Can Classic+WBJr trigger events based on Ah in/out of battery bank?

Started by openplanet, November 15, 2019, 01:27:12 AM

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openplanet

As most people who have LiFePO4 batteries know, SOC is difficult to determine because of the very flat charge\discharge curve.  To the degree that SOC can be estimated based on voltage, in order to have any hope of accuracy this must be resting voltage, where "resting" can mean anything from 4 to 12 hours.

Now suppose you have a LiFePO4 bank that you want to keep between 20% and 80% SOC to maximize cycle life.  You run the batteries down to the point where the resting voltage matches 20% SOC.  If you could now keep track of Ah into and out of the battery bank, and trigger events such as "stop charging" and "start charging" based on those values, wouldn't this be extremely useful to LiFePO4 owners? 

Suppose you have a 100 Ah LiFePO4 bank. In this instance, starting at the known 20% SOC point, you'd set charging to stop when 60 Ah have gone into the bank, because this represents 80% SOC. Likewise, if the Ah ever goes into negative territory, you know you've dipped below 20% SOC, and you could use and AUX to trigger a relay to disconnect loads.

I may well be missing something, but it doesn't look to me like this is, um, currently (sorry) possible with the WBJr/Classic.  Here's hoping I AM missing something! 

I welcome any thoughts.  THx.
_______________________________________
We are star dust [on a] pale blue dot.
[And yes,] there is grandeur in this view of life.
Joni Mitchell, Carl Sagan, Charles Darwin

https://www.youtube.com/watch?v=cIANk7zQ05w

Steve_S

Ideally, the interaction / interoperation with the BMS of the battery would be the best of all options and in several BMS' like Orion, Batrium, TinyBMS have Modbus, canbus or other methods & protocols to interact with them.  I am also setting up to install a 24V/400AH lifepo pack which does not have a BMS that can be interacted with and this is an obvious concern for me as well.  If I have to change the BMS, that's fine but from what I could find there is limits to what can be done with a Classic.   If you have a Midnite Battery Monitor, that also won't be much use either for the lifepo because of how Lifepo discharges and it's voltage curve.

ClassicCrazy

I had some LiFePo4 batteries and was  using a top voltage where they should be at 80% and then used ending amps to go from absorb to float and was using bottom balancing. I think you would only need to be able to cut out batteries at a low voltage like a BMS does to prevent the batteries from being damaged.
I was not using BMS at the time - had a couple things I goofed up that a low voltage cutout would have helped - and it should be independent of the Classic .
At the time I got my batteries there weren't a lot of BMS or cell balancing products available - now there are lots of them.
Look in past forum discussions about bottom balancing and also Ross had mentioned something that balances the cells but is not really like a typical BMS.

Larry
system 1
Classic 150 , 5s3p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system 2
 5s 135w Kyocero , 3s3p 270w Kyocera  to Classic 150 ,   8s Kyocera 225w to Hawkes Bay Jakiper 48v 15kwh LiFePO4 , Outback VFX 3648 inverter
system 3
KID / Brat portable

Steve_S

Kind of highlights some issues here.  Low Volt Cutoff is critical to keep the cells healthy & happy as much as high volt cut off.  HI temp is an obvious must but in my case low temp sensing is also a must.  It's -16c / 3F outside right now (-30c/-22F is not unusual)  and IF I lost heat in my powerhouse it would be too cold to charge and if the batt's were freezing up and a charge is applied (bad things happen)  I also get heatwaves in summer to 40c / 105F.   

Case in point:  On the 13th, our first real cold & snow fall, the small Furnace in the powerhouse failed.  Luckily the thermal mass & hyper insulation prevented freeze up (my batteries, 50 gal water pressure tank are all in there) and I've been keeping it warm with a backup heater.  Today's task is to replace it with another, so a $500 solution that could have cost several thousand very quickly.  FYI:  The building is only 14'x7' and I am using a small direct RV Furnace (12vdc, with own solar panel & battery) and LPG to maintain that building at this time.

Would really be nice if there was updates for LifePO and Li-Ion and a WizBang Senior or similar for Lithium which can interact with a BMS (cut offs etc).  I "really" dislike mixing different products if I can avoid it...  Much to be said for K.I.S.S.   I had hoped that Midnite would have come up with their own LifePO Packs or small stackable ESS/HSS... Had also hoped they would have had an Inverter ready to go when I had to replace my 3kw one with a 4kw one.

RossW

Quote from: Steve_S on November 16, 2019, 05:22:44 AM
Kind of highlights some issues here.  Low Volt Cutoff is critical to keep the cells healthy & happy as much as high volt cut off.

