Simple battery confusion

[john61ct]

Originally Posted by Booyah45828

finding them online seems to be difficult or inconclusive.

If you buy proper deep cycling units from the quality makers, they not only have detailed datasheets and user manuals readily available, their very qualified technical support people are standing by to field specific questions relative to your use case. Sometimes members of the family that founded the company, the actual engineers that designed the batteries pick up the phone!


> What's the end result of not getting back to full quickly? Is that when sulfation occurs?

Yes, but there are other chemical/physics issues.

Bottom line is, precisely benchmark actual Ah capacity when at peak level (not new OTS but after breaking in period + commissioning protocols run)

then run that test all same conditions after a year or two, as the bank wears, capacity loses % that is State of Health.

Industry standard is proactively replace at 80% SoH, but consumers in non-mission critical cases can push to 75 or even 70%.

Gross observable symptoms may be past that, which is when unexpected "sudden failure events" become inevitable.

> Does the specific gravity of the acid drop permanently?

No, that and voltage are just SoC% neither reveal the unit's health.



relative SoC between 100% and 0% still exist, but the absolute Ah between them shrinks a little bit every cycle.

How much depends on how they are treated compared to optimal, for that chemistry, make / model.


_______
Really the best idea IMO is to see FF sources as supplementary, and shoot for "mostly solar" as much as possible.

Every dollar invested in high efficiency pays off a lot in lowering the Ah per day you must produce.

And of course, a strategy of lowering your daily avg Ah consumption, keeping it lower than your avg Ah production.

Home style electrical appliances and crazy wasteful stuff like aircon are not part of that strategy


> Are there DC-DC charge controllers out there so that one could charge a battery back up to full in the correct stages, vs charging and holding at the 14.5 volts the alternator creates?

Yes, for lead that is exactly what DCDC chargers (are supposed to) do.



> I have an onboard diesel generator with a 60 amp alternator. I'm hoping to install a house battery bank of 3 group 31 deep cycle batteries

Better to go with 6x 6V GCs, ideally FLA. Cheaper, easier and last much longer, if cared for.

> The fridge won't be on all the time, only when camping, and in that scenario the generator will likely be running anyways to power the air conditioner.

Well if you mean like 8hrs a day, and a powerful enough genset to feed the aircon and recharge the bank, fine

but I would not pay those running costs more than a few weeks a year.

> Would I be fine charging the bank with the alternator

If you're driving 8hrs a day and have a DCDC or fit a proper external regulator, maybe.

> no solar, and have battery charging accomplished by running the generator

No FF source is enough if you are off grid days at a time. Only solar or mains gets you to 100% Full.

[Ronnie]

Just from a practical view, my previous camper had the house batteries charged only from the vehicle alternator. 2 years was about all I got out of the batteries. My bus with charging when driving by the alternator and solar when parked already has two years on the batteries, and they are doing very well. I also am much more careful about not letting them get below 50% SOC. Normal bus stuff will not do that, but charging boat batteries, scooter and other things can run them down, so being careful with that and all is well. I expect many more years out of them. So just from experience getting a full and proper charge, and not draining them to nothing, does make a real difference.

[john61ct]

Yes if you spring for top quality FLA units (usually 2-4V, maybe 6V) like Rolls / Surrette, and care for them properly, 13-15 years is pretty normal.

But for even medium pricey AGM (usually in 12V units), 6-7 years is pushing it, and they are much fussier, more sensitive to the normal abuses, require more precise infrastructure to care for properly.

So long as the bank is proper deep cycling, even cheap Deka 6V GCs at $1 per Ah, can get 7 maybe 9yrs before hitting 80% SoC.

All these assuming daily use, calendar wear and care while in storage is a different story.

But most owners just don't care about the tech details, replacing more frequently as needed NBD, certainly a valid approach if you can afford that.

[dzl_]

Originally Posted by Booyah45828

Are there DC-DC charge controllers out there so that one could charge a battery back up to full in the correct stages, vs charging and holding at the 14.5 volts the alternator creates?

Correct, these are common (largely necessary) with LiFePO4 battery banks. Generally they are called 'DC-DC Chargers' or 'Battery to Battery Chargers'.


Victron, Sterling Power, Renogy, and CTEK offer them. Usually in the 20-60A range.



