36V Battery voltage and time settings?

[sigp2101]

sigp2101,

Thanks for the info on your system.

Please do not thank me, THANK YOU for such unselfish support for my project.

So,  you are running the three SW-235 PVs in series,  for a String Vmp of about 90-ish volts (at STC) to the Classic,   assumed.

Correct!

With absolutely no loads on the batteries,  except the Classic itself,  you could expect to run a number of weeks with no charging at all.

That is very encouraging, ultimate goal is to eventually be able to leave fridge run over summer months mostly.

In your absence,  you could Float the batteries at the suggested Float voltage.   Or,  even Float at a somewhat reduced Vfloat.

And to do that I assume I will have to set all voltages to float desired level. absorb = float. Correct?

THANKS!

[Resthome]

sigp2101,

In your absence,  you could Float the batteries at the suggested Float voltage.   Or,  even Float at a somewhat reduced Vfloat.

And to do that I assume I will have to set all voltages to float desired level. absorb = float. Correct?

THANKS!

No, you would set Skip DAYS to the number of days you want the CC/Batteries to only go to Float set point. Once that number of days is met it will charge you batteries with Bulk-Absorb-Float set point and the following day start the Float only cycle again.

Really recommend you add the WBjr and Shunt to you system so you can use END AMPS to terminate Absorb rather than a set amount of time.

Oh wait someone said you had a light, you would have to program this from a computer with the Midnite Local Staus App. Also suggest you invest in the MNGP which provides a lot of control over the Midnite CC

[sigp2101]

Oh wait someone said you had a light, you would have to program this from a computer with the Midnite Local Staus App. Also suggest you invest in the MNGP which provides a lot of control over the Midnite CC

Plan is to have light in my cottage, that is why I am doing all this.
I do have MNGP it came with Classic 150. That is how I will do all programing on CC.

[Vic]

sigp2101,

Thanks for the info on your system.

Please do not thank me, THANK YOU for such unselfish support for my project.

So,  you are running the three SW-235 PVs in series,  for a String Vmp of about 90-ish volts (at STC) to the Classic,   assumed.

Correct!

With absolutely no loads on the batteries,  except the Classic itself,  you could expect to run a number of weeks with no charging at all.

That is very encouraging, ultimate goal is to eventually be able to leave fridge run over summer months mostly.

In your absence,  you could Float the batteries at the suggested Float voltage.   Or,  even Float at a somewhat reduced Vfloat.

And to do that I assume I will have to set all voltages to float desired level. absorb = float. Correct?
THANKS!

Hi sigp..,

First,  just to try to be clear.   There is a Classic Lite  --  the Lite is the Classic without the MNGP,  it has only some switches and LEDs.

You DO have the MidNite Classic 150 with the MNGP.   This is very good.

If you would want to run a fridge in the Summer in your absence,  things become less certain.   One would need to know the amount of energy that the fridge uses in a typical day,   the amount of Solar Insolation (in kWh per day)  for the months that the fridge would need to run,  and so on.  One would need to know your approximate location,  and the nature of any shading of the PVs from trees,  hills,  etc.

I become a bit reluctant to give much advice on setting up systems that will be unattended for a period of time.   The longer the period of absence,  the more difficult the situation can become.

If there are essentially no loads on the batteries during the absence,   the power system is much more predictable than if there are varying loads,  like a fridge.

If one has considerable battery Capacity,   and significant PV power available,  the risks to unattended systems  us really quite small.

Today was a transit day,  will try to catch up on any other of your other Posts.

More Later,   Vic

[sigp2101]

Hi sigp..,

First,  just to try to be clear.   There is a Classic Lite  --  the Lite is the Classic without the MNGP,  it has only some switches and LEDs.

You DO have the MidNite Classic 150 with the MNGP.   This is very good.

If you would want to run a fridge in the Summer in your absence,  things become less certain.   One would need to know the amount of energy that the fridge uses in a typical day,   the amount of Solar Insolation (in kWh per day)  for the months that the fridge would need to run,  and so on.  One would need to know your approximate location,  and the nature of any shading of the PVs from trees,  hills,  etc.