I'm of the old school that "an ounce of prevention is worth a pound of cure". LVD to me is an absolute, last-ditch effort. In 15 years off-grid, the only LVD events I've had have been from other people stupidity and refusal to follow stated procedures. (Long story I won't bother with right now). Since my family and I moved in, we have not had a single LVD event, ever. Because the system will kick in the generator long before that happens. And if for some reason the generator doesn't start, IT generates an alarm so we can intervene.

For a completely unattended site, or a site with zero technical capacity on site, LVD is probably a reasonable inclusion. For the rest of us, a properly designed and implemented system will never need it.

Quote
in my case low temp sensing is also a must.  It's -16c / 3F outside right now (-30c/-22F is not unusual)

A  civilised person such as myself would consider such environmental conditions "not fit for human habitation"!
I can't remember ever seeing less than -7C here, although we do get 48C and above in summer.

3600W on 6 tracking arrays.
7200W on 2 fixed array.
Midnite Classic 150
Outback Flexmax FM80
16 x LiFePO4 600AH cells
16 x LiFePO4 300AH cells
Selectronics SP-PRO 481 5kW inverter
Fronius 6kW AC coupled inverter
Home-brew 4-cyl propane powered 14kVa genset
2kW wind turbine

Steve_S

Ross, sounds like your in Australia or something.  I am in North Eastern Ontario Canada near the Algonquin Park (easy to find on google map).    Agreed that LVD is a last resort fail safe but it IS a fail safe.  Yes, the Inverter (Samlex EVO) can start my generator and charge the batteries BUT Temperatures is another issue. 

My old Yiyen Inverter had low volt cutoff & AGS (dip sw settings no software) and that would be too low (too low for FLA too) but that's a cheapo $600 USD jobby that is basic but works so you want to protect from equipment that isn't capable.

As for not having any and all "safeties" available is akin to the designers of the Titanic deciding to not have a lifeboat seat for everyone...  nothing is ever 100% fool proof.   15 Years of IT Engineering for the Military, I can tell you about backups & triple redundancies and them still failing because of a single weak point or something stupidly omitted.

ClassicCrazy

I have always been hoping that in a future Classic firmware they would add a batt temperature charge cutoff so we would have at least that layer of lithium cold weather charge protection. It could just be an Aux feature  too.

Larry
system 1
Classic 150 , 5s3p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system 2
 5s 135w Kyocero , 3s3p 270w Kyocera  to Classic 150 ,   8s Kyocera 225w to Hawkes Bay Jakiper 48v 15kwh LiFePO4 , Outback VFX 3648 inverter
system 3
KID / Brat portable

Steve_S

TBH, I am actually very surprised that Midnite has not done more to accommodate LifePo & Lithium battery systems.  The cost of LifePO versus FLA is now at the point where it's ridiculous to not go LifePO.  Being in Canada and having temps like -18 this morning when I got up, low temp safeties are a must IF something goes awry. 

Case in Point, the small furnace in my powerhouse packed it in on the 13th (of course it had to be on the 13th) while it was -16...   Luckily I have manual backups and the new mini-furnace goers in tomorrow.   My battery bank (still FLA, LifePo arrives Tuesday) was at 3 degrees before I found out the furnace quit.

I hope no one takes it wrong.  I love my Classic, it's a great piece of kit BUT if I was starting out today and looking for gear, it wouldn't be a Midnite Classic simply because of it's inability to do some of the things other Quality products do.  Gosh, even some of the Chinese "Value" gear does...   I'm just hoping that SOON Midnite will come up with something to address the Battery Types & interacting with them as needed, otherwise I'll have to kludge something together, which is not my style.

ClassicCrazy

Yes -  a temperature cutoff would be a nice feature for a controller to have - for those of us in the cold country !
I guess we should get going on the Node Red project again since we can add all those features in pretty easily using the Classic battery temperature data  via modbus.

Larry
system 1
Classic 150 , 5s3p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system 2
 5s 135w Kyocero , 3s3p 270w Kyocera  to Classic 150 ,   8s Kyocera 225w to Hawkes Bay Jakiper 48v 15kwh LiFePO4 , Outback VFX 3648 inverter
system 3
KID / Brat portable

Steve_S

Indeed, I intend to get back to my wee project sometime in December, too much todo right now and ol father winter is being generally a curmudgeon and quite hostile at this time.

I hope someone @ Midnite reads these posts and maybe can motivate some updates to 2020 realities.

boB

Quote from: Steve_S on November 16, 2019, 05:46:49 PM
Indeed, I intend to get back to my wee project sometime in December, too much todo right now and ol father winter is being generally a curmudgeon and quite hostile at this time.

