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Battery life in daily use


viceroy
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Since I got the new battery bank going and running the house, which admittedly has only been 4 days, I've been wondering a few things.

The bank size 400Ah @ C10, together with the 3000W of PV, pretty much runs my house.

My deepest discharge was yesterday where we went down to 82% according to the BMV.

Now my question, on a good solar day with the maid maybe doing 1 load of washing, we'll be fully charged by 1pm.

On a bad day like today where we've peaked at 500W PV, the batteries wont get fully charged, and we'll hover around 85% SOC.

How does this hovering between 95% and 80% SOC affect battery life as opposed to discharging to 80% and then fully charging to 100%?

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Viceroy, welcome to my world. ;)

Cannot recall what batts you have, but what tends to happen is every 2 or 3rd day there should have been enough to charge them fully. I equalize at least every 27 days.

BUT, that is assuming you run to 50% DOD with 1 days backup.

So at 82% DOD (?), you do not have any reserves for a 2nd day of low sunlight? 

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Well the intention was never to be fully off grid, it's just how it's panned out so far.

My Batteries are Omni Power Gel/AGM so I dont think equalizing is really an option for me?

I think perhaps me using SOC rather than DOD has confused matters.

My lowest discharge has been 18% DOD, mostly around 15% DOD, so I do have reserve for a second (and possibly 3rd) day of low sunlight before I would hit 50% DOD.

I'm just interested if the batteries hovering between 10% and 20% DOD would shorten their lives compared to discharging down to 20% DOD and then fully charging back to 100%

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Ag dankie tog!!! That is good news. I also get the SOC and DOD mixed at times.

It does not matter if they hover there, or lower, for a few days at all. You are good to go.

Well done by the way.

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Viceroy now you know why I am working on AICC to switch you to grid if it will see that it wont get the bank charged and carry the load of the house. So instead of putting a load on the bank I want to go to grid and then the power that the panels make will go to the bank. So the solar power is not wasted and you are not working the batteries hard up and down all the time becouse of a cloudy day. I think I have a way of working it out without any external sensors and weather checks. 

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It is a good idea to use about 20% of the batts daily.

If the batts can carry the load, no Eskom needed, then go for it!

If batts hit say 40-50% DOD, then switch back to Eskom ... what I would have done here.

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2 hours ago, jdp said:

Viceroy now you know why I am working on AICC to switch you to grid if it will see that it wont get the bank charged and carry the load of the house. So instead of putting a load on the bank I want to go to grid and then the power that the panels make will go to the bank. So the solar power is not wasted and you are not working the batteries hard up and down all the time becouse of a cloudy day. I think I have a way of working it out without any external sensors and weather checks. 

I have similar pipe dreams, just a way to detect an abnormal day and take a "grid day" when that happens. First prize is just being able to do it remotely. In theory, very easy. I already have a switch that tells the Multiplus not to go off grid. Only have to put a relay on that and let the Pi switch it. I can also use the PowerAssist feature via the mk2 to do this (you can tell it to go off-grid by setting the grid current to zero), but if I do that I lose the safety feature where it goes back to grid under high load. So sadly, extra hardware will be required :-)

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Why? Read the higher load for 1 minute or what, then switch the relay back that the inverter uses Eskom again?

If load drops for 1 minute, re-engage the relay if BMV says all is fine on batts?

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Simple reason really. I want to switch to solar as soon as there is enough power to carry the loads. As the available power increases, my batteries recharge while I continue to carry load. Around lunch time the batteries are full, and we carry loads only until around 4PM. Then we slowly start digging into the battery again and around 85% SoC we go back to grid. Repeat that every day. Except... if yesterday was a cloudy day, and today appears to be no better... or it started out looking well and then some clouds came in from the South West (as they do in Cape Town)... I want to be able to just override this. Those are good days for giving them a good charge... the up and down as clouds move past isn't a good thing anyway. Sit it out, try again tomorrow. I want to be able to do that remotely, and possibly even automatically.

