1st Battery Capacity complete

[Pass me]

Agreed. It's important to me to know what shape my battery(s) are in, (good, fair, poor) compared to the original specs. That's now around the corner so to speak.
Having said that all I really wanna know is how much wattage is available? Establishing a standard capacity run will give me that. This then will help to determine the SOC % before my generator is req'd.
It's an old battery so I'm thinking 50% depletion but my next "quest" will be to determine the minimum generator run time to restore a practical SOC for my needs. I understand ~80% full is achieved quickly and after that it ain't "worth the gas" to comtinue.
The old girl was equalized for 12 hrs @ 13.8V/.5A, has rested for 14 hrs now & is showing 13.4V. The capacity run will be with my Bose Wave radio (50W) as it's more fun to use than a light. I will post the results.
This all started with a question and I'm indebted to all for being so helpful but.......another question pls.
Quote
"measuring with an ammeter will get you the closest."
I have never owned one, it just tells me the Amps flowing through the wire? Is it best to get the alligator style? I've considered the attached before, ~$50 Canadian ($1000 US, lol).

 

[Mark_K5LXP]

all I really wanna know is how much wattage is available?

That's going to depend on how much current you're drawing. For light draws you get one amount of Ah, for heavy draws you get "less". This is a function of battery efficiency, which is both chemical and mechanical. "Better" and larger batteries are more efficient at delivering power at higher currents. This is just a consequence of lead acid batteries - they are what they are. Generally though, through prudent system design they work OK, billions of them have been successfully used for decades. Lithium obviates most of these foibles but at a price, so one has to decide just what their definition of a system solution is then pick the best configuration that accomplishes it.

This then will help to determine the SOC % before my generator is req'd.
It's an old battery so I'm thinking 50% depletion

You can pick whatever arbitrary SOC you like but in my opinion, 50% will result in a frequent generator run times. As you observe, bulk phase takes to you ~80% but the next 20% takes hours. So practically speaking you're only using and restoring a fraction of capacity fairly frequently. Running it down to 20 or 30% SOC instead still leaves lots of operating margin and less frequent genset runs. Eventually you'll establish what use patterns you will want, so I wouldn't put any SOC stakes in the sand. Don't die on a hill of a specific SOC, it will work out that charging will be dictated more by your opportunities to do so than anything else.

Do you have a battery monitor? That will go a long way towards knowing where your battery is at and making recharge decisions.

The old girl was equalized for 12 hrs @ 13.8V/.5A

No. Equalization happens at an elevated voltage, ~15.5V. 13.8V is a float/trickle voltage.

The capacity run will be with my Bose Wave radio (50W) as it's more fun to use than a light.

I wouldn't do that. Over the span of hours the power averages out but unless it becomes your load standard going forward you can't use to make any direct comparison. Lamps are cheap, easy and consistent.

"measuring with an ammeter will get you the closest."
it just tells me the Amps flowing through the wire?

Yep. A house battery monitor will do the same.

Is it best to get the alligator style?

I have both. For accuracy an inline meter gets my nod, for convenience/quick checks the clamp one wins. I didn't do a deep dive into the one you referenced but the high current range ones tend to suffer with low current resolution and accuracy. There's no reason you can't have both. For my house battery tester I use a $20 cheep chinese monitor that gives me simultaneous voltage and current, it uses a shunt. It also counts Ah. The hall effect (clamp) monitor I have does OK too though portable ones tend to "wander" a bit (need to set/reset zero). Even your basic harbor freight $10 meters will tell you what you need to know, so get something, anything and you won't have to wonder or guess what's going on.

Mark B.
Albuquerque, NM

 

[Gary RV_Wizard]

Converting either CCA or RC to AH is merely an approximation. RC to AH is distorted a bit by the Puckert Effect and the fact that amperage vs voltage is a curve rather than a straight-line.

But at least with RC it's an Ah rating and not an approximation, just not Ah at the 20 hour rate.

93 AH is about right for a Group 27 size battery,

The RC is 160 which is 67Ah, for this to jump to 93Ah at the 20 hour rate would be a pretty high peukert number. My guess is it's closer to 75 to 80Ah. One could always test it to the RC spec at 25A and see how many minutes it goes. When I was testing GC2's as traction batteries I used a 75A load, the rate the Trojans used for their model names (T105 - 105 minutes at 75A).