I have fridge and its power rating is only 159Kw per year. That is bit over 400 Watts in 24 hours period according to simple calculations. I was conducting test last weekend using http://www.homedepot.com/p/Kill-A-Watt-Electricity-Monitor-P4400/202196386  and reading was 0.17 KWh in 25 hours. I will also have up to 50W LED lights and laptop. That is it that is all.

Location is 45.9 and insolation is 4 hours summer 2 hours winter. No shading during these hours.

Today was a transit day,  will try to catch up on any other of your other Posts.

More Later,   Vic

Thanks so much again and there is no rush ever. I come here for bit of the knowledge at the time, and then go and try to apply it over the weekend.

[sigp2101]

The Absorb time required to recharge batteries depends mainly,  upon the Depth Of Discharge (DOD) that the battery bank experienced in the previous discharge cycle.

Does this mean that I will have to manually monitor DOD of my batteries every day and set absorb time for the next day??

The Classic "knows" to stop charging in the Absorb stage,  based upon the time that is set in the Charge > Time menu page.   

Assuming I set it up right the previous day. Right???

That was original intention of this thread to find out to what value to set time parameter. I am still confused and do not know answer to this I feel very important question. What happens if Time parameter is left at default value 00:00. Will classic charge BB at all?

[Vic]

Hi sigp..,

If your loads are quite similar every day,  a fixed Absorb time can work well.  You will just need to determine what is that value, experimentally.

Flooded batteries are very forgiving,  AND,  trying to err a bit on the side of a bit of overcharge,  verses a bit of undercharge each day.

But,  if your loads vary considerably every day,  a fixed Absorb time does not work so well.   It is all a matter of degrees.   For systems with reasonably large amounts of PV power available,  and reasonably large battery Capacity relative to daily discharge of the batteries,   NOT charging every day can be a good approach.   Am not certain that your system quite qualifies as such a system.

IIRC,  you do NOT have the WhizBangJr battery current sensing module.  The WBjr would allow your system to terminate Absorb,  based on the Return Current (End Amps).  And,  it alloys you to accurately measure the actual battery charge current with very good precision,  all you would need is a 50 mV/500 A Shunt and the WBjr.   This has a cost of about U$D 100,  including a bit for shipping if you are in North America.

As mentioned before,   we have always used End Amps  --  first it was just EA based on the CC's output current.  The Outback MX-60 allowed this.  With the Classic CC and the WBjr,  it is quite inexpensive to end Absorb using actual battery charge current,  allowing the ability of generally being able to ignore the system loads on the inverter.  Shunt EA is a very good way to end Absorb at an appropriate time on systems with relatively large and intermittent loads.

Does this make sense to you?   Am NOT trying to sell hardware,  however.   FWIW,  Vic

[sigp2101]

Hi sigp..,

If your loads are quite similar every day,  a fixed Absorb time can work well.  You will just need to determine what is that value, experimentally.

Flooded batteries are very forgiving,  AND,  trying to err a bit on the side of a bit of overcharge,  verses a bit of undercharge each day.

But,  if your loads vary considerably every day,  a fixed Absorb time does not work so well.   It is all a matter of degrees.   For systems with reasonably large amounts of PV power available,  and reasonably large battery Capacity relative to daily discharge of the batteries,   NOT charging every day can be a good approach.   Am not certain that your system quite qualifies as such a system.

IIRC,  you do NOT have the WhizBangJr battery current sensing module.  The WBjr would allow your system to terminate Absorb,  based on the Return Current (End Amps).  And,  it alloys you to accurately measure the actual battery charge current with very good precision,  all you would need is a 50 mV/500 A Shunt and the WBjr.   This has a cost of about U$D 100,  including a bit for shipping if you are in North America.

As mentioned before,   we have always used End Amps  --  first it was just EA based on the CC's output current.  The Outback MX-60 allowed this.  With the Classic CC and the WBjr,  it is quite inexpensive to end Absorb using actual battery charge current,  allowing the ability of generally being able to ignore the system loads on the inverter.  Shunt EA is a very good way to end Absorb at an appropriate time on systems with relatively large and intermittent loads.