I have heard that for a primary vehicle alternator, a 'rule of thirds' is a good rule of thumb for sizing the charger (roughly 1/3 of the alternators total capacity is earmarked for the vehicle charging system, 1/3 is overhead/safety margin, and 1/3 can be dedicated to house bank charging). I can't say how accurate this is or what caveats there may be, its just a rule of thumb I've heard a few times.

[john61ct]

Consumer alts, their rating is fake news, but a good external VR like Balmar MC-614 can derate current output to keep temps down and voltage output steady.

DCDC rarely have much granularity over amps adjustment, but all that is really just a LFP problem anyway, not an issue for lead.

The high-output alternators designed for ambulances and fire trucks, military use etc, are designed to put out their full rated amps output, even 200+A for hours no problem.

DCDC for lead is also to maintain the right voltage, overcome V drop over long cable runs without requiring huge gauge heavy copper runs.

When the vehicle does not allow alternator / VR swapping.

[cadillackid]

Originally Posted by john61ct

If you camp off grid, just using FF sources is not practical for maintaining your bank properly

OK for high-amps Bulk for a couple hours in the morning, but you really should use solar for the 4-6hrs remaining required to get to Full.

Using your vehicle alternator while stationary is silly, get a little genset.

Or overnight on shore power, at least a couple nights a week.

Or just replace the bank more frequently.

Or invest in LFP.

Yes, any lead bank allowed to drop regularly below 50% is being abused, just as much as not quickly getting back to 100% Full.

my main use is daily for dinin g / mobile office / coffee, etc.. I dont use the vehicle alternator while stationary unless i were to run the system down too low.. theres usually a fair amount of driving.. sometimes all day on a road trip.. I do agree that if im parked for awhile using my little generator is better than idling.. UNLESS i need heat.. currently i sit parked with my diesel heater on and engine off. . however if I ran the batteries low i would sit parked with engine running and diesel heater off.. (remember I dont camp off-grid like most here do)..



I imagine when it gets to the cold part of the winter there will be times its cold enough I'll need to idle and run the diesel heater to keep warm.. I cant imagine a 12kw heater keeping my bone stock uninsulated bus warm in 0f degree weather...



I ordered a victron smart charger so when i plug in at night not only can the block heater keep the engine warm, i can keep the pack topped off..



John that .005C is the MAGIC number I was looking for.. thank you for that!!!



so let me do some math out loud to help myself learn.. my pack is rated at 200ah. so 1C would be 200 amps? .1C would be 20amps? .01C would be 2 amps? thus .005C would be 1amp? at what voltage? 14.6? (2 volts over full standing?) thats where i get confused..



the "wasteful" stuff is my whole purpose behind having batteries at all.. climate control and running my on-board internet / POE switch / VoIP router / Telematics.. the electronics take very little. but the heat is a different story.. considering i built the thing for winter use.. living in ohio where its cloudy at least 60% of the winter days.. and sun angle from noiv 1 to feb 1 is below 30 degrees means Solar is pretty worthless for me..



in summer when its time for A/C, i idle the bus as needed. (remember again I dont camp much..). but most times I like the outdoors when im parked so the A/C isnt needed.. (A/C absolute must for driving but then im making power and the A/C's are engine driven)..

[john61ct]

I do not even know what you mean by "not camping off grid" you rent spaces in powered camp sites? Mains power being available even just a few nights a week changes **everything**, no need for anything else with a big enough bank

Engine driven aircon is of course completely separate.

Use propane for heat, Propex 2211 is good, or parking heaters that burn the same FF as the vehicle. **Must** get the bus well insulated of course, or at least a certain subset part of it.

Electricity only for control electronics and fans or hydronic circulation if you go that way, pipes under the flooring.

You got C-rate math correct.

Voltage setpoint depends on the battery chemistry, even specific model, get the specs from the battery maker or vendor.

The resting Full voltage comes from observing the unit after a proper charge, 24hrs fully isolated, some take 72 to settle for accuracy.

Solar is not useless in even Arctic conditions, just that you need more panels and lower usage.

It isn't the amps it provides, it's the genset / engine runtime hours it eliminates, when the bank is only accepting 0.0x C anyway.

In summer, move north or to higher altitude, follow the 60's.

[cadillackid]

Originally Posted by john61ct

I do not even know what you mean by "not camping off grid" you rent spaces in powered camp sites? Mains power being available even just a few nights a week changes **everything**, no need for anything else with a big enough bank

Engine driven aircon is of course completely separate.