I hope someone @ Midnite reads these posts and maybe can motivate some updates to 2020 realities.

We are listening.  We are also working on a lot of new things, including LiFePo stuff...

Not sure when something might change in the Classic though as our resources are kind of used up at the moment.

What features of other's products would help here ?  From the first post, stopping charging at a maximum SOC seems like one feature ?

It's pretty much all software except for the BMS built into the battery system.  A single board computer "could" handle all of that of course but I think you would like it done in the Classic.

Curious of some of the foreign controller features you like.

K7IQ 🌛  He/She/Me

openplanet

Really glad you're listening boB!

So...Hear Ye!  Hear Ye!

When I had FLA I didn't pay much attention to WB Jr. net Ah, since voltage and SG together give a good read on SOC.

Now that I have LiFePO4, I'm convinced that TWO SIMPLE ENHANCEMENTS could HUGELY increase a Classic's functionality with these batteries. The most important rule LiFePO4 owners should adhere to (aside from temp constraints) is to keep depth of discharge between 20% and 80%.  The super flat discharge curve makes voltage essentially useless for this purpose, at least on a daily basis.  What voltage changes there are, are in the 10s of mV range.  While the Classic can't see those differences, your BMS can.  What to do?  Simple: (1) calculate 60% of the bank's total Ah capacity; (2) carefully study the (resting!) voltage, as reported by your BMS, as you charge and discharge, so that you can (3) establish an accurate 20% or 80% SOC point, then (4) track net Ah.

HERE'S THE KEY: If you can configure the Classic to STOP CHARGING when net Ah reaches a specified positive value, you're preventing the bank from being over charged.  If you can configure the Classic to TOGGLE AN AUX LOGIC LEVEL when net Ah reaches a specified negative value, you have a way to throw a contactor and disconnect some or all loads (but NOT the Classic!)

I know everyone at Midnite is maxed out.  So many initiatives, so little time...  But truly, these two changes in the software would go SO FAR toward accommodating the most critical needs of LiFePO4 owners.  What can we do to entice you.  Beer?  A Home Depot gift certificate?  Weekend for two at the world-famous Motel 6 in Peoria?  A year's supply of blinker fluid and muffler bearing grease for your ride?

Thoughts?  Thanks!
_______________________________________
We are star dust [on a] pale blue dot.
[And yes,] there is grandeur in this view of life.
Joni Mitchell, Carl Sagan, Charles Darwin

https://www.youtube.com/watch?v=cIANk7zQ05w

boB

Quote from: openplanet on November 18, 2019, 12:42:26 PM
Really glad you're listening boB!
  A year's supply of blinker fluid and muffler bearing grease for your ride?

Thoughts?  Thanks!

Well, I don't drink (anymore) but maybe some blinker fluid might make me feel good.

Will chat with others about this but cannot guarantee any immediate action.

Over and out   :)
K7IQ 🌛  He/She/Me

Vic

Have been wanting the Classic to have a Rate Of Change of WB current as an additional means of ending Absorb,  in addition to  the present EA function.

Also,   if the Jitter of the WB current could be reduced (further),   this would be a large help for anything that uses WB currents.

boB,  you are speaking of FirmWare enhancements,   BUT,   if we could ever see battery voltage Sense terminals on a Classic,   that would be SO useful.   Know that the new covey of MN CCs all seem to have this function,   and adding hardware functions are probably not in the cards  for Classics  ...

If the rate-of-change in measured battery charge current function could be included in the FirmWare for the new CCs this would be a large plus,   here.

FWIW,   THANKS   for asking,   Vic
Off Grid - Sys 1: 2ea SW+ 5548, Surrette 4KS25 1280 AH, 5.25 KW PV, Classic 150,WB, Beta Barcelona, Beta KID
Sys 2: SW+ 5548s, 4KS25s, 5.88 KW PV, 2 ea. Classic 150, WB, HB CC-needs remote Monitoring/Control, site=remote.
 MN Bkrs/Bxs/Combiners. Thanks MN for Great Products/Svc/Support&This Forum!!

boB


Yeah, you won't be seeing battery voltage sense on a Classic but the new stuff has it.

I would have liked to add V sense to the WB Jr. cuz it could have used the same communications wire method.

I don't think that there is actually any jitter in the WB Jr. values themselves.  Just jitter in the Classic's charging during absorb at high input voltages.

Don't know if I remember hearing about SOC rate of change ?  Sounds like an interesting idea though.


K7IQ 🌛  He/She/Me