Estimating power use from Classic display?

[JohnsIsland]

Good day!

I have three Classic 250, one WizBang Jr, connected using follow me, FLA batteries.  I am wondering if I can estimate the power used from either the state of charge or total and remaining amp hour displayź.  For instance, if I see the state of charge saying 70% in the morning, before the sun starts charging and I have programmed the Classic with a batter bank of 500 AH, then would I be correct in assuming the system used 30% of the 460 AH (138 AH) since the batteries were fully charged?  This wouldn't give me the 24 hour use, since it doesnt account for the use while the system was charging. 

Would the remaining capacity display work in a similar manner or is the remaining AH affected by temp compensation? 

I am not trying to find a precise number, just an idea of how many amp hours I have used, as I am about to purchase new batteries.

Thanks for any insight, thoughts and ideas on whether my logic is flawed,

Jeff

[ClassicCrazy]

you would have to have all the batteries going to a bus bar and that one negative going through the whizbang shunt. That way the shunt could read everything in the system.
Every other negative from every controller and inverter etc would be on the other side of that shunt .
That would give you a good SOC estimate of all your batteries ( if Whizbang data is properly configured) . For example if your new battery is 1200 ah compared to old battery at 1000 ah then change capacity to 1200 ah. - Also change the efficiency - for lead acid that is usually 80% efficiency though an older lead acid has lower efficiency than new lead acid . If you are talking about getting lithium batteries the efficiency is more like 98%. And yes the Whizbang will compensate capacity according to the temperature compensation , but lithium there is no temperature compensation.
What I ended up doing on my system was to get a Victron Smart shunt mainly because I didn't want to take apart and rewire the Whizbang shunt to the correct location when I added new batteries and controllers to my system.
I have the smart shunt on the negative battery  bus bar using  1/4 x 1 inch copper bar which is the same as the battery bus bar and it holds it solid and is of proper amp rating for everything.
Larry

[JohnsIsland]

Larry,

Thanks for the reply!

I have batteries on one side of the WizBang Jr and all other negative connections on the other side of the WizBang Jr.  Batteries-->WizBang-->busbar.  Busbar has Classics, AC chargers and loads connected to it.   Well, I have a Victron SmartSense battery voltage and temp sensor connected directly to the batteries. 

So, in My Midnite, if I see SOC in the morning at 83%, and given FLA batteries of 460 AH @ C/20, efficiency set at 70% (batteries are seven years old), would I be correct in assuming that I had used 78.2 AH since charging stopped the night before?

I just realized this doesnt correlate with the Net AH (shown in My Midnite at the same time as the SOC), I see it shows Net AH of of -38.  All of the above numbers are before the Classics show AH above zero.

Do you have any thoughts or comments on the discrepancy between the numbers?  I wondered if battery temp would cause this, but battery temp was higher last night than this morning.  When is SOC reset? I remember there us an option for when SOC resets. 

Wizbang Jr amps is usually steady around 5-6 amps, with peaks to 8 or 9 amps and occasionally peaks to 14-15. 

Thanks,
Jeff
My Midnite Jones on Johns

[ClassicCrazy]

When I had flooded lead acid batteries, I checked the specific gravity to make sure it was close to when the batteries SOC went to 100%. I used ending amps at that time too so I wanted that to correlate also.
The ah out of the battery won't be derated. It is just that it will take 30% more power at the top of charge before it goes to float.
The SOC does reset to 100% when it goes to float, but like you mentioned there is another setting for that but I forget how that works. I think it will carry over the SOC instead of resetting it when it goes to float ?
I think you assumption is correct using 83% of 460 ah should be what is used .
I used to tweak the efficiency and capacity to get me numbers I was comfortable with - and to also give me some extra capacity at the bottom of discharge .
I don't use mymidnite anymore so forget what it looks like. But it seems like when I looked back at it in the past , that as the batteries filled up , the SOC would be pretty much at 100% at the right point. 
Larry

[JohnsIsland]

Larry,

I also use Grahams app, which shows the same sort of info.

I do watch the specific gravity, and I can see the batteries reaching 1.26.  However, the batteries I have used for the last few years are a part of some rejects (Rolls 6v 230 AH "golf cart" batteries") from a scissor lift (from the place I workes befoee I retired).  I picked the best 4 out of 6 batteries via testing and equalizing.  Recently the amps are not dropping during absorption.  I think they are at the end of there life. 

The reason I  trying.to figure out my daily AH, is because I want to order some new batteries and trying decide which ones.

I am wondering if 4 S6 L16 EX or 2 6CS 17P would be best.  I am going to check today and see if the EX and 6CS 17P are available, they may have only the HC. I suspect the only ones available are the HC, at least without a two month delay.

Thanks for your comments and thoughts on AH usage.

Jeff

 

[ClassicCrazy]

the self discharge rate goes up on old lead acid. So kind of like filling a bucket with holes in it.
Why don't you get lithium ? These days you can get a 314 ah 48v battery ( around 16 or 17 kwh) for $2000 shipped price.
But maybe you are running 24v system ? There are some 24v lithium options out there . But upgrading to 48v really is the way to go these days.
maybe you aren't in usa ?
Larry

[JohnsIsland]

I am in Washington state.  I wont go lithium this time because I live on a remote island without a fire department, and I would have to upgrade my victron AC chargers and victron inverter since I am not 48 volts. 

I realize the danger of a fire from lithium batteries is remote and I suppose even FLA and AGM batteries present a fire risk.

I know my AH use will increase with time and lithium are thr future, so I will probably convert to lithium at some point in a few years, first by switching to 48v, then to lithium when the new batteries reach the end of there life.

Thanks,
Jeff

[Vic]

Hi Jeff,  &  Larry,
IIRC,  boB,  a Member here,  who passed,  within the past year-ish, did measure this nominal current,  and did post it on this Forum,  but no time to look,  just now ...  sure do miss boB !!  He was a great guy,  who did much of the design work on the Classics (and the Outback MX-60 CC, IIRC).

My opinion on this current,  Vic