Use propane for heat, Propex 2211 is good, or parking heaters that burn the same FF as the vehicle. **Must** get the bus well insulated of course, or at least a certain subset part of it.

Electricity only for control electronics and fans or hydronic circulation if you go that way, pipes under the flooring.

You got C-rate math correct.

Voltage setpoint depends on the battery chemistry, even specific model, get the specs from the battery maker or vendor.

The resting Full voltage comes from observing the unit after a proper charge, 24hrs fully isolated, some take 72 to settle for accuracy.

Solar is not useless in even Arctic conditions, just that you need more panels and lower usage.

It isn't the amps it provides, it's the genset / engine runtime hours it eliminates, when the bank is only accepting 0.0x C anyway.

In summer, move north or to higher altitude, follow the 60's.

not camping off grid means I dont camp.. my bus is a mobile traveller / office / dining-room. it gets parked in a hotel parking lot overnight when I am travelling.. when i travel i follow the 80s and wont be using much of the battery pack as the electronics use a small amount.. or the drivetime is 6-8 hours+ / day where the engine is running..



when im at home the routine is that the bus is out and back from home or "real" office several times and is parked where 110VAC is available esp overnight.. it sounds like the best scenerio for the battery is for the LEAST amount of the battery to be used? unlike the the old NiCad where you were supposed to fully cycle them.. these type batteries you want to use as little of it as possible and get it back up to 100% as quick as possible after you use it?



my heater is a diesel heater.. i wouldnt try to heat a bus with electric heat.. however there are electric blowers.. the bus heater fans.. I have the rear and front right heaters wired to the house batteries. . of course when im driving they get their power while the alternator is charging.. and when parked the diesel heater heats the coolant and then i use the bus heaters to warm the inside..



the bus is stock and that wont change.. my mental health esp in winter needs the daylight so all of those non-tinted extra tall school bus windows and school bus doors are staying.. it allows me to drive someplace where the scenery inspires my artist brain to be creative..


my diesel heater puts out 12kw. that is fine in the fall and milder winter but I expect that it wont keep the bus interior the 75-80f i like when it gets down to 0f outside. . thus why I expect for those few days a year we get that I'll be idling the bus some..



the bus is 30 years old and no im not going to destroy its classic interior to install extra insulation..



I installed 120k BTU of road air-conditioning so i could keep my classic-bus interior (yes with most of its seats), un-tinted windows and still stay cool in 105 degree texas august heat on the freeway. (i seem to end up always going to the south in summer at least once).. I rarely use the bus parked in summer.. even with covid I could sit on patio at coffee house , restaraun, and in my bag chairs outside when parked away from society.. so using A/C while parked is not expected from my batteries


as for the battery data.. ha! I guess thats what I get for buying batteries from a consumerized store (batteries plus). they give me internal resistance (2.2 meg ohm), reserve capacity 220 minutes and 20 hour capacity of 103AH, nothing about charge , float, or maintain voltages or voltage per cell, etc.. i have 2 of those in parallel.

[Dclewis]

Originally Posted by john61ct

If you camp off grid, just using FF sources is not practical for maintaining your bank properly

OK for high-amps Bulk for a couple hours in the morning, but you really should use solar for the 4-6hrs remaining required to get to Full.

Using your vehicle alternator while stationary is silly, get a little genset.

Or overnight on shore power, at least a couple nights a week.

Or just replace the bank more frequently.

Or invest in LFP.

Yes, any lead bank allowed to drop regularly below 50% is being abused, just as much as not quickly getting back to 100% Full.

I read an interesting post here https://tab-rv.vanillacommunity.com/...ge-myth-busted

that I haven’t completely vetted, but what the author is saying for AGM batteries is that you don’t have to freak out about the 50% dod rule. Using the curve for a Trojan agm battery for example you get more cycles out of the battery if you only go to 50% dod but you get more energy out of the battery per cycle if you go to 80% dod. The product of the two results in only a 6% penalty of total energy delivered over the lifetime of the battery if you regularly discharge to 80% dod.
Has he overlooked something? If not I’m going to relax a bit.

