New Beta code REV 1609 -- 10/4/2013

[Halfcrazy]

We have some new Beta code. it has support for the now available WBjr current sense module and also has "Days between Bulk charges"

http://www.midnitesolar.com/firmwareReport.php?firmware_ID=5&firmwareProduct_ID=1&act=edit

boB will be doing the instruction sheet for the WBjr today and I will get it up on the website with the Classics.

Ryan

[Vic]

Hi Ryan and the MN Crew.

Thanks for getting the WBjr AND the Days Between Bulk in this new code.

Will be a week or so before I can get to  a Classic CCed site,  but will be working with the new FW very soon.  Thank You very much!  Vic

[Tons001]

Under what circumstances would one use the "Days between bulk" setting? Just curious.

[Vic]

Hi Tons ..

Many of us with Flooded Lead Acid batteries,  full recharge every day is not desirable.

Some off-grid systems do not have consistent daily loads and are not always taken below 90% SOC.  It is generally best to cycle FLAs below 90% before recharging,  but should be recharged every 5 - 7 days even if the batteries are not cycled below 90% SOC.  There is some difference in opinion on the exact details of this.  Furthermore,  in Summer heat,  daily recharge from shallow discharges does tend to dump quite a lot of heat into the battery bank,  as the final charge stage -- Absorption -- is not very efficient.  This efficiency loss occurs within the battery bank,  and shows up as battery heating.  Doing a full recharge from a lower SOC will extend the Absorption stage when one chooses to do it,  but on average,  quite a bit of battery heating can be avoided.

Some of us have been manually avoiding complete recharge by either shutting Off the PV input for some number of days,  or have set the Absorption voltage on the Classic to Vfloat + 0.1 V  or similar,  to gradually reduce the SOC of the battery over a period of days.

Having an automatic way of delaying full recharge can be helpful in cases as noted above.

At unattended sites,  delaying full recharge automatically is a great benefit (verses having to drive to the remote location to do this).

My opinions.    FWIW,  Vic

Some of us have been asking for having some level of doing some of this automatically.

[Tons001]

Thanks for the explanation! And now I get it.

[offgridQLD]

Many of us with Flooded Lead Acid batteries,  full recharge every day is not desirable.

It is generally best to cycle FLAs below 90% before recharging

Vic, this has got my attention!

I have a 1330Ah of flooded lead Acid batterys.Made up of 2volt Exide cells for 48v system. Being a reasonably big battery bank at 63kwh on paper and given that Monday - Friday there is only house base loads on the system. Perhaps 3kwh -maximum each day . The system spends a lot of its time in the mid to high 90% range. With lots of sun and a 4000w array. Every day after going through the bulk and absorb change it quickly reaches (end amps) by about 9:30 - 10:00AM and spend most of the weekdays in float.

Spending all this time cycling from say 95% full to 100% I have noticed my efficiency,  as in Kwh consumed (around 3kwh) vs what the classic has to put back in each weekday to go through this cycle isn't to good. Perhaps 3kwh out vs 5-6kwh back so 50 - 60% efficiency . I'm sure with a deeper DOD the efficiency would be better and I usually find it is on the weekends when I am there.

So could you fill be in more on the theory behind not fully charging each day and whats a good plan for my system. It's always drummed into you that flooded cells like shallow cycles for example on cycle life graphs my cells are rated to 5000cycles at 10% DOD . So that's always been my rule and I don't think my cells have spent any time below 10% DOD.

So it would have you think its a good thing to keen them topped up each day. Or is the theory just not to go through the bulk-absorb stage every day and have them come up to 100% full slowly just using float voltage  to charge and then only do a bulk-absorb charge every few days?

Or is this only for situations where you have no load at all on the bank ?

Kurt

[Westbranch]

It is not so much theory but fact that recharging in the 50 - 80% range is most efficient.   the next is 80-90%,
the idea is if you float every 3 - 5 days  you give your battery a good workout and a good charge through the range exposing surfaces that otherwise ( float daily) would never get touched.

IIRC it is Chris Olson that has written a  lot over at NAWS BB.

[offgridQLD]

Ok yes I agree that charging up to 80% soc is more efficient then from 80- 100% So yes sorry yes that part is fact not theory.

So this new setting "Days between bulk" if I was to set that to say 2 or 3 days what happens on the no bulk days? Will the classic just wont charge at all (effectively go to sleep) for a few days?

Can you set it for particular days of the week or is it just a ongoing tally? (Sorry my pc with the app isn't with me)

One part of me is thinking why not just increase the 24hr load on the battery's , at least the PV is being used each day then. Some kind of work could be done .Extra deep freezer, swimming pool pump, Pump water to high ground, something usefull. Rather than just have the 4000w of pv sit there for days while the pack SOC comes down.

What about salfation, is a few days at less than 100% not enough to bring that on?

I will give the setting a try just to see what difference it makes say charging every 2nd day just for a week. If it shakes my pack up a little and  improves over all efficiency. 

Kurt

[zoneblue]

The recent thread on optimum SOC is here:

http://www.wind-sun.com/ForumVB/showthread.php?20840-What-is-the-optimal-SOC-range-for-cycling-lead-acid-batteries&highlight=optimum+battery+charge

Its long and not completely resolved, but plenty to think about for sure.

[Westbranch]

Kurt, If I had loads to run that were not taking advantage of excess PV,   OPPORTUNITY LOADS!,   that is what I would run before going to a no Bulk setting, especially if they were in periods when you weren't there. The Classic can do this nicely, then if still not enough, go to the No Bulk, for a few days...