Mark B.
Albuquerque, NM

I was using the Trojan Product Spec Guide as a reference. They rate their 27TMX flooded cell at 175 RC minutes and 105 AH @ 20 hour rate. AGMs are typically lower and the Trojan 27AGM is rated at 158 RC minutes and 89 AH.

 

[Gary RV_Wizard]

So my 40W bulb would e better served using a 50W bulb type thing. A 50W draw would be more accurate in the capacity test.

No, a smaller bulb rather than a larger one (see Mark's excellent explanation).

Also be aware that the wattage rating om an incandescent bulb is only an approximation and could easily be off by 10% itself. If you are trying to base calculations on it, you really need to measure the actual current draw of your test set-up.

I think this sort of measurement is an interesting technical exercise to learn about battery capacity but the results should be considered a broad-brush indicator rather than a precise measure of capacity.

 

[Pass me]

Oops, I meant to type 15.8V for equalize run. See attached for the charger I use. It allows 0-15+V and 0-60A control output. It shows 15.8V maxed out, my Voltmeter shows this as 15.4V at its clamps but it's the best I got for now. Considering the Genius10 charger still.
Yer recommended battery use to 20-30% SOC: is this because it's getting old? A new LAB will deteriorate quicker if used beyond 50% consistently, I want to get 7+ yrs use type thing.
I'm considering a LiFePO4 100Ah for my next battery but that's "next year" stuff, mine I'm thinking with growing confidence is just fine.
Great heads-up on ammeter selection, accurate low amperage is important as thats where I'll be most always. I'll be googling a clamp/pins style simultaneous voltage and current meter.

 

[Pass me]

Forgot to attach this and I'm going to pick up a 30W bulb for the capacity test. I see Tru bulbs that have this wattage rating.

 

[Gary RV_Wizard]

The old saw about "measuring with a micrometer but cutting with an axe" comes to mind...

 

[Mark_K5LXP]

Looks like a handy charger, having adjustments and limiting allows a variety of testing. That's basically a portable bench supply.

Considering the Genius10 charger still.

I have a couple similar to that, with the idea that plug and forget is most often what you want.

Yer recommended battery use to 20-30% SOC: is this because it's getting old?

No, its because bouncing between 50% and 80% SOC doesn't give you much run time between charges. Think about it, for an example 100Ah battery, that's only 30Ah - what are you hauling around a 100Ah battery for if you only use 30? I'm in the camp (as others here on the forum are well familiar with...) that batteries are here to serve me, and I have no qualms about running them until the battery monitor screams zero percent. In practice I don't run them to zero percent every time because I'll gauge what rate I'm using versus the next charge opportunity and refill accordingly. The way it works out for my typical usage is I can enjoy a long weekend genset free, or during travel they get topped off by the alternator frequently enough. But I don't have a minimum SOC I'll automatically recharge at, other than zero percent. For myself, and the vast majority of RV'ers using lead acid it is impossible to wear out a battery at any level of cycling, so why bother watching. An exception to that might be marine batteries as their cycle life isn't as much, but if that's a consideration then it's a misapplication in the first place. Not sure what the history is for your battery but if it's still hanging in at 5 years, odds are pretty good you're not anywhere close to cycling out even a marine battery.

A new LAB will deteriorate quicker if used beyond 50% consistently,

Calendar life is but one consideration but careful what that means in a practical sense. If you only use 30% of your battery versus say 60%, you use half as much but twice as often (to deliver the same energy). So it's not really buying you anything to lightly cycle a battery. Another thing to look at is you buy a given battery to deliver a quantity of Ah over it's life, and that number is fixed by the topology of the battery. If you pamper it and operate it super conservatively all you've accomplished is buying more battery than you needed, you don't run your stuff as much or as often and run your generator a lot. Then when the battery ultimately expires from age or other trauma you take unused delivered Ah to the recycler. All that farting around for what? That's not to say you intentionally thrash a battery but it's a use it or lose is proposition, not unlike RV tires. Batteries are going to crap out whether you use them or not, so might as well get as much out of them as you can and get your money's worth, along with the comfort and convenience that affords. In terms of delivered energy the most cost effective battery you'll ever have is one you wear out before it ages out. Ideally those two lines cross at the same time but in terms of cost efficiency, one you wear out beats one you age out every time.