[cadillackid]

I feel like im on the right track now.. im finding using the new victron IP67 charger i got that after charging and letting the batteries sit that im getting closer to 13 volts standing .. this charger is set up for AGM batteries from what I can tell and it is giving me a much better charge than just the alternator or a regular car battery charger..



so what im doing is still letting the bus charge the batteries while im charging but am plugging in the charger when im parked near an electrical outlet,



I havent yet gotten the IP67 to connect to my victron app yet to truly view the settings.. but my battery monitor shows the voltage and amps the batteries are taking.. and its a lot more aH than with the bus or my regular car battery charger..

[john61ct]

Originally Posted by Dclewis

you don’t have to freak out about the 50% dod rule

No one says freak out.

50% is not any magic hard line, every battery chemistry not just AGM has a smooth gentle curve, average DoD goes lower, so does cycle lifetime.

The **guideline** is, don't go **much** under 50% **too often** if you want to avoid replacing your bank more frequently.

Many owners don't care, that's fine.

Personally, counting cycles is the proper metric, that whole "total Ah" malarkey never made sense to me.

Plus in my use cases, having sime capacity in Reserve is a good thing.

But people buying into vendor claims, "hey this one can go down to 80%" need to be corrected, yes it is true, every battery "can" do that, it just will get murdered much faster, than if you only do it occasionally, ideally only when truly necessary.

Batteries properly built for deep cycling will last longer than those that just claim that label.

With LFP, if normal (mis)treatment still gets you 4000 cycles, then many owners say what the heck doesn't matter, who wants 6000 or 8000 anyway!

Up to each owner, do what you like, just make conscious decisions properly informed!

[cadillackid]

I think part of the thing with batteries is many people remember the woes and f the not to distant past of “battery memory” on rechargeable devices.. while vehicles are different there seems to be some degree esp with house batteries of “kill em tjen charge em “

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”?

[dzl_]

Originally Posted by cadillackid

I think part of the thing with batteries is many people remember the woes and f the not to distant past of “battery memory” on rechargeable devices.. while vehicles are different there seems to be some degree esp with house batteries of “kill em tjen charge em “

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”?

It may not be that simple,

I don't know much about lead acid, and lead acid is different than lithium (specifically what is good for lead acid is not always good for lithium and vice versa), but here is an example graph that pertains to lithium that shows you cycle life with varying cycle 'bandwidths.' While the specific number and trends may not apply to lead acid, there might still be some useful takeaways, and I suspect if you look into it you can find similar charts for your battery chemistry. This chart came from "Battery University" which is a battery education website.

[Native]

Well ... the image did not come up for me. Perhaps the next time I visit the post it will be there ... as sometimes does happen.

[dzl_]

I'll try again:





And here is a chart for Sealed Lead Acid




EDIT: I don't know what is happening with the pictures.. They show up for the first 10 minutes and then dissapear. Not sure if it is on BatteryUniversity.com's side or Skoolie.net, in either case here is a link to the picture I'm trying to post

[cadillackid]

that chart is confusing.. if you read it literally then it seems like you get more cycles with as lower DOC? I wouldve thought you'd get more cycles from a lower DOD when talking to people here...



if I only use up 25-30% of my capacity then it appears i'd get a lot longer life than if i use up more.. and a "cycle" seems to be when i finish discharging and then go back up to 100% charged.. at least im guessing?

[Ronnie]

I found a chart from Trojan batteries. This is for their AGM batteries. They give a life cycle of 1000 cycles at 50% DOD, (depth of discharge) At 20% DOD it is over 2000 cycles, and at 100% DOD it is about 300 cycles. So yes DOD does matter for AGM as well as FLA.






https://www.trojanbattery.com/pdf/AG...tLineSheet.pdf

[dzl_]

Originally Posted by cadillackid

that chart is confusing.. if you read it literally then it seems like you get more cycles with as lower DOC? I would've thought you'd get more cycles from a lower DOD when talking to people here...

I'm not following you here, it reads like you are saying the same thing twice.


I think the takeaway from that graph is the more shallow your depth of discharge, the more cycles. Where a cycle is defined as one discharge-charge (or charge-discharge).

if I only use up 25-30% of my capacity then it appears i'd get a lot longer life than if i use up more.. and a "cycle" seems to be when i finish discharging and then go back up to 100% charged.. at least im guessing?

Correct, at least that is how I interpret the graph and understand things. Lower DOD = longer cycle life, but less energy per cycle.

[Ronnie]

So similer energy overall no matter the depth of cycle, or the number of cycles, it all evens out. A different way of looking at it, then to just read the life cycle chart. Interesting.

[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????



now im really glad I named this thread battery confusiom


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