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You said:

1 hour ago, plonkster said:

... relay on that and let the Pi switch it. I can also use the PowerAssist feature via the mk2 to do this (you can tell it to go off-grid by setting the grid current to zero), but if I do that I lose the safety feature where it goes back to grid under high load. 

So therefor I said:

54 minutes ago, The Terrible Triplett said:

Read the higher load for 1 minute or what, then switch the relay back that the inverter uses Eskom again? If load drops for 1 minute, re-engage the relay if BMV says all is fine on batts?

I switch loads on ASAP in mornings, with clouds it will switch back automatically and if not, the batts have the whole day to charge, whilst load is powered.

Then I choose the day for just charging to float level, equalise, check water and then syncing and Zero'ing the BMV for the next cycle.

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26 minutes ago, viper_za said:

TTT is a special kind that likes running batteries to predetermined  SOC no matter what the conditions are like ;)

YES!!! :D 

Even MORE special if you make it in Winter, set it at say 5% DOD (SOC 95%) to go back to Eskom and at 2% DOD (98% SOC) back to inverter in the week so that one can get back to solar ASAP early mornings, yet have ample spare the entire 24 hour cycle. Summer I adjust lower. :D

Having been through load shedding the 1st time round, when this plan was conceived, then as in the last round, by using SOC, it saved my bacon every single time, day and night, having had a lot of spare battery capacity at all times. :P

For IF there is no Eskom and not enough solar, the override kicks in keeping the system running off batteries / solar until batts are flat ... giving me about 12+ hours for the core load. 
 

Truth be told, at 95% SOC, swapping back to Eskom, I have loads that are 24/7 on solar, so we looking at more like SOC +-85% very early in morning. So by 8h30 I am running off solar till about 6h30pm'ish.

If there is insufficient sun next morning, batts can take the whole day for all I care, to get charged. 

Tree in your path, go left, go right, climb thought it or chop if off, all depends on what works best for your specific scenario.

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On ‎2016‎/‎03‎/‎23 at 11:17 AM, jdp said:

Viceroy now you know why I am working on AICC to switch you to grid if it will see that it wont get the bank charged and carry the load of the house. So instead of putting a load on the bank I want to go to grid and then the power that the panels make will go to the bank. So the solar power is not wasted and you are not working the batteries hard up and down all the time becouse of a cloudy day. I think I have a way of working it out without any external sensors and weather checks. 

That sort of functionality would be great.

How are you planning on doing it? By monitoring the rate of charge, and if it wont reach 100% by a predetermined time, then switch over to grid?

One thing I would love in the software is a bit more flexibility in the scheduling, ie, being able to setup more times when one would switch over to grid, possibly linking in SOC to that, so for example if my SOC @ 16:00 is below 90% then switch to grid until it gets to over 90% or 20:00 (after high demand dinner time period has passed)

Would be great for the upcoming winter period where I am already switching to grid when the geyser is set to come on @ 06:00 if it's not at temp, and if I could setup further grid times for early evening.

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So last night I found documentation on the batteries which has me shocked.

Because of the summer (and car) heat in my garage, I had taken values according to the document from sinetech on my batteries and set my float voltage at 2.21V (53V) and the bulk at 2.31V (55.4V)

Omnipower OPS260 Battery Spec.png

However, actually looking on the batteries themselves and at the data provided on the sustainable website, I'm under volting the batteries at bulk stage.

Omnipower OPS260 Battery Spec 2.png

Can not putting enough volts in harm the batteries or shorten the life?

Do Gel AGM batteries really like such a high bulk voltage compared to lead acid or regular AGM batteries.
2.4V ~ 2.45V in my case would be 57.6V ~ 58.8V. Seems Excessive to me.

Temps are now dropping and constant monitoring the battery case temps show they remain reasonably constant at 25 ~ 26C, so I'd like to up the voltages from my current 53V / 55.9V to settings more in line with the temps, but I just wonder...

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As I recall, 2.45V is standard for a lead acid. I believe that's what we used back in the 80s when my father installed his first setup (bank of Willard 2V 350Ah cells). We'd go up right to 2.55V per cell before the controller kicked out. It was before PWM became main stream.

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