Mark B.
Albuquerque, NM

 

[Pass me]

I might add most everything is.....
"going to crap out whether you use them or not, so might as well get as much out of them as you can and get your money's worth, along with the comfort and convenience that affords."
I believe yer right, I've most always leaned towards making things last as long as possible but retirement has a way of rearranging priorities. After all I have an expiry date as well!

 

[Pass me]

Hey again, my last capacity test is now done. Using a 29W bulb I got almost exactly 20 hrs to trip the Inverter - so the 70 Ah determination is pretty accurate. Curiously the voltmeter was showing 11.1V (the lnverters low V alarm=10.5V & trips @ 10V so ... dunno. It had been tripped maybe 15 min before I arrived so V could have recovered that much/fast?).
I'm resting the battery for a bit then I'll restore full charge.
After that I'll let it rest for 12 hrs r so and post the resulting voltage.
I started this adventure as this battery fully charged showed 12.1V, was noticeably dropping off quickly and I wanted to restore it. With this forums help I've been successful, thank you all. Sooooo
Does it matter if it ends up over 13V? I'm using the attached LAB chart as my reference. I was getting 13.1V from it rested ~8 hrs and after the 1st equalize/capacity run.

 

[Mark_K5LXP]

the 70 Ah determination is pretty accurate.

The datasheet is the real answer but for today, the capacity for this battery is was it is today. You have your baseline data and test method so 6 months from now or whenever you can run it again and know if it's hanging in or degrading.

the voltmeter was showing 11.1V ...could have recovered that much/fast?).

Yep. You could repeat that state if you want. Run the inverter again, even with the battery dead. It will poop out in a minute or two and you can watch the voltage climb back up. Or, just use your imagination.

I'll let it rest for 12 hrs r so and post the resulting voltage.

A takeaway to this exercise is terminal voltage is not a conclusive indicator of battery merit. Just as I wouldn't pull the plug for low voltage, 'good' voltage isn't an automatic pass. Where it's important is making sure it's sitting at 100% during idle periods.

Does it matter if it ends up over 13V?

Depends on when. In order to finish the absorption charge phase the voltage needs to hang around 14.4V for several hours. A good battery will be north of 13V for a day or more after that until that surface charge dissipates. The specific battery type (brand, model) as well as ambient temperature along with state of charge will drive resting voltage, so voltage alone is just a snapshot of status. That's what makes the voltage tables you find online somewhat arbitrary - you don't know what battery type or conditions they're for. The chart to go by is the one from the manufacturer. If they don't offer one you pick one that most closely matches the battery type you have and not just what google pops up.

Mark B.
Albuquerque, NM

 

[Pass me]

A few posts back Gary mentioned you develope a feel for a battery and thats starting to make sense.
Ive got a usable battery that I'll now use till it complains, I'll charge it up with the genset to ~80% and repeat, nice.
I've been using the Interstate charge perameters here, it takes ~9hrs for 100% SOC...not practical when burning gas so next I'm gonna set my charger to match the PD9130 - 30A at 14.4V and time the result.
Some notes from my learnings
•70Ah 》20hr rate= 70÷20= 3.5A
for~20hrs
Interstate Charge Perameters
•Bulk: 9.1A/14.4V
•Abs: 2.8A/15.8V
•Float: "0"A/13.2V
•Equalize: 16V
•Capacity test: 3.5Ax12v= 42W for~20hrs
•Factored deficiencies=29W for~20hr
Available Power: 70Ahx12v=840Wh
My Inverter manual has this info:
■To Calculate load draw @ 120V■
e.g. 1500W ac load.
Formula
¤÷♤= Time to "0%" SOC
1. W÷120=♤ 2. Ah÷10=¤
Keurig: 1500W÷120v=125+15%=~144A(♤)
70÷10=7(¤)
7(¤)÷ 144(♤)=2.91 minutes》0% SOC
So 1500W draw for 99 seconds》》》
battery@50%
If accurate....enough said, larger AC loads via an Inverter (with 70Ah) are not practical & will quickly damage my battery.