[offgridQLD]

Well I just read through the 14 page discussion on the wind and sun forum. A few things I could agree on but a lot of it needed tweaking to my personal situation and system and a lot of it depends on so many factors and weighing up pro's and cons.

As soon as My 63kwh of lead is dead I will be going to a small 20kwh lithium lifepo4 bank. I have much more experience with this chemistry and its benefits are huge. Then all this black art of bubbling boxes of acid and watering the dam things like pot plants will be a distant memory.

One load we do have that is a great place to dump our excess PV energy is our EV (Mitsubishi Imiev) it has  16kwh lithium battery and puts a nice 2200w load on our system when on charge.It charges in the 90% + efficiency range and you get the energy back out of it at about the same efficiency 10kwh in = 100km of driving for us. Its only a 16kwh battery but I can discharge the battery at 50kw rate! and recharge it at the same rate (public fast charger). I can let it sit for months at 50% SOC  or work it in the 40 - 80% range and it will be doing it a favor not harming it like FLA.Other than a balance charge once a month of so there is no black art like FLA its simple. Even functioning at the high rates I get out of it about what I put into it so efficiency is way better. Lithium is just so much easier to work with and performs so much better than FLA. If Mitsubishi can give that battery a 8 year warranty when it gets abused that much then a similar battery  will last a lot longer in a lightly loaded/charged off grid application.

Kurt

[Vic]

Hi Kurt,

Well,  in my opinion,  much of the exact ins and outs of recharging FLAs is theory,  not fact.  There are many variables,  and many opinions.

In looking at cycle life of FLAs,  almost all of the charts from different manufacturers stop at 90% SOC.  This means that most of the manufacturers recommend that the batteries be cycled to 90% or lower SOC.   Cycles to 80% for my banks seem about ideal.   But,  when one is not around to consume power it takes more days of no Bulk to reach this level of discharge.  Discharge cycles that do not get to/below 90% SOC have been noted as causing earlier battery failure than cycles to 80%,  for example.   This is apparently due to Lead Dioxide clumping on the plates,  rather than being evenly distributed over the entire positive plate.  Those of us with larger battery banks,  especially those of us who are not always present to consume life-style energy can run into this.

Many Opportunity Loads require for a human or more to be around to need to use these loads,  like some A/C,  hot water,  running pumps for domestic water etc.  One can run heaters to heat the great outdoors in the absence of humans,  but,  I do not like to have such functions run unattended.

I have not studied or tried the Days before Bulk function mentioned earlier in this Thread,  so cannot comment.  I have been using a manual change in Absorption voltage to around the Float voltage setting,  and if time permits,  on returning to the off-grid location,  further depleting the battery by running heater loads with the PV shut off to get down to about 80% SOC,  if that level has not been reached while away.

This is all a bit experimental.   A poster on the Wind-Sun Forum that was the first person to mention delaying days between recharges was member  "stephendv"  on the Wind Sun forum,  who noted that several European manufacturers of CCs (and perhaps inverters)  had an algorithm to avoid recharging the batteries for N days if the battery voltage remained above V volts,  or similar,  and cited some supporting info on such an approach.

In days past,  most of us off-gridders were quite satisfied to fully recharge our batteries each and every day.

I am happy that MidNite is beginning to allow multiple strategies for recharging batteries via the Classic  CCs.

An added comment --  Off grid systems are not very efficient.  FLAs are not very efficient.  We all waste a lot of power almost every day, if our systems are well designed.  And,  to me,  obsessing too much about any of this wasted power is personally inefficient -- life is to short.    My opinions,    Vic

[offgridQLD]

Well I can use this new feature to once on lithium battery's. As they give the best service life running around the 50% soc mark Ideal would be 49-51% but only using 2% of the capacity isn't practical but in reality 30-70% or 20-80%  would be a example option. With the odd 100% soc run just to balance them. So this new feature could be used to obtain that.

my FLA batterys would only get a 2.5% dod weekdays but on the weekends they would get about 5% DOD. Its just so hard as for me 10% DOD is 6kwh and I would have to use that 6kwh in a time that I am just running on battery's 5pm - 5am , or in reality 5pm - 11pm when we sleep.As soon as the sun comes up our system is pumping the power in and Not even charging the EV car and welding,washing and so on will take anything from the battery.Basically our battery is to big for our needs (previous owners choice) but being FLA chemistry I need that large capacity to give me the C rating to run my big workshop loads, plasma cuter, welder, lathe, air compressor and so on. A small lithium battery has a much better C rating than FLA. So you don't need the big reserve of defunct battery for the odd high C load.

Kurt

[Resthome]

So this new setting "Days between bulk" if I was to set that to say 2 or 3 days what happens on the no bulk days? Will the classic just wont charge at all (effectively go to sleep) for a few days?

Can you set it for particular days of the week or is it just a ongoing tally? (Sorry my pc with the app isn't with me)


Kurt

On the no bulk days it just goes to Float - no bulk or absorb cycle. It's just a single number to set no choice of which days. And from what I could tell only tested it once. It is not recurring, in other words once it skips the set amount of days the counter reaches 0 and bulk & absorb restart. So you would have to reset this counter again to initiate a skip cycle again. It's a start but when you are like us and gone for long period of time in the winter months it would be nice if it could cycle for some number of cycles with charging occurring in between.

Edited 12/09/2013:   I stand corrected per Ryan this function does reset and the cycle will reoccur.
http://midniteforum.com/index.php?topic=1541.msg13039#msg13039

[Vic]

Hi John,

Thanks for the summary for DBB.  It is a start,  and am happy to see MN beginning down this road.

Hope to get the WB installed within a week and the FW Updated to the latest.

Vic