little engine idling here and there works out best for cost and logistics


-Christopher

[john61ct]

Originally Posted by cadillackid

So how do you count a cycle? If i consistently use up 25% of a battery then charge it full do a times it by 4 and call that a “cycle”?

No, each time you go down to 25% then back to full is a deep cycle.

That "deep cycling" term is just used to distinguish from Starter usage pattern, which is kept Floating within 0.01% of Full its entire lifespan,

thus a different design type.

Even 5% or 10% DoD counts as a cycle.

Getting back to true 100% Full as per endAmps can still be an important challenge even then.

[john61ct]

Originally Posted by cadillackid

the gist it seems is to use as little of the battery as possible before charging it back up to full

Absolutely, but many use cases just can't carry that much "dead lead" around.

Rule of thumb guidelines are "stay above 50% as much as possible" combined with "go below that as rarely as possible" and with "get back to 100% Full as often and as quickly as possible".

But if your context makes frequent abuse inevitable, then buy as cheap as possible (still true deep cycling type) because you will be replacing the bank more frequently.

[john61ct]

DOC is not a thing, afaik

[cadillackid]

That’s right it’s SOC..

I do notice with my new charger that it takes a good amount of time to charge , float and then go to .005C for even a shallow use case.

[john61ct]

Yes, the early stage Bulk/CC you can speed up with high-amp sources, get done in an hour or two with AGM, even if very depleted

if you have a lot of amps available.

But once acceptance rate starts declining, after CV, say 80-85% SoC, drops off to say below 0.1C

there are still many hours left, that is unavoidable using lead banks.

The difference between a source that offers 400A and one that offers 40A, might only be 20-30min over seven+ hours.

That is all spelled out in the MaineSail article I believe you were linked to early in the thread.

That is (one strong reason) why many are willing to pay so much more for LFP.

With the same 400A source, even a piggish consuming boat can fully recharge in an hour, maybe 2-3x a week.

[john61ct]

New link direct to the MS post on that specific topic

https://marinehowto.com/how-fast-can...ery-be-charged

Everyone interested in DC electrickery, well worth the time reading, carefully parsing, regularly coming back and re-reading his stuff on the topic, as you spiral up the learning curve, you understand more and more of the details, starts to hang together. . .

[dzl_]

MarineHowTo is a great resource!


I've read his article on LiFePO4 maybe 4 times and still feel like I would need to read it at least a few more before I start to internalize it.