 

[Mark_K5LXP]

A few posts back Gary mentioned you develope a feel for a battery and thats starting to make sense.

Yep. Part of the reason I don't have a fancy battery monitor. After messing with batteries a few decades I can just watch current and voltage and know how things are going.

I'll now use till it complains,

It's paid for and there's no prize for pretty when they're recycled.

it takes ~9hrs for 100% SOC..

From 0% but not every cycle is from 0%. Practically speaking too, few people observe the13% max charge rate, it will be whatever converter they have can stuff in. (Curious how proponents of the 50% Rule don't seem to have a problem breaking that rule.) Aggressive charging can impact service life but most consider that a fair tradeoff to prolonged charge times. The long pole in the tent is absorb/last 20%, which is why it's often skipped, or people get solar to top them off. Incomplete charging can have an impact to service life as well but it comes down to what charge you can restore when you can, and it is what it is.

next I'm gonna set my charger to match the PD9130

Excellent use of a discharge test - prove out your charger profile.

Some notes from my learnings
•70Ah 》20hr rate= 70÷20= 3.5A for~20hrs

For extra credit you could run a 2nd test at a different current (like 7A), get the delivered Ah and plug the numbers into a peukert calculator. The peukert number you get can now be used to calculate delivered amp hours over a range of currents now. Basically this is how fancier monitors predict estimated remaining time/Ah.

Interstate Charge Perameters
•Bulk: 9.1A/14.4V
•Abs: 2.8A/15.8V

Correction - absorption is at 14.4V for somewhere between 2-4 hours. Equalize is ~15.5V.

•Equalize: 16V

16V is kinda hot. There are varying methods that use a fixed voltage, constant current, SG monitoring and such. I wouldn't sweat the details too much, as long as it's not done too often or too long. There's a point of diminishing return where you can start to reduce capacity so apply this phase judiciously.

Available Power: 70Ahx12v=840Wh

At 3.5A. At other currents, this number will be different.

My Inverter manual has this info:
■To Calculate load draw @ 120V■

The calculations didn't make it through (odd ASCII characters) so not sure how it gets from A to B but end result is the same - when you put the whammy on a lead battery the energy delivery is reduced. "Good" lead batteries can be rated to C/5, I've seen some lithiums at C/1. Pulling ~140A out of a 70Ah battery (C/.5) is off the datasheet for sure. The source needs to be matched to the anticipated loads.

AC loads via an Inverter (with 70Ah) are not practical & will quickly damage my battery.

Not practical yes, damaging probably not. It's kind of a self solving problem in a way. You start to pull too much current out, the voltage drops quickly to a useless level. So there's only so much you're going to get. As a data point I routinely drew 600A out of T105's and they would put up with it for several years, so max practical current comes down to application.

Mark B.
Albuquerque, NM

 

[Tulecreeper]

Maybe just my Spidey-sense, but isn't running this/these batteries all the way down and charging them back up again 20 times just to try to get milliamp readings just going to ruin them?

And, all this experimenting on one (set) of batteries is kind of moot. When the batteries are eventually replaced the OP is just going to have to start over again because no two batteries are alike - even the same lot # produced on the same day.

 

[Mark_K5LXP]

Over a nominal service life you might do this a dozen times. A marine battery is conservatively good for 150 cycles, a premium GC2 500 cycles or more. Coming into an unknown battery there are limited options to determine serviceability - wonder and guess or measure and know. If it tests bad then you're done. If it tests good you can eliminate them as an unknown. You can head into the hinterlands and not have to wonder where they stand.

I test mine a minimum of twice a year, when I winterize and dewinterize. It's simple and I would rather discover a problem or degradation in my driveway than on a trip. Yes, it uses a small fraction of their life. Between testing and regular use I won't come anywhere close to using them up before they age out so testing cycles are a don't care.