Does this make sense to you?   Am NOT trying to sell hardware,  however.   FWIW,  Vic

I like idea of terminating Absorb charge based on EA since my system will be very stable between weekends. Meaning no loads at all. Now, how do I figure the EA number.

[Vic]

sigp..,

OK  but with NO loads at all,  there will only be the self-discharge of the battery to think about.   This discharge is temperature-dependent.   But should not exceed about 5% per week ...  something like that with the Inverter OFF,  and the Classic's input and battery breakers OFF.

If the above is the case,  you cannot charge,  of course,  but you would have several weeks of off time before you would need to be concerned about charging the batteries.

Know,  that you had wondered about running the refer during summer months,  and this would,  of course,  would be a different matter altogether.

Determining the proper EA value with Flooded batteries is relatively simple.   With stable and light loads on the system,  set a long Absorb time,  let's say 360 minutes.   Watch the CC's output current during Absorb.   As absorb progresses the output current of the CC will taper,  to a lower and lower value.  When this value does not change for about 20 minutes,  or so,  this is a good beginning start for YOUR EA.   You can measure the SGs of the battery to confirm that this is in the ballpark.   Reset the long Absorb time to a reasonable value.

But,  without the WBJr,  if the loads on the system increase,  the Absorb might not ever terminate,  based upon EA.   But the time set for Absorb will be the thing that will end Absorb,  in this case,  so using a reasonable value there should be a good backup to EA.

One other thing.   The EA setting required will need to be changed if you choose to change the Absorb voltage  --  if you raise the Vabs,  the EA value will probably need to be increased,  and if the Vabs is lowered the EA value may need to be reduced.  If you are only making one or two tenths of a volt change Vabs,  EA may not need to be changed.

Enter your Vabs,  Absorb times,  and EA values in your Battery Logbook.   This will help you track the effects of changes upon battery SGs.

None of this need be perfect,  as you have Flooded batteries and your trusty Hydrometer,  so you can actually measure how well charged that batteries actually are.

FWIW,    Vic

[sigp2101]

sigp..,

OK  but with NO loads at all,  there will only be the self-discharge of the battery to think about.   This discharge is temperature-dependent.   But should not exceed about 5% per week ...  something like that with the Inverter OFF,  and the Classic's input and battery breakers OFF.

If the above is the case,  you cannot charge,  of course,  but you would have several weeks of off time before you would need to be concerned about charging the batteries.

Know,  that you had wondered about running the refer during summer months,  and this would,  of course,  would be a different matter altogether.

Determining the proper EA value with Flooded batteries is relatively simple.   With stable and light loads on the system,  set a long Absorb time,  let's say 360 minutes.   Watch the CC's output current during Absorb.   As absorb progresses the output current of the CC will taper,  to a lower and lower value.  When this value does not change for about 20 minutes,  or so,  this is a good beginning start for YOUR EA.   You can measure the SGs of the battery to confirm that this is in the ballpark.   Reset the long Absorb time to a reasonable value.

But,  without the WBJr,  if the loads on the system increase,  the Absorb might not ever terminate,  based upon EA.   But the time set for Absorb will be the thing that will end Absorb,  in this case,  so using a reasonable value there should be a good backup to EA.

One other thing.   The EA setting required will need to be changed if you choose to change the Absorb voltage  --  if you raise the Vabs,  the EA value will probably need to be increased,  and if the Vabs is lowered the EA value may need to be reduced.  If you are only making one or two tenths of a volt change Vabs,  EA may not need to be changed.

Enter your Vabs,  Absorb times,  and EA values in your Battery Logbook.   This will help you track the effects of changes upon battery SGs.

None of this need be perfect,  as you have Flooded batteries and your trusty Hydrometer,  so you can actually measure how well charged that batteries actually are.

FWIW,    Vic

Hi Vic,

Thanks for long explanation, everything is starting to make sense now. All these little tweaks are what is needed. Your input is of tremendous help.
One more question, how do I go about setting to skip two days in the row but I want those two days to fall on weekend?

SIGP2101