Mark B.
Albuquerque, NM

 

[Pass me]

Good morning, there you go using another strange word...."peukert number." That woke me up more than this cuppa Joe I'm enjoying, (more on that in a bit). This will be Rabbit hole # 19 since my 1st thread, lol. Its now on the to do list so be warned - there will be questions.
Great to know I can apply 60A/14.4V as I wasn't sure about that. My charger suggests (for longevity) I step this down to 48A max so gonna use 50A.
Those charge perameters came from Interstate itself & they did seen a weee bit wonky (16V??), I'll edit my perameters.
How did you know 840 Wh were at 3.5A pls?
The attached is from the Inverter's manual, I created ¤ & ♤ in place of "x" & "y" as their not on this phone. My own "formula" if you will.
And last....this damn Keurig Coffee Machine!, it's responsible for this whole journey. I originally charged up the battery with my original 20 yr old "smart" charger (Canadian Tire special) and got 12.6V if memory serves. Ran the Keurig and the Inverter howled immediately and kicked off. That was then.
This morning I am sipping the aforementioned coffee courtesy of the battery, didn't even chirp low voltage. It did drop to 11.6V during the heating cycle ~(45 sec) & returned to 12.1V...I'll see where it levels off in a hr or 2.
The battery won't be at ~100 SOC when I try this 1st "next" morning camping (furnace, a few LED lights, water pump use overnight) but I'll be trying it anyways.
Most always these trips are on trout streams where I don't have the patience to dawdle come 1st light so this is important to me, I'll run the genset in the afternoon to repeat this cycle. We'll see.
And this is why I'm starting to google "LiFePO4"
After peukert number of coarse........
Sure appreciate yer input Mark, enjoy this day and all the best in '24 to you and everybody.

 

[Pass me]

Maybe just my Spidey-sense, but isn't running this/these batteries all the way down and charging them back up again 20 times just to try to get milliamp readings just going to ruin them?

And, all this experimenting on one (set) of batteries is kind of moot. When the batteries are eventually replaced the OP is just going to have to start over again because no two batteries are alike - even the same lot # produced on the same day.

Good morning, my motivation with batteries stems from the years we spent using our RV's as cottages where I'd plug into shore power for 6 months, set n forget type thing. Come winter the battery came home & when I had it tested....suprise suprise ‐ it was in bad shape/lunched.
Put up with this for a few yrs, eventually got tired of buying a new battery every other year so I started reading up on the charge system in my RV. Sure enough like most everything coming out of this industry it was garbage. "Tricklecharged it to death".
When we bought our 2011 Forest River 390BH motorhome it introduced me to proper (well somewhat) battery maintenance.
And I've been learning ever since. My continued motivation is fed by the desire to not get ripped off and in my humble opinion the RV industry has perfected this to an absolute art form. I'm grateful in one way, "if you want something done right you might as well do it yerself" type thing. I fix most everything myself now - it's an ongoing experience with these complicated machines right ...there's always something to fix.

 

[Arch Hoagland]

It might be interesting to buy a brand new battery and run the same tests.

 

[Tulecreeper]

It might be interesting to buy a brand new battery and run the same tests.

with all the discharging and recharging, that's going to be a given anyway.

 

[Mark_K5LXP]

strange word...."peukert number."

Not something you'll use day to day but it illustrates the impact of current delivery vs available capacity. "Better" batteries publish this data, but it can be measured with any battery.

Great to know I can apply 60A/14.4V

Know that hammering current into a battery, like drawing large currents out, has it's limits. Blasting current in is like microwaving a frozen dinner. The outside can be boiling but inside still frozen. There's a mechanical aspect of the liquid electrolyte that has to diffuse through porous lead plates and grid paste. Larger currents accentuate gradients in the structure and can incrementally damage it with each cycle. So one has to decide the tradeoff of recharge time vs service life. I would consider C/5 to be the high end of an aggressive charge profile, 50 or 60A into a ~70Ah battery would be well beyond that.

How did you know 840 Wh were at 3.5A pls?

12V * 3.5A = 42W * 20hrs = 840Wh

And last....this damn Keurig Coffee Machine!

Cup style coffee makers

This morning I am sipping the aforementioned coffee courtesy of the battery,

Nothing like an empirical test.

I don't have the patience to dawdle come 1st light

Back when I tent camped I'd boil water on the campfire at night and put it in a thermos for the next morning.

I'm starting to google "LiFePO4"

They're a better battery in most respects and offer advantages for RV use. Comes down to working the cost/feature matrix to see what the best fit is for your use.

Mark B.
Albuquerque, NM